Download 21st Century Approaches to the Global Land Degradation

21st Century Approaches to the Global Land Degradation
Monitoring Problem
• Three common ecological syndromes resulting
from large-scale managed grazing practices are
desertification, woody encroachment and
deforestation. All alter vegetation composition
and structure, as well as the biogeochemical
cycles of carbon and nutrients.
• Managed grazing systems occupy nearly 80%
dryland regions –savannas, shrublands,
grasslands and deserts (MAP < 750 mm/yr).
This is the single largest form of land use on the
planet.
• Common remote sensing approaches are often
inadequate for detecting, quantifying and
monitoring degradation throughout dryland
regions.
• Decision information systems can improve if
appropriate remote sensing are combined with
tactical field measurements.
The Persistent (multi-decadal) Problem
“Assessment of the current global status of desertification
and land degradation has shown that accurate hard data,
which would allow it to be stated with some preciseness to
which degree and with what rate desertification is taking
place in various parts of the world, are still lacking.”
--The United Nations Environment Programme (UNEP1992)
The Questions
•
What is the global environmental footprint of the grazing enterprise? Are there
typological responses of ecosystems to managed grazing that are mediated by
bioclimatic and edaphic conditions?
•
What do the aboveground characteristics of these ecological syndromes indicate
about remote sensing requirements for larger scale monitoring?
•
Can we design a system for strategic assessment of ecological changes in global
drylands….to understand the vulnerability of these major “production” biomes to land
use – climate variations?
Animal stocking Density and Area
FAO/WRI 2000
The Questions
•
What is the global environmental footprint of the grazing enterprise? Are there
typological responses of ecosystems to managed grazing that are mediated by
bioclimatic and edaphic conditions?
•
What do the aboveground characteristics of these ecological syndromes indicate
about remote sensing requirements for larger scale monitoring?
•
Can we design a system for strategic assessment of ecological changes in global
drylands….to understand the vulnerability of these major “production” biomes to land
use – climate variations?
Animal stocking Density and Area
FAO/WRI 2000
The Bioclimatic Problem
Managed Grazing and AET: An Index of Bioclimatic Stress
FAO 2000, Klein-Goldwiejk 2001, Asner et al. 2004
The Bioclimatic Problem
Total
Area
(M km2)
% of
Global
Land
Area
Area
Grazed
(M km2)
Savanna
19.31
15
Grassland/Steppe
14.22
Desert
% of
Biome
Grazed
Mean
AET of
Grazed
Area
Mean
AET of
Biome
Grazed
AET:
Biome AET
9.48
49.1
595
781
0.76
11
7.68
54.0
321
401
0.80
15.45
12
1.97
12.8
71
88
0.81
Dense Shrubland
6.01
5
2.73
45.4
314
339
0.93
Tropical Evergreen
Forest/Woodland
17.43
13
1.72
9.9
1114
1141
0.98
Temperate Broadleaf
Evergreen Forest/Woodland
1.26
1
0.71
56.0
821
818
1.00
Tropical Deciduous
Forest/Woodland
5.96
5
1.20
20.2
935
859
1.09
Boreal Evergreen
Forest/Woodland
6.36
5
0.08
1.2
424
354
1.20
Boreal Deciduous
Forest/Woodland
2.18
2
0.02
1.1
435
352
1.24
Temperate Deciduous
Forest/Woodland
5.10
4
1.49
29.1
793
611
1.30
Temperate Needleleaf
Evergreen Forest/Woodland
3.62
3
0.76
20.9
689
463
1.49
Mixed Evergreen/Deciduous
Forest/Woodland
15.68
12
1.26
8.0
642
369
1.74
Tundra
7.32
6
0.17
2.3
431
247
1.75
BIOME
The Bioclimatic Problem
Bioclimatic variability throughout global drylands
Asner et al. 2004
The global distribution of managed grazing systems and the inter-annual variability of
vegetation production, as indicated by the satellite metric normalized difference vegetation
index (NDVI). Mean NDVI deviation is the inter-annual variability of vegetation greenness,
after accounting for mean monthly greenness.
