by Pam Owen, Spring 2005

Loss and fragmentation of habitat due to urban sprawl, rather than population increases, are the most significant factors in the decline of our native species, according to the Natural Resources Defense Council (www.nrdc.org). Such fragmentation most often results from timber harvesting, development, and roads. Because Virginia was primarily forest before humans arrived, most of our animal species are woodland inhabitants and loss of forest means decline and even extinction to those species.

According to the Virginia Department of Forestry (www.dof.virginia.gov), in 1999 Virginia had about 16 million acres of forest, which made up 61 percent of its total land cover. This percentage had increased from 56 percent in 1940 to 63 percent in 1976 and has been declining ever since. The Journal of Forestry reports that in Virginia the number of forested tracts less than 100 acres has been steadily increasing, and about 8 percent of total private forest area in the country now in parcels smaller than 20 acres. Numerous studies show that landowners of small tracts, particularly 25 acres or less, are less likely to manage them for income, aesthetic, or wildlife goals. In Virginia, 77 percent of our forested land is owned by private, non-industrial landowners, and private forests are the most likely to suffer from fragmentation.

Soaring real-estate prices encourage the fragmentation of land parcels. Another factor in fragmentation is our aging population. According the Journal of Forestry, the estimated 93 million acres of forest owned by people older than 65 is undergoing some form of intergenerational transfer, in which property is subdivided among heirs, or subdivided and sold to meet the competing interests of heirs or because there are no heirs.

Albert Todd, in the February 1999 issue of Journal of Forestry, summed up the impact of forest fragmentation: "Forest fragmentation affects water quality and quantity, fish and wildlife populations, and the biological health and diversity of the forest itself. When many small habitat losses occur over time, the combined effect may be as dramatic as one large loss. Forest fragmentation can disrupt animal travel corridors, increase flooding, promote the invasion of exotic vegetation, expose forest interiors, and create conflicts between people and wildlife. Habitat loss reduces the number of many wildlife species and totally eliminates others."

By limiting gene pools with physical barriers such as roads and landscape that is not familiar habitat to species, populations become isolated and inbred, or individuals have become isolated from potential mating partners and therefore do not breed. Studies have shown that roads have affected the genetic makeup of populations of many species, from grizzlies to the common frog.

Species that prefer the forest interior and are either wide-ranging or that can't easily disperse are more likely hurt by habitat fragmentation. The former include migratory songbirds, such as orioles, tanagers, purple martins, and wood thrushes; black bears; and cougars. The latter include reptiles and amphibians.

Some species need large habitats, others need varied habitats as their resource needs vary over time and space, and some need both. Some turtles can't get from their normal aquatic habitat to upland nesting habitat, and amphibians can't get from terrestrial habitat to aquatic breeding sites. One study (www.sciencelives.com/rabbit.html) indicates that New England cottontails on small patches are not as healthy as those on large patches because they depleted their food supply sooner and were forced to eat lower-quality food, or to search for food in areas where there was more risk of being killed by a predator.

Wildlife, like humans, tend to be creatures of habit, using the same breeding, nesting, and feeding areas year after year. If their routines are altered by habitat fragmentation, their health and reproduction can suffer. Small forest areas where migratory birds nest but may not successfully reproduce are called "sinks." As crucial stopover areas for migratory songbirds are rapidly being fragmented, more species end up in these sinks, where they may not be raising enough young to replenish their population, as reported by the West Virginia University Extension Service at www.wvu.edu/~agexten/wildlife/neotrop.htm.

A survey sponsored by the U.S. Fish and Wildlife Service shows drops ranging from 11 percent to 88 percent among more than two dozen species of songbirds over the past decade. Studies indicate that bird nests that are within 70 feet of forest edges or clearings suffer the highest predation from cats, raccoons, snakes, and blue jays. In general, prey species are more easily preyed upon when their habitat is fragmented and they are limited to small islands of suitable habitat that makes escape into thick, protective cover difficult. According to the Virginia Department of Forestry, "the absence or deterioration of suitable habitat, not predators, is the primary reason that game populations are below desired levels. Only when habitat conditions are marginal and escape cover is lacking, can predation be excessive."

Turtles are long lived and slow to breed. They can end up road kill before they have a chance to replenish themselves.

Female wood turtles range over 2 miles and reach reproductive age at 15 years. In her life, she might travel two miles from her riparian habitat. Because most female turtles need a half century to produce a handful of offspring that survive to reproductive age, there's a good chance they'll be road kill before they get to that age.

Studies show that many animals—from salamanders to adult female grizzlies—are reluctant to cross roads and therefore cannot reach critical habitat, food, or breeding partners. If animals do venture across roads, it can lead to bad results for both them and the human population. Animal-vehicle collisions can be deadly, so the installation of wildlife crossing structures on roadways is gaining popularity among transportation agencies. VDOT is evaluating seven underpass structures throughout Virginia to see if they are being used by large mammals, such as deer and black bear, which are most likely to cause collisions.

What is a barrier to some species is an opportunity to others. This can cause an imbalance between predator and prey, or between competing species. Animal species that are more opportunistic, prefer forest edge to interior, and very mobile, or have very small-scale habitats—including deer, squirrels, Canada geese, and rabbits—do well with a mixture of open, brushy, and wooded areas. One of the most significant reasons why deer populations have recently exploded is the replacement of forest, which provides limited food for deer, to lawns, golf courses, and other nutrient-rich grass and shrub areas.

What can we do to stop fragmentation of wildlife habitat? Sources suggest several strategies for protecting habitat, particularly forest, from further fragmentation: