Carbon and phosphorus content in soil influences the localized abundance of tree fern Alosphila spinulosa in panchase protected forest area, Nepal

Tree ferns hold significant ecological and socioeconomic value. In Nepal, they have restricted distribution, occurring in a few patches from eastern to central Nepal. In the localities where they occur, tree ferns are threatened by various anthropogenic pressures. Despite these threats, the influence of environmental variables on the localized distribution and abundance of the species is poorly understood in the country, hindering our ability to devise and implement tailored conservation actions. Our study aimed to investigate the influence of edaphic factors on tree fern abundance in the Panchase Protected Forest Area (PPFA), Central Nepal. This investigation may provide insights into specific factors that can be managed on a fine scale to conserve their populations. We surveyed 43 plots measuring 20 m × 20 m to record the tree fern abundance and collect soil samples. Composite soil samples obtained from the four corners of each plot at a depth of 15 cm were prepared and further analyzed in the laboratory using standard methods for each parameter. An independent sample t-test was applied to assess the difference in site characteristics between tree fern-present and absent sites. Generalized linear regression (Poisson family) was used to examine the fine-scale factors associated with tree fern abundance. Tree fern abundance was found to be correlated with the availability of soil phosphorus and soil carbon. Soil carbon was found to be the most important factor determining the tree fern abundance. A unit increase in percentage soil carbon increases the abundance of tree fern by 47 %, while a unit increase in phosphorus increases the abundance by 1.1 %. Soil pH has a positive influence on the abundance, while nitrogen content has a negative influence, though the relationship was not significant. Our findings emphasize the importance of managing edaphic variables for the conservation of the species.