Lantana camara and Ageratina adenophora invasion alter the understory species composition and diversity of chir pine forest in central Himalaya, India.
Plant invasion has been a major threat to biodiversity and ecosystem stability. In the present study, we have estimated the effect of two invasive alien species, Lantana camara and Ageratina adenophora on the understory vegetation composition and species diversity of chir pine (Pinus roxburghii) forests in the central Himalaya. We have selected three sites in pine forests and each site was divided into three subsites i.e. non-invaded (NI), Lantana camara invaded (LI) and Ageratina adenophora invaded (AI). In each subsite, 10 random quadrats for herbs (1 × 1 m) and shrubs (5 × 5 m) were laid down. In all the study sites, native herbs and shrubs species richness, diversity, and evenness changed due to invasive species. The presence of both the invasive species caused a reduction in native understory herbs and shrubs species number by 29-40% indicating a strong effect on native vegetation. Shrub density ranged from 6720 to 9680 individuals ha-1 and 8960 to 12000 individuals ha-1 in LI and AI sites, respectively. Total shrub basal area varied between 1.64 and 2.52 m2 ha-1 in LI sites and 1.76 and 2.24 m2 ha-1 in AI sites. Shrub density and basal area in NI sites (4200-6960 individual ha-1 and 0.60-0.96 m2 ha-1) were 2-3 times lower than LI and AI sites. Higher shrub density and basal area in LI and AI sites altered the vegetation composition and diversity of understory vegetation in pine forests. The dominance of invasive species also altered the soil physico-chemical properties. Their interrelationship among species assemblage, study sites and environmental variables showed the adverse impact of invasion on native species. This depletion of native flora is worrisome for both ecological as well as socio-economical perspectives and needs urgent attention of forest managers and policymakers.