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Forecasting Change

Throughout the Assessment, we place emphasis on understanding historical change and ongoing trends. We also evaluate possible futures. Forecasting changes in forest ecosystems and the values that derive from them is necessarily fraught with uncertainty. Forests and linked social systems change in response to multiple factors. Current trajectories of change often reflect the legacies of historical land use and resource management. Some past actions have irreversible consequences, such as the hydrologic effects of dams. In other cases, altered ecosystems may be restored or renewed. In all situations, the future of forested ecosystems will be the product of the working and adaptation of complex systems and the impacts of unanticipated events.

We use an integrated modeling system to forecast timber harvesting, forest investment, forest growth, and land use up to the year 2040. This system, called the Southeastern Regional Timber Supply Model is described in chapter 13. It incorporates the land use model described in chapter 6. Forecasting these outcomes requires that we make assumptions about the future course of certain core variables. Three key assumptions are:

• Demand for timber products is projected to increase at the rate of 1.6 percent per year. This is the demand projection developed for the South in the most recent Resources Planning Act assessment (see chapter 13) and is based on trends in macroeconomic variables such as gross national product and population as well as on trends in international timber markets

• Population and income growth projections are those used by the U.S. Global Change Program (see chapter 6). These projections are constructed at the county level and hold especially strong influence on projections of land uses.

• The timber productivity of pine forests is based on the expected adoption of management activities. Projected adoption rates for industrial and nonindustrial private forests are taken from expert surveys of industrial owners and States, respectively (see chapter 14). Assumed productivity rates for pine plantations owned by industry are consistent with management regimes that include site preparation, planting, fertilizer application, thinning, and vegetation control with herbicides or other methods. For nonindustrial owners, the management of plantations is assumed to be somewhat less intensive but still would include site preparation, planting, and some thinning. The resulting increase in productivity from current levels to 2040 is assumed to be 75 percent for industrial owners and 37.5 percent for nonindustrial private owners.

As with any forecasting exercise, assumptions play a large role in outcomes. To understand the sensitivity of models to these assumptions, models were run with alternative scenarios. These are discussed in detail in chapter 6 and chapter 13. In this Summary Report we refer strictly to the base scenario constructed with the assumptions described above. Sensitivity analysis reveals that future land uses and forest conditions are especially sensitive to assumptions regarding timber demand and productivity growth. For example, weaker demand growth would lead to lower prices, less harvesting, and less area of forest than projected for the base scenario. If timber productivity growth were not realized, then timber prices and the area of planted pine could be substantially higher than was projected for the base scenario.

In the discussions that follow, we attempt to estimate the direction of change and, in some case, explicitly forecast future conditions. These forecasts explore possible futures and project the potential consequences of ongoing and anticipated changes. They should be viewed as “what could happen,” rather than “what will happen.”