Methodology for assessing desertification risk in areas cultivated with vines
Author: Constantinos Kosmas <lsos2kok@aua.gr>

g Indicator selection

A methodology has been developed for defining land desertification risk in areas cultivated with vines 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

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g Data collection

Data were collected in the mainland of Greece (Corinth, Achaia, and Thiva) from 111 field sites. The field sites were located on topographic maps in grids of 400 meters by 400 meters. Some were selected by applying a systematic sampling design (Webster, 1977), but others were selected by travelling through the area until a farmer was found on his land. 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, family size, farm size, number of parcels, size of the study field site, age of the farmer, parallel employment (if any), tillage operations, application of fertilizers, source of the available irrigation water, quantity of water, and available subsidies were defined in collaboration with the land user.
• The average tillage depth was defined by digging the upper 30-45 cm soil and measuring the depth of the plough layer. The dominant tillage direction was defined by observing in the field the direction of the furrows.
• The quality of the water was defined by measuring the electrical conductivity of the water using an electrical conductivity meter.
• The application of sustainable farming was defined for each study field site. The main types of sustainable farming existing in the study areas included actions such as: (i) no tillage or minimum tillage, (ii) tillage of soil in the up-slope direction, (iii) enhancement of vegetation cover.
  
• Land terracing was determined by the extent to which a field site was covered by terraces (i.e. ratio of the terraced area to the total area) and the degree to which they were protected from collapsing (i.e. ratio of protected terraces to total terraces).
• Storage of water runoff was defined in terms of land management for reducing surface water runoff and increasing the soil infiltration rate. For example, the presence of adequate shrubby or annual vegetation cover, construction of terraces, shallow ploughing of the soil, concentrating runoff water in small ponds and retarding runoff, keeping plant residuals or rock fragments on the soil surface.
  
• 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.
  
• Increase in soil organic matter content for protecting soil crusting were often related to the crop residue management. Crop rotations involving grasses and legumes have long been recognized in the study areas for increasing soil aggregation and maintaining higher organic matter contents than continuous growing of row crops. The incorporation of animal manure has been also considered as a management technique for increasing soil organic matter content in the study areas.
  
• Soil erosion control measures have been already mentioned above. Some other measures undertaken in the study areas were contour farming, stabilization structures, grassed waterways, and fallow. Contour farming has been recently applied in extensive areas cultivated with olives. Following the contour farming, each furrow acts as a reservoir to receive and retain the runoff water. Stabilization structures along waterways consisted of reinforced concrete or monolithic reinforced concrete such as drop spillways, drop inlets, as well as temporary structures made by rocks, logs, brush, woven wire and other nondurable materials to dissipate the energy of running water and stabilize the soil in cuts from landslides. The effectiveness of the existing soil erosion control measures were rated as adequate, moderate, low, very low and none defined in a self explanatory way.
  
• 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.
  

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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 erosion was assessed qualitatively in the field. It was characterised, according to: (i) the presence or not of the A-horizon, (ii) the existence and percentage of eroded spots, (iii) the degree of exposure of the parent material on the soil surface, and (iv) the presence of erosional gullies. In each study field site, three transects of thirty meters each were chosen perpendicular to the contour lines, and the length of the eroded areas and of the rock outcrops were measured. Eroded areas were defined spots in which current erosion features could be easily distinguished, such as washing out or deposition of soil materials (Kosmas et al., 2000). The degree of erosion was then assessed by the ratio of the total length of the eroded areas plus rock outcrops to the total length of the transect, expressed as a percentage(Kosmas et al., 2000). Five classes of erosion were used, very severe, severe, moderate, slight and no erosion.

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

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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= (0.83)+(0.40*farmers age)+(0.73*tillage operations)-(0.32*tillage direction)-(0.40*vegetation cover)+
(0.98*gradient)+(0.47*parent material)-(0.54*rock fragments)+ (0.28*aridity index)-(0.26*flooding frequency )+
(0.83*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

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g References

• 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., Danalatos, N.G, and Gerontidis, St., 2000. The effect of land parameters on vegetation performance and degree of erosion under Mediterranean conditions. Catena, 40:3-17.
• Webster, R. 1977. Quantitative and numerical methods in soil classification and survey. Clarendon Press, Oxford, p. 255.

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