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Accueil du site → Doctorat → États-Unis → 2014 → Quantifying some key ecological responses to natural climate variability and anthropogenic climate change in Great Basin and Sierra Nevada ecosystems

UNIVERSITY OF NEVADA, RENO (2014)

Quantifying some key ecological responses to natural climate variability and anthropogenic climate change in Great Basin and Sierra Nevada ecosystems

Johnson, Brittany G

Titre : Quantifying some key ecological responses to natural climate variability and anthropogenic climate change in Great Basin and Sierra Nevada ecosystems

Auteur : Johnson, Brittany G

Université de soutenance : UNIVERSITY OF NEVADA, RENO

Grade : Doctor of Philosophy (PhD) 2014

Résumé
Changes in Earth’s climate are predicted to strongly affect temperatures and droughts in the southwestern U.S. which will influence plant species distributions, soil biogeochemistry, and ecosystem function. The objectives of these studies were to quantitatively explore the effects that climate change may have on several key ecosystem functions, specifically (a) the effects of natural and simulated gradients in snowpack on decomposition and soil biotic activity in the Sierra Nevada, (b) canopy influence on soil nutrients along latitudinal-elevational gradients in the Great Basin and northern Mojave, and (c) spring and growing season environmental controls of transpiration in Great Basin tree species.
Results from the snowpack gradient study showed that natural gradients in snow cover among tree-bole, under-canopy, and inter-canopy microsites of a Sierra Nevada forest as well as manipulated gradients where snow cover was experimentally reduced or supplemented, altered soil water content (SWC) for months and even years but differences in soil temperatures were typically short-lived (weeks-months). Although significant changes in soil biotic activity (litter decomposition, soil respiration or soil nutrients) between stand microsites or between manipulated plots were not detected during the study, the large and persistent decreases in SWC observed when snow cover was reduced suggest that biotic effects will eventually ensue. The second study, which examined the effects of canopy and plant species on surface soil chemistry, indicated that vegetation canopy is a driving factor in defining how soil chemical properties of Great Basin ecosystems respond to climate and anthropogenic climate change. Results also suggest that species migration that may result from changes in climate, the movement of desert shrub ecosystems, can significantly alter soil chemistry and ecosystem biogeochemistry and function in the Great Basin. Finally, the initiation of spring transpiration as well as growing season transpiration depended on multiple above- and below-ground environmental factors but that changes in photosynthetically active radiation (>70% of trees) and SWC (>60% of trees) were the most frequent environmental drivers for both periods. The results suggest that changes in climate that lead to alterations in the amount of available light and lower amounts of plant available soil water will have the most significant effects on transpiration in the high elevation, semi-arid forests of the Great Basin.

Mots clés : Ecology, Sap flow, Biogeochemistry, Elevation gradients, Soil sciences, Climate change Plant-soil interactions, Transpiration, Earth sciences, Biological sciences

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