A review of southern pine decline in North America
The southeastern United States is among the most productive forested areas in the world. Four endemic southern pine species – loblolly, longleaf, shortleaf, and slash - contribute significantly to the economic and ecological values in the region. A recently described phenomenon known as Southern Pine Decline (SPD) has been reported as having widespread impact in the southern pine region, particularly on loblolly pine. Root-feeding weevils and their associated fungi have been suggested as causal agents, even though literature and empirical research suggests that they are secondary insects colonizing weakened trees. Further, no published information exists about whether their associated fungi can cause mortality of mature trees in the southeastern U.S. Since there are significant management implications for pine health, we reviewed and critically examined the SPD phenomena on the southern landscape. Our regional analyses of USDA Forest Inventory and Analysis data show no discernable patterns related to pine growth or mortality, especially as related to topographic factors. There are no large-scale patterns related to pine mortality suggesting multiple interacting factors impacting tree health at stand-level. As such, the hypothesis that SPD is a regionally important decline syndrome and labeling declining southern pine stands as SPD is not supported. Instead, we discuss many abiotic (soil types, climate) and biotic (insects, pathogens, genetics) factors that may be interacting with each other and affecting southern pine health. Finally, we suggest management recommendations for landowners with pine health issues.