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MINISTRY OF AGRICULTURE, FISHERIES AND FOOD CSG 15Research and Development

Final Project Report(Not to be used for LINK projects)

Two hard copies of this form should be returned to:Research Policy and International Division, Final Reports UnitMAFF, Area 6/011A Page Street, London SW1P 4PQ

An electronic version should be e-mailed to [email protected]

Project title Development of sward-based guidelines for grassland management in ESAs and Countryside Stewardship

MAFF project code BD1412

Contractor organisation and location

ADAS Consulting LtdWoodthorneWergs RoadWolverhamptonWV6 8TQ

Total MAFF project costs £ 124,000

Project start date 01/08/97 Project end date 31/01/01

Executive summary (maximum 2 sides A4)

The overall objective of this project was to develop a new framework of sward-based guidelines for the management of grazed grassland in Environmentally Sensitive Areas (ESAs) and Countryside Stewardship (CS). Until recently, grazing prescriptions within ESA’s have referred to terms such as ‘over-grazing’ and ‘under-grazing’ without any clear definition of either. Grazing influences vegetation change predominantly through changes in sward height and structure. There was therefore a need to establish a framework within which grazing management guidelines are defined in an objective and precise manner in terms of sward structure and composition. This would allow grazing management to be monitored in terms of the effect on sward structure to ensure that the character of valuable grasslands is maintained, or that the desired long-term changes in vegetation structure and composition occur.

All available information was first collated on techniques for measuring sward structure, and on the structural requirements of swards for conservation objectives. Three techniques of measuring sward height were compared: the HFRO swardstick; a 10cm diameter drop-disc and a 30 cm drop-disc. The latter was in quite common use by conservation organisations. Drop-discs were found to under-estimate mean sward height compared to the swardstick and gave less information on sward heterogeneity (variation in height). Moreover, there is much information in the literature relating swardstick heights to animal production, particularly in improved grassland, but no equivalent information for drop-disc heights. The swardstick was therefore adopted as the preferred method. Assessments were made of the accuracy of overall visual estimates of sward height, bare ground cover and herb cover made at the field scale, compared to a more systematic approach, including the use of the swardstick. Sward height and herb cover could be assessed quite accurately at the field scale with practice, but bare ground estimates were more difficult and required a more systematic approach.

CSG 15 (Rev. 12/99) 1

Projecttitle

Development of sward-based guidelines for grassland management in ESAs and Countryside Stewardship

MAFFproject code

BD1412

In developing criteria and target values for sward structural variables, the information gathered by review and consultation was supplemented by data collected from an extensive sample of sites within this project. These sites were chosen as good examples of a range of calcareous, mesotrophic and acid enclosed lowland grasslands, where the management of each site was likely to be optimum, or close to optimum, for its conservation objectives. Various measures of sward structure and composition were made, including sward height, bare ground cover, herb cover, and cover of weeds, and different techniques and approaches to measuring these variables were compared. A number of Farming and Rural Conservation Agency (FRCA) Project Officers participated in the study to field test the techniques and the draft guidelines developed during the course of the project. Feedback from these and other key personnel was an essential element in developing and refining a framework of sward-based guidelines. These guidelines were formulated at three levels of complexity, allowing for different levels of botanical expertise or quality of botanical data available for a site. The guidelines form part of a detailed protocol developed during the project, for establishing, monitoring and reviewing the management of grasslands within the context of management agreements in agri-environment schemes.

Information available on animal performance from semi-natural grasslands, and relationships with sward height, were reviewed. Although information was limited, individual animal performance varied considerably between studies, with growth rates obtainable from semi-natural grasslands ranging from poor (e.g. 0.3 kg live weight/ day) to very good (>1.0 kg / day). The lower growth rates were associated with situations where grazing was being used to restore biodiversity to sites which had previously been abandoned and which had reverted to rank vegetation.

Recommendations arising from the project are:Methodology The HFRO swardstick should be adopted as the preferred apparatus for measuring sward height. Opportunities should be taken or created to develop an extensive database of sward heights from a wider range of

valuable sites, covering all semi-natural communities. Further, more extensive comparisons of swardstick and 30 cm drop disc heights should be made, so that existing

criteria based on the latter can be more confidently converted to swardstick heights for a range of grassland types. Visual assessments of sward height and herb, weed and tussock cover, and of spatial patterns in distribution of

vegetation height, are feasible at the field scale. Assessments of bare ground cover at the field scale are more difficult, and a more systematic approach is recommended if/when accurate assessments of this variable are required.

Further aids to visual assessment of sward height and structure should be developed, including use of existing photographs taken at a range of sites within the project.

A technique for assessing litter cover needs to be developed. Techniques for assessing sward heterogeneity need further development. This could include more extensive use of

diagrams produced for this study, and development of an index combining these with mean vegetation height. Clearer definitions are required for terminology relating to sward heterogeneity and these need to be generally agreed,

e.g. distinction needs to be made between a ‘tussock’ and a ‘clump’ of vegetation. Further discussion is required, e.g. between FRCA and English Nature, on the value of sward heterogeneity and how

to define the specific requirements of particular fauna for inclusion in sward-based management guidelines.

Technology transfer Update the review of information provided within this project, including an expansion of its scope to cover

management for specific rare plants small mammals (e.g. brown hare). Establish a network of demonstration sites based on the high quality, well managed sites studied in this project, but

also including a number of sites managed specifically for fauna. Expand the scope of the work to encompass management of lower quality grasslands, including sward-based

techniques for restoration of biodiversity, and develop protocols for the identification of potentially valuable sites.

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MAFFproject code

BD1412

Scientific report (maximum 20 sides A4)

INTRODUCTIONEnvironmentally Sensitive Areas (ESAs) and Countryside Stewardship (CS) aim to maintain and enhance the conservation value of grasslands under agricultural management. Until recently, grazing prescriptions within ESA’s have referred to terms such as ‘over-grazing’ and ‘under-grazing’ without there being a clear definition of either. Grazing influences vegetation change predominantly through changes in sward height and structure. There is therefore a need to establish a framework within which grazing management guidelines are defined in an objective and precise manner in terms of sward structure and composition. The immediate effect of grazing management on sward structure can then be closely monitored in order to ensure that guidelines are adhered to, and that the character of valuable grasslands is maintained, or that the desired long-term changes in vegetation structure and composition occur.

MAFF is keen to encourage the establishment of management agreements within ESA’s and CS that are based on site-specific objectives. The establishment of such objectives for individual agreements provides the opportunity to tailor management agreements to the needs of individual sites and thus maximise the benefits provided by agri-environment schemes. Given appropriate guidelines, Project Officers could monitor sward characteristics (rather than stocking rates) and hence adjust livestock management to maintain optimal vegetation structure for the achievement of conservation objectives.

ObjectivesTo develop a new framework of guidelines for management of grazed grassland in ESAs and CS, which enables viable livestock production systems to be continued, whilst maximising environmental benefits.

Detailed objectivesa) Identify by review and consultation with relevant organisations, techniques of sward measurement and management guidelines based on them.

b) Assess the potential for use of these techniques alongside assessments of sward structure, stocking levels and livestock performance. This will take into account the effectiveness of the techniques in enabling objectives to be met, and their ease of use.

c) Test the most promising techniques with a range of users on key types of enclosed grassland and in different geographical locations.

d) Recommend a framework of sward-based guidelines for the management of grassland, which can be modified to facilitate the achievement of objectives across the whole range of ESAs and CS

e) Undertake preliminary field-testing of framework.

ApproachFirstly, all available information was collated on techniques for measuring sward structure, and on the structural requirements of swards for conservation objectives. This was then supplemented by data collected from an extensive sample of sites within this project. These sites were chosen as good examples of a range of calcareous, mesotrophic and acid enclosed lowland grasslands, where the management of each site was likely to be optimum, or close to optimum, for its conservation objectives. Various measures of sward structure and composition were made, including sward height, bare ground cover, herb cover, and cover of weeds, and different techniques and approaches to measuring these variables were compared. Litter abundance is an important variable, an excess of which can indicate under-grazing, but it was considered difficult to assess in an objective and standardised manner. This variable was not therefore measured at study sites, but values quoted elsewhere are used in setting guidelines.

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MAFFproject code

BD1412

A number of FRCA Project Officers participated in the study to field test techniques and draft guidelines developed during the course of the project. Feedback from these and other key personnel was an essential element in developing and refining a framework of sward-based guidelines.

METHODS

Sward height measurement techniques - literature review and consultationA literature review and extensive consultation was carried out to identify and evaluate sward assessment techniques relevant to grassland management for conservation objectives. A comprehensive literature search was complemented by extensive consultation with personnel involved in the management of semi-natural grasslands, including English Nature, Butterfly Conservation, The Institute of Grassland and Environmental Research (IGER), The Royal Society for the Protection of Birds (RSPB), ESA project officers, and local Nature Trust personnel. The current, most commonly used techniques in both highly productive ‘agricultural’ grasslands and less productive semi-natural grasslands were reviewed to provide a brief evaluation of their suitability for use in this project.

