Agroclimatic Evaluation of Net Primary Productivity of Natural Vegetation

This report describes the assessment of the total net primary production (TNP) in Japan. TNP for the respective prefectures and for the whole country was estimated fromTNPi=Σ4j=1Aij⋅Ej⋅NPPiTNP0=Σ47i=1TNPiwhere TNPi and TNP0 denote, respectively, TNP for the i-th prefecture in Japan and the whole country, Aij is the area of the j-th land class in the i-th prefecture, Ej is the production efficiency of the j-th land class, NPPi denotes the average of net primary productivity of natural vegetation of the i-th prefecture.The geographical distribution map of NPP presented in a previous paper (Uchijima and Seino, 1985) was used to obtain the values of NPPi. The following values proposed by Matsuda et al. (1982) were used as Ej:j=1 forest lands E1=1.0j=2 fruit tree lands E2=0.80j=3 cultivated lands E3=0.81j=4 grass lands E4=0.625The land area Aij of the j-th land class in the i-th prefecture was evaluated using the statistical data of land utilization in Japan (1980).Table 1 summarizes the assessment of TNPi and TNP0. NPPi increased from about 10t DW/(ha yr) in Hokkaido to about 20t DW/(ha yr) in Okinawa prefecture. This is mainly because climatic resources for primary production are more plentiful in Okinawa prefecture than in Hokkaido. Table 1 also shows the prefectural variation in energy efficiency (ε) of TNPi on the basis of annual global solar radiation (St) and photosynthetically active radiation (Spar), and on the basis of the respective radiations (St, 10 and Spar, 10) for the plant growing period (Ta≥10°C). Although ε of TNPi on the annaul amount basis in Okinawa prefecture is about twice as large as that in Hokkaido, ε of TNPi in Hokkaido on the basis of radiation amount for the plant growing period is larger than that in Okinawa prefecture.Fig. 1 shows the comparison of TNPi obtained in this report with the results estimated by Iwaki (1984) using a plant ecological method. The points are well distributed around 1:1 line, indicating that there is a good agreement between them.Table 2 shows the comparison of TNP0 for the whole country of Japan presented by several researchers. TNP0 in Japan was assessed to be 380Mt DW/yr by Chikugo model, agreeing well with the results of Iwaki (1981, 1984), Murata (1981) and Matsuda et al. (1982) by plant ecological method.Fig. 1 and Tables 1 and 2 give a strong support to the validity and applicability of the Chikugo model based on theoretical considerations of fluxes of water vapor and carbon dioxide due to transpiration and photosynthesis.