The current increase in European forest resources forms a singularity across the globe. Whether this trend will persist, and how biological and economic trends feature it form crucial issues to green ...economy challenges and C sequestration. The present screening of Forest Europe 2015 statistics explored the features, inertia and limits of this expansion, and its relationships with countries' development, forest management and trade, intense in this area of the world. Persisting footprint of past demographic pressure on forests was identified, with opposed traces on their area and growing stock density. Steady growing stock (GS) increases, proportional to GS, not density-limited, and sustained by forest area increases, supported the view of an inflationary forest dynamic. Economic development and liberalism fostered both forest exploitation and production, yielding no significant impact on GS changes. Wood exports exerted a tension on forest exploitation and GS changes, thus lowering GS inflation but providing a resource security margin in the face of expected climate threats. Conflicting a common view, GS inflation and moderate felling-to-increment ratios make increased use of wood resources and C sequestration reconcilable, and GS expansion timely for ongoing EU forest policy processes. Anticipated adverse impacts of ongoing climate change were not clearly identified in these statistics.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Aims
Spatially balanced sampling is the most efficient method for surveying continuous and spatially structured populations. The spatial sampling of large‐scale surveys is mostly based on grids whose ...properties drive and potentially limit the possibility of building flexible samples. Periodicity causes high sampling constraints when an increase in the frequency of information delivery is sought. The sampling stratification of the adaptive sampling intensity also conflicts with the grid‐based approach. Although some surveys seemingly exploit these properties, no formal developments have been made available in the survey sampling literature across the fields of application.
Methods
We define and demonstrate the geometric properties of square grids, demonstrate how they can be used to produce nested hierarchical grids compatible with multiple periodicity values of interest for natural monitoring, and adapt the sampling intensity across space and time. A simulation study was conducted to quantify how spatial balance can be traded slowly for sample size reduction.
Results
We showed that square grids have geometric properties that can be exploited to cope with spatial flexibility in the sampling effort and the spatiotemporal coordination of samples. We also provide an original extension of this framework intended to tune the sampling effort gradually while preserving spatial systematicity. The simulation study showed that a nested hierarchical grid can be used to progressively reduce the sampling intensity while preserving regularity in the spatial arrangement of units.
Conclusions
We demonstrate the flexibility and diversity of sampling schemes that can be implemented with square grids, answering the need for periodicity and the coordination of multiple samples and the limits of their use.
Square grids support advanced samplings with multiple periodicities (numbers from 1 to 5 here for a period of five years) and hierarchical nesting that result in a subsampling preserving spatial balance.
There is a rising interest in the role of species diversity in ecosystem functioning and services, including productivity. Yet, how the diversity–productivity relationship depends on species identity ...and abiotic conditions remains a challenging issue. We analysed mixture effects on species productivity along site productivity gradients, calculated from a set of abiotic factors, in two biogeographic contexts (highlands and lowlands). We compared the productivity of 5 two‐species mixtures (i.e. 10 cases of mixed species) with that of monocultures of the same species. Five main European tree species were considered: sessile oak (Quercus petraea Liebl.), Scots pine (Pinus sylvestris L.), European beech (Fagus sylvatica L.), silver fir (Abies alba Mill.) and Norway spruce (Picea abies (L.) H. Karst). Our data set was compiled from the 2006 to 2010 French National Forest Inventory data base and covers 2361 plots including pure and mixed stands. Overall productivity of mixtures in highlands, that is European beech–Norway spruce, European beech–silver fir and to a lesser extent, silver fir–Norway spruce, was found to be higher than expected from the productivity of corresponding monospecific stands. Overyielding was mainly due to European beech for the first two mixtures and to silver fir for the third one. No effect of mixture was found for sessile oak–Scots pine and sessile oak–European beech stands in lowlands. Overyielding of sessile oak mixed with Scots pine was not strong enough to significantly increase overall stand productivity. Overyielding of European beech was balanced by an underyielding of sessile oak. The mixture effect changed along site productivity gradients for six cases out of the 10 studied, with a stronger and positive effect on sites with low productivity. The magnitude of this change along site productivity gradients varied up to 89% depending on the tree species. Synthesis. The nature of species interaction in mixtures with regard to productivity changes with species assemblage and abiotic conditions. Overyielding is strongest when species grow in highlands on less productive sites. A negative link between mixture effect and site productivity was found, in line with the stress‐gradient hypothesis.
