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The main objective for even-aged plantation (EAP) management of producing sawlog material has driven practices towards low initial planting densities and lower post thinning densities. For semi-shade tolerant species, the resulting stand density potentially leaves enough growing space for the introduction of a second cohort of trees in the understory, making it a two-aged plantation (TAP). TAP could have many silvicultural benefits, especially in sensitive areas where intensive treatments associated with EAP are incompatible with local management objectives. White spruce (Picea glauca) is a good candidate species for modeling TAP because it is the most widely planted tree species in Canada and has proven tolerance to understory planting. SORTIE-ND, a single-tree spatially explicit growth model was used to explore the yield of variable density and rotation length scenarios when each white spruce cohort is introduced mid rotation, compared to traditional even-aged management. All TAP scenarios tested produced more sawlog volume and more merchantable volume than equivalent densities of EAPs. The lowest density tested, 400 stems ha-1 planted every 35 years, had the highest sawlog yields (3.23 m3 ha-1 yr-1). Considering smaller size products changes the optimum TAP scenario but maintains the advantage over EAPs.

Malaysia and Indonesia have been affected by deforestation caused in great part by the proliferation of oil palm plantations. To survey this loss of forest, several studies have monitored these sou...

Terrestrial laser scanning (TLS) often makes use of multiple scans in forests to allow for a complete view of a given area. Combining measurements from multiple locations requires accurate co-registration of the scans to a common reference coordinate system, which currently relies on markers, an often cumbersome process in forests. Existing algorithms for achieving marker-free registration of TLS scans in forests promise to significantly decrease field work time, but are not yet operational and their results have not been validated against traditional methods. Here we present a new implementation of an existing approach which runs in parallel mode and is able to process TLS data acquired over large forest areas. To validate our algorithm, point cloud registration matrices (translation and rotation) derived from our algorithm were compared to those obtained using reflective markers in multiple forest types. The results show that our approach can be used operationally in forests with relatively clear understory, and it provides accuracy similar to that obtained from using reflective markers. Furthermore, we identified factors that can lead to this approach falling short of providing acceptable results in terms of accuracy.

Foliage clumping is a forest canopy structural feature influencing light interception, the inversion of light interception for estimating leaf area index, and photosynthesis rates. In this study we estimated clumping factor values at the branch level from different heights in broadleaf tree species at four sites in two climatic zones (two sites in dry climate and two sites in humid climate) using laser light. We found that branch level foliage distribution tends to be random at dry sites where water is the main limiting resource, and that foliage aggregation at the top of emergent canopy tops increases with branch height at humid site where competition for light is high. Our results suggest that high competition for light leads to the production of large amounts of leaves grouped together in high irradiance areas of the canopy, even though this significantly reduces the light interception efficiency on a per leaf area basis. A comparison of these results with foliage clumping factor values derived at larger spatial scales for two sites (one dry and one humid) revealed a crossover in the scales at which clumping arises: leaves are essentially clumped at the branch level but much less so at the plot level for the humid site, and leaves are clumped at the plot level but not at the branch level for the dry site. This suggests that the occurrence of foliage clumping may be related to the intensity of resource limitation (light or water in this case) and its availability in 3D space. Additional research is required to confirm the role of environmental conditions in determining foliage clumping across various forest biomes. Further confirmation and understanding of causal relations between abiotic stresses and canopy foliage clumping may lead to significant refinement in forest canopy radiative transfer modelling schemes.

Foliage clumping is known to have a significant effect on the radiative transfer and mass and energy exchanges in forests. It is an important component of canopy structure to consider for the estimation of photosynthesis rates and the interpretation of observed solar induced fluorescence (SIF). Yet, relatively little is known about the drivers of foliage clumping, and few observations of foliage clumping are available at the branch scale. Here, we report on a study using laser light to estimate foliage clumping at the tree branch scale in eight broadleaf species, at different heights above ground, from four sites located in two climatic zones: one water limited, and one light limited. We also integrate our results with published foliage clumping estimates from two sites (one in each climatic zone). We find that foliage arrangement on branches exposed to high solar irradiance tend to be random at the dry sites, but are very clumped at humid sites where competition for light is high. Branches sampled at the top of tall canopies at humid sites showed that foliage clumping increased with tree height, suggesting that higher competition for light results in the production of larger numbers of leaves grouped together which reduces the light interception efficiency on a per leaf area basis. Comparison with landscape clumping values suggests that the spatial availability of a limiting resource is a major driver of foliage clumping in forests.

