Studies have found little empirical evidence for universal emergent properties of ecotones, suggesting that the patterns widely attributed to them are context dependent. Ecotones are theorized to have higher species diversity, follow a sharp change in physiognomy, and contain higher numbers of exotics than their adjacent communities. Elucidating the contexts in which these theorized properties hold true is one of the major challenges in current ecotone theory. We hypothesize that ecotone properties will vary depending on the transition’s landscape position, age and disturbance regime. To test this hypothesis, we constructed vegetation transects across field/forest edges which varied in their age (1,2 or 3 years), disturbance regime (mowed or burned) and aspect. At each transect, we examined patterns of overall species richness, exotic species richness, physiognomy and species turnover. Species compositional data taken at 1-meter intervals along each transect were analyzed using a moving-window regression technique, modified to delineate the area of highest turnover. This area, the boundary zone, was then examined against data from the adjacent field and forest.
Results/Conclusions
We found that, in general, our ecotones had higher species richness than the adjacent matrix vegetation, which was due to both a mixing of species specific to either side of the transition as well as attributable to a unique set of ecotonal species. Disturbance regime did have a small effect on species turnover, with mowed ecotones showing a sharper transition, although the time since last disturbance did not have an influence. The physiognomic change was sharper in mowed, younger fields. Exotic species richness was not significantly different between disturbance regimes, and was not significantly higher in the boundary zone. No ecotone patterns varied with the aspect of the transect. The results of this study allow us to link patterns of diversity, exotic species richness and physiognomic turnover with ecotone properties.
