The response of two inverted tree lines under possible elevational-dependent warming: Southern Sierra Nevada, California USA
Assigned Session: FS 3.135: Elevational stratification of climate change: impacts and driving mechanisms in global mountain ecosystems
Abstract ID: 3.11730 | Not reviewed | Requested as: Talk | TBA | TBA
Louis Scuderi (1)
(1) University of New Mexico, Northrop Hall MSC03 2040, 87031 Albuquerque, US
Abstract
Elevational-Dependent Warming (EDW) implies that mountain warming rates may exceed those found in non-mountainous environments with possible systematic differences expressed as an increase in warming rates with elevation. Temperature profiles across inverted tree lines in mountainous environments are opposite of the normal elevational trend with temperatures increasing above the cold air pool. One consequence of elevation dependent warming in mountain environments is a potential for a reduction of temperature inversions in cold air pools as both the cold air pool and surrounding higher terrain warm at different rates possibly resulting in a decrease in inversions in both depth and intensity due to greatly increased temperatures in the cold air pool. Few long-term profiles of cold air pool/inverted tree line boundaries exist. Because this ecotone boundary is typically below the resolution of satellite sensors there is a need for in situ monitoring. Here we investigate the change in temperature along two adjacent inverted tree lines in California’s southern Sierra Nevada oriented in opposite directions on north and south facing slopes. A combined canopy and soil temperature sensor transect across the two inverted tree line boundaries and cold pools monitored since 2006 shows a decrease in temperature inversions and intensity over time associated with significant warming of the cold air pool. Annual canopy temperatures increased for all sites on south facing slopes and meadow cold air pockets while decreasing on average for north facing slopes. Normally, temperature inversions at night occur in all months, however the study site shows a disappearance of nighttime inversions during April and early May, a key time associated with the timing of conifer bud break. This change allows the establishment of seedlings at the meadow edge and the advance of the inverted tree line into the cold pool resulting in an increase in meadow edge albedo which in turn impacts the energy balance and snow cover duration along the ecotone. Areas with cold air pool degradation may be indicative of climate hotspots where temperature increase leads to change in ecosystem function including change in hydrologic response and decreases in biodiversity.
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