Review Article Eucalyptus and Water Use in South Africa · InternationalJournalofForestryResearch...

Hindawi Publishing CorporationInternational Journal of Forestry ResearchVolume 2013 Article ID 852540 11 pageshttpdxdoiorg1011552013852540

Review ArticleEucalyptus and Water Use in South Africa

Janine M Albaugh1 Peter J Dye2 and John S King1

1 Department of Forestry and Environmental Resources North Carolina State UniversityPO Box 8008 Raleigh NC 27695-8008 USA

2 School of Animal Plant and Environmental Sciences University of the Witwatersrand Private Bag 3Johannesburg 2050 South Africa

Correspondence should be addressed to Janine M Albaugh janine albaughncsuedu

Received 15 June 2012 Accepted 5 February 2013

Academic Editor John Stanturf

Copyright copy 2013 Janine M Albaugh et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

The Eucalyptus genus yields high rates of productivity and can be grown across a wide range of site types and climates for productssuch as pulp fuelwood or construction lumber In addition many eucalypts have the ability to coppice making this genus an idealcandidate for use as a biofuel feedstock However the water use of Eucalyptus is a controversial issue and the impacts of thesefast-growing trees on water resources are well documented Regardless the demand for wood products and water continues to riseproviding a challenge to increase the productivity of forest plantations within water constraints This is of particular relevance forwater-limited countries such as South Africa which relies on exotic plantations to meet its timber needs Research results fromwater use studies in South Africa are well documented and legislation restrictions limit further afforestation This paper outlinestechniques used to quantify the water use of eucalypt plantations and provides recommendations on where to focus future researchefforts Greater insights into the water use efficiency of clonal material are needed as certain eucalypt clones show fast growth andlow water use To better understand water use efficiency estimates should be combined with monitoring of stand canopy structureand measurements of physiological processes

1 Introduction

Eucalyptus is the most widely planted hardwood genus inthe world covering more than 19 million hectares withgrowth rates that routinely exceed 35m3 haminus1 yearminus1 [1 2]These fast-growing plantations can be grown under a rangeof different climates for products that include pulp andpaper charcoal fuelwood and solid wood products such aspoles furniture and timber construction Given their fastgrowth rates and coppicing ability eucalypts have also beenidentified as potential feedstocks for lignocellulosic biofuelsBeing endemic to Australia southeast Asia and the Pacificeucalypts are grown mainly as exotic species Consequentlythere is much concern about their water consumption frommany countries around the world [3ndash7]

One such country is South Africa which relies heavily onplantations of exotic forestry species particularly Eucalyptusto meet its timber needs South Africa is a water-limitedcountry with an average annual rainfall of 560mm yearminus1

which results in fierce competition for this limited resource[5] Concerns over the effects of exotic plantations on SouthAfrican streamflow and catchment water yields led to theestablishment of a network of long-term paired catchmentexperiments in the major forestry areas of the country Theseexperiments were set up as early as 1937 and since thenhave been supplemented by a wide variety of process studiescomparing transpiration or evapotranspiration from forestgrassland and other vegetation types Information from thesestudies and the paired catchment experiments have been usedto calibrate catchment models that have provided estimatesof the hydrological impacts of forest plantations As a resultthe impacts of plantation forestry on water resources arewell documented and legislation restrictions limit furtherafforestation

Nevertheless demand for wood water and energy con-tinues to grow providing a challenge to increase the produc-tivity of forest plantations within water constraints Eucalyp-tus species managed as short-rotation crops for bioenergy are

2 International Journal of Forestry Research

of increasing interest in many parts of the world In countrieswhere eucalypts are introduced species there is a need tounderstand key environmental issues for example water userelated to themanagement and growth of these treesOnewayin which information needs can be identified and prioritizedis to draw on the knowledge and experience gained fromdecades of water research in South Africa Research intowater use of South African timber plantations commenced in1937 the historical nature of the data collected the length ofrecord and the range of sites involved make the experimentsunique and invaluable [8]

The objective of this paper is to provide a comprehen-sive synthesis of the available South African literature onthe effects of eucalypt planting on water resources and toproduce new insights into future research needs This paperis organized into five main sections as follows

(i) background to South African forestry and limitedwater resources

(ii) techniques used to measure and model water use(iii) methods for determining water use efficiency(iv) current South African legislation and(v) future considerations including a new research focus

and tree-based bioenergy feedstocks

2 South African Forestry andLimited Water Resources

South Africa has limited indigenous timber-producingforests The first plantations of exotic trees mainly pineand eucalypts were established in the country in 1875 afterrecognizing that demand for timber had exceeded the supplyavailable from indigenous forests These exotic species werepreferred for afforestation because none of the indigenoustree species which yield useful timber grew at rates consid-ered profitable [9] There has since been a steady expansionin the total area of forest plantations culminating in 12million hectares (11 of South African land area) of which515000 ha are planted to eucalypts [10] This genus is grownpredominantly for pulpwood and mining timber over anormal rotation length of seven to ten years [11] Productivityfrom these plantations is relatively high and ranges from 10 to68m3 haminus1 yrminus1

Plantations of exotic species were established in thehigher-rainfall (gt700mm) regions of the country coincidingwith a large proportion of the surface water resources whichemanate from relatively small but important catchment areasconcentrated along east- and south-facing escarpments andmountain slopes [12ndash14] The dominant vegetation in manyof these areas was originally montane grassland and fyn-bos (macchia) shrublands Annual evapotranspiration ratesof this indigenous vegetation range from 700 to 900mm[15] This indigenous vegetation has relatively shallow rootsystems and is seasonally dormant resulting in limitedevapotranspiration over the dry season [12 15] In strongcontrast plantation forests are characterized by deep rootsystems and tall dense evergreen canopies that maintain

a relatively high leaf area index over the entire year [1416] Evapotranspiration from established forest plantationsis commonly in the range of 1100ndash1200mm and is limitedby rainfall available on the site [14] Numerous local andinternational studies have indicated conclusively that forestplantations established in former natural forests grasslandsor shrubland areas consume more water than the baselinevegetation reducing water yield (streamflow) as a result[8 13 14 17ndash20] Concerns over the effects of these forestplantations on streamflows and catchment water yields aroseas far back as 1915 and were thoroughly debated during theEmpire Forestry Conference that took place in South Africain 1935 [14] A decision taken at this conference led to theestablishment of a network of long-term paired catchmentexperiments in various catchments located in the majorforestry areas of South Africa [14]

3 Techniques Used to Measure andModel Water Use

A range of techniques has been used to measure and modelwater use of South African forest plantations across a rangeof temporal and spatial scales These include paired catch-ment experiments micrometeorological techniques sapflowestimates using heat pulse velocity modeling efforts andremote sensing estimates of stand scale water use Each ofthese techniques is discussed in turn pertinent results arepresented and the short-comings of each method have beenhighlighted

31 Paired Catchment Experiments The paired catchmentmethod involves the long-term monitoring of streamflowfrom pairs of catchments before and after a major vegetationchange in one of them [8] Van Lill et al [21] reported onresults of a paired catchment experiment with E grandisversus natural grass cover on the eastern escarpment of SouthAfrica Afforestation with E grandis exerted an observableinfluence from the third year after planting with a maximumapparent reduction in flow between 300 and 380mm yearminus1andwithmaximum reductions in seasonal flow of about 200ndash260mm yearminus1 in summer and 100ndash130mm yearminus1 in winter[21]

Catchment experiments have shown that eucalypts causea faster reduction in streamflow compared to afforestationwith pines [13] Further these effects were more marked foreucalypts (90ndash100 water reduction) than with pines (40ndash60 reductions in the first eight years or so after treat-ment) but Smith and Scott [22] suggested these differencesmay diminish as the pine stands become well-establishedStreamflow reductionwas significant from the third year afterplanting eucalypts for both the wet and dry seasons and thestream dried up completely in the ninth year after planting[13] After afforestationwith pines reductions in total andwetseason streamflow became significant in the fourth year andstopped flowing completely in the twelfth year [13] Analysesshowed peak reductions of 470mmyearminus1 for eucalypts in theseventh and ninth years both particularly wet years [13] Thehighest estimated flow reduction due to pine was 257mm

