Restoring Degraded Drylands – An Exploration of the Biotic and Abiotic Factors That Support Desirable Plant Communities

Abstract

With ecological restoration, land managers seek to reestablish desirable ecosystem processes andservices to degraded landscapes, commonly by adding plants. The outcome of restoration practices is not solely determined by the methods; rather, the outcome is dependent on a web of interacting ecosystem factors. This dissertation explores some of the biotic and abiotic factors that influence plant survival and thus restoration outcomes in the drylands of Southern Arizona. In the first section, I investigate the management, ecology, and competitive interactions of buffelgrass (Pennisetum ciliare; an invasive, drought tolerant bunchgrass) with a) a review of treatment methods and b) a greenhouse competition experiment. I found buffelgrass to be highly competitive against native grasses due to its plasticity, where it can create self-reinforcing feedback loops through its use of resources. Buffelgrass was found to require multiple treatment strategies used in tandem to increase treatment efficacy. Fortunately, my results also show that active restoration through seeding native drought tolerant species after buffelgrass treatment shows potential to suppress buffelgrass regrowth. In the second section, I examine how soil and precipitation interact with restoration practices to determine vegetation communities on a disturbed pipeline corridor. Five years after the pipeline was restored, I found that the seeded and unseeded plant communities converged in terms of plant cover, species richness, and functional groups (but not species). Additionally, I found that the soil treatment/manipulation and soil organisms had major implications for the plant communities, regardless of seeding practices. I hope that this research helps inform restoration solutions that incorporate the complexities, feedbacks, and non-linearities of dryland ecosystems.