Question: Does juniper invasion proceed through a series of pulse events, or is expansion a slow, steady process?
Question: How do grazing and climate affect rates and patterns of juniper establishment?
Question: How does Utah juniper expansion affect landscape structure in invaded grasslands?
Aerial view of Utah juniper woodlands near Baggs, Wyoming.
In this portion of the project, we are using a time series of aerial photography (1940s-Present) to generate GIS based land-cover maps tracking the expansion of Utah juniper at 4 sites in Wyoming (Fig. 1). While the exact dates for photography differ at each site, the land-cover maps will show expansion over roughly ten-year intervals. For each photograph, outlines of Utah juniper populations are traced onto Mylar sheets, scanned into an ARC/INFO (ESRI, Redlands, CA) GIS, and stored as polygon coverages. Once digitized, the polygons from each photograph are geo-rectified using a minimum of four control points per photograph. Polygons are then joined into seamless coverages and converted to a common projection and scale. The size, location, and shape of these populations will be compared through time using the FRAGSTATS (McGaragil and Marks 1995) spatial-pattern analysis program. In addition, we are harvesting junipers (for ring counts) and collecting plot-based data to complement the aerial photography at each site.