Are trees on islands more exposed to lightning-strokes than trees at mainland? :

Abstract: All vegetation is subject to different kinds of disturbances. Before human intervention, lightning strikes were the principal natural cause of ignition in conifer dominated European forests (Gromtsev 2002; Granström 2001). Spatial variation in strokes can provide valuable information about fire regimes in the past, but is not very well investigated. It has been claimed that ignition occurs more often on islands in lakes, than in corresponding habitat in mainland. The isolation and/or elevation would thus contribute to the high susceptibility to lightning strikes on islands. There may also be a difference in the attraction of lightning by different tree species. In this study, approximately 200 ha forest were investigated for lightning scars in trees on islands in the lake Allgunnen, and on adjacent mainland. To discover potential differences in scars distribution between the areas, the scars were classified into three categories according to the degree of certainty of lightning being the cause of the scar, “confident”, “likely” and “uncertain lightning scars”. More scars were found on islands (37.9/100ha) than in mainland (25.6/100ha). Scots pine (Pinus sylvestris) was incomparably the most frequently damaged species accordingly to tree species distribution in the investigated areas, being struck relatively more than other species. The findings suggest that there may be a difference in lightning strikes in trees on islands in lake Allgunnen compared to trees in corresponding mainland areas. And there may, as well, exist preferences in lightning-scars distribution on different tree species.