Ten Years of Prescribed Fire on a Cross Timbers Woodland Community
A long-term demonstration of the effects of prescribed fire on a southern Oklahoma Cross Timbers community was initiated in 1988 on the 2,593-acre Noble Research Institute D. Joyce Coffey Ranch, located six miles west of Marietta, Oklahoma. About 1,100 acres of the ranch consist of open herbaceous plant communities, primarily native range, while the remaining area is occupied by woody vegetation typical of the Cross Timbers. Many landowners have resources similar to those of the Coffey Ranch, and they manage them for wildlife and cattle. Often, these landowners make the mistake of clearing too much of their wooded areas, reducing the quality of wildlife habitat in favor of increasing cattle forage. Woody vegetation can limit total forage production but is an important component of any ranch with wildlife management goals. It should be well distributed and consist of various successional stages to be of maximum benefit while being managed for a diversity of wildlife species.
Prescribed fire is often recommended as a tool to open up or thin woody vegetation typical of the Cross Timbers. More open timber may increase plant diversity for wildlife and forage for cattle.
Following are the results of ten years of prescribed fire on woody vegetation dominated by post oak (Quercus stellata).
Two fire frequency treatments were initiated on wooded areas in February and March of 1988. Prescribed fire was applied yearly to one pasture (YT) and every other year to another pasture (EOYT). All burning was conducted in the fall, early winter or late winter, as soon after leaf drop as possible.
The objectives of these fire treatments were to demonstrate the effects of fire frequency on the woody plant community, wildlife habitat and cattle forage. Transects were monitored in the YT, EOYT, and an adjacent unburned area (UB) to measure woody plant canopy cover and density, and grass and forb densityin 1998.
There was a difference in canopy cover percentage between the UB and YT (figure 1). There was little difference in canopy cover percentage between the EOYT and the YT.
There was little difference in post oak canopy or density (figure 2). Post oak is the dominant woody plant in the demonstration area. Hackberry (Celtis laevigata) and black oak (Quercus velutina) canopy cover percentage was less in the burned treatments than in the UB and hackberry canopy percentage in the YT was lower than that in the EOYT (figure 3). There was more eastern red cedar (Juniperus virginiana) canopy in the UB than in the YT and the EOYT (figure 3).
Elm (Ulmus spp.) and green ash (Fraxinus pennsylvanica) were not in canopy measurements. Elm densities (figure 4) were not different between treatments or between treatments and the UB. Green ash density (figure 4) was reduced in both treatments compared with that in the UB. Visually, there appeared to be more eastern red cedar, elm, and green ash in the UB versus the treatments. However, our sampling method may not have been sensitive enough to test our visual observation or previous years' burning affected species composition before transects were established. We believe that burning in years before transect establishment may have reduced canopy and density of hackberry, black oak, eastern red cedar, elm, and green ash. We also believe that in addition to hackberry and black oak, eastern red cedar, elm, and green ash contributed to the total reduction in canopy cover.
Grass density (figure 5) was higher in the YT than in the EOYT and higher in the YT and EOYT than in the UB, probably because of the decrease in total woody canopy cover. The grasses that grew after the burns were mainly high seral species: indiangrass (Sorghastrum nutans), switchgrass (Panicum virgatum), and little bluestem (Schizachyrium scoparium).
Forb density (figure 5) was higher in the EOYT than the UB and YT. The difference between the EOYT and the YT may have been due to the higher grass density in YT. A number of species of forbs appeared, including Desmodium, Lespedeza, Ambrosia, Helianthus, and Croton.
Even though burning every year decreased canopy cover percentage, this difference was not enough to achieve our desired canopy reduction goals. Burning every year or every other year may reduce woody plant diversity over time, decreasing habitat quality for some wildlife species. However, for some wildlife species this effect may be offset by the increase in grass and forb density. Although their diversity was not measured, numerous grass and forb species were in both treatments. The increase in grass density in the YT was not enough to increase the cattle stocking rate.
This project demonstrates the need to consider techniques in addition to fire, such as chemicals and brush sculpting methods, for improving wildlife habitat and increasing forage for cattle in this wooded Cross Timbers plant community. Fire may better serve as a tool to maintain open areas rather than create open areas in mature post oak timber.