Impact of forest fire frequency on floristic diversity in the forests of Uttarakhand, western Himalaya

Abstract

The Uttarakhand State of India is rich in forest wealth with 45.4% forest cover (India State of Forest Report (2021). However, forest cover may change due to a number of anthropogenic and environmental factors. One of the factors leading to forest degradation is forest fires. Forest fires are related to factors that may be biotic, such as heavy accumulation of Chir pine (Pinus roxburghii, a dominant forest forming tree) needles on the forest floor influencing fuel load accumulation and flammability, or abiotic, such as climate, topography, or soil type influencing fuel moisture and fire spread. This study was carried out using satellite images of study area where fire was classified using the geographical information system (GIS) into four frequency classes (no fire, low fire, moderate fire, and high fire). We sampled a total of 160 quadrates for trees, 320 for shrubs and 480 for herbaceous plants to assess vegetation diversity for each forest fire frequency class. No fire was recorded for 13,619 sample points, which covers an area of 84% of the study area, whereas low fire frequency was recorded for 1784 sample points covering an area of 11%. In the present study, significant differences in species diversity were observed across the fire frequency classes. While species diversity increased in the low fire frequency class, an increase in fire frequency led to a decline in diversity and increased dominance of certain fire-tolerant species. Our results show that species richness and density decreased in higher fire frequency classes, which could be due to a poor regeneration process. We found that tree species diversity was higher for the low fire frequency class, followed by moderate fire frequency class, no fire frequency class, and was lowest for the high fire frequency class. The diversity of herbs decreased with increasing fire frequency, from a minimum of 12 species in the high fire frequency class to a maximum of 37 in the no fire frequency class. Some of the fire-adapted species were Myrica esculenta, Pyrus pashia, Lyonia ovalifolia, Carissa spinarum, Pyracantha crenulata, Desmodium microphyllum, and Micromeria biflora the regeneration of which should be promoted rehabilitate the fire damage forest ecosystem of Uttarakhand.