The study is the first of a larger project concerning fire ecology in the Finnish boreal forests. Ulvinsalo strict nature reserve (63E 55' N 30E 24' E, area 2,500 hectares),where modern forestry has never been practised. represents in this project an area where forest fires have been uncommon because of its mosaic of mineral and peat soils and site types (Fig. 2, Table 1). The forest stands are mostly Norway spruce (Picea abies) dominated with Scots pine (Pinus silvestris) often as the oldest trees of a stand. Forest fires have been aged by counting annual rings from cambium to the fire scar in pines. Wood samples were got by boring wood cylinders. It was surveyed 73 stands covering 1207.3 hectares or over 80 per cent of stands on mineral soil (Table 1, Fig. 2). 50 per cent of the areas surveyed was burned at least once during the life time of the present old pine trees. 48 different forest firs were found. The first has been in 1712 and the last in 1969. In the stands where fire scars were found the average time elapse between fires was about 82 ± 43 years, range 18-219 years. (Fig. 1 and Table 4.). It is assumed that the stands where no fire scars were found, have, however, regenerated after fires but no fires have been there since then. In these cases the time elapse between forest fires was 191 ± 59 years (Fig. 1 and Table 4). In all stands surveyed, the average time elapse between fires has 120 years and range 18-372 years (Table 4). In the latter part of the 19th century 21 forest fires were dated, in other half centuries 4-9 (Table 2). The increased human activity in the late 1800*s may be seen in. this fire peak.. The mean area burned at a time has been at most 24 hectares. The fire rotation (according to Heinselman, 1973) of the area is 280 years. The spruce is almost the only tree species, which can regenerate in present situations (Table 60).