The purpose of this study was to develop, test and evaluate a software prototype capable of modeling forest growth in consideration of winter storm disturbance and to simulate storm damage in forests ...under different forest management regimes. The results of a test application showed that simulated storm damage was more strongly influenced by the input data (e.g. tree species and tree height) than by the different forest management regimes. However, early, intense thinnings as well as reducing target diameters by 10% led to reduced storm damage, with decreases as large as 50% of the damage in certain forest stands. The coupled modeling framework was able to simulate interactions between forest growth, storm damage and forest management regimes. Further testing of the prototype appears necessary to investigate a wider range of tree species, soil and site conditions. Also, the use of computational system resources needs improvement.
•We establish and evaluate a coupled forest growth and storm damage modeling system.•The impact of forest management on storm damage risk can be simulated.•Measures to stabilize forest ecosystems against storm disturbance were identified.•Heavy thinnings and a 10% reduction of target diameters proved effective.•Storm damage in coniferous forests could be lowered up to 50% by adapted management.
Software applications for life cycle assessment of greenhouse gas (GHG) emissions have become popular over the last decade. Their objective is to provide insight into how GHG emissions could be ...reduced in the sectors defined by the UNFCCC. However, boundaries between these sectors are not closed and current tools are not designed to represent this complexity or to assess the numerous sources of uncertainties.
In this paper, we present CAT v1.0, software developed for managed forests in the LULUCF sector, but whose emission life cycle is linked to that of other sectors. While the structure of the software follows IPCC Guidelines, it also contains additional features such as an embedded Monte-Carlo error propagation technique and a user-friendly flux manager that allows for complex cradle-to-grave representations of the wood transformation industry. The flexibility of the software is illustrated through two case studies in northeastern France.
•We developed a software platform to assess complex cross-sectoral GHG emission life cycles.•CAT software provides a user-friendly interface that allows for the representation of complex life cycles.•CAT uses the Monte Carlo technique for prediction uncertainty assessment.•Two case studies of cradle-to-grave forestry supply chains exemplify CAT's potential.•Managers can use CAT to design policies for achieving IPCC emission reduction targets.
Background and AimsThere is considerable evidence for the presence of positive species diversity–productivity relationships in plant populations, but the population parameters determining the type ...and strength of the relationship are poorly defined. Relationships between species evenness and tree survival or species coexistence are not well established. The objective of this study was to quantify the joint effects of density and species evenness on tree productivity and species coexistence.MethodsA 12-year-old experimental tree plantation mixing two species according to a double gradient of density and species proportion was used. A neighbourhood approach was employed and descriptors of local competition were used to model individual tree growth. Fagus sylvatica and Acer pseudoplatanus were used as model species, as they can be considered as ecologically equivalent in their young stages.Key ResultsDensity and tree size were primary factors determining individual growth and stand productivity. Species identity had a significant, but less pronounced, role. Stand productivity was highest when species evenness was close to 1 and slightly lower in uneven mixtures. The reduction in stand productivity when species evenness decreased was of similar magnitude irrespective of which species became dominant, indicating symmetric effects for the two species. When examining individual tree growth in response to species proportion for each species separately, it was observed for both species that individual trees exhibited greater growth in uneven mixtures in which the other species was more frequent.ConclusionsThe results suggest that mixtures of these two functionally similar species have the highest production at maximum evenness, indicating a complementary effect between them. The presence of a mixture combines both stabilizing mechanisms (individuals from both species show higher growth when surrounded by individuals from the other species) and equalizing mechanisms (the two species have very similar growth curves) that, in turn, determine the species' relative dominance. These processes should act to ensure the long-term coexistence of species.
KEY MESSAGE : According to biomechanical processes, tree morphology (trunk inclination, height-to-diameter ratio and crown area) explains statistically silvicultural effects on growth stress ...variation. Growth stresses constitute the main mechanism allowing the tree to control its posture against its mechanical environment, but are also among the most important factors contributing to the depreciation of timber value. This study aimed at assessing the link between stand planting density and growth stress level in European beech (Fagus sylvatica) stands. Beech seedlings were planted in four plots corresponding to four planting densities: 2,500, 5,000, 10,000 and 40,000 stems/ha. They were left to grow for 26 years without any intervention, resulting in trees with highly different morphologies but of the same age and provenance. After 26 years of growth, both the tree morphology and growth stress indicators were measured on the standing trees in each plot and an attempt was made to establish a link between them. Our results showed that initial stand density influences growth stresses of the first order as a result of its impact on tree morphology. The best predictors of high growth stresses were high trunk inclination, high height-to-diameter ratio (slenderness factor) and low crown area. According to mechanosensing theories, these morphological criteria emphasised that growth stresses are due to a global mechanical stimulation rather than to local stem inclination alone. Research now has to be undertaken on new methods that combine the integrative assessment of tree morphology as well as its monitoring over time.
The importance of plant litter traits and decomposability for nutrient cycling processes and plant community dynamics through plantplant–litter–feedbacks has been largely emphasized. However, the ...role of biotic interactions as drivers of intraspecific variability in litter traits remains surprisingly little studied. In this study, we used a large-scale, multi-site network of long-term tree removal experiments manipulating the abundance of a foundation tree species, i.e., Quercus petraea, to assess how plant interactions control intraspecific variation in oak leaf litter traits and decomposability. We studied 19 plots across eight experimental sites covering a large gradient of oak abundance, stand age, and local abiotic context. Oak leaf litter quality strongly declined with tree removal in early forest successional stage. Litter became poorer in nutrients such as N and Mg and richer in secondary metabolites such as lignin and condensed tannins. This in turn slowed its decomposition. Importantly, litter N loss switched from N release to N immobilization. Variance partitioning indicated that oak abundance explained as much variation in oak leaf litter traits as oak age and twice as much as soil inherent fertility. Confirmatory path analysis revealed that the decline of oak leaf litter quality induced by tree removal was most likely driven by a shift in understory plant species composition. Plasticity of oak leaf litter traits to the shortage of nutrient supply related to the development of understory plants competitors with higher nutrient capture and retention ability could potentially explain this response pattern. Our data also give consistent but weaker support that the decline of oak leaf litter quality could be driven by alleviated competition for light among canopy trees and subsequent enhanced crown exposure to light. Overall, our study provides evidence that biotic factors such as plant interactions are major drivers of plasticity in leaf litter traits and decomposability. This finding contributes to the emerging view that phenotypic plasticity is fundamentally related to biotic interactions for sessile organisms, especially for long-lived and large plant species such as trees. Taking this source of functional diversity into account could help us to better understand plant community dynamics and ecological processes in terrestrial ecosystems.
