Factors controlling long-term community development of a sagebrush steppe ecosystem
Date
2010
Authors
Hoelzle, Timothy Brian, author
Paschke, Mark W., advisor
McLendon, Terry, committee member
Redente, Edward F., committee member
Stark, John M., committee member
Stromberger, Mary E., committee member
Journal Title
Journal ISSN
Volume Title
Abstract
A study was established in 1984 in the Piceance Basin of northwest Colorado to examine how nutrient availability, soil organisms, and seed availability affect plant and microbial community development following disturbance. Initial results showed that increased nitrogen (N) availability and removal of soil organism limited plant community recovery, while decreased N availability and seeding with late seral species accelerated community development. Nutrient addition and immobilization treatments continued through 1999. Here, I examined how these treatments affected plant and microbial community composition 25 years after the initial disturbance. Supporting earlier findings, repeated N addition limited plant community succession, while phosphorus (P) addition had little effect. However, addition of N and P together worked synergistically to further retard successional recovery through the promotion of the invasive winter annual, Bromus tectorum L. Although nutrient additions resulted in differences in the rate of ecosystem development, few differences were observed in microbial biomass and composition, indicating that these treatments did not strongly affect these communities. Initial results showed that the rate of plant community development was accelerated by N immobilization through the addition of sucrose; however, I found that plant community composition was similar between these communities and those receiving N, indicating convergence in successional trajectories ten years after the cessation of treatments. Soil fungi, which often increase with community development, were higher in plots receiving the sucrose amendment. This suggests that, even though differences in successional development of the plant community were not found, succession in the belowground system was accelerated through sucrose additions. Although removal of soil organisms by fumigation initially slowed plant ecosystem recovery, these differences were no longer apparent 25 years later, illustrating that plant and microbial communities can recover from this type of disturbance. However, differences in successional trajectories were observed as a result of seed mix. Seeding with early seral species resulted in a community with significantly more exotic species and mid seral shrubs, while seeding with late seral species resulted in a community dominated by perennial grasses. This suggests that seed mix can alter successional trajectory, providing long-term evidence for the role of priority effects in community development.