Summary1 Although drought frequency and severity are predicted to increase across numerous continental interiors, the consequences of these changes for dominant plants are largely unknown. Over the last decade, the south-western US has experienced six drought years, including the extreme droughts of 1996 and 2002, which led to widespread tree mortality across northern Arizona. 2 We examined the impact of these droughts on the co-dominant tree species of the pinyon-juniper woodland ( Pinus edulis and Juniperus monosperma ), a major vegetation type in the US. 3 Pinyon mortality following both droughts was 6.5-fold higher than juniper mortality. In addition, large pinyons suffered 2-6-fold greater mortality than small pinyons, a pattern associated with higher mortality of reproductively mature trees and survival of smaller pinyons resulting from facilitation by established vegetation. Differential mortality of large pinyons resulted in a vegetation shift such that the pinyon-juniper woodlands are becoming dominated by juniper, a species that is typical of lower elevations and more arid conditions. 4 Sites that experienced high pinyon mortality during the first drought suffered additional mortality during the second drought, so that reductions in tree densities and the resulting release from below-ground competition did not buffer surviving pinyons against additional mortality during the second drought. Such repeated mortality events also suggest that these stands may suffer chronic stress. 5 Reductions in biotic associations (e.g. avian seed dispersers, ectomycorrhizas and nurse plants) that will probably result from extreme mortality of large pinyons ensure that the observed vegetation shifts will be persistent. Because approximately 1000 species are associated with pinyon pine, the shift in the structure of these woodlands has large-scale community consequences.
Increased emphasis on community collaboration indicates the need for consensus regarding the definition of community within public health. This study examined whether members of diverse US communities described community in similar ways. To identify strategies to support community collaboration in HIV vaccine trials, qualitative interviews were conducted with 25 African Americans in Durham, NC; 26 gay men in San Francisco, Calif; 25 injection drug users in Philadelphia, Pa; and 42 HIV vaccine researchers across the United States. Verbatim responses to the question "What does the word community mean to you?" were analyzed. Cluster analysis was used to identify similarities in the way community was described. A common definition of community emerged as a group of people with diverse characteristics who are linked by social ties, share common perspectives, and engage in joint action in geographical locations or settings. The participants differed in the emphasis they placed on particular elements of the definition. Community was defined similarly but experienced differently by people with diverse backgrounds. These results parallel similar social science findings and confirm the viability of a common definition for participatory public health.
Rapid assessment projects are expanding in the arenas of public health policy, planning, and program development in both developing and developed nations. This article reviews the methodological advances that have changed rapid assessment from a primarily "quick and dirty" approach for data collection into a public health tool for time-sensitive development of changes in intervention strategies, community-based organizational structure, program evaluation, and policy decisions. The methodological design of the Rapid Assessment, Response, and Evaluation Project, adopted by the Office of HIV/AIDS Policy (U.S. Department of Health and Human Services) in 1999, is presented as a model for using revised rapid assessment approaches within the context of public health policy development.
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