The Effects Of Disturbance And Soil Nutrient Enrichment On Grassland Community Biodiversity Across Spatial Scales

Abstract

It is well known that soil fertility, habitat productivity and disturbance can influence the species diversity of plant communities, though most studies addressing this issue measure plant diversity at only one spatial scale. This study utilizes data collected from a long-term field experiment in which the abiotic factors of nutrient enrichment and disturbance were experimentally manipulated in a grassland system. The experiment was established at the KU Field station in 2001 in an abandoned cool-season hayfield. Here we evaluate the singular and interactive effects of nutrient fertilization and haying treatments on plant species richness measured at spatial scales ranging from 0.25 – 6 m2. Applying the widely accepted concept of the species-area curve, S = c A z, to this empirical experiment allows for an analysis of scale dependence of the treatments. The formula expresses species richness (S, a measure of biodiversity) as a power function of area (A) increasing by a rate of species accumulation (z) that is scaled by a constant (c). The slope of the species area curve, reflected in the z value, indicates how species richness is structured spatially within a community, allowing an assessment of spatial dependence. If z-values are statistically different among treatments, then the effects of treatments on richness are scale dependent. This study’s results indicate that nutrient enrichment and disturbance interacted strongly to effect species richness at all spatial scales. Generally, nutrient enrichment reduced species richness but to a lesser degree in hayed plots. Though these effects were consistent in rank across all scales, the results do indicate significant spatial dependence in the magnitude of the combined effects of disturbance and nutrient enrichment on species richness.

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F Statistic
Area m2
ANOVA Results
Fertilization
Haying
Interaction of Fertilization
and Haying
(Figure 3) Interactive Effects of Fertilization
& Haying: Fertilization reduced richness but
this effect was tempered by haying at all
spatial scales.
THE EFFECTS OF DISTURBANCE AND SOIL NUTRIENT ENRICHMENT ON
GRASSLAND COMMUNITY BIODIVERSITY ACROSS SPATIAL SCALES
Jeremy Forsythe & Dr. Bryan Foster
Department of Biology, University at Albany ; Department of Ecology & Evolution, Kansas University
Introduction
It is well known that many ecological patterns and the processes that generate
them vary with spatial scale. To better predict the impact of environmental
change on ecological systems it is important to incorporate scale explicitly
into ecological studies. Numerous studies have shown that soil nutrient
availability and disturbance are important determinants of species richness in
many plant communities (Huston 1994). However, because richness scales
with area (Shiner et all. 2000), our perceptions of how nutrients and
disturbance influence richness may be dependent on the scale which richness
is estimated. In this study we examine potential scale-dependence of plant
species richness in response to nutrient enrichment and haying disturbance in
a long term experiment of grassland management.
Question & Focus
How do nutrient enrichment and haying affect plant species richness?
Are these effects scale-invariant or scale-dependent in terms of their
sign, magnitude, and statistical significance?
Methodology & Design
Discussion
Long term experiment set up in 2001 on an abandoned cool season
hayfield at the Kansas University Field Station.
2x2x2 factorial design representing each combination of the treatments
of seed addition, haying, and fertilization in 4 replications.
Species occurrence data collected using .25 m2and 1 m2quadrats with 6
predetermined survey points within each subplot.
Data analyzed to produce species area curves for each subplot with
scales ranging from .25 m2–6 m2.
The species area curve, S = c AZgives the ability of assessing scale
dependence by a comparison of Z-values for set of treatments.
(S= Species Richness, c= Scalar Constant, A= Area, Z= Rate of
Accumulation.)
Results
(Figure 1) Split plot design of
4 blocks each containing one
replication of each set of
treatments.
(Figure 2) ANOVAs conducted
separately for each spatial scale show
that the main effects of fertilization,
haying and their interaction vary
strongly in magnitude with scale.
*= Not statistically significant (P>.05)
*
(Figure 5) A comparison of
rates of accumulation between
treatments indicates spatial
dependence through differing Z –
values. (ANOVA P-Value <.03)
(Figure 4) Mean species area curves
showing the interactive effects of
fertilization and haying across all scales.
Power functions were fitted to each data set
with the equation posted next to each trend
line.
Soil nutrient enrichment and disturbance interacted strongly to effect
species richness at all spatial scales.
Nutrient enrichment generally reduced species richness but to a lesser
extent in the presence of disturbance. Disturbance increased species
richness but only in the presence of nutrient enrichment.
The interactive effects of nutrient enrichment and disturbance on
species richness increased in magnitude with spatial scale, indicating
strong scale dependence of these effects.
These findings suggest that to fully understand environmental drivers
of species richness, spatial scale must be considered in studies of
biodiversity. As the fields of restoration and conservation continue to
grow it is important for future studies to include a spatial component to
ensure a proper management plan can be implemented.
References
Scheiner, Samuel M., et al. "Species richness, species-area curves and Simpson's paradox.”Evolutionary Ecology Research 2.6
(2000): 791-802.
Huston, M. A. (1994)Biological Diversity. Cambridge University Press, Cambridge.
Weiher, E., The combined effects of scale and productivity on species richness. Journal of Ecology, (1999)87:1005–1011.
Acknowledgements
National Science Foundation Grants NSF DBI-1262795 & 0950100
Mari Pesek, Sheena Parsons, Alex Bittel & The Foster Lab
Kansas University, Kansas University Field Station, Kansas Biological Survey
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y = 12.934x0.4031
y = 10.299x0.51
y = 4.111x0.3078
y = 9.0391x0.3977
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01234567
Average Species Richness
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Species Area Plot with Fitted Power Functions
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