The Substrate (Edaphic) Problem
Global distribution of managed grazing systems and soil taxonomic Order
Asner et al. 2004
The Substrate (Edaphic) Problem
CLASS
Mode of Soil Order
Within Each Biome
Class and Within 1990
Grazing Extent
Mode of Soil Order
Within Each Biome Class
Tropical Evergreen Forest/Woodland
Ultisols
Oxisols
Tropical Deciduous Forest/Woodland
Ultisols
Oxisols
Temperate Broadleaf Evergreen
Forest/Woodlands
Ultisols
Histosols
Temperate Needleleaf Evergreen
Forest/Woodland
Alfisols
Alfisols
Inceptisols
Inceptisols
Boreal Evergreen Forest/Woodland
Alfisols
Gelisols
Boreal Deciduous Forest/Woodland
Spodosols
Gelisols
Evergreen/Deciduous Mixed
Forest/Woodland
Inceptisols
Gelisols
Savanna
Entisols
Alfisols
Grassland/Steppe
Entisols
Mollisols
Dense Shrubland
Aridisols
Alfisols
Open Shrubland
Aridisols
Alfisols
Desert
Aridisols
Entisols
Temperate Deciduous
Forest/Woodland
Why does this matter?
Precursors:
Average bioclimatology
Bioclimatic variability
Soil chemistry-physics
Desertification in arid/windy zones
with poor soils.
Woody Encroachment
in mesic zones.
Desertification is a common typological response in arid zones,
under certain conditions…
Processes mediating desertification in arid grazing systems.
Over-grazing/
Over-use
Climate
Change and
Variability
Scrub
Development and
Grassland
Degeneration
Increased Spatial
Heterogeneity of
Scrubland
Soil Compaction
Wind Erosion,
Nutrient Losses,
Water Run-off
Woody encroachment is a common typological response in
mesic zones … under certain conditions…
Processes mediating woody encroachment in mesic grazing systems.
Active Fire
Suppression
Increased
atmospheri
c
Climate
variability
CO2
Reduction of
fine fuels in
the understory
Grazing
Decreased
competition of
grasses with
woody plant
seedlings for
water and
nutrients
Decreased
fire
frequency
Increased
germinatio
n and
survival of
tree and
shrub
seedlings
Increased numbers
of woody plants in
the environment
Annual AET for Western United States
(1)
(2)
(3)
(4)
(5)
The Questions
•
What is the global environmental footprint of the grazing enterprise? Are there
typological responses of ecosystems to managed grazing that are mediated by
bioclimatic and edaphic conditions?
•
What do the aboveground characteristics of these ecological syndromes indicate
about remote sensing requirements for larger scale monitoring?
•
Can we design a system for strategic assessment of ecological changes in global
drylands….to understand the vulnerability of these major “production” biomes to land
use – climate variations?
Animal stocking Density and Area
FAO/WRI 2000
Common Vegetation Responses
Common responses to light and heavy grazing, and to release from grazing with or
without fire as a recovery technique (n = 452)
Ecosystems with AET < 750 mm/year
Asner et al. 2004
Biogeochemical Responses: Desertification & Woody Encroachment
Before
Change in Flux
After
Insignificant change in ANPP 5
Desertification
Asner et al. (49)
Gallardo and Schlesinger (61)
3 Schlesinger et al. (62)
4 Hartley and Schlesinger (63)
4 Schlesinger and Peterjohn (64)
4 Peterjohn and Schlesinger (65)
5 Huenneke et al. (66)
1
2
0.7-2.3 increase in N gas loss 4
C 2.5–40.0 5*
N ?
C 0.7-1.21 0.33-1.99% 2 10cm depth
N
0.07-0.16% 2
Desertification
Increased spatial heterogeneity
of C and nutrients
C?
N 0.15 increase in runoff 3
* assumes that biomass is 50% C
Woody
Encroachment
6 Asner
et al. (43)
7 Jackson et al. (67)
8 Hughes et al. (175)
9 Hibbard et al. (68)
10 Geesing et al. (69)
11 Martin et al. (70,71)
N 0-0.8
as NO 11
C 400-3800 6,8
N 1-68 8
C 3.3-23.0 5*
N?