Although crop tree release (CTR) in hardwood stands is an accepted variant of precommercial thinning (PCT), the lack of an affordable and feasible method hinders its adoption. CTR implies selecting between 150 and 500 trees ha when trees are between 7 and 12 m high and cutting only stems competing with the target crop trees. We performed a field trial of a CTR variant of PCT in a 27.8 ha hardwood stand using a backpack mounted chain saw. A detailed time study was performed to document the trial over 13 days. Compared to conventional PCT performed earlier in the life of a stand, precommercial crop tree release required cutting larger stems, which showed to be feasible and productive using a backpack mounted chain saw. Productivity varied between 0.22 to 0.47 ha h during the trial, Although productivity could vary with stand characteristics and worker, this proof of concept trial demonstrates some of the potential uses that this new saw configuration offers and sets the basis for an eventual larger scale deployment of this treatment.–1–1

Airborne laser scanning (LiDAR) is used in forest inventories to quantify stand structure with three-dimensional point clouds. However, the 3D distribution of the point clouds depends not only on stand structure, but also on scan angle, because the probability for an oblique beam to be reflected by the canopy increases with the distance it must travel through the canopy. Thus, the canopy appears to increase in density as the incidence angle increases, all else being equal. The resulting variation between and within datasets can induce bias in LiDAR metrics derived from the vertical distribution of points. In this study, we modelled the effect of scan angle on the vertical structure of the point clouds to predict the bias of metrics derived from points sampled off-nadir. Comparison with paired observations from different flightlines (off- and at-nadir observations of the same point) demonstrated that the model accurately reproduced the bias of metrics calculated for a northern hardwood forest with relatively continuous canopy. Thus, the model could be used to correct the bias of LiDAR metrics, and provides a mathematical framework that could be used to inform the selection of maximum incidence angle in LiDAR surveys, considering the trade-off between decreasing acquisition costs and obtaining unbiased measurements.

With an increasing pressure on forested landscapes, conservation areas may fail to maintain biodiversity if they are not supported by the surrounding managed forest matrix. Worldwide, forests are managed by one of two broad approaches—even‐ and uneven‐aged silviculture. In recent decades, there has been rising public pressure against the systematic use of even‐aged silviculture (especially clear‐cutting) because of its perceived negative esthetic and ecological impacts. This led to an increased interest for uneven‐aged silviculture. However, to date, there has been no worldwide ecological comparison of the two approaches, based on multiple indicators. Overall, for the 99 combinations of properties or processes verified (one study may have evaluated more than one property or process), we found nineteen (23) combinations that clearly showed uneven‐aged silviculture improved the evaluated metrics compared to even‐aged silviculture, eleven (16) combinations that showed the opposite, and 60 combinations that were equivocal. Furthermore, many studies were based on a limited study design without either a timescale (44 of the 76) or spatial (54 of the 76) scale consideration. Current views that uneven‐aged silviculture is better suited than even‐aged silviculture for maintaining ecological diversity and processes are not substantiated by our analyses. Our review, by studying a large range of indicators and many different taxonomic groups, also clearly demonstrates that no single approach can be relied on and that both approaches are needed to ensure a greater number of positive impacts. Moreover, the review clearly highlights the importance of maintaining protected areas as some taxonomic groups were found to be negatively affected no matter the management approach used. Finally, our review points to a lack of knowledge for determining the use of even‐ or uneven‐aged silviculture in terms of both their respective proportion in the landscape and their spatial agency.