Pure and even-aged (PEA) forests of fast-growing conifer species have for a long time been key providers of industrial raw material. Despite recent concerns regarding their greater sensitivity to ...major natural disturbances, their impacts on biodiversity and their funding efficiency, PEA conifer forests could remain a major economic target given the ongoing European strategy for bioeconomy. These forests are encountered in contrasted climates and in both native and introduced contexts across Europe, giving rise to high uncertainties regarding their growth responses to current climate change. Using the French National Forest Inventory data, we studied the radial growth of eight major conifer species in European forestry across 16 regional native and introduced PEA forest systems (n > 10 000 trees). Growth trends over the 2006-2016 period exhibited a significant negative association with the absolute growth level in 2006, with the strongest negative growth trends found for emblematic PEA forestry species (e.g. Norway spruce and Douglas fir), and the strongest positive trends for pine species (e.g. Scots pine). While the greater growth rate advantage of some species may shorten rotation and lower risk exposures for future decades, their recent lowered productivity may affect the forest sector in the long run. The prevalence of PEA forests across European forest landscapes and their increasingly reported lower resilience to climate change compared to more complex forest systems call for the establishment of a long-term European forest policy strategy. Maintaining the environmental, social and economic benefits of forests should remain a priority in the European agenda, regardless of the financial costs at stake.
Forest growth changes have been a matter of intense research efforts since the 1980s. Owing to the variety of their environmental causes – mainly atmospheric CO2 increase, atmospheric N deposition, ...changes in temperature and water availability, and their interactions – their interpretation has remained challenging. Recent isolated researches suggest further effects of neglected environmental factors, namely changes in the diffuse fraction of light, more efficient to photosynthesis, and galactic cosmic rays (GCR), both emphasized in this Discussion paper. With growing awareness of GCR influence on global cloudiness (the cosmoclimatologic theory by H. Svensmark), GCR may thus cause trends in diffuse-light, and distinguishing between their direct/indirect influences on forest growth remains uncertain. This link between cosmic rays and diffuse sunlight also forms an alternative explanation to the geological evidence of a negative correlation between GCR and atmospheric CO2 concentration over the past 500 Myr. After a careful scrutiny of this literature and of key contributions in the field, we draw research options to progress further in this attribution. These include i) observational strategies intending to build on differences in the spatio-temporal dynamics of environmental growth factors, ranging from quasi-experiments to meta-analyses, ii) simulation strategies intending to quantify environmental factor's effects based on process-based ecosystem modelling, in a context where progresses for accounting for diffuse-light fraction are ongoing. Also, the hunt for tree-ring based proxies of GCR may offer the perspective of testing the GCR hypothesis on fully coupled forest growth samples.
•Diffuse light is more efficient than direct light to terrestrial productivity.•Increased aerosols and cloudiness may hence have caused global forest growth trends.•A link between cloudiness and cosmic rays is gaining ground (cosmoclimatology).•Isolated studies have also suggested cosmic rays to affect forest growth.•Observation and simulation strategies are exposed to clarify these neglected issues.
In the framework of sustainable forest management, measuring site quality and predicting site productivity remain a major forestry topic. Over the past years, it has been fostered by a number of ...site-growth modelling studies seeking to establish quantitative relationships between site index and explicit biophysical indicators. In addition, comparative modelling studies of site index and site productivity have highlighted limited accordance of their environmental determinism, questioning site index as a reliable indicator of site quality. Lastly, process-based modelling approaches have recently arisen as a means to predict site productivity over large regions. All these investigations have however drawn limited attention in recent syntheses. In this review, we provide an overview of the literature on these site-growth studies. Concepts and vocabulary related to site productivity are introduced. Taking regional studies as a baseline, we first highlight recent progress regarding the geographic areas encompassed, and the major role played by NFI programmes and spatialized environmental information. A trade-off between model accuracy and geographic extent is suggested, pointing out potential deficiencies in the modelling of site-growth associations, insufficient accuracy or resolution in climatic data, or uncontrolled factors in site-growth models that emerge on a higher spatial scale. Inappropriate use of biophysical classifications where environmental factors remain implicit is also emphasized. In a next step, we discuss early and most recent indications on weaknesses of the site index concept when applied over large regions, including its differential response to climate relative to site productivity, regional variations in site index curves, site index dependence on stand density and subsequently on regional silvicultural practices. The role of genetic structure of tree populations and its integration into site-growth studies is also reviewed and discussed. The interests, limits and recent advances of process-based models as an alternative to evaluate site productivity are considered, as they may overcome some of the previous limitations. We last draw challenges and perspectives on the issue. We suggest that the accuracy – and the need – of site index as a founding concept of forestry science is questioned, by building direct productivity–environment relationships based on NFI databases as a realistic option at hand. We formulate perspectives regarding the accuracy, resolution and enlargement of environmental indicators currently used, the inclusion of information on genetic structure of tree populations in the context of adaptation to future climate change, as well as the use of site productivity models in forest management.