International Journal of Forestry Research 3

recorded in the twentieth year of the rotation [13] Thesefinding were verified by a study performed by Scott et al [8]who reported peak reductions in streamflow between 5 and10 years after planting eucalypts and between 10 and 20 yearsafter planting with pines with the size of the reductions beinglimited primarily by water availability In analyses presentedby Scott and Smith [18] reduction in annual streamflow dueto pine averaged over the first eight years after afforestationwas 47mm (between 35 and 119 ha were afforested) Incomparison eucalypts reduced streamflow by 239mm (overan afforestation range of 25ndash40 ha) In the case of the pinesbetween 82 and 100 of the catchment area was afforested inthe case of the eucalypts entire catchments (ie 100) wereafforested

In addition to afforestation effects on total streamflow animportant consideration is the effect on low flows definedby Scott and Smith [18] as the driest three months of anaverage year or as those monthly flows below the 75thpercentile level At the low flow time of the year during thedry period immediately prior to the rainy season a reliablewater supply is most critical for downstream water users[18] Consequently the effect on low flows may be moreimportant than the overall impacts on streamflow [22] Usingthe paired catchment approach to investigate low flows infive catchments in the winter and summer rainfall regions ofSouth Africa Smith and Scott [22] found afforestation signif-icantly affected low flows in all five catchment experimentswith flows being reduced by up to 100 in some cases Thelow flows in catchments planted with eucalypts showed asignificant response to treatment from the third year afterafforestation whereas the catchments plantedwith pines onlyresponded from the fifth year onwards [22]

Streamflow reductions are very variable from year to yearbeing a function of the following factors

(i) Water availability (see [13 17 18]) According to Scottet al [8] the most important determinant of flowreductions is water availability where wet catchmentswith high water availability have the highest flowreductions Conversely lowwater availability can leadto bigger relative reductions for example one catch-ment planted to eucalypts reached 100 reduction inthe fourth year of the rotation under a dry cycle

(ii) Species selection and extent of afforestation [8]

(iii) Plantation age or growth rate (see [8 18]) Smithand Scott [22] suggested that faster growth rates ofeucalypts compared to pines in the first eight yearsafter planting may explain their earlier and greaterimpact on low flows Similarly Bosch and Hewlett[17] stated that decreases in water yield followingafforestation seem proportional to the growth rate ofthe stand while gains in water yield after clearfellingdiminish in proportion to the rate of recovery of thevegetation

(iv) Rotation length Mathematical models developed byScott and Smith [18] indicated that the longer therotation the greater the mean impact of the crop and

the lower the frequency of ldquorecharge opportunitiesrdquo(periods after clearfelling when evapotranspirationlosses would be low) These models predicted thatflow reductions caused by pines grown for sawlogs(on a 30-year rotation) were likely to be similar tothose caused by a shorter rotation (8 to 10 years)eucalypt crop

Whilst these paired catchment experiments confirmed adecline in streamflow following the establishment of forestplantations Dye and Olbrich [12] and Gush et al [16]cautioned that results cannot be extrapolated to other areaswith confidence because of the lack of climatic represen-tativeness The research catchments studied have a meanannual precipitation greater than 1100mm whereas 63 ofall afforestation in SouthAfrica receives less than 900mmperyear [16] In addition in the studies cited by Smith and Scott[22] tree seedlings were planted into shallowly prepared pitswithout fertilization in contrast to typical forestry practicewhich involves intensive site preparation and in some casesfertilizer application to boost early growth Such establish-ment practices are likely to cause earlier reductions of lowflows from the afforested catchments because the site is fullyexploited by the trees sooner [22] Further in the study ofScott and Lesch [13] two entire catchments were afforestedincluding the riparian zones to indicate the potential effectsof afforestationHowever under current forestry law in SouthAfrica riparian zones are not planted but are kept open underindigenous vegetation for soil and water conservation andseldom would more than 75 of a single large catchmentbe afforested Scott et al [8] suggested replicating catchmentexperiments with different species at different sites and overdifferent time periods as results from a single catchment andclimatic pattern cannot provide proper understanding of howresponses may vary under different conditions HoweverHewlett and Pienaar [23] stated that the paired catchmentapproach while powerful is also costly and time-consuming

Findings and recommendations emanating from thepaired catchment experiments led to regulation of newafforestation to protect water supplies In 1972 legislation wasintroduced that required timber growers to apply for permits(afforestation permit system) to establish new commercialplantations [20 24] These applications became mandatoryand were granted or refused based on an assessment of theexpected impact of plantations on water yields from thecatchment areas [5]

There was thus a need for a model that could be usedas a guideline for decision-making and planning regardingafforestation effects and permit allocations Scott and Smith[18] developedmathematical models using age as a predictorvariable to provide estimates of reductions in low flowand total flow resulting from pine and eucalypt plantationson a regional and national scale Scott et al [8] suggestedadding environmental drivers such as rainfall temperaturesoil depth or tree rooting in addition to using age as a pre-dictor variable to enable explanation of observed variationHowever because of the lack of climatic representativenessthese models remain empirical and extrapolation outside theconditions encountered could be misleading


8

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Dai

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ee-le

vel

tran

spira

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(985747da

yminus1)

Dai

ly st

and-

leve

ltr

ansp

iratio

n (m

m)

1400

1200

1000

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600

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0

PAR

(120583m

ol mminus2

sminus1)

300

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050

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92

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2

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92

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92

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-92

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-92

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-92

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93

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93

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-93

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93

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-93

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93

Vapo

r pre

ssur

e defi

cit (

kPa)

(a)

(b)

(c)Figure 1 Mean daily transpiration of three-year-old E grandis trees (a) photosynthetically active radiation (PAR) (b) and daytime (6 amndash6 pm) vapor pressure deficit (c) for the period June 1992 to June 1993 (after Dye [25] Dye et al [26])

32 Sapflow Measurements and Micrometeorological Tech-niques Since the mid 1980s the paired catchment exper-iments were supplemented by a variety of process-basedstudies where transpiration or evapotranspiration weremea-sured above forest grassland and other vegetation typesusing heat pulse and micrometeorological techniques [14]Transpiration (sapflow) rates measured using the heat pulsevelocity technique have been verified in 3- and 16-year-oldE grandis trees [27] Sapflow rates exhibit distinct seasonalpatterns where mid-summer values are characteristicallyhighest due to long day lengths and high vapor pressuredeficit (VPD) associated with higher temperatures [28] Incontrast winter sap flow rates were much reduced not onlyby day length and VPD but also by soil water deficits [28]One of the mechanisms trees use to avoid drought conditionsis stomatal closure either in response to increasing VPD orsoil water deficit [29 30] Closure of stomata to maintain leafwater potential above a critical threshold protects the xylemfrom damage by cavitation and embolism [31]

Transpiration from Eucalyptus trees in South Africa hasbeen shown to be mainly a function of VPD and photosyn-thetically active radiation [12 32] Evidence of this is seenin Figure 1 where peak daily water use of three-year-old Egrandis exceeded 90 ℓ dayminus1 (70mm dayminus1) on hot dry daysin midsummer and then declined during the fall as tem-peratures decreased and the photoperiod shortened Averagedaily water use was approximately 30 ℓ dayminus1 (22mm dayminus1)during the 1992 winter but rose markedly in the spring inresponse to increased VPD [25] Median daily sapflows instands of E grandis times camaldulensis hybrid clones coveringa wide range in age (15ndash70 years) and site growth potentialranged from approximately 30 to 64 ℓ per day for treesgrowing onmore productive sites and from 15 to 34 ℓ per dayfor the less productive sites [33]

