Structural and Spatial Characteristics of Old-Growth Temperate Deciduous Forests at Their Northern Distribution Limit

Abstract

Relic old-growth forests are unique witnesses of long-term forest dynamics that can be used as reference conditions for ecosystem-based forest management. In temperate deciduous forests, catastrophic stand-replacing disturbances are rare, and stand dynamics are controlled by endogenous tree-by-tree replacement. Processes might be different at the northern distribution limit of temperate deciduous forests, because of differences in climate and disturbance regimes. We studied tree species composition, diameter, age, and spatial structures of 11 old-growth temperate deciduous stands across an age gradient. Stand characteristics differed from expectation, based on previous studies that were conducted in the central region of the range of temperate deciduous forests. Instead of increasing with age, tree species richness was higher in stands <120 years old because of the presence of relatively short-lived species such as Abies balsamea and Acer rubrum. All diameter distributions followed a two- or three-parameter Weibull model, instead of a rotated sigmoid. Some age structures showed recruitment pulses, contrary to the expectation of constant recruitment, and the spatial distribution of living trees was mostly random with regard to age and species at assessed distances (<14 m). In the context of ecosystem-based forest management, our results suggest that harvest levels should vary across harvesting blocks and selection silviculture should occasionally include larger, multiple-tree gaps in addition to single-tree gaps.