Plant-species richness in corridor intersections: is intersection shape influential? |
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Authors: | Samuel K Riffell Kevin J Gutzwiller |
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Institution: | (1) Department of Environmental Studies, Baylor University, 76798 Waco, TX, USA;(2) Department of Biology, Baylor University, 76798 Waco, TX, USA;(3) Present address: Department of Zoology, Michigan State University, 48824 East Lansing, MI, USA |
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Abstract: | Corridor intersections constitute nodes that can be more mesic than the intersecting corridors themselves. Such microclimatic
conditions may lead to an “intersection effect,” in which plant richness is higher in the intersection than in the corridors.
We hypothesized that an additional factor contributing to intersection effects is the movement of plants along corridors into
intersections by way of bird- and mammal-dispersed seeds. If this hypothesis is correct, one would expect intersection-shape
effects, defined herein as differences in intersection section richness associated with the number of possible avenues for
plant influx into the intersection. Specifically, richness in intersections should be lowest for L-shape intersections (two
avenues), higher for T-shape intersections (three avenues), and highest for X-shape intersections (four avenues). We used
data from fencerow networks to test this hypothesis about corridor intersections. During October 1992 and March 1993, we determined
woody- and herbaceous-plant richness for 25 intersections and their associated fencerows in central Texas, USA. We compared
two measures of intersection richness among the three intersection shapes: richness of plants dispersed primarily by birds
and mammals (vertebrate-dispersed plant richness), and richness of plants dispersed primarily by wind, ants or other means
(non-vertebrate dispersed plant richness). Vertebrate-dispersed plant richness differed significantly among intersection shapes,
but no differences in nonvertebrate dispersed plant richness were evident, which is what one would expect if the number of
avenues for vertebrate vectors into an intersection was an important factor influencing intersection richness. The intersection-shape
effects we found were not attributable to fencerow features (amount of woody cover, width, pressence of breaks) or intersection
characteristics (amount of woody cover, size, distance to nearest connected intersection or patch). Our results from fencerow
networks support the hypothesis that intersection effects on plant richness are influenced by intersection shape via the number
of intersecting corridors. Understanding patterns and processes that occur in networks is important for conservation biologists
because intersections in networks have the potential to function as refugia for plant species that require conditions more
mesic than those of the surrounding matrix. Networks also may be valuable asin situ sources of seed for managers attempting to restore plant communities in the matrix. |
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Keywords: | agricultural landscapes conservation biology corridors fencerows intersection shape networks nodes plant dispersal plant-species richness restoration ecology |
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