Scale-dependent interactive effects of long-term nutrient enrichment, haying disturbance, and seed pool manipulation on grassland diversity

Link To Share This Poster: https://cdmcd.co/dEyWBk
Live Discussion Link: https://cdmcd.co/bYGbAp

Bryan L. Foster and Naomi Betson, Department of Ecology and Evolutionary Biology and Kansas Biological Survey, University of Kansas, Lawrence, KS, Jeremy D. Forsythe, Department of Forestry and Environmental Conservation, Clemson University, Clemson, SC

Background/Question/Methods
It is widely appreciated that the factors controlling species coexistence and diversity in plant communities are sensitive to spatial scale. Exploring such scale-dependencies is critical to better understand biodiversity patterns and to predict responses of communities to multiple natural and anthropogenic environmental changes. We present results from a long-term 2 x 2 x 2 factorial field experiment, established in eastern Kansas USA in 2001, to investigate interactive effects of fertilization, annual haying, and supplemental seeding on plant community structure and restoration of tallgrass prairie on abandoned agricultural land. In previous analyses focused on early years of the study, we investigated plant community responses measured at a single spatial scale. To investigate potential scale-dependencies of treatment effects, we expanded sampling in the fourteenth year of the study to span multiple scales (1 - 8 square meters) within each of 32 10 x 10 m plots. To these data we employed a three-way mixed model evaluating responses of the rate of species accumulation (z) and per unit area constant (c) from the species-area relationship (S = cA^z) to experimental treatments of fertilization, haying, and seed supplementation. Scale-dependent effects manifest in the varied slopes of species accumulation curves (z-values) among treatments.

Results/Conclusions
We found a general negative effect of fertilization on species richness that was much greater in magnitude in non-hayed than hayed plots, and a positive effect of haying on richness that manifest only in fertilized plots (fertilization x haying interaction on c-parameter). Scale-dependence of this interaction manifest as a fertilization x haying interaction on the z-parameter and reflects an increase in magnitude of the positive effect of haying on richness with scale in fertilized plots only. We also found a scale-dependent interaction between fertilization and seed supplementation as indicated by the fertilization x seed supplementation interaction on the z-parameter. In non-fertilized plots there was a positive effect of seed supplementation on richness that was invariant across scales, indicating a similar degree of seed limitation at all scales. However, in fertilized plots, seed limitation of richness was negligible at small scales but increased in magnitude with scale. Our findings indicate that the interplay of multiple factors modulating species richness can be scale-dependent and that studies with observations taken at a single scale should be interpreted with care. We recommend the explicit consideration of scale in experimental studies to better understand the impacts of multiple environmental perturbations on communities.