C 0.6-0.81 0.25- 0.57% 2
10cm depth
N
0.07-0.10% 2
C 0 – 1400 increase in ANPP 8,10
N 9-40 increase in N production 8,10
(large increases require N fixing shrub)
Woody Encroachment
C 3000-21000 6,8
N 40-536 8
Increased spatial heterogeneity
of C and nutrients
C 11650-22000 8,9
10cm depth
N 910-2000 8,9
C 27800-33800 7 3m depth
N 4400-26400 7
C?
N 36 increase in leaching 9
C 15500-33520 8,9
N 1500-2920 8,9 10cm depth
C 21700-41600 7 3m depth
N 4400-23700 7
Asner et al. 2004
Remote Analysis of Net Primary Production (NPP)
In the past 3 decades, the remote sensing community has focused heavily on canopy greenness, and thus
energy absorption, to estimate net primary production (NPP).
NPP = PARi x fPAR x LUE
PARi = incoming photosynthetically active radiation
fPAR = canopy fractional PAR absorption
LUE = light-use efficiency
fPAR = f(NDVI)
NDVI = canopy reflectance in IR minus red
divided by their sum
Does this work for desertification monitoring?
Tucker et al. 1991
Detection and Monitoring
NDVI is not specifically sensitive to land degradation or desertification
Rainfall deficit
Sahara extent
(greenness)
Greenness (NDVI)
trend
Prince et al. 1998
Biogeochemical Responses: Desertification & Woody Encroachment
Before
Change in Flux
After
Insignificant change in ANPP 5
Desertification
Asner et al. (49)
Gallardo and Schlesinger (61)
3 Schlesinger et al. (62)
4 Hartley and Schlesinger (63)
4 Schlesinger and Peterjohn (64)
4 Peterjohn and Schlesinger (65)
5 Huenneke et al. (66)
1
2
0.7-2.3 increase in N gas loss 4
C 2.5–40.0 5*
N ?
C 0.7-1.21 0.33-1.99% 2 10cm depth
N
0.07-0.16% 2
Desertification
Increased spatial heterogeneity
of C and nutrients
C?
N 0.15 increase in runoff 3
* assumes that biomass is 50% C
Woody
Encroachment
6 Asner
et al. (43)
7 Jackson et al. (67)
8 Hughes et al. (175)
9 Hibbard et al. (68)
10 Geesing et al. (69)
11 Martin et al. (70,71)
N 0-0.8
as NO 11
C 400-3800 6,8
N 1-68 8
C 3.3-23.0 5*
N?
C 0.6-0.81 0.25- 0.57% 2
10cm depth
N
0.07-0.10% 2
C 0 – 1400 increase in ANPP 8,10
N 9-40 increase in N production 8,10
(large increases require N fixing shrub)
Woody Encroachment
C 3000-21000 6,8
N 40-536 8
Increased spatial heterogeneity
of C and nutrients
C 11650-22000 8,9
10cm depth
N 910-2000 8,9
C 27800-33800 7 3m depth
N 4400-26400 7
C?
N 36 increase in leaching 9
C 15500-33520 8,9
N 1500-2920 8,9 10cm depth
C 21700-41600 7 3m depth
N 4400-23700 7
Asner et al. 2004
So what changes with dryland degradation?
Landscape Greenness (NDVI(NDVI-compatible)
Not often
Primary Production
None or not much; sometimes even an
increase
Secondary Production
Common: decrease in large herbivores
Severe: decrease in small mammals (e.g.,
rodents), reptiles, birds
VegetationVegetation-Ecosystem Structure
All cases reported and synthesized by
Asner et al. (2004)
Soil organic matter or carbon
Highly variable
The Questions
•
What is the global environmental footprint of the grazing enterprise? Are there
typological responses of ecosystems to managed grazing that are mediated by
bioclimatic and edaphic conditions?
•
What do the aboveground characteristics of these ecological syndromes indicate
about remote sensing requirements for larger scale monitoring?
•
Can we design a system for strategic assessment of ecological changes in global
drylands….to understand the vulnerability of these major “production” biomes to land
use – climate variations?
