Vegetation Dynamics in an Experimentally Fragmented Landscape

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. In spatially heterogeneous habitats, plant community change may reflect spatially localized population-level processes that are sensitive to the size of an average habitat patch. However, local species turnover can also be determined by initial conditions and large-scale processes, in which case patch size effects may be overridden. To examine the role of patch size in directing secondary succession, we subdivided a newly abandoned agricultural field into an array of experimental patches (32, 288, and 5000 m2, grouped to sample equivalent portions of the field), and have thereafter censused the resident plant and animal communities at regular intervals. Here we report results from the first 6 yr of studies on the changing vascular plant community in an experimentally fragmented landscape. The general course of change in all patches followed a trajectory typical of old-field succession, toward increasing dominance by longer lived and larger plant species. The same group of species that dominated at the start of the study continued to dominate after 6 yr, although in very different proportional abundances. Larger patches were more species rich than their smaller counterparts, and had a higher proportion of nonshared species, but the additional species were transient and low in abundance. Spatial heterogeneity in vegetation, measured as local community dissimilarity, increased in all patches but to a lesser extent in the largest patches, where censuses of nearby permanent quadrats indicated less divergence over time. At a population level, the strongest effect of patch size was that local populations of clonal species were more prone to disappear from the smallest patches. Nevertheless, summary measures of temporal community change did not reflect significant differences in localized species turnover. We conclude that patch size does not markedly affect the rate or pattern of early secondary succession, at the scales imposed in our experiment.

A large-scale forest fragmentation experiment: the Stability of Altered Forest Ecosystems Project

“…This differs from the square plots used at previous forest fragmentation experiments, and ensures that the negative impacts of edge effects will be kept to a minimum in this experiment. Fragments within plots are located to ensure that there is (i) equal sampling effort across plot size classes and (ii) an equal spatial distribution of sampling effort in the four plots (figure 1), analogous to the design of the Kansas Fragmentation Study [34]. Plots with fragments will be separated by 178 m (10 2.25 m).…”

The Interaction of Habitat Fragmentation, Plant, and Small Mammal Succession in an Old Field

“…These effects include changes in abiotic regimes (Saunders et al 1991), shifts in habitat use (Kareiva 1987, Lavorel et al 1994, altered population dynamics (Pulliam 1988, Pulliam and Danielson 1992, Diffendorfer et al 1995b, and shifts in community composition (Usher 1987, Diffendorfer et al 1996, Turner 1996. However, the impact of fragmentation on long-term ecological processes, such as succession, is still largely unknown (Holt et al 1995). Secondary succession has been thoroughly studied, especially within old fields (e.g., Gleason 1928, Egler 1954, Connell and Slatyer 1977, Tilman 1987, Bazzaz 1990).…”

“…Secondary succession has been thoroughly studied, especially within old fields (e.g., Gleason 1928, Egler 1954, Connell and Slatyer 1977, Tilman 1987, Bazzaz 1990). Yet, in over a thousand studies reviewed by M. Rejmánek ( personal communication) very few experiments looked explicitly at the effect of patch size or other landscape metrics on succession (see also Phillips and Shure 1990, Glenn-Lewin et al 1992, Holt et al 1995. Studies of long-term temporal dynamics have emphasized local mechanisms such as competition, herbivory, and variation in life history strategies as the factors driving successional shifts in community composition (e.g., Glenn-Lewin 1980, Tilman 1988, Bazzaz 1990, Davidson 1993, Halpern et al 1997.…”

“…For a description of the site see Figure 1, Foster and Gaines (1991), Robinson et al (1992), Holt et al (1995), and Diffendorfer et al (1995aDiffendorfer et al ( , b, 1996. Prior studies in our system have documented in detail fragmentation effects on small mammal species composition and demography Gaines 1991, Diffendorfer et al 1995b), dispersal (Diffendorfer et al 1995a), and plant colonization and succession (Holt et al 1995, Yao et al 1999.The most abundant small mammal species on our site include prairie voles (Microtus ochrogaster), deer and white-footed mice (Peromyscus maniculatus, P. leucopus), and cotton rats (Sigmodon hispidus). The design of the system, including the three patch sizes and the distances between patches, was based on the biology of the small mammal and dominant plant species in the system.…”

Metapopulation Extinction Thresholds in Rain Forest Remnants

“…However, the causal mechanisms underlying plant species loss from habitat isolates remain poorly understood (Bruna 2003). Increased extinction risk in isolates can result from interactions between local and regional population dynamics (Holt et al 1995;Lande 1999;Davies et al 2001). At the regional scale, increased insularity associated with fragmentation potentially reduces interisolate migration rates relative to patch extinction, resulting in a nonequilibrium metapopulation dynamic (Harrison 1991;Hanski et al 1996).…”