The suitability of montane ecotones as indicators of global climatic change

Abstract

Because of the difficulties involved with separating natural fluctuations in climatic variables from possible directional changes related to human activities (e.g., heightened atmospheric CO 2 concentrations related to fossil fuel consumption), some researchers have focused on developing alternative indicators to detect hypothesized climate changes. It has, for example, been suggested that the locations of ecotones, transitions between adjacent ecosystems or biomes, should be monitored. It is assumed that changes in climate, especially increases in atmospheric temperature, will result in shifts in the location (altitude or latitude) of ecotones as plants respond to the newly imposed climatic conditions. In this article, we address the use of two montane ecotones, the alpine tree-line ecotone and the deciduous/Boreal forest ecotone, in monitoring global climatic change. In so doing, we 1) outline the factors that create and maintain each ecotone's position at a given location; 2) assess the projected response of the ecotones to various aspects of global warming; and 3) discuss the usefulness of both ecotones as indicators of global climate change. While it is likely that extended periods of directional climate change would bring about an altitudinal shift in the ranges of montane species and the associated ecotones, we question whether the response at either ecotone will be at a timescale useful for detecting climate change (a few decades) owing to disequilibrium related to upslope edaphic limitations and competitive interactions with established canopy and subcanopy individuals. Further, limitations related to the prediction of the complex and interacting effects of projected changes in temperature, precipitation and site water balance on photosynthetic processes of plant species raise uncertainties about the expected responses of both ecotones.

Annual monitoring reveals rapid upward movement of exotic plants in a montane ecosystem

“…°C warming over a seven-year period (assuming a dry adiabatic lapse rate of 1.0 °C decrease for every 100 m in elevation); such increase is improbable and cannot be ascertained within such short time-span (Kupfer and Cairns 1996). Although a few consecutive warm years could mimic the long-term effects of climate change, especially for annual plants, our own temperature observations did not show a significant temperature increase for any of the elevational bands (Table 2).…”

High solar radiation hinders tree regeneration above the alpine treeline in northern Ecuador

“…Temperature is generally considered to be the main natural determinant of treeline position (Kö rner and Paulsen 2004), and treelines are therefore expected to react strongly to global warming (Kullman 2001;Kupfer and Cairns 1996). However, if a treeline lies below its climatic potential, for whatever reason, the forest could extend upwards even if there is no increase in temperature.…”

A rapid upward shift of a forest ecotone during 40 years of warming in the Green Mountains of Vermont

“…Montane environments provide an ideal environment for detecting shifts in forest distribution in response to climate change because of steep climatic gradients across elevation, which in many respects are analogous to latitudinal climatic gradients, but with distinct boundaries between forest types that facilitate detection of range shifts ( Fig. 1) (20,21).…”