General information
Site number:This number will have only local significance but is particularly valuable for the coordination of descriptive and statistical data.
Date of examination: Self explanatory only.
Author(s) describing: Self explanatory only.
Location: The description of the location should serve two purposes. Firstly, it should enable readers to locate the study site and for this purpose it may be necessary to relate the position to small villages or minor roads. Secondly, it should serve to indicate the position of the study site approximately in relation to large towns, or other features which will shown on small scale maps of the pilot area, for the benefit of readers who are unfamiliar with the area.
Elevation: Elevation above sea level will be quoted in meters using a GPS or topographic maps.
Altitude: Altitude will be quoted using a GPS for locating study sites in GIS or in a topographic map.
Longitude: Altitude will be quoted using a GPS for locating study sites in GIS or in a topographic map.
Physiographic position: Physiographic position is required for interpretation of the combined influence of slope and run-off processes of water and tillage erosion. The following terms are recommended: Plateau, summit, crest (escarpment), backslope, footslope, toeslope, terrace, valley bottom, plain, depression. Then the shape of the slope is defined as following: convex slope, concave slope, linear slope.
Slope length: Slope length it is measured in meters. It corresponds to the length of the study field site in the direction perpendicular to the contour lines.
Tillage erosion features:Tillage erosion is considered one of the most important processes of land degradation in hilly cultivated areas. Tillage erosion is a progressive down slope translocation of soil caused mechanically by tillage implements. Displacement of soil materials mainly occurs in upper convex parts (summit, shoulder, backslope) of a hillslope and deposition in the concave parts (footslope, toeslope). Tillage erosion features such as ridges along field boundaries, or soil rings around tree trunks can be observed in areas highly affected from this process. Such features can be measured (in meters) and they will be used as an indicator in assessing the rate of tillage erosion by the methodology proposed.
Estimation of tillage erosion: The flux of soil in the direction of ploughing (Qs, in kg m-1) for each tillage operation can be estimated in grids of 1 m using the equation (Govers et al.,1994)
Qs = D x BD x G x B
Where, D is the plough depth (m), BD is the bulk density of the top soil (kg m-3), G is slope gradient (tan), B is a coefficient corresponding to plough depth D and estimated as the slope of the linear regression of slope gradient versus soil displacement.
Tillage erosion is considered as a diffusion process. The tillage transport coefficient (k in kg m-1 per tillage pass) can be estimated with the equation: k = BD x B x D. Experimental data obtained during the execution of the EU research project TERON (2000) shown that k for mouldboard plowing can be estimated for up- and downslope tillage by the equation:
Klong = 2.026BD x D1.989 x V0.406
and for contour tillage:
Klat = 0.406BD x D x V 0.385
Where V is the tillage speed in m s-1
When tillage is carried out in opposing directions with the same frequency, a net downslope soil movement occurs on the hillslope. The net unit transport rate (Qs,net), i.e. the net amount of soil material that is displaced downslope across a line segment with unit width due to a single tillage pass can be calculated as:
Qs,net = (Qdown - Qup)/2
The erosion rate Et due to tillage can be calculated for the elementary slope element with unit with as the difference between the amount of soil leaving (Qs,out) and entering (Qs,in) the slope element or:
Et = (Q s,out - Q s,in) / Δx
Where Δx is the horizontal length of slope segment under consideration. The soil material was assumed to be uniformly distributed in each grid. The decrease or increase in soil thickness (h, in m) is calculated by the equation:
h = W / S x BD
where W is the soil weight (kg), S is the surface area of each grid (m2).
Defining environmentally sensitive area to desertification: The environmentally sensitive areas (ESAs) to desertification are defined using the methodology developed in the EU research project MEDALUS III (Mediterranean Desertification and Land Use). Environmentally Sensitive Areas (ESAs) to desertification around the Mediterranean region exhibit different sensitivity to desertification for various reasons. (Kosmas et al., 1999). For example there are areas presenting high sensitivity to low rainfall and extreme events due to low vegetation cover, low resistance of vegetation to drought, steep slopes, highly erodible parent materials, etc. High sensitivity can be also related to the type of land use, since land use can promote desertification in climatically and topographically marginal areas. Four general types of ESAs 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 ESAs 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, for example, (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 ESAs 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 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 textured soils, under semi-arid or wetter climatic conditions, independently of vegetation, are considered as being non-threatened by desertification.
The various types of ESAs to desertification are distinguished and mapped by using certain key indicators or parameters for assessing the land capability to withstand further degradation, or the land suitability for supporting specific types of land use. A simple methodology has been developed by Kosmas et al. (1999) to identify ESAs to desertification by using 15 simple indicators related to soil, climate, vegetation, and land management characteristics. After the definition of classes and the assignment of weighing indices for each indicator, soil, climate, vegetation and management qualities are defined by combining the various indicators. Then the ESAs were identified based on these qualities (see manual on "key indicators of desertification and mapping environmentally sensitive areas to desertification", European Commission, EUR 18882).
