33. Predictions of Southern Pine Beetle Populations Using a Forest Ecosystem Model

Dendroctonus fi-ontaiis Zimm. (southern pine beetle (SPB)) has caused over $900 million in damage to pines in the southern United States between 1960 and 1990 (Price et al.. 1992). The damage of SPB to loblolly (Pinus tuedu L.), shortleaf (Pinus echinata Mill.), and pitch (Pinus rigida Mill.) pine has long been established (Hopkins. 1899), however, extensive mapping of SPB infestations has only existed since 1960 (Price and Doggett, 1982). Early detection of SPB outbreak areas is essential to controlling population increases (Swain and Remion, 198 l), but the range of SPB is large, SPB have six to eight generations per year, and there is inconsistency in the monitoring methods used to measure SPB populations across its range. Therefore, various models have been developed that attempt to predict SPB outbreak severity across the region (Hansen et al., 1973; Kalkstein, 1973; Michaels. 1984). In addition to predicting SPB outbreak areas based on present-day climates, models could be useful for assessing the influence of Wure climate change on SPB populations. One unknown regarding climate change and forest ecosystems involves the effect that chronically warmer air temperature could have on insect populations. For example, a 1 “C increase in average annual air temperature caused a tripling of a principal insect herbivore that feeds on mountain birch (Herms, 1991). When combined with the potential for increased forest stress resulting from climate change, increased insect populations could seriously reduce forest productivity across the region. Because the SPB has six to eight generations per year, it is impossible to