Effect of a Nitrogen-Fixing Actinorhizal Shrub on Herbaceous Vegetation in a Mixed Conifer Forest of Central Himalaya

In this study, we examined the effect of a nitrogen-fixing shrub Coriaria nepalensis Wall on herb species composition, diversity and biomass. The effect was measured in terms of species richness, diversity and biomass of herb species in three sites varying in Coriaria density viz. site 1 (low Coriaria density; 20 ind. ha-1), site-2 (medium Coriaria density; 120 ind. ha-1) and site-3 (high Coriaria density 190 ind. ha -1 ). Species richness was minimum at Site-1 (16 species), and maximum at site-2 (27 species). G. aparine dominated site-1 and Arthraxon sp dominated site-2 and 3. The individual herb density ranged between 0.40 - 42.40 m -2 , and total herb density ranged between 138- 170.4 m -2 and was maximum at site-2. Value for species richness (27) and Shannon Index (3.72) was highest for medium Coriaria density site and lowest for low Coriaria density site. Simpson Index ranged between 0.11 and 0.14 and was lowest for site-2 (medium Coriaria density) indicating that at this the dominance was shared by many species. Along the gradient of Coriaria density, maximum biomass was recorded at site-3 with highest Coriaria density and lowest at site-2 with medium Coriaria density. This may be due to the symbiotic nitrogen fixing ability of Coriaria that improve the habitat quality. The facilitative effect of C. nepalensis in terms of soil amelioration and herb growth can be used to regenerate degraded forest ecosystems.