Abstract Tree recruitment is affected by numerous biotic and abiotic factors, including climate. However, the relative importance of climate variables in empirical models of tree recruitment remains to be evaluated. We fitted models of tree recruitment to 26 species in the province of Quebec, Canada. For a better understanding of the recruitment process, we used a two-part model to distinguish recruitment occurrence from abundance. The relative importance of the different variables was assessed using Akaike weights. Our main hypothesis was that climate is one of the major drivers of tree recruitment. Our results showed that growing degree-days counted among the major drivers of recruitment occurrence but not of recruitment abundance. Stand variables, such as the presence and abundance of adult trees of the species, and broadleaved and coniferous basal areas were found to be relatively more important than all the climate variables for both recruitment occurrence and abundance. Species occupancy within a 10-km radius also had a significant effect on recruitment occurrence for two-thirds of the species, but it was less important than growing degree-days and other stand variables. Climate change is expected to improve the suitability of habitats located at the northern edge of species distributions. However, our model predictions point to a low probability of colonization in newly suitable habitats in the short term.
Background tree mortality can be defined as the death of trees that naturally occurs as stands develop, in the absence of major or sudden stand disturbances. The phenomenon is often linked to ontogeny and competition and generally affects individual trees, unlike catastrophic mortality, which affects most trees in the stand. To forecast stand characteristics and to estimate how stand development could change in response to changing climate, it is necessary to quantify background mortality and to identify the most important factors involved. Using data from 10,045 permanent sample plots, we modeled background tree mortality for the 9 most abundant tree species of the eastern Canadian boreal forest. We used explanatory variables related to stand and tree ontogeny, competition, site characteristics and climate to calibrate the models. We found that an increase in age, competition and the presence of partial cut increased the mortality risk. However, the effect of DBH and site-related variables varied among species. We also found that higher temperatures, less precipitation, and higher aridity index values increased background tree mortality. According to mortality simulations under different future climate scenarios, background tree mortality could increase in the next decades for 6 of the 9 tree species studied.
Forests provide ecosystem services such as timber production and carbon sequestration. However, forests are sensitive to climate change, and financial and amenity losses are expected for forest owners and society, respectively. The forests in the Grand-Est region, France, are dominated by European beech, for which a decline is anticipated due to repeated drought events induced by climate change. These forest ecosystems are also threatened by windstorm events. Beech forests need to adapt and diversification can decrease drought and windstorm risks. In this context, the objective of the paper was to compare different forest adaptation strategies from an economic perspective with the objective of reducing drought- and windstorm-induced risks of dieback. For this purpose, we studied two types of diversification that we analysed separately and jointly: Mixing beech with oak and diversifying stand structure (i.e. from an even-aged to an uneven-aged forest). We also considered two types of loss (financial, and in terms of carbon sequestration) under different recurrences of drought and windstorm risks. We combined a forest growth simulator with a forest economic approach through the computation of land expectation value (LEV). Maximizing the LEV criterion made it possible to identify the best adaptation strategies in economic terms. The results show that diversification increases timber production and LEV, but reduces carbon storage. The two risks as well as the adaptation strategies show some synergies. Finally, trade-offs between the financial balance and the carbon balance (i.e. adaptation vs. mitigation) are possible.
Au cours d’une table-ronde, quatre professionnels ont échangé sur leurs pratiques en matière d’éducation, prévention et promotion de la santé à destination des jeunes. Après avoir décrit les problématiques vécues par les jeunes et leurs réactions quant aux actions menées, ils ont souligné l’importance du partenariat pour que la santé devienne le dénominateur commun de la pluralité des interventions des acteurs jeunesse tout en restant dans une optique de complémentarité des réponses apportées. Parole à Mathieu Fortin, coordonnateur santé à la Ville de Villeurbanne ; Florence Karsenti, assistante sociale et référente santé à la mission locale Rhône Sud-Est ; Laurent Moulin, référent régional prévention et promotion de la santé à la Mutualité française Rhône-Alpes ; et Marie Sandoz, coordinatrice santé à l’Urhaj Rhône-Alpes (Union régionale pour l’habitat des jeunes).
In this work, several models have been co upled in order to represent the who le forest -to-energy production chain: the growth phase, the primary transformation, and the ultimate conversion to heat and/or electricity. Combined with literature data for wood transportation, they gave a complete balance of emissions to compare with fossil -based alternatives. An economic analysis completes the work. The results show that wood-based scenarios do perform better than their fossil counterparts, but also that the primary transformation and transportation items can greatly diminish this advantage. Further work will focus on determining the best metric to assess the climate change impact of forestry scenarios based on the timing of carbo dioxide emissions as well as geophysical effects such as albedo and evapotranspiration.
