Still other threats were not an original part of the landscape but have been in the South so long that they’d be missed if they suddenly disappeared. Examples are mimosa and wisteria, two of the most destructive nonnative plants in the region which some would argue are as much a part of the southern culture as grits and red-eye gravy.

Global Change Recipe Calls for Adding Heat …

The August 2007 online issue of the journal Nature reported predictions that the Earth will become more than 6 degrees Fahrenheit warmer by the end of this century—and that every degree of temperature increase will shift ecological zones by about 55 miles. If these predictions prove true, our children could see palm trees as far north as Washington, DC, and our grandchildren will most certainly see them in New York.

The implications of this shift for forest management in the South would be profound, especially in the context of threats. According to the same issue of Nature, the plants and animals that survive will be those that can colonize new territory or can adapt their biological functions and mating behaviors to seasonal changes. Within any ecological community, rather than a coordinated northward shift of all species, some will opt for colonizing while others will adapt to the new conditions or die out. Complicating the picture further will be the effects of wildfire and the addition of new species, either those colonizing from further south or those introduced from other parts of the world.

Ron Neilson, a research bioclimatologist with the Pacific Northwest Research Station, has been studying weather systems to understand how a warming climate might affect the size and destructiveness of wildfires in various parts of the world. From one season to the next, high and low pressure systems tend to migrate and form into cells as different parts of the Earth receive varying degrees of sunlight. These cells have variations within their boundaries; their cores are subject to greater evaporation and are, therefore, drier, while their outer edges have significantly more rainfall.

Initially, a warmer climate should increase evaporation and produce more rainfall in some areas. Increased rainfall stimulates growth of trees and other vegetation, eventually resulting in more moisture being drawn out of the soil in which they grow. With continued warming, the edges of weather cells move outward, expanding the drier core and parching the newly greened vegetation, causing it to turn brown and become fuel for wildfires.

Neilson’s models show that the South is of particular concern for two reasons. First is its location in the Bermuda cell, which will divert rainfall to other U.S. regions and Canada when warming causes it to expand. Secondly, once wildfires get started, they will spread easily over many areas of the South, whose topography and climate are less variable than other regions. As an example, Neilson points to the Georgia-Florida border where two fires, one started in the Okefenokee Swamp, burned an area the size of Rhode Island.

And Then Stirring in New Ingredients...

Because of their mobility, reproductive success, and short life cycles, invasive organisms can wreak havoc in forest environments, especially those that have already been subjected to fire, drought, and other disturbances.

Native insects and diseases usually attack in cycles followed by periods of relative inactivity. However, recent studies show that for some like the southern pine beetle, the periods of attack are becoming continuous. This phenomenon is most common in environments where the periods between dry spells are compressing, which is predicted to occur more often as climates warm. In addition to invasive populations increasing under warmer and drier conditions, their plant hosts often become more susceptible to attack as their internal chemistry changes in response to climate variations.

Nonnative insects, diseases, and plants present additional challenges, partly because they lack the predators that kept them in check back in their native environments. Whether global warming will increase or decrease invasive organisms is a question that currently has as many answers as species studied. To provide a clearer understanding Qinfeng Guo, research ecologist at the SRS Eastern Forest Environmental Threat Assessment Center in Asheville, NC, has begun to study the likely effects of global warming on nonnative invasives using a combination of remote sensing, data mapping tools, and mathematical modeling. His goal is to identify the factors that control distribution and population growth of invasives by comparing their native and introduced ranges.

Guo’s early research included work on sudden oak death, a nonnative pathogen caused by Phytophthora ramorum, introduced in shipments of rhododendron and other nursery plants and which has killed many trees in the Pacific Northwest. He and his cooperators examined five models, all predicting different levels of risk for spread to other regions, and then developed predictions based on where the models were in agreement. According to the consensus predictions, if sudden oak death escapes from the Pacific Northwest, it could move eastward to 9 of the 13 Southern States (Virginia, North and South Carolina, Georgia, Kentucky, Tennessee, Alabama, Arkansas, and Oklahoma).

In the area of nonnative invasive plants, Guo and his cooperators are mapping 20 of the most dominant species from Asia and another 20 North American species introduced into Asia. In addition to monitoring the differences in native and introduced ranges when subjected to climate change over the years, the researchers will collect information on the species’ genetic and physical characteristics, distribution patterns, and rates of invasions. The results of this study will help in predicting how global warming will affect the incidence and success of future invasions and in coping with their effects.

New Recipes Needed for Forest Management

Threat assessment center director Danny Lee says that Guo’s work on invasive organisms is part of a larger effort to evaluate and guard against synergistic and antagonistic threats throughout the Eastern United States. “Our center was established to apply rigorous scientific methods in anticipating future threats and then to supply the tools necessary for making wise decisions and implementing those decisions on public and private lands,” says Lee. “Understanding both the vulnerabilities of forest ecosystems and the potential of forest threats to take advantage of those vulnerabilities will be critical to the success of future forest management.”

Lee’s approach is in line with Neilson’s belief that global change places us in a new environment where the future will no longer echo the past: “Historically the goal of foresters has been to manage for the status quo. In this new environment, we no longer will have the luxury of trying to maintain species but will have to look beyond species to the functions they serve within a forest ecosystem. The new challenge for the natural resource community will be to manage for change.”