Global forest area is declining rapidly, along with degradation of the ecological condition of remaining forests. Hence it is necessary to adopt forest management approaches that can achieve a balance between (1) human management designs based on homogenization of forest structure to efficiently deliver economic values and (2) naturally emerging self-organized ecosystem dynamics that foster heterogeneity, biodiversity, resilience and adaptive capacity. Natural disturbance-based management is suggested to provide such an approach. It is grounded on the premise that disturbance is a key process maintaining diversity of ecosystem structures, species and functions, and adaptive and evolutionary potential, which functionally link to sustainability of ecosystem services supporting human well-being. We review the development, ecological and evolutionary foundations and applications of natural disturbance-based forest management. With emphasis on boreal forests, we compare this approach with two mainstream approaches to sustainable forest management, retention and continuous-cover forestry. Compared with these approaches, natural disturbance-based management provides a more comprehensive framework, which is compatible with current understanding of multiple-scale ecological processes and structures, which underlie biodiversity, resilience and adaptive potential of forest ecosystems. We conclude that natural disturbance-based management provides a comprehensive ecosystem-based framework for managing forests for human needs of commodity production and immaterial values, while maintaining forest health in the rapidly changing global environment.

1. Considering intraspecific trait variability (ITV) in ecological studies has improved our understanding of species persistence and coexistence. These advances are based on the growing number of leaf ITV studies over local gradients, but logistical constraints have prevented a solid examination of ITV in root traits or at scales reflecting species’ geographic ranges.
2. We compared the magnitude of ITV in above? and below?ground plant organs across three spatial scales (biophysical region, locality and plot). We focused on six understorey species (four herbs and two shrubs) that occur both in disturbed and undisturbed habitats across boreal and temperate Canadian forests. We aimed to document ITV structure over broad ecological and geographical scales by asking: (a) What is the breadth of ITV across species range?scale? (b) What proportion of ITV is captured at different spatial scales, particularly when local scale disturbances are considered? and (c) Is the variance structure consistent between analogous leaf and root traits, and between morphological and chemical traits?
3. Following standardized methods, we sampled 818 populations across 79 forest plots simultaneously, including disturbed and undisturbed stands, spanning four biophysical regions (~5,200 km). Traits measured included specific leaf area (SLA), specific root length (SRL) and leaf and root nutrient concentrations (N, P, K, Mg, Ca). We used variance decomposition techniques to characterize ITV structure across scales.
4. Our results show that an important proportion of ITV occurred at the local scale when sampling included contrasting environmental conditions resulting from local disturbance. A certain proportion of the variability in both leaf and root traits remained unaccounted for by the three sampling scales included in the design (36% on average), with the largest amount for SRL (54%). Substantial differences in magnitude of ITV were found among the six species, and between analogous traits, suggesting that trait distribution was influenced by species strategy and reflects the extent of understorey environment heterogeneity.
5. Even for species with broad geographical distributions, a large proportion of within?species trait variability can be captured by sampling locally across ecological gradients. This has practical implications for sampling design and trait selection for both local studies and continental?scale modelling.

The southern portions of the boreal region across Canada are dominated by boreal mixedwoods forests, which are characterized by varying canopy dominance of boreal broadleaf and conifer trees. This forest region encompasses a large east-to-west gradient of climate and disturbance regimes. Although the same major boreal tree species occur in all parts of the boreal mixedwood region, they vary greatly in relative abundance. This is a reflection of the interactions among the different abiotic and biotic components. As a result, there is considerable variation in post-disturbance stand development, producing a wide variety of mixedwood forest conditions existing as a mosaic in time and space. Post-disturbance dominance by broadleaf species followed by a transition to conifers is the “classic” pathway in all regions. However, there is wide variation in the transition rate and the species sequence across the gradient depending on factors such as moisture, abundance of each species, fire cycle, climate and secondary disturbances (mainly insect outbreaks). Future changes in climate and disturbance regime could influence the nature of stand dynamics of boreal mixedwoods and the prominence of different pathways among regions. Focussing on the commonality of processes in mixedwood stand development across the boreal is a promising way to address the management of this important forest ecosystem.