Dye [25] carried out sapflow studies at two field sites onthree- and nine-year-old E grandis trees subjected to soildrying by laying plastic sheeting on the ground to preventsoil water recharge There was no indication that water use


declined as a result of increasing soil water deficits Dye [25]attributed this to the ability of the three-year-old trees toabstract soil water to a depth of at least 8m whereas nine-year-old trees obtainedmost of their water fromdepths belowthis level (deep drilling revealed live roots at 28m belowthe surface) During dry periods deep-rooted eucalypts areable to maintain transpiration at rates which enable the treesto function by accessing water stored in the soil profile[34] As available soil water is recognized as the main factorinfluencing the growth of commercial plantations in southernAfrica [35 36] a crucial question is whether water storedin the soil profile can be recharged during continuous Euca-lyptus cropping particularly in short-rotation unthinnedplantations grown for pulp or bioenergywhere leaf area index(and hence water use) remains high throughout the rotation[25] Leaf area index is a key determinant of plantation wateruse [37ndash39]

Successive rotations of demanding species such as Egrandis may deplete soil water reserves leading to increasedsoil water deficits and declining growth yields [26 36]In the paired catchment experiments studied by Scott andLesch [13] eucalypts were clearfelled when 16 years old butfull perennial streamflow did not return until five yearslater This lag in streamflow recovery was attributed to theabstraction and desiccation of deep soil-water stores by theeucalypts which had to be replenished before the streamscould return to normal behavior [13] Greater understandingof the long-term water balance of eucalypt plantations istherefore required to assess the sustainability of continuouseucalypt cropping and evaluate what management practicescan be adopted to minimize growth losses [26]

In addition to sapflow studies micrometeorological tech-niques such as the Bowen ratio and eddy correlation havebeen investigated however these are less suited to Eucalyptusmeasurements as they require a structure to gain access to thefoliage or to serve as a platform for instrumentationmountedabove the canopy which is made difficult by the height ofthe trees In addition leaf-based techniques such as porom-etry require adequate canopy sampling to allow estimationof whole-tree transpiration rates and micrometeorologicalmethods have theoretical constraints that are difficult tosatisfy in undulating discontinuous forest terrain [27]

An additional drawback of micrometeorological tech-niques and sapflow measurements is the expense both interms of equipment and time [28] Sustaining high-qualitysapflow measurements by the heat pulse technique over longperiods of time is difficult as equipment malfunctions oris stolen probes can become corroded by gum or sampletrees can be felled accidentally There is limited ability toextrapolate results from relatively few research areas to theentire forestry region [28] In addition growth and wateruse is especially sensitive to soil water availability but this isoften impractical to measure because of deep rooting depthshighly variable depth to bedrock and uncertainty over lateralsoil water flow [28]

33 Modeling Efforts Another assessment tool used todetermine the impact of commercial afforestation onSouth African water resources was the ACRU (Agricultural

Catchments Research Unit) model [44] which simulatesstreamflow total evaporation and land covermanagementimpacts on water resources at a daily time step [45]Model inputs include daily rainfall and other climaticdata catchment characteristics such as catchment areaaltitude vegetationland cover and soil information ACRUmodel processes include infiltration evapotranspirationreservoir storage surface runoff and plant growth Thehydrology component of the model utilises a multilayersoil water budget to calculate evapotranspiration Jewitt andSchulze [45] performed a verification of the ACRU modelby comparing simulated and observed streamflow at threeforested catchment locations across a range of catchmentsizes forest species and plantation age The ACRU modelperformed acceptably at most sites but Jewitt and Schulze[45] encountered problems related to temporal distributionof streamflow Similarly in another ACRUmodel verificationstudy Gush et al [16] showed that mean annual streamflowreductions resulting from afforestation were satisfactorilysimulated for most of the long-term research catchmentsHowever model predictions for dryer regions or those withwinter rainfall were poor and Gush et al [16] concluded thatthe model could not account for the full storage capacity ofsoils and the year-to-year carryover of water storage or usageGush et al [16] cautioned that in these types of situationswhere forest hydrology is less well understood there isincreased risk of erroneous predictions

34 Remote Sensing Techniques Remote sensing techniquesusing satellite imagery have successfully beenused to estimateevapotranspiration across a range of spatial scales [46ndash48]These techniques are of increasing interest for operationalforestry applications in South Africa such as estimatesof catchment scale evapotranspiration However wide-scaleadoption of remote sensing techniques may be limitedby image costs and data-processing times and costs [49]poor image quality (resulting from cloud cover or smoke)uncertainty regarding the number and timing of imagesneeded to accurately describe annual evapotranspiration andinappropriate satellite pass-over times However a simplifiedremote sensing regression model proposed by Wang et al[47] holds promise In this model surface net radiationair or land temperature and vegetation indices are usedto predict evapotranspiration over a wide range of soilmoisture contents and land cover types Wang et al [47]reported a correlation coefficient of 091 between measuredand predicted evapotranspiration Independent validationof the model using measurements on grassland croplandand forest collected by the eddy covariance method showedthat evapotranspiration could be reasonably predicted witha correlation coefficient that varied from 084 to 095 a rootmean square error that ranged from about 30 to 40Wmminus2and a bias that ranged from3 to 15Wmminus2 According toWanget al [47] the errors encountered could partly be attributedto uncertainty in the eddy covariance method

35 Water Use Efficiency Water use estimates measuredusing heat pulse velocity have often been paired with pro-ductivity or biomass values to provide water use efficiency


(WUE) estimates Depending on the objective of a particularstudy WUE can be expressed as stem volume production perunit water used or in the case of bioenergy (see Section 52below) expressed as biomass production (ie all componentsthat will be used for bioenergy) per unit water used Wateruse efficiency expressed as annual stemvolume increment perunit volume of water transpired for Eucalyptus species acrossage classes and site types in South Africa ranges from 00008to 00123m3 stemwood produced per m3 water consumed([5 26 28 40ndash43] Table 1)

Water use efficiency varies significantly among Eucalyp-tus clones (for the same age and site) [28] Evidence of thiswas presented by Olbrich et al [5] who found significantclonal differences in WUE between four E grandis clonesgrowing on a high quality site Clonal WUE which rangedfrom 00060 to 00123m3mminus3 was related to growth ratewith the most water use efficient clones tending to be thefastest growing [5] In a lysimeter study Le Roux et al [42]investigated variation in WUE among six Eucalyptus clonesup to the age of 16 months and found significant clonalvariation in WUE as well as patterns of growth allocation toroots stems branches and leaves

Water use efficiency is not a constant characteristic ofa given genotype but varies according to the particularcombination of site conditions weather and tree age [24]Thefrequency and duration of soil water deficits is believed to beespecially important in governing WUE which is sensitiveto year-to-year variation in rainfall amount as well as rainfalldistribution through the year [24] Dye et al [28] attributedlower WUE in Eucalyptus clones compared to other sampletrees to a severe growing-season drought during the periodof measurement Water use efficiency is also influenced byatmospheric humidity (VPD) and changes in carbon parti-tioning brought about by soil water and nutrient availability[24 28] Stomatal closure in response to increasing VPDreduces water loss and generally results in higher WUE butwith a concomitant reduction in photosynthesis and treegrowth [39 50ndash52]

In nutrient-limited or dry environments relatively moredry matter is contained in below-ground components (par-ticularly fine roots) of eucalypts than on moist high-nutrientsites [53ndash55] Patterns of carbon allocation can significantlyaffect WUE which is higher in trees experiencing bettergrowing conditions than in those experiencing poorer con-ditions [28 56 57] Therefore at the plantation manage-ment level WUE can be maximized by adopting measureswhich minimize soil water and nutrient deficits [24] Thesemeasures include avoiding removal of forest floor litterpreventing excessive topsoil damage by vehicles minimizingintense fires which kill herbaceous plants and promote soilerosion practicing effective weed control and fertilizingwhere economically feasible [24]

