(1) past assessments of trends (2) new definitions and

Global Trends in Land Degradation

(1) Past assessments of trends(2) New definitions and approaches(3) Projected trends(4) Research needs

GLASOD

Soil degradation severity

Soil degradation severity and vegetation

Soil

degr

adat

ion

High

Low

HighLowVegetation index

Soil degradation in Drylands

Where are the drylands?precipitation

~ 1.5 lower thanevapotranspiration

= DesertificationSoil degradation in Drylands

How much of drylands is desertified?

0.31.0204.1106MA-LUCC

297043GLASOD (Soil and

Veg.)

2.0117.582012GLASOD (Soil)

Deser-tified

35.520014161MADrylands

% of global

% ofdrylands

Million people

% of global

% ofdryland

Million km2

Population size (year 2000)Land area

Source

GLADOD (soil): expert opinion, travelers’ descriptions, research reports

GLADOD (+ Veg. – mean of 100 monthly [1983-1990] NDVIs of highest weekly value)

• Relatively reliable literature data • Change through 1980-2000

MA-commissioned desk study – Erica Lepers (2003),Land-Use Land-Cover Change (IGBP’s LUCC)

Dryland not covered by data

Not dryland

Not degradedHyperarid


0.31.0204106MA-LUCC


Veg.)

2.0117.582012GLASOD (Soil)

Deser-tified


% of global

% ofdrylands

Million people

% of global

% ofdryland

Million km2


Source

The source of differences?


0.31.0204106MA-LUCC


Veg.)

2.0117.582012GLASOD (Soil)

Deser-tified


% of global

% ofdrylands

Million people

% of global

% ofdryland

Million km2


Source

How many people are affected?

The source of differences?

Dryland not covered by

data

susceptiblemay

•Misuse of terms•Controversial definitions•Disputed methodologies

DesertificationDegradationSusceptabilityDrylands

Hyperarid

Arid

Semiarid

Dry subhumid

Humid

Cold climate

•Misuse of terms•Controversial definitions•Disputed methodologies

Land degradation in the drylands

“terrestrial bio-productive system that comprises soil, vegetation, other biota, and the ecological and hydrological processes that operate within the system”


A terrestrial ecosystem


A terrestrial ecosystem “reduction or loss … of the biological … productivity …resulting from land uses …. or … combination of (other) processes, such as…”


A terrestrial ecosystem Loss of ecosystem services, most notably – primary production



Cultural services

Regulating services• Pollination, seed dispersal• Water regulation• Climate regulation• Carbon sequestration

Provisioning services• Food, Forage, fiber• Fuelwood• Freshwater• biochemicals

Ecosystem Services



Cultural services• Spiritual, religious, cultural heritage• Indigenous ecological knowledge• Ecotourism

Regulating services• Pollination, seed dispersal• Water regulation• Climate regulation• Carbon sequestration

Provisioning services• Food, Forage, fiber• Fuelwood• Freshwater• biochemicals

Supporting services• Nutrient cycling • Soil conservation• Soil formation• Supporting biodiversity

• Primary production

Ecosystem Services

Primary production

Soil conservation

FoodFuelwoodFreshwater

Water regulation

Dryland

productivity

desertification

Reduction inproductivity

desertificationExpression of

below its potential



below its potential

Net Primary Productivity (NPP)

Normalized Difference Vegetation Index (NDVI)



below its potential

Net Primary Productivity (NPP)

Normalized Difference Vegetation Index (NDVI)

1. Define (large) region2. Obtain digitized thematic maps:

• Soils• Climate• Vegetation structure

3. Classify region into homogenous land classes4. Overlay a layer of several-years’ mean NDVIs 5. Highest NPPs of each land class - estimators of it potential NPP6. Normalize NPP values; potential for each class = 100%7. All other pixels in the class represent percentage of potential8. Lowest percentages represent sites undergoing desertification

Pixels of Potential NPP, non-degraded

Pixels of degradation Zimbabwe

Local NPP Scaling (LNS) – Stephen Prince, Inbal Reshef

Mean NDVI of 5 years (1998-2002) SPOT-VEGETATION, 1 km2 resolution

Not recordedLowModerateHighVery high

Risk

b.

Biomes, soils, climate, population (NRCS )

Risk

c.GLASOD

Mean NDVI of 1998-2002 What is the trend?

South AfricaDegradation criteria:

Former homelands

• Reduced Vegetation cover• Changed plant composition• Bush encroachment• Livestock density in communal

areas twice larger than in commercial farms



3. Classify the region into homogenous land classes 4. Overlay a layer of several-years’ mean NDVIs

Local NPP Scaling



3. Classify the region into homogenous land classes4. Overlay a layer of NDVI values for each year of a long time-series

with non-degrading and degrading land uses



3. Classify the region into homogenous land classes 4. Overlay a layer of NDVI values for each year of a long time-series

with non-degrading and degrading land uses

5. Calculate annual NDVIs for pairs (degraded, non-degraded) pixels of each land class for each year of the long time-series

Local NPP Scaling

86 89 92 94 98 00 03

50

40

60

70

80

sum

ND

VI

16 growing seasons

Non-degraded

degradedWhat is the source of interannual variation?

