Forests for People

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organs, decomposition of soil organic compounds, and the result-

ant carbon cycle in land ecosystems. The response of vegetation to

high CO

concentration, one of the essential parts of the module

for projecting future behaviour of vegetation, is also formulated

in most cases considering the balance of photosynthesis, stomatal

response, and availability of environmental resources such as soil,

water and nutrients. Combination of the physics and physiology

module enables the projection of changes in vegetation dynamics

due to those occurring in the future climate.

The investigation of possible transitions in vegetation distribution

under a changing environment also needs to take into account the time

lag between changes in climate and actual shifts in biome. A dynamic

global vegetationmodel (DGVM) used for this purpose deals with proc-

esses such as settlement of trees and competition for light and water

among different species in order to estimate the time lag. Many available

DGVMs assume that the model’s single grid is shared by multiple plant

types and that their respective assignments evolve gradually, based on

indices such as productivity of the plant types involved.

Another scheme to describe competition involves directly simulat-

ing the life cycles of individual trees. The merits of this approach

include the fact that competition for light can be expressed in an

explicit way and that parameter values obtained in observations can

be reflected with ease and utilized for model improvement. In the

light of these advantages, the Japan Agency for Marine-Earth Science

and Technology’s Earth system model for interdisci-

plinary research on climate (MIROC-ESM) adopts a

terrestrial vegetation sub-model, the Spatially-Explicit,

Individual-Based DGVM (SEIB-DGVM).

Under the framework of the Coupled Model

Intercomparison Project Phase 5 (CMIP5), which is

expected to contribute to the fifth Assessment Report

of the Intergovernmental Panel on Climate Change,

MIROC-ESM has been used for projection of the global

environment for the next 100 years, or 300 years for

certain scenarios, as completion of a biome shift would

require an extremely long time. The scenarios used

are called Representative Concentration Pathways

(RCPs) and consist of four datasets, that is, RCP3PD,

RCP4.5, RCP6.0 and RCP8.5, with an ascending order

of projected CO

concentration. RCPs include LUC

projection, and SEIB-DGVM has been modified so it

can evaluate impacts of LUC on vegetation distribution,

carbon cycle and climate.

Forest management and the carbon cycle

In a study of the global mean surface temperature

projected by MIROC-ESM for the four RCPs, it can

be seen that RCP3PD is the scenario that roughly

Projected transitions in vegetation distribution

Source: JAMSTEC/MEXT

Distribution of boreal deciduous (left) and evergreen (right) forest at 2007 and 2300, simulated by MIROC-ESM based on the RCP4.5 scenario