Collaborative Research: Scale-dependent processes as the drivers for understanding range- and niche-expansion in a widespread native species

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Eastern Red Cedar (Juniperus virginiana) is native to the eastern United States, where this attractive tree has been a popular choice for landscaping. But out in the Great Plains, Red Cedar is known as the "green glacier", because this slow-growing species is taking over once-productive grasslands. Ranchers face substantial economic costs in removing Red Cedar from grazing lands, and it reduces grassland biodiversity through competition with native species. But how do you stop a "green glacier"? Populations might be expanding because environmental variability has altered frost and drought regimes, or because humans have implemented prairie management practices such as fire suppression, or even because of changes in the migration patterns of seed-dispersing birds. It is more likely, however, that many factors are at work. For example, environmental variability might allow plants to move into a new region, but seed dispersal by birds could promote population expansion within a region. Rather than focus on one factor, this study will determine the relative importance of several causal factors. Data from experiments will be used in a model that predicts the rate and locations where Red Cedar range expansion is likely to occur. Findings will be presented to the public at the Holden Arboretum Scientist Lecture Series and incorporated into Holden Arboretum's "Working with Nature" K-12 Camp and "Tree Corp" adult workforce development program. Uncovering scale-dependent mechanisms controlling range and niche expansion of plants is a key issue in biodiversity research. This work integrates physiological and ecological processes across scales to determine the potential for further range expansion. The central hypothesis is that, at a large spatial scale, changes in prairie management are more important than physiological climate tolerance for promoting range expansion, while at smaller scales, biotic factors such as avian dispersal, competition and facilitation are more important. The spatial scale of variation will be determined using microsatellites in historical, encroaching and niche expanding populations. The effects of fire will be examined using long-term data from the Konza Prairie NSF-LTER, while manipulative and field experiments will determine how the interaction of frost and drought impact Red Cedar performance. Seed dispersal by birds and changes in bird migration over time will be examined to determine how far, and where, birds disseminate Red Cedar. Empirical data will be integrated into a spatially explicit population-level age/stage matrix model, based on inputs from structural equation modeling at all three spatial scales, with spatial resolution determined by the results of microsatellite studies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.