Fuel Reduction Treatment Effects on Semiarid Woodland Ecohydrology

Mechanical fuel reduction projects are finding increasing use to reduce accumulation of biomass in dense forests, to reduce fire danger, and to improve forest health in wildland-urban interface areas. In many projects, biomass resulting from the thinning is chipped and applied as mulch to the treated area in an effort to promote reestablishment of herbaceous cover and as an efficient method of disposal. Changes in overstory composition coupled with the instantaneous introduction of a litter layer may dramatically alter the ecohydrology of these water-limited systems. However, the effects of various fuel reduction techniques on the ecology and hydrology of Southwestern woodlands are largely unknown. This paper presents results of an investigation of edaphic and vegetative responses to a fuel reduction project in piñon-juniper woodlands in central New Mexico. Using paired plots in mulched and un-mulched patches, the vegetation changes over one year following a thinning project were measured. Vegetative cover was not significantly impacted by mulch application at any layer. In addition, no significant differences were observed in herbaceous plant diversity and the relative cover of nonnative species was similar. However, a large increase in soil moisture under mulched patches indicated a considerable change in soil water content which may support additional plant biomass or potentially contribute to deep drainage beyond the root zone. Soil temperature was less variable and significantly lower, by as much as 20oC, under the wood mulch. Erosion from mulched patches, based on MSLE predictions, was approximately three times less than adjacent, un-mulched areas. Although there were no significant differences in initial vegetation response, the magnitude of observed differences in erosion, soil moisture and temperature patterns will likely affect vegetation patterns and local hydrology over time. Includes as Appendix 3: Technical release (United States. Soil Conservation Service. Engineering Division) ; no. 51 (rev. 2), Procedure for computing sheet and rill erosion on project area