Life-forms and clonality of vascular plants along an altitudinal gradient in E Ladakh (NW Himalayas)

Altitudinal distribution of life-forms of vascular plants was studied in E Ladakh (W Himalayas, NW India) along one of the world's most prominent altitudinal gradients, ranging from 4180 to 6000 m a.s.l., in an area of 10,227 km(2). Among 404 species recorded in total, hemicryptophytes prevailed strongly (251 species, 62.1%), followed by therophytes with 90 species (22.3%). Chamaephytes comprised 22 species (5.4%) and geophytes 17 species (4.2%). Phanerophytes (14 species, 3.5%) and hydrophytes (7 species, 1.7%) were rare. The life-form spectrum reflects prevailing desert-steppe and steppe vegetation in the study area. A Monte Carlo test was used to obtain expected ranges in life-form diversity and abundance of individual life-forms along the altitudinal gradient. The number of actually present life-forms recorded from 50 m altitudinal steps was usually within the range expected from that null model, rarely lower than expected. The number of species belonging to chamaephytes, geophytes, hydrophytes and phanerophytes along the altitudinal gradient fall within the range predicted by the null model. Therophytes were under-represented in most altitudinal segments above 4900 m a.s.l. Nevertheless, many therophytes reach remarkably high altitudes in Ladakh as compared to other regions of Central Asia and the W Himalayas. Complementary to this pattern, hemicryptophytes were over-represented in most altitudinal steps from 4900 to 5600 m a.s.l. Relative abundance of geophytes and chamaephytes between 4150 and 5800 m a.s.l. was remarkably constant. Clonal plants comprised 26.7% of the total species number. About 30% of plant species were clonal from the lowest altitudes up to 5000 m a.s.l., from where the proportion of clonal plants gradually declined down to zero at the highest altitudes. Different factors are likely to be responsible for the relatively low proportion of clonal plants and their decline at higher altitudes. At the highest altitudes clonal plants with persisting inter-connections between widely spaced ramets are damaged by virtue of repeated freezing and thawing of the soil, breaking their integrated systems. In large screes at intermediate altitudes most types of clonal plants are injured by their mobility and at the lower altitudes tough soil texture prevents horizontal growth in the below-ground. Therefore, diversity of clonal plant types is small in prevailing habitats of the study area and most clonal plants are restricted to small patches of wetlands at intermediate and lower altitudes.