Abstract. The condition of forest ecosystems depends on the temporal and spatial pattern of management interventions and natural disturbances. Remnants of previous conditions persisting after disturbances, or ecosystem legacies, collectively comprise ecosystem memory. Ecosystem memory in turn contributes to resilience and possibilities of ecosystem reorganization following further disturbance. Understanding the role of disturbance and legacies is a prerequisite for maintaining resilience in the face of global change. Several legacy concepts discussed in the peer-reviewed literature, including disturbance, biological, soil, land-use, and silvicultural legacies, overlap in complex ways. Here, we review these established legacy concepts and propose that the new terms "material legacy" (individuals or matter, e.g., survivors, coarse woody debris, nutrients left after disturbance) and "information legacy" (adaptations to historical disturbance regimes) cut across these previous concepts and lead to a new classification of legacies. This includes six categories: material legacies with above-and belowground, and biotic and abiotic categories, and information legacies with above-and belowground categories. These six legacies are influenced by differential patterns of editing and conditioning by "legacy syndromes" that result from natural or human-manipulated disturbance regimes that can be arranged along a gradient of naturalness. This scheme is applied to a case study of hemiboreal forests in the Baltic States of Estonia, Latvia, and Lithuania, where natural disturbance, traditional clearcut silviculture, and afforestation of abandoned agricultural lands constitute the three main legacy syndromes. These legacy syndromes in turn influence forest response to management actions and constrain resilience, leading to a mosaic of natural, manipulated, and artificial (novel) ecosystems across the landscape, depending on how the legacies in each syndrome affect ecological memory.

In light of the difficulties in stand volume estimation of natural forests, we analyzed height–diameter relationships and derived a set of height estimation equations for volume estimation for naturally developing forest ecosystems, using the Järvselja old-growth and the Laeva commercial forest in Estonia as a case study. This contribution presents an approach to model individual tree height–diameter relationships for Scots pine, common aspen, silver and downy birch, Norway spruce, black alder, gray alder, linden species, European ash, Norway maple, deciduous species and coniferous species in multi-size and mixed-species naturally developing stands in Estonia. Single-tree-level data were collected in 2013. Two methods were used to obtain stand-level data: whole surface inventory and partial surface inventory. To model the height–diameter relationship in naturally developed mixed-species forest stands in order to predict single tree height based on observed diameter at breast height, we applied nonlinear mixed models where we applied the Chapman–Richards and Näslund models as fixed-effects and the influence of the species contribution at the sites as random effects. The fixed-effects followed a set of criteria: (1) height starts at h = 1.3; d = 0; (2) the applied functions are monotonically increasing with a clear inflection point and 3) the fixed-effect model has an asymptotic value) in a naturally developed mixed-species forest.

The study area is in the Järvselja Training and Experimental Forest Centre, Estonia. The conservation of Järvselja old-growth forest started in 1924 when the area was excluded from all management activities and left to natural development. The aim of this study is to analyse the methods for calculating single tree height, tree stem lateral surface area, tree volume and carbon content for standing live trees, standing dead trees and for downed deadwood in old-growth forests. The study used the data of 6205 live trees, 1119 snags, 270 standing dead trees and 2983 deadwood trunks from the measured area. The most abundant tree species in Järvselja old-growth forest were Norway spruce and linden. During the last hundred years, the number of dominating tree species has increased slightly. The standing volume of birch, common aspen and Scots pine have been declining while for linden and black alder it has been increasing. In the comparison of tree height curves, the best results were obtained with the Näslund function, however, the Chapman-Richards function with fitting showed slightly better results for two tree species.