Shigeaki Hattori

Development of a numerical model for evaluating the effect of litter layer on evaporation

A numerical model (LITEM) to evaluate the effect of the litter layer on evaporation was developed and used to estimate evaporation, soil temperature and soil water content. This model includes a sub-model to estimate the resistance of the litter layer to evaporation with its thickness and volumetric water content. The resistance of the litter layer to evaporation increases as volumetric water content of the litter layer decreases and as its thickness increases. Evaporation data in a deciduous broad-leaved forest measured using microlysimeter was simulated by the LITEM. The simulation showed good agreement with the measurement, and sound performance of the sub-model in simulation was also certified. According to the measurement for 2 days, evaporation from soil of 1.5 cm and 2 cm litter layers to that from bare soil was reduced to 47% and 61%, respectively. Loss of soil water content in three soils (bare soil, 1.5 cm litter layer and 2 cm litter layer) by evaporation was simulated by the LITEM, and the LITEM reasonably expressed the trend of volumetric soil water content. The simulated soil temperatures also showed good agreement with the field data.

Applicability of Stand Structural Characteristics to Stemflow Modeling

A stemflow (SF) estimation model, based on the correlation between coefficients (a andb) of the regression equation (SF=aPg −b, wherePg is gross rainfall) obtained from sample tree and their diameter at breast height (DBH), is presented. Estimation by the model forSF from two deciduous broad-leaved forests shows favorable agreement with the measurement. Once the equations for regression coefficients are determined, the model has the potential to easily estimateSF from an entire stand through sampling of some representative trees. However, the model is site-specific. In order to mitigate the weakness of this model, the combination of previous results provided generalized equations for the coefficients. The generalized equation adequately estimatedSF of some forests while its estimation was biased for other forests, which indicates thatSF variation between forests is closely related to structural differences. Actually, theSF frequency distribution of two forest stands was significantly different. So, influence of structural factors onSF was also studied using funneling ratio (FR) that integrates the efficiency of trunk and canopy characteristics toSF. Comparison ofFR showed thatSF was significantly correlated to crown-projection area (CPA) and basal area at breast height (BA). Parameters (β1 andβ2) within the model were significantly correlated to respective stand density and leaf area index (LAI).

The influence of NGO involvement on local people's perception of forest management: a case study of community forestry in Nepal

Despite high expectations of nongovernmental organizations (NGOs) as project partners in bilateral-aid community forestry (CF) projects in Nepal, it remains unclear whether the NGO involvement favored by donors is efficient. This study examined the influence of NGOs on local peoples perceptions of CF management by using a quantitative analysis based on a questionnaire survey. Three different forest user groups (FUGs) supported by the Nepal Swiss Community Forestry Project were selected from the Dolakha and Ramecchap districts: an FUG supported by another FUG acting as an NGO, an FUG supported by an NGO specializing in CF, and an FUG without NGO support. A structured survey examined the perception of CF management based on satisfaction, involvement, and self-reliance in 244 selected households belonging to the three FUGs. Knowledge of CF and personal information was also surveyed and analyzed. The results showed that NGO involvement influences factors such as self-reliance and knowledge of CF. FUG members who were supported by an NGO or an FUG had a significantly higher perception with respect to self-reliance and knowledge than did members without such support. This indicates that experienced FUGs can serve as adequate service providers for the CF formation procedure, in a manner similar to that of NGOs. On the other hand, the limited support from NGOs or FUGs during the formation process seemed insufficient to fulfill the expectations of aid agencies with respect to the enhancement of satisfaction and active participation on the part of FUG members. If aid agencies expect NGOs and FUGs to enhance the satisfaction and participation of members, these intermediary organizations should be assigned to support more CF activities than just the formation procedure. Aid agencies should take responsibility for strengthening the capabilities of NGOs and FUGs, as needed.

Stomatal Response Characteristics of Dry Evergreen and Dry Deciduous Forests in Kampong Thom, Cambodia

We explored diurnal and seasonal variations in stomatal conductance in dry evergreen and dry deciduous forests in Cambodia and examined the stomatal response characteristics at two sites using a Jarvis-type model. Although stomatal conductance had maximum values at 9:00 (0900) or 10:00 (1000) in the morning and decreased continuously during the evening, transpiration showed peak values in the daytime and minimum values in the morning or evening at both sites in correspondence with the vapor pressure deficit. Stomatal conductance decreased in the rainy season to the late dry season; the pattern was clearer in the dry evergreen forest than in the dry deciduous forest. Stomatal conductance and volumetric soil water content had similar seasonal patterns, although these patterns differed between the dry evergreen and dry deciduous forests. The seasonal patterns of stomatal conductance and transpiration were different in the dry evergreen forest in the rainy season as a result of the moist air conditions. Clear differences were observed in maximum stomatal conductance and the function of the vapor pressure deficit between the two sites. In particular, compared to the results of other studies, the two sites showed large differences in their responses to the vapor pressure deficit. The functions of photosynthetically active radiation and the vapor pressure deficit showed wide daily change, suggesting that these factors may greatly impact the diurnal change of stomatal conductance. The vapor pressure deficit and volumetric soil water content also showed large seasonal variations and remarkable differences in function. The vapor pressure deficit had a large influence on stomatal conductance in the early dry season, whereas volumetric soil water content had a large effect in the late dry season.

Seasonal Variations in Radiation and Energy Balance in a Deciduous Broad-Leaved Forest

This study was conducted to document the effects of canopy change on radiation and energy balances in a deciduous broad-leaved forest. Global solar radiation was highly variable with a maximum close to 28.7 MJ m−2 day−1 and a minimum of about 0.7 MJ m−2 day−1. The high daily variation of net radiation was the result of the frequency and duration of rainfall. The mean annual albedo in this study site was 0.126. Seasonal variation of albedo was characterized by steadily decreasing values with leaf-fall, but at the time when new leaves sprouted the trend did turn upwards. The mean annual radiation efficiency at this study site was 0.564, and the seasonal variation of the radiation efficiency was dependent upon the net long-wave radiation rather than albedo. This study also illustrated the seasonal variation of the proportion of the actual evaporation to the equilibrium evaporation as a means for estimating the latent heat flux from forest using the equilibrium evaporation model. Seasonal variation of the proportion of the actual evaporation to the equilibrium evaporation reflected the physiological and productive activities of trees. Latent heat flux dominated the energy balance and, in particular, reached about 96% of net radiation in July.

Evaluation of Forest Canopy Shape from Standpoint of Thermal Exchange above Forest

Shape of forest canopy surface was evaluated in a deciduous forest from a viewpoint of thermal exchange. The analysis of canopy shape with Morishita’s dispersion index showed that projected size of dominant convex and concave shapes on the forest canopy surface were around 5.0m square in a foliate season and 5.0–7.5m square in a defoliate season. On the other hand, each vertical size of the convex and concave shapes was estimated to be larger in a foliate season than in a defoliate season. Thus, this study concludes that the canopy shape was smoother in a defoliate season than in a foliate season in this case.