At What Scales and Why Does Forest Structure Vary in Naturally Dynamic Boreal Forests? An Analysis of Forest Landscapes on Two Continents

Identifying the scales of variation in forest structures and the underlying processes are fundamental for understanding forest dynamics. Here, we studied these scale-dependencies in forest structure in naturally dynamic boreal forests on two continents. We identified the spatial scales at which forest structures varied, and analyzed how the scales of variation and the underlying drivers differed among the regions and at particular scales. We studied three 2kmx2km landscapes in northeastern Finland and two in eastern Canada. We estimated canopy cover in contiguous 0.1-ha cells from aerial photographs and used scale-derivative analysis to identify characteristic scales of variation in the canopy cover data. We analyzed the patterns of variation at these scales using Bayesian scale space analysis. We identified structural variation at three spatial scales in each landscape. Among landscapes, the largest scale of variation showed the greatest variability (20.1-321.4ha), related to topography, soil variability, and long-term disturbance history. Superimposed on this large-scale variation, forest structure varied at similar scales (1.3-2.8ha) in all landscapes. This variation correlated with recent disturbances, soil variability, and topographic position. We also detected intense variation at the smallest scale analyzed (0.1ha, grain of our data), partly driven by recent disturbances. The distinct scales of variation indicated hierarchical structure in the landscapes studied. Except for the large-scale variation, these scales were remarkably similar among the landscapes. This suggests that boreal forests may display characteristic scales of variation that occur somewhat independent of the tree species characteristics or the disturbance regime.Peer reviewe

The structure of boreal old-growth forests changes at multiple spatial scales over decades

Context: Changes in the structure of boreal old-growth forests are typically studied at a specific spatial scale. Consequently, little is known about forest development across different spatial scales. Objectives: We investigated how and at what spatial scales forest structure changed over several decades in three 4 km² boreal old-growth forests landscapes in northeastern Finland and two in Quebec, Canada. Methods: We used canopy cover values visually interpreted to 0.1-ha grid cells from aerial photographs taken at three time points between the years 1959 and 2011, and error distributions quantified for the interpretation. We identified the spatial scales at which canopy cover changed between the time points, and examined the credibility of changes at these scales using the error distributions in Bayesian inference. Results: Canopy cover changed at three to four spatial scales, the number of scales depending on the studied landscape and time interval. At large scales (15.4–321.7 ha), canopy cover increased in Finland during all time intervals. In Quebec, the direction of the large-scale change varied between the studied time intervals, owing to the occurrence of an insect outbreak and a consequent recovery. However, parts of these landscapes also showed canopy cover increase. Superimposed on the large-scale developments, canopy cover changed variably at smaller scales (1.3–2.8-ha and 0.1-ha). Conclusions: Our findings support the idea that the structure of boreal old-growth forests changes at discernible spatial scales. Instead of being driven by gap dynamics, the old-growth forests in the studied regions are currently reacting to large-scale drivers by an increase in canopy cover.Peer reviewe

Globally consistent climate sensitivity of natural disturbances across boreal and temperate forest ecosystems

Disturbance regimes are changing in forests across the world in response to global climate change. Despite the profound impacts of disturbances on ecosystem services and biodiversity, assessments of disturbances at the global scale remain scarce. Here, we analyzed natural disturbances in boreal and temperate forest ecosystems for the period 2001-2014, aiming to 1) quantify their within- and between-biome variation and 2) compare the climate sensitivity of disturbances across biomes. We studied 103 unmanaged forest landscapes with a total land area of 28.2 x 10(6) ha, distributed across five continents. A consistent and comprehensive quantification of disturbances was derived by combining satellite-based disturbance maps with local expert knowledge of disturbance agents. We used Gaussian finite mixture models to identify clusters of landscapes with similar disturbance activity as indicated by the percent forest area disturbed as well as the size, edge density and perimeter-area-ratio of disturbed patches. The climate sensitivity of disturbances was analyzed using Bayesian generalized linear mixed effect models and a globally consistent climate dataset. Within-biome variation in natural disturbances was high in both boreal and temperate biomes, and disturbance patterns did not vary systematically with latitude or biome. The emergent clusters of disturbance activity in the boreal zone were similar to those in the temperate zone, but boreal landscapes were more likely to experience high disturbance activity than their temperate counterparts. Across both biomes high disturbance activity was particularly associated with wildfire, and was consistently linked to years with warmer and drier than average conditions. Natural disturbances are a key driver of variability in boreal and temperate forest ecosystems, with high similarity in the disturbance patterns between both biomes. The universally high climate sensitivity of disturbances across boreal and temperate ecosystems indicates that future climate change could substantially increase disturbance activity.Peer reviewe

