huge contributions of forest to the present water cycle - findings from recent...
TRANSCRIPT
Huge Contributions of Forest to the Present
Water Cycle
- Findings from Recent Hydro-meteorological
Studies -
5th WWF in Istanbul
March 20, 2009
Makoto Tani
Kyoto University
http://www.shinrin-ringyou.com/forest_japan/jinkou_tennen.php
Forest influences on the water cycle are highly evaluated in general.
Science tends to reject the exaggerated effects. Debates are
continued for example about the flood control effect:
Introduction
In this presentation, we wish to reconsider the forest influences
from the following geographical classification.
- region with a high tectonic activity and heavy rainstorms
- a stable continent
Bradshow et al. (2007) made a statistical analysis and detected a forest influence on the flood frequency. Albert et al. (2009) reanalyzed the data and drew a negative result. Laurence (2007) raised a question about the forest effects on floods driven by extreme events such as typhoons.FAO-CIFOR (2005) suggested the mechanism of forest soil acting as sponges was negligible for these extreme events.
Due to a high tectonic activity, forest is exposed to threat of ground collapses.
Steep
landscape
Landslide
Findings from Regions
with a high Tectonic
activity
Runoff responses are highly controlled by the water storage behaviour within the soil layer.
Bare-land in a granite mountain
i
0 24 48 72 96 120 144 168 192 216.001
0.01
0.1
1
10
Bareland
Reforested
Tani, 2005 Storm runoff comparisonHou
r
Ru
no
ff
m
m/h
In our human history, we can often see severe forest uses resulting in
bare lands. An example occurred in Shogun era (1600-1868) in
granite mountains in Japan.
Once either forest-soil system or bare-land is established, each ground cover system persists stably. Soil produced by weathering is eroded every year on a bared hillslope, whereas thick soil is retained for long years on a forested hillslope.
A tree root system protects the soil from frequent erosion and contributes to a stabile river-runoff regime.
Weathering
Tectonicuplift
Heavy storm
Forest withsubsurface flow
Bareland withsurface flow
Terrace work needed
The relationship between tree and thick soil with water buffering potential may be interdependent.
A hard task with terrace work is needed for reforestation from the bare land to forest.
Biwako office of Ministry of Construction, 1985
Even on a hillslope with virgin forest, the soil layer is sometimes
eroded by landslide occurrences. However, the soil layer is again
developed because soil supplied from the surrounded area and
from the underlying weathered bedrock is trapped by tree roots
(Shimokawa, 1984). On the other hand, once a bare land is created, this bared
condition is fixed by the frequent soil erosion because the spatial
scale of bare land is larger than that of landslide and beyond one
unit of hillslope.
Forest and bare land are both sustainable under the same
climate.
What is important in regions with a high tectonic activity?
This strongly demonstrates an interdependent
relationship of forest and soil, and to evaluate a
threshold between the sustainability of forest
and falling down to bare land is the most
important for the forest and watershed
management.
Forest
Bare land
Threshold
Biome of the World http://www.digitalpencil.org/Projects_AllGrades/aroundtheworld/biomes/biomes.aspx?GS=431&GK=10&S=5&C=19&Sd=16&E=1を使用
67
8
13
2 Distance from seacoast km
Distance from seacoast km
Ann
ual rainfall m
mA
nnual rainfall
mm
12
3
67
8
Rain does not decease
Rain decrease
( A. M. Makarieva and V. G. Gorshkov: Biotic pump of atmospheric moisture as driver of the hydrological cycle on land, Hydrol. Earth Syst. Sci., 11, 1013–1033, 2007. より引用 , 一部改変。)
There are two types of rainfall
distributions along the distance from the
seacoast in stable continents. Why is the
humid climate for forest in inland area?
Findings from stable continents
The relationship between forest and humid climate may be interdependent.
Evapotranspiration is lower than rainfall on the land because the water balance shows the river runoff is their difference. Both vapor from the sea and evapotranspiration from the land are needed for much rainfall.
Distance from seacoast
Annual rainfall
The large rainfall amount in an inland area is strongly supported by the water recycle system driven by a large evapotranspiration from the forest.
Vapor from sea
River flow
Water cycle between land and sea
Rain>ET Rain<ET
Recycle system
Makarieva and Gorshkov, Global Change Biology 2007
The climate will become much dryer after a continental-scale deforestation because the dynamic water cycle stops.
Forests pump up deep water even in a dry season.
Dynamic pump Poor pump
Simulation result about the effect of
root depth on transpirationTanaka K. et al., JGR 2004
High evapotranspiration during a
late dry season in tropical monsoon
forest.
R
ainf
all
Eva
potr
ansp
irat
ion
mm month-1
Month0 3 6 9 12
100
200
300
400
Tanaka N. et al., Agric. For. Meteorol., 2008
Dry season
Max. ET
Hydrological studies support the recycle system.
A continuous evapotranspiration in a dry season supporting a
dynamic water recycle between land and the atmosphere is only
possible based on the pumping-up of water from deep zones by
tree roots.
Therefore, once forest is destroyed, the non-forest condition
is also fixed due to another dryer climate. Both types of
vegetations are sustainable under these different climate
conditions.
What is important in a stable continent?
This strongly demonstrates an interdependent
relationship of forest and climate, and to
evaluate a threshold between the
sustainability of forest and falling down to
non-forest condition is the most important for
the forest and watershed management.
Forest
Non forest
Threshold
The both relationships for the forest-soil system and the forest-climate system are interdependent and contribute to a present stable river-runoff regime and a present humid climate.
Although forest contributions are huge, forest products are continuously needed for humankind. Minimum disturbances by forestry cannot be avoided on earth.
Huge forest contributions
How to keep the huge contribution and the sustainable forest management is critical now.
Virgin forest Manmade forest Devastation
failure
SuccessWe are here
We should promote the sustainable forest management by making
active use of these scientific findings in order to maintain the present
water cycle.
Summary
A local-scale forest disturbance may cause severe floods.
A continental-scale forest extinction may destroy the humid climate.
The interdependent system between forest and its environment is a
key controller.
Forest products are needed for humankind. The most important
subject is how to keep a huge contribution of the interdependent forest
system to the present water cycle regardless of the increasing demand
of forest products.
We are standing at the threshold.