Abstract
Global warming is triggering some species to shift towards the poles or higher elevations, but spatial translocation is also influenced by land-use regime or intensity. The Himalayan climate is getting warmer and land use has changed, reducing in intensity in some areas. We estimated the upper species limit (USL) and tree limit of Abies spectabilis (D. Don) Spach and assessed whether these have changed over recent years. We hypothesise an upslope shift in response to enhanced temperature and changes in land-use intensity. Our four transects were located in treeline ecotones of two protected areas in Nepal, namely Manaslu Conservation Area (3 transects) and Gaurishankar Conservation Area (1 transect). Transects (20 m wide) ran from the USL of A. spectabilis down towards the treeline and beyond to the forest line. Length of each transect varied depending on local conditions. Co-ordinates, elevation, height and age of each A. spectabilis individual along the transects were recorded. We noted an upward shift of both the USL and the tree limit. The rate of shift was ca. 20 m per decade for the USL and 12 m per decade for the tree limit in the area of reduced land-use intensity and in the area with no change in land use, 5 m per decade for the USL, but almost nil for tree limit. The seedling density was higher below the treeline than above. Reduced intensity of land use was the dominant factor in upslope shift of A. spectabilis at both the USL and the tree limit.
Highlights
The treeline in the mountains is one of the most fundamental ecological and conspicuous physiognomic boundaries along the elevation gradient (Harsch et al 2009; Holtmeier 2009; Schickhoff 2005)
The natural alpine treelines are the result of heat deficiency that adversely affects growth, regeneration and survival of trees, and they are sensitive to climate change (Korner and Paulsen 2004)
The upslope shift for different species ranged from 586 to 787 m on the Chimborazo volcano in Ecuador over a 210-year period (MoruetaHolme et al 2015); in the Engadine valley of Swiss Alps, more than 100 m upslope shift has been reported during the last nine decades (Frei et al 2010) and 87 percent of 124 endemic plants species have expanded their range in Sikkim Himalaya during the last ca. 150 years (Telwala et al 2013)
Summary
The treeline in the mountains is one of the most fundamental ecological and conspicuous physiognomic boundaries along the elevation gradient (Harsch et al 2009; Holtmeier 2009; Schickhoff 2005). The natural alpine treelines are the result of heat deficiency that adversely affects growth, regeneration and survival of trees, and they are sensitive to climate change (Korner and Paulsen 2004). Several recent studies document an upslope or poleward shift of species at the treeline and suggest that this is partly as a result of recent global warming Chen et al 2011; Lenoir et al 2008; Telwala et al 2013), making it difficult to determine the role played by climate in any changed scenario. The treeline has shifted upwards in Barun valley in central Himalaya in the last 130 years (Chhetri and Cairns 2015), and A. spectabilis has shifted upslope in Manaslu region, central Himalaya in the last ca. The treeline has shifted upwards in Barun valley in central Himalaya in the last 130 years (Chhetri and Cairns 2015), and A. spectabilis has shifted upslope in Manaslu region, central Himalaya in the last ca. 160 years (Gaire et al 2014)
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