Net Primary Productivity of Natural Vegetation in the World

We developed a climatic model (Chikugo model) for evaluating NPP of natural vegetation (Uchijima & Seino, 1985). The Chikugo model is expressed as follows:

NPP=0.29*[exp(-0.216*RDI**2]Rn

Rn: Annual net radiation (kcal/cm**2)

RDI: Radiative dryness index (=Rn/(L*R))

L : Latent heat of evaporation (580cal/gH2O)

R : Annual precipitation (cm)

Under the current climate condition, the isopleths of NPP of 1 t/ha/yr runs along the 70 degree on the Northern hemisphere. In northern area than this isopleths, NPP is extremely low and approaches to zero. This is chiefly because ice-cap climate becomes predominant in this area.

The isopleths of NPP of 5 t/ha/yr corresponding roughly to the southern limit of boreal forest is observed between 50 degree and 60 degree on both the North American and Eurasian Continents. However, this isopleths extends considerably southward in the inner central part of the Eurasian Continent. This is mainly due to the existence of drier regions such as the Caspian-Aral sea plains, and most of the plateaus and basin of Mongolia and Sinkiang.

A high-middle latitude belt of Europe, East Asia, and East and West Coastal regions of North America with relatively plentiful precipitation is covered with cool temperate forest having NPP-value between 10 and 15 t/ha/yr. As described above, this belt is interrupted by the drier plateaus, basins and plains in the western U.S., the Caspian-Aral sea district and Mongolia.

There are more productive regions in the south of cool temperate forest belt. If there was no disturbance due to human activity, these regions could be well covered with warm temperate forest having NPP-values above 15 t/ha/yr. Although the Mediterranean district belongs to the same latitudinal belt, the NPP- value in this district is estimated to be considerably lower than that of the same latitudinal zone. This is mainly because of the development of the so-called Mediterranean climate with less precipitation and higher temperature in summer season. Due to the unfavorable combination of precipitation and temperature, there is sclerophyllous forest in this district.

The major arid belts with extremely low NPP-values less than 1 t/ha/yr lie beneath the subtropical high that is near 20 to 30 degrees in both hemispheres. because of very high solar irradiation and extremely high temperature.

The southern North America, part of Central America, Southeast Asia, a narrow strip of coastal eastern Madagascar, and northern part of Australian Continent have plentiful precipitation and higher temperature throughout a large part of the year, allowing the growth of subtropical evergreen forest or summer-green forest with NPP-values higher than 20 t/ha/yr. In the equatorial zone with the favorable combination of abundant rainfall and high temperature throughout the year, the photosynthetic activity of vegetation is so vigorous that the NPP-values of tropical rainforest are between 25 and 30 t/ha/yr.

Under the Current Climate
mesh map Under the GFDL Scenario
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Under the GISS Scenario
mesh map Under the UKMO Scenario
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