Biomass and diversity of dry alpine plant communities along altitudinal gradients in the Himalayas

Abstract

A non-linear relationship between phytodiversity and altitude has widely been reported, but the relationship between phytomass and altitude remains little understood. We examined the phytomass and diversity of vascular plants along altitudinal gradients on the dry alpine rangelands of Ladakh, western Himalaya. We used generalized linear and generalized additive models to assess the relationship between these vegetation parameters and altitude. We found a hump-shaped relationship between aboveground phytomass and altitude. We suspect that this is engendered by low rainfall and trampling/excessive grazing at lower slopes by domestic livestock, and low temperature and low nutrient levels at higher slopes. We also found a unimodal relationship between plant species-richness and altitude at a single mountain as well as at the scale of entire Ladakh. The species-richness at the single mountain peaked between 5,000 and 5,200 m, while it peaked between 3,500 and 4,000 m at entire Ladakh level. Perhaps biotic factors such as grazing and precipitation are, respectively, important in generating this pattern at the single mountain and entire Ladakh.

Fig. 1

The Ladakh region with different study sites (1 proposed Ridzong Wildlife Sanctuary, 2 Hemis National Park, 3 proposed Gya-Miru Wildlife Sanctuary, 4 Changthang Wildlife Sanctuary), and the transects (broken line: trail = vegetation cover; dotted line: road = plant species richness) marked

Fig. 2

Non-linear relationship between aboveground phytomass (dry weight) and altitude in Ladakh

Fig. 3

Relationship between graminoid (a, c) and non-graminoid (b, d) species richness and altitude at a local scale (Hanle Valley). In c, d the solid lines are the cubic smooth splines and the dashed lines are 95% confidence limits

Fig. 4

Relationship between plant species richness and altitude at a regional scale (entire Ladakh). In b the solid line is the cubic smooth spline and the dashed lines are the 95% confidence limits

Fig. 5

CCA ordination of some common plant species in Ladakh and the environmental variables. See Table 1 for species identity. PreWetQ precipitation in the wettest quarter of the year, AnnPrec mean annual precipitation, PreDriQ precipitation in the driest quarter, AnMeTe annual mean temperature, MTeCoQ mean temperature of the coldest quarter, MTeWaQ mean temperature of the warmest quarter)

Fig. 6

Vegetation cover (%) as a function of slope angle and altitude during peak growth season in the mountainous region of Ladakh, India