Using functional traits to explore the plant diversity patterns across the elevation ranges of the Teesta river basin of Sikkim Himalayan region

Roy, Sourav (2019) Using functional traits to explore the plant diversity patterns across the elevation ranges of the Teesta river basin of Sikkim Himalayan region. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

To know how plant fitness and phenotypic expression change along environmental gradients is necessary for understanding the response of plant communities to global change drivers. In our study, we used the functional trait approach in order to understand this aspect. The power of the functional trait approach is firstly, it takes into account the relative abundances of the plant species and secondly, the traits of interest are easily measured allowing one to generate a distribution of species-level trait values even in extraordinarily species diverse communities. Spatial variation in filters imposed by the abiotic environment causes variation in functional traits within and among plant species which is sufficiently clear for plant species along altitudinal gradients, where parallel abiotic selection pressures give rise to predictable variation in leaf phenotypes among ecosystems. Understanding the factors responsible for such patterns may provide insight into the current and future drivers of biodiversity, local community structure and ecosystem function. In order to explore patterns in trait variation along elevational gradients, we conducted a study across the elevation ranges of the Teesta river basin of Sikkim Himalayan region. These functional trait studies are relatively well studied for temperate ecosystems, but may well be critically important for tropical forest ecosystems. We measured functional traits like specific leaf area, Leaf C:N ratio, wood density, petiole length and Leaf dry matter content for 56 plant species across the elevation range 600-3000m above sea level, which was further divided into three elevation bands viz. Low(600-1300m), Mid(1400-2100m) and High(2200-3000m).Leaf and wood core samples were collected from 147 plots across different elevations, which were then measured by using various techniques. Our results pointed out to a very interesting conclusion which we would like to mention. In the graphs of community weighted mean(CWM) of specific leaf area vs. altitudinal range and CWM of leaf dry matter content vs. altitudinal range, we found a hump shape in the curve at around 1400m which was our mid elevation. A previous study by (Terborgh et al.1977) points to the fact that a peak in species richness around 1400 m will be observed, as the result of a local "hot-spot" in resources(species richness doesn’t take into consideration the relative abundances of the species but functional trait takes relative abundance of the species into consideration). Our results indicate that even if we consider functional trait variation with elevation, then also the result of Terborgh et al.1977 holds.

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