Studies in Treeline Ecology
E-Book, Englisch, 354 Seiten, eBook
ISBN: 978-3-540-27365-3
Verlag: Springer
Format: PDF
Kopierschutz: Wasserzeichen (»Systemvoraussetzungen)
Zielgruppe
Research
Autoren/Hrsg.
Weitere Infos & Material
Mountains Ecosystems Studies in Treeline Ecology General Aspects of Vegetation and Soils in Cold Environments.- Guideline for Describing Soil Profiles in Mountain Ecosystems.- Peripheral Plant Population Survival in Polar Regions.- Climate Change and High Mountain Vegetation Shifts.- Mountain Ecosystems Studies in Treeline Ecology Regional Treeline Studies in America.- Regeneration of Whitebark Pine in the Timberline Ecotone of the Beartooth Plateau, U.S.A.: Spatial Distribution and Responsible Agents.- Structure and the Composition of Species in Timberline Ecotones of the Southern Andes.- Pocket Gopher — Actor under the Stage. Studies on Niwot Ridge, Colorado Front Range, U.S.A..- The Impact of Seed Dispersal by Clark’s Nutcracker on Whitebark Pine: Multi-scale Perspective on a High Mountain Mutualism.- Mountain Ecosystems Studies in Treeline Ecology Regional Treeline Studies in Europe.- Humus Forms and Reforestation of an Abandoned Pasture at the Alpine Timberline (Upper Engadine, Central Alps, Switzerland).- A Discontinuous Tree-ring Record AD 320–1994 From Dividalen, Norway: Inferences on Climate and Treeline History.- Woodland Recolonisation and Postagricultural Development in Italy.- Mountain Ecosystems Studies in Treeline Ecology Regional Treeline Studies in Asia.- Isolated Mountain Forests in Central Asian Deserts: A Case Study from the Govi Altay, Mongolia.- The Upper Timberline in the Himalayas, Hindu Kush and Karakorum: a Review of Geographical and Ecological Aspects.
Structure and the Composition of Species in Timberline Ecotones of the Southern Andes (P. 117)
William Pollmann and Renate Hildebrand
Abstract
The subalpine southern Andean timberline is characterized by deciduous Nothofagus pumilio forests, which change with increasing altitude to Nothofagus krummholz, built of deciduous N. pumilio and N. antarctica. The current study examines the structure and species composition in timberline ecotones of the southern Andes to assess whether the deciduous timberline in the Andes results as convergent structure of, for example, Betula-timberlines of the Northern Hemisphere.
Through a Braun-Blanquet phytosociological approach, we show how the characteristic structure and combination of timberline vegetation in the southern Andes vary in latitudes from 33°S to 55°S and altitudes between 2000 m and 600 m. Timberline composition was distinct at sites and included a variety of assemblages ranging from northern Azaro-Nothofagetalia communities to assemblages of the Adenocaulo-Nothofagetalia and Violo- Nothofagetalia in the South.
Krummholz generally occurred in a ten to some hundred meter wide ecotone. Four distinctive N. pumilio growth forms were identified, (1) ‘elfin woods’ where trees become more and more stunted as they approach the woodland limit readily observed in previous studies, (2) ‘cornice-like’ growth form characterized by branches close to the ground, (3) restricted to the leeward side, a single-stemmed habit occurred that was characterized by stems aligned downhill before curving up into vertical alignment, and (4) on the wind-exposed side, growth forms were characterized by single-stemmed habit and long branches running uphill. These growth form changes were apparently controlled by changes in abiotic factors and climate rather than genetically determined.
In conclusion, the recognition of the deciduous foliage and deformed habit of timberline trees in the southern Andes is explained by extreme climate. Comparison of same latitudes revealed that maximum altitudes of southern Andean timberline were generally higher than those of evergreen Nothofagus limits in New Zealand but lower than timberlines of Holarctic mountain ranges. These results serve to emphasize that understanding structure and physiognomy of the southern Andean timberline and its apparent stability may require attention to ecophysiological adaptations and responses of timberline Nothofagus to high-mountain environment.
1 Introduction
Latitudinal and altitudinal timberlines are ecotones between continuous forests of erect trees and adjacent non-forested vegetation (Holtmeier 1985, 2003). At high altitudes, the transition between these two communities includes a ‘krummholz’ forest, trees of low stature with decurrent and deformed stems (Daubenmire 1954, Wardle 1965, Tranquillini 1979, Grace 1989, Armand 1992, Körner 1998, Miehe and Miehe 2000, Holtmeier 2003).
Krummholz growth forms are genetically determined in some species, but are more frequently a phenotypic response to climatic stress (J. Wardle 1974, P. Wardle1998, Holtmeier 2003). Holtmeier (1981) differentiated between environmentally determined and genetically determined dwarf trees, applying the term ‘krummholz’ to the latter only (e.g. Pinus mugo var. prostrata, Alnus viridis). However, in many studies krummholz is used in a wider sense, applying this term to all stunted and dwarfed trees at upper limit of forest margin (cf. Tranquillini 1979, Holtmeier 2003).
