Spatial and temporal patterns of changes in protected areas across the Southwestern United States

Protected areas are the core units for preserving habitats and ecological processes. Yet in most regions of the world their geographic, categorical, and institutional evolution remains poorly understood. Here, we report on changes in protected areas in the Southwestern US from 1890 to 2005. Our analysis used the dates of protection of individual parcels in the region to analyze changes by: (a) designating authority (e.g., congressional, administrative), (b) managing agency, (c) protected area types (e.g., wilderness), (d) elevation, (e) ecoregion, and (f) land cover class. In the 1990s, protected area additions tripled compared with the previous decade. Bureau of Land Management (BLM) managed the most protected area after 1990, surpassing that of the US Forest Service. Prior to 1990, most protected areas were found at high elevations, but more recent additions occurred at lower elevations. Land cover types represented in protected areas changed significantly over the last century, with protected areas in forest and woodland systems added prior to 1930 and shrubland, steppe, and savanna systems added after 1980. Additions by BLM occurred mostly by administrative designation. These areas are not permanently protected and so do not provide the level of protection afforded other additions. However these additions are critical for conservation of biodiversity across the region because they occur at elevations and in ecoregions and land cover types that are minimally protected otherwise. Our analysis yielded new insights about permanency, level of protection, and spatial distribution of protected areas, characteristics critical for biodiversity conservation.