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  • Thumbnail for The climatic effects of tree growth in Colorado : the influences of climate change on the Colorado Rockies’ treeline
    The climatic effects of tree growth in Colorado : the influences of climate change on the Colorado Rockies’ treeline by Naylor, Jacqueline Nicole

    Throughout the past century, there has been a global shift in climate. Temperatures have been rising, and while precipitation has been fluctuating, it has exhibited not obvious trends. This change in climate has led to global treeline advancement, and has presented ecological, economic, and social implications. Two of the most relevant implications, especially within the context of the western United States, are changing ecosystem dynamics and water yields. Therefore this study aims to explore the effects of climate change at treeline throughout the Colorado Rockies, with the objective to use simple meteorological data to explain and predict radial tree growth. Data was collected at ten individual mountains in five mountain ranges throughout the state. The subsequent dendrochronologies for each mountain were correlated with time, local and regional meteorology, and the other nine sites. The correlation between sites was compared to the distance between sites. Chronologies were also compared to regional wind and storm patterns. Ultimately, no significant climatic trends appeared to influence individual tree growth on a regional scale throughout the Colorado Rockies. In some sites, such as those bordering the western Colorado deserts, increasing precipitation led to increased radial growth. At a small number of sites in the Front Range and the Sawatch Range, increased summer and annual temperatures led to increased radial growth as well. The remaining sites showed no connection between radial tree growth and simple local and regional meteorological data. The dendrochronologies between most mountains were significantly correlated; the correlations ranged from 0.93 to 0.25, with most of the sites correlated at 0.6 and above. Surprisingly, the correlation coefficients between sites did not respond to the distance between mountains in a statistically significant way. Based on an analysis between site correlations, three groups emerged with inter-site correlation at 0.7 and above: west of the Continental Divide, Front Range and Central Rockies, and along the Continental Divide. In general, these groups showed a southwest to northeast orientation. Storm patterns that flow from the southwest to the northeast throughout the state act as the central variable in correlating chronologies between sites. Conclusively this study does not support the hypotheses that claim climate significantly affects radial growth, but instead provides important information that can be used to further understand the implications of climate on treeline dynamics in the Colorado Rockies.

  • Thumbnail for Controls on radial growth of mountain big sagebrush and implications for climate change
    Controls on radial growth of mountain big sagebrush and implications for climate change by Lamanna, Christine A. , Poore, Rebecca E. , Enquist, Brian J. , Ebersole, James J.

    Mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana) covers large areas in arid regions of western North America. Climate-change models predict a decrease in the range of sagebrush, but few studies have examined details of predicted changes on sagebrush growth and the potential impacts of these changes on the community. We analyzed effects of temperature, precipitation, and snow depth on sagebrush annual ring width for 1969 to 2007 in the Gunnison Basin of Colorado. Temperature at all times of year except winter had negative correlations with ring widths; summer temperature had the strongest negative relationship. Ring widths correlated positively with precipitation in various seasons except summer; winter precipitation had the strongest relationship with growth. Maximum snow depth also correlated positively and strongly with ring width. Multiple regressions showed that summer temperature and either winter precipitation or maximum snow depth, which recharges deeper soil horizons, are both important in controlling growth. Overall, water stress and perhaps especially maximum snow depth appear to limit growth of this species. With predicted increases in temperature and probable reduced snow depth, sagebrush growth rates are likely to decrease. If so, sagebrush populations and cover may decline, which may have substantial effects on community composition and carbon balance.