PS 13-124 - Overstory tree falls generate spatial variation important for maintaining diversity in hyperdiverse communities of annual plants

Background/Question/Methods

Understanding how spatial variation and diversity maintenance are linked is a pillar of plant community ecology. Theoretically, if different species trade off in performing better or worse across heterogenous patches then more species might sustainably coexist than in a homogenous environment. Evidence documenting such trade-offs is growing, but studies typically investigate species’ performance in response to standing variation in the abiotic environment. In this study we ask if annual plant community composition and demographic rates differentially respond to experimentally induced spatial variation and determine which aspects of the environment explain such differences. We induced spatial variation by moving, removing, and/or substituting PVC “logs” for fallen logs in the understory of York gum-jam woodlands of Western Australia. This experiment allowed us to measure community turnover and the demographic rates of three common species sown into each log patch type, as well as pinpoint the variables explaining such responses.

Results/Conclusions

Community turnover between patch types was high but did not significantly differ before and after our experimental manipulation, indicating that community compositional responses to fallen logs exhibit a dispersal limitation induced lag. Sown species did not vary in their end-of-season presence/absence in different patch types, but end-of-season abundance varied among species and patch types. This result indicates that species trade off in their performance across heterogenous patches in the landscape; it also suggests the potential for coexistence via differential germination rates and fitness-density covariance. Our results highlight that rather than being a static background against which annual plant diversity dynamics play out, overstory trees and their population dynamics generate variation in the environment that may have considerable bearing on the spatial coexistence of understory annual plants.