Abstract: Understanding how plant communities assemble across gradients of environmental stress is a major goal in the field of community ecology. Understanding community assembly rules have important implications for conservation and restoration as human activities are placing additional stress on many plant communities.
Coastal dune plant communities are the perfect system to study how community assembly rules change due to their very short, but intense, environmental gradients. In addition, dune plant communities play key roles in the ecosystem services and functions of these ecosystems, and yet, coastal dunes are understudied. I surveyed plant species abundances and their functional traits along with their stressful microclimates in these dune ecosystems to better understand how community assembly rules change in these vulnerable plant communities along stark environmental gradients.
I used a unique 3-layer approach to sample the dune plant communities of California. The first layer is the plot level where I used nested quadrats (1x1m inside of a 2x2m) to test if focal communities are similar in both plant composition and functional traits to their immediate surroundings and if their relative similarities correlate with environmental stressors such as salinity, elevation, windspeed, soil nitrogen, and more. At level two, I compared plots within each dune site to parse out the relative effect of spatial autocorrelation on the similarity of plots. Finally, at the largest scale, I replicated the study at three sites and compared the effects of environmental stress on community similarities across a macroenvironmental gradient spanning southern and northern California dune communities.
Preliminarily, my results indicate that there are changes in how similar plant communities are to their surroundings along stress gradients, but these trends are not necessarily consistent between sites. In coastal dune ecosystems, distance from the ocean correlates with decreasing environmental stress. At the within plot level, the northernmost (F1,37=0.138, p =0.712, R2=0.004) and southernmost (F1,38=0.873, p =0.356, R2=0.022) sites saw no significant change of focal community dissimilarity to its surroundings. However, the middlemost site did see plant community dissimilarity increase with distance from the ocean (F1,41=4.680, p =0.036, R2=0.102).
Much more analysis is needed, but my study should allow me to demonstrate how communities assemble differently along gradients of environmental stress. I will also demonstrate this relationship at three different scales which would be a unique contribution to the community assembly literature.
