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Wageningen University (2009)

Soil temperatures under a catchment scale experimental fire

Drooger, S.

Titre : Soil temperatures under a catchment scale experimental fire

Auteur : Drooger, S.

Université de soutenance : Wageningen University

Grade : Master of Science (MS) 2009

Within the Desire project a Portuguese catchment area of 10 hectares was burned by experimental fire, to see the impact of fire on soil temperature. Soil temperature beneath the fire was measured at 57 sites with thermocouples at soil surface, 1cm and 3cm depth. This study is among the first to study soil temperatures during a catchment scale fire. The fire was started with low intensity, but half way the fire fronts were combined into a climax fire with high intensity. Maximum soil temperature and derived variables : delay before maximum temperature, heating velocity, heat index above 30°C, if temperature exceeded threshold values and delay before heating propagation were interpolated and mapped over the whole catchment. By means of regression analysis relations between soil temperatures and factors determined before the fire were sought. Average soil temperatures were low : 104°C at soil surface, 27°C at 1cm and 13°C at 3cm depth, while average flame temperature was 735°C. High intensity fire did not increase soil temperatures more than low intensity fire. At soil surface temperature was affected by the fire, but at 1cm depth it was no higher than as can be expected on a hot day, and at 3cm depth fire effects on soil heating were even smaller. Although the air was very dry, vegetation at the north facing slope was still wet and was burned to lesser extent than vegetation at the south facing slope. Vegetation and litter on the north facing slope were therefore not completely consumed by the fire, and restricted soil heating. Soil temperatures had some weak correlations with soil properties, vegetation characteristics and topographical factors. Soil moisture content, vegetation height, vegetation cover, rock cover inclination of slope, aspect of slope and organic matter content were significant regressors in maximum temperature.

Mots clés : watersheds / fire / fire effects / fires / controlled burning / soil physical properties / soil temperature / portugal


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