Habitat characteristics, population structure, and vegetative and reproductive traits of Juniperus indica Bertol. along elevation gradient in Manang, Nepal

Abstract

Elevation gradients are complex involving different co-varying factors that influence plant population structure and in traits related to life history. Studies pertaining to variation in such traits along the gradient provide opportunities to examine performance of plant populations under a range of environmental conditions. This study aims to assess variations in population structure and vegetative and reproductive traits of Juniperus indica Bertol. along elevation gradient in Manang, north-central Nepal. The whole of its distribution range was divided into lower- (3350-3580 m), mid- (3650-3880 m) and higher- (3950-4250 m) elevation bands, where populations were sampled in a total of 54 plots (18 plots per band) of 10 m x 10 m size. In each plot, we recorded habitat characteristics; number of individuals of J. indica classified into seedling, juvenile and adult; and vegetative (plant height, trunk diameter, canopy radius and leaf biomass) and reproductive (number of fruits per plant) traits of its adult individuals. J. indica preferred dry, rocky habitats in SE- to SW-facing slopes, along with Rosa-Berberis-Juniper shrubland, subalpine and alpine grasslands, and open forests. Altogether, 88 plant species, associated with J. indica, were identified. Plots in the lower- and mid-elevation bands mostly comprised woody shrubs, whereas herbaceous species dominated the higher-elevation band. Mid-elevation band tended to show highest density of seedlings and juveniles, but adult density was high in the plots at lower-elevation band. J. indica exhibited almost similar population structure in three bands, with high contribution of juveniles than seedlings and adults. However, proportion of adult was high in lower-elevation, whereas proportions of seedling and juvenile tended to be high in mid- and higher-elevations. Density-diameter (d-d) curve for adult J. indica was reverse J-shaped, indicating continuous regeneration. Most of the individuals were of moderate to small size. Mean leaf dry biomass was 28.98 kg per ha. The number of fruits per plant ranged 10-1040 (mean 202.9). J. indica showed higher values of all studied traits in lower-elevation than in mid- and higher-elevation bands. Trunk diameter, leaf dry weight and fruits set parameters spatially varied within the same elevation band. Regression analysis showed that the canopy area was the strongest allometric variable for predicting total leaf biomass.

Population density of J. Indica and its vegetative and reproductive traits are influenced differently by the variations in elevation. It is concluded that J. indica in Manang exhibits successful regeneration despite harsh ecological conditions. Higher regeneration at mid- and higher-elevation bands indicates plants ability to tolerate adverse environmental conditions as well as a tendency for expansion of its distribution niche towards cooler habitat of high elevation. The use of outer canopy area is the best option for nondestructively estimating above ground biomass of J. indica.

Key words: biomass, population density, regeneration, reproductive trait, vegetative trait.