g Indicator selection

A methodology has been developed for defining land desertification risk in areas affected by salinization by using simple indicators related to soil, climate, vegetation, socio-economic, and management characteristics. The list of indicators were defined based on: (a) the existing experience obtained in other desertification projects such as MEDALUS I, II, and II, MEDACTION, etc., (b) contacting farmers and land planners, and (c) organizing focus group workshops. In the present study 40 indicators were used which can be easily measured or made available. Most of the used indicators are related to local conditions (farm level) as shown in the Example Survey Form below.

Each indicator was described according to classes, which were defined using existing classification systems such as the geo-referenced soil data base, or existing research data.

Example Survey Form

5 top

g Data collection

Data for plain areas were collected in 98 field sites from the Kalloni plain (Lesvos island), Argolis plain (eastern Peloponnesus), Pinios alluvial plain (Achaia and Ilia region of Peloponnesus), Kalamas alluvial plain (Thesprotia, western Epirus)), and Acherontas alluvial plain (Preveza, western Epirus). The field sites were located on topographic maps in grids of 400 meters by 400 meters applying a systematic sampling design (Webster, 1977). The location of each field site was accurately defined by using a GPS (Magellan, 500 DX).

The indicators were assessed using the following methods:

• Land ownership, period of existing land use type, source of the available irrigation water, quantity of water, frequency of flooding and ground water recharge were defined in collaboration with the land user.
• Soil textural classes of particles <2 mm of the non-consolidated parent material, or the parent material, were estimated using the USDA system of soil texture designation. The parent material was defined using the geological map of the study area. The average soil depth was measured in auger holes or in soil cuts. The slope gradient was described using topographic maps of the appropriate scale. The following dominant slope classes were distinguished: <6%, 6-18%, 18-35%, and >35%. The rock fragments cover (>6 mm) in the soil surface were defined according to the percentage cover in three classes: >40%, 15-40%, and <15%. The drainage conditions were defined on the basis of the depth of hydromorphic features such as iron or manganese mottles or gray colors, and depth of the groundwater table. The following drainage classes were distinguished:
  Very well to well drained soils (soils with any Fe or Mn mottles or gray colors at some depth greater than 100 cm from the soil surface. The soil is not wet enough near the soil surface or the soil does not remain wet during the growing period of the plants. Water is removed from the soil rapidly.) Moderately well to somewhat poorly drained soils (Fe, Mn or gray mottles are present in the soil, at some depth between 30 and 100 cm from the soil surface. The soil is wet enough near the soil surface or the soil remain wet during the early growing period of the plants. Water is removed from the soil slowly.) Poorly to very poorly drained soils (Mottles of Fe and Mn are present in the upper 30 cm of the soil, or gray colors of reducing conditions are present. A permanent water table usually exist at a depth greater than 75 cm. In some of these soils the ground water may reach to the surface during the wet period of the year. Water is removed from the soil so slowly that the soils are wet at shallow depth for long periods.)
• The reclamation of affected soils (if any) such as poorly drained, salinized or acidified was described. Management techniques for reclaiming the soils were: (i) construction of channel network, (ii) application of excess of good water quality for leaching of soluble salts, (iii) application of lime for reducing soil acidity. The efficacy of land reclamation was rated as adequate, moderate, low, very low and none.
• Cultivation of plant species of low water requirements is an effective measure that might combat further the land degradation. The various vegetation types were classified in three categories in relation to water requirements such as high, moderate and low. For example cereals were graded as high water requirements plant species, while olive and pine trees as low water requirements.
• Soil water conservation techniques, important for the study areas, included mulching, weed control, management of soil surface for maximum water vapour adsorption, tillage and covering soil surface by rock fragments. Enhancement of water vapour adsorption was achieved by: (a) reducing the density of the growing vegetation and increasing the soil-atmosphere interface, (b) using surface mulches such as rock fragments or plant residues partially covering the soil surface, and (c) ploughing the soil for increasing macro-porosity (Kosmas et al., 2001a). The existing techniques on soil water conservation, if any, were recorded for each study field site.
• The effectiveness of the policies on environmental protection depends on the degree of enforcement, while they are rated based on their degree of effectiveness. Hence, the information collected on the existing policies depended and their implementation /enforcement of the policy under consideration. For example, in the case of terracing protection policy, a relevant piece of information was the ratio of protected terraces to existing terraces in the study field site.
  
• Long-term weather records were supplied by the nearby meteorological stations such as Mytilene, Nauplion, Patra, Andravida, Preveza, Egoumentitsa. (45 years records - Greek National Meteorological Service). Bagnouls-Gaussen aridity index (BGI) was defined as following:
  

  where: ti is the mean air temperature for month i (oC), Pi is the total precipitation for month i (mm); and ki represents the proportion of the month during which 2ti - Pi >0.

