Ideas and approaches for studying treelines in the himalayas: Expanding the concept from a landmark to community and ecosystem levels

Abstract

Here, we report research design, methodological framework and preliminary findings of a treeline research, based on several sites covering much of the Indian Himalayas. Apart from investigating tree populations, this study expands the treeline concept to community and ecosystem levels. A treeline ecotone consists not only of trees but also several species of herbs and other growth forms. The paper sheds light on methods to delineate treelines and timberlines and to characterize species distribution patterns. Treeline landscapes have complex mosaics of ecosystems, diverse in physiognomy, such as forests, juniper mats and rhododendron krummholz, isolated trees and trees in clusters and rows. Several ecosystem characters change rapidly as forests approach treelines, including a drastic drop in biomass accumulation, which leads to treeline formation. A compilation of treeline elevation studies at the regional level indicates that its elevation can vary widely, by 1800 m across the Himalayan Arc. A similar elevational range is indicated by mapping with the help of remote sensing. The common treeline genera are Betula, Abies, Picea and Juniperus, forming almost all treeline forms described in the literature. We found a relatively lower Temperature Lapse Rate (TLR) value, partly because of elevation-dependent warming (EDW) which needs to be analysed. The upward movement of treelines due to climatic warming could be restricted by pre-monsoon droughts as the studies based on tree ring width chronology suggest. During winters, trees have access to water for only a limited part of the day as the soil remains frozen most of the time. Response to early snowmelt seems to vary from species to species.