Biomass

Abstract

Forests are characterized by the accumulation of biomass and they include the terrestrial ecosystems having the largest biomass per unit ground area. Table 10 includes examples of published data on forest stands with some of the largest reported total weights. There are many publications concerning the biomass of the overstorey tree layer, but information about the biomass of undergrowth is more limited. The biomass of the undergrowth is influenced by the overstorey both qualitatively as well as quantitatively (Fig. 3). For example, there was hardly any undergrowth beneath the canopy of a stand of Thujopsis dolabrata which carried 35.6 t/ha of leaves (Fig. 2), whereas the average weight of understorey in 20 stands of Pinus densiflora with an average canopy foliage weight of 6.9 t/ha was 40.2 t/ha. As there are often woody plants in the undergrowth which accumulate dry matter year by year, the biomass of undergrowth tends to increase with the age of the forest. For example, a 16-year-old forest of Pinus densiflora having 5.3 t/ha of leaves in the canopy had 6.2 t/ha of undergrowth biomass whereas a 55-year-old forest of the same species having 6.9 t/ha of leaves in the canopy had 40.2 t/ha of undergrowth. In managed forests, the undergrowth is often cut during management operations such as thinning, while in some forests it has been a general practice to harvest undergrowth as fuel for the local people.