Developing an integrated terrestrial ecosystem model

for global changing predictions

Hisashi SATO (FRSGC) & Takashi KOHYAMA (Hokkaido Univ.)

陸域統合モデルへの結合を念頭にした植生動態モデルの構築（設計と進捗状況の報告）

Toward developing the land surface model

Land surface carbon cycle model

Vegetation dynamics model

原図：伊藤昭彦

Land surface physical process model

For simulating long time scales, vegetation dynamics model must be added to predict changes in vegetation distribution

TRIFFIDHYBRID 3.0

ロトカ・ヴォルテラ方程式を用いて、大胆なパラメタライズを断行。これを、陸上植生の様に本質的に混ざり合うことのないシステムに対して適用することは適切ではない。

唯一、個体ベースモデル。ただし、 FORSKA という極めて原始的なモデルを使用しており、また植生内の水平方向の地理的ヘテロ性も扱っていない。要するに 1 Patch モデルをグリッド毎に複数走らせ、その平均値をグリッドを代表する値として用いている。

Feature of dynamics modules within previous DGVMs

水平方向のヘテロ性を無視した Area-based model 。各 PFT の優先度を葉群投影被度で表現し、これが 1.0 を超えた段階で、 PFT 間の光を巡る競争が生じる。

IBIS/ LPJ/ SDGVM

* Dynamic Global Vegetation Models

*

Limited computation power inhibit to directly incorporate spatial hetero-structure of vegetations into the DGVMs.

However, spatial hetero-structure plays a central role in vegetation dynamics

Gap dynamics

例えば Pacala et al.(1995) は、光環境を空間的に平均してしまうモデルでは樹種の交代の様子が変化するだけでなく、総バイオマスも実際の森林の半分くらいになってしまうことを示している。ギャップの下にはとても明るい環境があるはずなのに、これを暗いところと併せて平均してしまうことで、ギャップ内での森林の再生が遅れてしまうためである。この結果は、森林の水平方向の構造を無視してしまうことの危険性を示唆している（竹中 2002 より引用）

Gap formation Competition among saplings

Feature of the DGVM (1)

A snap shot of the simulated forest stand (30m×30m). Individual tree is composed of crown, stem, and root. Shape of crown and stem are approximated by cylinder.

Crown : biomass, diameter, depth Stem : biomass, height, sapwood & heartwood diameter Root : biomass

+ reserve resource for sprouting

--- Individual characteristics for woody PFTs ---

Major advances from the previous DGVMs

(1) Individual Based Model (except for herbaceous PFTs)(2) Explicitly simulate spatial structures of vegetations

*

* Plant Functional Types

Feature of the DGVM (2)

Estimate light intensity on the top of the crown by using canopy location within the forest stand (SORTIE like)

To avoid ‘edge effect’, this scanning is performed among replicated forest stands, which surround the examining area.

Estimate light distribution within canopy using leaf area concentration and light attenuation index

By explicitly treating forest 3D structure, the model can reasonably calculate individual light conditions

Calculate NPP, and adjust bole height by perishing deficit crown layer

NPP0.0

Estimated light intensity

Feature of the DGVM (3)

Competition between woody PFTs and herbaceous PFTs

Grass layer can only use light on the forest floor

Luxuriant grass layer inhibit establishment of woody PFTs.

Grass layer 草本 PFTs のバイオマス

木本

PF

Ts

の定着率

Characteristics of herbaceous PFTs

Leaf : biomass in a forest standStem : biomass in a forest standRoot : biomass in a forest stand

Output example (1): Dynamics of temperate summer-green forest

・ tentative modules for daily processes, mortality, and phenology・ parameters, which have not adjusted yet

Current version uses

Output examples (2): Dynamics of temperate summer-green forest 200 years

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1000

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Litter production ( Kg / ha year )

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0.5

1

1.5

Leaf Area Index ( m2 / m2 )

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50

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10000

20000

30000

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Foliage

Stem

Root

Biomass ( Kg / ha ) Sum of stem diameter at breast height ( m / ha )

Module that comprise the dynamic global vegetation models, and its computation time steps.

Use modules of Sim-CYCLE

To see more details of the DGVM ….

Scheme for connecting phenology module and photosynthesis module

Simulation will be conducted on the T42 global grid (128×64), each of which includes 10 replication forest stands.

Thus, assuming 1/3 of the earth surface is terrene, about 27000 independent forest stand will be independently simulated.

To date, this would be the most complex ecosystem model that have ever made.

Simulation procedure (1)

小サイズの林分を複数シミュレートさせる主な理由としては、攪乱の問題があげられる。例えば寒帯林で頻発する森林火災は、一度生じると、シミュレートしている林分の大きさが 30×30 ｍだろうが 1ha だろうが、その殆ど全てが壊滅してしまう。このように機会的に大きく変動する単一の林分をもって、グリッドの代表値とさせることは適当ではない。

Simulation procedure (2)

Simulation 1 (free seed dispersal)

assumes that all PFTs establish all grid, irrespective of previous or current vegetation distribution

Simulation 2 (no seed dispersal)

assumes that PFTs that currently distribute for each grid only establish in the grid permanently

The former simulation should provide maximum estimate of vegetation change, while the latter should provide minimum estimate.

Estimate parameters and algorithm of a tree growthso that tree-form and leaf-density are reasonably simulated for each PFT

Estimate dynamics parameters (Establishment, Mortality, Disturbance):so that density and age distribution of tree are reasonably simulated when only one PFT composes the forest

Estimate metabolic parameters (Photosynthesis, Respiration, Allocation):So that biomass, LAI, and distribution of DBH are reasonably simulated. This will be conducted on forest that was composed of only one PFT.

By repeating above (2) and (3), convergence parameters

Conduct test run on global gridthen examine that distribution of vegetation and GPP at equilibrium are reasonably simulated.

Procedure for parameter estimation and tuning

(1)

(2)

(3)

(4)

(5)

Complete to develop the the DGVM program except daily processes

Link it with daily process modules of Sim-CYCLE

Parameter estimation and tuning

Vectorize the program and conduct simulation at global scale on the earth simulator

　Schedule

・ within Oct

・ 2 to 4 month

・ 1 to 3 month

・ ?