Animal stocking Density and Area
FAO/WRI 2000
Detection and Monitoring
A methodology that combines strategic and tactical ecosystem analysis approaches
rre
u
C
P
Co
t
n
ns
o
i
it
nd
e?
c
n
Tactical
Soil Carbon & Carbon Isotope Analyses
is
os
Data Assimilation for
Model Hindcast and Prediction
te
s
i
ers
gn
o
r
P
Strategic Remote Sensing Assessment of
Surface Material Covers
Detection and Monitoring
A methodology that combines strategic and tactical ecosystem analysis approaches
Strategic Remote Sensing Assessment of
Surface Material Covers
Tactical
Soil Carbon & Carbon Isotope Analyses
Data Assimilation for
Model Hindcast and Prediction
Strategic Remote Sensing Assessment of
Surface Material Covers
Full Spectral Sensing
The Imaging Spectroscopy Concept
Passive Remote Sensing Basics
Plant leaves, stems, flowers “interact” with sunlight
The reflection of sunlight is affected by canopy properties such as amount of leaves and architecture of canopies
The reflection of sunlight is also modified by shadows and thus the placement of the vegetation on the land
14
Canopy water
12
Many leaves
Photosynthesis
Dry matter showing
Chl.
8
6
4
palisade
Many trees
layer
spongy tissue
Leaf carbon and nitrogen
lower epidermis
Few leaves
Atmospheric
Carbon Dioxide.
Leaf Chlorophyll
and Other Key Pigments
10
Atmospheric Oxygen
upper epidermis
6H2O + 6CO2 + photon ==> C6O6H12 + 6O2
2
Radiance (µW/cm /nm/sr)
16
2
0
400
700
1000
1300
1600
Wavelength (nm)
1900
2200
2500
Airborne spectroscopic techniques isolate
fractional cover of materials…autonomously
Global range of variability
Condensed down to…
ter
a
W
Photosynthetic
Vegetation
Non-Photosynthetic
Vegetation
llu
e
C
gn
i
L
e/
s
o
l
in
-
Bare Substrate
n
Mi
l
era
So
H
O
l
i
Carnegie Automated Spectral Model (CASM) – “inflight analysis”
Spectral Measurement
SWIR Databases
Live, NPV, Bare,
Other
(AVIRIS-05 data)
Decompose
Image Pixel
Each Aircraft Image Pixel
Sub-pixel Cover
Fractions in %
Monte Carlo Analysis
Mean estimate
of each cover fraction
Chemical Remote Sensing from Aircraft
HighHigh-fidelity imaging spectroscopy (achieved in 2001)
Desertification and Woody Encroachment Studies in Dryland Regions
Validation and Application
Escalante, Utah
Waggoner Ranch, Texas
Jornada, New Mexico
Nacunan Reserve, Argentina
Desertification and Vegetation-Climate Interactions from Multi-temporal AVIRIS-05
Jornada LTER, New Mexico USA
1997 to 2001
Mesquite
May ‘97
May ‘98
Sep ‘98
May ‘99
Sep ‘99
May ‘00
Sep ‘00
May ‘01
Grassland
N
km
SOIL
PV
NPV
0
5
10
Asner and Heidebrecht 2005
Spatial Variability & Validation of Autonomous Remote
Sensing Results
od
o
W
y-
ee
r
G
Dr
n
ge
e
V
eg
V
y
e
io
ta t
io
ta t
n
n
validation campaigns
in 26 of 35 Holdridge biomes
Temporal Distribution
ee
r
G
Mesquite Dunes
Dr
n
ge
e
V
eg
V
y
e
io
ta t
io
ta t
n
n
Transition
Grassland
oi l
S
re
Ba
Ecosystem – Climate Interactions Following Desertification
Mean greenness (NDVI) same or
even higher for degraded area
How do you know it changed?
Escalante, Utah U.S.A.
Relic (Mesa) Comparisons
Comparisons to Relict or Protected Sites
Escalante, Utah U.S.A.
Red = Scrub, Green = Dry material, Blue = bare soil
Harris et al. 2003
Historical Aerial Photography
Waggoner, Texas U.S.A.
y
p
co
s
ro s)
t
ec nth
p
S mo
e
n nr
o rso
b
ce pe
a
Sp .01
(0
hy )
p
ra ths
g
to on
o
h -m
p
n
l
ir a rso
Ae pe
(6
1937
<10%
1999
Woody Plant Cover
>90%
Historical Aerial Photography
Waggoner, Texas U.S.A.