Comparison of sward height measurement techniquesIn 1998, 10cm and 30cm drop-discs and the Hill Framing Research Organisation (HFRO) swardstick were tested on four sites which varied in topography and sward structure. Measurements taken using each technique on the same fields were then compared by analysis of variance (ANOVA) and by calibrating each against the other using regression analyses. Regressions comparing drop-disc and swardstick measurements used two different approaches. First, swardstick measurements were used as the explanatory variable, i.e. assuming that these were ‘true’ heights. The second analysis used the 30cm drop-disc as the explanatory variable, to produce equations which would allow similar data from elsewhere to be converted to swardstick height.

Use of the HFRO swardstick in a range of sitesThe HFRO swardstick was selected as the preferred technique for measuring sward height, on the basis of both the literature review and the preliminary study described above. In 1998/99, the swardstick was used to take measurements at each of 21 sites, representing a range of sward types and topographical conditions (see Appendix 2, Table A2.1). Several of these sites were in National Nature Reserves managed by English Nature, and the rest were either Sites of Special Scientific Interest and/or were under ESA agreements. Measurements were repeated at 4-5 week intervals, with between 50 and 100 measurements taken per site on each occasion, depending upon the variability in sward height at the site. Height readings were taken at evenly-spaced points on a W-shaped transect at each site, recording the height of the first contact (from above) of green leaf at each location. Contacts with flowering stems, dead material and, with the exception of Site 3 (Myrus Sutton), rushes, were disregarded at all sites. At Site 3, two sets of heights were recorded on the same transect, the first excluding rushes and the second set including rushes where contact was made with these, so that the influence on mean sward height and variability of including rushes could be assessed. The full data set was used to investigate both differences in sward height between sites at particular times of year, and changes within sites, during the course of the year. The data were also used to compare the precision possible for a given number of height readings in contrasting vegetation types. Measurements were repeated in 1999 and 2000 on a subset of 10 sites covering the original range of grassland types (See Appendix 2, Table A2.1). The original timescale for completion of the project meant that no assessment was made at any site after September 2000 in order to provide time for collation, analysis and reporting of the data.

Bare ground measurementThis variable was assessed at all 10 sites in 1999 and 2000, on the same transects as height measurements. At each point along the transect in 1999, the observer assessed an area of 2 m radius in a semi-circle in front of him/her (using tape measure/metre rule as a guide initially). In 2000, a smaller area of 1m was used, following field testing of both sizes in an assessor trial (described below). In both years, an estimate was made of the percentage cover of bare ground visible from above (without any disturbance of the sward) within this area, bare ground consisting of exposed bare soil, with no vegetation (dead or alive) or moss cover. A simple visual guide was developed to aid in this assessment (see Appendix 3)

Herb coverThis was assessed in a method analogous to that used for bare ground assessment and on the same occasions in 1999 and 2000 (using a 2m arc in 1999 and a 1m arc in 2000). The percentage cover of herbs (i.e. broad-leaved plants) and

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MAFFproject code

BD1412

non-grass species (including sedges and rushes) was estimated as a percentage of the existing vegetation cover within the area. No distinction was made between legumes and other broad-leaved plants within any vegetation type.

Abundance of weeds and tussocksOn each visit to the 10 sites in 1999 and 2000, an overall estimate of percentage cover was made for each of the following: bracken, ragwort, thistles and tussocks. A tussock was defined as a single-species group of densely clumped shoots originating from a single rootstock, with a diameter of 15cm or more. Tussocks defined in this way were most likely to be found in wet grasslands, and formed by species such as tufted hair-grass (Deschampsia caespitosa), purple moor-grass (Molinia caerulea), larger sedges (Carex acutiformis, C. elata, C. paniculata, C. riparia) and soft rush (Juncus effusus), hard rush (J. inflexus) and common rush (J. conglomeratus).

Heterogeneity assessmentsNine sites were assessed for heterogeneity in the spatial distribution of vegetation height on five occasions in 2000, by reference to the series of diagrams shown in Appendix 1, Figure 7. Three of the diagrams (A,B and E) refer to ‘tussocks’, but in this context the term included clumps of vegetation of greater height than the surrounding vegetation, not confined to tussock-forming species as described above. Note that where these diagrams are presented in the field guidelines in Appendix 6, the word ‘tussock’ has been replaced by ‘clump’, defined as a patch of vegetation at least 5cm higher than the surrounding vegetation and typically 30-60cm in diameter. This corresponds to the definition used by Milsom et al. (2000) for a tussock.

Accuracy of visual assessments at the field scaleOn each occasion during 1999 and 2000 when the detailed sward measurements were made at each of the 10 sites, a preliminary walk was made over the transect and overall visual assessments were made at the field scale of mean sward height, herb and ground cover. These results were later compared with data from the detailed assessments made during a second walk of the transect, to assess the accuracy of overall visual scoring.

Assessor trial A trial was also conducted to assess objectivity and repeatability of the methods described above for assessing sward height, herb and ground cover. This trial was carried out on September 1 1999 in two fields at Aston Rowant National Nature Reserve, one of which was a site used in the main study (Site 8, NVC community CG2). Six assessors took part, four from FRCA and two from ADAS. Assessors each made assessments at 50 approximately evenly spaced locations within an individual W-shaped transect covering the whole field. For herb and bare ground cover, assessments were made in both a 1m and a 2m arc. All assessments were made completely independantly by each assessor, with no preliminary calibration between them. Development of the sward guidelines frameworkParticular key periods were considered appropriate for assessment of each of the three main sward structure variables in grazed pastures. For sward height, these periods were early spring (April), summer (June-July), and late autumn (October-November), corresponding to the start of the growing season, peak summer growth and the end of the growing season respectively. For herb and weed cover, early-mid summer was chosen as the period when cover of these components could be expected to be at their peak. April and September were considered appropriate months for the assessment of bare ground, representing periods of peak seedling germination. Consultation with English Nature (EN) in particular suggested that grassland types, as identified within the National Vegetation Classification (NVC, Rodwell 1991 et seq.), could be grouped according to their management requirements. This approach, closely reflects that developed by EN as part of their rapid assessment methodology for monitoring the condition of lowland grassland SSSIs (Robertson & Jefferson 2000). The groupings adopted for the development of guidelines in this project are shown later in the Results section.

To support the approach of grouping sites within this data set, differences in mean sward height between these grassland groups were tested by one-way analysis of variance (ANOVA) within each of the three key periods in each year. These analyses used the mean height for each site calculated over each period as individual units in the analysis. This gave between 2 and 4 replicates for each group within each period in 1998, but the reduction in the number of sites in 1999 and 2000 meant that few groups were replicated at all, with a maximum of two replicates for any one group within each period. Some caution is required in interpreting these results, however, since it is debatable as to whether the sites can be said to have been a strictly random example of each grassland type on a national scale.

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MAFFproject code

BD1412

The use of data from study sites to develop the guidelines, in conjunction with information from other sources, is described in more detail after the next section (see Development of Sward Guidelines).

RESULTS AND ANALYSIS OF STUDY SITE DATA

Literature review and consultationA full report on this review is appended to this report (Appendix 4). The review identified a number of potential key sward characteristics and methods for their measurement. These were sward height, bare ground, litter cover and herb cover. Estimates of species composition were considered too intensive for use routinely by Project Officers or farmers. Sward height methods included use of estimation by eye, HFRO swardstick and 10cm and 30cm diameter drop-disks. Given the need for rapidity and relative ease of use, the most applicable abundance assessment methods for bare ground, litter and herb abundance comprised either a) estimating cover by eye (at various scales), or b) use of subdivided quadrats for frequency counts.

Comparison of sward height measurement techniquesDrop-disc measurements were shorter and less variable in general than swardstick measurements, whilst the 30 cm diameter disc produced consistently higher mean sward heights than 10 cm discs (Table 1). Differences between swardstick and drop-disc mean heights were highly significant at each site (P<0.001 compared to both sizes of disc), and differences between the two drop-discs were also significant (P<0.01 all sites except Aston Rowant, P<0.05). Coefficients of variation were notably higher with swardstick than drop-disc measurements, except in the tussocky vegetation at Winnall Moor, where the difference was only noticeable compared to the 30 cm diameter disc (Table 1).

Within-site relationships between swardstick (treated as the explanatory variable) and drop-disc readings were consistently closer for 10 cm discs than for 30 cm. The precision of the relationships derived, as indicated by the proportion of the variance accounted for by the regression, was positively related to the mean height of the sward. These proportions ranged from 20% to 56% of the variance for 10 cm discs, and from 0% to 51% for 30 cm discs, with Wotton-under-edge and Winnall Moor site producing the least and most precise relationships respectively for both types of disc. All relationships were significant at P<0.001, except for those with 30 cm discs at Asham Mead (P=0.005) and Wotton-under-edge sites (P=0.361, N.S.). All these regression relationships showed highly significant (P<0.001) positive intercept values, as did 30 cm disc values plotted against 10 cm values. This suggests both an inability of drop-discs to detect fine-scale variation in shorter vegetation (confirming impressions gained at the time) and an increased compressing effect in taller swards. Note that contact with rushes and flowering heads was avoided as far as possible during sward height measurements. The larger diameter disc was less able to respond to fine-scale heterogeneity in sward surface height than the 10 cm disc, resulting in greater mean sward heights, particularly in the tussocky vegetation at Winnall Moor. The poor correlation between methods in the short grazed sward at Wotton-under-edge reflects the difficulty of comparing methods where the range of sward heights is small in relation to the variation in readings accounted for by the sloping and uneven ground surface.

