Plant-species richness in corridor intersections: is intersection shape influential?

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 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, presence 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 as in situ sources of seed for managers attempting to restore plant communities in the matrix.

Influência de fragmentos de cerrado na distribuição de ácaros em seringal

“…Uma rede de áreas nativas como cercas vivas, faixas preservadas de mata nativa, refúgios constituídos de vegetação específi ca que atraia presas alternativas e áreas de mata ciliar, podem ampliar o movimento dos inimigos naturais entre os elementos da paisagem, melhorando a acessibilidade a esses elementos e provendo muitos recursos para a entrada de espécies benéfi cas nos agroecossistemas (Riffel & Gutzwiller 1996). Segundo Baxter (1979) apud Altieri et al (2003) os maiores níveis de controle biológico ocorrem nas bordas das culturas vizinhas à vegetação nativa.…”

Habitat features and genetic integrity of wild grapevine Vitis vinifera L. subsp. sylvestris (C.C. Gmel.) Hegi populations: A case study from Sicily

“…As a result, many plants are dispersed by birds (especially Turdidae) migrating along the riparian zones (van Dorp and Kalkhoven, 1988). Besides, plant movements or exchanges may increase at nodes where riparian and other corridors, such as roads, railways and hedgerows, intersect (Riffel and Gutzwiller, 1996). Overall, in the present study-case it is suggested that the combination of river dynamics and zoochory favours gene flow of wild grapevine germplasm among all the riparian populations, whereas the screetype population FAV is maintained ecologically isolated.…”

Modelling the effect of intersections in linear habitat on spatial distribution and local population density

“…For example, a high level of connectivity between adjoining hedgerows typically maintains a high density of small mammals (Fitzgibbon 1997, Gelling et al 2007, and increasing hedgerow width and length is related to increasing abundance of birds (Green et al 1994, Hinsley and Bellamy 2000, Némethová and Tirinda 2005, Lindenmayer et al 2007) and small mammals (Gelling et al 2007, Michel et al 2007). Many plant, bird and mammal species are found to be concentrated in the intersections of linear elements (Forman and Godron 1986, Lack 1988, Riffell and Gutzwiller 1996, Lindenmayer et al 2007, which is attributed to higher habitat quality in these intersections compared with linear elements (Forman andGodron 1986, Lack 1988) or their width and higher structural diversity (Gutzwiller and Anderson 1987). However, spatial structure is also thought to play a role in determining these concentrations, that is, high local density of individuals (Lindenmayer et al 2007).…”