Long-term effects of vegetation treatments in the Chaparral transition zone

Abstract

Since European settlement, the impacts of cattle production and wood harvesting in the West have affected the structure and transformed the composition of juniper-pinyon and chaparral. In the past, wildfires were more common in the juniper-pinyon and chaparral communities of the Southwest where they burned at intervals of 10-30 years. The regular occurrence of fire appears to have restricted the establishment of woody species to more shallow, rocky soils on which grasses do not thrive. The canopy cover and density of juniper-pinyon and chaparral can have a direct impact on the production of grasses and herbaceous plants. The removal of this canopy by various means has been implemented in many woody plant communities in an attempt to increase the production of herbaceous forage for livestock and habitat improvement for wildlife. The main objective of the application of original herbicide, fire, and mechanical push vegetation treatments (applied in 1964-1981) sampled in this study was to encourage the growth of herbaceous vegetation for cattle production. The disturbances caused by the treatments were intended to, at a minimum, set succession back to a grass/forb community, or ideally to shift the community towards a stable more permanent herbaceous community. The three range treatment techniques were undertaken to improve the potential for herbaceous species to effectively compete with larger woody species in an ecosystem affected by climatic and edaphic constraints, and impacted by livestock grazing. Tree abundance, dominance, and cover were to be limited on chosen sites. In 1997, we compared the effectiveness of herbicide, fire and mechanical push range treatment techniques decades after they were implemented. Long-term assessment is critical for both economic and ecological reasons. Economically, it is important to know how long "woodland conversion" range treatments last given the expense that can be incurred to implement them. Ecologically, it is important to monitor species diversity and abundance in post-treatment communities to evaluate the effects that different treatment methods have on biodiversity.