Composition and Ecology of Bryophyte Communities on Oak (Quercus spp.) Woody Debris in a Mixed-oak Forest of Southern Ohio, USA

Darrin L. Rubino1, Robert A. Klips2, Brian C. McCarthy3

1Department of Biology, Hanover College, Hanover, IN; 2Department of Evolution, Ecology, and Organismal Biology, The Ohio State University at Marion, Marion, OH; 3Department of

Environmental and Plant Biology, Ohio University, Athens, OHAbstractBryophytes are a ubiquitous component of forested ecosystems, but little is known about their community composition and the factors that influence their distribution in many forest types. The goals of this investigation were to identify the members of the bryophyte community found on woody debris in topographically dissected mixed-oak forests and to identify parameters that influence community composition and species distributions. In a southern Ohio forest, 50 plots were constructed across slope aspects and slope positions throughout the landscape to maximize microsite variability; 165 oak (Quercus spp.) logs were selected for analysis. Twenty-five bryophyte species (24 mosses; 1 liverwort) were collected. Total moss cover was significantly (P < 0.05) positively correlated with slope aspect, log volume, and lichen cover. Cover of Platygyrium repens, the most commonly encountered species, was significantly correlated with tree basal area (+), lichen cover (+), percent of the log that was solid (+), percent of the log that was fragmented (-), and landform index (a quantitative measure of slope position;-). Canonical correspondence analysis revealed that slope aspect, landform index, log volume, plot woody debris volume, percent lichen cover, and the percentages of the log that were fragmented or solid explained a significant amount of variation in the bryophyte community. Species separated along a proposed moisture and decay gradient suggesting that dry, casehardened logs and moist, friable logs support unique bryophyte communities. Ultimately, bryophyte distribution and abundance is influenced by factors that vary at the landscape, plot, and log scales.

Discussion & Conclusions•Distribution of individual species, like vascular plants, are influenced by factors that vary at both micro- and macroscales•Overall moisture and decay gradients likely influences bryophyte species distributions •Bryophyte community consists of mesic and xeric “specialists”

•Platygyrium repens found mainly on solid, casehardened logs (photos below) found in xeric microhabitats (e.g., ridges)•Nowellia curvifolia prefers larger (slower to dry), fragmented logs in valleys and on mesic slope aspects

•Future work•Explore relationships between relative importance of individual species and environmental variables•Identify bryophyte community composition of other species of woody debris

Results•165 logs studied•13,591 sampling points•Twenty-five bryophyte species collected

•24 mosses•1 liverwort• Species area curve does not reveal asymptote (Fig.1)

•Species richness and distribution•Range: 0 – 7 species log-1

•1.7 ± 0.1 species log-1 (mean ± SE )•Great among species variability in commonness (Fig. 2)

•Bryophyte cover•16.7 ± 1.3% (mean ± SE)•Range: 0 – 81.8%•Cover correlated with various plot- and log-level parameters (Table 1)

•Platygyrium repens •Most commonly encountered bryophyte •70% of logs•Cover: 10.7 ± 1.0% (mean ± SE)•Cover correlated with various plot- and log-level parameters (Table 1)

IntroductionBryophytes•Mosses, liverworts, and hornworts•Distribution influenced by microhabitat

•Substrate (decaying wood, rock, soil, etc.)•Light quantity and quality•Moisture availability

•Represent a unique and diverse community•Approximately 535 bryophytes in Ohio•All too often understudied ecosystem component

Coarse Woody Debris•Dead and downed tree limbs and boles (≥ 10 cm diameter; ≥0.5 m length)•Ubiquitous and conspicuous in forested systems•Serves many roles

•Nutrient reservoir•Important microhabitat for a wide range of organisms•Maintains biodiversity

AcknowledgementsOhio Department of Natural Resources (Dave Swanson)Hanover College Faculty Development CommitteeBarbara Andreas

Methods and MaterialsStudy Site•Waterloo Wildlife Research Station, Southeast Ohio (Athens County)•Mixed-oak forest•Second growth (150 yr-old)•Allegheny Plateau•Highly dissected topography•Much microsite variability related to daily insolation and moisture•Complex mixture of microhabitats throughout the landscape

•Xeric conditions: steep slopes, ridges, southwest-facing slopes•Mesic conditions: gentle slopes, valleys, northeast-facing slopes

Northeast- and southwest-facing slopes showing the change in microsite conditions related to topographic

gradients. (Note: photos taken seconds apart).

Northeast Southwest

Platygyrium repens is common and widely distributed on logs, stumps and tree trunks. Despite its small size, it is distinctive because it forms spreading patches that have a peculiarly oily-looking, shiny, dark-green sheen. Many of the branches are terminated by dense clusters of asexual reproductive structures.

Nowellia curvifolia is a common leafy liverwort found almost exclusively on decorticated logs. The leaves are deeply concave, giving the slender stems a tubular appearance.

Hypnum imponens is a distinctive, relatively large pleurocarp that often covers logs. It is pinnate, and its shiny tapered leaves are swept to opposite sides of the branches (secund). Three other Hypnum species were also found in this study.

