Effect of elevation and canopy on population structure and bark characteristics of Daphne bholua and edgeworthia gardneri in Dolakha, Nepal

Abstract

Traditionally, hand-made papers are made from the inner bark of species belonging to the family Thymelaeaceae. Thymelaeaceae species, particularly Daphne bholua and Edgeworthia gardneri, are commonly used in Nepal to create paper and are referred to as ‘Nepali Kagaj’. These traditional hand-made papers are in high demand among the international buyers due to its superior quality. The bark produced by plants is a key factor in determining the quality of paper, and this is influenced by the conditions in which they grow. This study attempts to assess population characteristics and bark-related traits of Daphne bholua and Edgeworthia gardneri along a gradient of elevation and canopy. For each species, altogether, 30 plots (10 × 10 m 2) were established, 10 each in three elevation sites (high mid and low). In each plot, all individuals of the target species were recorded with their girth size (measured at 20 cm above ground) and height. For measuring bark-related traits, individuals were sampled from three canopy types (close, semi-close and open) in each elevation site. Further, individuals of target species in each canopy type were grouped into different girth size classes (< 10 cm and > 10 cm for D. bholua; < 15 cm, ≥ 15 ≤ 20 cm and > 20 cm). Altogether, 15 bark samples (one sample per individual) per species per girth size were collected for the measurement of fibre length, bark thickness and dry weight. In total, 1070 individual ramets of D. bholua per plot (100 m 2) were recorded as highest density at the high elevation site, while density of E. gardneri was highest at the mid elevation site with 257 ramets per plot (100 m 2 ). The lower density of ramets at the lower elevation site was found to be associated with anthropogenic disturbances. In D. bholua, density of new ramet recruits was higher than that of adults and juvenile ramets while E. gardneri exhibited lower density of new ramet recruits than that of adults and juveniles. The longest average fiber lengths were observed measuring 7.78 mm and 5.83 mm in D. bholua and E. gardneri respectively. In conclusion, the study suggest higher elevation was important site for D. bholua while 2200 m was suitable site for E. gardneri in the study area. Similarly, D. bholua population are more successful in regeneration than E. gardneri in the particular area. The research also highlights elevation as important factor that determine bark-related traits in D. bholua, whereas both elevation and canopy were equally important in E. gardneri. However, combined forces of elevation, canopy and girth were more influential than independent factors upon bark-related traits. But the effects are not strong enough to explain exact cause. Therefore, future researches should explore other environmental factors, particularly those related to soil to make better inferences related to the factors governing bark traits. Overall, the study underscores the need for continued conservation programs to support the growth new ramet recruits and preserve the current population of these valuable species.