REGENERATION PULSES AND CLIMATE VEGETATION INTERACTIONS IN NONPYROGENIC BOREAL SCOTS PINE STANDS

1 Age and diameter distributions of nonpyrogenic, virgin Scots pine (P inus sylvestris) populations were studied at six different sites of th e Empetrum-Vaccinium type along a latitudinal gradient (65 degrees 54' -68 degrees 15'N) in northern Sweden. 1910 trees, including saplings a nd seedlings, were aged at their root collars in order to reconstruct regeneration patterns. 2 All populations had multimodal age structures . Obvious regeneration pulses occurred in the 1770s-80s and 1950s-70s. The three southernmost stands exhibited an additional regeneration pu lse in the 1870s-80s. A regeneration cycle of about 100 years in the s outh and 200 years in the north were thus clearly expressed. Correlati on with temperature changes over the past 300 years showed that recrui tment peaks of Scots pine lagged 20-30 years behind the warm climate p eriods and fell to zero in the intervening cold periods. 3 A much smal ler number of experimentally planted pine and spruce seeds established and survived in vegetation dominated by Empetrum hermaphroditum than in that dominated by Cladina spp. After two growing seasons, fresh wei ghts of pine seedlings were also much lower in E. hermaphroditum veget ation than in Cladina spp. Spruce established less frequently than pin e in both vegetation types. Naturally established pine seedlings were found almost exclusively in vegetation dominated by Cladina spp. 4 The wave-like regeneration pattern of pine may therefore result from succ essful establishment in periods with good seed production on ground do minated by Vaccinium spp. and Cladina spp. This vegetation type is fav oured by warm dry conditions but its establishment possibly lagged beh ind climate change. The extreme amplitude between regeneration failure s and successes found over the period studied may be caused by the spe cific complex of vegetation responses to climate variability found in this forest type. 5 The results have implications for predicting the e ffect of climatic warming.