Impact of forest fires on vegetation composition and soil properties of Pinus roxburghii forests in the Western Himalaya

Fire is a commom phenomenon in the Western Himalaya, particularly in the Pinus roxburghii (Chir Pine) forests. The frequent incidence of devastating fire events in these forests can result in serious ecological consequences, such as loss of biodiversity, changes in vegetation composition, and alterations in soil properties. Therefore, the current investigation was conducted to assess the impact of wildfires on the composition, species richness, dominance, and diversity of vegetation, as well as soil properties, in the P. roxburghii forests of the Western Himalaya. The findings indicated that the fire led to an increase (p<0.05) in the shrub species. On the contrary, the total number of tree species seedlings and herb species remained unchanged after the fire event. Further, results showed that the two pre-existing shrub species disappeared, and the three new species of shrubs emerged after the fire. Likewise, fire led to the emergence of five new herb species, while five pre-existing herb species disappeared. The overall seedling density of shrubs, herbs, and trees exhibited an increasing (p<0.05) trend in the post-fire scenario. Interestingly, the density and frequency of P. roxburghii trees were almost same both before and after the fire. The density and frequency of Berberis asiatica, Lantana camara, and Rhus parviflora shrubs increased following the fire, while Rubus ellipticus shrub exhibited a declining trend. Furthermore, in the post-fire conditions, the seedling density of P. roxburghii and Myrica esculenta trees increased (p<0.05), while the density of Quercus leucotrichophora decreased (p<0.05). Similarly, the density of Rumex hastatus and Oxalis latifolia herbs increased, while that of Desmodium elegans and Parthenium hysterophorus herbs decreased in the post-fire scenario. Among the different species, P. roxburghii (tree) , L. camara (shrub) , and P. hysterophorus (herb), were the most prevalent in both the pre- and post-fire scenarios. The diversity and abundance of tree seedlings decreased, shrubs increased, and the diversity of herbs remained unaffected in post-fire scenarios. The results further showed that the forest fire increased the soil pH, EC, and nitrogen levels, although organic carbon and potassium content decreased. Moreover, fire did not alter the levels of bulk density, phosphorus, and sulphur in the soil. Overall present study suggested that fire affects structure and composition of vegetation as well as alters soil properties in the Pinus roxburghii forests.