Using forest stand reconstructions to assess the role of structural continuity for late-successional species

Abstract

Historical reconstructions of past forest dynamics and stand structures have been used to establish reference conditions for managing present forest ecosystems. In this study we (1) developed and combined a suite of stand reconstruction techniques to describe past stand characteristics, and (2) applied these stand histories to evaluate the relationship between wood-decay fungi and forest continuity. Ten previous selectively logged stands of Norway spruce ( Picea abies L. Karst.), in the middle boreal zone of southeastern Norway, were studied. We reconstructed stand structures during the 20th century using tree-ring series, growth patterns, age structures, and decay classification and datings of stumps and logs. All stands were selectively logged between 1890 and 1965, with a mean logging interval of 25 years. Harvested volumes (1900–1965) constituted 25–99% of present standing volumes and present volumes were 2.6–21 (median 4) times higher than the lowest estimated historic volumes. Dead wood was categorized into eight decay classes, where one is recently fallen, and eight is almost completely decayed. Six fungus species, assumed to indicate dead-wood continuity, were found on logs in decay classes 2–4, all of which were estimated to be <30 years old. Logs in decay classes 1–4 constituted 85% of logs ≥20 cm. Expectedly, fungus abundance increased linearly with increasing number of available logs, but we failed to find a positive correlation between fungi abundance and number of old logs present (decay classes 5–8), when the effect of younger logs (2–4) was accounted for. This finding, together with the stand histories, does not lend support to the hypothesis that a continuous supply of dead wood, at the scale of forest stands, is crucial for the occurrence of the surveyed wood-decay fungi. We propose forest stand reconstructions to hold promise as a tool to assess the role of structural continuity for the occurrence of late-successional and old-growth species.