| Title Upslope Migration of Trees and Plants- Is Global Warming the Cause? | ||||||||||||||||
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Author George Dunning American River College, Geography 350: Data Acquisition in GIS; Fall 2013 Contact Information (geo_dunning@yahoo.com) | ||||||||||||||||
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Abstract Anecdotal observations by the author over the span of twenty five years in the Sierra Nevada range led to the speculation that upslope migration of plants was taking place on a general scale. Lacking scientific evidence, it set me to wondering just how much evidence there was of such a phenomena? At what rate, if any, was it occurring? Did global warming have anything to do with it, or were other factors at work such as air pollution? If what I suspected was happening, how long had it been going on? I set out on an internet search and found much more than expected. Some general reading led me to three recent studies that detailed upslope migration of trees and plants at a suprising rate. A unique study in the Santa Rosa Mountains of California pointed to warming temperatures of less than 2 degrees Farenheit over a 30 year period had led to a 100 foot or more migration upslope. The rate of change is more rapid than first thought. Given current rates of change, some high altitude plants may reach extinction soon over lack of habitat or increased competition. | ||||||||||||||||
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Introduction The Intergovermental Panel on Climate Change (IPCC), in their latest report, states the “linear warming trend over the 50 years from 1956-2005is nearly twice that for the 100 years from 1906-2005.”(1) Their observations show that it’s “very likely”(2) that Northern Hemisphere temperatures are now higher than any 50 year period in the last 500 years, and “likely”(3) the highest in the past 1,300 years(4). Another nugget is “of the more than 29,000 observational data series, from 75 studies, that show significant change in many physical and biological systems, more than 89% are consistent with the direction of change expected as a response to warming”(5). Fairly compelling evidence that warming is occurring, and it’s probably warming at a faster rate now than it was 100 years ago. At this point, there doesn’t seem much use in debating if it’s happening. More importantly, the question should be what’s causing it. Some of the warming could be attributable to warming trends of the planet, but how much of the warming is human caused? The problem might lie in the “greenhouse gasses” we emit as an industrialized world. As the IPCC points out, “the annual carbon dioxide concentration growth rate was larger during the last 10 years (’95-’05) than it has been since the beginning of continuous direct atmospheric measurements” (6). Unless I read the report wrong, it would appear the IPCC and I agree the overall temperature of the atmosphere is indeed warming at a rate faster than first thought. What I wanted to know was there a connection between what I observed and global warming, or was there some other reason that could explain it? | ||||||||||||||||
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Background In a University of Vienna, Austria, study conducted in the Austrian Alps, a total of 26 summits over 9,000 feet were surveyed for plant location and type. They found that nearly all species of plants they found were at higher than historical elevations, ie, plants were being found at elevations they had never occupied before on the mountain. Under normal circumstances, temperature decreases around 1 degree F. for every 100 yards one goes upslope. (7) Knowing of a 1-1.5 degree increase in temperatures the last century in the Alps, scientists extrapolated that plants would need to move some 30 feet in order to reach their optimum range. What they actually measured was closer to 3 feet, a mere 10% of what they had expected to find. It seems as though the temperature increase rate is faster than the plants ability to move. If the measured rate of warming stays the same and the plants could move fast enough, eventually they will run out of summit to move to. Not only that, but all species at the summit will have increased competition the more move to higher elevation. Some 40-50 species in the Alps are limited to high mountain regions, already at the limit they could go. Extinction seems to be end result should nothing change. In another study, Lief Kullman of Umea University in Sweden has found 7 to 9,000 year old mountain birch remnants left exposed by retreating glaciers, some 500 m. above the current tree line. He found growing on glacial till near a glacier Epilobium angustifolium ( a large herb), some 110 m. above the limit it had been found in the 1950’s. (8) Kullman said the evidence points to how “highly unusual” the current climate is. Another of his findings were exotic tree species moving into sub-alpine and alpine environments, confirming predictions of some climate models. Another of his studies covered the same area of a 1952 study. Above the 1,095 m. elevation of the study area, zero birch saplings were found in the ’52 survey. In 2000, Kullman found 34 individual saplings ranging from 13 cm. to 41cm. tall. (9) Ring counting of the saplings showed them to be 7-12 years old, so it was a safe bet each of the trees had germinated sometime after 1987. Strong and consistent winter warming along with warmer summers since that time had taken place in the region. He speculated the trees could have colonized the area in the late 20th century, probably the 90’s. | ||||||||||||||||