Les préoccupations environnementales croissantes en foresterie ont provoqué un intérêt pour l’aménagement mixte comme une stratégie possible dans un contexte d’aménagement forestier durable. Cette revue de littérature se concentre sur les effets des peuplements mixtes sur la biodiversité, incluant les plantes de sous-bois, la faune aviaire, la faune du sol, et les ectomycorrhizes (ECM). Elle examine la diversité et la composition spécifiques à l’échelle des peuplements mais focalise particulièrement sur l’échelle du paysage (diversité gamma) en recherchant la présence d’espèces indicatrices des peuplements mixtes. Les principales conclusions sont les suivantes : (i) L’existence de différentes espèces d’arbres dans la canopée est associée avec une plus grande diversité de microhabitats, permettant l’addition des espèces de plantes de sous-bois associées à chacune des espèces de la canopée. Il n’y a toutefois que peu d’indications quant à l’existence d’espèces de plantes de sous-bois associées exclusivement aux peuplements mixtes. (ii) Certaines espèces d’oiseaux exigent ou préfèrent la présence de différentes espèces d’arbres dans un paysage ou un peuplement. Les peuplements ou paysages forestiers mixtes sont donc critiques pour la conservation de telles espèces. (iii) Quelques études ont montré un effet positif des peuplements ou litières mélangés sur certains groupes d’organismes du sol, mais la forte variabilité de ces résultats rend toute conclusion hasardeuse. (iv) Certains taxa d’ECM sont associés à des hôtes multiples, et pourraient donc bénéficier de la disponibilité de plusieurs hôtes dans les peuplements mixtes. Plusieurs études ont confirmé la plus grande abondance de ces taxa à hôtes multiples dans les peuplements mixtes.

In eastern Canada, boreal forests develop structural diversity in association with time since stand replacing fire. In some regions, this is associated with significant changes in the bryophyte community (Sphagnum moss invasion) and paludification (thick waterlogged forest floor development). The bryophyte community responds to opening of the canopy, and increasing moisture by replacement of slow growing species by faster growing Sphagnum spp. (e.g. magellanicum, fallax) that are dependent on constant hydration. Within a forest management context, partial harvest systems have been proposed as a strategy to maintain structural diversity, which is currently not accomplished with low retention systems. However, it is unknown whether these interventions will effectively accelerate community succession. The questions addressed in this study were: (1) is the composition of Sphagnum colonies in partially cut stands more similar to old-growth communities than in control, and low retention cut stands, (2) what aspects of harvest disturbance drive these changes, and (3) is the growth rate of Sphagnum capillifolium (an early successional shade tolerant species) different in partial versus low retention harvest systems? After harvest, Sphagnum patch size was reduced by 19.8% and 11.7% after low retention and partial harvest, respectively. While trends were not constant across three separate partial cut trials, the proportion of Sphagnum magellanicum, Sphagnum fallax and Sphagnum fuscum increased compared to controls and low retention 1–2 years after harvest. Models of percent Sphagnum cover indicated machinery track cover, percent cover of vascular plants, and patch depth were positive factors, while the influence of open canopy varied among species. Despite the inclusion of individual disturbance variables, the summary variable ‘treatment’ was significant in all models. Growth of S. capillifolium in partial cuts was intermediate to growth rates in control and low-retention cuts. Growth was positively influenced by slash cover and, contrary to the patch level, negatively influenced by track cover. These results indicate that partial harvest does represent an intermediate level of disturbance, as direct and indirect harvest effects were reduced, as was Sphagnum death. Change in composition 1 and 2 years after harvest indicates that partial harvests may effectively shift the bryophyte community towards an older community type and may thus be used to create landscape diversity. Long term trends and entire community compositions need to be assessed before this can be stated definitively. However, as paludified stands are less productive, the capacity of these partially harvested sites to produce merchantable timber is questioned.© 2007 Elsevier B.V. All rights reserved.

The simultaneous influence from multiple edges on remnant forest patches (such as wildlife corridors, protection buffers, small unharvested remnants or corners of larger patches) in harvested forest landscapes could impair, or possibly enhance, their effectiveness. When multiple edges are in close proximity, there may be interactions of edge influence such that the observed response is greater or less than would result from the influence of either edge alone. We examined possible ways in which two nearby forest edges of similar or different types might interact in terms of their influence on forest structure. We present an ‘edge interaction’ model for three possible types of interaction of edge influence: (1) no interaction, edge influence is limited to the strongest influence from either edge, (2) positive interaction, observed edge influence is greater than from either edge alone; (3) negative interaction or resistance, the influence from both edges is less than from a single edge (e.g., an older edge is resistant to effects from a younger edge). Empirical data for forest structure at the edges of cutblocks (harvested areas) and water bodies were entered into the models to predict edge influence in narrow forest corridors assuming the null hypothesis of no interaction. Randomization tests were used to compare predictions to observed edge influence on recently-fallen logs and Populus spp. (P. tremuloides Michx. and P. balsamifera L.) sapling density in lakeshore buffers in boreal mixedwood forest as well as on canopy cover and log, tree and snag abundance in riparian buffers and forested corridors separating cutblocks in Picea mariana (Mill.) BSP. forest. In lakeshore buffers, there was evidence of both positive and negative interaction at different locations within the buffer or at different times since buffer creation for both the abundance of logs and Populus sapling density. Trends suggested positive interaction for canopy cover and live tree density in riparian buffers and cutblock separators, and for snag density near the cut edges of riparian buffers. Testing hypotheses arising from our model of interaction of edge influence could lead to a clearer understanding of edge influence in fragmented landscapes.