Forecasting Short- and Long-Term Southern Pine Beetle Risk in the Southeastern US

2019 southern pine beetle predicted distribution map

Southern pine beetles (SPB) are destructive insect pests that cause tens- to hundreds-of-millions of dollars in economic losses annually in the southeastern US. The SPB outbreaks usually start in stressed stands, but healthy trees become susceptible to attack and mortality as beetle populations grow. Large scale outbreaks can also last several years if not suppressed, and have resulted  in over a billion dollars in timber losses over the past several decades. Early SPB detection and treatment can help reduce the spread and impact. Forest land managers need better information to identify and prepare for SPB outbreaks so that they can focus their limited resources to quickly treat SPB population explosions.

To address this need, the USDA Southeast Climate Hub (SERCH) developed the Southern Pine Beetle Outbreak Model version 1.0 (SPBOM). SPBOM forecasts SPB risk using a combination of; 1) the previous year’s SPB spot (i.e., infestation) data; 2) the most recent NOAA monthly weather forecasts for the southeastern US; 3) the most recent stand origin, species composition, and stand density data from the USDA Forest Inventory and Analysis Program; and 4) WaSSI hydrologic model predictions of pine evapotranspiration (a measure of tree stress) to predict SPB outbreaks at a county level resolution. Validation of SPBOM with reserved (not used in model development) SPB spot data indicated that the model had an accuracy rate of 72% in predicting beetle outbreak areas using historic climate.

SPBOM 1.0 was released in June 2019 to forecast the distribution and severity of SPBs, and alert forest managers to areas of high southern pine beetle risk. SPBOM will be used each spring to provide outbreak forecasts for the coming growing season (i.e., spring, summer, and fall). Each October SPBOM will be rerun with the current years observed SPB population data to help inform management planning for the next years growing season. The map above shows the latest SPB forecast from the USDA Southeast Climate Hub. Region-wide, 2019 is predicted to be a less severe year for SPB outbreaks compared to 2018, but there are noted areas of intense beetle activity.

Another important function of SPBOM is the ability to forecast SPB outbreaks under different climate change scenarios. The model runs using changes in air temperature and precipitation indicate that a 2°C increase in southeastern US air temperature and a 20% reduction in southeastern precipitation will increase the amount of area in marginal, enhanced, or moderate infestation by 15-30%. 

If you have questions about the SPBOM, please contact Steve McNulty, Director, USDA Southeast Climate Hub, steve.mcnulty@usda.gov.