Factors determining the invasion pattern of Ageratina adenophora Spreng. in Kumaun Himalaya India

Abstract

Factors such as topography, soil composition, and nutrient availability significantly influence the density patterns of Ageratina adenophora. Understanding these dynamics addresses a gap in our knowledge of the species' adaptive mechanisms in mountainous regions. Furthermore, the impact of habitat features along road corridors on the population dynamics of invasive plants remains underexplored, particularly regarding the effects of disturbance levels, light availability, and soil properties on their establishment. A species-specific rapid ecological assessment was conducted using stratified random sampling, with parallel transects of 50 × 2 m established in triplicates at 20 m intervals. This resulted in 43 main transects across the identified plots and 67 parallel transects in adjacent habitats. The number of individuals of A. adenophora and its clumps were recorded from each quadrat. Chemical and physical parameters of soil were measured for soil collected from 0 to 15 cm depth. Linear Mixed Model analysis revealed a significant negative effect of elevation (p<0.05) on the density of clumped individuals (Estimate: −0.31, t-value: −3.05), total individuals (Estimate: −0.27, t-value: −2.61), and clump number (Estimate: −0.30, t-value: −4.78). Western aspect also showed a significant decrease (p<0.05) in clumped individuals (Estimate: −1.83, t-value: −2.80), total individuals (Estimate: −2.24, t-value: −3.47), and clump number (Estimate: −0.81, t-value: −1.97). Total A. adenophora density was highest near settlements (133 ind. m², Estimate: 1.19) and grasslands (103 ind. m², Estimate: 1.16), but lowest in broadleaf forests (26 ind. m²). Density decreased significantly with increasing distance from road verges (Estimate: −0.24, t-value: −2.34). Soil moisture content positively influenced total individuals (Estimate: 0.19, t-value: 2.75), clumped individuals (Estimate: 0.23, t-value: 3.20), clump numbers (Estimate: 0.05, t-value: 1.09), and individuals per clump (Estimate: 0.37, t-value: 3.28). Available nitrogen positively influenced non-clumped individuals (Estimate: 0.17, t-value: 2.04) but negatively affected individuals per clump (Estimate: −0.25, t-value: −2.21), indicating that lower nitrogen levels correlate with higher individual density per clump. Hence, effective restoration efforts are needed including soil improvement, invasive species removal and control, and the planting of native species.