Facilitative effects of a dwarf shrub increases diversity of an alpine rangeland
Siddharth Iyengar1, Sumanta Bagchi2, Charudutt Mishra3, Deepak Barua1, Mahesh Sankaran4; 1 Iiser Pune, 2 Ii Sc Bangalore, 3 Ncf, Mysore And 4 Ncbs Bangalore
Rangelands of the upper Spiti Valley are dominated by a dwarf shrub Caragana versicolor. Many plants grow within its canopy; suggesting that Caragana may facilitate plant growth in this harsh and heavily grazed environment. The importance of this to the rangeland has not been studied. We have estimated the contribution of the Caragana microenvironment to diversity of the plant community, and how this effect varies with altitude and different grazers.
During June-July 2012, 90 shrubs and paired outside plots of equal area were sampled, across three watersheds differing in altitude and grazing type. All plants growing in the plots were recorded, classified as growing in the centre or edge of the shrub. Paired soil samples were collected from within and outside the shrub. Pairwise comparisons of plot level species richness (SR) and abundance (AB) were used to estimate the effect of the Caragana on the community.
The community within Caragana had 27% greater SR than that outside. Forbs and grasses, which are important forage, had 30% greater SR and 95% greater AB within the canopy. The canopy edge harboured greater SR and AB than the larger centre, and similar SR to outside plots the size of the whole plant. Soil organic matter was higher under Caragana. With increase in altitude, SR decline is lower within the canopy centre than outside. These support our hypothesis of facilitation.
This study shows that Caragana significantly modifies the plant community of this sparse rangeland, enhancing biodiversity of the entire landscape. It may provide a better microenvironment for germination and growth, and provide refuge from herbivory. Caragana grows very slowly, but is harvested by villagers for use in roofing. Further studies can reach a better understanding of mechanisms causing these patterns and the implications of its removal.