Thuidium delicatulum is aptly termed the “fern moss” due to its bipinnate growth form. It commonly covers stumps and logs. The leaf cells have projecting points (papillae), and the stem is clothed with minute filiform appendages (paraphyllia).

Dicranum flagellare is a narrow-leaved acrocarp that occurs mainly on coarse woody debris at the study site. In addition to producing spores, this species reproduces by means of asexual brood branchlets.

Commonly Encountered Bryophytes*

*Moss line drawings from Crum and Anderson 1981; Nowellia from Hicks 1992.

Correlation Coefficients

Parameter Mean (± SE)All

Bryophytes P. repens

Plot:

Percent slope 23.5 ± 1.7

Landform index† 16.2 ± 0.8 -0.299

Slope aspect (˚) 180.9 ± 13.3 0.237

Dominant tree age (yr) 145.9 ± 4.0

Dominant tree height (m) 29.4 ± 0.7

Canopy cover (%) 80.8 ± 0.8

CWD volume (m3 ha-1) 42.0 ± 5.1

CWD density (pieces ha-1) 282.8 ± 19.3

Tree density (stems ha-1) 320.8 ± 11.7

Tree basal area (m2 ha-1) 31.1 ± 1.3 0.194

Sapling density (stems ha-1) 2702.8 ± 120.3

Sapling basal area (m2 ha-1) 1.7 ± 0.1

Study log:

Aerial (%) 14.5 ± 1.7

Volume (m3) 1.0 ± 0.1 0.332

Litter cover (%) 6.7 ± 0.7

Lichen cover (%) 5.1 ± 0.7 0.291 0.383

Surface structure (%):

Bark 8.6 ± 1.7

Solid 11.1 ± 1.6 0.256

Punky 67.0 ± 2.1 -0.228

Fragmented 13.2 ± 1.4

Table 1. Plot and study log parameters and correlation with percent bryophyte cover and Platygyrium repens cover. Only

significant correlation coefficients (P < 0.05) are reported.

†Landform index is a measure of slope position; small values = ridges, and large values = valleys.

Field Methods•Fifty 500 m2 plots created across various slope aspects, slope positions, and aspect-position combinations •Measured variety of plot and log characteristics (Table 1)•Woody debris

•Identified to lowest possible taxonomic level•Assigned decay classes (low to high)

•Up to five moderately decayed oak (Quercus spp.) logs in each plot selected for bryophyte study•Moderately decayed logs characterized by

•Little to no bark•Moderate to complete sapwood degradation•Pockets of punky and fragmented wood•No twigs or fine branches

•Transect created across the top of each study log from butt to tip•Every 10 cm along the transect, the surface structure of the log was noted

•Bark – bark cover•Solid –unfragmented, sound wood•Punky –wood easily dented with fingernail•Fragmented – loose wood fragments that could be dislodged with a flicking motion; friable

•At each 10 cm point, the presence or absence of bryophyte cover was recorded and a collection was made if a bryophyte was present

Data Analysis•Correlation analysis to investigate possible relationships between bryophyte cover and measured parameters•Canonical Correspondence Analysis (CCA) used to simultaneously study environmental variables and community response

•Stepwise variable selection used to select important environmental parameters for analysis•Only species present on 5% of logs included in analysis (9 species)

Goals•Determine the bryophyte community composition on woody debris •Identify factors that influence bryophyte species distribution and community composition

Casehardened log lacking sapwood and exhibiting a dry, gray rind. Bryophytes growing on log are Platygyrium repens and

Dicranum sp.

Figure 1. Species-area curve of bryophytes collected from 165 Quercus spp. logs. The curve was constructed with the

first log as the smallest and the last log as the largest.

Log

0 20 40 60 80 100 120 140 160

Num

ber

of s

peci

es

0

5

10

15

20

25

Figure 3. CCA biplot of bryophyte species and environmental variables (blue). Note: Individual logs not shown for clarity.

Examples of moderately decayed woody debris

Results•Canonical correspondence analysis (Fig 3)

•Seven of the 20 environmental parameters explained a significant amount of variation in species distribution•Environmental parameters explained 15.6% of variation in species data on Axes 1 and 2•Axes 1 and 2 strongly correlated with various parameters (Fig. 3; see trends in red)

Axis 1

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2

Ax

is 2

-1.0

-0.5

0.0

0.5

1.0

1.5

Plot CWD Volume

Percent Solid

Lichen Cover Percent Fragmented

Log Volume

Landform IndexSlope Aspect

Hypnum curvifolium

Platygyrium repens

Nowelliacurvifolia

Pylaisiadelpha

Dicranum montanum

Thuidium delicatulum

Steerecleus serrulatus

Hypnum

flagellareDicranum

tenuirostris

imponens

Solid log Fragmented logSmall log Large logSouthwest slope Northeast slopeRidge Valley

Sm

all w

oody

deb

ris lo

ad

Larg

e w

oody

deb

ris lo

adE

leva

ted

liche

n co

ver

Low

lich

en c

over

Figure 2. Frequency of bryophyte species occurrences on 165 Quercus spp. logs.

Percentage of logs

0-1 1-5 5-10 10-25 25-50 50-75 75-100

Num

ber

of b

ryop

hyte

spe

cies

0

2

4

6

8

10

12