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.

植物入侵已成为对生物多样性和生态系统稳定性的主要威胁。在本研究中，我们已经估计了喜马拉雅中部的两种入侵外来物种，马Lan丹（Lantana camara）和紫茎泽兰（Ageratina adenophora）对赤松林（Pinus roxburghii）林下植被组成和物种多样性的影响。我们在松树林中选择了三个地点，每个地点都分为三个子地点，即非入侵（NI），马Lan丹（Lantana camara）入侵（LI）和紫茎泽兰入侵（AI）。在每个子站点中，放置了10个随机的四方方型的草药（1×1 m）和灌木（5×5 m）。在所有研究地点，由于入侵物种，当地草药和灌木物种的丰富性，多样性和均匀性发生了变化。两种入侵物种的存在都导致天然林下草药和灌木物种数量减少了29–40％，这表明对原生植被的影响很大。LI和AI站点的灌木密度分别为6720至9680个ha ^-1和8960至12000个ha ^-1。LI位置的灌木总面积在1.64至2.52 m ²  ha ^-1之间，而在1.76至2.24 m ² ha ^{-1之间变化}在AI网站中。NI地点（4200–6960个人ha ^-1和0.60–0.96 m ²  ha ^-1）的灌木密度和基础面积比LI和AI地点低2-3倍。LI和AI地区较高的灌木密度和基础面积改变了松树林的植被组成和林下植被的多样性。外来入侵物种的优势也改变了土壤的理化特性。它们在物种集合，研究地点和环境变量之间的相互关系表明入侵对本地物种的不利影响。这种原生植物的枯竭对于生态和社会经济观点都是令人担忧的，需要森林管理者和决策者紧急关注。