Table 1. Comparison of three methods of measuring sward height. Cofficients of variation and S.E.s for individual method and site refer to within-site variation, S.E.s given under Method are the effective standard errors (with appropriate degrees of freedom, df) from an analysis of variance (ANOVA) for height technique at each site. Values in brackets are means and S.E.s of log10-transformed data, where transformed data were used in the ANOVA.

Site, NVC type and description Method

Mean height (cm)

Coefft. of variation (%) S.E. Precision1

Asham Mead, MG5 Sward stick 6.3 29.0 0.21 0.42Cut c. 4 weeks 10cm drop disc 4.0 23.8 0.11 0.22previously, aftermath 30cm drop disc 4.6 16.2 0.09 0.17evenly grazed (sheep) S.E. (df=222) 0.15

Wotton-under-edge, Sward stick 5.7 29.8 0.24 0.48CG5 Short, steep, 10cm drop disc 3.1 19.5 0.08 0.17very uneven and 30cm drop disc 3.7 13.9 0.07 0.14

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MAFFproject code

BD1412

Site, NVC type and description Method

Mean height (cm)

Coefft. of variation (%) S.E. Precision1

stoney ground S.E. (df=147) 0.15

Aston Rowant, CG3 Sward stick 10.9 (0.87) 32.1 0.35 0.70Fairly even, small 10cm drop disc 7.5 (0.73) 22.0 0.17 0.33clumps and occasional

30cm drop disc 8.4 (0.79) 17.2 0.14 0.29

scrub seedlings S.E. (df=297) (0.014) Winnall Moor, M22 Sward stick 11.9 (0.98) 54.8 0.65 1.29Short grazed areas 10cm drop disc 6.3 (0.74) 54.6 0.34 0.68between tall, ungrazed 30cm drop disc 7.6 (0.84) 44.6 0.34 0.67tussocks. S.E. (df=297) (0.024)1Precision defined as 95% confidence limits (±)

Regressions were also carried out using 30 cm drop-disc data as the explanatory variable to allow swardstick heights to be predicted for 30 cm drop disc values, such as those used by organisations such as English Nature (Robertson, Bingham & Slater 2000) and Butterfly Conservation (BUTT 1986). Note that the nature of regression analysis is such that these relationships are not simply mirror images of those described above (Kent & Coker 1992). A regression including data from all sites together showed that swardstick heights were about 1.3 times those produced by 30 cm drop-discs (Table 2). However, as with the relationships described above, the relationship differed markedly between sites, resulting in somewhat different swardstick heights predicted for a given range of drop-disc readings (Table 2). It is not clear to what extent this was simply a reflection of differences in vegetation height and range between sites. For example, a regression using Winnall Moor data restricted to drop-disc readings within the range encountered at Aston Rowant still differed markedly in both slope (2.0 vs. 1.26) and constant (-2.7 vs. +0.22) compared to that for Aston Rowant.

Table 2. Sward surface heights, as measured by the HFRO swardstick, for given 30 cm drop-disc readings, predicted from regression analyses using data from four different sites. Values in italics and beneath the line in each column were derived from drop-disc disc values outside the range encountered at that particular site. Note that no significant relationship was shown between the two techniques at Wooton-under-edge. The overall relationship for all sites was derived from log10-transformed values for both drop-disc and swardstick.30 cm drop- disc height

Winnall Moor (M22)

Aston Rowant (CG3)

Asham MeadMG5 aftermath

Wotton-under-edge1 (CG5) All sites

0 -0.4 0.2 2.7 4.1 -1 1.3 1.5 3.5 4.5 1.32 2.9 2.7 4.2 5.0 2.63 4.5 4.0 5.0 5.4 4.04 6.1 5.3 5.8 5.9 5.35 7.7 6.5 6.6 6.3 6.76 9.3 7.8 7.4 6.7 8.07 10.9 9.1 8.1 7.2 9.48 12.5 10.3 8.9 7.6 10.79 14.1 11.6 9.7 8.1 12.1

10 15.8 12.9 10.5 8.5 13.411 17.4 14.1 11.3 9.0 14.812 19.0 15.4 12.0 9.4 16.213 20.6 16.7 12.8 9.8 17.514 22.2 17.9 13.6 10.3 18.915 23.8 19.2 14.4 10.7 20.2

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MAFFproject code

BD1412

30 cm drop- disc height

Winnall Moor (M22)

Aston Rowant (CG3)

Asham MeadMG5 aftermath

Wotton-under-edge1 (CG5) All sites

16 25.4 20.4 15.2 11.2 21.617 27.0 21.7 15.9 11.6 23.018 28.7 23.0 16.7 12.0 24.319 30.3 24.2 17.5 12.5 25.720 31.9 25.5 18.3 12.9 27.121 33.5 26.8 19.1 13.4 28.422 35.1 28.0 19.8 13.8 29.823 36.7 29.3 20.6 14.2 31.224 38.3 30.6 21.4 14.7 32.525 39.9 31.8 22.2 15.1 33.926 41.6 33.1 23.0 15.6 35.327 43.2 34.3 23.7 16.0 36.628 44.8 35.6 24.5 16.4 38.029 46.4 36.9 25.3 16.9 39.430 48.0 38.1 26.1 17.3 40.7

Regression equations (SS= Swardstick height; DD=30 cm drop-disc)Winnall Moor:. SS= 1.61DD - 0.4 P<0.001 Variance accounted for: 51.1%Aston Rowant: SS = 0.2+1.26DD P<0.001 “ “ 26.5%Asham Mead: SS = 2.7+0.78DD P=0.005 “ “ 9.0%Wotton-u-edge: SS = 4.1+0.44DD N.S. “ “ 0%1

All sites: log10SS = 0.119 + 1.010(log10DD) P<0.001 “ “ 51.2%

Analyses of 1998 sward height data from 21 sites

Seasonal variationSwardstick heights varied very significantly between assessments at most sites, with only aftermath growth at Asham Mead (Site 10) showing no significant effect in the ANOVA. The effect was highly significant at all other sites (P<0.001), with the exception of Myrus Sutton (Site 3) when rushes were included in the measurements ( P<0.05 with rushes included, P<0.001 with rushes excluded). Including rushes in measurements at this site increased mean sward height by about 32% on average and increased the variation (standard error) by about 83%. Sward heights tended to be greatest in June-August, even in sites grazed throughout the summer, with peaks occurring towards the end of this period where swards were rested in spring-summer (see Figures 1-4 in Appendix 1).

PrecisionConsultation and trialing with several Project Officers suggested that time would allow no more than 30 measurements to be taken on most site visits, although they accepted that more heights would be needed in large or very variable fields. Analyses showed that, in most cases, 30 readings would provide a reasonably accurate estimated of the mean (within 1-2 cm at 95% confidence limits) throughout the season. Precision varied with mean sward height. Within the range 0-10 cm, heights could be estimated confidently to within 1 cm, whereas sites with monthly mean heights up to 20 cm were estimated to 2-3 cm precision. At Myrus Sutton, incorporation of rushes into the measurements reduced the precision nearly three-fold (i.e. on average from 0.6 cm to 1.5 cm). This suggests that more than 30 heights may be required to give an accurate measure of heterogeneity on very heterogeneous swards (see later).

Patterns of sward height at individual sites in three years Sward heights recorded at each site in 1998, 1999 and 2000 are shown in Figures 1-4 in Appendix 1, grouped into calcareous, acid, and mesotrophic grasslands and fen meadows respectively. These show considerable variation both within season and between years in many cases, due both to grazing management and weather patterns. Exceptional rainfall in 2000 meant that sward heights were greatest in that year at most sites. Calcareous sites, which were typically

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BD1412

grazed in autumn and winter, with only light grazing, or none at all, in mid summer (see Appendix 2, Table A2.1), showed considerable accumulation of herbage by summer and autumn, particularly in 2000. Sward heights in the dry U1 grassland at Eriswell Warren (Site 6), which is grazed only in autumn, were considered to be well above optimum during the whole the spring and summer of 2000. At site 3 (M22), a very large amount of growth accumulated during the spring as swards were not grazed in that year until after a hay cut in July, in contrast to previous years. At Sites 12,14,16, heights were measured, erroneously, to a maximum of 30 cm in all three years, a problem which became clear only in 2000 when swards were taller than in previous years. Much of the data collected from these sites in 2000 had to be discarded, since a considerable number of readings were above 30 cm, and similarly with data collected between June and September 1999 at Site 14. There was a large accumulation of growth in the wet grassland community (MG8) at Site 16 in 2000 due to lack of grazing, which had been prevented by flooding in spring followed by prolonged waterlogging.

Analysis of sward height data grouped by grassland typeThe grouping of grassland types used in these analyses, and the number of sites for which data were available for each group within each year and period, are shown in Table 3. The mean heights and ranges given in Table 3 for each grassland group and period are aggregated from field means taken over all sites, assessments and years within the relevant period. These values illustrate the overall differences between groups, and contributed to the development of the sward height guidelines described later. Mean values for each period within each year at sites grouped as in Table 3 are given in Appendix Table A2.2.

