Home Góis, Portugal Evaluating the desertification risk assessment tool with local experimental results

Evaluating the desertification risk assessment tool with local experimental results Print

Author: Victor Jetten


Like many Mediterranean countries Portugal suffers from forest fire due to its dry and hot climate. The problem is not only degradation of forest and the emission of carbon dioxide to the atmosphere but it also increases soil losses and pollution of water and air. The Mação Region in Portugal suffered massive fires in 2003 and 2005 affecting more than 70% of the municipality area. To protect the forest from wild fire strip network is constructed. The Vale Torto area near Góis in Portugal was burned by several fires in the 1970s and the early 1980s. Similarly the Camelo catchment near Góis also suffers from forest fire with the recent fire taking place in July 2008. Experiments included strip corridors (Macao) and prescribed burning (Vale Torto).


The area has shallow Cambisols (< 30 cm deep) over metamorphic shists and steep slopes. The main vegetation is pine forest, Eucalypt and shrubs, but fire destroys this and decreases the vegetation cover. The climate shows a strong seasonality despite the overall high precipitation (600-1000 mm per year) with dry summers. The landscape has steep slopes and a deeply incised drainage system.


Desertification indices
The index was calculated for water erosion, overgrazing, water stress and fire risk. The values depend on the selection for intact forest or for a burned area, which affects mainly water erosion and overgrazing. On the next page the result of three calculations are shown: intact forest, heavily burned forest and forest with fire protection measures. The differences between the areas are not sufficient to distinguish them in the desertification index tool.


Oddly enough the desertification index scores highest for overgrazing, and fire risk, for which the area is known, scores only as low risk. The fire risk depends on land use intensity which is difficult to estimate: if tourism is counted (which is one of the causes of forest fire) and the land use intensity is increased from low to high, the fire risk increases also from 1.49 to 1.65.


Water erosion and overgrazing give the highest risk factors, respectively 3.8 and 5.4 for an intact forest with a cover of 0.5-0.75. The fire risk is low: 1.7 and there is no water stress. After a forest fire with a low cover and high percentage of forest fire these values change to 4.5 for water erosion and 4.7 for overgrazing, presumably because there is less vegetation to graze upon.


The fire risk is not affected by the burning. This may indicate a false effect: in reality a forest fire would decrease the fuel load available and greatly decrease the risk. This is in fact the purpose one of prescribed burning, which is one of the control measures tested in the project. Fire protection also hardly affects fire risk, the index decreases from 1.65 to 1.48, both in the low risk zone.


Intact forest (50-75% cover, no burning) Burned forest (< 10% cover, heavy buring)
Extreme fire protection measures (>75% area protected)


The desertification index gives a correct assessment that it shows water erosion as clear a risk in this area with shallow soils and steep slopes, as is also one of the objectives in the DESIRE project. Howver the erosion risk is also high for the natural situation of intact forest which is less clear. Overgrazing is also a risk in these fragile ecosystems which is not taking place yet because of the low animal density. Forest fire risk is not so well indicated, the index does not sem to e affected by variables that are related to forest fire for unclear reasons.


More details ... general conclusions and results from other study sites
»Evaluating the Desertification Risk Assessment Tool with experimental results




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