Regional vegetation die-off in response to global-change-type drought. Proc Natl Acad Sci USA

School of Natural Resources, Institute for the Study of Planet Earth, and Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721-0043, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 11/2005; 102(42):15144-8. DOI: 10.1073/pnas.0505734102
Source: PubMed


Future drought is projected to occur under warmer temperature conditions as climate change progresses, referred to here as global-change-type drought, yet quantitative assessments of the triggers and potential extent of drought-induced vegetation die-off remain pivotal uncertainties in assessing climate-change impacts. Of particular concern is regional-scale mortality of overstory trees, which rapidly alters ecosystem type, associated ecosystem properties, and land surface conditions for decades. Here, we quantify regional-scale vegetation die-off across southwestern North American woodlands in 2002-2003 in response to drought and associated bark beetle infestations. At an intensively studied site within the region, we quantified that after 15 months of depleted soil water content, >90% of the dominant, overstory tree species (Pinus edulis, a piñon) died. The die-off was reflected in changes in a remotely sensed index of vegetation greenness (Normalized Difference Vegetation Index), not only at the intensively studied site but also across the region, extending over 12,000 km2 or more; aerial and field surveys confirmed the general extent of the die-off. Notably, the recent drought was warmer than the previous subcontinental drought of the 1950s. The limited, available observations suggest that die-off from the recent drought was more extensive than that from the previous drought, extending into wetter sites within the tree species' distribution. Our results quantify a trigger leading to rapid, drought-induced die-off of overstory woody plants at subcontinental scale and highlight the potential for such die-off to be more severe and extensive for future global-change-type drought under warmer conditions.

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    • "We measure species variation in facilitation in a post-drought community in the Colorado Desert in southeastern California using field and greenhouse experiments. Between 1999 and 2004, this region experienced exceptional drought conditions (Breshears et al., 2005), resulting in 64% adult shrub mortality (Miriti, 2007). Subsequent reestablishment of species has been slow to nonexistent such that no seedlings have been documented since 2004 (personal observation, Miriti lab) even after years of above average precipitation (2005, 2010e2011 "
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    ABSTRACT: We present results from a study that examines species-specific facilitation of germination in an arid perennial community. This system suffered 64% adult mortality and the local extinction of two common species as a consequence of drought that occurred between 1999 and 2004. Ambrosia dumosa, Larrea tridentata, and Tetracoccus hallii are included as candidate benefactor species based on their high abundance and broad distribution at the study site. Using complementary field and greenhouse experiments, we measured the effects of facilitation, light and nitrogen on germination of four species common to the region, L. tridentata, A. dumosa, Sphaeralcea ambigua and Eriogonum fasciculatum.Our results show that benefactor species do not uniquely influence germination. Species-specific effects among beneficiaries largely explained differences in percent germination in the field, and the interaction between beneficiary species and microhabitat was significant for only one species. E. fasciculatum consistently showed significantly higher germination than more abundant species and showed reduced germination in the interspace. In the greenhouse, germination responses differed at each light level, beneficiaries responding most uniquely at full light. These results refine expectations from previous studies of facilitation at this site by showing that facilitation does not strongly enhance germination.
    Journal of Arid Environments 01/2016; 124:72-79. DOI:10.1016/j.jaridenv.2015.07.012 · 1.64 Impact Factor
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    • "Due to increasing temperature-driven aridity and greater rainfall variability, the type of deleterious drought events that have produced widespread forest deterioration in the 20th century are likely to persist and perhaps intensify (Breshears et al., 2005; Huxman et al., 2004; Williams et al., 2013). Piñon -juniper woodlands are among the most sensitive southwestern US ecosystems to drought events, yet much of this is due to the high susceptibility of isohydric piñon pines to moisture limitation than it is to anisohydric junipers, which are less sensitive to both high and low moisture availability (Breshears et al., 2005, 2009; Shaw et al., 2005; Kleinman et al., 2012; Plaut et al., 2012; Limousin et al., 2013). The deleterious impacts of moisture limitation may be produced by even short-duration events – experimental research in piñon -juniper stands shows that extreme moisture limitation in a single year is sufficient to severely restrict gas exchange and hydraulic conductance in piñon pines and induce significant (67%) mortality in already drought-stressed piñon trees (Plaut et al., 2012). "
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    ABSTRACT: Piñon pine-juniper (Pinus edulis-Juniperus monosperma) woodlands constitute a large proportion of land area in the southwestern United States and have experienced widespread vegetation mortality during regional drought events over the past century. Piñon pines have been especially affected by these events, and drought severity is predicted to increase in this region in the future. Based on research that suggests winter climate may influence growing season productivity in semiarid ecosystems, we evaluated the potential for small changes in average winter climate to affect spring growing season conditions in piñon-juniper woodlands, New Mexico, USA. We developed a low-dimensional ecohydrological model of piñon-juniper woodland ecosystems on moderate slopes (5%) and on steep slopes (25%) and simulated the responses of ecosystem water availability, surface conditions, and water and carbon flux dynamics to a climate change scenario of increased temperature and decreased winter precipitation. The climate change scenario reduced average winter snowcover, decreased surface albedo, increased net radiation, and altered the timing of spring evaporation (E) towards earlier dates. Moderate slope piñon and juniper trees experienced small reductions in transpiration (Tr) and carbon assimilation (A), and those on steep slopes experienced small but relatively larger reductions in Tr and A, as well as higher increases in soil moisture (Â) variance and E variance. As a result of climate change, the peak of spring Tr occurred on average 6 days earlier on moderate slopes and 10 days earlier on steep slopes, the timing of A shifted towards earlier March dates, and A was reduced during April and May. Steep slope piñon pines experienced greater proportional reductions in Tr and A than junipers. Our results suggests that winter climate change will promote an earlier growing season in piñon-juniper woodlands, will increase daily variance in  and E during spring, and will produce slight reductions in A in woodlands with steep slopes and a large proportion of piñon pines. In a more arid future climate, a shift towards lower soil moisture availability and carbon assimilation in April and May may intensify the effects of early summer drought events for piñon-juniper woodlands, thus exacerbating the impacts of larger changes in climate dynamics. Published by Elsevier B.V.
    Agricultural and Forest Meteorology 12/2015; 214215:357-368. DOI:10.1016/j.agrformet.2015.08.269 · 3.76 Impact Factor
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    • "Global change-type drought occurs in conjunction with warmer temperatures due to climate change (Breshears et al. 2005), and is more extreme in intensity and duration than normal rainless periods experienced by vegetation annually in arid climates (Field 2014). Recent reports of drought-induced mortality of woody species are documented from locations worldwide (Allen et al. 2010), raising the importance of predicting future mortality risk in natural vegetation. "
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