Local and regional expansion of native species due to migration, climate change or land use offer additional opportunities to study patterns and effects of invasion. Ongoing, natural invasions provide model systems to forecast biotic movements and consequences as climate and land use change in the future. This grant will use paleoecological and ecological methods to study the ongoing invasion of Utah juniper (Juniperus osteosperma) in central and eastern Wyoming and adjacent Montana, initiated when Utah juniper crossed the Rocky Mountains and the Continental Divide during the late Holocene. This invasion can be showcased as a model system for addressing central issues about natural invasions because: (1) it is ongoing and has been proceeding for at least 2000 years, long enough to encompass both long and short-distance dispersal events as well as population infilling at older sites; (2) it can be documented at unprecedented spatiotemporal resolution using fossil woodrat-middens, tree-ring based demographic analyses, and both ground and aerial repeat photography; (3) it has the potential to generate important hypotheses as well as provide diverse opportunities to study population dynamics, genetic consequences, and ecosystem effects across a chronosequence of sites representing different stages of invasion, and (4) it underscores the value of historical evidence in reexamining current paradigms about tree invasions in rangelands.
