Global Trends in Land Degradation

Transcription

1 Global Trends in Land Degradation (1) Past assessments of trends (2) New definitions and approaches (3) Projected trends (4) Research needs GLASOD

2 Soil degradation severity Soil degradation severity and vegetation Soil degradation Low High Low High Vegetation index

3 Soil degradation in Drylands

4 Where are the drylands? precipitation ~ 1.5 lower than evapotranspiration

5 Soil degradation in Drylands = Desertification

6 How much of drylands is desertified? Source Million km 2 Land area % of dryland % of global Million people Population size (year 2000) % of drylands % of global Drylands MA Desertified GLASOD (Soil) GLASOD (Soil and Veg.) MA-LUCC GLADOD (soil): expert opinion, travelers descriptions, research reports GLADOD (+ Veg. mean of 100 monthly [ ] NDVIs of highest weekly value)

7 MA-commissioned desk study Erica Lepers (2003), Land-Use Land-Cover Change (IGBP s LUCC) Relatively reliable literature data Change through Not dryland Hyperarid Not degraded Dryland not covered by data

8 How much of drylands is desertified? Source Million km 2 Land area % of dryland % of global Million people Population size (year 2000) % of drylands % of global Drylands MA Desertified GLASOD (Soil) GLASOD (Soil and Veg.) MA-LUCC The source of differences?

9 How much of drylands is desertified? Source How many people are affected? Million km 2 Land area % of dryland % of global Million people Population size (year 2000) % of drylands % of global Drylands MA Desertified GLASOD (Soil) GLASOD (Soil and Veg.) Dryland not covered by data 2.0 MA-LUCC The source of differences?

10 susceptible may

11 Misuse of terms Controversial definitions Disputed methodologies

12 Hyperarid Arid Semiarid Dry subhumid Desertification Degradation Susceptability Drylands Humid Cold climate Misuse of terms Controversial definitions Disputed methodologies

13 terrestrial bio-productive system that comprises soil, vegetation, other biota, and the ecological and hydrological processes that operate within the system Land degradation in the drylands

14 Land degradation in the drylands A terrestrial ecosystem

15 Land degradation in the drylands A terrestrial ecosystem reduction or loss of the biological productivity resulting from land uses. or combination of (other) processes, such as

16 Land degradation in the drylands A terrestrial ecosystem Loss of ecosystem services, most notably primary production

17 Land degradation in the drylands A terrestrial ecosystem Loss of ecosystem services, most notably primary production Ecosystem Services Provisioning services Food, Forage, fiber Fuelwood Freshwater biochemicals Regulating services Pollination, seed dispersal Water regulation Climate regulation Carbon sequestration Cultural services

18 Land degradation in the drylands A terrestrial ecosystem Loss of ecosystem services, most notably primary production Dryland Ecosystem Services Provisioning services Food, Forage, fiber Supporting services Fuelwood Freshwater Nutrient cycling biochemicals Soil conservation Regulating services Soil formation Pollination, seed dispersal Supporting biodiversity Water regulation Climate regulation Carbon sequestration Cultural services Primary production Spiritual, religious, cultural heritage Indigenous ecological knowledge Ecotourism

19 productivity desertification

20 Reduction in productivity below its potential Expression of desertification

21 Reduction in productivity below its potential Net Primary Productivity (NPP) Normalized Difference Vegetation Index (NDVI) Expression of desertification

22 Reduction in productivity below its potential Net Primary Productivity (NPP) Normalized Difference Vegetation Index (NDVI) Expression of desertification 1. Define (large) region 2. Obtain digitized thematic maps: Soils Climate Vegetation structure 3. Classify region into homogenous land classes 4. Overlay a layer of several-years mean NDVIs 5. Highest NPPs of each land class - estimators of it potential NPP 6. Normalize NPP values; potential for each class = 100% 7. All other pixels in the class represent percentage of potential 8. Lowest percentages represent sites undergoing desertification

23 Mean NDVI of 5 years ( ) SPOT-VEGETATION, 1 km 2 resolution Pixels of degradation Zimbabwe Pixels of Potential NPP, non-degraded Local NPP Scaling (LNS) Stephen Prince, Inbal Reshef

24 b.

25 b. c ĠLASOD Risk Risk Not recorded Low Moderate High Very high Biomes, soils, climate, population (NRCS ) Mean NDVI of What is the trend?

26 South Africa Former homelands Degradation criteria: Reduced Vegetation cover Changed plant composition Bush encroachment Livestock density in communal areas twice larger than in commercial farms

27 Local NPP Scaling 1. Define (large) region 2. Obtain digitized thematic maps: Soils Climate Vegetation structure 3. Classify the region into homogenous land classes 4. Overlay a layer of several-years mean NDVIs

28 1. Define (large) region with non-degrading and degrading land uses 2. Obtain digitized thematic maps: Soils Climate Vegetation structure 3. Classify the region into homogenous land classes 4. Overlay a layer of NDVI values for each year of a long time-series

29 Local NPP Scaling 1. Define (large) region with non-degrading and degrading land uses 2. Obtain digitized thematic maps: Soils Climate Vegetation structure 3. Classify the region into homogenous land classes 4. Overlay a layer of NDVI values for each year of a long time-series 5. Calculate annual NDVIs for pairs (degraded, non-degraded) pixels of each land class for each year of the long time-series 80 Non-degraded sumndvi degraded What is the source of interannual variation? growing seasons

