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The influence of local and regional parameters on species richness in riparian vegetation.
Arnold, Heather*,1, Aarssen, Lonnie*,1, 1 Queen's University, Kingston, ON, Canada
ABSTRACT- Streams provide a linear, continuous habitat along which community patterns and dynamics have long been examined. The discrete nature of riparian habitat creates a convenient study system in which the influence of elusive regional factors such as dispersal and effective regional species pool size can be estimated. If hydrochory, or diaspore transport by water, is the principal means of dispersal along streams then seeds are preferentially dispersed downstream. Models predict that the available species pool is constantly increasing downstream as seeds and species accumulate from upstream communities. We extend this model by predicting that the more community-types the stream traverses, the greater the number of species that can potentially accumulate at the downstream 'sink'. Our hypotheses were that: 1) both local and regional parameters can explain more of the variation in site richness than can local variables alone; 2) streams flowing through highly heterogeneous landscapes have the largest species pool available for recruitment, and consequently the highest species richness at the downstream study site. We established study sites on 100 streams that represented a range of upstream heterogeneities and lengths in SE New Brunswick . At each study site we inventoried 60m2 of streamside vegetation, and recorded data for local variables hypothesized to influence plant richness: canopy cover, channel width, bank slope, and ground cover (rock, moss, soil and litter). Regional factors hypothesized to influence richness (i.e. habitat heterogeneity, stream tortuosity and length) were extracted from GIS data. Richness ranged from 21 to 109 species per site. Despite the range in plant richness observed, and the number of local and regional variables considered, we were able to explain very little of the variation in riparian plant richness.
Key words: plant dispersal, community structure, riparian vegetation, species pool