Philip C. Stouffer
What do red-cockaded woodpeckers and gopher tortoises have in common? They are endangered species, and both require a habitat becoming rare in Louisiana and throughout the southern United States. To thrive, they need open pine forests, known as longleaf pine savannahs.In addition to the woodpecker and tortoise, these forests are home to a spectacular array of plants and animals.
As longleaf pine forests have disappeared over the past century to less than10 percent of their original extent in Louisiana, many of these species have made their way onto the state’s list of Species of Conservation Concern. Active management, especially prescribed burning,will be required to maintain these elements of Louisiana’s natural heritage.
Longleaf pine forests once covered vast areas of central, southwestern and southeastern Louisiana north of Lake Pontchartrain. About 4 million acres were once longleaf pine forest in Louisiana.Botanists and geologists often subdivide the longleaf forests into flatwoods and savannahs, depending on the topography and soils, but the basic structure remains the same. Longleaf pine trees form a sparse overstory, the midstory is open, and the ground vegetation includes lush growth of grasses and other herbaceous vegetation.
Persistence of longleaf pine forests requires one regular disturbance – fire. Fire stimulates flowering by many of the herbaceous plants, reduces invasion by woody species common in hardwood forests, and allows dominance by longleaf pine. Indeed, the entire system has evolved over millennia in response to lightning-induced fires during the growing season. Most areas historically burned every one to four years. In the absence of fire, the midstory becomes crowded, ground vegetation thins, and the canopy eventually closes with a mixture of hardwoods and pines. These conditions eliminate many of the specialized plants and animals of the open forest.
Although these forests get their name from the magnificent tree that dominates the park-like landscape, the heart of the biological diversity resides in the sublime vegetation underfoot. Some 300 plant species grow in Louisiana’s savannahs, with as many as 30 species in an area the size of a hula hoop. At this scale, not even rainforests have a diversity of species comparable to our native grasslands. Characteristic plants include dozens of species of grasses, sedges and rushes, as well as showier plants like orchids, asters and pitcher plants. Many of these species are said to be endemic to fire-maintained habitats, which means that they do not occur in other habitats. Indeed, according to the Louisiana Natural Heritage database, the savannahs of southeastern Louisiana host more of the state’s rare plants than any other habitat.
Animals of the longleaf pine forests show a similar pattern. Several species, including the red-cockaded woodpecker, require longleaf pine trees. Most species, however, are more closely associated with the ground vegetation. The Louisiana Department of Wildlife and Fisheries’ list of Species of Conservation Concern includes more than 25 vertebrate species from longleaf pine forests. More than half of the amphibians, terrestrial reptiles and terrestrial mammals on the list occur in these habitats. Among birds, these grasslands are home for some of the most habitat-specific species in the state, including Bachman’s and Henslow’s sparrows, as well as game species like turkey and bobwhite quail.
LSU AgCenter researchers have been studying Henslow’s sparrows in longleaf savannahs for six years. Results demonstrate how fire helps to maintain habitat quality for savannah species. Henslow’s sparrows breed in grasslands of the Midwest and Northeast, where their numbers have declined precipitously in tandem with the conversion of native prairie to agriculture. They arrive in Louisiana in October and November and remain here until March or April. By tracking bird abundance in the same savannahs over multiple years, we have shown how birds respond to growing-season fire. Henslow’s sparrow abundance peaks in the first winter after burning, then declines with each successive year without burning. After three years without fire, the birds are gone. Data suggest that the important change in vegetation during this period is the gradual closing of herbaceous vegetation right at ground level. These birds are extremely secretive, moving like rodents at ground level beneath the leaves of herbaceous plants. They probably use the small openings between bunches of grass as they forage for a diverse variety of seeds available on the ground.
The research with Henslow’s sparrows reinforces historical data in showing that longleaf forests require regular burning. In 21st Century Louisiana, this means prescribed burning by managers. Central to this management is public recognition of the critical importance of fire. Fortunately, the extensive areas of longleaf forest in Kistachie National Forest and Fort Polk are being actively managed with fire, as are smaller areas such as Sandy Hollow and Lake Ramsay Wildlife Management Areas and the Nature Conservancy’s Abita Flatwoods Preserve. Some of these areas have required removal of undesirable plants to recover from years of fire suppression.
Given the limited extent of longleaf forests in Louisiana, even small areas could support native biodiversity, especially for plants. Although using fire makes management more difficult for owners of small parcels of land, some landowners are attempting to restore or maintain longleaf forests. Longleaf pine doesn’t produce the return of short-rotation loblolly pine, but it is valuable timber when harvested.
What does the future hold for Louisiana’s longleaf savannahs and their wildlife? Savannahs on public land should persist, if managed properly. These large blocks of forest hold the most promise for wildlife, as some species have already disappeared from smaller remnants. Unfortunately, some species have declined to such small populations that their survival remains in the balance. Gopher tortoises, red-cockaded woodpeckers, and dozens of less charismatic plants and animals need every bit of longleaf savannah that remains. Philip C. Stouffer, Associate Professor, School of Renewable Natural Resources, LSU AgCenter, Baton Rouge, La.
(This article was published in the spring 2006 issue of Louisiana Agriculture.)