Linking climate change and community dynamics: Pinyon pine stability and sensitivity in a heterogeneous landscape

The advent of anthropogenic climate change makes understanding the relationships between climate and communities of critical importance. Yet, little has been done to model the response of communities to climate. Here I show that the links between these variables are tractable within the pinyon-juniper woodlands of the southwest.; First, I establish the relationship between topography and the relative drought risk for pinyons. Analyses of sites which experienced high rates of pinyon mortality during the 1996 drought shows regions with steep slopes, southwestern aspects, and mid-to-high elevations are at greatest risk for pinyon mortality. Because each of these variables demonstrated a strong relationship with spatial patterns of tree death, I was able to use these parameters in a geographic information system to build a model of the expected spatial patterns of high pinyon mortality across a topographically heterogeneous landscape. The model correctly intersects areas of observed high mortality with a 75% accuracy level.; Second, I examine the relationship between the level of water stress experienced by pinyon pine, and the associated canopy arthropod community. Parametric analyses show that both mean per-tree abundance and richness, across herbivores, predators, and parasites is reduced on trees growing under high stress. I also show that although species richness and abundance are reduced on high stress trees, this community is not simply a subset of the low stress community, but represents a different community composition.; Finally, I show that the parametric analyses used in the previous section are inadequate for scaling efforts, and propose a new method based on integrating Species Accumulation Function (SAF), termed the Integrated Accumulation Function (IAF). Community analysis by this method suggests three major patterns; first, that landscape level patterns of maximum species richness are provided by large landscapes in which most of the landscape is experiencing high stress. Second, that large landscapes are resilient to changes in arthropod species richness across broad ranges of landscape stress. And finally, although this system shows resilience, at the extremes of stress (either low or high), the community experiences threshold events beyond which arthropod species are lost at extreme rates.