Table 3. Mean sward surface heights and range (cm) recorded using the HFRO swardstick at 21 sites in 1998 and 10 sites in 1999 and 2000. Sites are grouped by grassland type with reference to the National Vegetation Classification (NVC, Rodwell 1991 et seq.), and values are aggregated over all sites, assessments and years within three key periods for each group. The number of contributing values for each period within each grassland type are given in the column headed n.

Grassland Number of sites Eng. Naturetype (NVC) Period Mean Range n 1998 1999 2000 heights†

1 CG2 April 3.8 (2.9 - 4.3) 7 3 2 22 CG3, CG5 “ 4.7 (4.3 - 5.4) 3 0 1 23 M22 “ 8.0 (5.9 - 13.6) 5 1 2 24 M24 “ 7.2 (6.3 - 8.1) 2 0 1 15 MG6/13 “ 7.2 (5.4 - 8.9) 4 2 1 16 MG8 “ 8.5 (7.0 - 10.8) 3 1 1 17 U1 “ 6.7 (4.0 - 9.2) 3 1 1 18 U2 “ 6.7 (6.7 - 6.7) 1 1 0 09 SD10 “ 7.6 (7.6 - 7.6) 1 1 0 0

1 CG2 June-July 9.3 (4.7 - 15.2) 14 4 2 1 2 - 102 CG3, CG5 “ 10.7 (8.2 - 14.5) 11 2 2 2 2 - 153 M22 “ 15.9 (6.0 - 41.4) 9 2 1 1 >2‡

4 M24 “ 21.1 (9.7 - 26.8) 10 3 1 1 >2‡

5 MG6/13 “ 11.4 (6.4 - 15.1) 8 2 1 1 5 - 15‡‡

6 MG8 “ 7.1 (5.7 - 8.5) 4 1 1 0 5 - 157 U1 “ 8.9 (5.9 - 12.4) 6 1 1 1 <58 U2 “ 13.1 (10.8 - 15.4) 2 1 0 09 SD10 “ 13.0 (12.4 - 13.5) 2 1 0 010 MG4, MG5 “ 7.1 (6.2 - 7.9) 2 2 0 0 5 - 15‡‡‡

1 CG2 Oct-Nov 8.7 (3.9 - 11.9) 6 4 2 02 CG3, CG5 “ 7.2 (6.0 - 8.9) 4 2 2 03 M22 “ 7.4 (6.3 - 8.9) 7 3 2 04 M24 “ 12.9 (8.3 - 16.9) 4 3 1 05 MG6/13 “ 9.1 (8.3 - 10.1) 5 2 1 06 MG8 “ 8.8 (5.2 - 11.4) 3 2 1 07 U1 “ 7.3 (5.6 - 9.2) 3 1 1 0

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Grassland Number of sites Eng. Naturetype (NVC) Period Mean Range n 1998 1999 2000 heights†

8 U2 “ 10.5 (10.2 - 10.8) 2 1 0 09 SD10 “ 8.4 (7.3 - 9.5) 2 1 0 010 MG4, MG5 “ 5.4 (4.8 - 6.0) 1 1 0 0

† English Nature guidelines from Robertson & Jefferson (2000). Recommended visiting times are mostly May-August, but the range of heights specified are intended to apply to any time of year.

‡ Guidelines also suggest limits to the proportion of the sward above a given height: M22, <25%>40 including Juncus spp.; M24a, <25%>60 incl. Juncus spp.; for M24b and c 25%>15.

‡‡ Applies to MG13-related swards‡‡‡ Applies to MG5 grazed only pastures. Study sites were hay meadows where June-July and Oct-

Nov heights refer to aftermath growth.

Despite the limited replication (i.e. the small number of sites within each grassland group), ANOVAs showed a significant influence of grassland type on mean sward height during each of the three periods in 1998 (April and June-July both P<0.001, October-November P=0.045). Only CG2 and MG6/13 types were represented by more than one site in April 1998 (see Table 3), when MG6/13 sites were very significantly taller than CG2 sites (P<0.001). M24 swards were the only ones to show significant differences compared to others during later periods. These swards were much taller than all others included in the analysis, both in June-July (i.e. compared to groups 1-5 and 10, P<0.001) and in October-November, when compared to groups 1 (P<0.05), 2 and 3 (P<0.01), and 6 (P<0.05), but not when compared to group 5 (MG6/13). There was no significant difference in 1999 and 2000 among the few groups for which there were data for more than one site within each period.

Bare ground coverValues recorded for bare ground cover at each of the 10 sites assessed in 1999 and 2000 are shown in Figure 5 in Appendix 1. The mean and range of values recorded in April and September of each year for each grassland type are given in Appendix 2 Table A2.3. and summarised in Table 4 below. Due to the small number of sites assessed in 1999 and 2000, no statistical analysis was carried out for differences between grassland types in either bare ground cover, herb cover or cover of weeds and tussocks.

Table 4. Mean and range of bare ground cover (%) in April and September aggregated over two years (1999 and 2000) for all sites of each grassland type. The number of contributing values for each period within each grassland type are given in the column headed n.

Grassland type (NVC) Month Mean Range nNo. of sites

1 CG2 April 2.1 (0.0 - 4.4) 4 22 CG3, CG5 “ 3.5 (0.0 - 8.3) 3 23 M22 “ 0.9 (0.0 - 2.2) 4 24 M24 “ 3.1 (2.8 - 3.4) 2 15 MG6/13 “ 2.4 (2.1 - 2.7) 2 16 MG8 “ 0.2 (0.0 - 0.4) 2 17 U1 “ 0.7 (0.6 - 0.7) 2 1

1 CG2 September 0.6 (0.0 - 2.0) 4 22 CG3, CG5 “ 0.6 (0.2 - 1.1) 4 23 M22 “ 0.7 (0.0 - 2.7) 4 24 M24 “ 0.8 (0.1 - 1.6) 2 15 MG6/13 “ 0.3 (0.2 - 0.4) 2 16 MG8 “ 0.2 (0.0 - 0.3) 2 17 U1 “ 1.4 (1.1 - 1.6) 2 1

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Bare ground cover tended to be lowest in 2000 at most sites, and lowest in mid-season, though the latter effect was not consistent between sites. Values were generally low, with no mean for a site greater than 8.3 in either April or September. This latter height was recorded at the CG5 site at Wotton-under-edge, the only calcareous site grazed by cattle in the sample of sites. Stocking intensity at this site was generally eased in mid-summer each year, which was reflected in a fairly rapid increase in sward height and a corresponding reduction in bare ground cover between April and June (see Figures 1 and 5).

Herb coverIn contrast to bare ground cover, herb cover tended to be greater in 2000 than in 1999, and greater in mid season than either spring or autumn (see Appendix 1, Figure 6). The latter effect was particularly noticeable at Site 9. The greatest contrast between years was at Site 19 (M24) where unexpectedly low values were recorded in 1999. These low herb cover values do not appear to be associated with particularly high values for bare ground cover, although the differences between years do correspond with differences in sward height.

Mean herb cover values for May-July are summarised over two years in Table 5 for each grassland type, data for each year separately are given in Appendix 2 Table A2.4. In each case where appropriate guidelines for herb cover exist for a particular grassland type (Robertson & Jefferson 2000), values fell within the expected range, i.e. calcareous grassland (CG2, CG3 and CG5) and species-rich parched grassland (U1). Highest mean herb cover values were recorded in these groups. The lowest values were recorded in the semi-improved grassland undergoing reversion to wetland (MG6/13) at Berney Marsh. No distinction was made in these assessments between legumes and other broad-leaved plants at any site, and a significant proportion of the herb cover in the drier areas at the Berney Marsh was of Trifolium repens. Note also that herb cover included rushes and sedges, and a significant proportion of the herb cover on M22 sites, for example, was accounted for by blunt-flowered rush (Juncus subnodulosus).

Table 5. Mean and range of herb cover (%), aggregated from data collected monthly in May-July in two years (1999 and 2000) and summarised by grassland type. The number of contributing values for each period within each grassland type are given in the column headed n.

Grassland type (NVC) Mean Range nNo. of sites

1 CG2 71.0 (43.3 - 92.7) 12 22 CG3, CG5 68.7 (47.3 - 80.3) 11 23 M22 59.7 (39.7 - 75.4) 12 24 M24 27.2 (9.2 - 54.9) 6 15 MG6/13 11.0 (9.5 - 12.5) 6 16 MG8 40.7 (24.7 - 61.7) 6 17 U1 65.8 (49.3 - 78.0) 6 1

Abundance of weedsWeeds were generally scarce at most sites (Table 6). No bracken was recorded at any site, and the cover of weeds at Berney Marsh (MG6/13) was entirely composed of thistles (Appendix 2 Table A2.5). There was a small presence of both thistles and ragwort at some of the calcareous sites, and ragwort attained up to 10% ground cover at the parched grassland (U1) site in 1999.

Table 6. Total weed cover (%), aggregated from data collected monthly in May-July in two years (1999 and 2000) and summarised by grassland type. The number of contributing values for each period within each grassland type are given in the column headed n.