Abstract Forests play a key role in the carbon cycle as they store huge quantities of organic carbon, most of which is stored in soils, with a smaller part being held in vegetation. While the carbon storage capacity of forests is influenced by forestry, the long-term impacts of forest managers’ decisions on soil organic carbon (SOC) remain unclear. Using a meta-analysis approach, we showed that conventional biomass harvests preserved the SOC of forests, unlike intensive harvests where logging residues were harvested to produce fuelwood. Conventional harvests caused a decrease in carbon storage in the forest floor, but when the whole soil profile was taken into account, we found that this loss in the forest floor was compensated by an accumulation of SOC in deeper soil layers. Conversely, we found that intensive harvests led to SOC losses in all layers of forest soils. We assessed the potential impact of intensive harvests on the carbon budget, focusing on managed European forests. Estimated carbon losses from forest soils suggested that intensive biomass harvests could constitute an important source of carbon transfer from forests to the atmosphere (142–497 Tg-C), partly neutralizing the role of a carbon sink played by forest soils.
Abstract The vertical distribution of foliage biomass is important because it is associated with photosynthesis and is closely related to some wood quality attributes such as branch diameter and sapwood content. In this article we propose a model to predict foliage biomass distribution within the crown for jack pine trees in Eastern Canada. This model has two parts. The first one distinguishes the proportion of nodal (formed at the end of each yearly shoot) and internodal (formed during the growing season) foliage biomass. The second part of the model predicts the distribution of the biomass depending on the type of foliage (nodal or internodal). This second part is based on a two-parameter beta cumulative distribution function (cdf). The parameterization of this cdf was performed using a mixed-effects nonlinear regression. The proportion of foliage biomass found in the nodal whorls is proportional to dbh and age and inversely proportional to total height. The distribution of the foliage biomass in the nodal whorls is dependent only on tree-level variables whereas the internodal foliage biomass is influenced by both tree- and stand-level variables. The internodal foliage biomass maximum is closer to the crown base than that of nodal foliage biomass. Decomposing the distribution into whorl types leads to a better description of crown characteristics.
In order to accommodate foreseen climate change in European forests, the following are recommended: (i) to increase the number of tree species and the structural diversity; (ii) to replace unsuitable species by native broadleaved tree species, and (iii) to apply close-to-nature silviculture. The state forest department of Baden-Württemberg (BW) currently follows the concept of Forest Development Types (FDTs). However, future climatic conditions will have an impact on these types of forest as well as timber harvesting operations. This Geographic Information System (GIS)-based analysis identified appropriate locations for main FDTs and timber harvesting and extraction methods through the use of species suitability maps, topography, and soil sensitivity data. Based on our findings, the most common FDT in the state forest of BW is expected to be coniferous-beech mixed forests with 29.0% of the total forest area, followed by beech-coniferous (20.5%) and beech-broadleaved (15.4%) mixed forests. Where access for fully mechanized systems is not possible, the main harvesting and extraction methods would be motor manual felling and cable yarding (29.1%). High proportions of large dimensioned trees will require timber extraction using forestry tractors, and these will need to be operated from tractor roads on sensitive soils (23.0%), and from skid trails on insensitive soils (18.4%).
A non-linear model is proposed to describe the growth evolution in mixedwood stands composed of balsam fir (Abies balsamea (L.) Mill.) and red spruce (Picea rubens Sarg.) following a diameter-limit cutting. All softwood stems having a stump diameter equal to or greater than 18 cm were removed during this cutting. The model approach considers the entire stand where the volumes of the two main species, balsam fir and red spruce, were individually modeled. The model was also calibrated for two forest sites identified using Heimburger (1941) forest sites plant index: Cornus and Oxalis-Cornus. On average, the rotation periods suggested by the model range from 25 to 30 years with yields of 4.0 m 3 ha –1 ear –1 of merchantable volume. In the Cornus forest site, the diameter-limit cutting enables maximization of the yield while maintaining red spruce dominance. In the Oxalis-Cornus forest site, the volume removal has been too important and residual stands were under optimal growth conditions. Furthermore, the cutting has favoured balsam fir instead of red spruce. A reduction of volume removal and an integral protection of red spruce stems having a diameter less than 35 cm at breast height would enable maximization of the yield and maintain the species proportions. Under the Quebec forest context, the selection method would constitute an adequate operation in stand management of forest sites corresponding to Oxalis-Cornus, while cutting with retention of small merchantable stems would be applicable to stands corresponding to the Cornus site. Key words: red spruce, balsam fir, mixedwood stands, productivity, modelling, partial cutting, yield, composition, silviculture
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