Agriculture in the U.S. has provided immense benefits to humans on both regional and global scales. In Indiana we can point with pride to the efficiency, ingenuity, and work ethic of farmers that regularly produce record yields of corn and soybeans. As with any successful enterprise, though, agriculture is associated with costs as well as benefits. Recognition of these costs is the first step toward reducing them. For instance, most of us are by now familiar with the economic and environmental costs of soil erosion caused by conventional tillage practices. And this awareness has played a large role in the switch to systems of conservation tillage over the last decade. But we are less familiar with the direct and indirect impacts that agriculture has had on native wildlife.

Changes in Habitat

Historically, the shift to agricultural landscapes in the midwest was accomplished by clearing of forests and draining of wetlands. More recently, conversion of native habitat has been due primarily to development. In Indiana, we have lost 78% of our original forest and 86% of our wetlands, many of which are forested. These losses are significant because the Central Hardwood Region is home to approximately 260 species of terrestrial vertebrates, and untold numbers of species use wetlands during at least part of each year. Although many wildlife species thrive in farmland, common sense suggests that such large reductions in amount of native habitat could also reduce the numbers of wildlife for some species. In intensively farmed areas such as northern and central Indiana, many native woodlands and wetlands occur as fragments of habitat surrounded by fields. A recent report of the Indiana Forest Roundtable ranked fragmentation and destruction of forestlands as the most important forest issue Facing Indiana today.

In fragmented landscapes, successful wildlife are those that have small area requirements, or these that are comfortable traveling across farmland to get to other habitat fragments. But which species fit this description, and which species are sensitive to the isolation or size of a fragment? Wildlife biologists at Purdue and elsewhere in the midwest have used trapping, radio telemetry, and calling and scent station surveys to attempt to answer this question. Below, we focus on selected species of mammals and amphibians.

Mammals in Farmland

Numerous mammals have adapted quite well to farmland. White-tailed deer are perhaps the best known example. Deer thrive in a mosaic of early successional habitats, and they make ready use of cropland, sometimes causing considerable economic damage. Although many woodlots are too small to harbor deer on a permanent basis, deer commonly move into them seasonally. Fox squirrels also do well in intensively farmed areas. Having evolved in the savanna-type habitat where deciduous forest and prairie meet, fox squirrels are comfortable traversing cropland if there is woody cover such as a brushy fencerow nearby. Among the furbearers, raccoons are the quintessential habitat generalist. They commonly forage in fields and along fencerows, while using woodlots, barns, and even chimneys as denning sites. Coyotes and red fox also travel freely across farmland. Interestingly, coyotes have increased substantially in Indiana over the past 25 years, and recent evidence indicates that red foxes are less common in areas visited by coyotes.

Some species, such as white-footed mice, thrive in small, isolated woodlots because they can make do with less. Their small body size enables them to successfully use forest habitat on a permanent basis that is inadequate for other wildlife. Their numbers in small woodlots can approach 100 per acre, which undoubtedly benefits a variety of owls and predatory mammals.

Not all mammals have fared as well as the species mentioned previously. Gray squirrels are found throughout the central hardwoods, where they are an important game species. But in intensively farmed areas of Indiana and Illinois, gray squirrel populations have declined. Although the reasons are unclear, gray squirrels apparently are sensitive to fragmentation of forest habitat, for they occur infrequently in isolated woodlots of less than 25 acres but are common or abundant in tracts of forest greater than 200 acres. Southern flying squirrels also are uncommon in small, isolated woodlots. Their sensitivity to forest fragmentation probably results from their reliance on a gliding style of locomotion, which is of no use when attempting to travel through crop fields.

Amphibians in Farmland

The word amphibian is derived from a Greek word meaning 'a being with a double life." And many amphibians in Indiana fit this description, because they rely on terrestrial habitat such as woodlands during part of the year, and on wetland habitat during the breeding season and varying portions of the remainder of the year. As we noted with mammals, amphibian species also differ in their responses to agriculture.

Among the frogs and toads, western chorus frogs, gray tree frogs, spring peepers and American toads are common in farmland. Not surprisingly, all 4 species have fairly general habitat requirements. Most notable is the American toad, which can be found almost anywhere that has invertebrates for food, moist resting sites, and a bit of temporary water for breeding. Tree frogs and spring peepers are found principally at sites with shrubs and second-growth woodlands in close proximity to wetlands. The larger ranid frogs (bullfrogs, northern leopard frogs, green frogs) are somewhat more specialized because they require permanent or semi-permanent bodies of water, consequently, they ore less common in some farmland areas. Unlike most other vertebrates of the state, northern leopard frogs actually exhibit an aversion to woodlands, preferring meadow and grassland habitat

Mole salamanders such as the eastern tiger salamander spend much of their lives in underground burrows, migrating to ponds in spring to mate and lay eggs. Tiger salamanders are common residents of farmland. Like the leopard frog, they are more likely to be found in grassland areas that are sparsely forested. In contrast, lungless salamanders such as the redback salamander are completely dependent upon woodlands for survival. Redback salamanders are entirely terrestrial and require moist resting places underneath rocks or fallen logs. In farmland they are found principally in woodlots of 25 acres or more, but only if woody debris is present.

Improvements for the Future

Forest and farmland in Indiana are closely bound, and much of the woodland in the northern half of the state occurs on privately owned farms. What can individual landowners do to reduce the negative impacts of forest fragmentation on wildlife? Based on the information outlined in the preceding paragraphs, several possibilities exist. Forest tracts of sufficient size can be managed to enhance their value to wildlife by encouraging regeneration and growth of nut-producing oaks and hickories. Many species of birds and mammals rely on tree cavities for nesting, so retention of snags and cavity trees can be extremely beneficial. Fallen logs and woody debris serve as important travel routes for many small mammals on the floor of a forest, and as refuges for lungless salamanders. In intensively farmed areas connections between forest fragments, or between forests and wetlands, are critical to the success of some species. Corridors between fragments can vary tremendously, and guidelines for corridors have nor yet been established. But it is safe to say that fencerows with wood cover are more likely to be used as corridors by wildlife than "clean" fencerows. And land set aside in CRP can provide valuable habitat and travel routes, especially for grassland species such as leopard frogs and tiger salamanders.

What can be done at the landscape or regional level to reduce costs of forest and wetland fragmentation? Wildlife rarely recognize property boundaries, so solutions at larger spatial scales depend upon cooperation of landowners, elected officials, and natural resource specialists. Incentive programs for cooperation show promise and should be examined. In addition, future planning and zoning decisions need to explicitly consider maintenance of forest corridors, especially along species-rich riparian habitat.

Our wildlife heritage, like our agricultural heritage, is rich. Although there are no easy answers to problems of habitat fragmentation, we owe it to ourselves, our children, and our grandchildren to search for ways of securing the future of native wildlife in Indiana's farmland.

For More Information:

Miller, B. K. Woodland wildlife management. FNR-102.

Miller, B. K., C. D. McCreedy, and W. L. Hoover. Managing for wildlife on agricultural lands: the economics of conservation alternatives. FNR-162.