Research in action

Hot droughts are of increasing concern for forests of the south. When temperatures are high and moisture is low, trees become vulnerable quickly. Meteorologists sometimes refer to these events as flash droughts, and one for the record books happened in Mississippi and Louisiana in 2023, emerging in late summer as the rains diminished, and the persistent heat shattered records.

Photo Credit

Jerry Groom, USDA Forest Service

Pine mortality near Alexandria, Louisiana, is evident in this aerial image. The reddish pine needles show signs of trees that are dead or dying from the drought and infestation of southern pine engraver beetles. Southwest Mississippi experienced 21 days of peak temperatures over 100 degrees in August. In 2023, based on long-term weather records, the state experienced the warmest late-growing season ever observed since 1895.

The consequences for the region’s forests were stunning. Between October and December, millions of pine trees turned red across southwest Mississippi and eastern Louisiana, dead due to the combination of drought stress and pine engraver beetles (likely Ips spp.).

Tree mortality affected all landowners – from urban homeowners in Jackson, Mississippi and Alexandria, Louisiana to industrial forest owners.

The early estimate is that well over 12 million trees died. That estimate represents years of dedicated work.

In mid-December, my colleague Bill Christie and I got a call from Chris Asaro, the Forest Service program manager for Forest Health Monitoring in the agency’s Southern Region. He knew this would be a big deal after the holidays.

Christie and I are the primary developers of HiForm, a free, innovative, and state-of-the-art tool that uses satellite data and cloud computing to reveal forest disturbances – insect outbreaks, wildfires, tornadoes, and more – across large areas at high resolution.

Immediately after Asaro’s call, we refined our HiForm workflow to isolate recently dead pines from earlier clearcut activity and late season change in hardwoods. We then shared these products with federal and state forest agencies.

Having a map of forest mortality that covers the entire landscape is essential for understanding the extent and potential long-term impacts of this extreme event.

“We shared the maps with our state legislature in support for other state agencies like the Mississippi Department of Transportation and the Mississippi Department of Emergency Management,” says Sean Hodges of the Mississippi Forestry Commission. The maps will help state agencies and utility companies prioritize areas where dead trees are hazardous and need to be removed.

The event may be the worst thing to happen to the forests of southwest Mississippi in a very long time. We don’t know because record keeping for unusual events like this was poor in the past. While we map southern pine beetle spots fairly well, pine engraver and associated drought mortality is more dispersed.

The population of pine engravers increases when trees are stressed by drought or other disturbances like hurricanes, but pine engravers usually kill few trees, and their behavior is much less well understood than that of the southern pine beetle which gets most of the attention. Pine engravers only become a major problem during severe drought, and the fall 2023 season was the hottest late-season drought seen since record-keeping began in 1895.

Since 2016, HiForm has mapped disturbances using change in a vegetation-sensitive measure called the Normalized Difference Vegetation Index, or NDVI. The team calculates seasonal NDVI at 10-meter resolution from the European Space Agency’s Sentinel-2 satellite sensors, which produce new imagery every five days.

Photo Credit

Ron Long, Simon Fraser University, Bugwood.org.

A pine engraver beetle, also known as an Ips beetle. Ips beetles and other pine beetles are about the size of a grain of rice. Even when trees are drought-stressed, it takes millions of these tiny insects to kill them. There are multiple species of Ips beetles, and they look similar to each other and to other beetles such as the southern pine beetle. 

Rapidly evolving technologies like HiForm are revolutionizing the way we monitor forests. These technologies let us monitor forests throughout the year and capture sudden disturbances in near-real-time.

This effort provided our best opportunity yet to demonstrate to our regional and state partners how valuable, effective, and efficient remote sensing technology can be. These tools help improve how we map forest disturbances, including those that are more extreme and sudden than unexpected.

The information also allows officials to make quicker decisions on the ground. We shared the HiForm workflows with the Mississippi Forestry Commission and with Louisiana officials. In February, legislation was introduced and then approved in March that directed USDA to use all available programs to help landowners.  

On April 16, U.S. Secretary of Agriculture Tom Vilsack approved the Emergency Forest Restoration Program to owners of nonindustrial forestland affected by the drought all counties in Mississippi and in May to 64 Louisiana parishes. The deadline to apply in Mississippi is Aug. 15; the deadline in Louisiana was July 12. For more information about drought and assistance, go to Farmers.gov.

This story was originally published as a Forest Service Feature Story.

For more information, visit the HiForm website or email Steve Norman at steve.norman@usda.gov.