Key message
The position of trees in the canopy impacts xylem structure and its inter-annual variation. After canopy release, the increase in the hydraulic conductivity of growth rings was driven by ...an increase in radial growth in large trees, and by both an increase in radial growth and changes in xylem structure in saplings.
Context
Forest canopies are frequently subjected to disturbances that allow understory trees to access the upper canopy. The effect of canopy release on xylem anatomy has been assessed in juvenile trees and saplings, while the potential acclimation of larger trees remains poorly documented.
Aims
We estimated the potential hydraulic conductivity of growth rings in large understory trees compared to overstory trees, and evaluated the responses to canopy release in large trees and in saplings.
Methods
We recorded radial growth, wood density, and vessel structure in beech trees according to their position within the canopy and their size. Xylem traits were followed during 6 years after canopy release for large trees, and during 2 years for saplings. Vessel diameter and frequency as well as ring area were used to compute the potential annual ring hydraulic conductivity.
Results
Large understory trees displayed lower radial growth increments and lower potential annual ring hydraulic conductivity than overstory trees. After canopy release, potential annual ring hydraulic conductivity increased in large trees, due exclusively to increased radial growth without any change in specific hydraulic conductivity. It increased in saplings due to both increased radial growth and increased specific conductivity.
Conclusion
Tree size impacted xylem structure and resulted in plasticity of the potential hydraulic conductivity of the annual tree ring following canopy release.
1. Global warming induces new constraints on forest ecosystems and requires forest management adaptation. The reduction in stand density is currently debated as a potential tool to face increasing ...summer drought risk by improving forest resistance to climate change-induced tree mortality. However, few studies have yet assessed the impacts of this management change on soil biodiversity. 2. We conducted a large-scale, multi-site assessment of the response of soil macro-detritivore assemblages and soil functioning to experimental manipulations of stand density. A total of 33 stands were studied covering a wide gradient of stand density, that is stand basal area from 2·5 to 43-7 m² ha⁻¹, stand age, that is 18-171 years old, and local abiotic context. 3. We observed contrasting responses as a function of both taxonomic and functional groupings. Exploratory analysis using causal diagrams, that is path analysis, highlights that these changes were mainly related to alterations in understorey vegetation, microclimatic and soil pH conditions. The response of soil macro-detritivore assemblages to stand density manipulation was consistent over the gradient of stand ages. 4. Among the litter-dwelling macro-detritivores, millipede abundance and diversity decreased with stand density reduction, while woodlice and epigeic earthworms were unaffected. Further, a shift in soil-dwelling earthworm community composition was observed in mull stands. Endogeic earthworm abundance showed a sharp increase with stand density reduction, which translated into an increase in soil respiration. In contrast, anecie earthworm abundance decreased and was strongly associated with a decline of the rate of forest floor turnover. 5. Synthesis and applications. Our study provides strong evidence that reductions of stand density will have substantial impacts on soil macro-detritivore assemblages and cascading effects on soil functioning, particularly in mull stands. Managing stand density of oak forests at an intermediate level, that is 25 m² ha⁻¹, appears to be best to optimize the trade-off between improving forest resistance to climate change and ensuring the conservation of functional diversity to preserve forest ecosystem functioning and stability.
► Sessile oak forking was recorded during 23 years in three initial spacings. ► Tree height, girth and forks were fitted simultaneously. ► Forks accumulated especially in initial density 1333 trees ...per ha. ► The two origins of forks traumatism and metamorphosis could not be distinguished.
For Quercus petraea (sessile oak), the origin of forks is either traumatic or related to crown base formation (“metamorphosis”). The objectives of this study were to quantify forking, distinguish the two origins and test the effect of initial stocking density and tree attributes on the number of forks and height to the lowest one.
The experiment took place in a 23-year-old sessile oak plantation in Normandy, France, where three initial planting densities were compared (1333, 2667 and 5333seedlings per ha). The forks were observed every 3years after the plantation. Fork number was modelled with a system of simultaneous linear equations that respectively predicted tree girth, height and the log-transformed fork frequency, with age and initial stocking density as explanatory variables. This model 1 was fitted as a seemingly unrelated regression with random effects to account for the tree and plot clustering. For trees having at least one fork, lowest fork height was quantified using a linear mixed model including predictors compatible with the response variables of model 1, age and stocking.
The results showed that the number of forks can be predicted using the expected explanatory variables and it is significantly correlated with height and girth as well. Traumatic and metamorphosis-related origins were not clearly distinguished, but significant differences between the initial seedling densities were found, with the lowest density showing the highest number of forks. Lowest fork height depended on response variables of model 1, age and stocking. The stocking effect was significant but small.
This study presents the first statistical quantification of tree forking ever made. From this quantification, it seemed obvious that the initial density of 2667 seedlings per ha could be a relevant initial density to avoid the emergence of too many forks and the insertion of the lowest forks too low down.
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