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Methods One study researched was conducted in the White Mountains of eastern California. There were found snags and logs of Pinus longaeva around 150 m. above the current tree line. Carbon dating showed the wood to be from about 6,000 ybp., when temperatures were estimated to be 3.5 degrees C. warmer. (10) They made climate models of the area assuming one degree jumps in temperature up to 6 above current levels. 10 of 14 kinds of alpine/sub-alpine plants were expected to go extinct in the central White Mountains if the increasing temperatures forced the plants upslope. They would simply run out of habitat. However, the best evidence I found is from a study done in the Santa Rosa Mountains of southern California, near Palm Desert. UC Irvine graduate students working nearby had been told of what appeared to be trees dying off at lower elevations by locals wanting to know what was happening. Because of those questions, a unique study was undertaken at the Boyd Deep Canyon Desert Research Center, a facility run by UC Riverside and part of the UC Natural Reserve System (of which there are 36- 6 run by UC Davis). It is a one of a kind facility, covering some 16,647 acres (11), and going from near sea level to the 8, 716 foot level. The study was unique because a similar study had been done over the same area just 30 years previous, and the study area was a region that had not experienced wildfire since the early 40’s. What had been found in the 1977 study theoretically would still be there in 2006 when the updated survey began. Anne Kelly and Michael Goulden went to the ’77 survey area with its author, Jan Zabriskie, prior to beginning so as to familiarize themselves with the area and to ensure they didn’t stray far from the original spots Zbriskie had covered. All plants found 150’ either side of the centerline were noted for species and location was mapped with GPS measurements. The two closest weather stations, Indio and Idyllwild, had measured over the 30 years since ’77 an overall increase of 1.4 degrees in the region. (12) Of the 141 species they found along their way, they selected ten that were the most abundant at different locations. What they found was rather striking. Overall, the desert, chapparal, and montane plants all had mean increases in elevation at about the same rate. (13) They found that depending on the species, a 33-50% death rate was occurring at lower elevations when a rate of 1-2% was what would be expected. (14) Ozone was ruled out, as it would kill trees at higher elevation as well, and that was not the case here. The southern California drought years alone could not explain what was happening. Bark beetle infestation was occurring in the region due to drought conditions, but only at lower, warmer elevations where the beetle could survive. They findings showed 9 of the 10 plants studied had moved upslope since 1977, and at an alarming rate. For unknown reasons Agave deserti actually moved downslope 50 m. in the 30 years. The other nine species all moved upslope- slower, such as Pinus jeffreyi at 28 m. of uphill movement, to the speedy Larrea tridentata at 142 m., from an elevation of 317 m. to one of 459 m. (15) Pinus jeffreyi has been considered more ozone sensitive than Quercus chrysolepis, yet it only moved upslope 28 m., to 47 m. for Q. chrysolepis. “The species elevation changes were unrelated to the known pattern of ozone sensitivity” (16) is how Kelly & Goulden described it. The highest elevation plant measured, Abies concolor, moved some 96 m. over the period covered as well, so movement is at low as well as high elevations. They note that while previous studies pointed to a much longer time frame between cause and effect, this study indicates otherwise, with an average of 65 m. movement in just 30 years time. That would be about 150 m. upslope migration in the span of my lifetime! | ||||||||||||||||
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Conclusions So, it would seem global warming is a catalyst for upslope migration, at least in part. Given the predictions that global climate models have made and knowing human nature, one can conclude that warming will continue, although estimates of the rate vary. However, the third IPCC analysis high end predictions for the future are where we are right now, meaning, of course, that they had predicted in ’07 a much slower rate of change than we’re actually experiencing. If the best people we have are estimating a rate of change that is that far off, it would appear the rate is a lot faster than everyone expected. That means if we can possibly do anything about it, it will have to be much sooner than anticipated. The amount of change exhibited in the Santa Rosa Mountains is quite dramatic, and much of what is happening there can only be explained by warming temperatures. Air pollution has been ruled out, as has drought conditions. The urban “heat island” of Los Angeles has been given as one possible counter to this argument, but the distance involved and the fact L.A. sits on the northwest side over the mountains southeast location make it highly unlikely I would think. Even if temperature increases at a much slower rate than it currently is, upslope migration would still only be slowed, not stopped. As more plants and trees try to find cooler habitat by moving upslope, there will be less habitat in which to live. That means increased competition among plants across the board at higher elevation. Any plants or trees already at the highest elevations will have no more options other than extinction, being crowded out of their environment. The folks in the Copenhagen conference might argue over whether the warming trend is human caused or not. The issue at hand is the planet as a whole is warming, it’s not really important who is at fault. The numbers don’t lie, and they tell us a warming trend is under way. If human induced, it’s imperative we find out they how and why and take measures to halt or turn the trend around if that’s a possibility. After all, if an ordinary camper like myself sees something’s happening just within my lifetime, then it would be reasonable to conclude it’s been going on for some time without my noticing. This brings up a pertinent question- how is it possible what appear to be “legitimate” studies can refute global warming when evidence point otherwise? Are they looking the other way, being paid off, or maybe simply don’t care? Hard to say for certain, but as in most cases, I suspect money. It costs much less to do nothing than it does to clean up or correct anything the way it’s supposed to be. And that means we’re all going to lose when we lose habitat and species. Today was a big snow day in our region, yet when I was in high school 30 years ago it was a common thing two or three times a winter. Rarely, if at all, does it snow at lower elevations nowadays. If it’s that noticeable in such a short time span, it would seem to me we are heading into very uncertain times indeed. | ||||||||||||||||
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References Zabriskie JG (1979) Plants of Deep Canyon and the Central Coachella Valley, California. Riverside, CA: Philip L. Boyd Deep Canyon Desert Research Center, University of California, Riverside | ||||||||||||||||