Himalayan Elevation Gradient Research Articles

Distribution pattern of reptiles along an eastern Himalayan elevation gradient, India

We examined the spatial distribution pattern of reptiles in an eastern Himalayan elevation gradient. The factors governing the distribution have been assessed with emphasis on the mid-domain effect. We surveyed reptiles along the elevation gradient (300–4800 m) of the Teesta valley in Sikkim, Eastern Himalaya, India using time constrained visual encounter survey. A total of 42 species of reptiles were observed during the study, and the species richness peaked at 500–1000 m with no species beyond 3000 m. The observed pattern was consistent with estimated richness, both showing significant negative relation with elevation. Lizards showed a linear decline with elevation, whereas snakes followed a non-linear relation with peak at 500–1000 m. Observed species richness deviated significantly from that predicted by a mid-domain null model. The regression between empirical and simulated richness was not significant for total reptiles as well as lizards and snakes separately. Most species distributed in the high elevation extended towards lower elevation, but low elevation species (around 50%) were restricted below 1000 m. Deviation of empirical from predicted richness indicates that the distributions of reptile species were least governed by geographic hard boundaries. Climatic factors especially temperature explained much variation of reptiles along the Himalayan elevation gradient. Most reptiles were narrowly distributed, especially those found in low elevation indicating the importance of tropical low-land forests in the conservation of reptiles in Eastern Himalayas.

Can Rapoport's rule explain tree species richness along the Himalayan elevation gradient, Nepal?

ABSTRACTRapoport's rule applied to an elevation gradient predicts a positive correlation between elevation ranges and elevation. This is supposed to be caused by the increasing magnitude of the climatic extremes at higher elevations, and thus, it is deduced that species richness should decrease with increasing elevation. The distribution of 614 tree species was used to test Rapoport's elevational rule along a gradient from 100 to 4300 m a.s.l., in the Nepalese Himalaya. The relationship between species richness and elevation was analysed by using generalized linear models (GLM). Generalized additive models (GAM) were used to examine the relationship between elevational range and the elevational mid‐point of a species along the gradient. The widest elevation ranges are observed at mid‐elevations, and narrow elevation ranges are observed at both ends of the gradient. This does not support Rapoport's elevation rule, as proposed by Stevens. There is a peak in species richness between 900 and 1000 m, and not in the tropical lowland as projected by Rapoport's elevation rule.

The environmental control of plant species density on a Himalayan elevation gradient

AbstractAim In eastern Nepal, forests occupy an elevation gradient of 4000 m with bioclimatic zones from near tropical to alpine. Understorey plants and trees were censused to measure species density and identify patterns of ecological change. By sampling in a manner robust against spurious mid‐domain effects, I aim to identify biologically valid controls on species density.Location The study area consists of land below 4250 m elevation between 27.1 and 27.8° N latitude, 86.5 and 88.0° E longitude on the southern slopes of the Himalaya Range in eastern Nepal. Sampling sites are limited to intact, natural forest with relatively little human impact.Methods Team members counted species of understorey plants and trees ≥ 10 cm d.b.h. in 0.04 ha plots throughout the study area. In addition, basal area, leafing phenology and species composition were determined for the trees in each plot. Estimates of regional species density were compiled for successive 250 m elevation bands from 250 to 4250 m elevation. Species density trends were identified and compared with the expectations of O'Brien's [Journal of Biogeography25 (1998) 379–398] climate‐based water–energy dynamics model.Results Stand basal area, tree leafing phenology and taxonomic composition (angiosperm vs. gymnosperm) show non‐random change with elevation. Understorey plant and tree species density both have a humped, unimodal trend with more species near the bottom of the gradient and fewest at the top. These trends are consistent with expected effects of the climatically active water and energy variables. After curve‐fitting, significant spatial structure in the residuals suggests that tree communities within the 1750–2250 m elevation range do not realize their climatic potential species richness.Main conclusions Neither mid‐domain effects nor biologically valid boundary effects like dispersal limitation explain the plant species density trends observed. Trends do fit a model in which species density is controlled by the same ‘active’ climatic variables that predict species richness on continental scales. Patterns of leafing phenology on the elevation gradient provide further support for the hypothesis of environmental control of species density. The productivity–diversity linkage that exists on continental scales may also apply on the smaller scale of a Himalayan elevation gradient. Human activity and possible competitive exclusion by Castanopsis tribuloides are the two best explanations for the observed decline in tree species density at 1750–2250 m elevation. Burning, lopping for fodder and livestock grazing might account for the decline, but this study does not assess the relative importance of these activities. The elevation richest for understorey plant and tree species (500–1500 m) also has the most severe reduction in forest cover. Local farmers deserve credit for sustaining plant biodiversity in forest enclaves, but further loss of forest at these elevations should be discouraged.

