Altitudinal gradients shaping tree diversity and regeneration dynamics in mountainous ecosystems

Himalayan forests are crucial for ecological roles but face threats from natural and human factors. This study examines tree diversity, regeneration patterns, and human-induced threats in the Kashmir Western Himalayas. We use indices and multivariate analysis to investigate species richness, composition shifts, and the impact of ongoing anthropogenic threats on forest ecosystems.

Vegetation sampling was conducted at 45 sites in the Kashmir Himalayas, at elevations of 600 to 3600 m. Data were collected using quadrat methods. To investigate species diversity, composition, and human influences, statistical analyses such as Shannon and Simpson indices, Non-metric multidimensional scaling (nMDS), Principal Component Analysis (PCA), Canonical Correspondence Analysis (CCA), and regression models were performed using R software and OriginPro.

A total of 33 tree species were recorded in different ecological zones: the temperate zone had the most species (22), followed by the subtropical zone (16) and the subalpine zone (7). The temperate zone had the highest Shannon index (2.15 ± 0.24) and Simpson index (0.86 ± 0.03), while the subalpine zone had the lowest Simpson index (0.48 ± 0.20). The subtropical zone had the highest evenness index (0.95 ± 0.04). PCA showed that PC1 explained 37.2% of the variation and PC2 explained 14.9%. Human-induced disturbances were significant drivers of species composition shifts, particularly in the subtropical and temperate zones, accounting for 11% of the variation. Picea smithiana had the highest density in the temperate zone (615.62 individuals per hectare). The regression analysis indicated a quadratic relationship between tree density and DBH (R² values from 0.66641 to 0.92089). Regeneration patterns varied: Pinus roxburghii had high seedling density in the subtropical zone, while Abies pindrow and Pinus wallichiana regenerated well in the temperate zone, and recruitment was limited in the subalpine zone.

Elevation significantly influences on tree diversity and regeneration patterns, while human-induced factors shape species composition. Anthropogenic activities notably affect tree diversity, especially at lower elevations, thereby threatening ecosystem resilience. This study emphasizes the necessity of sustainable forest management practices to mitigate human impacts and promote forest regeneration, particularly in subtropical and temperate zones.