Net Changes in Woody Plant Cover and AG-Carbon, 1937-1999
1937
Cover (%)
1999 Cover
(%)
Clay Loam
Shallow Clay
Riparian
41.4
26.5
41.8
Whole Region
32.6
Area
% Change
1937
Biomass
1999
Biomass
% Change
47.7
33.4
55.5
+15%
+26%
+33%
58.1
38.5
---
71.2
47.7
---
22%
24%
---
41.5
+30%
249.0
312.1
25%
Historical Aerial Photography
Waggoner, Texas U.S.A.
Changes in the Structure of the Landscape
‘Brush Management’ is critical to
sustainable livestock production
in many rangelands.
Mechanical (top panel), herbicidal
(bottom panel), and fire treatments are
common; results are usually short-lived.
Within a region, woody plant cover/
biomass varies depending on site
management history.
The Drawback of Measuring Net Changes
Widespread brush ‘control’
(herbicides, grubbing, etc.)
and 1950s drought
Trend w/ no fire, no herbicides
Regional
Woody
Biomass
or Cover
Follow-up
management
1900
1930s aerial
photos
!
!
1950 Burned pastures 1990
2005 satellite imagery
Potential mismatch of remote sensing and ecosystem & disturbance dynamics
may mislead analyses
Setbacks and rates of recovery from disturbance depend on:
–
–
–
–
Type, intensity and spatial extent of disturbance
Soil type
Environmental conditions proceeding and following disturbance
Regenerative traits
Detection and Monitoring
A methodology that combines strategic and tactical ecosystem analysis approaches
rre
u
C
P
Co
t
n
ns
o
i
it
nd
te
s
i
ers
e?
c
n
Strategic Remote Sensing Assessment of
Surface Material Covers
Tactical
Soil Carbon & Carbon Isotope Analyses
Data Assimilation for
Model Hindcast and Prediction
Historical and Contemporary Analyses – Woody Ecroachment
Waggoner, Texas U.S.A.
y
p
co
s
ro s)
t
ec nth
p
S mo
e
n nr
o rso
b
ce pe
a
Sp .25
(0
hy )
p
ra ths
g
to on
o
h -m
p
n
l
ir a rso
Ae pe
(6
1937
<10%
1999
Woody Plant Cover
>90%
Effects of Woody Encroachment on Soil Carbon
Waggoner, Texas U.S.A.
Belowground Changes in C and N Stocks
Indicate Long-term Effects of
Woody Encroachment
Desertification in Central Argentina
Grazed
Protected
W
United Nations
Man-in-Biosphere
Nacunan Reserve
E
W
Protected
Grazed
E
0
PV
NPV
km
4
8
Soil
Asner et al. 2003
Linking Multi-parameter Remote Sensing and
Changes in Soil Carbon Stocks
Woody Vegetation +
Dry Herbaceous
Woody Vegetation only
Asner et al. 2003
Confusion Regarding Soil C Responses to Woody Cover Change
Jackson et al. (2002, Nature)
Even more confusion…
Asner and Martin (2004)
Soil Carbon Isotope Analysis
Waggoner, Texas U.S.A.
On sites where vegetation history is
not known, 13C/12C ratios provide
direct, spatially explicit evidence
that C3 shrubs have displaced C4
grasses.
Also, soil C at depth, indicates past
domination of the site by C4 grasses
Soil Carbon Isotope Analysis
Sonora, Arizona U.S.A.
Conclusions and Future Directions
• Airborne imaging spectroscopy is
integral to autonomous analysis of
surface and soil properties most
indicative of land degradation, woody
encroachment and desertification.
• Regional scale assessments of
surface composition and structure are
now routinely achievable and can aid
in our global understanding of land use
impacts on dryland ecosystems.
• Analyses must address historical
land-use change (relict sites, aerial
photography often not sufficient). Soil
carbon isotopes can help in many
dryland regions.
• Modeling is a pathway to prognostic
analysis (another talk).
NASA EO-1 Hyperion: First Spaceborne Earth-Imaging Spectrometer
FLORA is being planned for the next global land systems monitoring mission