SEED REGENERATION OF SCOTS PINE IN BOREAL FOREST STANDS DOMINATED BY LICHEN AND FEATHER MOSS

Six old-growth, late postfire Scots pine (Pinus sylvestris L.) dominat ed forest stands of the Vaccinium-Cladina type were selected along a l atitudinal gradient in northern Sweden. In two of the stands, Scots pi ne seedlings that had naturally regenerated during the last 40 years w ere surveyed in relation to field- and bottom-layer vegetation. The mo st abundant forest floor species, viz. Cladina spp., occupied 41% of t he ground cover and dominated the microhabitat of Scots pine seedlings less than or equal to 10 years old. The second most common species, P leurozium schreberi (Bird.) Mitt., which occupied 10 and 20% of the gr ound cover at the two sites, was, in contrast, only found to cover les s than 3% of the microhabitat of the seedlings less than or equal to 1 0 years old. With increasing age of seedlings (>10 years), however, th e cover of Cladina spp. significantly decreased and the cover of P. sc hreberi and various ericaceous species slightly increased. Thus Scots pine seedlings initially establish in lichen-dominated vegetation but as they develop P. schreberi and ericaceous species gradually become m ore abundant in the ground vegetation. The relationships between natur al establishment patterns and microhabitat were further empirically te sted by sowing seeds of Scots pine in patches of Cladina spp. and patc hes of P. schreberi. Seeding was performed in six sites during 3 conse cutive years. A significant higher number of established Scots pine se edlings were found in Cladina spp. vegetation than in P. schreberi dom inated vegetation, and Scots pine seedlings in P. schreberi experience d a significantly higher mortality. Laboratory studies indicated a neg ative chemical influence by P. schreberi on Scots pine seed germinatio n but not on radicle growth of pregerminated seeds. The negative influ ence of P. schreberi on Scots pine seed germination and seedling survi val in the field experiments is interpreted as an effect of moisture f actors, chemical interference, and barriers of nutrient availability. Age structures of naturally established Scots pine showed evidence of continuous regeneration over the last 40 years. The study emphasizes t he importance of biotically mediated regeneration patterns in explaini ng spatial stand structure and temporal dynamics in northern boreal Sc ots pine forest ecosystems during prolonged absence of fire. Tree rege neration tends not to be associated with mesoscale characteristics suc h as gaps and tip-up mounds, but rather with microhabitat conditions. The results have implications for predicting the effect of climatic wa rming.