1 CG2 0.4 (0 - 2) 12 22 CG3, CG5 0.7 (0 - 2) 11 2

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3 M22 0.4 (0 - 2) 12 24 M24 1.7 (1 - 3) 6 15 MG6/13 7.5 (5 - 10) 6 16 MG8 0.7 (0 - 2) 6 17 U1 2.3 (0 - 10) 6 1

Abundance of tussocksTussocks were recorded within all the grassland types assessed in 1999 and 2000 except U1, including in calcareous grasslands at Aston Rowant (Sites 8 and 9), where the species responsible was tentatively identified as a Bromus sp., possibly B. erecta. Tussocks were most abundant in the Molinia-dominated fen meadow (M24) site (where species such as Deschampsia caespitosa and Juncus also contributed to tussock cover), with a much smaller presence in the MG8 and M22 sites.

Table 7. Mean and range of tussock cover (%), aggregated from data collected monthly in May-July in two years (1999 and 2000) and summarised by grassland type. The number of contributing values for each period within each grassland type are given in the column headed n.


1 CG2 0.3 (0 - 4) 12 22 CG3, CG5 0.1 (0 - 1) 11 23 M22 5.8 (0 - 15) 12 24 M24 35.8 (20 - 60) 6 15 MG6/13 0.0 (0 - 0) 6 16 MG8 3.3 (0 - 10) 6 17 U1 0.0 (0 - 0) 6 1

Heterogeneity assessmentsResults of the assessmensts of spatial heterogeneity in sward height, made at nine sites by reference to the series of diagrams shown in Appendix 1, Figure 7, are given in Table 8. As noted in the Methods section, whilst some of the diagrams in Figure 7 refer to ‘tussocks’, a broader interpretation was applied than the tight definition of a tussock used for tussock cover assessments (i.e. a single-species group of densely clumped shoots originating from a single rootstock, with a diameter of 15cm or more). The term ‘clump’, as defined in the Methods section and the legend to the heterogeneity diagrams presented in Appendix 6 (i.e. not resticted to single-species clumps), is more appropriate.

For a proper interpretation of this information it is necessary to refer also to trends in sward height, since the heterogeneity scores refer only to variation in the sward surface. For example, at the CG2 site at Aston Rowant (Site 8), sward height increased progressively in the absence of grazing until the end of July, declining somewhat by early September (see Appendix 1, Figure 1). Grazing did not begin until after this final assessment, and, in common with the remaining sites in these assessments, no cutting took place at the site. The trends seen were therefore presumaby related to accumulation of herbage and phenological development of the constituent plants, and possibly to heerogeneity in growing conditions across the site. Patterns of heterogeneity at Site 8 were seen to be different on each occasion during this period assessed. A sequence appears to have developed, from an even distribution of tussocks in April (B) (see Appendix 1, Figure 7), through a phase of fewer tussocks in May (A) to an accumulation of larger blocks of longer vegetation in June (D). This apparently developed further into two distinct areas of tall vegetation by late July (C), returning to a more evenly heterogeneous pattern by early September (B). Other sites showed much less changing patterns of heterogeneity, including the other CG2 site at Aston Rowant (Site 9). This site was also ungrazed between April and September, but there grazing ceased a week after the April assessment, in contrast to Site 8 where grazing had ceased at the end of January. It is not possible to tell whether the apparent differences in sward structural development between the two sites were due to differences in grazing management or to other innate differences between the sites (e.g. species distribution patterns or topography).

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Table 8. Heterogeneity codes (see Appendix 1, Figure 7) attributed to vegetation at nine contrasting sites on five occasions during 2000

Site and NVC community Date

Hetero-geneity

code

2 Berney Marshes (Field B) MG6/13 27-April B" " " " 22-May B" " " " 16-June B" " " " 17-July D" " " " 25-August B

3 Myrus Sutton M22 27-April B" " " " 22-May B" " " " 16-June D" " " " 17-July B" " " " 25-August B

6 Eriswell Low Warren U1 27-April C" " " " 22-May C" " " " 16-June D" " " " 17-July D" " " " 25-August D

8 Aston Rowant - Beacon Hill CG2 11-April B" " " " 11-May A" " " " 16-June D" " " " 31-July C" " " " 08-September B

9 Aston Rowant - Compartment 8.0 CG3 11-April B" " " " 11-May C" " " " 16-June B" " " " 31-July B" " " " 08-September B

12 Old Winchester Hill CG2 13-April B" " " " 24-May F" " " " 05-July F" " " " 03-August F" " " " 20-September F

14 Winnall Moor - pasture M22 13-April D" " " " 24-May D" " " " 05-July D" " " " 03-August D" " " " 20-September D

16 Braemore (ungrazed this year) MG8 13-April D" " " " 24-May D" " " " 05-July E" " " " 03-August B" " " " 21-September E

18 Wotton-under-edge CG5 12-April A" " " " 05-May A" " " " 12-June A" " " " 01-August A" " " " 06-September B

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Sward height profiles for three sites in July 1998, 1999 and 2000 (including Site 8) are shown in Figure 8 (Appendix 1). Profiles differed noticeably between sites and between years at a particular site, and it is possible to see how the heterogeneity pattern attributed to each site in 2000 relates to the corresponding profile. At Site 8 (Code C, two distinct areas with vegetation at different heights), there are two portions of the profile consisting of a large number of consecutive readings at or above the mean, mirrored by other portions where the heights are predominantly below the mean. Note that these readings were taken on a W-shaped profile, not a straight transect. Sites 2 (code D) and Site 3 (Code B), show discernibly different patterns, although the differences are fairly subtle. It seems unlikely that a smaller number of height measurements would have been sufficient to show the patterns at these sights, particularly at Site 3 where heterogeneity was at a finer scale in 2000 than at the other two sites.

Accuracy of visual assessments at the field scaleVisual assessments of sward height at a field scale were closely correlated with sward height means calculated using the swardstick, when both sets of data for all sites were compared for each year (R2=0.54 in 1999, R2=0.83 in 2000, both P<0.001). Regression coefficients (0.94 and 0.87 for 1999 and 2000 respectively) suggested that visual estimates tended to under estimate heights slightly, but this effect was very marginal. Field-scale herb cover estimates were very closely correlated in both years with those made more systematically (R2=0.92 and 0.81 respectively, both P<0.001), with regression coefficients suggesting a slight overall tendency for field-scale assessments to underestimate (regression coefficients = 0.92 and 0.84 for 1999 and 2000 respectively).

Bare ground cover proved much more difficult to assess accurately by field-scale assessment. Although relationships were significant in both years, due to the large number of pairs of values (n=67 in 1999 and 49 in 2000), field scale estimates were quite poorly correlated with those estimated systematically (R2=0.11 in 1999, P<0.01; and R2=0.29 in 2000 P<0.001). There was a strong tendency to under-estimate bare ground in 1999, by a factor of about two (regression cofficient=0.49), and a slight tendency to over-estimate in 2000 (coefficient =1.17). However, these results do suggest a considerable improvement in accuracy between 1999 and 2000. It should also be noted that the range of bare ground cover values encompassed was very low, with maximum values recorded in systematic assessments for all sites of 8.3% in 1999 and only 3.6% in 2000. Better relationships between the two forms of assessment would no doubt have been achieved from a wider range of values.

Note that these assessments were made by four different assessors at a total of 10 sites each year, although each site was assessed by the same person on each occasion in each year, and in three out of the four cases, by the same person in both years.

Inter-assessor accuracyThe scope of this trial was limited, with only six assessors operating in two fields on one occasion. The results are presented in Appendix 2, Table A2.7. Mean sward heights (measured by swardstick) for individual assessors deviated from the overall mean, calculated from all six sets of readings for a field, by between -18.4% and +19.6% of this mean. The same assessor was responsible for both these extremes. Other assessors generally deviated by less than 10% from the overall mean. Herb cover estimates showed slightly less variation between assessors, particularly when estimating cover within a 1m arc (-12% to +14% deviation from the overall mean) compared with a 2m arc (-14.0% to +15.0%). Most assessors noted difficulties with assessing herb cover at the larger scale. The data confirmed the general opinion that using the larger diameter arc would lead to an underestimate of herb cover. However, although 2m arc estimates were consistently lower than 1m arc measures, the differences were marginal (between 0.5% and 5.3% cover for an overall mean of 77.3% cover).

Inter-assessor variation was much greater with bare ground assessments, although bare ground cover was generally very low (estimates using a 1m arc ranged between 0.9% and 3.5% cover over the two fields). Estimates deviated by between –48% and +115% of the overall mean for 1m arc estimates, and by between –70% and +108% for the 2m arc. In contrast to herb cover estimates, bare ground cover estimates at the 2m scale were mostly greater than at the 1m scale, although the differences were slight (overall estimate at 1m scale = 1.7% cover compared to 2.2% cover at the 2m scale).

These results confirm those of a published study showing that inter-assessor variability in bare ground assessments is much greater than for visual estimates of sward height or herb cover (Robertson, Bingham and Slater 2000). It should

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also be noted that, before the day of the trial, only one of the six assessors taking part had any more than a passing familiarity with the techniques being used.

DEVELOPMENT OF GUIDELINESA fairly detailed protocol for arriving at a management agreement for a particular site is proposed in a separate Appendix to this report (Appendix 5). This includes a recommended procedure for defining, implementing and reviewing management guidelines, as well as information on the specific sward structure requirements of a range of avian and invertebrate species. Three sets of sward structure guidelines are provided in Appendix 6, each at a different level of detail in terms of the number of classes that grasslands are broken down into, and for which specific guidelines are defined. The remainder of this section describes how these guidelines were developed.