Carbon isotopes can also be used to provide estimates ofWUE Isotopic composition of plant carbon (120575 13C) correlateswithWUE where a higherWUE is evidenced by less negativevalues of 120575 13C [58 59] Olbrich et al [5] presented resultsshowing this relationship for clonal E grandis the clone withthe lowest WUE had more negative 120575 13C values than the

Table 1 Comparative water use efficiency (WUE) values amongEucalyptus species and clones grown in South Africa expressed asannual stem volume increment per unit volume of water transpired(m3 wood mminus3 water)

Eucalypt speciesclone WUE(m3 wood mminus3 water) Reference

E grandis clones 00060 [5]E grandis clones 00123 [5]E grandis clones 00094 [5]E grandis clones 00095 [5]E grandis 00042 [26]E grandis 00032 [26]E grandis 00086 [28]E grandis 00060 [28]E grandis 00058 [28]E grandis 00045 [28]E grandis 00071 [28]E grandis 00057 [28]E grandis 00024 [28]E grandis 00018 [28]E grandis 00033 [28]E grandis 00024 [28]E grandis 00110 [40]E grandis 00064 [40]E grandis 00094 [40]E grandis 00053 [40]E grandis 00077 [40]E grandis 00064 [40]E grandis 00044 [40]E grandis 00050 [40]E grandis 00074 [40]E grandis 00038 [40]E grandis 00050 [40]E grandis 00041 [40]E grandis 00048 [40]E grandis 00082 [40]E grandis 00045 [40]E grandis 00069 [40]E grandis 00055 [40]GC15 00028 [41]GC15 00048 [41]GC15 00033 [41]GT529 00032 [41]GT529 00049 [41]GT529 00058 [41]TAG5 00045 [41]TAG5 00038 [41]TAG5 00035 [41]Eucalyptus and hybrid clones 00015 [42]Eucalyptus and hybrid clones 00013 [42]Eucalyptus and hybrid clones 00011 [42]


Table 1 Continued


Eucalyptus and hybrid clones 00008 [42]Eucalyptus and hybrid clones 00010 [42]Eucalyptus and hybrid clones 00014 [42]Eucalyptus species 00034 [43]

other three clones In a lysimeter study with six Eucalyptusclones grown for 16 months under two water regimes (soilwater maintained at 100 and 80 of field capacity resp) LeRoux et al [42] reported significant relationships between leaf12057513C values and instantaneous water use efficiencies in the

high soil water treatment However the lack of relationshipsbetween leaf 120575 13C values and whole-plant shoot or stemwater use efficiencies in either soil water treatment led theseauthors to conclude that 120575 13Cmay not be a reliable indicatorof WUE but may be useful as a screening tool Olbrichet al [5] stated that it is unclear how 120575 13C varies withineucalypt canopies (eg with aspect and branch length) andadvised that itmay be crucial to follow a rigid sampling proce-dure These authors also suggested that canopy microclimate(especially vapor pressure deficit and leaf temperature) mayconfound relationships between 120575 13C andWUE

4 Legislation and Application of Research

Results from the numerous water use studies discussed abovehave been collated and simplified to provide a scientific basisfor South African water use legislation decisions Since the1972 law which dictated that timber growers needed to applyfor planting permits to establish new commercial plantationsSouth African water legislation has undergone a series ofrefinements as research results and simulation models haveimproved [20] In South Africarsquos new National Water Act of1998 (httpwwwdwafgovzaDocumentsLegislaturenwactNWApdf accessed 01272012) all water users arerequired to register and license and pay for their use of waterPayment for water used by plantation forests is calculatedthrough models developed from the long history of foresthydrological research using tabulated outputs from pairedcatchment experiments process-based studies and water useestimates using heat pulse velocity and micrometeorologicaltechniques [14]

As of 1999 commercial plantation forestry is classified inthe Water Act as a streamflow reduction activity defined asldquo any activity (including the cultivation of any particularcrop or other vegetation) (that) is likely to reducethe availability of water in a watercourse to the Reserveto meet international obligations or to other water userssignificantlyrdquo [60] The Reserve is the amount of water setaside (ie reserved) for environmental flows and to providefor basic human needs such as drinking food preparationand hygiene [61] Under this new water-use licensing sys-tem planning authorities (catchment management agencies)predict the likely hydrological impacts of afforestation and

limit the spread of further afforestation in catchments whereavailable water resources are already committed [14 43]Ideally this system should allow sustainablemanagement andequitable distribution of available water resources amongst allwater users [16] As regulation regarding sustainable waterresource management needs to be based on results fromscientifically defendable work there is renewed emphasis onthe need to understand accurately model and manage foresthydrological processes on a national scale [16 20 61]

5 Future Considerations

51 A New Research Focus Variable WUE exhibited betweendifferent Eucalyptus clones should be seen as an opportunityto determine whether it can be exploited to improve theoverall production and efficiency of plantation water use[28]This could be particularly beneficial for forestry situatedin marginally dry regions of South Africa where futureincreases in plantation area are likely to take place givennew afforestation constraints under the water law and asthe availability of high-rainfall areas diminishes [5 24 28]In addition there is also more recent and growing concernover the effects of climate change especially with regard todecreases in rainfall which are forecast for some forestryareas Increased efficiency of water use may to some extentoffset such detrimental change and provide the industry witha means of adaptation to a changing climate

The ongoing development of new hybrid Eucalyptusclones incorporating diverse genetic potential offers greatscope for breeding trees with improved WUE and droughtresistance [24 28] The challenge however will be to teaseapart the genetic and environmental influences on WUE fora range of clones and sites [28] Dye [24] stated that thefull potential for improving Eucalyptus yields and optimizingWUE will not be achieved without improvements in ourunderstanding of key physiological processes that governhow trees function Further advances in understandingWUEwill stem from process-based models which allow the sep-arate influences of weather stand characteristics and siteconditions on carbon allocation patterns and transpirationrates to be assessed [28] These models need to be validatedagainst critical physiological measurements such as sap flowrates leaf area index and growth rates to improve ourunderstanding of the linkages between growth and wateruse [28] One such model (3-PG) has been verified and canrealistically simulate growth and water use in stands of Egrandis times camaldulensis hybrid clones covering a wide rangein age and site growth potential [33]

Given this early stage in our understanding of WUE ofplantation trees and the range of site types in the forestryregions of SouthAfrica it will be necessary to compare a widevariety of genotypes on uniform sites to obtain comparativeWUE data In particular the following guidelines are recom-mended for new research

(i) Establish trials among a wide variety of clones onuniformhigh- and low-rainfall sites to compareWUEthrough direct measurements of growth and sap flowBecause new afforestation is more likely to take place


in drier areas which are considered marginal forforestry growth and WUE on these sites need to beinvestigated [24] WUE must be measured over atleast a full year to cover seasonal variations in carbonallocation and water use

(ii) Compare growth and water use among clones thatdisplay variation in properties such as stem growthrate leaf area angle and density leaf phenology andresponse to drought

(iii) Perform detailed analyses of canopy structure andphysiology to understand differences in patterns oftranspiration and photosynthesis Establish the age atwhich any differences can be recognized

(iv) Initiate drought resistance studies that investigategrowth vulnerability to cavitation water use andWUE