Foliage clumping refers to the aggregation of leaves around branches and tree crowns. It has been shown to influence considerably light interception in forests and is increasingly being used in terrestrial biosphere models (TBMs) to estimate canopy photosynthesis, represented by a single value encompassing all spatial scales (shoot, branch, crown and plot): the clumping factor (Ω). Several studies have pointed to possible vertical variations in foliage clumping, and a recent study confirmed very low clumping factor values (high leaf aggregation) at the top of deciduous broadleaf forests. However complete profiles of clumping factors have never been described in tall forest canopies. As TBMs are currently moving towards multilayer schemes for the computation of photosynthesis, we investigated whether vertical profiles of foliage clumping should be considered within those schemes. We first used ground lidar combined with hemispherical photos to characterise branch level clumping factor (Ωv) at different heights in a deciduous broadleaf forest. We then applied the branch level clumping factor profile to four forests plots where complete 3D structure derived from ground lidar was available to produce vertical profiles (30 cm resolution) for foliage clumping (Ωl) and leaf area index (LAI). We ran radiative transfer simulations using different scenarios for representing vertical structure to assess its effect on canopy photosynthesis (without considering energy balance, temperature, kinetics or water balance). We found that when considering branch level clumping, the plot level clumping factor values were considerably lower (leaves more clumped together) than the average values commonly used for broadleaf forests. Modeling light fluxes using this lower value increased canopy photosynthesis because of a combination of greater light penetration to lower layers and non-linearity in the light-response curve. Considering the vertical profiles of foliage clumping further increased canopy photosynthesis through a greater contribution from shaded leaves in the lower and upper canopy levels. Further, we find that there is an optimal range of value for clumping factor which maximises photosynthesis, and the four sites surveyed (LAIs above 4) display clumping factors values close to this optimum. Solely on the basis of the effect of radiative transfer, we did not find notable differences in canopy photosynthesis when the LAI profile was considered. We find that it may be of interest to consider foliage clumping vertical profiles within TBM multilayer schemes, and we present a generic profile equation for use in dense deciduous forests.

Airborne laser scanning (LiDAR) is used in forest inventories to quantify stand structure with three dimensional point clouds. However, the structure of point clouds depends not only on stand structure, but also on the LiDAR instrument, its settings, and the pattern of flight. The resulting variation between and within datasets (particularly variation in pulse density and footprint size) can induce spurious variation in LiDAR metrics such as maximum height (hmax) and mean height of the canopy surface model (Cmean). In this study, we first compare two LiDAR datasets acquired with different parameters, and observe that hmax and Cmean are 56 cm and 1.0 m higher, respectively, when calculated using the high-density dataset with a small footprint. Then, we present a model that explains the observed bias using probability theory, and allows us to recompute the metrics as if the density of pulses were infinite and the size of the two footprints were equivalent. The model is our first step in developing methods for correcting various LiDAR metrics that are used for area-based prediction of stand structure. Such methods may be particularly useful for monitoring forest growth over time, given that acquisition parameters often change between inventories.

In the late 1980s, large forest companies began precommercial thinning (PCT) operations in young northern hardwood cutovers in New Brunswick, Canada. To provide supporting growth and yield information, an industrial experiment was established at residual stand densities of 1300, 1600, 1900, and 2200 stems ha−1. Stand responses were examined for measurements recorded at 0 (1987), 5 (1992), 10 (1997), 16 (2003), and 23 (2010) years after establishment. Average diameter at breast height, quadratic mean diameter, stand basal area, and stand total volume growth increased as stem density decreased from PCT. There were significant linear differences for many of these variables between treatments and time periods (year). No significant differences were detected in tree height between treatments. In 2010, the four PCT thinning treatments did not exhibit any differences in potential sawlogs at 2.4 m (8 ft) and 3.6 m (12 ft) lengths. Significant differences were observed for 4.9 m (16 ft) sawlogs that were p...

