UNM scientists concerned about rising wildfire threats to southwestern U.S. forests

By Mariah Rosales

Scientists at the University of New Mexico (UNM) recently published a research article describing a new method of modeling reforestation after wildfires. Research has shown an important link between topography and how plants recover after a fire. Topography refers to the natural shape and features of the land, such as its hills, valleys, and overall terrain. Previous models often overlooked this important factor, primarily focusing on weather patterns instead. UNM scientists wanted to focus on the link between topography and how plants recover after a fire, and better understand reforestation in severely burned forests using an updated simulation model while factoring in climate change.

The study looked at what happened after the 2011 Las Conchas Fire in the Jemez Mountains of New Mexico. It showed that this fire, and others like it, have a significant impact on forest ecosystems due to the number of trees that are killed, which makes it hard for new ones to grow in the affected areas. 

Researchers realized that earlier predictions were overly optimistic about how well the trees could grow back. This discovery prompted the UNM team to plant their own seedlings in areas where the fire had hit hard, closely observing how they coped. Using the data they gathered, they came up with a new way to predict how the forest might recover after a fire. They built a new regeneration algorithm in the model to better understand the tough conditions after a wildfire and how new trees can take root.

The updated model used a computer program called LANDIS-II (version 7.0), which lets researchers create a virtual forest and see how the trees might change over the years after a fire. To get a clearer picture, the team divided the area based on things like soil and weather. They used additional software programs, like Photosynthesis and EvapoTranspiration (PnET), to understand how carbon and water move, and Dynamic Fire and Fuels System (DFFS) to figure out how fires might start and spread.

Researchers ran a simulation from the years 2012 to 2099, using real and expected climate data. The data from the simulation indicated that previous models overestimated how many piñon, ponderosa pine, and Douglas-fir trees would grow back in affected areas.

Before the Las Conchas fire, the landscape contained mixed-conifer forests. These mixed-conifer forests included different kinds of trees like piñon-juniper, ponderosa pine, Douglas-fir, southwestern white pine, white fir, and Engelmann spruce, depending on the location and elevation. Researchers thought that after the fire, there would be fewer new trees growing back, especially for certain types like Douglas-fir. They found that the climate could play a big part in how well different trees did after the fire. In the end, the study showed that more trees dying after a fire could mean fewer forests overall, regardless of how the climate changes.

These findings are a reminder of the tough challenges brought about by climate change and the more frequent, intense wildfires that are reshaping where new trees can grow and the local climate in fire-affected places.

UNM Biology Professor Matthew Hurteau, who was part of the study, says, "The climate has been changing, and it will keep changing, especially with how we use and take care of the land and our environment, places are now more prone to catching fire." This underscores the need to better understand how trees grow back so researchers can predict how forests will change and how they affect the environment and the benefits they provide.

Researchers used Center for Advanced Research Computing resources to run their simulations. This made it possible for them to run multiple replicate simulations due to the complexity of variables that they used to create the updated model in order to get the best results.

To improve future models for tree regrowth, researchers will need to do more tests with different types of trees in various places while looking at how topography might affect the data.

“This work is important because it helps us understand how these uncharacteristically large patches of tree-killing fires are going to reshape these ecosystems and how the species will respond to that,” says Hurteau.