Ayres Abstracts

Ayres, M. P. and G. A. Reams. 1997. Global change and disturbance in southern forest ecosystems. Pages 741-753 in R. A. Mickler and S. Fox, editors. The productivity and sustainability of southern forest ecosystems in a changing environment. Springer-Verlag, New York.
Global change seems certain to alter spatial and temporal patterns of perturbation and disturbance in southern forests. It is probable that perturbations will become less frequent and/or less severe in some areas but more frequent and/or more severe in other areas. Some climatologists expect that global change will lead to an overall increase in the frequency of extreme climatic events (perturbations). However, even if the average frequency and severity of perturbations remains the same across the southeastern United States as a whole, changes in the spatial and temporal patterns of perturbation will probably lead to increased ecological impacts because we expect that: (1) a given level of perturbation will produce the greatest disturbance in forest communities with a limited history of perturbation and (2) forests with a history of frequent perturbations will acquire different characteristics if perturbations are relaxed. By analogous reasoning, changes in the spatial and temporal patterns of perturbation will probably introduce unavoidable social impacts and economic costs. For example, a large expensive infrastructure exists within the United States Forest Service (Forest Health) and the private sector (timber salvage operators) to control infestations of southern pine beetles. The personnel, equipment, and expertise of this infrastructure tend to be concentrated in areas where the frequency of bark beetle infestations is greatest. If bark beetle infestations become less frequent in these areas and more frequent in others, the average efficacy of control is likely to decrease and the average losses associated with infestations are likely to increase because the control expertise will be located elsewhere and because risk mitigation measures, such as frequent thinning of pine forests, tend to be less common in areas with less history of bark beetle outbreaks. Similarly, if hurricane tracks change (even with no change in hurricane frequency), there will be increased impacts and costs because landowners in former high risk areas will tend to be overinsured and landowners in new high risk areas will tend to be underinsured. Other ecological and socioeconomic consequences may be even more difficult to remedy. Parks, preserves, and conservation easements have value based upon the contemporary distribution of organisms and cannot easily be expanded or relocated if the selected sites become unsuitable for valued organisms because of climatic changes. Because of agriculture, losses of forest due to climate change in some areas will not be easily matched by gains in other areas. Municipalities and school districts make long term investments that are dependent on a stable or growing tax base; global change can threaten these investments because in many areas of the southeastern U.S. timberland is a large portion of the tax base and forest product revenues are a large portion of the local economy.

In some regions, perturbations associated with global change are likely to alter optimal land-use strategies (e.g., forest vs. range vs. agriculture, pine vs hardwood, loblolly pine vs longleaf pine, long rotations vs. short rotations, etc.). Assuming that present land-use strategies are approximately optimal, environmental changes that alter optimal land-use introduce unavoidable costs. These costs will be minimized by (1) early recognition of the changes, (2) accurate predictions of the consequences of changes in land-use strategies, and (3) timely transitions, when appropriate, from the status quo to appropriate new strategies. Research such as that reported in this volume represents progress toward steps 1 and 2 of this process. Step 2 in particular, will require further significant advances in scientific knowledge. Step 3 hinges upon effective decisionmaking by public and private landowners.