J Plant Ecol ›› 2015, Vol. 8 ›› Issue (4): 347-358 .DOI: 10.1093/jpe/rtu035

• Research Articles • Previous Articles     Next Articles

Recent treeline dynamics are similar between dry and mesic areas of Nepal, central Himalaya

Krishna B. Shrestha1,2,*, Annika Hofgaard3 and Vigdis Vandvik1   

  1. 1 Department of Biology, University of Bergen, PO Box 7803, NO-5020, Bergen, Norway; 2 UiB Global, University of Bergen, Jekteviksbakken 31, PO Box 7800, NO-5020, Bergen, Norway; 3 Norwegian Institute for Nature Research, PO Box 5685 Sluppen, NO-7485, Trondheim, Norway
  • Received:2013-11-30 Accepted:2014-10-29 Published:2015-07-24
  • Contact: Shrestha, Krishna

Recent treeline dynamics are similar between dry and mesic areas of Nepal, central Himalaya

Abstract: Aims We investigated the treeline dynamics of two environmentally contrasting areas in the Nepalese Himalaya to address the following questions: (i) Does the timing of establishment of the current treeline differ between the two study areas, and can area-specific treeline developments be identified? (ii) Do recruitment patterns and height growth indicate recent climate-driven treeline advance, following 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 species 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 decades may explain the stationary to weakly receding Pinus treeline, which appears more climatically controlled with decreased recruitment 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.

Key words: Abies spectabilis, Himalaya, Pinus wallichiana, slope aspect, treeline ecotone dynamics

摘要:
Aims We investigated the treeline dynamics of two environmentally contrasting areas in the Nepalese Himalaya to address the following questions: (i) Does the timing of establishment of the current treeline differ between the two study areas, and can area-specific treeline developments be identified? (ii) Do recruitment patterns and height growth indicate recent climate-driven treeline advance, following 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 species 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 decades may explain the stationary to weakly receding Pinus treeline, which appears more climatically controlled with decreased recruitment 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.