摘要
Aims We investigated the treeline dynamics of two environmentally con-trasting areas in the Nepalese Himalaya to address the following questions:(i)Does the timing of establishment of the current tree-line differ between the two study areas,and can area-specific tree-line developments be identified?(ii)Do recruitment patterns and height growth indicate recent climate-driven treeline advance,fol-lowing the general prediction for the central Himalayan region,in the two study areas?Methods a dry-climate treeline dominated by Pinus wallichiana and a mesic-climate treeline with Abies spectabilis were selected for study.In each area,we sampled the size and age structure of the study spe-cies along three elevational transects(20-m wide)from the forest line to the tree species line crossing the treeline.We also sampled treeline trees from within and outside transects to reconstruct past treeline establishment dynamics.Important Findings Despite differences in moisture regimes,tree species and recent climate trends,our two study areas showed very similar treeline dynamics over the past six decades.In both areas,the recruitment of treeline trees indicates stationary treelines over the past six decades with the current treelines being dominated by trees that were established around 1990.the mesic area has experienced an overall climatic warming trend,and the stationary Abies treeline is hypothesized to be regulated by non-climatic factors,notably grazing.the dry area has not experienced warming but increased climatic variability and some very cool summers in the recent dec-ades may explain the stationary to weakly receding Pinus treeline,which appears more climatically controlled with decreased recruit-ment over the past decades and decreased growth towards higher elevations.In both areas,there is a potential for treeline advance,depending on future land use and climate change.our results highlight the importance of conducting treeline ecotone analyses for several sites or areas,and considering both climatic and non-climatic drivers of the treeline dynamics within each of these areas,for understanding regional treeline dynamics.
基金
Research Council of Norway under the project HimaLines(190153/V10)
RCN funds to A.H.under the‘The PPS Arctic project’,Grolle Olsen fund and University fund from Faculty of Mathematics and Natural Science at the University of Bergen supported for the field.
