Small-scale spatial heterogeneity, diversity and community structure in regenerating plant communities

This study centers around a series of experiments that manipulate heterogeneity in a range of regenerating plant communities, including experimental wetland and successional terrestrial communities. I examined plant community responses, particularly changes in diversity, to different patterns of soil nutrient- and microtopographic heterogeneity.; In one experiment, using experimental wetland communities, I tested whether interspecific differences existed in habitat preference for different microtopographic positions and whether diversity was associated with microtopographic heterogeneity. Small-scale variability in microtopography produced highly significant differences in plant community structure. Floristic diversity was consistently greater in heterogeneous communities. Most species growing within the heterogeneous environments showed habitat preferences for hummock or hollow microhabitats.; Soil nutrient heterogeneity is thought to be a major factor influencing the structure and dynamics of many terrestrial plant communities, including successional fields. In a descriptive study of heterogeneity in early successional fields I found that different scales and intensity of pattern exist for plant community structure and that multiple scales of heterogeneity may exist for some variables. In a separate experimental study I investigated how different patterns of small-scale soil nutrient heterogeneity and herbivory affected plant community structure in one and seven year old fields. The annual-dominated one year field showed greater response to soil nutrient heterogeneity and herbivore manipulations than the perennial-dominated seven year field. One component of diversity, evenness, increased with greater soil nutrient heterogeneity, but only in the younger field. While herbivores interacted with soil nutrient heterogeneity in the one year field by altering patch structure, this interaction was not apparent at the whole-plot scale for the community level parameters measured. I also conducted a study of tropical and temperate successional community responses to soil nutrient enrichment, heterogeneity and woody seed addition. Heterogeneity did not have any effect upon woody plant establishment or plant community structure in either community. Soil nutrient addition produced small, but significant reductions in species richness at both sites, but heterogeneity did not affect either component of diversity (richness or evenness). In both of the successional field experiments conducted, larger-scale site heterogeneity or patchiness was a major factor controlling plant community structure in all communities examined.