New research from the University of California, Davis, sheds light on when and where to plant tree seedlings to help restore forests after high-severity wildfires…and the research involves lots and lots of shrubs.
The paper, published in the Forest Ecology and Management journal, concludes that in hotter, drier areas where natural regeneration is weaker, well-timed tree planting can boost recovery by up to 200%. However, the outcome also depends on competition with shrubs.
“Generally, where there are more shrubs, the climate and soil are more hospitable for plant growth,” according to lead author and assistant professional researcher Derek Young. “But that also means there’s more competition for trees.”
In areas with many shrubs, it’s best to plant seedlings within a year of a wildfire to avoid competition from these woody plants. In areas with fewer shrubs, planting three years after a fire would be more effective because some of these woody plants would have grown back, but not so many to consume available nutrients and water: “Some vegetation in those really harsh sites might actually facilitate tree establishment by providing shade,” Young said.
Understanding how to foster recovery is critical to restoration efforts as climate change intensifies the frequency and severity of forest fires. According to Andrew Latimer, senior author of the paper and a professor in the Department of Plant Sciences, land managers must also use data to help direct limited resources.
“We’re aiming to help optimize tree planting by targeting it to where it’s needed,” Latimer said. “Doing this matters because we’re facing a reforestation backlog – limited capacity to replant and a lot of severely burned area.”
Researchers surveyed areas in the Sierra Nevada that were representative of a mix of climates and management strategies in California and had been replanted with conifer tree seedlings one to three years after intense wildfires. The team counted seedlings, shrub cover and other environmental details in the five 400-square-meter circular plots, including replanted and nonplanted areas.
This allowed researchers to gauge how replanting affects forest composition and map out the best strategies across vast swaths of land that would be challenging to survey on foot: “I think the real benefit is making those predictions across a huge landscape,” Young said. “Now we have quantified the effects of certain environmental variables that allow us to make those maps.”
Latimer is experimenting to see how removing shrubs two years after a fire affects tree regeneration. Young will soon use aerial imagery and drones at wildfire sites to determine how management actions affected forests in the 40 years since the trees burned.
- This article has been republished in parts from an article on the University of California, Davis website. To read the complete study, click here.