Twenty-Eight Years of Changes in Landscape Heterogeneity of Mixedwood Boreal Forest Under Management in Quebec, Canada

Changes in natural and anthropogenic disturbances in the mixedwood boreal forests of northwest Quebec have modified the landscape heterogeneity in terms of its composition and configuration. The aim of this study was to evaluate the heterogeneity (composition and configuration) of 78,000 km2 of mixedwood boreal forest landscape during recent decades (using Landsat imagery from 1985 to 2013) in areas affected by forest management. The classes Conifer, Mixed-Conifer, Mixed-Hardwood, and Hardwood were differentiated with an object-based classification (accuracy >80.2, Kappa coefficient >0.7). Also, 5 metrics (mean area, largest patch index, percentage the landscape of the core area, perimeter-area fractal dimension, and aggregation index) were calculated. This study showed that conifer-dominant cover dominates the mosaic and accounted for one third of the study area. Nevertheless, the conifer-dominant class showed the greatest decrease (reduction of 35% of its initial area at a rate of 1.7% per year). The metrics indicated that forest management in recent years produced a more heterogeneous landscape in 2013 unlike the landscape in 1985. The fire-influenced, old-growth conifer forests that previously dominated the landscape in northwestern Quebec were transformed by forestry practices into a more heterogeneous landscape. RÉSUMÉ Les régimes des perturbations naturelles et anthropiques dans les forêts boréales mixtes du nord-ouest du Québec ont modifié l'hétérogénéité du paysage en termes de composition et de configuration. L'objectif de cette étude était d'évaluer l'hétérogénéité (composition et configuration) d'un territoire de 78,000 Km2 de la forêt boréale mixte aménagée au cours des dernières décennies en utilisant des images Landsat de 1985 à 2013. Les classes de couvertures forestières Résineux, Résineux mélangés, Feuillus mélangés et Feuillus ont été différenciées à l'aide d'une méthode de classification basée sur l'identification d'objets (précision >80.2, coefficient Kappa >0.7). En outre, cinq paramètres (superficie moyenne, indice de la taille de la plus grande parcelle, pourcentage du paysage de l'aire centrale, dimension fractale entre périmètre et surface et indice d'agrégation) ont été calculés. Les résultats de cette étude ont montré que la classe Résineux, domine la mosaïque et représente un tiers de la zone d'étude. Nonobstant, cette même classe a enregistré la plus forte diminution au cours de la période d'évaluation avec une réduction de 35% de sa superficie initiale au taux de 1,7% par an. Les paramètres indiquent que l'aménagement forestier au cours des dernières années a produit un paysage plus hétérogène en 2013, contrairement au paysage en 1985. Ces résultats indiquent que les forêts anciennes résineuses et influencées par le feu qui dominaient auparavant le paysage dans le nord-ouest du Québec ont été transformées par les pratiques forestières en un paysage plus hétérogène

Early avian functional assemblages after fire, clearcutting, and post-fire salvage logging in North American forests

Increased demand for timber, the reduction in the available timber resources, and more frequent and severe forest fires under a changing climate have increased the use of salvage logging in North American forests despite concerns regarding impacts on biodiversity and long-term forest productivity. We aimed to complement previous approaches that used bird species richness or individual abundance in salvage-logged habitats to assess the sustainability of this practice. We looked for commonalities in the taxonomic, functional, and phylogenetic components of bird assemblages among these three post-disturbance habitats across a broad geographic range. We compiled six North American datasets selected from primary and grey literature that documented species composition of avian assemblages in habitats after recent fire, post-fire salvage logging, and traditional logging. Our results revealed contrasting patterns of bird trait assemblage among burned, post-fire salvage, and traditionally logged habitats. In salvage-logged habitats, taxonomic diversity, functional diversity, and functional and phylogenetic redundancy were significantly lower than in both burned and traditionally logged habitats. The frequency of insectivores was significantly lower after salvage logging than after both fire and traditional logging. These findings suggest that cumulative disturbances have a negative effect on early assembly of bird communities. The outcomes of this study encourage further assessments, at landscape level, of salvage logging intensity, burn size, and fire severity on bird functional structure to better plan for their conservation.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author