Moisture content of fine forest fuels in the Central Portugal ( Lousã) for the Period 1996–2004

Abstract

The moisture content of forest fuels is very important in terms of forest fire research given its implication in many aspects of fire risk, fire spread and fire ecology. In the present research program, living and dead tree foliage from Pinus pinaster and Eucalyptus globulus and living shrub foliage and extremities from Calluna vulgaris and Chamaespartium tridentatum (very common in the forests of Central Portugal) moisture content were measured by field sampling throughout the year from 1986 to present date. Samples were collected daily at Lousa (Central Portugal) during the Summer months and once a week during the rest of the year. In this paper the available values for the period 1996-2004, were systematized and analysed. In this program, moisture content was determined by oven-drying the fuel samples for 24 hours at 105oC. This methodology was compared with that of using an electronic balance that controls automatically the sample heating and the overall drying process. Seasonal moisture content patterns were analysed, as well as the relations between the moisture content values for the different studied species and the rainfall measured in the meteorological station from the Water Institute, located in Lousa. The obtained empirical relations show good results for dead tree species. During the period of 1996-1999 samples were collected at three sites located in the same region: Lousa, Silvares (Ponto Intermedio) and Olho Marinho. The relations between the moisture content values for the different species measured in these sampling sites were analysed. These relations enable the assessment of spatial moisture content patterns. The obtained empirical relations show good results for dead tree species and live shrub species. The relations between the moisture content values with fire occurrence for the different studied species were also analysed. These relations were systematized considering alternatively all data for the period 1996-2004, considering only the data corresponding the period of AprilSeptember, the period of October-March and considering only the data corresponding to moisture content values for dead tree species below 20%. The obtained empirical relations show good results for dead tree species and live shrub species. Dead tree species moisture content evolution after a summer precipitation episode was studied with the purpose of establishing a safe time period regarding the occurrence of forest fires.