The protective role of bark against fire damage: a comparative study on selected introduced and indigenous tree species in the Western Cape,South Africa

The objective of this study was to compare the protective role of bark against fire for three selected indigenous and five exotic species in the Western Cape, South Africa. Bark thickness, compass direction, stem diameter at breast height, bark moisture content and relative height of the sample in the stem were tested for their effect on heat insulation capacity of bark. Trees were felled and heating experiments were conducted at 400 ºC on fresh billets with intact bark. Time to heat the cambium to lethal 60 ºC was determined. Statistical analysis based on correlation, multi-model inference and multiple regression revealed no significant influence of compass direction and diameter at breast height. Heat resistance was mainly determined by bark thickness, to a lesser degree by moisture content. In several species relative height at the stem modulated the bark thickness effect. Higher up the stem bark of the same thickness offered less protection against heat. Significant species-specific differences in heat resistance were apparent in the results, which could not be explained by bark thickness thus indicating further need for research in scrutinising these factors, which might help to explain the relative higher fire tolerance of certain species compared to others.