Fern species richness along a central Himalayan elevational gradient, Nepal

AbstractAim The study explores fern species richness patterns along a central Himalayan elevational gradient (100–4800 m a.s.l.) and evaluates factors influencing the spatial increase and decrease of fern richness.Location The Himalayas stretch from west to east by 20°, i.e. 75–95° east, and Nepal is located from 80 to 88° east in this range.Methods We used published data of the distribution of ferns and fern allies to interpolate species elevational ranges. Defining species presence between upper and lower elevation limit is the basis for richness estimates. The richness pattern was regressed against the total number of rainy days, and gradients that are linearly related to elevation, such as length of the growing season, potential evapotranspiration (PET, energy), and a moisture index (MI = PET/mean annual rainfall). The regressions were performed by generalized linear models.Results A unimodal relationship between species richness and elevation was observed, with maximum species richness at 2000 m. Fern richness has a unimodal response along the energy gradients, and a linear response with moisture gradients.Main conclusions The study confirms the importance of moisture on fern distributions as the peak coincides spatially with climatic factors that enhance moisture levels; the maximum number of rainy days and the cloud zone. Energy‐related variables probably control species richness directly at higher elevations but at the lower end the effect is more probably related to moisture.

Distribution of vascular plant species richness and endemic richness along the Himalayan elevation gradient in Nepal

AbstractAim Species richness and endemic richness vary along elevation gradients, but not necessarily in the same way. This study tests if the maxima in gamma diversity for flowering plants and the endemic subset of these plants are coherent or not.Location The study was conducted in Nepal, between 1000 and 5000 m a.s.l.Methods We used published data on distribution and elevational ranges of the Nepalese flora to interpolate presence between maximum and minimum elevations. Correlation, regression and graphical analyses were used to evaluate the diversity pattern between 1000 and 5000 m a.s.l.Results The interval of maximum species endemic to Nepal or the Himalayas (3800–4200 m) is above the interval of maximum richness (1500–2500 m). The exact location of maximum species density is uncertain and its accuracy depends on ecologically sound estimates of area in the elevation zones. There is no positive statistically significant correlation between log‐area and richness (total or endemic). Total richness is positively correlated with log‐area‐adjusted, i.e. estimated area adjusted for the degree of topographic heterogeneity. The proportion of endemic species increases steadily from low to high elevations. The peak in endemism (c. 4000 m) corresponds to the start of a rapid decrease in species richness above 4000 m. This may relate to the last glacial maximum (equilibrium line at c. 4000 m) that penetrated down to 2500–3000 m. This dynamic hard boundary may have caused an increase in the extinction rate above 4000 m, and enhanced the probability of isolation and facilitated speciation of neoendemics, especially among genera with a high proportion of polyploids.Main conclusions The results reject the idea of corresponding maxima in endemic species and species richness in the lowlands tentatively deduced from Stevens’ elevational Rapoport effect. They confirm predictions based on hard boundary theory, but hard‐boundaries should be viewed as dynamic rather than static when broad‐scale biogeographical patterns with a historical component are being interpreted.

Commercially important medicinal and aromatic plants of Nepal and their distribution pattern and conservation measure along the elevation gradient of the Himalayas

This study aims to assess and evaluate the number of commercially important medicinal and aromatic plants (MAPs) found in the trade and explore their distribution pattern and conservation measures along the Himalayan elevation gradient of Nepal. The species data for this study are based on primary as well as secondary sources, where as elevation range data are based only on secondary sources. The number of MAPs species and number of conservation sites present in each 100 m elevation band is estimated by interpolation. The assessed numbers of commercial MAPs are assigned in to different life forms group to find the life form spectrum of commercial species. The number of MAPs species and conservation sites present in each 100 m elevation band are evaluated as a response variable where as elevation gradient is the predictor. The relationship between them is elucidated by scatter plot as well as generalised liner models.
 
 In this study, we have assessed 143 species as commercial MAPs. The variation of MAPs species is found related to elevation. The MAPs species richness increases with increasing the elevation up to 1000 m then decrease with further increasing the elevation thus unimodal type of pattern is observed. The maximum numbers of MAPs are found at 1000 m but maximum numbers of conservation sites are found above this elevation range. We did not find the significant pattern between conservation sites and MAPs species richness along the elevation gradient of the Himalayas. The conservation sites of Nepal are less concentrated where MAPs species diversity is rich. 
 
 Key words: Medicinal and aromatic plants, elevation gradient, species richness, generalised linear model 
 
 Banko Janakari Vol.16(1) 2006 pp3-13