Abstract In forested ecosystems, shrubs must succeed in persisting in low-light environments, while simultaneously having the ability to rapidly expand and occupy newly created canopy openings, yet little is known about the traits that make this possible. We hypothesize that shrub species that are abundant in the understory exhibit a specific set of functional traits that define their ability to persist during unfavorable periods and to rapidly exploit newly created habitats. We tested this by comparing field-measured functional traits such as biomass allocation, leaf display, crown morphology, and leaf traits, across individual size classes and two gap-forest environments of five shrub species. We observed significant differences in traits between species, size classes, and gap-forest environments. These differences were primarily related to biomass allocation traits, followed by leaf display, crown morphology, and leaf traits. Abundant shrubs like mountain maple (Acer spicatum) and hazelnut (Corylus cornuta) invested significantly more biomass in roots, had a larger total leaf area, and displayed leaves in a more efficient manner to intercept light. The high investment in root biomass can be interpreted as shrubs exploiting the persistence and colonization strategy through resprouting. Permanent sub-canopy status likely explains the importance of efficient leaf display, wherein abundant shrubs had a large leaf area with minimal support structures.

Questions

We investigated whether the gap disturbance rate (percentage area disturbed by canopy gaps per year) differed at the northern range limit of sugar maple (Acer saccharum)–yellow birch (Betula alleghaniensis) forests compared to broad-leaf temperate deciduous forests located more to the south. As an ancillary question, we assessed the relationship between species composition and gap disturbance rate at the stand scale.

Location

Late successional sugar maple–yellow birch forests at their northern range limit in western Quebec, Canada.

Methods

To reconstruct past gap disturbances, we identified growth releases using the boundary line method applied to tree-ring chronologies obtained from 0.25-ha plots sampled within 11 late successional forest stands. We reconstructed past canopy gaps using release events, calculated historical gap disturbance rates and used redundancy analysis to evaluate the relationship between gap disturbance rate and species composition at the stand scale.

Results

The mean gap disturbance rate across the 11 late successional stands was 0.96 ± 0.51%·yr−1. Mean gap size was 39 ± 44 m2 and almost 85% of the gaps were <50 m2. Stands with smaller gaps and lower gap disturbance rates had high importance values for balsam fir (Abies balsamea) and/or yellow birch.

Conclusions

The gap disturbance rate at the northern limit of sugar maple–yellow birch forest was similar to that reported in broad-leaf temperate deciduous forests located ca. 575–1300 km to the south. However, gaps were more numerous and smaller, which could be related to latitudinal differences in allometric traits of the dominant tree species and climate.

Les impacts des changements climatiques (CCs) sur la forêt sont déjà observés et iront en s'amplifiant dans le futur. Dans ce contexte, il importe de comprendre comment les communautés et l'industrie forestière seront affectées. Des professionnels du secteur forestier québécois ont été consultés lors d'un atelier afin de recueillir leurs perceptions des impacts potentiels des CCs et des possibles mesures d'adaptation. Les préoccupations touchaient les écosystèmes naturels, ainsi que les collectivités et l'industrie forestière. Les impacts identifiés incluaient l'augmentation des évènements météorologiques extrêmes et des perturbations naturelles, une diminution quantitative et qualitative du bois, ainsi que de plus grandes difficultés d'accès aux territoires et des coûts additionnels pour les opérations. Les mesures d'adaptation pourraient comprendre de nouvelles règlementations, une meilleure sensibilisation aux enjeux, et des ajustements locaux et régionaux dans la gestion et les opérations. Les barrières à l'adaptation identifiées incluaient une faible compréhension des enjeux au niveau des intervenants du milieu forestier, ainsi qu'un manque de soutien scientifique, de transfert des connaissances, et de leadership à l’échelle régionale. Cette synthèse aidera à orienter les besoins en matière de planification et de gestion et à identifier des solutions pour augmenter la capacité d'adaptation du secteur forestier.

The opening and closure of “gaps” in forest canopies plays an important role in the structure, turnover, and overall ecological processes of natural forests. Gap characterization was until recently mostly based on field studies and relied on sampling approaches. ALS (Airborne Laser Scanning) has now revolutionized this field of scientific enquiry by giving researchers the capacity to detect and measure gaps rapidly over large areas. We first provide a brief scientific background on gaps and then succinctly review field and other conventional remote sensing methods to characterize them. We then turn our attention to the principles of ALS-based gap detection and review different methods of automated gap delineation and measurement. We explain how gap types can be automatically classified, and how multitemporal ALS can be used to not only monitor gap dynamics, but also to reveal the complex role of gaps in influencing tree growth within and around them.

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.

L'intérêt du secteur de la recherche et développement pour les connaissances traditionnelles est considérable. La contribution des savoirs traditionnels à la conservation et à l'aménagement est de plus en plus reconnue et des expériences terrain en ce sens sont en cours dans plusieurs pays. Le niveau de dégradation des écosystèmes justifie le besoin d'interventions de restauration. Il est de plus en plus reconnu que l'intégration des connaissances scientifiques et traditionnelles est nécessaire au succès des efforts de restauration. Cette synthèse évalue les contributions actuelles et potentielles des savoirs traditionnels à la restauration écologique. Malgré qu'un nombre croissant d'articles soient publiés à propos des connaissances traditionnelles, peu concernent la contribution à la restauration écologique. Les principales contributions des connaissances traditionnelles à la restauration écologique sont l'identification d'écosystèmes de référence, en particulier lorsque les informations historiques ne sont pas disponibles; la sélection d'espèces pour les plantations; la sélection de sites pour la restauration; la connaissance de l'historique local des pratiques d'aménagement; la gestion des espèces envahissantes; et le suivi post-restauration. Les connaissances traditionnelles et scientifiques sont complémentaires et devraient être utilisées conjointement dans les projets de restauration écologique. L'inclusion des connaissances traditionnelles peut contribuer à construire un partenariat solide pour le succès de mise en oeuvre de projets de restauration et pour en augmenter l'acceptabilité sociale, la faisabilité économique et la viabilité écologique.