Hierarchical relationships between plant species communities and their ecological constraints at multiple scales in an oak woodland/annual grassland system of the Sierra Nevada foothills, California

This study contributes to the determination of the hierarchical structure of oak woodland/annual grassland systems in the Sierra Nevada foothills of California. It quantified relationships between ecosystem measurement scale and: (1) plant community classification, (2) plant community- and species-environment relationships, and (3) the predictive capacity of environmental variables for species and communities in three watersheds at the University of California Sierra Foothill Research and Extension Center, Yuba County.; Differences were observed in species dominance, indicator species, and community distribution between watersheds. Overall compositional differences (Sörensen distances) between communities defined at different measurement scales were less important than differences in specific indicator species captured at different scales. Using a consistent cutoff eigenvalue of 0.23 for all classifications, four community types were identified at the 10-m measurement scale, and two were identified for each of the 35- and 55-m scales.; This study revealed three important conclusions relevant to multi-scale community-environment relationships: (1) species occurring within defined communities relate to environmental attributes at varying scales, (2) environmental attributes constrain species distributions at multiple scales, and (3) scale dependencies in species- and community-environment relationships confound efforts to “scale-up” results from small scale studies to larger scale applications.; For assessment or mapping of abundant species (e.g., LOMU), coarse or mid-scale attributes such as tree cover class, mid-scale percent slope or slope position appear to constrain distributions at any field plot scale, and may be adequate predictors for many applications. However, if information is desired on the constraints on small-scale plant communities that may contain species of concern (e.g., 10-m scale LOMU/TACA communities where the invasive TACA is most abundant), data on fine scale tree cover will provide the most powerful predictive capacity. (Abstract shortened by UMI.)...