Assessing Forest Structure and Composition along the Altitudinal Gradient in the State of Sikkim, Eastern Himalayas, India

Abstract

Understanding the structure and composition of native forests is a prerequisite in developing an adaptive forest management plan for Himalayan forest ecosystems where climate change is rapid. However, basic information on forest structure and composition are still limited in many places of the Eastern Himalayas. In this study, we aimed to understand the diversity, structure, and composition of forests and their variations along an altitudinal gradient in Himalayan forests. The study was conducted in the Indian federal state of Sikkim, Eastern Himalayas. We carried out a comprehensive and comparative evaluation of species diversity, stand basal area, and stem density along the altitudinal gradient from 900 m a.s.l. to 3200 m a.s.l. We used stratified random sampling to survey eighty-three plots each 0.1 ha in forest communities that occurred along the altitudinal gradient: (a) lower (900-1700 m) altitude forest (N = 24), (b) mid (1700-2500 m) altitude forests (N = 37), and (c) higher (2500-3200 m)altitude forests (N = 22). We measured and identified all living trees with a >3 cm diameter at breast height in each plot. We counted 10,344 individual plants, representing 114 woody species belonging to 42 families and 75 genera. The family Fagaceae and its species Lithocarpus pachyphyllus (Kurz) Rehder. were reported as the most dominant forest trees with the highest Importance Value Index. The Shannon diversity index was recorded as being the highest for the low-altitude forests, whereas measures of structural diversity varied among forests along with altitude: the mid-altitude forests recorded the highest stem density and the high-altitude forests showed the highest mean stem DBH (diameter at 1.3 m height). One significant finding of our study was the disparity of the size class distribution among forests along the altitudinal gradient. Overall, we found a reverse J-shape distribution of tree diameter signifying the uneven-agedness. However, we showed, for the first time, a complete lack of large trees (>93 cm DBH) in the lower altitude forests. Our study highlights conservation concerns for the low-altitude forests that record high species diversity, although lacked large-diameter trees. We anticipate that our study will provide a comprehensive understanding of forest diversity, composition, and structure along the altitudinal gradient to design conservation and sustainable management strategies

Forest Structure and Composition under Contrasting Precipitation Regimes in the High Mountains, Western Nepal

“…Furthermore, the inverse J-shaped pattern documented for overall size class distribution in this study is similar to the findings of Bhutia et al [32] who found the highest number of individuals in the smallest DBH class of 3 to 13 cm and least in the highest class in Eastern Himalayan, India. This pattern is further supported by the findings of Shrestha et al [139], Dar et al [140], Pandey et al [127], and Schwab [141].…”

“…In lower-elevation tropical forests, higher species diversity and richness were recorded in high precipitation regions than dry regions in Myanmar by Khaine et al [123], and in mangrove forest [124] and sub-Saharan Africa [125] as well. Regarding forest structure, most studies [1,32,[126][127][128] have focused on Himalayan vegetation patterns along altitudinal gradients, though few have mentioned the importance of climate variables in predicting forest stand structure [21,129,130]. Considering forest structure varies with water availability [131], and environmental and biological factors control forest structure at higher elevations [132,133], this study tried to assess differences in forest structure along a precipitation gradient in the Annapurna range.…”

Differential water-use strategies in co-occurring pioneers and late-successional tree species in secondary tropical montane forests of Eastern Himalaya

“…The forest stand represents the East Himalayan broad-leaved wet montane forests (Sudhakar et al 2008, Kanade andJohn 2018) characterized by (a) the dominance of broad-leaved evergreen species and (b) sub-tropical montane climate with high precipitation and strong diurnal and seasonal temperature gradients. The vegetation data were derived from five 0.1 ha (100 m X 10 m) vegetation survey plots laid in FWS as part of another study (Bhutia et al 2019). In each plot, all individuals above 30 cm circumference at breast height were enumerated and voucher samples were collected for identification.…”

Population structure and regeneration of Himalayan endemic Larix species in three high-altitude valleys in Nepal Himalaya

“…Forests have traditionally been exploited in the study sites in multiple ways to maximize economic and social benefits. Recently, the socioeconomic organization in the highaltitude areas and public attitudes towards the forest and forestry have changed dramatically with the growth of tourism and other recreational activities (Nepal 2002;Stevens 2003;Sacareau 2009;Neupane et al 2014;Mu et al 2019), and the goals of forest management now extend far beyond those of the past to embrace the demand for new ecological and recreational functions (Maren and Sharma 2018;Bhutiya et al 2019).…”

“…Understanding the structure and composition of native forests is a prerequisite in developing an adaptive forest management plan for Himalayan forest ecosystems where climate change is rapid (Bhutiya et al 2019). Population demography is crucial to understand current species distribution patterns (Gaston 2009;Purves 2009;Bell et al 2013) and to predict their future dynamics (Pagel and Schurr 2012;Normand et al 2014).…”