Recovery of soil properties, sagebrush steppe community structure, and environmental heterogeneity following drastic disturbance and reclamation

The objective of this research was to investigate vegetation and soil property structure in sagebrush steppe ecosystems as they recover from drastic disturbance, particularly in assessing the variability of properties across space. On reclaimed pipelines, I collected vegetation data and analyzed soil for organic carbon, total nitrogen, microbial community structure, moisture, salinity, and alkalinity. Using a Bayesian hierarchical mixed model, I quantified soil properties with posterior predictive distributions to compare reclaimed areas with the reference areas. The variance of most soil properties was affected by disturbance, and not always accompanied by a shift in the mean. Distributions for soil properties in reclaimed areas became more similar to those of undisturbed reference areas as recovery time increased. I then explored the differences in sampling designs, analysis, and inference gained from spatial and non-spatial soil data. I also conducted side-by-side analyses of each data type for a reclaimed area and an undisturbed area. The analysis of random data revealed differences in soil property averages between treatments. These differences were also apparent in the geostatistical analysis, which also provided information about the spatial structure in soil properties at the scale of individual plant effects (10 cm - 10 m). The third project expanded the assessment in both space and time, by including reclaimed pipelines that spanned 55 years, and by sampling at a scale up to 100 meters. I used Bayesian geostatistical models to quantify the correlation structure and to create surface predictions for measured properties. The reclaimed areas maintained uniform grass cover with low diversity and shrub establishment, while the responses of soil properties to disturbance and reclamation were variable. All three modeling approaches indicated that soil properties closely associated with vegetation experienced reduced variability and homogenization across space following disturbance. Soil abiotic properties appeared to be affected by the physical effects of disturbance, but were not associated with homogenization. Development of belowground heterogeneity was possibly delayed by the slow recovery of the plant community, particularly the shrub component. This research illustrates some long lasting ecological consequences of disturbance in sagebrush steppe and emphasizes the need for establishing shrubs in reclaimed sagebrush steppe.