Location: Rangeland Resources & Systems ResearchTitle: Development of edge effects around experimental ecosystem hotspots is affected by edge density and matrix type
|YOUNG, TRUMAN - University Of California|
Submitted to: Landscape Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2016
Publication Date: 2/4/2016
Citation: Porensky, L.M., Young, T. 2016. Development of edge effects around experimental ecosystem hotspots is affected by edge density and matrix type. Landscape Ecology. 31:1663–1680. doi:10.1007/s10980-016-0344-3.
Interpretive Summary: In sub-Saharan Africa, pastoralists and ranchers use temporary corrals (“bomas”) to protect livestock at night. Bomas develop into ecosystem hotspots (“glades”) that have palatable forage and are used heavily by cattle and wild herbivores. Previous work indicated that when multiple glades were located close together (more glades per square mile), areas around glades had more trees, less palatable forage and less herbivore use. However, it was unclear whether these patterns were driven by glade density or by some other correlated factor (e.g., herders placing more bomas in areas with more trees). We set up an experiment to ask the question: are glade edge effects altered by the presence and proximity of additional nearby glades? We assigned eleven 400 x 400m sites to three treatments: one glade, two glades 200m apart, or two glades 100m apart. We sampled soil nutrients, foliar nutrients, plant communities, and large herbivore use inside and around these experimental glades. As expected, experimental glade hotspots had elevated soil and plant nutrient concentrations, altered plant species composition, reduced tree density, and elevated use by large herbivores. Moreover, glade density treatments had significant impacts on the development of glade sites. As in previous work, the presence of a second glade 200m away made glade sites less palatable and less attractive to large herbivores. However, to our surprise, the presence of a second glade 100m away made glades more palatable and more attractive. Despite their complexity, these results demonstrate that glade development is strongly impacted by the presence and proximity of other nearby glades. Depending on their objectives, managers may want to avoid or promote certain glade densities.
Technical Abstract: Ecological edge effects are sensitive to landscape context. In particular, edge effects can be altered by matrix type and by the presence of other nearby edges. We experimentally altered patch configurations in an African savanna to determine how edge density and matrix type influence edge effect development. In our study system, temporary cattle corrals (bomas) develop into productive nutrient hotspots (glades) that attract diverse wildlife and persist for decades. We randomly assigned eleven 400 x 400 m sites to three treatments: one boma, two bomas 200m apart, or two bomas 100m apart. Before boma establishment and =18 months after boma abandonment, we sampled soil nutrients, foliar nutrients, plant communities, and large herbivore use at each site. Bomas developed into glade hotspots with elevated soil and plant nutrient concentrations, altered plant species composition, reduced tree density, and elevated use by large herbivores. For most response variables, glade edge effects were not detectable at distances =50 m. Both boma density and matrix type altered the development of edge effects around experimental glades. The presence of a second glade 100m away was associated with unchanged or strengthened edge effects (e.g., more difference between glade and matrix), but the presence of a second glade 200m away was associated with weakened edge effects. In general, stronger edge effects developed between glades and open plains than between glades and bushland. Our results highlight the potential for edge effect variability in complex landscapes, and show that broad-scale experiments can help illuminate causes and consequences of that variability.