Mart Jan Schelhaas

The influences of forest stand management on biotic and abiotic risks of damage

Abstract• This article synthesizes and reviews the available information on the effects of forestry practices on the occurrence of biotic and abiotic hazards, as well as on stand susceptibility to these damaging agents, concentrating on mammal herbivores, pest insects, pathogenic fungi, wind and fire.• The management operations examined are site selection, site preparation, stand composition, regeneration method, cleaning and weed control, thinning and pruning, and harvesting. For each of these operations we have examined how they influence the occurrence of biotic and abiotic damaging agents, the susceptibility of European forests, and describe the ecological processes that may explain these influences.• Overall, we find that the silvicultural operations that have the largest influence on both biotic and abiotic risks to European forest stands are closely related to species composition and the structure of the overstorey. Four main processes that drive the causal relationships between stand management and susceptibility have been identified: effect on local microclimate, provision of fuel and resources to biotic and abiotic hazards, enhancement of biological control by natural enemies and changes in individual tree physiology and development.• The review demonstrates an opportunity to develop silvicultural methods that achieve forest management objectives at the same time as minimising biotic and abiotic risks.Résumé• Cette revue bibliographique s’intéresse aux effets de la sylviculture sur la sensibilité des peuplements forestiers aux principaux agents de dégâts biotiques et abiotiques que sont les mammifères herbivores, les insectes ravageurs, les champignons pathogènes, le feu et les vents forts.• Les pratiques forestières analysées sont la sélection et la préparation des sites de reboisement, la définition de la composition en essences et le choix du matériel génétique, les méthodes de régénération et d’entretien, les modalités d’éclaircie et d’élagage, le mode de récolte finale. L’influence de chacune de ces opérations sur l’occurrence des agents de dégâts biotiques et abiotiques et sur la sensibilité des peuplements est examinée ainsi que les processus écologiques sous-jacents.• Les opérations sylvicoles qui se révèlent les plus déterminantes pour la sensibilité des forêts en Europe sont celles qui affectent la composition et la structure de la strate arborée. Quatre principaux processus écologiques semblent expliquer la relation entre sylviculture et sensibilité des peuplements : la modification du micro-climat, l’apport de ressources ou de combustible aux agents de dégâts, l’amélioration du contrôle biologique par les ennemis naturels et l’altération de la physiologie et du développement des arbres.• Cette revue permet donc d’envisager le développement de méthodes de gestion des peuplements forestiers qui permettent d’atteindre les objectifs de production tout en minimisant les risques de dégâts sanitaires.

Reconstructed forest age structure in Europe 1950–2010

Forest age structure is an important factor for understanding the history of forests, their current functioning and their future development. It is, for instance, crucial information to be able to assess sustainable harvesting potentials. Furthermore, since the development of growing stock and increment, and thus the patterns of net carbon exchange, are strongly affected by the age of the forest, information about the age structure is needed to understand the temporal variability of the greenhouse gas budgets and potential contributions of forest management (i.e. their additionality) to long-term removal of carbon from the atmosphere. European forests have changed drastically in recent decades, but to date no European level compilation of historical forest age structure data is available. In this study, country level historical age-class data was combined with a backcasting method to reconstruct the age-class structure for 25 European countries from 1950 to 2010 (total forest area in 2010: 118.3 million ha). Based on the results, dynamic maps of forest age-class distributions on 0.25° × 0.25° grid were generated, and the change in the forest age structure was analysed. Results show that the share of old forests (>100 years) has decreased from 26% in 1950 to 17% in 2010, and the mean age over the studied area decreased from 67 to 60 years. However, when looking at the change of the mean age from 1950 to 2010 at country level, there is a large variation between the countries. We discuss implications of the results and argue that the development of forest age structure contributed less than previously thought to the carbon sink in European forests from 1950 onwards.

Assessing the influence of historic net and gross land changes on the carbon fluxes of Europe.

Legacy effects of land cover/use on carbon fluxes require considering both present and past land cover/use change dynamics. To assess past land use dynamics, model-based reconstructions of historic land cover/use are needed. Most historic reconstructions consider only the net area difference between two time steps (net changes) instead of accounting for all area gains and losses (gross changes). Studies about the impact of gross and net land change accounting methods on the carbon balance are still lacking. In this study, we assessed historic changes in carbon in soils for five land cover/use types and of carbon in above-ground biomass of forests. The assessment focused on Europe for the period 1950 to 2010 with decadal time steps at 1-km spatial resolution using a bookkeeping approach. To assess the implications of gross land change data, we also used net land changes for comparison. Main contributors to carbon sequestration between 1950 and 2010 were afforestation and cropland abandonment leading to 14.6 PgC sequestered carbon (of which 7.6 PgC was in forest biomass). Sequestration was highest for old-growth forest areas. A sequestration dip was reached during the 1970s due to changes in forest management practices. Main contributors to carbon emissions were deforestation (1.7 PgC) and stable cropland areas on peaty soils (0.8 PgC). In total, net fluxes summed up to 203xa0TgCxa0yr(-1) (98xa0TgCxa0yr(-1) in forest biomass and 105xa0TgCxa0yr(-1) in soils). For areas that were subject to land changes in both reconstructions (35% of total area), the differences in carbon fluxes were about 68%. Overall for Europe the difference between accounting for either gross or net land changes led to 7% difference (up to 11% per decade) in carbon fluxes with systematically higher fluxes for gross land change data.

Overview of methods and tools for evaluating future woody biomass availability in European countries

Key messageThis analysis of the tools and methods currently in use for reporting woody biomass availability in 21 European countries has shown that most countries use, or are developing, National Forest Inventory-oriented models whereas the others use standwise forest inventory--oriented methods.ContextKnowledge of realistic and sustainable wood availability in Europe is highly relevant to define climate change mitigation strategies at national and European level, to support the development of realistic targets for increased use of renewable energy sources and of industry wood. Future scenarios at European level highlight a deficit of domestic wood supply compared to wood consumption, and some European countries state they are harvesting above the increment.AimsSeveral country-level studies on wood availability have been performed for international reporting. However, it remains essential to improve the knowledge on the projection methods used across Europe to better evaluate forecasts.MethodsAnalysis was based on descriptions supplied by the national correspondentsinvolved in USEWOOD COST Action (FP1001), and further enriched with additionaldata from international reports that allowedcharacterisation of the forests in these countries for the same base year.ResultsMethods currently used for projecting wood availability were described for 21 European countries. Projection systems based on National Forest Inventory (NFI) data prevail over methods based on forest management plans. Only a few countries lack nationwide projection tools, still using tools developed for specific areas.ConclusionsA wide range of NFI-based systems for projecting wood availability exists, being under permanent improvement. The validation of projection forecasts and the inclusion of climate sensitive growth models into these tools are common aims for most countries. Cooperation among countries would result in higher efficiency when developing and improving projection tools and better comparability among them.

Comment on "critical wind speed at which trees break"

Virot etxa0al. [E. Virot et al., Phys. Rev. E 93, 023001 (2016)10.1103/PhysRevE.93.023001] assert that the critical wind speed at which ⩾50% of all trees in a population break is ≈42 m/s, regardless of tree characteristics. We show that empirical data do not support this assertion, and that the assumptions underlying the theory used by Virot etxa0al. are inconsistent with the biomechanics of trees.