While uneven-aged silviculture may appear preferable to even-aged silviculture in terms of stand susceptibility to windthrow (major wind damage), the scientific evidence is equivocal on this issue, because the two systems do not operate over the same time frame. The goal of this study was to evaluate the windthrow susceptibility of even- and uneven-aged stands over a 100-year period. Susceptibility to windthrow of North American hardwood stands was evaluated by coupling a stand growth model (Forest Vegetation Simulator, or FVS) to stem windthrow probability equations from the literature. This coupling was straightforward given that FVS provides the diameter at breast height (DBH) of each tree within a stand over the simulation period. Windthrow susceptibility equations also use DBH to calculate stem windthrow probability. Our results show that average loss due to windthrow under uneven-aged management can be twice that observed under even-aged management at moderate wind severity for sugar maple-dominated stands. This result should be interpreted with caution because of the impossibility in our simulations of considering differences in tree form development between the two approaches. Nevertheless, this study clearly shows that even-/uneven-aged silviculture comparisons should be made on a long-term basis since uneven-aged stands are continuously susceptible to windthrow, while even-aged stands tend to be little affected by windthrow in their early developmental stages.

Forest canopy structure has long been known to be a major driver of the processes regulating the exchange of CO2 and water vapour between terrestrial ecosystems and the atmosphere. It is also an important driver of terrestrial vegetation dynamics. Information about fine-scale ecosystem structure is needed to better understand and predict how terrestrial ecosystems respond to and affect environmental change. LiDAR remote sensing from ground-based instruments is a promising technology for providing such information, and physically-based models are ideally suited to process the data and derive reliable products. While complex ray tracing algorithms have been developed to help in the interpretation of LiDAR data, none of these tools are currently widely available. In this paper we present the VoxLAD model; a parametric model using computational geometry that allows to compute estimates of leaf area density at the voxel scale on the basis of terrestrial LiDAR data. This modelling framework removes the need to compute the exact point of entry and exit into and out of the voxels for all individual laser pulses, and thus allows for easier usage. The model requires that each point in the LiDAR point cloud should be classified as wood, foliage, or noise. Here we provide the algorithmic details of the model, and demonstrate that the output of the model closely fits the output of a model using more complex ray tracing techniques. A parametric model (VoxLAD) for estimating leaf area density (LAD) from ground-based LiDAR is proposed.The LAD estimates agree well with those obtained from a complex ray-tracing model.The physically based VoxLAD model will improve accessibility of LiDAR processing methods.

Forest structure is an important driver of ecosystem dynamics, including the exchange of carbon, water and energy between canopies and the atmosphere. Structural descriptors are also used in numerous studies of ecological processes and ecosystem services. Over the last 20+ years, lidar technology has fundamentally changed the way we observe and describe forest structure, and it will continue to impact the ways in which we investigate and monitor the relations between forest structure and functions. Here we present the currently available lidar system types (ground, air, and space-based), we highlight opportunities and challenges associated with each system, as well as challenges associated with a wider use of lidar technology and wider availability of lidar derived products. We also suggest pathways for lidar to further contribute to addressing questions in forest ecosystem science and increase benefits to a wider community of researchers.

A 3-D Monte Carlo ray-tracing simulation of LiDAR propagation models the reflection, transmission and ab- sorption interactions of laser energy with materials in a simulated scene. In this presentation, a model scene consisting of a single Victorian Boxwood ( Pittosporum undulatum ) tree is generated by the high-fidelity tree voxel model VoxLAD using high-spatial resolution point cloud data from a Riegl VZ-400 terrestrial laser scanner. The VoxLAD model uses terrestrial LiDAR scanner data to determine Leaf Area Density (LAD) measurements for small volume voxels (20 cm sides) of a single tree canopy. VoxLAD is also used in a non-traditional fashion in this case to generate a voxel model of wood density. Information from the VoxLAD model is used within the LiDAR simulation to determine the probability of LiDAR energy interacting with materials at a given voxel location. The LiDAR simulation is defined to replicate the scanning arrangement of the Riegl VZ-400; the resulting simulated full-waveform LiDAR signals compare favorably to those obtained with the Riegl VZ-400 terrestrial laser scanner.

