No abstract

Background: Forest biomass is helpful to assess its productivity and carbon (C) sequestration capacity. Several disturbance activities in tropical forests have reduced the biomass and net primary production (NPP) leading to climate change. Therefore, an accurate estimation of forest biomass and C cycling in context of disturbances is required for implementing REDD (Reducing Emissions from Deforestation and Forest Degradation) policy. Methods: Biomass and NPP of trees and shrubs were estimated by using allometric equations while herbaceous biomass was estimated by harvest method. Fine root biomass was determined from soil monolith. The C stock in vegetation was calculated by multiplying C concentration to dry weight.

Fine root biomass (<5 mm diameter) was estimated in 0-15 cm and 15- 30 cm soil depths of disturbed and undisturbed stands of tropical moist forest in eastern Nepal. The value of root mass was higher (4.28 t ha-1) in the undisturbed stand than the disturbed stand (2.04 t ha-1). The biomass of smaller fine roots (<2 mm diameter) was 1.51 and 3.2 t ha-1 in the disturbed and undisturbed stands respectively. Most of the fine roots were present in the surface soil layer (0-15 cm), in both the disturbed and undisturbed stands (67% in the disturbed and 64% in the undisturbed). The nitrogen stock in the fine roots was more (38.61 kg ha-1) in undisturbed stand than the disturbed stand (16.93 kg ha-1). More nitrogen was confined in the fine roots of <2 mm diameter in both undisturbed (28.8 kg ha-1) and disturbed (13.59 kg ha-1) stands. DOI: http://dx.doi.org/10.3126/njbs.v2i0.7484 Nepalese Journal of Biosciences 2 : 10-16 (2012)

The physico-chemical properties of soils of tropical moist forest (Charkoshe jungle) in Sunsari district of eastern Nepal were analyzed. The samples were collected during summer season from three depths: upper (0-15 cm), middle (15-30 cm) and deep (30-45 cm). They were analyzed for texture, pH, moisture, water holding capacity, organic carbon, total nitrogen, organic matter and microbial biomass carbon and nitrogen. The forest soil of upper and middle layers was loamy whereas that of deep layer was sandy loam. The pH value was lower (5.6) in upper layer than in the deep layer (6.6). The moisture content, water holding capacity, organic carbon, total nitrogen and organic matter were higher in upper layer and decreased with increasing depth. The higher level of soil nutrients in upper layer was due partly to reduction in the loss of top soil and partly to the increased supply of nutrients from the decomposed form of litter and fine roots of the forest plants. The average value of microbial biomass carbon in the soil was 676.6 µg g -¹ and microbial biomass nitrogen was 59.0 µg g -¹ .

Species diversity is a key factor for the stability of ecosystems but the increasing disturbances in tropical forests resulted in the shrinkage of biological diversity. This study was conducted in undisturbed and disturbed stands of Sal (Shorea robusta Gaertn.) dominated moist tropical forest of Sunsari district, eastern Nepal in order to understand the herb, shrub and tree diversity. Present study reported the 47, 16 and 60 species of herbs, shrubs and trees, respectively. The species richness and the Shannon–Wiener index for tree species were higher in undisturbed forest (9.11 and 3.08, respectively), while the Simpson’s index (index of dominance) was higher in disturbed forest (0.11).  On the other hand, reverse case was found for shrubs and herbs where species richness and Shannon–Wiener index were higher but index of dominance was lower in disturbed forest. Changes in species diversity pattern reflect the effect of disturbance.