(v) Reevaluate the usefulness of carbon isotope ratios forcorrelations with WUE

(vi) Estimate below-ground carbon allocation and lossesto respiration

(vii) Use remotely-sensed evapotranspiration techniquesfor long-term monitoring

In addition many breeders have developed plant ldquoideo-typesrdquo to provide conceptual direction for tree selection andimprovement programs [62] The concept of an ideotypein forestry was pioneered by Dickmann [63] as a precisedescriptive model of the traits considered desirable fortrees in a defined environment Pereira and Pallardy [62]provided examples of attributes that might be incorporatedinto a ldquowater-limited biomass production ideotyperdquo Theseattributes include trees that retain foliage under droughtwhich would permit continued photosynthesis and growthin environments characterized by substantial but transientdrought periods degree of genetic control over the patternof stomatal behavior and thus WUE and the most effectivestructure for a root system to provide access to water storedin deep soil horizons [62]

Dye [24] suggested an ideotype for eucalypt clones whichincludes attributes relating to the following key processes

(i) canopy structure and efficiency of light interceptionand transpiration

(ii) rate of canopy photosynthesis(iii) patterns of assimilate allocation(iv) root system architecture(v) turnover rate of fine roots(vi) xylem anatomy and hydraulic architecture(vii) drought resistance mechanisms and(viii) efficiency of nutrient cycling

52 Growing Eucalypts for Bioenergy Production There isgrowing interest in numerous countries for eucalypt plan-tation-grown bioenergy production In southern USA forexample Eucalyptus has been shown to be a promising

biomass for energy production and commercial plantationsare being established at a rate of 5000 to 10000 ha peryear [64 65] According to Dougherty and Wright [65]demand for hardwood from plantation-grown stands forpulp and bioenergy in southern USA is more than 90million metric tons per year and is increasing The focuson bioenergy production over the past decade has beenlargely due to its perceived potential in securing energysupply reducing greenhouse gas emissions achieving sus-tainable development and improving local economy [66]However an increased demand for food in combination witha shift from fossil fuels towards industrial-scale production ofenergy from lignocellulosic sources will require water largelyfrom evapotranspiration of biomass production creatingadditional demand that must be carefully managed in viewof competing users [67ndash70]

Any type of large-scale changes in land use (eg replacingnatural grassland with short-rotation eucalypts for bioen-ergy) could have significant hydrological implications if thewater use of the introduced species differs significantly fromthe vegetation it replaces [61] The potential impact of landuse change therefore depends on the type of native vegetationreplaced and on the extent of the land area covered by the newspecies Inmost cases entire landscapes will not be planted toEucalyptus For this reason it will be necessary to determinethe proportion of land area occupied by eucalypts before asignificant change in streamflow is detected and how thelocation of these plantations within catchments (ie distancefrom streams) may relate to streamflow

Where large-scale changes in vegetation cover are pro-posed the differences in evapotranspiration between thecurrent and the proposed vegetation may ultimately translateinto changes in available streamflow from that catchment[61] It is imperative that bioenergy strategies being developedfor any country consider water resource impacts togetherwith all other relevant social economic and environmentalconsiderations associated with development of this industry[61 71] Gush [61] stressed that this is particularly importantin countries where there is increasing competition for waternow virtually a global phenomenon

South Africa in anticipation of a large demand for landsuitable for biofuel production has developed a nationalBiofuel Industrial Strategy (BIS) [72] Under the BIS and newWater Act it is necessary to assess water use of potentialbiofuel feedstocks [73] Water footprint estimates (defined asthe amount of water required to produce a unit of energy)have been produced for a range of crops industries andcountries [67 69] However Jewitt and Kunz [73] stated thatwhilst these are useful in providing values of the amount ofwater needed to produce a crop they are limited for tworeasons Firstly no consideration is made of a reference orbaseline condition so no assessment of impact is possible andsecondly such ldquofootprintsrdquo are typically described at coarsespatial and temporal resolution whereas water resourceimpacts are most severely felt at a local level at specific timesof the year for example low flows prior to the rainy season[18 73] Ridoutt and Pfister [74] argued that there is no clearrelationship between a water footprint and potential environ-mental andor social impact and introduced a revisedmethod


which allows comparisons between production systems interms of their potential to contribute to water scarcity

King et al [75] performed a comparative analysis ofwater use by representative lignocellulosic bioenergy speciesto provide insight on the best candidate crops for spe-cific climates In the analysis the higher biomass pro-ductivity group (which included Eucalyptus species) hada precipitation evapotranspiration ratio close to 10 com-pared to the lower productivity group with a precipita-tion evapotranspiration value of about 17 indicating that theproductive systems were operating at the limit of availablewater (ie using almost all of it) This suggests that futureproductivity could be vulnerable in regions where wateravailability is decreased by climate change In addition corre-lations among agroclimatic variables and their relationship tophysiological process rates and biomass production suggestthat bioenergy productivity will be more sensitive to changesin water availability than temperature under future changesin climate [75] It is obvious then that water availability willbe a key determinant of where and howmuch biomass-basedenergy can be produced as human demand for water growsand climate change increases drought stress in many parts ofthe world [75]

Based on experience gained in South Africa Gush [61]providedmethodology for assessing the hydrological impactsof tree-based bioenergy feedstocks from individual treewater use rates to national-scale impacts on water resourcesMethodology is needed because large-scale changes in land-use constitute a change in the structure and functioning ofvegetation which has implications for water use and avail-ability of water for downstreamusers [61] Gush [61] intendedfor this to be a generic methodology not just for SouthAfrica but with applicability to tree-based bioenergy devel-opments worldwide and his methods include identifying thegeographical area of interest selecting an appropriate hydro-logical response unit identifying ldquobaselinerdquo vegetation in thearea of interest running an appropriate hydrologicalmodel tosimulate streamflow and evapotranspiration under baselineand future land use scenarios and drawing conclusions onthe likely water resource impacts of the proposed land-use

6 Conclusions

This review has indicated that extensive information can bedrawn from South African studies quantifying the water useof Eucalyptus species Average daily transpiration rates ofeucalypts in South Africa range from 2 to 7mm these varywith season-associated climatic variables soil water availabil-ity stand age and site growth potential The techniques usedto estimate water use that is paired catchment experimentssapflow modeling estimates and remote sensing are widelytransferable to other regions

Results from the long history of forest plantation hydrol-ogy have been compiled and are currently used to provide ascientific basis for South African legislation decisions relatingto water use estimates and water resource allocation amongusers The methodology developed to meet the requirementsof South Africarsquos Water Law has worldwide relevance asit has the potential to influence future policy and the

sustainable management of water in any country faced withwater resource management challenges [61] This type offramework has particular relevance for those countries whereproposed land use changes (such as wide scale planting ofeucalypts for biomass) may have potential impacts on waterresources

Demand for water energy and wood products is steadilyincreasing and continued efforts to minimize the impactsof forest plantations on water resources while conservingproductivity gains are required [24] A critical componentfor meeting these increased demands is to improve theefficiency with which afforested areas use available water [543] In addition WUE is anticipated to become an importantcriterion for comparing competing land-use scenarios underthe new South African Water Act [24] Water use efficiencyof South African Eucalyptus species ranges from 00008to 00123m3 stemwood produced per m3 water consumedThese estimates vary with genotype site conditions weatherand tree age Deeper insights into the WUE of eucalyptclones are needed as certain clones show low water usebut fast growth To further our understanding of WUEestimates should be paired with physiological measurementsand monitoring of stand canopy structure

References

[1] J L Stape J L M Goncalves and A N Goncalves ldquoRela-tionships between nursery practices and field performance forEucalyptus plantations in BrazilrdquoNew Forests vol 22 pp 19ndash412001

[2] D Binkley and J L Stape ldquoSustainable management of Euca-lyptus plantations in a changing worldrdquo in Proceedings of theIUFRO Conference of Eucalyptus in a Changing World NBorralho J S Pereira C Marques J Coutinho M Madeiraand M Tome Eds pp 11ndash17 Aveiro Portugal October 2004

