Consequences of piñon-juniper woodland fuel reduction: Prescribed fire increases soil erosion while mastication does not

Authors: KARBAN, CLAIRE - University Of Colorado; MILLER, MARK - National Park Service; Herrick, Jeffrey - Jeff; BARGER, NICHOLE - University Of Colorado

Submitted to: Ecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2021
Publication Date: 5/7/2021
Citation: Karban, C., Miller, M., Herrick, J.E., Barger, N. 2021. Consequences of piñon-juniper woodland fuel reduction: Prescribed fire increases soil erosion while mastication does not. Ecosystems. 25:122-135. https://doi.org/10.1007/s10021-021-00644-6.
DOI: https://doi.org/10.1007/s10021-021-00644-6

Interpretive Summary: Fuel reduction treatments are widely used to reduce the risk of wildfires throughout the world. In savanna ecosystems where woody vegetation has increased, they can also promote increased herbaceous production, which can both reduce soil erosion and provide more forage for livestock and wildlife. However, some of these treatments can increase bare ground which may increase soil erosion. There are very few studies quantitatively evaluating these potential impacts. In this study, we examined the effects of common fuel reduction strategies (mechanical mastication and two techniques for prescribed burning) on wind and water erosion in upland piñon -juniper woodlands in southeast Utah. We also tested the impact of broadcast seeding coupled with fuel reduction as a way to mitigate erosional soil loss. We found that fuel reduction strategies had significant effects on erosional losses, while seeding did not. Both techniques for prescribed burning – pile burning and broadcast burning - increased wind-related sediment fluxes by an average of 11-fold and 58-fold, respectively, over our 2-year study period. Mechanical mastication did not increase wind-related losses over untreated controls. Erosional fluxes measured at silt fences, that capture water-driven erosion but trapped wind-borne sediments as well, followed similar trends with moderate increases from pile burning (5-fold on average) but larger increases from broadcast burning (17-fold on average) over the 2-year study period. In contrast, seeding of native species did not have any effect on either wind or water erosion rates.

Technical Abstract: Fire suppression and exclusion practices have altered forests and woodlands and increased the risk of catastrophic fires across large expanses of the Western United States. In an effort to reduce fuel loads and restore historical forest structure, function, and diversity, land managers have implemented fuel reduction treatments on millions of acres across the U.S. Reducing fuel loads protects people, structures, and in some cases, improves ecosystem health. However, the ecological risks of soil surface disturbance related to fuel reduction strategies, and subsequent soil erosion in lower elevation semi-arid woodlands, may be significant. In this study, we examined the effects of common fuel reduction strategies (mechanical mastication and two techniques for prescribed burning) on wind and water erosion in upland piñon -juniper woodlands in southeast Utah. We also tested the impact of broadcast seeding coupled with fuel reduction as a way to mitigate erosional soil loss. Finally, we used plant, tree, and soil cover variables that correlate with erosion to develop land management cover thresholds to prevent significant soil loss following fuels treatments. We found that fuel reduction strategies had significant effects on erosional losses, while seeding did not. Both techniques for prescribed burning – pile burning and broadcast burning - increased wind-related sediment fluxes by an average of 11-fold and 58-fold, respectively, over our 2-year study period. Mechanical mastication did not increase wind-related losses over untreated controls. Erosional fluxes measured at silt fences, that capture water-driven erosion but trapped wind-borne sediments as well, followed similar trends with moderate increases from pile burning (5-fold on average) but larger increases from broadcast burning (17-fold on average) over the 2-year study period. In contrast, seeding of native species did not have any effect on either wind or water erosion rates. Our results provide evidence that fuel reduction strategies can have large impacts on wind and water erosion in upland piñon-juniper woodlands. When soil erosion is of concern, mastication is the preferred fuels management technique over prescribed burning in semi-arid upland piñon-juniper woodlands.