Insects, diseases, droughts, and fire threaten forests. Each year, the U.S. Forest Service assesses threats facing the nation’s forests. Forest managers, scientists, and decision-makers rely on the annual reports.
“This report is a valuable resource for everyone who cares about the big picture of forest health across the United States,” says Kevin Potter.
Potter is the lead editor of the report, which Barbara Conkling co-edited. Conkling and Potter are researchers at North Carolina State University and cooperators with the SRS Eastern Forest Threat Center.
Scientists from across the Forest Service contribute to the annual report, as do university researchers, state partners, and many other experts.
“The report is the only national assessment of forest health undertaken on an annual basis,” says Potter. “It includes both short-term and long-term evaluations of our forest resources across broad regions.”
The report includes forest health assessments from the continental U.S. as well as Alaska and Hawai’i. It also summarizes the status and trends of a variety of forest health indicators from a national or regional perspective. Key findings include:
Insect Activity and Tree Mortality
- In 2015, scientists detected 70 tree-killing pests and pathogens across 5.5 million acres of forest in the lower 48 states.
- In the West, bark beetle infestations caused geographic hot spots of forest mortality. In the East, hemlock woolly adelgids and emerald ash borers were the most destructive forest insects. Hot spots of defoliation were associated with spruce budworm in the West, and with several different insects in the East.
- The insect and disease surveys detected tree mortality across approximately 1,700 acres of southern forests. Ips engraver beetles and other beetles were responsible for some of this mortality, but most causes of death could not be determined.
- Scientists detected 58 defoliating pests on approximately 12 million acres. Defoliating insects, such as the yellow poplar weevil, sometimes strip trees of all their leaves. The yellow poplar weevil was the most widespread defoliator in the South, affecting about 5 million acres.
Wildland Fire Occurrence
- Wildland fire is widespread and can have positive or negative effects on forests. The report uses satellite data to show the geographic distribution of wildland fire occurrences.
- In 2015, MODIS satellites detected over 80,000 wildland fire occurrences in the U.S., the smallest number since 2011. However, the number is 25 percent higher than the mean for the previous 14 years.
- Most fires occurred in the Pacific Northwest – particularly northwestern California and southeastern Oregon. In the South, parts of Texas, Oklahoma, and Florida had moderate numbers of fires in 2015.
Drought and Moisture Surpluses
- Rainfall in much of the Eastern and Central U.S. was near normal in 2015, and some areas had moderate moisture surpluses.
- The Pacific Coast and much of the northern Rocky Mountains experienced at least moderate drought conditions. Parts of northern California and Washington, as well as Idaho and Montana, suffered from extreme drought.
- In 2015, the South saw scattered areas of moderate drought, mostly in northern Florida and parts of Georgia. Texas experienced large surpluses of rainfall, mostly in areas without forests.
- Analysis over 3 and 5 year periods revealed pockets of drought in the South, particularly in southern Florida. In parts of Arkansas, Kentucky, Louisiana, and North Carolina, scientists detected severe or extreme moisture surpluses.
“In general, forests are resistant to short-term droughts,” says Potter. “Drought duration may have more impact on forests than drought intensity.” Droughts that last more than a year are much more likely to kill trees.
The national Forest Health Monitoring program also funds Evaluation Monitoring projects, which are in-depth assessments of forest health concerns at smaller scales. Some of the projects that took place in the South address:
- Southern pine beetle’s impact on forests and fuels in wildfire-prone areas.
- Interactions between biotic and abiotic factors that affect pine forests.
- Estimates of tree death and species distribution probabilities.
The report also presents new ways to analyze forest health data and longer-term assessments of forest health.
For example, the report discusses the Vegetation Diversity and Structure Indicator. Forest Inventory and Analysis staff used the indicator on more than 500 plots in the North Central and Northeastern states, where understory vegetation has been measured several times. Managers and scientists can use the data to assess changes in plant communities.
“Healthy forests are vital to our future,” says Potter. “Identifying forests that might be deteriorating requires consistent, broad-scale, and long-term monitoring.”
A draft of the next FHM report will be available around the end of 2017. The final version will be published by the middle of 2018.
For more information, email Kevin Potter at email@example.com.