Regeneration microsites of Picea abies seedlings in a windthrow area of a boreal old-growth forest in southern Finland

Microsite characteristics of established Picea abies seedlings were studied in a windthrow area of a Picea-dominated old-growth forest in the southern boreal zone of Finland. The seedling (height 3-30 cm) density, most of which was Picea (87%, ca. 31000 ha(-1)), was high (ca. 36 000 ha(-1)). Seedlings of Betula pubescens (ca. 2000 ha(-1)) and Sorbus aucuparia (ca. 2100 ha(-1)) were also abundant. The distribution of Picea seedlings across microsite types was significantly nonrandom. Picea seedlings were found in microsites created by windthrow disturbance, particularly advanced-decay wood, and uprooting pits and mounds. Sixty-three percent of the Picea seedlings occurred in these microsites, although they only covered ca. 28% of the study area. As a result of this pattern, Picea seedlings were aggregated in space and the majority of seedlings grew on microsites located above average local ground level. These results demonstrate the importance of disturbed microsites for the natural regeneration of Picea after windthrow disturbance. In managed forests, when naturally regenerating Picea on fertile sites, effort should be taken to create regeneration microsites similar to those created by natural disturbances, i.e. uprooting niches and decaying logs. These microsites are also important for the maintenance of biodiversity in managed forests.