Forests for People

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there is a need for projections of future human land use

to tackle this complex problem of foreseeing the forests.

Modelling forests

The structure of a simulation model for terrestrial

vegetation can be divided into two categories, a physics

module and a physiology module. The former deals with

heat and water budgets as well as microscopic meteoro-

logical processes near the surface. This module is often

treated separately as part of a land surface model and

incorporated in a climate model even when vegetation

dynamics is not explicitly taken into account, since the

above mentioned processes are so important for surface

climate. The latter module covers physiological and

ecological processes such as photosynthesis, stomatal

conductance (facility for gas exchange through the leaf

surface), respiration, leaf phenology, turnover of plant

and that projecting its future on time scales longer than a century

requires consideration of those interactions. This is why it is becom-

ing common to incorporate geographical dynamics for vegetation

into Earth system models (climate simulation models with biological

and chemical processes used to project how the global environment

changes as a result of human emission of greenhouse gases).

Another anthropogenic factor that has to be taken into account

is land use change (LUC) such as transformation from forest to

agricultural land or cities, or vice versa. Human pressure on natural

vegetation is rapidly growing and cropland now occupies a signif-

icant portion of the Earth’s surface. Carbon emission from LUC,

largely deforestation, is never negligible compared to that from fossil

fuel burning, and is the largest source of uncertainty for total anthro-

pogenic carbon emission. Human activities are posing considerable

constraints on vegetation dynamics, including the carbon cycle, and

there is no reason to believe that the constraints will diminish in

future. On top of the interactions between climate and vegetation,

Global environment projections

Source: JAMSTEC/MEXT

Time series for (upper-left) CO

concentration scenarios, (upper-right) global mean temperature rise relative to mean for 1980-1999 simulated by MIROC-

ESM, (lower-left) CO

emission pathways required to achieve the concentrations in the upper-left panel, calculated based on MIROC-ESM simulation, and

(lower-right) changes in land carbon simulated by MIROC-ESM