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6 Climate Averages and Extremes 49 Along with Euro-American settlement came an unprecedented increase in Nevada’s woody vegetation. The causes are widely debated. Some plant ecologists believe that the temperature increase of 0.6˚F–1.1˚F since 1900 has increased the growth of perennial forbs and woody plants.1 Others have pointed out that the primary impacts of climate result from extreme events—a reflection of the fact the climate is inherently variable.2 Semiarid regions such as Nevada are particularly erratic, being influenced by wide variations in climatic extremes much more than humid regions are. Thus, one might expect short-term changes in woody vegetation to be influenced more by extreme events than by climatic averages. In fact, extreme events are an essential aspect of the functioning of ecosystems.3 Plants in a particular region are adapted to a composite of weather conditions that includes the timing of frost and frost-free periods, temperature, humidity, precipitation, sunshine, and winds. Every farmer and gardener is aware that plants respond to the frequency and magnitude of extremes in these weather events. Plant growth in the Great Basin can be six times greater in wet years than in dry years.4 A year of high moisture can promote an abundance of sagebrush or pinyon pine seedlings. Two or more consecutive moist years may be needed for successful reproduction of perennials—one to produce more seeds than needed by ants and rodents, and then additional amounts of rainfall to promote germination and establishment. Extensive die-offs of desert shrubs occur during or following successive years of above average precipitation. During periods of drought, shallow-rooted perennial grasses may die because of insufficient moisture while deep-rooted shrubs survive.5 Likewise,moisture-stressed pinyon becomes susceptible to being killed by insects when precipitation is deficient. These and other examples clearly show that plant growth is inextricably linked to large fluctuations in seasonal temperature and precipitation. 50 | n e v a d a ’ s c h a n g i n g w i l d l i f e h a b i t a t Ernst Anteves’ classic 1930s study of tree growth in the Susanville region provides a snapshot of fluctuating weather patterns of the past.6 Knowing that growth patterns are sensitive to the vicissitudes of precipitation and temperature , he used trees as an indicator of past weather and climate. The growth rings of trees are narrow in drought years and wide in wet years, when conditions for growth are optimum. Using growth rings of trees in a virgin forest just bordering the Great Basin, Anteves was able to determine the general growing conditions that occurred during a span of four hundred years. Contributing to his study were trees that became established during the beginning years of the Little Ice Age, which ended in the mid-1800s. Anteves identified thirteen periods during which precipitation was extremely light. These included two long intervals of serious drought, one lasting some twenty-seven years, from 1621 to 1648, and the second lasting thirteen years during the birth of the nation, from 1776 to 1789. Anteves believed that conditions during these years were even more severe than the Dust Bowl years (1924–34) during which he was completing his study. The severe drought of 1776–89 was followed a dozen years later by the twelve wettest years of the four-hundred-year study. Fluctuating periods of wetness and drought were influencing lake levels before Euro-American settlement. James Clyman, a fur trapper and contemporary of Jim Bridger, bore witness to that.Visiting Utah’s Great Salt Lake on June 1, 1846, he “observed that this lake like all the rest of this wide spread Sterility has nearly wasted away one half of its surface since 1825 when I floated around it in my Bull Boate and we crossed a large Bay of this Lake with our horses which is now dry.” The signs of drought he was observing in 1846 were widespread . Earlier, at the Humboldt Sink, Clyman had noted:“This entire region is now entirely dried up and has the most thirsty appearance of any place I have ever witnessed.”7 Anteves also observed a pattern of drought and moisture abundance at Walker and Pyramid lakes from historical accounts he analyzed. Walker Lake was at a low level in 1861 when its surface stood at 4,060 feet above sea level. Fed by the Walker River and unimpeded by reservoir...

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