30 Persistent reduction in productivity Productivity 80 sumndvi degraded Non-degraded Rainfall (mm) growing seasons

31 NPP + Residuals Small residuals actual NPP close to potential NPP Large residuals actual NPP deviates from potential NPP -

32 NPP + Residuals Small residuals actual NPP close to potential NPP Large residuals actual NPP deviates from potential NPP - Rainfall 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 Residual Year Rainfall

33 Regression slope

34 Residual Trends (RESTREND) Konrad Wessels and Stephen Prince Is this persistent productivity loss irreversible? Local NPP Scaling (LNS) (mean )

35 Residual Trends (RESTREND) Konrad Wessels and Stephen Prince - Temporal Trend of Deviation from Potential Is this persistent productivity loss irreversible? + 0 % Local NPP Scaling (LNS) (mean ) Percentage of Potential Productivity 100%

36 Future trends Millennium Ecosystems Assessment Scenarios Present Conditions & Trends 50-year projections Reactive Globalized Reactive Regionalized Reactive Regionalized Proactive Proactive Globalized Proactive Ecosystem management approach Fragmented, Regionalized Globalized Transition of Global society

37 Rate of change in the extent of desertified areas Desertification trends Time

38 Rate of change in the extent of desertified areas Desertification trends Poverty: Small increase Strong increase Time Climate Change: No increase Strong increase Pressure of desertification drivers

39 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

40 Sinai Negev

41 Number of shrubs/km Recovery in Negev 1948 border closed 1967 border opened Negev: delayed response of herders; Sinai: overgrazed Negev and Sinai overgrazed 1982 border closed Negev recovers; Sinai overgrazed Negev Sinai Years of airphotos Tsoar et al. 1995

42 Number of shrubs/km Recovery in Negev 1948 border closed 1967 border opened Negev: delayed response of herders; Sinai: overgrazed Negev and Sinai overgrazed 1982 border closed Negev recovers; Sinai overgrazed? Negev Sinai Years of airphotos Tsoar et al. 1995

43 Desertification Persistent reduced productivity Soil erosion Climate change

44 Desertification Persistent reduced productivity Soil erosion Climate change Biodiversity loss

45 Desertification Persistent reduced productivity Soil erosion Climate change Biodiversity loss

46 Desertification Persistent reduced productivity Soil erosion Climate change Biodiversity loss Vegetation changes

47 Desertification Persistent reduced productivity Soil erosion Climate change Biodiversity loss Vegetation changes

48 Arid dryland Negev Desert watershed Loess sediments wind-transported from the Sahara Mid Pleistocene 60K 20K Late Pleistocene last pluvial phase

49 Arid dryland Negev Desert watershed Loess sediments wind-transported from the Sahara 5-10m thick 2m Mid Pleistocene 60K 20K Late Pleistocene last pluvial phase

50 Arid dryland Negev Desert watershed Loess sediments wind-transported from the Sahara Less dust Less but higher intensity rain 5-10m thick 2m Mid Pleistocene 60K 20K Late Pleistocene last pluvial phase 16K Holocene Postpluvial climate change

51 Arid dryland Negev Desert watershed Loess sediments wind-transported from the Sahara Less dust Less but higher intensity rain Land management Agriculture 5-10m thick 2m Mid Pleistocene 60K 20K Late Pleistocene last pluvial phase 16K Holocene Postpluvial climate change 3K Bronze age

52 Arid dryland Negev Desert watershed Loess sediments wind-transported from the Sahara Less dust Less but higher intensity rain Land management Agriculture Cultivation abandoned 5-10m thick 4 m 2m Mid Pleistocene 60K 20K Late Pleistocene last pluvial phase 16K Holocene Postpluvial climate change 3K Bronze age 1.5K Byzantine period Peak agriculture 1.4K 1.2K Early Islamic period

53 Last few centuries Bedouin use of Byzantine terraces

54 Last few centuries Bedouin use of Byzantine terraces

55 Last few centuries Bedouin use of Byzantine terraces

56 Last few centuries Bedouin use of Byzantine terraces Current rates ( )/year Gully incision 1-23 m Soil loss m 3 Loss since Byzantine cultivation peak 10% of arid Negev land

57 Some watersheds already lost most of their soil

58 100% Soil for agriculture within the watershed No soil for agriculture 0% Soil loss -15,000 Years 0 +5,000

59 100% Soil for agriculture within the watershed Rocky surfaces within the watershed Runoff increase 0% No runoff for agriculture No soil for agriculture Soil loss -15,000 Years 0 +5,000

60 100% Soil for agriculture within the watershed Agriculture window Rocky surfaces within the watershed Runoff increase 0% No runoff for agriculture No soil for agriculture Soil loss -15,000 Years 0 +5,000

61 100% Soil for agriculture within the watershed Agriculture window Rocky surfaces within the watershed Runoff increase 0% No runoff for agriculture No soil for agriculture Soil loss -15,000 Years 0 +5,000 60K 20K Late Pleistocene last pluvial phase 16K Holocene Postpluvial climate change 3K Bronze age 1.5K Byzantine period Peak agriculture 1.4K 1.2K Early Islamic period

62 100% Soil for agriculture within the watershed Agriculture window Rocky surfaces within the watershed Runoff increase 0% No runoff for agriculture No soil for agriculture Soil loss -15,000 Years 0 +5,000 Desertification NOT driven by human over-use NOT driven by anthropogenic global climate change But due to NATURAL climate change