[3] P J Dye ldquoEstimating water use by Eucalyptus grandis with thePenman-Monteith equationrdquo in Proceedings of the VancouverSymposium of Forest Hydrology and Watershed Management RH Swanson P Y Bernier and P DWoodard Eds pp 329ndash337IAHS Publication Oxfordshire UK August 1987

[4] M E D Poore and C Fries ldquoThe ecological effects of Eucalyp-tusrdquo FAO Forestry Paper 59 FAO Rome Italy 1985

[5] B W Olbrich D Le Roux A G Poulter W J Bond and WD Stock ldquoVariation in water use efficiency and 12057513C levels inEucalyptus grandis clonesrdquo Journal of Hydrology vol 150 no 2ndash4 pp 615ndash633 1993

[6] J Kallarackal and C K Somen ldquoAn ecophysiological evaluationof the suitability of Eucalyptus grandis for planting in thetropicsrdquo Forest Ecology and Management vol 95 no 1 pp 53ndash61 1997

[7] J V Soares and A C Almeida ldquoModeling the water balanceand soil water fluxes in a fast growing Eucalyptus plantation inBrazilrdquo Journal of Hydrology vol 253 no 1ndash4 pp 130ndash147 2001

[8] D F Scott F W Prinsloo G Moses M Mehlomakulu and AD A Simmers ldquoA re-analysis of the South African catchmentafforestation experimental datardquo WRC Report 810100 WaterResearch Commission Pretoria South Africa 2000

[9] M Grut Forestry and forest industry in South Africa BalkemaCape Town South Africa 1965


[10] Forestry South Africa South African Forestry Facts for the Year20082009 Forestry South Africa Pretoria South Africa 2010

[11] The South African Forest Owners Association Understandingour Forestry Heritage Rainbird Pretoria South Africa 1997

[12] P J Dye and B W Olbrich ldquoEstimating transpiration from6-year-old Eucalyptus grandis trees development of a canopyconductance model and comparison with independent sap fluxmeasurementsrdquo Plant Cell and Environment vol 16 pp 45ndash531993

[13] D F Scott andW Lesch ldquoStreamflow responses to afforestationwith Eucalyptus grandis and Pinus patula and to felling in theMokobulaan experimental catchments South Africardquo Journalof Hydrology vol 199 no 3-4 pp 360ndash377 1997

[14] P Dye and D Versfeld ldquoManaging the hydrological impacts ofSouth African plantation forests an overviewrdquo Forest Ecologyand Management vol 251 no 1-2 pp 121ndash128 2007

[15] P J Dye ldquoClimate forest and streamflow relationships inSouth African afforested catchmentsrdquo Commonwealth ForestryReview vol 75 pp 31ndash38 1996

[16] M B Gush D F Scott G P W Jewitt et al ldquoEstimation ofstreamflow reductions resulting from commercial afforestationin South Africardquo WRC Report TT 17302 Water ResearchCommission Pretoria South Africa 2002

[17] J M Bosch and J D Hewlett ldquoA review of catchment exper-iments to determine the effect of vegetation changes on wateryield and evapotranspirationrdquo Journal of Hydrology vol 55 no1ndash4 pp 3ndash23 1982

[18] D F Scott and R E Smith ldquoPreliminary empirical modelsto predict reductions in annual and low flows resulting fromafforestationrdquoWater SA vol 23 pp 135ndash140 1997

[19] L Zhang W R Dawes and G R Walker ldquoPredicting the effectof vegetation changes on catchment average water balancerdquoCSIRO Technical Report 9912 CSIRO Canberra Australia1999

[20] M B Gush ldquoModelling streamflow reductions resulting fromcommercial afforestation in South Africa from research toapplicationrdquo in Proceedings of the International Conference onForest and Water China August 2006

[21] W S Van Lill F J Kruger and D B Van Wyk ldquoThe effect ofafforestation with Eucalyptus grandis Hill ex Maiden and Pinuspatula Schlecht et Cham on streamflow from experimentalcatchments at Mokobulaan Transvaalrdquo Journal of Hydrologyvol 48 no 1-2 pp 107ndash118 1980

[22] R E Smith and D F Scott ldquoThe effects of afforestation on lowflows in various regions of South Africardquo in Water SA vol 18pp 185ndash194 1992

[23] J D Hewlett and L Pienaar ldquoDesign and analysis of thecatchment experimentrdquo in Proceedings of a symposium on use ofsmall watersheds in determining effects of forest land use on waterquality E H White Ed pp 88ndash106 University of KentuckyLexington Ky USA May 1973

[24] P J Dye ldquoHow efficiently do Eucalyptus plantations userainfallrdquo CSIR Report ENV-P-I 98204 Division of WaterEnvironment and Forest Technology CSIR Pretoria SouthAfrica 1999

[25] P J Dye ldquoResponse of Eucalyptus grandis trees to soil waterdeficitsrdquo Tree Physiology vol 16 pp 233ndash238 1996

[26] P J Dye A G Poulter S Soko and D Maphanga ldquoThedetermination of the relationship between transpiration rateand declining available water for Eucalyptus grandisrdquo WRCReport 441197 Water Resource Commission Pretoria SouthAfrica 1997

[27] B W Olbrich ldquoThe verification of the heat pulse velocity tech-nique for measuring sap flow in Eucalyptus grandisrdquo CanadianJournal of Forest Research vol 21 pp 836ndash841 1991

[28] P Dye P Vilakazi M Gush R Ndlela and M RoyappenldquoInvestigation of the feasibility of using trunk growth incre-ments to estimate water use of Eucalyptus grandis and Pinuspatula plantationsrdquo WRC Report 809101 Water ResearchCommission Pretoria South Africa 2001

[29] O L Lange R Losch E D Schulze and L Kappen ldquoResponsesof stomata to changes in humidityrdquo Planta vol 100 pp 76ndash861971

[30] E D Schulze ldquoCarbon dioxide and water vapor exchange inresponse to drought in the atmosphere and in the soilrdquo AnnualReview of Plant Physiology vol 37 pp 247ndash274 1986

[31] M T Tyree and J S Sperry ldquoDo woody plants operate nearthe point of catastrophic xylem dysfunction caused by dynamicwater stressrdquo Plant Physiology vol 88 pp 575ndash580 1988

[32] J M Campion P J Dye and M C Scholes ldquoModellingmaximum canopy conductance and transpiration in Eucalyptusgrandis stands not subjected to soil water deficitsrdquo SouthernAfrican Forestry Journal no 202 pp 3ndash11 2004

[33] P J Dye S Jacobs and D Drew ldquoVerification of 3-PG growthand water-use predictions in twelve Eucalyptus plantationstands in Zululand South Africardquo Forest Ecology and Manage-ment vol 193 no 1-2 pp 197ndash218 2004

[34] J H Knight ldquoRoot distributions and water uptake patterns ineucalypts and other speciesrdquo in The Ways Trees Use Water JLandsberg Ed Water and Salinity Issues in Agroforestry No5 pp 66ndash102 RIRDC Barton Australia 1999

[35] A P G Schonau and D C Grey ldquoSite requirements of exotictree speciesrdquo in Forest Handbook K von Gadow Ed pp 82ndash94 South African Institute of Forestry Pretoria South Africa1987

[36] D I Boden ldquoThe relationship between soil water status rainfalland the growth of Eucalyptus grandisrdquo South African ForestryJournal vol 156 pp 49ndash55 1990

[37] H L Gholz K C Ewel and R O Teskey ldquoWater and forestproductivityrdquo Forest Ecology and Management vol 30 no 1ndash4pp 1ndash18 1990

[38] J J Landsberg K H Johnsen T J Albaugh H L Allen andS E McKeand ldquoApplying 3-PG a simple process-based modeldesigned to produce practical results to data from loblolly pineexperimentsrdquo Forest Science vol 47 no 1 pp 43ndash51 2001

[39] D White M Battaglia J Bruce et al ldquoWater-use efficientplantationsmdashseparating the wood from the leavesrdquo in Forestand Wood Products Project No PNC073-0708 p 25 AustraliaLimited 2009

