Process-based management of downy brome in salt desert shrublands: assessing pre- and post- rehabilitation soil and vegetation attributes
Hirsch, M. C.. 2011. M.S. thesis. Utah State Universityμ
Abstract
As an ecosystem driver, downy brome (Bromus tectorumL.) presents obstacles to
land rehabilitation efforts, including restoring desirable species cover. Because damaged
ecosystems may have crossed both abiotic and biotic thresholds, ecologically-based
control strategies may assist with altering successional trajectories and restoring desirable
plant species. My thesis research had three objectives: 1) assess soil and vegetation
relationships in degraded salt desert ecosystems prior to implementing downy brome
control treatments, 2) determine the effects of control treatments on soil properties and
resident plant species, and 3) evaluate the relative importance of shrubland soil type,
herbicide type, and herbicide rate on seedling germination, growth, and establishment of
perennial grasses and downy brome in a greenhouse experiment.
Two salt desert shrubland sites in Box Elder County, Utah were chosen for
objectives 1 and 2. Objective 1 evaluated the relationships between downy brome, soil
water, water infiltration, pH, electrical conductivity, sand, nitrate, phosphate, potassium,
and magnesium using principal components analysis (PCA), factor analysis, and Pearson
product-moment correlation coefficients. Objective 2 determined the effectsof burning,
herbicide, and mowing on downy brome, litter, bare ground, soil water, nitrate, carbon,
phosphate, and magnesium using analysis of variance (ANOVA) and Wilcoxon sign rank
tests. Objective 3 evaluated the effects of rimsulfuron and imazapic on emergence and
growth of downy brome and two revegetation grass species using ANOVA.
For objective 1, I observed negative correlations between downy brome
abundance and soil nitrate and water content which suggests that downy brome
abundance is significantly impacting the content of these two soil properties. Objective 2
data indicate that control treatments significantly impacted downy brome abundance, soil
resource availability, and resource fluctuation, which implies that downy brome can be
reduced by control treatments, that its control can increase the availability of soil
resources like nitrate and water, and can stabilize soil resource fluctuations. The results
for objective 3 illustrate the importance of shrubland soil properties when using
herbicides to reduce annual grasses and show that organic matter content and pH can
significantly impact the relative performance of herbicides. Collectively this research
helps identify the impacts on soil properties when using process-based management
practices that reduce downy brome abundance.
