Journal Article

Differential tree mortality in response to severe drought: evidence for long-term vegetation shifts

Scudder, C.M, Porter, M.E, Mueller, R.C, Trotter, R.T. III, Whitham, T.G, Gehring, C.A

2005

Overview

1. 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.

• Publisher: British Ecological Society,Blackwell Science Ltd,Blackwell Science,Blackwell Publishing Ltd
• Subject: altitude / Animal and plant ecology / Animal, plant and microbial ecology / Applied ecology / Arizona / Biological and medical sciences / botanical composition / Climate change / differential mortality / Dominant species / Drought / drought tolerance / Ecology / Ecosystems / Ecotoxicology, biological effects of pollution / facilitation / forest communities / forest trees / Fundamental and applied biological sciences. Psychology / General aspects / Human ecology / Juniperus monosperma / Mortality / Pinus edulis / plant competition / Plant ecology / Plants / Seedlings / stand density / Survival analysis / tree age / tree mortality / Trees / Vegetation / Vegetation mapping / water stress / Woodlands