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Historical and modern distrubance regimes, strand structures, and landscape dynamics in pinon-juniper vegetation of the western United States

Permanent URL:
http://handle.nal.usda.gov/10113/58435
File:
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Abstract:
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 for piñon, juniper, or a mix of both; fires have always been infrequent in these woodlands. Piñon–juniper savannas are found where local soils and climate are suitable for both trees and grasses; it is logical that low-severity fires may have maintained low tree densities before disruption of fire regimes following Euro-American settlement, but information is insufficient to support any confident statements about historical disturbance regimes in these savannas. Wooded shrublands are found where local soils and climate support a shrub community, but trees can increase during moist climatic conditions and periods without disturbance and decrease during droughts and following disturbance. Dramatic increases in tree density have occurred in portions of all three types of piñon–juniper vegetation, although equally dramatic mortality events have also occurred in some areas. The potential mechanisms driving increases in tree density—such as recovery from past disturbance, natural range expansion, livestock grazing, fire exclusion, climatic variability, and CO2 fertilization—generally have not received enough empirical or experimental investigation to predict which is most important in any given location. The intent of this synthesis is 1) to provide a source of information for managers and policy makers; and 2) to stimulate researchers to address the most important unanswered questions.
Author(s):
William H. Romme , Craig D. Allen , John D. Bailey , William L. Baker , Brandon T. Bestelmeyer , Peter M. Brown , Karen S. Eisenhart , M. Lisa Floyd , David W. Huffman , Brian F. Jacobs , Richard F. Miller , Esteban H. Muldavin , Thomas W. Swetnam , Robin J. Tausch
Subject(s):
Juniperus , carbon dioxide , climatic factors , drought , ecosystems , fire regime , fires , grasses , grazing , habitat destruction , herbs , issues and policy , livestock , managers , mortality , pinyon-juniper , plant density , researchers , savannas , shrublands , shrubs , soil , trees , vegetation structure , wet environmental conditions , woodlands , Western United States
Source:
Rangeland ecology & management 2009 v.62 no.3
Language:
English
Year:
2009
Collection:
Journal Articles, USDA Authors, Peer-Reviewed
Rights:
Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted.