With regard to the exposure to monsoon rain (June to September), the Himalayas are split into two parts: (i) the outer moist ranges, directly exposed to monsoon thrust, generally receiving > 1500 mm annual precipitation, and (ii) the inner, monsoon-shadow dry ranges, generally with 70% in outer ranges, and ~ 30% to 70% in inner ranges. The dominant conifers include species of Cedrus, Abies, Pinus, Picea, Tsuga, Larix and others, and they vary in their distribution in relation to outer and inner ranges. The PCA shows a strong climatic structuring of conifer species distribution along precipitation gradients. The first two principal components explain a substantial share of environmental variance (PC1 = 54.3%, PC2 = 20.5%), indicating that species distributions are largely structured by temperature, precipitation, and elevation-related factors. On average, plant species richness is significantly lower in the dry inner ranges (25.5 species per forest type) than moist outer ranges (52 species per forest type). Winter snowfall which is a conspicuous feature in the inner ranges provides melt water for plant growth, and protection to the seeds lying on ground for several months.
Singh et al. (Mon,) studied this question.