Consultation during the course of the project produced a list of grassland types for which guidelines were desirable. This corresponds quite closely with those for which English Nature have developed a rapid assessment methodology (Robertson & Jefferson 2000). Grassland types are defined in terms of plant communities and sub-communities within the National Vegetation Classification (NVC, Rodwell 1991 et seq.) and are grouped largely as in Robertson & Jefferson (2000). This grouping therefore corresponds with that used for analysis of data from the study sites, although a relatively small proportion of the total number of plant communities and sub-communities considered here were represented by sites studied in this project. In drawing up a framework of guidelines, the target values and acceptable ranges arrived at rely quite heavily on information form Robertson & Jefferson (2000) and other sources, modified as appropriate by the results from the study sites.

Sward heightsThe basic approach was to use data from the study sites to identify target sward heights for each of the key periods, and in some cases the range (maximum and minimum) of acceptable values, but relying on English Nature (EN) guidelines (Robertson & Jefferson 2000) particularly to provide acceptable ranges. However, almost all the ranges of acceptable sward heights given in EN guidelines cover the whole growing season, whereas, for this project, guideline values were required for three key periods: April; June-July; and October-November. In several cases, the maximum and/or minimum value in an EN range was applied to an individual period but adjusted to reflect seasonal differences in mean (target) sward height shown by data from the relevant sites.

This overall approach was modified extensively in the light of information on grazing management for individual sites. Considerable emphasis was placed upon comments made by site managers as to the extent to which they felt that grazing had achieved the desired result in a particular year. For example, several noted that herbage growth was exceptional in 2000 and that greater control would have been preferable. Thus, there were some cases where data from 2000 were used to define an upper acceptable limit for sward height, but target heights were based upon relevant study site mean heights calculated without 2000 data.

Target sward heights and acceptable ranges for three key periods are given in Table 9. This table includes extensive footnotes explaining the sources of data and how they were used. The guideline values quoted are for grazed swards only and it is important to note that values near the extremes of the ranges would serve as a warning signal. It would not be acceptable for sward heights to remain at or near these extremes for any length of time. Data were not used from periods when ungrazed growth had accumulated, e.g. in summer where a site had been shut up for hay or where, unintentionally, no grazing occurred in a particular year. This occurred in 2000 at Meshaw Moor (M24), due to problems with graziers (Ross Bower, Devon Wildlife Trust, personal communication). Exceptions to this rule were made where it was normal practice to graze only in autumn-winter or to rest the pasture in mid season each year (e.g. at the U1 site and in some calcareous grassland sites – see Appendix 2, Table A1). Some data for M22 and M24 sites were disregarded in the calculation of target mean heights, because the proportion of sward heights above a certain maximum (see footnotes to Table 9) exceeded that prescribed in Robertson and Jefferson (2000). This applied at Site 3 (M22) in June 2000, at Site 20 and 21 (M24) in all months except January 1999 (these sites were not assessed after January 1999), and at Site 19 in June-August 1998, and at all assessments in 2000 except April.

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Table 9. Development of sward surface height guidelines for grassland types. NVC communities represented by sites in this study are in bold type. Unless noted otherwise, values are based upon data from this project. All heights exclude rushes and flowering stems and target values assume optimum grazing management for grazed pastures (see text and footnotes). Values in brackets represent an acceptable range of values for each period, although values near the limits of the range would serve as a warning signal, and swards would not be expected to remain at or close to these limits. Note that data for the October-November period were obtained only in 1998 and 1999 from sites assessed in this project.

Target sward surface height and range (cm)Grassland type (NVC) April June/July Oct/Nov

CG2 4 (2-5)11 9 (2-10)1 9 (2-10)1a

CG3,4 &5 5 (2-7)11 9 (2-15)1 9 (2-15)1a

CG8, CG9a,b,c (2-15)1

CG7a,b,d,e; U1b,c,d,f 4 (<9) 2 <7 (1-12) 2 <5 (1-9) 2

U1a;CG7c <51

U1e (1-5)1

U2 <7 <13 <11U3,U4a (1-5) 1

U4c (3-10) 1

M22 8 (2–14)3 13 (see below)3 7 (see below)3

M23 8 (2–14)4 13 (see below)4 7 (see below )4

M24a,M25c >8 1 (see below)5

M24b,c/M25a,b 7 (2-14)5 10 (see below)5 10 (see below)5

MG4 ? (5<)7 >106 ?>101

MG5 ? (5<)7 106 (5-15)7 56 (3–7)8

MG6/13 7 (5-10)9 11 (5-15)10 9 (5-12)9

MG8 8 (5-12)9 10 (5-15)1 9 (5-13)9

MG9/10 ?(5-15?)12

? Indicates that there is a lack of information to provide a definitive guideline. Figures given are tentative and are not backed up by published scientific work.

1Taken from English Nature (EN) guidelines (Robertson & Jefferson 2000). Ranges given in EN guidelines encompass assessment at any time of year. For M22-25 communities, note that EN guidelines include a minimum overall sward height and maximum proportion of the vegetation above certain heights, but no prescribed range for overall heights

1aUpper limit assuming further grazing to follow during the winter.2 The target and maximum heights are based on project data modified after consultation with the

site manager. Sward heights recorded at this site were considered generally above optimum (due to unusually high rainfall), particularly in 2000 which provided the maximum value for the ranges quoted.

3Target heights based upon data from this project, but excluding June-July in 2000 when the site for which data are available was shut up for hay. Lower limits for range in April are based upon EN guidelines. EN guidelines suggest limits to the proportion of the sward above a given height as no more than 25% at greater than 40 cm, including Juncus spp.

4Based upon data for M22 sites from this project and EN guidelines5 Target heights for April based upon data for M24 sites from 1999 and 2000 in this project, and

the lower limit for the range upon EN guidelines. Target heights for June-July are based upon data from Site 19 in 1999 (June-July) and those for October-November upon data from the same site in both 1998 and 1999. The site was ungrazed in 2000 so data from that year were excluded, and all other sites in previous years exceeded EN guidelines which specify for M24a,M25c: no more than 25% at >60 cm excluding. Juncus spp.; and for M24b,c and M25a,b: <25% at >15 including Juncus. Note that management guidelines for Culm grassland (Rhos pasture) state that the sward over the majority of the field should be less than 15cm for at least part of the year (Wolton, undated).

6Sward heights during aftermath growth at MG4 and MG5 sites in this project were very similar, averaging 7 cm in late July and 5cm in October-November. Higher summer targets of >13 cm for grazed MG4 (Robertson & Jefferson 2000) and 10 cm for grazed MG5 are considered more appropriate for grazing-only management, the latter intermediate between those achieved by

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Target sward surface height and range (cm)Grassland type (NVC) April June/July Oct/Nov

‘lenient’ and ‘moderate’ grazing intensities in MG5 pastures in project BD1440 (Ecologically sustainable grazing management of lowland unimproved neutral grassland and its effects on livestock performance, J.Tallowin, unpublished)

7Range taken from English Nature guidelines (Robertson & Jefferson 2000) for grazed MG5 at any time of year.

8 Range as for MG5 pastures from Gibson (1997)9Values for range based upon EN guideline range for whole season, with the maximum scaled

down in proportion to difference in target height compared to June-July period10Range based upon EN guidelines for MG1311Values for range based upon EN guideline range for whole season, with the maximum scaled

down in proportion to difference in target height compared to June-July period, assuming swards will have been grazed during the autumn-late winter period.

12There are no guidelines available for these communities but those for MG8 may be appropriate. The range quoted here is equivalent to that given in EN guidelines for MG8

Bare ground, herb and weed coverThe approach used to developing guidelines for bare ground, herb cover and weed cover was similar to that used for sward height, although even more reliance was placed on EN guidelines (Robertson & Jefferson 2000). Values recorded for all three variables within this project fell within the ranges given in EN guidelines for those communities included in the guidelines, and bare ground values were generally towards the lower end of the range quoted. Acceptable ranges and maxima for the key assessment periods for each variable are given in Table 10. As with sward heights, this table includes extensive footnotes explaining the sources of data and rationale used to produce the values. It is important to note, particularly for weed cover, that values near the extremes of the ranges would serve as a warning signal, indicating that remediation was necessary. The guideline for herb cover in MG6/13 swards (>10%) is exclusive of Trifolium repens. This species is referred to specifically in the context of MG6 pastures, since it is likely to be more abundant here than in unimproved grasslands where a significant presence of the species would be considered undesirable. The occurrence of T. repens in the MG6/13 swards was very variable. In drier areas it was equal in abundance during the summer to species such as Ranunculus repens and Bellis perennis, but was seldom present in wetter areas (Bill Parkin, personal communication).

Table 10. Development of bare ground cover and herb and weed cover guidelines for grassland types. NVC communities represented by sites in this study are in bold type. Values of weed cover near the top of the range quoted should be seen as a warning signal. See also footnote* and text in relation to the Weeds Act 1959.