86 89 92 94 98 00 03

600

1400

1000

200 Rai

nfal

l (m

m)

50

40

60

70

80Productivity

reduction in productivityPersistent

sum

ND

VI

16 growing seasons

Non-degraded

degraded

Residuals+

-

NPP

• Small residuals – actual NPP close to potential NPP

• Large residuals – actual NPP deviates from potential NPP

Residuals+

-

NPP

Rainfall

Year

Rai

nfal

l

Res

idua

l

• Small residuals – actual NPP close to potential NPP

• Large residuals – actual NPP deviates from potential NPP

• Negative residuals –NPP lower than potential NPP

• Positive residuals –NPP higher than potential NPP

• As time advances –residuals more negative

• Degradation increased with time during the studied period

Regression slope

Residual Trends (RESTREND) – Konrad Wessels and Stephen Prince

Local NPP Scaling (LNS)

(mean 1998-2002)

Is this persistent productivity loss irreversible?

Residual Trends (RESTREND) – Konrad Wessels and Stephen Prince

Local NPP Scaling (LNS)

-

+

Percentage of Potential Productivity

0 %

100%

(mean 1998-2002)

Is this persistent productivity loss irreversible?

Temporal Trend of Deviation from Potential

ProactiveReactive Tran

sitio

n of

Glo

bal

soci

ety

Ecosystem management approach

Glob

alize

d

Frag

men

ted,

Regi

onal

ized

GlobalizedReactive

RegionalizedReactive

RegionalizedProactive

GlobalizedProactive

Present Conditions &

Trends

50-year projections

Millennium Ecosystems Assessment Scenarios

Future trends

Rate of change in the extent ofdesertified areas

Time

Des

ertif

icat

ion

tren

ds

Rate of change in the extent ofdesertified areas

Time

Des

ertif

icat

ion

tren

ds

Pressure of desertification drivers

Small increase Strong increasePoverty:

Climate Change: No increase Strong increase

Research needs• Detect and distinguish desertification from

desertification risk at all scales• Identify and detect thresholds beyond which dryland

productivity change irreversibly• Decouple effects of desertification from effect of

dryland’s low productivity on poverty• Quantify the feedback loops between desertification

and climate change

SinaiNegev

Tsoar et al. 1995

1948 border closed

1967 border opened

1982 border closed

1945 1956 1968 1976 1982 1984 1989

Years of airphotos

100

200

300

400

500

600

Num

ber o

f shr

ubs/

km2

Recovery in Negev Negev: delayed response of herders; Sinai: overgrazed

Negev and Sinai overgrazed

Negev recovers; Sinai overgrazed

NegevSinai

Tsoar et al. 1995

1948 border closed

1967 border opened

1982 border closed

1945 1956 1968 1976 1982 1984 1989

Years of airphotos

100

200

300

400

500

600

Num

ber o

f shr

ubs/

km2

Recovery in Negev Negev: delayed response of herders; Sinai: overgrazed

Negev and Sinai overgrazed

Negev recovers; Sinai overgrazed

NegevSinai

?

Desertification

Climate change

Persistent reduced productivity

Soil erosion

Desertification

Climate change


Soil erosion

Biodiversity loss

Desertification

Vegetation changes

Climate change


Soil erosion

Biodiversity loss

Desertification

Vegetation changes

Climate change Biodiversity loss


Soil erosion

Desertification

Climate change

Arid drylandNegev Desert

watershed

Mid Pleistocene

60K 20KLate Pleistocene last pluvial

phase

Loess sediments wind-transported from the Sahara


watershed

Mid Pleistocene


phase


2m

5-10m thick


watershed

Mid Pleistocene


phase


16K

Less dustLess but higher

intensity rain

2m

5-10m thick

HolocenePost-

pluvial climate change


watershed

Mid Pleistocene


phase


16KHolocenePost-



intensity rain

3KBronze

age

Land management Agriculture

2m

5-10m thick


watershed

Mid Pleistocene


phase


16KHolocenePost-



intensity rain

3KBronze

age

Land management Agriculture

1.5K

Byzantine periodPeak

agriculture

1.4K 1.2KEarly

Islamic period

Cultivation abandoned

2m

5-10m thick 4 m

Last few centuries – Bedouin use of Byzantine terraces

Last few centuries – Bedouin use of Byzantine terraces

Current rates (1990-2001)/year• Gully incision 1-23 m• Soil loss 81-818 m3

Loss since Byzantine cultivation peak –10% of arid Negev land

20011984

Some watersheds already lost most of their soil

Years-15,000 +5,0000

Soil loss0%

100%Soil for

agriculture within the watershed

No soil for agriculture

Years-15,000 +5,0000

Soil loss0%

100%

Runoff incre

ase

Soil for agriculture within the watershed


No runoff for agriculture

Rocky surfaces

within the watershed

Years-15,000 +5,0000

Soil loss0%

100%

Runoff incre

ase




Rocky surfaces


Agriculture window

Years-15,000 +5,0000

Soil loss0%

100%

Runoff incre

ase




Rocky surfaces


Agriculture window


phase

16KHolocenePost-


3KBronze

age1.5K

Byzantine periodPeak

agriculture

1.4K 1.2KEarly

Islamic period

DesertificationNOT driven by human over-use

NOT driven by anthropogenic global climate changeBut due to NATURAL climate change

Years-15,000 +5,0000

Soil loss0%

100%

Runoff incre

ase




Rocky surfaces


Agriculture window

(1) past assessments of trends (2) new definitions and

Documents