Dispersal ecology of desert mosses along gradients of elevation, wildfire disturbance and local niche

Much of the variation in plant communities can be explained by the dispersal of individuals across landscapes, an ecological process that contributes to clinal variation, post-disturbance recovery and habitat occupancy. The role of dispersal is of particular concern for Mojave Desert plant communities that may not be able to tolerate recent departures from historical fire regimes. The aim of this thesis was to infer how dispersal is reflected by patterns of diversity in disturbed and undisturbed bryophyte communities in the Spring Mountains of southern Nevada. Chapter 2 presents an examination of sub-surface bryophyte communities (propagule "soil-banks") along a 1400 m elevational gradient spanning three major vegetation zones. Compositional changes and three measures of diversity were positively associated with elevation and climatic moisture, a pattern consistent with increasing spore deposition in proximity to fecund, high-elevation source populations. Chapter 3 is an assessment of the roles of dispersal in time and in space as bryophyte communities recover from wildfires at Red Rock Canyon. Sub-surface soil-banks harbored greater diversity than either the spore rain or existing surface communities, although the reduced diversity associated with recent and severe wildfires implied that recovery could be negatively impacted if changing fire regimes inhibit soil-bank replenishment. Finally, Chapter 4 considers habitat limitation versus dispersal limitation as possible constraints on local-scale bryophyte diversity in a single undisturbed community at Red Rock Canyon. Variation in species composition was a nearly equal balance of purely spatial influences (dispersal) and of spatially structured habitats afforded by the arrangement of perennial shrubs. Collectively, this thesis demonstrates that the movement of individuals across landscapes promotes variation in non-vascular plant communities along ecological gradients in the Mojave Desert. Appreciation of the mechanisms that structure diversity can be a starting point for conscientious land use policies and practices, including those that impact both individual disturbances and entire disturbance regimes.