Grassland type (NVC)Bare Ground cover

(%)Herb Cover

(%)Weed* cover

(%)April Sept. June June

CG2 <101 40–901 <51

CG3,4 &5 <101 40–901 <51

CG8, CG9a,b,c <101 30-901 <5 & <10 P.a.4

CG7a,b,d,e; U1b,d,f <151 40-805 <51

U1a;CG7c 10–501 N/A <51

U1c <301 40-806 <51

U1e <101 ?N/A <5 & <10 P.a.4

U2 ? N/A <5?U3,U4a <101 N/A <5 & <10 P.a.4

U4c <101 N/A <5 & <10 P.a.4

M22 <101 20–757 <51

M23 <101 20–90? <51

M24a,M25c <101 20–80? <59

M24b,c/M25a,b <101 10–80?8 <59

MG4,MG5 <51 40–901 <51

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Grassland type (NVC)Bare Ground cover

(%)Herb Cover

(%)Weed* cover

(%)April Sept. June June

MG6/13 <152 >1011 <1010

MG8 <152 <103 25–6512 <51

MG9/10 ?<1513 ?<1013 ?20–5013 ?<513

*Plants classed as ’Weeds’ within this project were thistles (Cirsium spp., excluding C. dissectum), ragwort (Senecio jacobaea / aquaticus) and bracken (Pteridium aquilinum). English Nature (EN) guidelines (Robertson & Jefferson 2000) class thistles and ragwort as ‘negative indicator’ species, usually along with a wider range of species within each community/grassland type, and sometimes with specific limits for certain individual species (e.g. bracken, ragwort). Criteria applied under the Weeds Act 1959 may result in lower allowable levels than those quoted here.

? Indicates that there is a lack of information to provide a definitive guideline. Figures given are tentative and are not backed up by published scientific work.

1 Ranges given in EN guidelines, which mostly encompass assessment at any time of year.2May-early June (Robertson & Jefferson 2000)3mid-June-July (Robertson & Jefferson 2000)4From EN guidelines, P.a. =Pteridium aquilinum5EN guidelines give no target herb cover values for ‘species-rich parched grassland’

(CG7a,b,d,e and U1b,c,d,f). The range given is based upon data from the U1b site in this project with the lower limit lowered to 40% to correspond to EN guidelines for most other species-rich grassland.

6Target as for other species-rich parched grasslands (U1b,d,f)7Based upon data from this project with the lowered limit lowered arbitrarily to better reflect

the known variation in floristic richness of this community8Lower limit based upon data from this project9Based upon EN guidelines which also stipulate <20% cover of Cirsium palustre.10Based upon the one MG6/13 site in this project, but may be high. EN guidelines for MG13

specify <5% total cover of a given range of weeds, plus <5% of Senecio aquaticus, which was not recorded at the project site.

11Based upon the single MG6/13 site data. May not be appropriate for typical MG13 or MG6 sites. Herb cover targets for the latter should be exclusive of Trifolium repens.

12Limits based upon data from this project. A higher upper limit may be appropriate.13There are no guidelines available for these communities. Values quoted are based upon

MG8, but with lower herb cover.

Project Officers in agri-environment must have regard to the Weeds Act 1959 when making judgements on agreement land. Different criteria to those outlined in Table 10, which are based on guidelines quoted by Robertson and Jefferson (2000), apply in the implementation of the Act. The Weeds Act criteria are based upon the number of individual plants of a particular noxious weed species (thistles, docks and ragwort) encountered on a transect of a given length though a patch or colony of the species. Depending upon the size and distribution of such patches in proportion to the field area, this could result in lower threshold values in terms of mean percentage cover than those quoted in Table 10, and these criteria would override the guidelines quoted here.

Note that a large proportion of bare ground is important in some parched grasslands, particularly lichen grassland (CG7c/U1a) where rabbit grazing often plays an important role. However, large areas of bare ground around warrens generally indicate that rabbit numbers have reached problem proportions (Robertson & Jefferson 2000)

Litter abundanceAs noted in the Introduction, litter abundance was not recorded at any of the study sites. Excessive litter can be a useful indicator of chronic under-grazing. English Nature guidelines set limits for litter cover “in a more or less continuous layer distributed either in patches or in one large area”. These limits are: no more than 25% for all the plant communities covered above except for lichen grassland (U1a, CG7c), where litter cover should not exceed 5% (Robertson & Jefferson 2000).

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Projecttitle


MAFFproject code

BD1412

DISCUSSIONThe framework of guidelinesThe overall objective of this project was to develop a new framework of sward-based guidelines for management of grazed grassland in ESAs and CS, which would enable viable livestock production systems to be continued whilst maximising environmental benefits. A workable protocol for monitoring sward structure in a range of grassland types was developed, based upon the use of the HFRO swardstick to measure sward surface height and a systematic approach to assessing bare ground, herb cover and other structural characteristics. The considerable amount of information collected from study sites, coupled with other information available, notably from English Nature guidelines (Robertson & Jefferson 2000), has allowed a set of sward-based guidelines to be produced for a range of named plant community types.

These guidelines are intended primarily for use by Project Officers within ESAs and Countryside Stewardship, and have been formulated at three levels of complexity, allowing for different levels of botanical expertise or quality of botanical data available for the site. There is inevitably some loss of precision involved in adopting the lower level guidelines, although the intermediate level is probably adequate in the majority of cases, with the exception of the most valuable sites. It is important that such sites are identified, so that detailed ecological surveys can be targeted on them (should such information not already be available) to allow Level 1 guidelines to be applied.

Although the guidelines appear definitive, there is still a need for further discussion and refinement, particularly as they have undergone considerable development during the final stage of the project (i.e. since the last opportunity for consultation and comment). For example, the three key periods for sward height assessment were based upon the timing of the beginning and end of the growing season, and peak growth in early summer. However, several swards are grazed primarily during the autumn-late winter period (notably calcareous grasslands), and sward heights are still relatively high in October-November. It may be more logical to set target heights for the late winter period in these grasslands, corresponding to the time when grazing ceases, instead of, or in addition to, the autumn. Swards may remain ungrazed between late winter-early spring and October, or may experience only a short spell of light grazing in mid summer.

Discussion with Project Officers and other professionals pointed strongly to the need to define specific target heights for a given period, rather than just a range. However, many arbitrary decisions were made in arriving at these target heights, mainly because the number of examples of each grassland type in the study was limited. There would undoubtedly be great value in building up a much more extensive database of sward heights from a wider range of valuable sites, covering all semi-natural communities. A further possible development would be to define criteria based upon proportions of short and long vegetation in a range of sward types, following the example of the guidelines quoted for wet grasslands and mire communities by Robertson and Jefferson (2000).

The guidelines produced by this project amply meet the objective of providing a framework for further development. They form part of a detailed protocol developed during the project, for establishing, monitoring and reviewing the management of grasslands within the context of management agreements in agri-environment schemes, which should be of immediate practical value (see Appendices 5 and 6).

Livestock performance from grasslands managed for conservation objectives It is important to view the management guidelines within the context of farming systems and to assess the implications for agricultural production of adopting management aimed primarily at conservation objectives. It was beyond the scope of this study to measure livestock performance at the study sites, and the quality of information available on stocking levels was variable. However, a review of available information from elsewhere is useful.

There has hitherto been little published information on livestock performance from semi-natural grasslands, particularly relating output to sward-based criteria such as sward height, although current and recently completed studies are beginning to rectify this. Low productivity per hectare can be expected from such grasslands, often due to a combination of low stocking rates and poor forage quality (Tallowin 1997). It is accepted that only low stocking rates will be possible compared to fertilised grasslands, but beyond this the issue of individual animal performance is important. It is sometimes assumed that this will be low, often on the basis on growth rates achieved during management aimed at restoring the ecological value of pastures where grazing has been abandoned. For example, live weight gain in a previously abandoned fen meadow dominated by purple moor grass (M24) averaged 0.5 kg/day May-June, and only 0.3 kg/day in July-September (Tallowin & Smith 1996). These rates compare with gains in excess of 0.75 kg/day achieved in agriculturally improved grassland close by (Tallowin et al. 1990). Grayson (2000) reported gains of 0.44 kg/day during the restoration of grazing management to abandoned limestone grassland dominated by blue sesleria (Sesleria caerulea),

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Projecttitle


MAFFproject code

BD1412

scrub and bracken. By contrast, growth rates of about 0.85 kg/day have been achieved in rush and fen pasture at Woodwalton Fen (Williams et al. 1974), and gains in excess of 1.0 kg/day in aftermath growth in species-rich MG5/MG8 grasslands on the Somerset Levels (Kirkham & Wilkins 1994). Scientific data are emerging to support anecdotal evidence that certain breeds of livestock will perform significantly better than others on semi-natural pastures. For example, Welsh Black cattle grew at 0.73 kg/day on purple moor grass pastures in Wales, compared to gains of only 0.43 kg/day from Charolais-cross steers on the same pasture (Wright et al. 2000). There was little difference between breeds on grass/white clover permanent grassland (1.02 and 0.91kg/day respectively).

