Effect of altitudinal gradients on forest structure and composition on ridge tops in Garhwal Himalaya

Energ. Ecol. Environ. DOI 10.1007/s40974-017-0067-6 ORIGINAL ARTICLE Effect of altitudinal gradients on forest structure and composition on ridge tops in Garhwal Himalaya C. M. Sharma1 • Ashish K. Mishra1,2 • O. P. Tiwari1 • Ram Krishan1 • Y. S. Rana1 1 2 Department of Botany, H.N.B. Garhwal University, Garhwal Srinagar, Uttarakhand 246174, India Department of Environmental Science, Babasaheb Bhimrao Ambedakar University, Lucknow, UP, India Received: 1 July 2016 / Revised: 20 May 2017 / Accepted: 7 July 2017  Joint Center on Global Change and Earth System Science of the University of Maryland and Beijing Normal University and Springer-Verlag GmbH Germany 2017 Abstract Ridge top ecosystems (RTEs) are considered to be more sensitive to global warming as they are characterized by uniform sunlight exposure and low human interferences and hence are perfect places for monitoring and comparing the effects of climate change in species composition. The present study was carried out on RTEs of four different mountain ranges, viz. (1) Narendranagar– Hindolakhal (2) Mussoorie–Dhanolti (3) Chaurangikhal– Harunta and (4) Dayara–Gidara, along altitudinal gradient (situated below 2000 to above 3500 m), in Garhwal Himalaya to understand the variation in tree composition and distribution range. 0.1 ha-sized sample plot was used to analyze the tree species, whereas 5 m 9 5 m for saplings and 1 m 9 1 m for seedlings. The tree layers on RTEs were consisted of total 69 tree species, belonging to 55 genera and 39 families. Shorea robusta, Pinus roxburghii, Rhododendron arboreum, Quercus leucotrichophora, Q. floribunda, Q. semecarpifolia, Cedrus deodara, Pinus wallichiana and Abies spectabilis were found as the dominant and well-occupied tree species on the RTEs from lower to higher elevations. The mean stand density was recorded as 597 ± 29 trees ha-1 (ranged between 546 and 616 trees ha-1) with a mean basal cover of 77.25 ± 17.90 m2 ha-1 (ranged between 54.43 and 102.83 m2 ha-1). A traditional pattern for tree diversity was recorded which decreased with increasing altitude. The detrended correspondence analysis ordination plot clumped the species together which shared the same habitat and C. M. Sharma and Ashish K. Mishra have contributed equally to this work. & Ashish K. Mishra environmental conditions which revealed that elevation and geographic location were the dominant factors for regional differences in species composition among RTEs. Keywords Climate change
Ecological indicators
Forest composition
Ridge top ecosystems
Detrended correspondence analysis 1 Introduction The ridge top ecosystems (RTEs) are considered to be more sensitive to global warming as they are characterized by uniform sunlight exposure and low human interferences and hence are perfect places for monitoring and comparing the effects of climate change and predicting the future changes in species composition. In Himalayan region, elevation and climatic factors are the governing factors for regional differences in species composition (Lee and Chun 2016; Sharma et al. 2016). Furthermore, it is supposed that in the event of a rise in temperature at lower elevations the movement/migration of vegetation would be toward upper elevational (Chen and Hill 2011). The recent global warming has resulted in disturbances of ecological relationships, alteration in plant life history and general upward shift in the species distributional ranges (Jurasinski and Kreyling 2007; Pauli et al. 2012). Climate controls the distribution of vegetation (Sharma et al. 2016), and thus, future changes in climate are projected to cause changes in the vegetation distribution ranges. Several studies have attributed widespread changes in plant growth or mortality to climate change, but these efforts have focused on general trends within a biome rather than identifying spatially 123 C. M. Sharma et al. coherent distribution pattern (Pauli et al. 2007; Engler et al. 2009). The composition and ecosystem services of Himalayan forests depend on forest structure, which is believed to be changing over time. Gottfried et al. (2012) reported ample evidences that ongoing climate change continuously affects the Himalayan Vegetation along with its different components. Rapid geo-climatic variations at different altitudes in Himalaya generate diverse vegetation structure and high species diversity (Chawla et al. 2008). Intensity of major threats to forest ecosystems and biodiversity along altitudinal gradient is directly measured by compositional changes in forest structure. Role of habitat loss due to fragmentation, overexploitation, invasion by alien species and global climate change is premier in disruption of community structure along the altitudinal gradient, which can be used to assess the status of forest composition and alert for future changes. Lots of work have been done on the effects of elevational gradients on forest structure and composition (Sharma et al. 2010; Gairola et al. 2012; Rawat and Chandra 2014), but the studies on change in species composition on RTEs along the altitudinal gradient in Himalaya are completely lacking. In the western Himalayan region, along lowest and highest elevational transects the changes in forest composition are evident, but they are required to be measured properly (Chitale et al. 2014; Sharma et al. 2014). Projecting future changes in species composition and distribution of vegetation on RTEs at different altitudes is a crucial step toward planning and mitigating the impacts of climate change on biodiversity. The aim of the study is to describe and analyze the forest structure, composition and distribution pattern along elevational gradients, in order to explain the changes in forest composition and characters of forests on RTEs in response to changing climate. 2 Methodology 2.1 Study area The study was conducted in four different mountain ranges, viz. (1) Narendranagar–Hindolakhal (\2000 m) (2) Mussoorie–Dhanolti (1900–2900 m) (3) Chaurangikhal–Harunta (2400–3300 m) and (4) Dayara–Gidara (2500–3750 m), of Garhwal Himalaya to assess tree species composition and distribution on different RTEs along the elevational gradient (Above sea level). For this purpose, we selected the RTEs from lower to higher elevations in aforesaid different mountain ranges. In these ranges, the selected RTEs were studied on five different elevations, viz. (a) \2000 m (b) 2000–2500 m (c) 2500–3000 m (d) 3000–3500 and (e) [3500 m. The study areas were 123 situated in the catchment of river Ganges (called Bhagirathi toward upstream). Details of study area, forest types and dominant tree species within the selected elevations are shown in Table 1 and Fig. 1. All the mountain ranges were characterized by undulating topography with gentle slopes on northern, northeastern and northwestern faces and somewhat steep slopes on southern and southwestern directions. Ridges are continuous elevated top made by chain of mountains ( (...truncated)