TY - JOUR
T1 - Plant species richness in ephemeral and perennial reaches of a dryland river
AU - Stromberg, Juliet
AU - Hazelton, A. F.
AU - White, M. S.
N1 - Funding Information:
Acknowledgments Support for this project was provided by the US Army Corps of Engineers Ecosystem Management and Restoration Research Program, the NSF’s Center for Sustainability of Semi-Arid Hydrology and Riparian Areas, and the US EPA Science to Achieve Results Program. We thank the Pima County Parks and Recreation Department for allowing site access; Bethany Lund, Elizabeth Makings, Theresa Price and Donna Shorrock for assisting with plant species identiWcation; and Mead Mier and Becky Eden for map preparation.
PY - 2009/3
Y1 - 2009/3
N2 - Ephemeral reaches are common along desert rivers but are less well studied than those with perennial stream flow. This study contrasted riparian plant species richness and composition (extant vegetation and soil seed bank) between stream reaches with different low-flow conditions (perennial vs. ephemeral flow) but similar flood patterns and similar watershed-derived species pools. Data were collected at Cienega Creek (Arizona, USA) over a 2 year period spanning drought conditions and wetter conditions. Consistent with expectations relating to water limitation effects on diversity, species richness in the riparian zone was lower at ephemeral-flow sites during a season with minimal precipitation and no overbank flooding; under these conditions, the more permanent water sources of the perennial-flow sites sustain the larger number of species. During seasons with greater precipitation and elevated stream flows, in contrast, species richness at ephemeral-flow sites increased to levels at or slightly above those of perennial-flow sites. For values pooled across two wet seasons of a calendar year, year-round richness was greater at the two ephemeral-flow sites (total of 92 vascular plant species) than at the two perennial-flow sites (68 species). This greater year-round richness was a combination of multiple factors: greater light, space, and bare ground, a diverse soil seed bank (with the seed banks equally species-rich among hydrologic types), and moderately abundant precipitation and flooding sufficient to stimulate establishment of opportunistic species (mainly annuals) during the bimodal wet seasons. These results indicate that long-term patterns of site water availability, by influencing woody plant cover, mediate the diversity response to episodic water pulses in dryland rivers. The results also have implications for riparian conservation efforts, which to date have focused primarily on perennial stream reaches: ephemeral reaches of spatially intermittent rivers harbor many riparian plant species, and warrant conservation efforts, as well.
AB - Ephemeral reaches are common along desert rivers but are less well studied than those with perennial stream flow. This study contrasted riparian plant species richness and composition (extant vegetation and soil seed bank) between stream reaches with different low-flow conditions (perennial vs. ephemeral flow) but similar flood patterns and similar watershed-derived species pools. Data were collected at Cienega Creek (Arizona, USA) over a 2 year period spanning drought conditions and wetter conditions. Consistent with expectations relating to water limitation effects on diversity, species richness in the riparian zone was lower at ephemeral-flow sites during a season with minimal precipitation and no overbank flooding; under these conditions, the more permanent water sources of the perennial-flow sites sustain the larger number of species. During seasons with greater precipitation and elevated stream flows, in contrast, species richness at ephemeral-flow sites increased to levels at or slightly above those of perennial-flow sites. For values pooled across two wet seasons of a calendar year, year-round richness was greater at the two ephemeral-flow sites (total of 92 vascular plant species) than at the two perennial-flow sites (68 species). This greater year-round richness was a combination of multiple factors: greater light, space, and bare ground, a diverse soil seed bank (with the seed banks equally species-rich among hydrologic types), and moderately abundant precipitation and flooding sufficient to stimulate establishment of opportunistic species (mainly annuals) during the bimodal wet seasons. These results indicate that long-term patterns of site water availability, by influencing woody plant cover, mediate the diversity response to episodic water pulses in dryland rivers. The results also have implications for riparian conservation efforts, which to date have focused primarily on perennial stream reaches: ephemeral reaches of spatially intermittent rivers harbor many riparian plant species, and warrant conservation efforts, as well.
KW - Dryland river
KW - Ephemeral stream
KW - Plant community
KW - Riparian ecosystem
KW - Soil seed bank
KW - Xeroriparian
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U2 - 10.1007/s10531-008-9532-z
DO - 10.1007/s10531-008-9532-z
M3 - Article
AN - SCOPUS:60449115820
SN - 0960-3115
VL - 18
SP - 663
EP - 677
JO - Biodiversity and Conservation
JF - Biodiversity and Conservation
IS - 3
ER -