Structure and regeneration patterns in a virgin Picea abies forest in northern Sweden

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Abstract
A high‐altitude boreal Picea abies forest, with tree ages of up to 410 yr, was studied with respect to age structure, spatial regeneration patterns, and substrate. The results suggest that recruitment is primarily dependent on germination substrate but also negatively correlated with the density of the tree layer. 60 % of all spruces < 1.3 m high grew on substrates connected with tree‐fall; ca. 40 % were found on decomposing logs and stumps, covering only ca. 6 % of the forest floor. Individual logs remain important as a regeneration substrate for ca. 150 yr. Continuous presence of decomposing coarse wood is a condition for the maintenance of the population structure under the prevailing climatic conditions. Peaks in the age distribution (the 1870's and the 1940's ‐ 1950's) are probably climatically induced. The results challenge the previous assumptions that this kind of forest undergoes cyclic development. Long‐term structural stability with climatically induced minor variations may be an alternative model.