Biomass, Productivity, Leaf Longevity, and Forest Structure in the Central Himalaya

Abstract

Patterns of leaf characteristics, forest structure, tree species diversity, biomass, and productivity across a gradient of 3300 m and 15.7°C in mean annual temperature in Kumaun, in the Indian central Himalaya, were summarized and compared to values from other similar forests. Throughout the elevational gradient, the annual rainfall was high (100—300 cm), but not correlated with elevation. Evergreen species with a 1—yr leaf life—span dominated most of the elevational transect; above 1800 m, species with deciduous and multiyear evergreen leaves were also well represented. Although variability among sites within forest types was high, a number of consistent patterns were apparent. Forests of Pinus roxburghii and those at high elevations were most consistently different from other forest types. Leaf life—span was not strongly correlated with leaf mass, specific leaf mass, or leaf production efficiency (net primary productivity per unit leaf mass), contrary to relationships presented in the literature. Tree species richness and basal area were lower than for most similar types in Nepal. Biomass and productivity of the forests in Kumaun were relatively high, compared to mean values for similar forest types elsewhere. Measured values for most variables describing these forests (but not all) fell within the ranges for the variables in similar forests worldwide. The maximal values for forest biomass remained high, 500—600 Mg/ha, up to 2600 m elevation, but declined sharply in birch forest (°170 Mg/ha) above 3100 m. Net primary productivity (NPP) varied little (15—20 Mg°ha—1°yr—1) below 2700 m, despite a 10°C gradient in mean annual temperature and marked changes in basal area, tree density, growth form, and leaf characters. The level of productivity appeared not to be limited by rainfall, forest structure, leaf type, or temperature above an annual mean of 11°C. Leaf mass (LM) varied considerably among forest types, being 3.7—8.6 Mg/ha for deciduous species, 5.7—8.9 Mg/ha for P. roxburghii, and 10.0—28.2 Mg/ha for evergreen broad—leaved species. Leaf mass duration (leaf mass x months of the year with leaves present) was related directly to NPP and inversely to leaf production efficiency (NPP/LM). These data add substantially to the data base for forest properties, especially for broad—leaved evergreen forests.