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Repeat photography samples were used to analyze how the structure and site-specific distribution of forests may or may not have changed during the past century in the San Juan Mountains, Colorado. Systematic evaluation of 146 photosets was combined with field observations to identify trends in vegetation change. Both conifers and deciduous trees (e.g., aspen) have increased in extent. Forest recovery from large disturbances that occurred during Euro-American settlement contributed substantially to this increase. Trees also encroached into grass/shrublands, but less than half of photosets show tree invasion, and invasion is more common in small grass/shrubland openings interspersed with forest than in large openings....
Piñon–juniper is a major vegetation type in western North America. Effective management of these ecosystems has been hindered by inadequate understanding of 1) the variability in ecosystem structure and ecological processes that exists among the diverse combinations of piñons, junipers, and associated shrubs, herbs, and soil organisms; 2) the prehistoric and historic disturbance regimes; and 3) the mechanisms driving changes in vegetation structure and composition during the past 150 yr. This article summarizes what we know (and don't know) about three fundamentally different kinds of piñon–juniper vegetation. Persistent woodlands are found where local soils, climate, and disturbance regimes are favorable...