VEGETATION AND CLIMATE HISTORY FROM ANCIENT WOODRAT MIDDENS OF THE NORTHERN MOJAVE DESERT

During the last ten years a group of scientists from the Desert Research Institute working with Dr. Wigand have sampled a series of several hundred woodrat midden strata in the southern Great Basin and northern Mojave Desert. This research is both difficult and dangerous. However, the reward has been a much clearer view of vegetation change in southern Nevada during the last 35,000 years. Our current understandings are a cumulative effort building upon the pioneering research in the 1960s and 1970s of Philip V. Wells, Peter J. Mehringer, Jr., Clive Jorgensen, and C. Wes Ferguson, and brought to its current standard of excellence by W. Geoff Spaulding and Robert S. Thompson in the 1980s and 1990s.

It is clear that subalpine woodland species had migrated down the mountain slopes of southern Nevada by at least 1,000 meters (over 3,600 feet) several times between 35,000 and 12,000 years ago, usually without displacing the ever present Utah Juniper. Species such as Limber Pine and White Fir that are currently associated with high elevation woodlands in the Great Basin reached elevations well below their current distributions indicating that mean annual temperatures in southern Nevada were at least 7°C (12.6°F) below their current level and that, at times, mean annual rainfall may have exceeded 2.5 times its current amount. Therefore, mean annual rainfall of between 560 to 635mm (22 and 25 in) at elevations of 1,600 m (5,250ft) characterized both the onset (24,000 to 21,000 years ago) and decline (16,000 to 13,000 years ago) of the Glacial Maximum. At elevations below 1,525 m (5,000 ft) conditions were only slightly wetter than today with mean annual rainfall estimates ranging between 130 to 190 % of current values. These estimates are confirmed by recently published modeling conducted by Pat Bartlein, Bob Thompson and Kathy Anderson.

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