Forests in East Texas, across the United States, and in the rest of the World are suffering losses as human actions shrink and put them in peril. One of the key actions that has caused many of these problems is human “forest fragmentation”, also known as “habitat fragmentation” and “habitat subdivision”. Human “forest fragmentation” involves all the human actions that break a forest into two or more “patches” (smaller areas of forest). “Habitats” consist of environments or ecosystems suitable for a species. An “environment” or “ecosystem” is an area with interactions between living organisms and non-living elements.
Connected with forest fragmentation is “habitat degradation, habitat loss, and habitat isolation”. All of these events result in environmental effects like altered behavior, biology, breeding patterns, social systems, dispersal (immigration and extinction rates), use of space, species interactions, loss of native vegetation cover, reduction in species diversity, landscape modification, ecosystem process modification, increased disturbance, more “edge effects” (increased light, wind, temperature, etc. at the edge of a forest), deterioration of physical environments, species loss, and other cascading landscape change effects (chain of events).
Forestry actions, which include logging, roading, skidding, log landings, loading, burning, site preparation, planting, and other forest management activities, result in increased forest fragmentation.
On an Earth-wide basis, an analysis of global forest cover documented that 70% of remaining forests are within 1 kilometer (0.62 mile) of their edge which means they are subject to degradation due to fragmentation. A variety of habitat fragmentation studies, when considered together, have documented reductions of biological diversity by 13 to 75%. Habitat fragmentation studies have also documented alteration of ecosystem functions by the reduction of biomass and the change of nutrient cycles. Effects were greatest in the smallest and most isolated patches and increased with the passage of time.
In Texas, in southern, and in the eastern United States, forest fragmentation has had several impacts. One impact that is directly related to human health is found in the eastern United States, where the risk that someone will contract Lyme disease is higher in fragmented forests with high rodent densities and low numbers of predators.
Forest size and level of fragmentation affects breeding birds. Increased urbanization leads to fragmentation and isolation of forests. In small, isolated, forest patches numbers of forest breeding migratory birds decline. Smaller forest patches result in increased nest predation or nest parasitism. In East Texas, researchers looked at how Chinese Tallow, an invasive tree species, spread in forests. The study stated that “Increasing anthropogenic impacts, via urban sprawl and road construction, and more frequent natural disturbances could further fragment forested areas and provide additional means of seed transport.”
Ways to Reduce Forest Fragmentation
To combat forest fragmentation, increased connectivity, buffers zones, and landscape “heterogeneity” (diversity) is needed. These ecological actions result in the maintenance and restoration of large and structurally complex patches of native vegetation; vegetation matrices of structurally similar native vegetation; buffers around sensitive areas; corridors and stepping stones; “environmental gradients” (changes in altitude, soil, moisture, etc.); species interactions and functional diversity; species of particular concern; appropriate disturbance (tree killing) regimes; the minimization of ecosystem specific threatening processes; and control of aggressive, overabundant, and invasive species.
It is important to understand the forests are more than a collection of trees. Different topographies (heights of the landscape); landforms (the folding and undulation of the land); soils (some moister, more porous, or permeable than others); habitats like wetlands, ponds, lakes, streams and rivers, thickets, snags (dead standing trees), root-wads, downed trees (fine and coarse woody debris); tree cavities and dens, groups and individuals of different tree species, etc., all play a role for a forest that is diverse (heterogeneous) and has many different plants and animals. This “shifting mosaic” of different habitats and stages they go through to become those habitats (vegetation succession) gives a landscape a very diverse aspect in the “matrix” (dominant forest on the landscape) they exist in.
Three strategies that combat fragmentation include core reserves, connectivity of areas, and buffers. “Core reserves” are the best and usually largest forested landscapes (matrix) where wildlife, vegetation, and other organisms and ecosystem processes, like fire, other disturbances, and erosion/accretion, can function in a natural way and shape how landscapes look and work. “Connectivity” refers to how “core reserves” and other areas are connected via corridors that allow for the migration (flow) of plants and animals over distances on the landscape.
“Buffers” provide protection from forest fragmentation by a reduction in the impacts of “forest edges”, which alter the temperature, amount of light, wind speeds, drying, and predator and parasite intrusions. This means the “interior” of forests are more shaded, have lower temperatures, moister, less subject to windthrow (blowdown), and more protected from predators. Buffers may be subject to economic uses (compatible) that are sustainable over the long-term.
The three strategies, core reserves, connectivity, and buffers, provide for a diverse landscape ecology and many different “niches” (occupations) for common, rare, and endangered plants and animals.
References
1) “Habitat Fragmentation and Landscape Change, An ecological and Conservation Synthesis”, David B. Lindenmayer and Joern Fischer, Island Press, 2006.
2) “Habitat fragmentation and its lasting impact on Earth’s ecosystems”, Nick M. Haddad, Lars A. Brudvig, Jean Clobert, Kendi F. Davies, Andrew Gonzalez, Robert D. Holt, Thomas E. Lovejoy, and others, Science Advances, Volume 1, Number 2, March 20, 2015.
3) “Forest ecology shapes Lyme disease risk in the eastern US”, Cary Institute of Ecosystem Studies, Science Daily, July 9, 2018.
4) “Effects or Urbanization on Forest Wildlife”, Southern Forest Resource Assessment, Final Report Technical, December 8, 2013.
5) “Factors associated with the spread of Chinese Tallow in East Texas forestlands,” Zhaofei Fan, Yuan Tan, and Michael K. Crosby, Open Journal of Ecology, Volume 2, Number 3, pp. 121-130, 2012.
6) “Conservation in Highly Fragmented Landscapes”, edited by Mark W. Schwartz, Chapman and Hall, 1997
7) “In Defense of Wildlife: Preserving Communities and Corridors”, Defenders of Wildlife, 1989.
8) “Corridor Ecology: The Science and Practice of Linking Landscapes for Biodiversity Conservation”, Jodi A. Hilty, Williams Z. Lidicker Jr., and Adina M. Merenlinder, Island Press, 2006.
9) “Continental Conservation, Scientific foundations of Regional Reserve Networks”, edited by Michael E. Soule and Joh Terborgh, The Wildlands Project, Island Press, 1999.
10) “Wildlife Reserves and Corridors in the Urban Environment, A Guide to Ecological Landscape Planning and Resource Conservation”, Lowell W. Adams and Louise E. Dove, National Institute for Urban Wildlife, U.S. Fish and Wildlife Service, U.S. Department of the Interior, 1989.
11) “Conservation Buffers, Design Guidelines for Buffers, Corridors, and Greenways”, Gary Bentrup, U.S. Forest Service, Southern Research Station, U.S. Department of Agriculture, General Technical Report SRS-109, September 2008.
12) “Practical Ecology for Planners, Developers, and Citizens”, Dan L. Perlman and Jeffrey C. Milder, Lincoln Institute of Land Policy, Island Press, 2004.
Brandt Mannchen
November 25, 2018