Houston ChandlerViews:
Longleaf pine ecosystems have been reduced to less than 5% of their original extent — creating many of the conservation challenges that exist today in the southeastern United States. Severe habitat loss also brings with it other associated conservation issues, which can further degrade remaining habitat and imperil wildlife populations. Habitat fragmentation or a loss of connectivity between habitat patches is a major issue in remaining portions of longleaf pine forests. Today, longleaf pine forests generally exist as relatively small habitat patches, mostly on public lands, that are surrounded by a matrix of altered environments (e.g., farmland, urban and residential areas, or other altered use environments), roads, and other barriers. Even suitable habitat patches that are close together are almost always separated by some sort of road, posing a significant barrier to movement for many species and potentially leading to population declines or even local extinctions in the adjoining areas with intact habitat (Beaudry et al. 2008). Connectivity can be thought of in multiple ways. At a broad scale, the ecological processes that form and maintain healthy ecosystems can link multiple environments together. On smaller scales, wildlife populations need to interact with members of their own species and other species to maintain the relationships that have evolved over time. Increasing fragmentation can impact natural processes on both of these scales.
A loss of connectivity at a landscape scale can impact entire ecosystems. In longleaf pine forests, increasing fragmentation combined with direct fire suppression during the 19th and 20th century began the process of removing fire as a regular disturbance across the southeast. These fires would have historically burned through vast swaths of longleaf pine forest, maintaining the biodiversity supported by this ecosystem. Natural fires that spread across a connected landscape from river to river will likely never return to the southeast, increasing longleaf pine forest’s dependency on active management. Similarly, the hydrologic processes that support rivers and wetlands across the southeast are often altered by anthropogenic disturbance. Floodplains lose connectivity to the main channel, and wetlands are ditched or drained, removing a link between terrestrial and aquatic ecosystems. Once altered, these large-scale connectivity issues are difficult and often labor intensive to repair.
Both individuals and populations of many species depend on movement through their environment at some point during their life history. Fragmented landscapes can have many negative effects on wildlife populations as individuals attempt to maintain important connections to other populations or habitats (Fischer and Lindenmayer 2007). Small disjunct habitat patches expose individuals to increased risk of mortality when making movements through degraded habitat. Decreased movement reduces genetic flow between populations and in severe cases can lead to inbreeding or a bottleneck effect. Predation and parasitism rates can increase in fragmented landscapes, and predator populations are often subsidized by human activity, further increasing their ability to negatively impact prey species (at a rate that far exceeds normal ecological interactions). For species that depend on different habitats at certain times of the year (i.e., amphibians that migrate to breeding wetlands), the loss of a single type of habitat or resource may doom a population to extinction (Means et al. 1996). In Georgia, wetlands are sometimes spared direct conversion to other land uses, but the negative effects of losing connections to upland forests are severe.
Given these and other issues that arise from a loss of landscape connectivity, the Longleaf Savannas Initiative works to improve connectivity by focusing management and restoration efforts in regions where large expanses land are protected. For example, the Altamaha River Corridor contains over 40,000 hectares of actively managed and protected lands both on private and public property. This region supports high biodiversity, in part because of its relatively intact and connected ecosystems (see our recent review of amphibian and reptile communities; Stevenson and Chandler 2017). The Altamaha Region is a focal area for our conservation efforts, and there is currently an effort to link this area with the ecosystems that are protected on and around Fort Stewart. This effort aims to create one of the largest expanses on longleaf pine forests and associated ecosystems remaining in the southeast.
Literature Cited
Beaudry, F., P. G. deMaynadier, and M. L. Hunter Jr. 2008. Identifying road mortality threat at multiple spatial scales for semi-aquatic turtles. Biological Conservation 141:2550–2563.
Fischer, J., and D. B. Lindenmayer. 2007. Landscape modification and habitat fragmentation: A synthesis. Global Ecology and Biogeography 16:265–280.
Means, D. B., J. G. Palis, and M. Baggett. 1996. Effects of slash pine silviculture on a Florida population of Flatwoods Salamander. Conservation Biology 10:426–437.
Stevenson, D. J., and H. C. Chandler. 2017. The herpetofauna of conservation lands along the Altamaha River, Georgia. Southeastern Naturalist 16:261–282.
