Invasive plants dominate habitats along transport corridor (roads) across elevation zones in eastern Bhutan

<title>Abstract</title> <p> Critical infrastructures like transport corridors (roads) create diverse ecological impacts by altering biotic and abiotic conditions, reshaping ecosystem structure from small patches to entire landscapes. Roadside vegetation reflects the balance between propagule arrival and seedling establishment, both of which are strongly shaped by local roadside conditions, surrounding landscape configuration, and elevation. Yet responses of native and invasive plant communities to elevation along these corridors remain poorly understood. Plant species richness was assessed across four elevation zones (624–2783 m above sea level) spanning ≈ 300 km of a transport corridor in eastern Bhutan, using linear and generalized linear mixed-effects models that accounted for quadrat-level variability. Roadside vegetation within 50 m of the road center was systematically sampled at 5 km intervals using a standard 1 × 1 m quadrat, with sampling locations carefully selected to avoid cliffs and duplication along winding sections of the road. Native species richness increased significantly with elevation, whereas invasive species richness declined. Linear mixed-effects models revealed moderate explanatory power for native (R²m = 29.54%, R²c = 61.49%, R ² m=marginal: measure of variance for fixed effect- elevation, R ² c= conditional: measure of variance for fixed effect + random effect- sampling points) and invasive species richness (R²m = 15.13%, R²c = 31.49%), indicating strong compensatory dynamics between species groups. Generalized linear mixed-effects models demonstrated a pronounced and highly significant difference between native and invasive species richness across elevation zones, explaining 95% (R2 = 0.95, p &lt; 0.001) of variance when accounting for random effects (variation by study site location). Native species richness showed a strong positive relationship with elevation (R² = 0.47, p &lt; 0.001), while invasive species richness declined with elevation (R² = 0.16, p &lt; 0.001); total richness was unrelated to elevation (R² = 0.02). These opposing trends indicate that elevation strongly structures plant community composition along transport corridors, favoring invasive dominance at lower elevations and promoting native species persistence at higher elevations, without altering overall species richness. The results demonstrate that development activities such as road penetration through ecosystems, along with trade and commercial thoroughfare lead to biodiversity alterations and the suppression of native species. </p>