Fractally Sampling Diversity-Environment Relationships to Understand Plant Assemblage Health Across Spatial Scales

Humans influence the health of ecosystems and rely on healthy ecosystems to support their livelihoods and well-being. By looking at how the parts of ecosystems interact we can understand and improve ecosystem health. Ecosystem interactions change across spatial scales or different size patches of area. For example, individual organisms interact with each other at small spatial scales, while at large spatial scales, communities of organisms interact with weather conditions. However, many research studies do not look at how ecosystem interactions change across spatial scales. To address this gap in ecological research, I use a fractal sampling design which samples at the vertices of equilateral triangles nested within each other. This design allows me to investigate how spatial scale influences the relationship between plant communities and the environments they live in. I tested this design in northeast Utah rangeland where the vegetation changes depending on whether a hill faces south (more shrubs and grasses) or north (more conifer trees). In the first chapter, I look at how plant biodiversity metrics based on the tree of life (phylogenetic diversity) change across terrain and spatial scale. This analysis identifies which spatial scales influence the relationship between diversity and environment at the fieldsite. In the second chapter, I assess how the characteristics that plants have adapted to survive and thrive (functional diversity) change in response to soil temperature and water dynamics. This chapter describes the potential for plants to respond to changing conditions in the future. In the third chapter, I look at diversity-environment relationships across a larger landscape to address rangeland management concerns about an increase in undesirable species and bare ground. Overall, both phylogenetic and functional diversity changed across south- to north-facing hills. In contrast to north-facing hills, the soil temperature on south-facing hills was hotter and more variable. Plant communities on south-facing hills were more closely related, shorter, and better adapted to survive with fewer resources, like water, and had more similar features than on north-facing hills. These communities might struggle to survive if this area becomes hotter for the following contrasting reasons. On south-facing hills, plant communities may not have enough difference in features to respond to more stressful conditions, but on north-facing hills, communities may not adapt to fewer resources quickly enough. In the context of range management, the amount of undesirable species and bare ground should be prioritized as a concern. Additional monitoring at relatively small spatial scales may help guide management actions. Maintaining different types of healthy vegetation and increasing the number of species in each vegetation type will help achieve the goal of decreasing undesirable species and bare ground. Overall, a fractal sampling design effectively assessed how plant diversity—both phylogenetic and functional—changed in different environmental and management conditions and identified when spatial scale influenced ecological interactions and ecosystem health