5 top

g Identification of ESAs and degree of soil erosion

The type of environmentally sensitive areas (ESAs) and the degree of soil erosion were estimated in each field site, relative to desertification risk. Four general types of environmentally sensitive areas (ESAs) to desertification have been distinguished based on the stage of land degradation (Kosmas et al., 1999):

• Critical ESAs: areas already highly degraded through past misuse, presenting a threat to the environment of the surrounding areas, i.e. badly eroded areas subject to high run-off and sediment loss. This may cause appreciable flooding downstream and reservoir sedimentation. Critical areas are subdivided in three sub-types C3, C2, and C1, in a decreasing stage of land desertification.
• Fragile ESAs: areas in which any change in the delicate balance between natural and human activity is likely to bring about desertification. For example, the impact of predicted climate change due to greenhouse effect is likely to enhance reduction in the biological potential due to drought causing areas to lose their vegetation cover, be subject to greater erosion, and finally shift to a critical ESA. A land use change (such as a shift towards cereals cultivation,) on sensitive soils might produce immediate increase in run-off and erosion, and perhaps pesticide and fertilizer pollution downstream. This type of ESA is subdivided in three sub-types F3, F2, and F1 in a decreasing stage of land desertification.
• Potential ESAs: areas threatened by desertification under significant climate change, if a particular combination of land use is implemented or where offsite impacts will produce severe problems elsewhere (for example pesticide transfer to downslope or downstream areas under variable land use or socio-economic conditions). This would also include abandoned land which is not properly managed. These ESAs are in a less severely desertified stage than fragile ESAs, for which nevertheless planning is necessary.
  
• Non Threatened ESAs: areas with deep to very deep soils, nearly flat, well drained, coarse-textured or finer soils, under semi-arid or wetter climatic conditions, independently of vegetation, are considered as being non-threatened by desertification.
  

The degree of soil salinization was assessed in the field by measuring the soil electrical conductivity using an EC-probe for salinity measurements (Eijelkamp earth sensitivity meter). The following categories of degree of salinization were used: (a) free of salts with electrical conductivity <400 µS, (b) slightly salinized with electrical conductivity 400-800 µS, moderately salinized with electrical conductivity 800-1500 µS, and severely salinized with electrical conductivity >1500 µS.

An empirical approach was adopted to define desertification risk based on the degree of soil salinization and the type of ESA. The type of ESA describes the existing condition of land degradation caused by various processes acting previously. In plain areas where this study was conducted, the main process of land degradation and desertification was soil salinization. Four categories of desertification risk were distinguished, high, moderate, low and none and they were associated with ESA status as follows.

5 top

g Analysis and results

The various classes of the indicators were rated according to the importance to desertification risk and indices were assigned to each class. For example:

The analysis was conducted by using the statistical package STATISTICA (1999 edition). A forward stepwise multiple regression was applied, with desertification risk being the dependent variable and all the indicators as independent variables. An algorithm was derived from the analysis relating the most important indicators (which are shown in the diagram).

Thus:

DR=(6.50)-(0.25*present land use)+(0.23*drainage)-(1.16*rainfall)-(0.29*elevation)-
(0.11*water quality)-(0.35*ground water depth)+(0.33*frequency of flooding)-
(0.41*reclaimation of affectected soils)+(0.84*policy enforcement)

Desertification risk was classified according to the following range in value of DR:

• No risk DR<1.49
• Low risk 1.50<DR<2.49
  
• Moderate risk 2.50<DR<5.49
  
• High risk DR>5.50

The analysis of the data showed that important indicators for defining desertification risk were related to land management, climate, soil, topography, and water. Important indicators related to management characteristics were frequency of flooding, land use type, efficacy of reclamation, and policy enforcement. As the frequency of flooding increased desertification risk increased. Frequency of flooding was also related to other important indicators such as topography and depth of ground water. Desertification risk decreased as land use type changes from pasture, wetland, recreation area, and agriculture. Reclamation of salt-affected areas was mainly related to the presence of a drainage network in the study field sites. As the efficacy of reclamation increased due to lowering of ground water increased desertification risk decreased.

Other important indicators defining desertification risk in salt-affected areas were: elevation, water quality, ground water depth, drainage and rainfall. Desertification risk increased as the elevation decreased. Good ground water quality decreased desertification risk. The worst the soil drainage conditions were, the higher the desertification risk was. Also the shallower the ground water table the higher the desertification risk. Reduction of annual rainfall increased desertification risk. Rainfall greatly affects the rate of soil salinization. Soils in areas with rainfall less than 300 mm were usually highly salinized.

5 top

g References

• Finke, P., Hatwich, R., Dudal, R., Ibanez, J., Jamagne, M., King, D., Montanarella, L., and Yassoglpu, N., 1998. Georeferenced soil data base for Europe, Manual of procedures. European Soil Bureau Scientific Committee. EUR 18092 EN, 170 p
  
• Kosmas, C., Kirkby, M. and Geeson, N. 1999. Manual on: Key indicators of desertification and mapping environmentally sensitive areas to desertification. European Commission, Energy, Environment and Sustainable Development, EUR 18882, 87 p.
  
• Kosmas, C., Marathianou, M., Gerontidis, S., Detsis, V., Tsara, M., & J. Poesen, 2001.Parameters affecting water vapour absorption by soil under semi-arid climatic conditions. Agricultural Water Management, Vol. 48, pp. 61-78.
  
• Webster, R. 1977. Quantitative and numerical methods in soil classification and survey. Clarendon Press, Oxford, p. 255.

5 top