New ecosystems lack diversity
Oct. 30, 2014 – In the southeastern United States, large forested areas were cleared, farmed, abandoned, and then burned to keep grasses under control. Some areas have been allowed to grow back into forests in recent decades, but whether they can even partially erase the centuries of human use is uncertain.
An article in the current issue of the journal Castanea looks at whether former farmlands that were then burned each winter could return to something resembling their original woods or would grow into a new ecosystem once burning stopped. It takes a long view, looking at the differences 44 years after annual grassfires ended in the study plot.
Repeated burning is a common cause of death to the upper sections of fire-sensitive species of trees. Still, the trees survive at their roots and continue to sprout small groups of saplings between burns. This cycle can continue until massive roots support a dense thicket of small trees. When such trees can't reach their normal height, they are said to be caught in a fire trap.
This article looks at such an area in northern Florida, examining the changes in vegetation between 1966, when it was last burned, and 2010. It also compared the vegetation to the plant life in an area that continued to burn annually. As part of the study, researchers took a census of the trees in each area, including their species, size, and location.
They found that when the burning stopped, the trees in the area quickly shot skyward from their well-developed roots. As a result, the key change over the 40-plus years was in the height of the trees; the numerous yet stunted hardwoods that had been in the area when it was last burned had grown to a normal height for their species.
Through this growth, an unbroken canopy formed that left little room for other types of trees to establish themselves in the studied area. Woody shrubs and vines continued to fill much of the space, making it difficult for pine tree seedlings to develop. Breeding birds did not seem to be attracted to the space. Overall, the changes in the area suggested that new ecosystems may be far less diverse than their historic ones.
The author concluded that there was little chance of turning back the clock in the area. He wrote that "With the possible exception of climate change towards warmer, drier conditions, I foresee little opportunity for the recovery of the original upland vegetation in the continued absence of fire."
The author also concluded that the lack of diversity in the area could point to a larger problem in land management and forest restoration. Stopping intentional burns may not be enough; native species may also need to be reintroduced to restore land to its former health.
Full text of the article "Forest development 44 years after fire exclusion in formerly annually burned oldfield pine woodland, Florida," Castanea, Vol. 79, No. 3, 2014, is now available.
Castanea is the journal of the Southern Appalachian Botanical Society and publishes articles relating to all aspects of botany in the entire eastern United States and adjoining areas. The Southern Appalachians—the nonglaciated mountainous areas of Alabama, Georgia, South Carolina, North Carolina, Tennessee, Kentucky, Virginia, West Virginia, Maryland, Pennsylvania, and southwestern New York—form an evolutionary center for native plant diversity for the northern temperate regions of the world. The society dates to 1935 and serves all persons interested in the botany of the Southern Appalachian Mountains. The journal encourages submissions of scientific papers dealing with basic research in any field of plant biology, systematics, floristics, ecology, physiology, and biochemistry. For more information about the journal or society, please visit: http://www.sabs.appstate.edu.