Soil seed bank and vegetation dynamics along an altitudinal gradient in Grewia optiva Drumm. ex Burret patches of the Western Himalaya

Grewia optiva Drumm. ex Burret, a multipurpose tree species of the Western Himalaya, plays a significant role in agroforestry systems and rural livelihoods. The present study investigates the phytosociological attributes and soil seed bank dynamics across 5 altitudinal gradients (500-1000 m asl) along National Highway 07 in Uttarakhand. Vegetation analysis was carried out using quadrat sampling and key community parameters such as density, frequency, abundance, Importance value index (IVI) and diversity indices (Shannon-Wiener, Simpson and species richness) were computed. Soil seed bank composition was assessed through seedling emergence under controlled conditions. Results revealed marked altitudinal variation in species composition and community structure. Lower altitudes (500-600 m) were of high dominance of Bidens pilosa, Andropogon spp. and Ocimum basilicum, with lower diversity (H′ = 2.05) but the highest seed bank density. In contrast, higher altitudes (900-1000 m) exhibited greater species diversity (H′ = 2.70), richness and evenness, with species such as Holcus lanatus and Ageratina adenophora contributing significantly, although seed bank density was comparatively low. Mid-altitudes (600-800 m) showed intermediate patterns in both vegetation and seed bank attributes. ANOVA test reveals a significant difference in diversity index and seed bank potential across altitudinal gradients. A contrasting trend was observed between above-ground diversity and soil seed bank density, with a negative correlation between seedling abundance and diversity (r = - 0.72) and a positive association with species dominance (r = 0.73). These findings suggest that lower altitudes act as seed reservoirs dominated by opportunistic species, while higher altitudes support more stable and diverse plant communities. The study highlights the complementary roles of standing vegetation and soil seed banks in maintaining ecosystem dynamics and provides insights for biodiversity conservation and sustainable management of Himalayan Agroforestry systems.