Vegetation in seven post-fire rehabilitation seedings from 2005 were monitored in the Vale district of the Bureau of Land Management in eastern Oregon. Setting initial quantitative objectives for arid lands in sagebrush ecosystems can be difficult since little information on previous rehabilitations is known. At these treatments, initial objectives were established using suggested target densities from other ecosystems with more mesic climates. Our goal was to evaluate these initial objectives and to identify reasonable target densities for future projects. We used a standardized monitoring procedure to enable comparison among similar projects with similar objectives. The monitoring procedure used typical design elements: Objectives, stratification, random plot location, control plots, and statistical analysis. Quantitative field methods included line-point intercept (cover), density, and basal gap intercept collected at multiple treatment and control plots. Plots were randomly established in defined monitoring units (ecological sites and common treatments) to explicitly identify the area of inference and enable direct measurement of the treatment effect.
Results/Conclusions
Preliminary results suggest the following: There was a low level of plant establishment for all seedings by 2008, ranging from 0.09 to 1.74 plants/m2. The primary reason for low densities was unfavorable timing and amount of precipitation in the 2007-2008 growing season. We found that measurements of density within the first 3 years provided the best estimate of initial seeding success. Increases in cover due to the seeding were not detectable in the first three years due to high variation in cover estimates. While cover of seeded species was not a good indication of seeding success, it was useful for identifying patterns common among multiple treatments. At all treatments, cover of annual grasses, primarily Bromus tectorum, increased from 2006 to 2007 and decreased slightly in 2008. There was also a rapid increase in litter cover and a corresponding decrease in bare ground from 2006 to 2008. When plots were combined among treatments, there was a consistent, negative linear relationship between cover of existing perennial grasses and cover of annual grasses, and a consistent positive relationship between percentage of transects occupied by large gaps (> 200 cm) in basal cover and cover and density of annual grasses. These initial findings suggest that correlating seedling establishment with site factors (such as soil, elevation, and climate) using standard monitoring protocols will aid efforts to set realistic objectives and improve seeding success through adaptive management.
