Does the urban matrix influence seed dispersal patterns in vacant lot plant communities?

Background/Question/Methods

Urbanization represents a global trend that is often defined by dramatic human-induced environmental changes.  These changes directly influence a number of factors including the regional and local processes responsible for structuring local plant communities.  Although a number of studies have explored both local effects and regional dispersal patterns in cities, results are inconclusive regarding the principle seed dispersal mechanisms in these environments.  This may be due to a number of factors, including the exposure and spatial configuration of local habits, which may differentially influence the dispersal of seeds into patches within the urban matrix.  We used a database of seed traits for sampled plant communities from 62 adjacent vacant lots in Baltimore, Maryland, USA.  These lots were classified into two groups based on their proximity to main streets and sidewalks.  The purpose was to explore whether seed dispersal traits shifted predictably between these sites and how this was represented functionally in the community.  A series of functional diversity metrics were used to identify the overall diversity of plant communities within each site, based on seed characteristics, and the functional dispersion (FDis) and functional divergence (FDiv) of specific seed dispersal traits represented in each community.

Results/Conclusions

We found clear shifts in seed dispersal strategies between these urban sites.  Overall, functional diversity was higher in sites located alongside sidewalks and roads, suggesting that these built features may act as corridors for a variety of dispersal mechanisms.  Conversely, more secluded sites, located away from main roads and sidewalks, had lower functional diversity, suggesting a narrower range of dispersal strategies are responsible for structuring these communities.  Additionally, we found significant differences in the representation of several specific dispersal strategies between these sites.  Despite the potential of the varying characteristics of the local environments to act as a filter for structuring plant communities, these results highlight the importance of dispersal strategies for determining local composition of urban plant communities.  Therefore, in order to make predictions about the way plant communities are structured, researchers must consider local variability of regional processes more closely.