Download Ecosystem function modelling

Ecosystem function
modelling
Presented by
Bob Scholes
CSIR Environmentek
Aspects and levels of biodiversity
Composition: what it contains
Biome envelope models
Species niche models
Gene
Ecosystem function
models
Population
Ecosystem
Ecosystem
Structure: what it looks like?
Function: how it works?
Dynamic Vegetation Models

All the major Global Circulation Models have
‘coupled’ models of the land surface
- Simulate carbon uptake/loss, albedo, bulk stomatal conductivity,
-
surface roughness
Have a crude representation of biomes or ‘functional types’
Some of the better ones (LPJ, Sheffield) have fire and mammals
in them
DGVMs continued…

Problems:
-
Very hard to use unless you have a supercomputer
Results are not freely available, unlike the GCM outputs
Mostly not optimised for Africa
Scale is inappropriate for protected areas
Equations are complex and untransparent
A ‘reduced form’ ecosystem model for
savannas under climate change




‘Functional types’ are restricted to those occurring
in savannas (but are expanded beyond the generic
global types)
Includes effects of temperature, rainfall,
seasonality, CO2, soil texture, fire and
megaherbivores
‘Quasi-mechanistic’ equations
-
Simple, reduced forms based on emergent properties at ecosystem
scale
Timestep of one year (‘implicit seasonality’) and
‘patch’ spatial scale
Basic savanna system model
Fire freq
Tree ht & BA
Fire intens
Elephants
Browsers
CO2
Tree prodn
Temperature
Sand %
Mixed
Carnivore
Sour grass
Coarse graz
Sweet grass
Fine grazers
Water balance modelling
(1) G =  Rain/E0 * daysmonth if Rain<E0, else R/E= 1
months
(2) E0 = open water evaporation
~ 0.8 x {700(T+0.006A)/(100-L)
+15(0.0023A+0.37T*0.53(TxTn)
+0.35Tann-10.9))/(80-Tx)}
T = mean air temperature ( C)
Tx= max air temp
Tn=min air temp
A=altitude (m)
L=latitude (deg)
[Linacre 1984]
Controls on grass growth at the annual
timescale

Rainfall in the current growing season
- Actually, it is the duration of growth opportunity that matters
- This is affected by evaporation as well as rain, and is
mediated by soil texture




The fertility of the soil
The amount of tree cover
Daytime temperature
[CO2]
Linear relation between grass production
and rainfall
Grass AG NPP (g/m2/y)
500
400
300
clay soil
sand soil
200
100
0
0
200
400
600
Annual rainfall
800
1000
Slope: Rain Use Efficiency (g/m2/mm)
Rain use efficiency (kg/ha/mm)
12
10
8
6
4
2
0
50
60
70
80
Sand %
90
100
Intercept: dependent on soil water holding capacity; co-varies with the
rain use efficiency
1500
1000
500
(kg/ha/y)
Intercept of AGGNPP vs Rain
2000
0
-500
0
5
10
-1000
-1500
-2000
-2500
-3000
Rain use efficiency (kg/ha/mm)
15
Fraction of treeless grass NPP
Effect of trees on grass
1.00
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
0.000
5.000
10.000
15.000
2
Tree basal area (m /ha)
P = P0 * e-0.1BA
20.000
Maximum tree basal area
Global Analysis: Tree BA vs. Days Available Soil Water
[C=Clay; L=Loam; S=Sand]
90
80
70
Tree BA (m2/ha)
L
S
60
L
50
L
L
See Sankaran et
al Nature (in
press Aug 2005)
L
S
40
L
S
S
30
L
C
20
L
L
0
0
50
C
S
S
S
S S
S
S
L
S
L
S
SL LLS
L
LC S
S
S
S
L
S
L
L
L
S
S
L
S
S
S SL S SL
L
L L SS L L S
S
L
L SC L CC
S
L
L
S
L
S
L
LL
L S
CL SL SS
L
LS L S
L
LS CC L S S S L
S LS L
LC
L
S S SS
SS
C
S SC
SS
C C S C
C
CS
S
C
C
S
10
C
S
L
100
C
S
150
200
250
Days with Available Soil Water (d/y)
300
S
350
What controls the growth rate of trees?
Predicted Relative Annual Increment (%)
Ptree = 1+ 19 e -0.2d * e -3(A/Amax)
where A = basal area, d = diameter (cm)
12.00
10.00
y = 0.9998x
R=2 0.6487
8.00
6.00