There is a limited amount of information relating growth rates to sward height. Sward heights varied greatly (5.5 – 53.4 cm) between sites and years and during the season at a range of purple moor-grass and rush pastures (mostly M25) in MAFF project BD1318 (J. Tallowin, personal communication). However, there was no correlation between animal performance and sward height within the data set, with cattle averaging 0.52 kg/day live weight gain. Cattle grazing species-rich MG5 grassland in Somerset (project BD1440, J. Tallowin, personal communication) showed high growth rates under ‘lenient’ and ‘moderate’ grazing intensity of 0.90 and 0.91kg /day respectively from May-October, where sward heights averaged 11.6 and 9.2 cm respectively. Growth rates were significantly lower (0.53 kg/day) in swards maintained under ‘severe’ grazing pressure (7.4 cm). Growth rates in fertilised paddocks did not differ from those achieved in unfertilised vegetation under ‘lenient’ of ‘moderate’ stocking rates, despite mean sward heights much closer to those under ‘severe’ stocking rates (i.e. 7.7 cm). The target height of 10 cm for MG5 in mid season given in Appendix 6 is intermediate between those for the ‘lenient’ and ‘moderate’ treatments quoted above, but lower heights are recommended for the autumn (5 cm, range 3-7, from Gibson 1997). This suggests that optimum growth rates might be compromised by adherence to these guidelines, although a more accurate comparison would need to take into account seasonal differences in sward height in project BD1440.

Management guidelines for restoration of biodiversity to lower quality grasslandsMany of the pastures under management agreements within agri-environment schemes have either undergone some agricultural improvement on the one hand, or have deteriorated through under-management on the other hand. In both cases, the objective of the agreement will be to improve the conservation value of the pasture. The framework of guidelines produced by this project is based upon the management of pastures of high ecological quality. It is possible that different grazing regimes may be required for restorative management, possibly involving either heavy stocking following abandonment, or release from grazing where pastures have been chronically over-grazed. English Nature and FRCA are currently developing management guidelines for ‘non statutory’ grasslands, i.e. grasslands of a quality not warranting SSSI status, and this work is still in progress. However, it is thought that, except in extreme cases, the management required in these grasslands will not differ greatly from that appropriate to the target communities to which it is hoped to restore them (Heather Robertson, personal communication). Botanical composition could provide a clue as to past management history and appropriate grazing policy in these situations. For example, an abundance of rosette weeds and annual meadow grass would indicate overgrazing, whereas well-established clumps of Arrhenatherum elatius and Dactylis glomerata, and excessive amounts of litter, would indicate undergrazing. Grazing management could be set at the appropriate end of the range in order to encourage transition to a more desirable balance of species.

Recommendations and further requirements

Some recommendations arising from the project, and suggestions for further development are summarised below.

Methodology and definitions for assessing sward structure The HFRO swardstick should be adopted as the preferred apparatus for measuring sward height. Opportunities should be taken or created to develop an extensive database of sward heights from a wider range of

valuable sites, covering all semi-natural communities. Further, more extensive comparisons of swardstick and 30 cm drop disc heights should be made, so that existing

criteria based on the latter can be more confidently converted to swardstick heights for a range of grassland types. Visual assessments of sward height and herb cover can be made at the field scale, along with assessments of weed

and tussock cover and spatial patterns in distribution of vegetation height. Visual assessments of bare ground cover at the field scale are more difficult, and a more systematic approach is recommended if/when accurate assessments of this variable are required.

Further aids to visual assessment of sward height and structure should be developed, including use of existing photographs taken at a range of site within the project

A technique for assessing litter cover needs to be developed

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Projecttitle


MAFFproject code

BD1412

Techniques for assessing sward heterogeneity need further development. This could include more extensive use of the diagrams produced for this study, and development of an index combining these with mean vegetation height.

Clearer definitions are required for terminology relating to sward heterogeneity and these need to be generally agreed. Distinction needs to be made between a ‘tussock’ and a ‘clump’ of vegetation. It is suggested that the term ‘tussock’ be reserved for single plants of a particular growth habit, whereas a ‘clump’ is a continuous area of vegetation of varying diameter and defined in relation to its greater height compared to the surrounding vegetation (see Milsom et al. 2000).

Further discussion is required, e.g. between FRCA and English Nature, on the value of sward heterogeneity and how to define the specific requirements of particular fauna in a way which can be used in sward-based management guidelines.

Technology transferAs part of the process of further refinement and acceptance of the sward-based approach developed here, the following are recommended:

Update the review of information provided within this project (Appendix 5), including an expansion of its scope to cover management for specific rare plants and to include small mammals (e.g. brown hare)

Establish a network of demonstration sites based on the high quality, well managed sites studied in this project, but also including a number of sites managed specifically for fauna

Expand the scope of the work to encompass management of lower quality grasslands, including sward-based techniques for restoration of biodiversity, and develop protocols for the identification of potentially valuable sites.

ACKNOWLEDGEMENTSA large number of people contributed to this project, which was initiated by Steve Peel (now of FRCA) who has maintained a keen interest and involvement throughout. Iain Diack (also now of FRCA), was Study Director for most of the first two years. Mike Burke, now with English Nature, was formerly ADAS Contract Manager for the study. John Doney, Sonia Brunton and Anna Gundrey of ADAS and Bill Parkin (formerly of ADAS) were responsible for most of the field work. The following all contributed valuable information and/or advice: Gill Swash, Claire Bains, Naomi Oakley, David Charman, Michelle Leek, George Gittens, Richard Belding, Dave Martin, Alison Tytherleigh, Steve Peters, Jonathan East, Monica O’Donnell, Susie Smith (FRCA); Heather Robertson, Richard Jefferson, Barry Proctor, Adrian Gardner, Malcom Wright, Graham Steven, Mark James (English Nature); Val Brown (Reading University); Harry Padgett-Wilkes (English Nature /RSPB), Will Peach, David Buckingham, Jim Rowe (RSPB); Ross Bower (Devon Nature Trust); Jess Pain, Mark Langford (Hampshire Wildlife Trust); Nigel Bourne, Martin Warren (Butterfly Conservation); Jerry Tallowin (IGER); and Jim Rudderham (Elvedon Estates).

REFERENCESBUTT (1986) The Management of Chalk Grassland for Butterflies. Focus on Nature Series No. 17. Nature Conservancy

Council, Peterborough.Gibson, C. W. D. (1997). The effects of horse and cattle grazing on English species-rich grasslands. English Nature

Research Report No. 210. English Nature: Peterborough.Grayson, F.W. (2000) The financial and ecological implications of restoring grazing regimes to grassland of high nature

conservation value suffering from long term agricultural abandonment; a case study. In: A.J. Rook & P.D. Penning (eds) Grazing Management. Proceedings of British Grassland Society Occasional Symposium No. 34, pp. 215-220. British Grassland Society, Reading.

Kent, M. & Coker, P. (1992) Vegetation Description and Analysis. Behaven Press, London.Kirkham, F.W. & Wilkins, R.J. (1994) The productivity and response to inorganic fertilisers of species-rich wetland hay

meadows on the Somerset Moors: nitrogen response under hay cutting and aftermath grazing. Grass and Forage Science, 49, 152-162.

Milsom, T.P., Langton, S.D., Parkin, W.K., Peel, S, Bishop, J.D. Hart, J.D. & Moore, N.P. (2000) Habitat models of bird species’ distribution: an aid to the management of coastal grazing marshes. Journal of Applied Ecology, 37, 706-727.

Robertson, H.J. & Jefferson, R.G. (2000) Monitoring the Condition of Lowland Grassland SSSIs. I. English Nature’s Rapid Assessment Method. English Nature Research Report No. 315. English Nature, Peterborough.

Robertson, H.J., Bingham, J. & Slater, I. (2000) Monitoring the Condition of Lowland Grassland SSSIs. II. A Test of the Rapid Assessment Method. English Nature Research Report No. 315. English Nature, Peterborough.

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BD1412

Rodwell J.S. (Ed.) (1991) British Plant Communities, Volume 2: Mires and Heaths. Cambridge: Cambridge University Press.

Rodwell J.S. (Ed.) (1992) British Plant Communities, Volume 3: Grasslands and montane Communities. Cambridge University Press, Cambridge. Rodwell J.S. (Ed.) (2000) British Plant Communities, Volume 5 Maritime Communities and Vegetation of Open Habitats. Cambridge University Press, Cambridge.

Tallowin, J.R.B.T. (1997) The agricultural productivity of lowland semi-natural grasslands: a review. English Nature Research Reports, No. 233. English Nature, Peterborough.

Tallowin, J.R.B. & Smith R.E.N. (1996) Management options to conserve a Cirsio-Molinietum and integrate its use into productive livestock systems. Aspects of Applied Biology, 44, 203-210.

Tallowin J.R.B., Kirkham F.W., Brookman S.K.E. & Patefield M. (1990) Response of an old pasture to applied nitrogen under steady-state continuous grazing. Journal of Agricultural Science, Cambridge, 115, 179-194.

Williams, O.B., Wells, T.C.E. & Wells, D.A. (1974) Grazing management of Woodwalton Fen: seasnal changes in the diet of cattle and rabbits. Journal of Applied Ecology, 11, 499-516.

Wolton, R.J. (undated) Wildlife Enhancement Scheme: Management Guidelines for Culm Grasslands. English Nature, Peterborough.

Wright, I.A. Davies, D.A. & Vale, J.E. (2000) Grazing of permanent pasture and Molinia-dominated pasture by different genotypes of cattle. In: A.J. Rook & P.D. Penning (eds) Grazing Management. Proceedings of British Grassland Society Occasional Symposium No. 34, pp. 167-168. British Grassland Society, Reading.

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