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15,000 years of increasing aridity and herbaceous taxa loss

Date: May 11, 2015

Plant macrofossils were sampled from woodrat middens in the western Great Basin of Nevada. These data were used to track changes in vegetation composition and climate over the last 35,000 years, with a focus on the last 15,000 years


Modern vegetation analysis techniques were used to statistically analyze 154 plant taxa from 52 fossil woodrat midden strata from a cold desert area adjacent to Pyramid Lake. These midden strata were located over an 800 meter elevation gradient and covered the last 35,000 years. Analysis results show significant trends from 35,000 years ago to the present of a decreasing number of forb taxa, and an increasing number of shrub taxa. From 15,000 years ago to the present there are also significant trends of decreasing numbers for total taxa and for total herbaceous taxa. These changes have resulted from a long-term trend over the 15,000 year time period of a warming and drying climate. The loss of total taxa is primarily the result of the concomitant loss of total herbaceous taxa, and these changes are resulting in an increasing dominance of the woody taxa. These long-term vegetation changes, particularly the herbaceous taxa losses, may have facilitated the recent increases in the establishment and dominance of exotic annuals, particularly cheatgrass. As climate continues to warm and dry these vegetation trends will intensity into the future.  



Principal Investigators: 
External Partners: 
Robert S. Nowak and Cheryl L. Nowak-Dept. of Natural Resources and Environmental Science, Univ. of Nevada, Reno