4.00

2.00
Size of the tree?
Competition with other
trees?
0.00
0.00
2.00
4.00
6.00
8.00
Observed Relative Annual Increment (%)
10.00
Shackleton data
Effect of CO2 on NEP
Retative performance
1.4
1.2
1
0.8
0.6
0.4
grass
0.2
trees
0
0
200
400
600
CO2 in atmosphere
F (CO2) = 1+  ln([CO2]/[CO2ref]
~ 0.4 for trees, 0.2 for grass
[CO2ref] = 360 ppm
800
Relative performance
Effects of temperature on NEP
1.200
trees
grass
1.000
0.800
0.600
0.400
0.200
0.000
0
10
20
30
40
50
Mean daytime temperature (C)
ƒ[T] = ec*(1-{[(b-T)/(b-a)]^d }/d *(b-T)/(b-a)c
a = position of optimum ~ 28°C for trees, ~33°C for
grasses
b =temperature below which no growth occurs ~5C
trees, 10C grass
c = steepness of curve below optimum ~3
d = steepness of curve above optimum ~7
What controls tree mortality?

Fire
Elephants
Fraction of landscape burned

0.400
0.350
0.300
0.250
0.200
0.150
0.100
0.050
0.000
0
50
100
150
Growth days
200
250
Mammal dynamics
dN/dt = rN - offtake
r = rmax * (f*N)/(c*Prey biomass)
Ln(rmax) = 3.269-0.00081 Body mass
f = food requirement (kg/head/d)
C = fraction of prey biomass than can be
consumed in a year
Keeping it together!

Complete competitors cannot coexist
- Give each herbivore a partly unique resource

The faster-growing prey must be more preferred by
predators
- Preference = N2/N2

Predators must grow slower than prey
Plants (m2/ha),(g/m2),(m)
Test 1: trees, grass and fire
60
50
40
Basal Area
30
Grass prod
20
Tree ht
10
0
2000
2020
2040
2060
Year
2080
2100
2500
2000
Test 2:
+herbivores,
carnivores
Coarse
1500
Browser
1000
500
0
2000 2020 2040 2060 2080 2100
Year
25
Carnivores (kg/km2)
Herbivores (kg/km2)
3000
20
15
10
5
0
2000
2020
2040
2060
Year
2080
2100
50
40
Basal Area
Grass prod
Tree ht
30
20
10
0
2000
2020
2040
2060
Year
Herbivores (kg/km2)
Plants (m2/ha),(g/m2),(m)
60
2080
Test 3:
+elephants
2100
5000
4000
Elephants
3000
Coarse
Browser
2000
1000
0
2000
2020
2040
2060
Year
2080
2100
The experiment design
B2 Scenario
Hadley model
550 ppm
A2 Scenario
Hadley Model
Upper estimate
+5C, -6% rain
B2 Scenario
CCModel
Lower estimate
+2.2C, -1.2%
A2 Scenario
CCModel
700 ppm
Change in production drivers
1.5
Water balance
f(CO2)g
f(CO2)t
f(T)g
f(T)t
1.0
0.5
2.0
0.0
2000 2020 2040 2060 2080 2100
Year
Production drivers
Production drivers
2.0
1.5
Water balance
f(CO2)g
f(CO2)t
f(T)g
f(T)t
1.0
0.5
0.0
2000 2020 2040 2060 2080 2100
Year
Plants
(m2/ha),(g/m2),(m)
60
50
40
Basal Area
Grass prod
Tree ht
30
20
10
Year
Plants (m2/ha),(g/m2),(m)
0
2000 2020 2040 2060 2080 2100
Change in
vegetation
structure
50
40
Basal Area
Grass prod
Tree ht
30
20
10
0
2000 2020 2040 2060 2080 2100
Year
2500
2000
Coarse
Browser
1500
Change in
herbivores
1000
500
0
2000 2020 2040 2060 2080 2100
Year
Herbivores (kg/km2)
Herbivores (kg/km2)
3000
2500
2000
1500
Coarse
1000
Browser
500
0
2000 2020 2040 2060 2080 2100
Year
Preliminary conclusions




Water and temperature effects can overwhelm
the CO2 effect
Substantial changes in herbivore stocking rate
are possible in the future
Elephants at high density put the tree cover
into a stable coppice state
The outcome of climate-change induced
habitat change depends on how you manage
fires and elephants
Check your understanding of
Chapter 7
PASS MARK 80%
Please do not proceed further
until you have PASSED
Chapter 7: test yourself
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7
The evidence for anthropogenic climate change
Global Climate Models
Climate change scenarios for Africa
Biodiversity response to past climates
Adaptations of biodiversity to climate change
Approaches to niche-based modelling
Ecosystem change under climate change
Chapter 8 Implications for strategic conservation planning
Chapter 9 Economic costs of conservation responses
I hope that found chapter 7 informative, and that you
enjoy chapter 8.