Roles of Forests for Global Environment and
Current Situation of World's Forests

Forests provide us many benefits, such as conserving land and water resources, providing forest products, and preserving bio-diversity. A long time ago, about a half of the land surface was covered by forests. However mainly due to human activities, forests covered area has been shrinking every year, and now less than half of the original cover is left. Forests have been considered as one of the important factors to determine the policy in various international conferences including Intergovernmental Panel on Climate Change (IPCC), and the Johannesburg Summit.

In this edition, we would like to introduce our research activities on roles of forests for global environment and current situation of world's forests.

Global Environment and Carbon Dynamics
of Forest Ecosystem

As raised its importance in the Kyoto Protocol, one of the important research elements of the forests is carbon budget. Dr. Ito will explain the research on this carbon budget, including its roles to the global environment.

Akihiko Ito ( Researcher, Ecosystem Change Research Program, FRSGC )

To understand carbon balance (budget) in forests, we should also understand structure and dynamics of forests, because about a half of plant biomass and soil organic matter is composed of carbon. Forest ecosystems uptake carbon dioxide (CO2) from the atmosphere through photosynthesis and release it through respiration. Since CO2 is the most important greenhouse gas, carbon budget of forest ecosystems can influence climate system of the earth. Currently, amount of carbon in world's forests is estimated to be twice as large as that of the atmospheric CO2. Therefore, a small change in forest carbon budget may result in a large impact on climate system. On the other hand, the amount of annual photosynthetic carbon uptaken by forests (about 60 x 109 ton) is ten times as large as that of the human emission, acting probably as a negative feedback to global warming. However, it is noteworthy that the rate of respiration in many forests is almost equivalent to that of photosynthesis, and then precise observation methods and evaluation models are required to quantify forest carbon budget. These carbon accounting studies have become increasingly important, because of the Kyoto Protocol, in which forest carbon budget is included into the national greenhouse gas budget.

Net Primary Productivity of Terrestrial Ecosystems in Monsoon Asia
Figure 1 Net primary productivity of terrestrial ecosystems in Monsoon Asia estimated by a carbon cycle (Sim-CYCLE), based on the high-resolution land cover map (5-minute mesh) derived from satellite data (Ito, 2003).
Hierarchy Model of Carbon Cycle
Figure 2 Conceptual diagram of the hierarchical simulation of carbon cycle in terrestrial ecosystems, from a single point to broad regions (e.g. Monsoon Asia).

Our research group is working on modeling and simulations of carbon cycle at the global scale, including evaluation of forest productivity, biomass, and carbon budget. Because forest ecosystems are very complicated and time-scale of forest dynamics is very long (decades to centuries), models should contain a wide variety of ecological processes. Moreover, forest ecosystems have a remarkable diversity from a tropical rain forest to a boreal deciduous forest, demanding flexibility of models. Figure 1 shows the estimated net photosynthetic productivity of terrestrial ecosystems in Monsoon Asia with our model (Sim-CYCLE), based on an actual land-cover map using satellite data. Apparently, those areas covered by tropical humid forests (e.g. Southeast Asia) exhibited higher productivities, compared to inner continental areas covered by grasslands or deserts. Similarly, the model can be applicable to estimate plant biomass and soil carbon storage. At present, we are trying to apply the model to simulate carbon budget under global environmental change and human impact. In addition, we should incorporate new observational data into the model, so that these data can improve our model accuracy. For example, micrometeorological measurement and satellite observation of forest processes can be useful to validate our model.

Until now, models have regarded climatic conditions (e.g. temperature and precipitation) as major factors influencing carbon budget, so that climatic change may affect photosynthesis, respiration, and consequently net carbon budget. Recently, direct disturbances, such as wildfire and human deforestation, are expected to have even larger impacts on carbon budget. Since variations in carbon budget induced by disturbances are closely related to the issue of carbon accounting for the Kyoto Protocol, modeling of wildfire and deforestation is strongly required. Although these processes were difficult to merge into largescale models (e.g. Fig.1), we are attempting to construct a hierarchy model system, allowing us to parameterize local disturbance effect. For example, as shown in Figure 2, the hierarchy model system revealed that frequent wildfire in boreal forest of Siberia may reduce carbon storage considerably, and that climate change may result in further reduction of carbon storage through increased fire frequency. It is evident that through these simulation studies, we must take diverse factors into account, in order to make a reliable projection of carbon budget under changing global environment. Thus, further modeling studies are required to accomplish our purpose.

Ito. A., 2003, High-resolution mapping of the netprimary productivity of terrestrial ecosystems in East Asia using a process-based model, Journal of Agricultural Meteorology. (in press)

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