This dissertation is divided into four chapters, each of which covers a particular topic related to the subject of biodiversity. Chapter 1: Many theories have been proposed to explain patterns of biodiversity at global, regional and local scales. Biodiversity theories fall into two main classes; equilibrium or non-equilibrium. Both classes of theory are currently invoked to explain patterns of diversity. However, non-equilibrium theories more realistically describe natural communities because the assumptions of equilibrium theory are frequently violated under natural conditions. Chapter 2: Riparian corridors are highly dynamic, non-equilibrium systems which contain unusually high numbers of plant species relative to the surrounding uplands. Much of this high diversity is attributable to several types of non-equilibrium processes occurring at multiple spatial and temporal scales. In this chapter I develop a conceptual framework for understanding how different non-equilibrium processes interact to influence plant diversity in the context of the riparian environment. Chapter 3: Analyses of productivity and vascular plant species richness among 16 emergent and forested wetland sites in southeast Alaska showed significant, unimodal, non-linear relationships. Species evenness peaked in sites of intermediate productivity and decreased monotonically as productivity increased. There was no correlation between species richness and the spatial variation of productivity within sites. Chapter 4: Microtopographical variation, flooding frequency and productivity were all correlated with plant (vascular and moss) species richness among wetlands on a coastal island in southeast Alaska. Studies of 16 sites between 1992 and 1994 in or near the Kadashan River basin showed that plant species richness increased linearly with microtopographical variation (r{dollar}sp2{dollar} = 0.60, p {dollar}<{dollar} 0.01), while non-linear, unimodal relations existed between flooding frequency and species richness (r{dollar}sp2{dollar} = 0.74, p {dollar}<{dollar} 0.01), and productivity and species richness (r{dollar}sp2{dollar} = 0.26, p {dollar}<{dollar} 0.05). A non-linear regression relating species diversity to microtopographical variation and flooding frequency suggests that these two parameters can explain much of the variation in species richness between wetlands (r{dollar}sp2{dollar} = 0.84, p {dollar}<{dollar} 0.01). My data supports some of the predictions of Huston's (1979, 1944) dynamic equilibrium model of species diversity.
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