Why have southern pine beetle outbreaks declined in the southeastern U.S. with the expansion of intensive pine silviculture? A brief review of hypotheses

- SPB outbreak frequency has decline over the last 20 years across the Southern U.S.
- Concurrently, pine plantation area has increased by 20 times since the 1950s.
- Variables such as weather or natural enemies fall short at explaining these trends.
- Changes to silvicultural practices may be partly responsible for lower SPB activity.

The southern pine beetle has shown a dramatic decline in outbreak activity over much of the southeastern United States since the turn of the 21st century compared to previous decades. Concurrently, from the 1950s through the present day, a twenty-fold increase in pine plantation area has occurred across the region while trends in genetic tree improvement and pine silvicultural advances have seen a marked increase in application towards the end of the 20th century. We examine southern pine beetle outbreaks in the Piedmont and Coastal Plain physiographic provinces of the southeastern U.S. relative to this increase in pine plantation area and intensive management. While climate and natural enemy hypotheses are discussed, the substantial changes to the management and condition of the southern pine resource in the form of plantations that are genetically improved, younger, faster growing, less overstocked or more fragmented may provide a more robust explanation for regional declines in SPB outbreak activity.