In August 2003 after a very dry summer, the region of Leuk (Kt. Valais) was the center of the largest forest fire in Switzerland for the last 30 years. 310 ha, 20% of which on protected forest, were burned along an altitudinal gradient of 800 to 2100 m a.s.l.. This range of altitude is reflected on a stratified forest regarding forest composition. Forest changes gradually along the altitudinal gradient from an oak forest at the lowest altitude to pine, spruce and larch forest at the highest altitude.
The objective of this study is to evaluate the fire-effect on the forest fire border. The focus lies on post-fire tree delayed mortality on residuals and on trees outside the burned area, in order to estimate the real perimeter of the damaged area on subsequent years and its relations to other external factors.
Several variables contribute to different responses from trees towards fire and its secondary effects. In this study, special attention is paid to tree species, tree height, tree location and altitude in relation to the increase of area affected by fire.
Colour infrared images (CIR) at a scale of 1:15'000 and 1:5'000 are used for digital stereo interpretation. The time series consists of pre-fire images from 1999, shortly after the fire 2003, 2005 and 2006.
The results indicate that P .abies was the species that reacted less well to post fire. P. sylvestris is the species with the most stable vitality. L. decidua and Q. pubescens are the species with higher values of regeneration. The same tendency was found for younger trees (exception of P. sylvestris), green island and for low and high altitudes. Q. pubescens revealed an ability to completely resprout from a totally scorched crown in two years. The differences in the survival of species along the altitudinal gradient are delineating a different forest mosaic for the area affected by fire and may lead to a different forest composition in future decades.
This study reveals particular importance to the forest fire impact assessment as well as for forest management studies and post-fire management activities.