Linking recruitment and population dynamics to tree range dynamics in the Rocky Mountains
Range dynamics ultimately arise from variation in demographic rates of species, and this variation may result from individual and species-specific responses to abiotic and biotic conditions. Mechanistically linking individual and population-level variation with broad-scale occurrence patterns presents complex theoretical and practical challenges, particularly for long-lived organisms such as trees which may show substantially lagged responses to environmental change. Early tree life stages (i.e. seedlings) integrate responses to recent environmental conditions and play a key role in regulating species persistence and migration through establishment and mortality patterns. We are examining the factors and processes that regulate the range dynamics of five dominant Rocky Mountain conifer species by evaluating dynamics and patterns of seedlings at the individual, population, community and range levels. We are integrating these processes and patterns through a unique hierarchical metamodeling framework that produces inference at the level of the species range. We are applying this approach to (1) relate variation in vital rates, biotic interactions, and local environmental conditions to seedling population dynamics, (2) relate patterns of seedling occurrence to broad-scale climate gradients, (3) quantify the impacts of ecological processes on seedling distributions, (4) characterize seedling niches, and (5) use seedling ranges and underlying processes to generate informed predictions of tree species ranges under a variety of simulated climate and disturbance scenarios.
*This study is in collaboration with Dr. Patrick Martin and Jeff Carroll at Colorado State University and Dr. Matt Talluto at Laboratoire d'Ecologie Alpine, CNRS, France
The relative contributions of climate and interspecific biotic interactions to tree species distribution patterns in the Rocky Mountains
Species distributions are hypothesized to be shaped by a variety of factors acting across multiple spatial scales. The role of biotic interactions has been particularly emphasized, but scale-dependencies in ecological factors have hampered comparisons of the relative effects of biotic interactions and climate on species distributions. In this research, we are using a Bayesian Joint Species Distribution Model (JSDM) to simultaneously model the co-occurrence patterns of ten dominant tree species across the US Rocky Mountains. The JSDM approach allows us to attribute species co-occurrence patterns to either environmental responses or potential interspecific biotic interactions. Our current results demonstrate that shared environmental responses can largely explain the co-occurrence patterns of Rocky Mountain tree species, with little to no importance of biotic interactions evident from our analysis. However, variation in model performance across species indicates that alternative factors not considered in the JSDM may contribute to distribution patterns, particularly among lower elevation tree species.
*This study is in collaboration with David Bell, USFS Pacific Northwest Research Station