1. Relationships between tropical rain forest biomass and environmental factors have been determined at regional scales, e.g. the Amazon Basin, but the reasons for the high variability in forest ...biomass at local scales are poorly understood. Interactions between topography, soil properties, tree growth and mortality rates, and treefalls are a likely reason for this variability. 2. We used repeated measurements of permanent plots in lowland rain forest in French Guiana to evaluate these relationships. The plots sampled topographic gradients from hilltops to slopes to bottomlands, with accompanying variation in soil waterlogging along these gradients. Biomass was calculated for >175 tree species in the plots, along with biomass productivity and recruitment rates. Mortality was determined as standing dead and treefalls. 3. Treefall rates were twice as high in bottomlands as on hilltops, and tree recruitment rates, radial growth rates and the abundance of light-demanding tree species were also higher. 4. In the bottomlands, the mean wood density was 10% lower than on hilltops, the basal area 29% lower and the height:diameter ratio of trees was lower, collectively resulting in a total woody biomass that was 43% lower in bottomlands than on hilltops. 5. Biomass productivity was 9% lower in bottomlands than on hilltops, even though soil Olsen P concentrations were higher in bottomlands. 6. Synthesis. Along a topographic gradient from hilltops to bottomlands there were higher rates of treefall, which decreased the stand basal area and favoured lower allocation to height growth and recruitment of light-demanding species with low wood density. The resultant large variation in tree biomass along the gradient shows the importance of determining site characteristics and including these characteristics when scaling up biomass estimates from stand to local or regional scales.
Key message
Fifteen species are most susceptible to require vegetation control during tree regeneration in the range of our study. Among these 15 species,
Rubus fruticosus
,
Pteridium aquilinum
, and
...Molinia caerulea
cover each more than 300,000 ha of open-canopy forests.
Context
Vegetation control, i.e., the reduction of competitive species cover, is often required to promote tree seedling establishment during the forest regeneration stage. The necessity to control understory vegetation largely depends on the species to be controlled. In order to plan forest renewal operations, it is critical to identify which species require vegetation control during the regeneration stage and to quantify the forest area affected by these species.
Aims
We aimed at identifying the main species requiring vegetation control and at estimating the forest area they cover at the national level.
Methods
Using National Forest Inventory data, we created four indicators based on two levels of plant cover, cross-referenced with two levels of canopy opening, and compared them to the outcome of a survey of forest manager practices.
Results
The best indicator was the one that represented the proportion of forests with open canopy where the species was present with a large cover in the understory. In non-Mediterranean France, according to the indicator, a total of 15 species were found to frequently require vegetation control during the tree regeneration stage.
Pteridium aquilinum
,
Molinia caerulea
, and
Rubus fruticosus
were the main species, and each covered more than 300,000 ha of forest with open canopies, representing about 13% of the total forest area with open canopies outside of the Mediterranean area.
Conclusions
Forests covered by species requiring vegetation control according to forest managers represent a large share of the forest area undergoing regeneration. This study provides the first list of species that require vegetation control based on a methodological protocol that makes it possible to calculate the area associated with each species.
• Background and Aims Our knowledge about the influences of environmental factors on tree growth is principally based on the study of dominant trees. However, tree social status may influence ...intra-annual dynamics of growth, leading to differential responses to environmental conditions. The aim was to determine whether withinstand differences in stem diameters of trees belonging to different crown classes resulted from variations in the length of the growing period or in the rate of cell production. • Methods Cambial activity was monitored weekly in 2006 for three crown classes in a 40-year-old silver-fir (Abies alba) plantation near Nancy (France). Timings, duration and rate of tracheid production were assessed from anatomical observations of the developing xylem. • Key Results Cambial activity started earlier, stopped later and lasted longer in dominant trees than in intermediate and suppressed ones. The onset of cambial activity was estimated to have taken 3 weeks to spread to 90 % of the trees in the stand, while the cessation needed 6 weeks. Cambial activity was more intense in dominant trees than in intermediate and suppressed ones. It was estimated that about 75 % of tree-ring width variability was attributable to the rate of cell production and only 25 % to its duration. Moreover, growth duration was correlated to tree height, while growth rate was better correlated to crown area. • Conclusions These results show that, in a closed conifer forest, stem diameter variations resulted principally from differences in the rate of xylem cell production rather than in its duration. Tree size interacts with environmental factors to control the timings, duration and rate of cambial activity through functional processes involving source-sink relationships principally, but also hormonal controls.
Le temps forestier s’est singulièrement diversifié et enrichi au cours des dernières décennies, entrant en résonance avec le développement anthropique et la crise environnementale. La découverte de ...phénomènes de grande échelle opérant à des échelles extrêmes a ainsi consacré un temps profond et un temps réel des forêts. Cette nouvelle appréhension a été permise par l’émergence et l’évolution des systèmes d’observation et de suivi systématique des forêts. Si ces derniers ont évolué très rapidement à l’échelle humaine, tirant parti des progrès de la statistique de sondage, de la télédétection et de leur hybridation, un regard historique montre qu’ils restent néanmoins en retard permanent sur les phénomènes réels à l’œuvre dans les forêts. Des processus globaux et d’intensité marquée comme les changements de croissance, les transitions forestières, ou les perturbations environnementales permettent ainsi de l’illustrer. Savoir construire une vision des futurs pour ces systèmes d’observation est un enjeu technologique et sociétal majeur face au changement climatique. Les forêts ont toujours été de notre temps. Les systèmes d’observation doivent aussi le devenir.
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