Floodplain plant diversity and conservation in regional and local contexts (Montana).

摘要

Alluvial floodplains are unique geomorphic features of lotic systems that are characterized by a shifting morphology in three spatial dimensions. This spatial and temporal heterogeneity is thought to explain why these aquatic-terrestrial ecotones are the most species-rich habitats on the terrestrial portions of earth. Many factors and processes influencing these high levels of species richness remain unstudied, however. Regional factors, such as regional species pools, and local factors, such as groundwater-surface water exchange have received little consideration as factors controlling local species richness on floodplains. Additionally, the conservation of these habitats and the biodiversity they support remains shortsighted without the consideration of regional and local factors that influence floodplain structure and function.; A large alluvial floodplain, the Nyack, on the Middle Fork Flathead River, Montana, was used as a study site to investigate the role of the regional species pool in determining local species composition. In this relatively pristine system, our data show that floodplain habitats host 63% of the 320 vascular plants identified within the regional pool, making these habitats the richest in plant species within this catchment. Of these species, 72% are found in at least one adjacent upland habitat indicating a strong local - regional connection; highlighting the importance of the regional species pool in determining local species composition on floodplains.; To investigate the local environmental controls on floodplain plant species richness, both the Nyack floodplain and a large floodplain system on the Talkeetna river, Alaska, were sampled to show that, without exception, species richness gradients are not explained by flooding frequency as commonly thought. On both systems, differences in species richness and productivity between differing floodplain positions were largely a product of groundwater-surface water interaction, where the highest species richness and growth rates of woody plants was found at sites where groundwater is upwelling.; While the conservation of regional plant biodiversity cannot be entirely achieved by merely protecting floodplain habitats, we conclude by proposing a methodology of reserving instream flows to maintain the structure of these habitats, as their physical and floristic diversity functions as critical habitat to faunal assemblages of unparalleled diversity. Flow variability inherent in native flow regimes is required to maintain a spatially and temporally heterogonous fluvially derived landscape.