Effect of invasive alien plant species on chir pine forest understory vegetation composition, diversity and soil properties in the central Himalaya, India

Abstract

Plant invasion has been considered as one of the major threats to biodiversity, soil cycle, ecosystem services and livelihood. In the present study, we have estimated the effect of two invasive alien species, Lantana camara and Ageratina adenophora on the understory vegetation composition, species diversity and soil properties of chir pine (Pinus roxburghii) forests in the central Himalaya. We have selected three sites (Chanfi, Matial and Mehra) in pine forests and each site was divided into three subsites i.e. non-invaded (NI), L. camara invaded (LI) and A. adenophora invaded (AI). In each subsite, 10 random quadrats for herbs (1 ×1 m) and shrubs (5 ×5 m) were laid down and soil samples were collected seasonally in triplicate from the surface (0–10 cm) and subsurface (10–20 and 20–30 cm) depths. The presence of both the invasive species changed species richness, diversity, evenness and caused a 29–40% reduction in native understory herbs and shrubs species number. Shrub density and basal area in NI sites (4200–6960 individual ha-1 and 0.60–0.96 m2 h-1) were 2–3 times lower than LI and AI sites. PCA and correlation analysis were conducted to explore the relationship between soil properties, status (invaded and non-invaded) and soil depths. The soil variables were further compared between status and depth using linear mixed-effect model (LMM) and Tukey’s HSD test. It was found that in LI and AI sites, soil properties such as moisture (Mo), porosity (Po), organic carbon (OC), total nitrogen (N), potassium (K), microbial biomass carbon (MBC) and nitrogen (MBN) were significantly (p <0.05) higher and bulk density (BD) was lower in the surface soil (0–10 cm) than NI site but the difference was less prominent in subsurface (10–20 and 20–30 cm) depths. The results indicated that L. camara and A. adenophora invasion altered vegetation composition and soil properties and develop nutrient-rich substratum which may further promote the invasiveness in chir pine forest. This depletion of native flora and change in soil properties is worrisome for both ecological as well as socio-economical perspectives and needs urgent attention of forest managers and policymakers.