Hydrologic and Vegetal Responses to Fuelwood Harvest and Slash Disposal in a Pinyon Pine and Juniper Dominated Grassland
Woodlands dominated by pinyon pine (Pinusspp.) and juniper (Juniperusspp.) species have expanded both in aerial extent and density during the last century and now occupy 8 to 12 million hectares in the western United States. Accelerated erosion has been observed in many of these former grass and shrublands that are now dominated by pinyon pine and junipers. The objective of this research project was to determine the effects of fuelwood harvesting and slash disposal of a pinyon pine and juniper woodland on understory plant responses, runoff, sediment concentration, and bedload. Five plots (25 x 12 meters) were located in each of four blocks and contained runoff subplots, which were 21.1 x 3.6 meters with a drop box, flume, and sediment sampler at the bottom. Calibration was conducted during 1988. Treatments were applied in 1989 and 1991. Vegetation responses, runoff, sediment concentration, and bedload were measured each monsoon season through 1999 for a total of 10 years. The treatments included: (1) four plots not clearcut (control plots), (2) four plots clearcut and slash completely removed in June 1989, (3) four plots clearcut with slash uniformly scattered in June 1989, (4) four plots clearcut with slash uniformly scattered in June 1989 and burned on October 31, 1989, and (5) four plots clearcut with slash uniformly scattered in June 1989 and burned on November 7, 1991.
The least amounts of runoff and erosion were from (1) plots that were clearcut and had the slash removed in June 1989, (2) plots that were clearcut with the slash homogenously scattered on the plots in June 1989, and (3) plots that were clearcut with the slash homogenously scattered on the plots in June 1989 and burned in November 1991. The slash scatter with no burn treatmentiv started protecting the site immediately after clearcutting. Removing the slash after clearcutting left the plots temporarily exposed, which resulted in high levels of runoff and erosion for a couple of years. However, results during subsequent years were similar to clearcutting with scattered slash.