Balsam fir ( Abies balsamea (L.) Mill.)-tolerant hardwood and spruce ( Picea sp.)-tolerant hardwood stands were compared along a gradient of hardwood composition (12–82%). Using permanent sample plot data, influences of stand hardwood content, past spruce budworm ( Choristoneura fumiferana Clem.) defoliation, insecticide spraying, and stand and site characteristics on survivor growth and mortality of the fir–spruce (spruce budworm host species) component of these stands were determined. Balsam fir basal area, spruce basal area, and percent hardwood were significantly related to fir–spruce survivor growth. Balsam fir mixedwood plots had four to five times higher fir–spruce cumulative mortality (3.7–13.3 m 2 ha −1 ) than spruce mixedwood plots (1.0–2.9 m 2 ha −1 ) from 1990 to 2004, and sustained higher wind-related mortality after the budworm outbreak ended in the late 1980s to early 1990s. A mortality regression tree model indicated that initial balsam fir basal area, % tolerant hardwood basal area, maximum cumulative defoliation from 1983 to 1987, and spruce budworm outbreak zone (north, central, south New Brunswick) all significantly influenced fir–spruce mortality. Results demonstrated differences in stand dynamics between these stand types, with lower spruce budworm vulnerability and higher longevity and more stable structure of spruce mixedwood than of fir mixedwood.

a b s t r a c t Vegetation structure parameters are key elements in the study of ecosystem functioning and global scale ecosystemic interactions. The detailed retrieval of many of these parameters by direct measurements is impractical due to the quantity of plant material in trees. Terrestrial LiDAR Scanners (TLSs) have been shown to hold great potential as an indirect means of estimating plant structure parameters with a high level of detail, while some studies identified a number of challenges inherent to this approach. In this study we investigate the use of a voxel-based approach to retrieve leaf area distribution of individual trees. The approach is based on the contact frequency method applied to co-registered TLS returns from two or more scanning positions. The contact frequency was computed for voxels being 10, 30, and 50 cm in size and subsequently corrected for the influence of occlusion effects, leaf inclination, the presence of non-photosynthetic material, and the laser beam size. The leaf area of voxels for which occlusion effects were too pronounced was estimated using modeled values based on the availability of light. We compared the TLS derived leaf area estimates against direct measurements, obtained by the harvesting of leaves, in a broad-leaved savanna of central Mali. The measured leaf area values of the sampled trees ranged from 30 to 530 m 2 , and crown LAI values between 0.8 and 7.2. The leaf area estimates lay on average 14% from the reference measurements (general bias). Our method provides vertical as well as radial distributions of leaf area in individual trees, and lends itself to the estimation of savanna vegetation structural parameters with a high level of detail.

This study examines the operational feasibility of six treatments to regenerate jack pine (Pinus banksiana Lamb.) naturally without fire following harvesting on clay soils in the southeastern boreal forest of Quebec. The experiment is a randomized complete block design. Techniques used were a final cutting in 1993 with manual on-site delimbing or roadside delimbing combined with three methods of soil scarification (WadellTM, La TaupeTM and a control) performed in the Spring of 1994 compared to an adjacent jack pine plantation established in 1994 after Wadell scarification. Seven growing seasons later, the present article compares stand composition, competing vegetation, regeneration and growth of jack pine between the different treatments as well as an adjacent plantation. Natural regeneration produced mixed stands with an adequate 52% average jack pine stocking. Roadside and on-site delimbing produced similar jack pine stocking on average. However, the plantation showed 83% stocking and better performance than natural regeneration in terms of height (2.48 m vs. 1.7 m for natural regeneration), diameter (41 mm vs. 22 mm for natural regeneration) and jack pine dominance. Therefore, if natural regeneration is desired, roadside delimbing is to be recommended since it provides sufficient seed and does avoid early jack pine growth reductions caused by slash. On clay soils, scarification seems to have been optional. Nevertheless, it slightly increased seedling growth and in this way, the treatment combining road-side delimbing and an extensive scarification can be an effective jack pine natural regeneration treatment.Key words: Pinus banksiana Lamb., natural regeneration, stocking coefficient, delimbing, scarification, boreal mixed wood, seedlings

