New West Network

A new biome for the northern U.S. Rockies?

By Lance Olsen, New West Unfiltered 8-06-07

A new biome for the Northern U.S. Rockies? I'd say sure.

But what kind of system will replace what we see now? Very hard to pin it down. But I don't think it far-fetched to take a look at the quite different system described below, from a publication of last year at this time.

This other biome plausibly won't be exactly what we're getting, and we can't take one article as the last word, but I'm sure willing to say it lays out some useful hints. After all, the Chihuahuan Desert really is already headed in this direction, as surely as the northern jet stream has already shifted closer to the Arctic.

Lance Olsen
PS - Because grizzlies once ranged into Mexico, we might assume that they'd do just fine if Mexico moves to Montana. But that would be to ignore that dry (or otherwise food-scarce) regions require individuals to establish larger home range sizes, which would force the Waterton to Yellowstone bear population to sprawl, and there seems pretty good agreement that we're already seeing problems as the bear needs to sprawl.

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"Plant macrofossil assemblages from packrat midden series in the northern Chihuahuan Desert show that C4 grasses and annuals typical of desert grassland persisted near their present northern limits throughout the last glacial-interglacial cycle. By contrast, key C3 desert shrubs appeared somewhat abruptly after 5000 cal. yr BP."

"The sudden expansion of desert shrublands after 5000 cal. yr BP may be a threshold response to warmer winters associated with increasing boreal winter insolation, and enhanced El Niño-Southern Oscillation variability."
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Holmgren, C. A., Norris, J. and Betancourt, J. L. "Inferences aboutwinter temperatures and summer rains from the late Quaternary record of C4 perennial grasses and C3 desert shrubs in the northern Chihuahuan Desert." Journal of Quaternary Science. ISSN 0267-8179.

Published Online: 30 Aug 2006

Abstract:
Late Quaternary histories of two North American desert biomes - C4 grasslands and C3 shrublands - are poorly known despite their sensitivity and potential value in reconstructing summer rains and winter temperatures. Plant macrofossil assemblages from packrat midden series in the northern Chihuahuan Desert show that C4 grasses
and annuals typical of desert grassland persisted near their present northern limits throughout the last glacial-interglacial cycle. Bycontrast, key C3 desert shrubs appeared somewhat abruptly after 5000 cal. yr BP. Bioclimatic envelopes for select C4 and C3 species
are mapped to interpret the glacial-interglacial persistence of desert grassland and the mid-to-late Holocene expansion of desert shrublands. The envelopes suggest relatively warm Pleistocene temperatures with moist summers allowed for persistence of C4 grasses, whereas winters were probably too cold (or too wet) for C3 desert shrubs. Contrary to climate model results, core processes
associated with the North American Monsoon and moisture transport to the northern Chihuahuan Desert remained intact throughout the last glacial-interglacial cycle. Mid-latitude effects, however, truncated midsummer (July-August) moisture transport north of 35° N. The sudden expansion of desert shrublands after 5000 cal. yr BP may be a threshold response to warmer winters associated with increasing boreal winter insolation, and enhanced El Niño-Southern Oscillationvariability.

Published in 2006 by John Wiley & Sons, Ltd.
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Received: 22 July 2005; Revised: 15 February 2006; Accepted: 20 February 2006
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