[40] P J Dye ldquoAn investigation of the use of tree growth parametersto infer spatial and temporal patterns of moisture stress andreduced water userdquo CSIR Report FOR-I 647 Division of WaterEnvironment and Forest Technology CSIR Pretoria SouthAfrica 1996

[41] P J Dye S Soko and D Maphanga ldquoIntra-annual variationin water use efficiency of three clones in kwaMbonambiZululandrdquo CSIR Report ENVPC 97048 Division of WaterEnvironment and Forest Technology CSIR Pretoria SouthAfrica 1997

[42] D Le Roux W D Stock W J Bond and D Maphanga ldquoDrymass allocation water use efficiency and 12057513C in clones ofEucalyptus grandis E grandis times camaldulensis and E grandistimes nitens grown under two irrigation regimesrdquo Tree Physiologyvol 16 no 4 pp 497ndash502 1996


[43] R M Wise P J Dye and M B Gush ldquoA comparison of thebiophysical and economic water-use efficiencies of indigenousand introduced forests in south africardquo Forest Ecology andManagement vol 262 no 6 pp 906ndash915 2011

[44] R E Schulze ldquoHydrology and agrohydrology a text to accom-pany the ACRU 300 Agrohydrological Modelling SystemrdquoWRC Report TT6995 Water Research Commission PretoriaSouth Africa 1995

[45] G P W Jewitt and R E Schulze ldquoVerification of the ACRUmodel for forest hydrology applicationsrdquoWater SA vol 25 no4 pp 483ndash489 1999

[46] R Rivas and V Caselles ldquoA simplified equation to estimate spa-tial reference evaporation from remote sensing-based surfacetemperature and local meteorological datardquo Remote Sensing ofEnvironment vol 93 no 1-2 pp 68ndash76 2004

[47] K Wang P Wang Z Li M Cribb and M Sparrow ldquoA simplemethod to estimate actual evapotranspiration from a combi-nation of net radiation vegetation index and temperaturerdquoJournal of Geophysical Research D vol 112 no 15 Article IDD15107 pp 1ndash14 2007

[48] R K Vinukollu E F Wood C R Ferguson and J B FisherldquoGlobal estimates of evapotranspiration for climate studiesusing multi-sensor remote sensing data evaluation of threeprocess-based approachesrdquoRemote Sensing of Environment vol115 no 3 pp 801ndash823 2011

[49] M Govender K Chetty and H Bulcock ldquoA review of hyper-spectral remote sensing and its application in vegetation andwater resource studiesrdquo Water SA vol 33 no 2 pp 145ndash1512007

[50] T C Hsiao ldquoPlant responses to water stressrdquo Annual Review ofPlant Physiology vol 24 pp 519ndash570 1973

[51] H R Barnard andMG Ryan ldquoA test of the hydraulic limitationhypothesis in fast-growing Eucalyptus salignardquo Plant Cell andEnvironment vol 26 no 8 pp 1235ndash1245 2003

[52] M M Chaves J P Maroco and J S Pereira ldquoUnderstandingplant responses to droughtmdashfrom genes to the whole plantrdquoFunctional Plant Biology vol 30 no 3 pp 239ndash264 2003

[53] A Fabiao M Madeira E Steen T Katterer C Ribeiro and CAraujo ldquoDevelopment of root biomass in anEucalyptus globulusplantation under different water and nutrient regimesrdquo Plantand Soil vol 168-169 pp 215ndash223 1995

[54] T S Grove B D Thomson and N Malajczuk ldquoNutritionalphysiology of eucalypts uptake distribution and utilizationrdquo inNutrition of Eucalypts P M Attiwill andM A Adams Eds pp77ndash108 CSIRO Collingwood Australia 1996

[55] J M Campion M Nkosana and M C Scholes ldquoBiomass andN and P pools in above- and below-ground components ofan irrigated and fertilised Eucalyptus grandis stand in SouthAfricardquo Australian Forestry vol 69 no 1 pp 48ndash57 2006

[56] D Binkley J L Stape and M G Ryan ldquoThinking aboutefficiency of resource use in forestsrdquo Forest Ecology and Man-agement vol 193 no 1-2 pp 5ndash16 2004

[57] J L Stape D Binkley and M G Ryan ldquoEucalyptus productionand the supply use and efficiency of use of water light andnitrogen across a geographic gradient in Brazilrdquo Forest Ecologyand Management vol 193 no 1-2 pp 17ndash31 2004

[58] G D Farquhar and R A Richards ldquoIsotopic compositionof plant carbon correlates with water-use efficiency of wheatgenotypesrdquo Australian Journal of Plant Physiology vol 11 no6 pp 539ndash552 1984

[59] S G Pallardy and T T Kozlowski Physiology of Woody PlantsElsevier Boston Mass USA 2008

[60] DWAF Water-Use Licensing the Policy and Procedure forLicensing Streamflow Reduction Activities Department ofWaterAffairs and Forestry Pretoria South Africa 1999

[61] M Gush ldquoAssessing hydrological impacts of tree-based bioen-ergy feedstockrdquo in Assessing the Sustainability of BioenergyProjects in Developing Countries A Framework for Policy Eval-uation J M Amezaga G von Maltitz and S Boyes Eds pp37ndash52 Newcastle University Tyne and Wear UK 2010

[62] J S Pereira and S Pallardy ldquoWater stress limitations to treeproductivityrdquo in Biomass Production by Fast-Growing Trees J SPereira and J J Landsberg Eds pp 37ndash56 Kluwer AcademicDodrecht The Netherlands 1989

[63] D I Dickmann ldquoThe ideotype concept applied to forest treesrdquoin Attributes of Trees as Crop Plants M G R Cannell and JE Jackson Eds pp 89ndash101 Institute of Terrestrial EcologyLancaster UK 1985

[64] R Gonzalez T Treasure J Wright et al ldquoExploring thepotential of Eucalyptus for energy production in the SouthernUnited States financial analysis of delivered biomass Part IrdquoBiomass and Bioenergy vol 35 no 2 pp 755ndash766 2011

[65] D Dougherty and J Wright ldquoSilviculture and economic evalu-ation of eucalypt plantations in the southern USrdquo Bioresourcesvol 7 pp 1994ndash2001 2012

[66] A Demirbas ldquoProgress and recent trends in biofuelsrdquo Progressin Energy and Combustion Science vol 33 no 1 pp 1ndash18 2007

[67] G Berndes ldquoBioenergy and watermdashthe implications of large-scale bioenergy production for water use and supplyrdquo GlobalEnvironmental Change vol 12 no 4 pp 253ndash271 2002

[68] J M Evans and M J Cohen ldquoRegional water resource impli-cations of bioethanol production in the Southeastern UnitedStatesrdquo Global Change Biology vol 15 no 9 pp 2261ndash22732009

[69] P W Gerbens-Leenes A Y Hoekstra and T van der MeerldquoThe water footprint of energy from biomass a quantitativeassessment and consequences of an increasing share of bio-energy in energy supplyrdquo Ecological Economics vol 68 no 4pp 1052ndash1060 2009

[70] T Beringer W Lucht and S Schapoff ldquoBioenergy productionpotential of global biomass plantations under environmentaland agricultural constraintsrdquo GCB Bioenergy vol 3 pp 299ndash312 2011

[71] A Buyx and J Tait ldquoEthical framework for biofuelsrdquo Sciencevol 332 no 6029 pp 540ndash541 2011

[72] BIS Biofuels Industrial Strategy of the Republic of South AfricaDepartment of Minerals and Energy Pretoria South Africa2007

[73] G Jewitt and R Kunz ldquoThe impact of biofuel feedstock pro-duction on water resources a developing country perspectiverdquoBiofuels Bioproducts and Biorefining vol 5 no 4 pp 387ndash3982011

