Consequences of fuel load management on erosional processes in pinyon-juniper systems

Background/Question/Methods

Over the past decade, millions of acres of fuels reduction treatments have been implemented across a range of western U.S. forest types, with the goal to reduce the risk of catastrophic fire while restoring forest and rangelands to their historical structure, function and diversity. While there are clear benefits associated with reducing hazardous fuel loads by decreasing the risk of catastrophic fire to people and ecosystems, there is a need to understand the potential risks of fuels reduction activities.  Soil surface disturbance and subsequent soil erosion is of concern, particularly for less resilient, lower elevation semi-arid ecosystems.  In these systems, biological soil crust communities are critically important for the stability and functioning of the soil system, but are highly susceptible to soil surface disturbance with significant recovery times. In this study, we measured wind and water erosion with wind aspirated dust samplers (BSNEs) and 1 m silt fences in 1 common mechanical and two prescribed fire fuels reduction treatments in piñon-juniper woodland ecosystems of Southeastern Utah.  

Results/Conclusions

Prescribed fire was shown to result in a 11-32 fold increase in wind borne sediment transport as compared to the untreated control and masticated sites the first two growing seasons after treatment. Transport of wind-borne material appeared to peak in the first growing season after treatment and declined thereafter. A similar pattern was observed in soils captured by silt fences. The prescribed fire treatments resulted in 20-40 fold higher sediment accumulation in silt fences relative to the control and masticated treatments after two growing seasons. Soil accumulation within the silt fences appeared to decline as vegetation cover increased during the spring and summer months and increased again during the fall (October). Our results suggest that the use of prescribed fire may result in significant soil loss in the year immediately following treatment, whereas mastication strategies that provide a protective mulch layer and less overall soil surface disturbance had similar soil losses to the untreated control site.  Increases in soil erosion with prescribed fire were likely due to significant declines in soil surface stability and biological soil crust cover.  Taken together, our results suggest that mastication should be the preferred fuels reduction method when there are concerns related to soil and site stability.