Climate Change

• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Canada; Pacific; Ursus arctos
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.521.7775; http://www.bearbiology.com/fileadmin/tpl/Downloads/URSUS/Vol_9/Moir_Huckaby_Vol_9.pdf

Abstract: Tree invasions into meadows near upper timberline reduce diversity of habitat and diminish high-elevation food sources for black (Ursus americanus) and grizzly (Ursus arctos) bears. How serious is this threat in view of future climate change? Tree invasions observed in the Pacific Northwest o New Mexico suggest that climatic restraints to forest expansion have relaxed since the end of the Little Ice Age. Because climate patterns are large-scale phenomena, geographic synchronicity in tree establishment might be expected if a warming trend began. When tree invasion chronologies from Canada to New Mexico were compared, 2 synchronicities of climate and tree invasions appeared, indicating a possible climatic influence. However, forest retreat and meadow advance are also commonly observed at high elevations. The mechanism of retreat is usually fire followed by slow or unsuccessful regeneration of forest. There is no clear evidence based upon tree seedling chronologies that meadows will continue to be lost on the basis of climate change alone. Climate warming may set the stage for forest advance, but tree invasions are highly sensitive to local conditions. Concentrated grazing by domestic or wild animals in high-elevation meadows may trigger tree invasion by reducing competition to tree seedlings from established meadow vegetation. Prescribed fires or natural fires allowed to burn within prescriptions can be used as a tool for maintaining meadows and bear habitat under some of the projected climate change scenarios for western North America.