[74] B G Ridoutt and S Pfister ldquoA revised approach to water foot-printing to make transparent the impacts of consumption andproduction on global freshwater scarcityrdquoGlobal EnvironmentalChange vol 20 no 1 pp 113ndash120 2010

[75] J S King R Ceulemans J M Albaugh et al ldquoThe challenge ofligno-cellulosic bioenergy in a water-limited worldrdquo BioSciencevol 63 pp 102ndash177 2013

Submit your manuscripts athttpwwwhindawicom

Forestry ResearchInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Environmental and Public Health

Journal of



EcosystemsJournal of


MeteorologyAdvances in

EcologyInternational Journal of


Marine BiologyJournal of


Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Advances in


Environmental Chemistry

Atmospheric SciencesInternational Journal of



Waste ManagementJournal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

Geophysics


Geological ResearchJournal of

EarthquakesJournal of


BiodiversityInternational Journal of


ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014


ClimatologyJournal of


of increasing interest in many parts of the world In countrieswhere eucalypts are introduced species there is a need tounderstand key environmental issues for example water userelated to themanagement and growth of these treesOnewayin which information needs can be identified and prioritizedis to draw on the knowledge and experience gained fromdecades of water research in South Africa Research intowater use of South African timber plantations commenced in1937 the historical nature of the data collected the length ofrecord and the range of sites involved make the experimentsunique and invaluable [8]

The objective of this paper is to provide a comprehen-sive synthesis of the available South African literature onthe effects of eucalypt planting on water resources and toproduce new insights into future research needs This paperis organized into five main sections as follows

(i) background to South African forestry and limitedwater resources

(ii) techniques used to measure and model water use(iii) methods for determining water use efficiency(iv) current South African legislation and(v) future considerations including a new research focus

and tree-based bioenergy feedstocks

2 South African Forestry andLimited Water Resources

South Africa has limited indigenous timber-producingforests The first plantations of exotic trees mainly pineand eucalypts were established in the country in 1875 afterrecognizing that demand for timber had exceeded the supplyavailable from indigenous forests These exotic species werepreferred for afforestation because none of the indigenoustree species which yield useful timber grew at rates consid-ered profitable [9] There has since been a steady expansionin the total area of forest plantations culminating in 12million hectares (11 of South African land area) of which515000 ha are planted to eucalypts [10] This genus is grownpredominantly for pulpwood and mining timber over anormal rotation length of seven to ten years [11] Productivityfrom these plantations is relatively high and ranges from 10 to68m3 haminus1 yrminus1

Plantations of exotic species were established in thehigher-rainfall (gt700mm) regions of the country coincidingwith a large proportion of the surface water resources whichemanate from relatively small but important catchment areasconcentrated along east- and south-facing escarpments andmountain slopes [12ndash14] The dominant vegetation in manyof these areas was originally montane grassland and fyn-bos (macchia) shrublands Annual evapotranspiration ratesof this indigenous vegetation range from 700 to 900mm[15] This indigenous vegetation has relatively shallow rootsystems and is seasonally dormant resulting in limitedevapotranspiration over the dry season [12 15] In strongcontrast plantation forests are characterized by deep rootsystems and tall dense evergreen canopies that maintain

a relatively high leaf area index over the entire year [1416] Evapotranspiration from established forest plantationsis commonly in the range of 1100ndash1200mm and is limitedby rainfall available on the site [14] Numerous local andinternational studies have indicated conclusively that forestplantations established in former natural forests grasslandsor shrubland areas consume more water than the baselinevegetation reducing water yield (streamflow) as a result[8 13 14 17ndash20] Concerns over the effects of these forestplantations on streamflows and catchment water yields aroseas far back as 1915 and were thoroughly debated during theEmpire Forestry Conference that took place in South Africain 1935 [14] A decision taken at this conference led to theestablishment of a network of long-term paired catchmentexperiments in various catchments located in the majorforestry areas of South Africa [14]

3 Techniques Used to Measure andModel Water Use

A range of techniques has been used to measure and modelwater use of South African forest plantations across a rangeof temporal and spatial scales These include paired catch-ment experiments micrometeorological techniques sapflowestimates using heat pulse velocity modeling efforts andremote sensing estimates of stand scale water use Each ofthese techniques is discussed in turn pertinent results arepresented and the short-comings of each method have beenhighlighted

31 Paired Catchment Experiments The paired catchmentmethod involves the long-term monitoring of streamflowfrom pairs of catchments before and after a major vegetationchange in one of them [8] Van Lill et al [21] reported onresults of a paired catchment experiment with E grandisversus natural grass cover on the eastern escarpment of SouthAfrica Afforestation with E grandis exerted an observableinfluence from the third year after planting with a maximumapparent reduction in flow between 300 and 380mm yearminus1andwithmaximum reductions in seasonal flow of about 200ndash260mm yearminus1 in summer and 100ndash130mm yearminus1 in winter[21]

Catchment experiments have shown that eucalypts causea faster reduction in streamflow compared to afforestationwith pines [13] Further these effects were more marked foreucalypts (90ndash100 water reduction) than with pines (40ndash60 reductions in the first eight years or so after treat-ment) but Smith and Scott [22] suggested these differencesmay diminish as the pine stands become well-establishedStreamflow reductionwas significant from the third year afterplanting eucalypts for both the wet and dry seasons and thestream dried up completely in the ninth year after planting[13] After afforestationwith pines reductions in total andwetseason streamflow became significant in the fourth year andstopped flowing completely in the twelfth year [13] Analysesshowed peak reductions of 470mmyearminus1 for eucalypts in theseventh and ninth years both particularly wet years [13] Thehighest estimated flow reduction due to pine was 257mm














8

7

6

5

4

3

2

1

100

90

80

70

60

50

40

30

20

10

00

Dai

ly tr

ee-le

vel

tran

spira

tion

(985747da

yminus1)

Dai

ly st

and-

leve

ltr

ansp

iratio

n (m

m)

1400

1200

1000

800

600

400

200

0

PAR

(120583m

ol mminus2

sminus1)

300

250

200

150

100

050

000

Jun-

92

Jul-9

2

Aug-

92

Sep-

92

Oct

-92

Nov

-92

Dec

-92

Jan-

93

Feb-

93

Mar

-93

Apr-

93

May

-93

Jun-

93

Vapo

r pre

ssur

e defi

cit (

kPa)

(a)

(b)
























Table 1 Continued



































6 Conclusions





References


















































































Journal of












Volume 2014

Advances in









Geophysics



























8

7

6

5

4

3

2

1

100

90

80

70

60

50

40

30

20

10

00

Dai

ly tr

ee-le

vel

tran

spira

tion

(985747da

yminus1)

Dai

ly st

and-

leve

ltr

ansp

iratio

n (m

m)

1400

1200

1000

800

600

400

200

0

PAR

(120583m

ol mminus2

sminus1)

300

250

200

150

100

050

000

Jun-

92

Jul-9

2

Aug-

92

Sep-

92

Oct

-92

Nov

-92

Dec

-92

Jan-

93

Feb-

93

Mar

-93

Apr-

93

May

-93

Jun-

93

Vapo

r pre

ssur

e defi

cit (

kPa)

(a)

(b)
























Table 1 Continued



































6 Conclusions





References


















































































Journal of












Volume 2014

Advances in









Geophysics

































Table 1 Continued



































6 Conclusions





References


















































































Journal of












Volume 2014

Advances in









Geophysics



































6 Conclusions





References


















































































Journal of












Volume 2014

Advances in









Geophysics






















































































Journal of












Volume 2014

Advances in









Geophysics














Review Article Eucalyptus and Water Use in South Africa · InternationalJournalofForestryResearch...

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Transcript of Review Article Eucalyptus and Water Use in South Africa · InternationalJournalofForestryResearch...