A Monte Carlo ray tracing simulation of LiDAR propagation has been expanded to 3 dimensions, and makes use of the high-fidelity tree voxel model VoxLAD for realistic simulation of a single tree canopy. The VoxLAD model uses terrestrial LiDAR scanner data to determine Leaf Area Density (LAD) measurements for small volume voxels (~5 – 20 cm side length). The LAD measurement, along with material surface normal orientation information, is used within the Monte Carlo LiDAR propagation model to determine the probability of LiDAR energy being absorbed, transmitted or reflected at each voxel location, and the direction of scattering should an interaction occur. The high spatial fidelity of the VoxLAD models enables simulation of small-footprint LiDAR systems. Results are presented demonstrating incorporation of the VoxLAD model for realistic tree canopy simulation, and the full-waveform simulation capability of the Monte Carlo LiDAR code.

Shrimp culture is a sector of aquaculture that has a high potential for poverty alleviation and rural development in Vietnam. However, the development of this activity induces changes that potentially have negative impacts on the environment, one of which is wetland deterioration. This paper describes the use of a proposed change detection methodology in the assessment of mangrove forest alterations caused by aquaculture development, as well as the effectiveness of the measures taken to mitigate deforestation in the district of Giao Thuy, Vietnam, between 1986, 1992 and 2001. Geometric and radiometric corrections were applied to Landsat images prior to identifying changes through comparison of unsupervised classifications. Changes were afterwards validated using a thresholding method based on Tasselled Cap feature image differencing and a rule‐based feature selection matrix. The matrix is used to identify the feature that is most efficient at detecting the presence of change between given land‐cover class...

A split–split-plot sowing experiment was undertaken on the effects of seedbed and competing vegetation on jack pine (Pinus banksiana Lamb.) establishment in the boreal mixed wood of northwestern Quebec. Between 3 and 33% of sown seeds germinated and survived as seedlings after two growing seasons. Negligible jack pine seeds or seedlings came from residual seed trees. Scarification had a lesser effect on pine seed germination on clay soil than on till or sand. This difference could be explained by lower soil surface temperatures. Vegetation control and absence of forest cover had a strong positive effect on seedling survival. Nothing indicates that jack pine regeneration would be more difficult on clay than on more typical coarse-textured sands. However, competing vegetation, mainly aspen (Populus tremuloides Michx.), on sites with clay soils could be a critical factor affecting jack pine seedling mortality because of its abundance and persistence through time. Jack pine regeneration after cutting is less abundant than after fire, probably because of the delay between the opening of the stand and seed dispersal.

A study was undertaken to evaluate the effect of Scots pine (Pinus sylvestris) shelterwood density and timing of removal on the regeneration of forests with improved wood quality. This paper focuses on the effect of scarification and seedfall on the success of natural regeneration of Scots pine under two shelterwood densities and in a clear-cut. Wood quality aspects will be addressed later in the study. After 4 yrs, natural regeneration of Scots pine under a 200 stems ha-1 shelterwood reached 90000 seedlings ha-1, 53000 under a 160 stems ha-1 shelterwood and 3700 in a clear-cut. The high natural regeneration under the densest shelterwood resulted from a high seedfall, slower invasion by competing vegetation, consequent prolonged recruitment and low mortality. Since mortality largely decreased for both shelterwood densities and recruitment seems to continue, the success of regeneration should be maintained in the future if proper release operations are conducted. The latter could begin when seedlings reach...

