Recharging the soil moisture battery

Photo Credit

USDA Forest Service Photo by Jackson Leonard

The above photo shows the recovery of vegetation over 15 years after the Dude Fire, which burned in 1990. Woody shrub species and weeping lovegrass grew to dominate within the burned area (foreground) which had previously been made up of mostly ponderosa pine and alligator juniper (background). Recent efforts to masticate the dense shrub stands has resulted in greater soil moisture availability throughout the year, helping speed the recovery of ponderosa pine. 

The Rocky Mountain Research Station is teaming up with Northern Arizona University and the Agricultural Research Service, in collaboration with the Tonto National Forest and the Salt River Project, a major utility provider in Arizona, to study the potential benefits to forest health and water security in the Southwest from landscape scale forest restoration treatments. It is one of the first studies of its kind in the region to leverage satellite-based, evapotranspiration data from a forested ecosystem, to look at the potential ecological and hydrologic benefits of shrub mastication treatments being conducted to reduce fire risk and speed ponderosa pine recovery.

Backstory: In 1990, the Dude Fire occurred in central Arizona, which was one of the first in a long line of high-severity, landscape scale wildfire events to impact at the southwest region. Following the fire, deep-rooted shrub species and non-native grass species came to dominate the burned area, which is similar to the recovery of other much larger wildfire events that have occurred since the Dude Fire. This has slowed the recovery of more desirable conifer species and increased the wildfire risk to nearby communities.

To address these concerns, the Tonto National Forest, with funding support from the Salt River Project, decided to conduct a series of shrub mastication treatments across the area to reduce fire risk and speed forest recovery, which has continued to lag nearly 35 years after the fire.

Early results from the study suggest that the reduction in evapotranspiration from the removal of less desirable shrub species increases soil moisture for several weeks into the dry season, when compared with nearby untreated areas. Further, these differences can be accurately calculated using remote sensing techniques, allowing for landscape scale estimates of the effects of similar treatments in the region. The increase in soil moisture availability and reduction in competition from nearby shrub species is already visibly accelerating the growth of reestablishing ponderosa pine trees within the burn scar. Future objectives of this study will look at the relationship of increased soil moisture and the flow of nearby, perennial headwater streams, as well as the potential for increasing fuel moisture levels longer into the summer season, decreasing wildfire risk. This information will undoubtably help land managers and major water utilities better understand the potential cost benefits to hydrology, wildfire risk, and forest health from current and future treatment efforts.