Bark thickness analysis of four dominant tree species of Central Himalayan forests varying in exposure to surface fires

Key message Our study on tree bark thickness across the major forest types of Central Himalayas indicates that the higher relative bark thickness at an early age is a key fire adaptational feature. In this study, we have primarily examined the relationship between fire incidence, bark thickness, relative bark thickness and related characters of the dominant tree species across the major forest type of Central Himalayas (29° 20′–29° 23′ N latitude and 79° 23′–79° 30′ E longitude) differing in fire incidences. The forest fires are human-ignited, small, and patchy surface fires and their incidences vary considerably across the forest types: 472.4 (fires/year) in Pinus roxburghii forests (between 1000 and 2000 m); 50.2 (fires/year) in Shorea robusta forests in the foothills; 7.4 (fires/year) in Quercus leucotrichophora forests (1200–2700 m); and rare in P. wallichiana forests (> 1800 m). With regard to bark traits, we focus on absolute bark thickness, and relative bark thickness. Our analysis of bark-related traits showed that bark thickness and bark development at an early age are directly correlated with fire exposure, indicating the role of fire in the species dominance. With increasing diameter of trees, bark thickness increases but relative bark thickness decreases in all tree species, indicating that allocation to bark decreases as trees become big hence less vulnerable to fire. The relative bark thickness declines more with tree size in species exposed more to fires than those less expose to fire. Our analysis has contributed to highlighting the bark thickness as a functional feature, with implication for community composition.