Field and laboratory gravimetric measurements were made of transpiration rates in several species of alpine plants from dry and moist environments in the Sierra Nevada. Maximum transpiration rates in, the field ranged from 0.26 to 1.46 g/g f.w.Jhr and were highest for plants from moist sites. Ivesia gordonii, a dry site plant, was more efficient in using soil moisture near the wilting percentage than was Caltha howellv'i, a moist site plant. Caltha and Polygonum bistortoides, both from moist sites, showed midday reductions in transpiration rates during periods of high evaporation stress; most other species showed single-peaked diurnal transpiration curves. Sod blocks from moist sites had evapotranspiration rates ranging from ca. 1,500 to 3,000 g H2O/m2/ 24 hr while evapotranspiration for a dry site was calculated to be under 1,000 g H20/m2/24 hr. Polygonum bistortoides phytometers containing plants originating fram 2,743 m were established at that elevation and also at 2,438 m, 2,134 m, and 1,829 m, the latter two stations below the natural limit of the species. Transpiration rates remained steady at the two uLpper stations and the plants were healthy at the end of 48 hours. Rates at the two lower stations -were twice those of the upper stations during the first 24 hours, were considerably reduced during the second 24 hours, and at the end of 48 hours the leaves were wilted and dried even though soil moisture was apparently adequate. Transpirationrate characteristics appear to be of importance in determining local distribution patterns of alpine plants in the Sierra. INTRODUCTION As compared with other alpine areas in North America, that of the Sierra Nevada is notable for its high degree of atmospheric aridity during the short summer growing season. In this regard, its nearest counterparts are the Sierra Nevada of Spain, the Atlas Mountains of Morocco, and parts of the Andes. In spite of the normally heavy winter snowfall, the snow is windswept into an alternation of deep drifts and almost snow-free ridges. This snow pattern causes an uneven distribution of available soil moisture during the almost rainless summers. The result is a sharp local patterning of the alpine vegetation. Green turf occurs mainly around seeps, springs, and runoff channels below large snowbanks. Screes, ridges, and rocky slopes are only sparsely vegetated, with drought-resistant endemics predominating. This is in contrast to the gradual continua of fellfields and meadows of the alpine areas in the Rocky Mountains and the northern Appalachians, which show greater similarity to Arctic vegetation. In view of this pronounced vegetational pattern in the Sierran I The research reported here is part of that supported by National Science Foundation Grant G13177 for which we express our appreciation. 2 Present address: Department of Botany, University of California, Los Angeles. 374 This content downloaded from 157.55.39.215 on Wed, 31 Aug 2016 05:12:54 UTC All use subject to http://about.jstor.org/terms 1965 MOONEY ET AL.: TRANSPIRATION RATES 375 alpine zone, we are faced with the following question: To what extent do different water requirements segregate alpine plant species into communities? Bliss (1960) suggests that differences in transpiration rates among species in the alpine zone of Wyoming exert so-mecontrol over their local distributions. His suggestion wois'based on observed differences in transpiration rates between two species of willows. Salix planifolia Pursh var. monica (Bebb.) Schn., a plant of wet areas, has higher transpiration rates than does Satix brachycarpa Nutt., which usually grows in drier soils. The major focus of the present work was on the magnitude of transpiration and the daily pattern of water loss in plants of several alpine species. Measurements were made during the summer of 1960 in the central Sierra Nevada. The specific study area is located in Alpine County, California, south of Carson Pass (38?4 2'N, 119057'W) at an elevation of 9,100 ft (2,774 m) near timbertkne on the mountain known as Elephant's Back. We selected plants of three communities for study: the meadow around a small spring, a wind-swept rocky plateau, and' a steep northfacing scree slope. These communities are spatially separated by several hundred meters. The apparent soil moisture available to plants during the growing season is highest at the spring and least on the plateau. METHODS For all transpiration measurements, we used the gravimetric or phytometer method. Transplanted from their native environment to 250 ml plastic containers, individual plants were allowed to reestablish for a period of about a month. At that time, the soil was brought to field capacity and the containers were sealed to prevent loss by evaporation. Sod blocks transplanted to 1-liter plastic containers were utilized to determine the transpiration of communities. Phytometers thus consisted either of individual plants in sealed containers or sod blocks in unsealed containers. These phytometers were weighed at oneor two-hour intervals during the experimental periods, although some daily weighings were made to determine total daily water loss. During the course of the experiments (July and August, 1960), air temperature and humidity were continuously recorded at ground level with a Bendix-Friez hygrothermograph. Incoming solar radiation was measured with a Robitzsch bimetallic actinograph calibrated against an Eppley pyrheliometer.
Journal Article Global Change and the Carbon Balance of Arctic Ecosystems: Carbon/nutrient interactions should act as major constraints on changes in global terrestrial carbon cycling Get access Gaius R. Shaver, Gaius R. Shaver Search for other works by this author on: Oxford Academic Google Scholar W. D. Billings, W. D. Billings Search for other works by this author on: Oxford Academic Google Scholar F. Stuart Chapin, III, F. Stuart Chapin, III Search for other works by this author on: Oxford Academic Google Scholar Anne E. Giblin, Anne E. Giblin Search for other works by this author on: Oxford Academic Google Scholar Knute J. Nadelhoffer, Knute J. Nadelhoffer Search for other works by this author on: Oxford Academic Google Scholar W. C. Oechel, W. C. Oechel Search for other works by this author on: Oxford Academic Google Scholar E. B. Rastetter E. B. Rastetter Search for other works by this author on: Oxford Academic Google Scholar BioScience, Volume 42, Issue 6, June 1992, Pages 433–441, https://doi.org/10.2307/1311862 Published: 01 June 1992
Life occurs, as far as we know, only as part of the earthly biosphere. Yet the earth's biotic resources are experiencing a spreading crisis that is leading not only to the most rapid loss of species in the last 65 million years, but also causing abrupt changes in the structure and function of natural communities. This disturbance, unfortunately, is the result of human carelessness in the name of advancing civilisation. As our technologies and societies continue to improve and grow, we remove ourselves more and more from our natural habitat; as a consequence, we destroy countless numbers of species of every style and complexity. To identify and begin rectifying this dangerous situation, a group of outstanding environmental scientists has compiled a collection of case studies that illustrate the changes being wrought on the biosphere by the human presence.
