Seasonal effects of environmental heterogeneity on plant community composition and richness

Background/Question/Methods

Spatial and temporal environmental heterogeneity impacts coexistence and diversity in natural systems.  Many studies have examined how plant species respond to individual abiotic factors, but few have explored how multiple, dynamic abiotic gradients affect patterns of plant species richness.  We used vegetative survey data from a natural resource agency in Northeast Ohio to answer two basic questions: 1) how does the environmental heterogeneity of multiple abiotic gradients relate to species richness?, and 2) how do these relationships change between seasons? Survey plots were randomly placed in properties owned by Cleveland Metroparks.  Each plot consisted of four discrete 10mx10m sampling units in which data were collected on tree and herbaceous species composition as well as a suite of abiotic factors including light, litter depth, depth to restrictive layer, and various soil characteristics such as pH, percent organic matter, and C:N ratio.  Spring data were compared to summer data in order to identify changes in community composition and species richness, as well as to assess which abiotic factors were sensitive to season.  Other response variables were explored as well, including proportion of generalist species to specialist species and proportion of native to invasive species.

Results/Conclusions:

Between seasons, plots were broadly classified as either depauperate in spring and summer, rich in spring and summer, or depauperate in one season and rich in the other.  Spatial patterns of abiotic factors exhibited a similar set of patterns defined as heterogeneous/homogeneous in both spring and summer, or differentially heterogeneous/homogenous in spring and summer.  The complexity of seasonal effects on multiple abiotic gradients and species richness/composition patterns provides strong motivation to further explore the dynamics of this relationship theoretically.