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Frequent and persistent droughts exacerbate the problems caused by the inherent scarcity of water in the semiarid to arid parts of the southwestern United States. The occurrence of drought is driven by climatic variability, which for years before about the beginning of the 20th century in the Southwest must be inferred from proxy records. As part of a multidisciplinary study of the potential hydrologic impact of severe sustained drought on the Colorado River, the physical basis and limitations of tree rings as indicators of severe sustained drought are reviewed, and tree-ring data are analyzed to delineate a “worst-case� drought scenario for the Upper Colorado River Basin (UCRB). Runs analysis of a 121-site...
Evidence from woodrat middens and tree rings at Dutch John Mountain (DJM) in northeastern Utah reveal spatiotemporal patterns of pinyon pine (Pinus edulis Engelm.) colonization and expansion in the past millennium. The DJM population, a northern outpost of pinyon, was established by long-distance dispersal (approximately 40 km). Growth of this isolate was markedly episodic and tracked multidecadal variability in precipitation. Initial colonization occurred by AD 1246, but expansion was forestalled by catastrophic drought (1250-1288), which we speculate produced extensive mortality of Utah Juniper (Juniperus osteosperma (Torr.) Little), the dominant tree at DJM for the previous approximately 8700 years. Pinyon then...
Abstract (from: http://link.springer.com/article/10.1007/s00442-014-2881-2): Forest biomass growth is almost universally assumed to peak early in stand development, near canopy closure, after which it will plateau or decline. The chronosequence and plot remeasurement approaches used to establish the decline pattern suffer from limitations and coarse temporal detail. We combined annual tree ring measurements and mortality models to address two questions: first, how do assumptions about tree growth and mortality influence reconstructions of biomass growth? Second, under what circumstances does biomass production follow the model that peaks early, then declines? We integrated three stochastic mortality models with...
This paper summarizes the current state of knowledge concerning the climate of the Southwest. Low annual precipitation, clear skies, and year-round warm weather over much of the Southwest are due in large part to a quasi-permanent subtropical high-pressure ridge over the region. However, the Southwest is located between the mid-latitude and subtropical atmospheric circulation regimes, and this positioning relative to shifts in these regimes is the fundamental reason for the region's climatic variability. El Nin?o, which is an increase in sea surface temperature of the eastern equatorial Pacific Ocean with an associated shift of the active center of atmospheric convection from the western to the central equatorial...
Samples from 107 piñon pines (Pinns edulis) at four sites were used to develop a proxy record of annual (June to June) precipitation spanning the 1226 to 2001 AD interval for the Uinta Basin Watershed of northeastern Utah. The reconstruction reveals significant precipitation variability at interannual to decadal scales. Single-year dry events before the instrumental period tended to be more severe than those after 1900. In general, decadal scale dry events were longer and more severe prior to 1900. In particular, dry events in the late 13th, 16th, and 18th Centuries surpass the magnitude and duration of droughts seen in the Uinta Basin after 1900. The last four decades of the 20th Century also represent one of the...
Evidence from woodrat middens and tree rings at Dutch John Mountain (DJM) in northeastern Utah reveal spatiotemporal patterns of pinyon pine (Pinus edulis Engelm.) colonization and expansion in the past millennium. The DJM population, a northern outpost of pinyon, was established by long-distance dispersal (approximately 40 km). Growth of this isolate was markedly episodic and tracked multidecadal variability in precipitation. Initial colonization occurred by AD 1246, but expansion was forestalled by catastrophic drought (1250-1288), which we speculate produced extensive mortality of Utah Juniper (Juniperus osteosperma (Torr.) Little), the dominant tree at DJM for the previous approximately 8700 years. Pinyon then...
Growing and changing demands on water supply, along with natural climate variability and possible anthropogenically induced climate change, make water resource management and planning increasingly challenging, particularly in arid regions. Instrumental climate and gaged streamflow records provide just a snapshop of recent natural hydrologic variability. In this paper, we use tree-ring-based annual streamflow reconstructions for the Sacramento River in California and the Blue River in western Colorado to analyze the temporal and spatial variability of widespread drought simultaneously affecting both basins over the past five centuries. Stability of joint-drought episodes and the covariation of reconstructed flows...
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These datasets provide spatially-explicit estimates of the magnitude of giant sequoia foliage dieback along selected trail corridors in Sequoia and Kings Canyon national parks, California, from 2014 through 2017. They additionally provide giant sequoia tree-ring measurements, through the year 1989, for two locations in the Giant Forest grove, Sequoia National Park, California. These data support the following publications: Nathan L. Stephenson, Adrian J. Das, Nicholas J. Ampersee, Kathleen G. Cahill, Anthony C. Caprio, John E. Sanders, A. Park Williams, Patterns and correlates of giant sequoia foliage dieback during California’s 2012–2016 hotter drought, Forest Ecology and Management, Available online 7 November...
In recent decades, intense droughts, insect outbreaks, and wildfires have led to decreasing tree growth and increasing mortality in many temperate forests. We compared annual tree-ring width data from 1,097 populations in the coterminous United States to climate data and evaluated site-specific tree responses to climate variations throughout the 20th century. For each population, we developed a climate-driven growth equation by using climate records to predict annual ring widths. Forests within the southwestern United States appear particularly sensitive to drought and warmth. We input 21st century climate projections to the equations to predict growth responses. Our results suggest that if temperature and aridity...
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In California, increased wildfire activity has been linked to decreasing snowpack and earlier snowmelt. Not only has this translated into a longer fire season, but reduced snowpack has cascading effects that impact streamflow, water supplies, agricultural productivity, and ecosystems. California receives 80% of its precipitation during the winter, so mountain snowpack plays a critical role in replenishing the state’s water supply. One factor that affects the amount of winter precipitation (and therefore snowpack) in California is the North Pacific Jet (NPJ)—a current of strong, high altitude winds that occur over the northern Pacific Ocean. Winters when the NPJ is located further north than normal are drier than...
Elk browsing and conifer species mixing with aspen (Populus tremuloides Michx.) present current challenges to aspen forest management in the western United States. We evaluated the effects of conifers and elk browsing on quaking aspen stands in and near Rocky Mountain National Park using tree rings to reconstruct patterns of aspen establishment, growth, and mortality over the past 120 years. High conifer encroachment and elk browse were both associated with decreased aspen recruitment, with mean recruitment dropping over 30% from pure aspen to mixed stands and over 50% from low-browse to high-browse stands. Maximum aspen recruitment was lower in mixed stands than in pure stands with the same tree basal area. High...


map background search result map search result map The Influence of the North Pacific Jet Stream on Future Fire in California Sequoia foliage dieback and tree-ring data from Sequoia National Park Sequoia foliage dieback and tree-ring data from Sequoia National Park The Influence of the North Pacific Jet Stream on Future Fire in California