A 36-ha experiment was carried out to assess the possibility of naturally regenerating jack pine stands following harvesting on clay soils of northwestern Quebec. Although differences between treatments were not statistically significant, there was a trend toward a positive effect of one treatment combining on-site delimbing and scarification with the Silva Wadell™ cone scarifier on jack pine seedling density (up to 10 000/ha) and distribution (50% of 1 m2 plots with at least one seedling, corresponding to 94% with 4 m2 plots), two years after harvest. However, scarified microsites contained fewer seedlings than expected and undisturbed humus contained more seedlings than expected. This result, contrary to what is generally reported in the literature may be explained either by the fairly humid conditions, favourable to germination and seedling establishment, occurring on clay sites or by the scarifier spreading the cone-bearing slash outward. Seedling abundance and distribution improved substantially from the first year to the second year following treatment. Although the irregular branch distribution over the cutover area appears to have limited regeneration success, combining on-site delimbing with soil scarification could lead to relatively good stocking of jack pine regeneration that could be enhanced by some fill-planting. This regeneration method could constitute an alternative to planting jack pine on clay. However, vegetation control to remove aspen competition might be necessary. Key words: jackpine, silviculture, natural regeneration, boreal mixed wood

Biochar can be defined as pyrolysed (charred) biomass produced for application to soils with the aim of mitigating global climate change while improving soil functions. Sustainable biochar application to soils has been estimated to reduce global greenhouse gas emissions by 71–130 Pg CO2-Ce over 100 years, indicating an important potential to mitigate climate change. However, these estimates ignored changes in soil surface reflection by the application of dark-coloured biochar. Through a laboratory experiment we show a strong tendency for soil surface albedo to decrease as a power decay function with increasing biochar application rate, depending on soil moisture content, biochar application method and land use. Surface application of biochar resulted in strong reductions in soil surface albedo even at relatively low application rates. As a first assessment of the implications for climate change mitigation of these biochar–albedo relationships, we applied a first order global energy balance model to compare negative radiative forcings (from avoided CO2 emissions) with positive radiative forcings (from reduced soil surface albedos). For a global-scale biochar application equivalent to 120 t ha−1, we obtained reductions in negative radiative forcings of 5 and 11% for croplands and 11 and 23% for grasslands, when incorporating biochar into the topsoil or applying it to the soil surface, respectively. For a lower global biochar application rate (equivalent to 10 t ha−1), these reductions amounted to 13 and 44% for croplands and 28 and 94% for grasslands. Thus, our findings revealed the importance of including changes in soil surface albedo in studies assessing the net climate change mitigation potential of biochar, and we discuss the urgent need for field studies and more detailed spatiotemporal modelling. We thank L Montanarella (Joint Research Centre) for making this study possible, W Mehl for help with the spectroscopy work and P Drahota for the mineralogy analyses. We thank the Portuguese Fundação para a Ciência e a Tecnologia (FCT) for providing F G A Verheijen with a postdoctoral grant (SFRH/BPD/74108/2010), and further want to acknowledge the financial support of the Czech Science Foundation (under grant No. GA 526/09/1762), and the Marie Curie CIG grant (No. GA 526/09/1762). We thank two anonymous reviewers for strengthening the letter. published

A combination of surface deposit and moisture regime class was used to investigate the utility of site type as a predictor of jack pine growth in northwestern Quebec. Height–age curves produced from stem analyses of dominant trees from 96 sample plots produced three jack pine (Pinusbanksiaina Lamb.) productivity classes. The low productivity class includes moderately dry shallow tills, shallow organic deposits over bedrock, and fluvioglacial sands with moisture regime classes moderately dry and fresh. Moderately dry to very moist deep tills and moderately dry to moist clays are classified as having high and very high productivity, respectively. The large difference in height growth between these latter two groups and the low productivity class precluded the definition of a moderate productivity class. The form of the height-growth curves was very similar among site types except for sandy, moderately dry sites, which showed a growth delay at young ages. On dry sites, particularly on well-drained tills, density and basal area were higher than on clay sites. Although volume yield of natural stands on tills and clays would thus be similar, it would likely be spread among a greater number of stems on tills. There was little difference in site index between natural jack pine growing on clays and tills. The low nutrient and moisture requirements and strong taproot of jack pine could explain why soil depth and bulk density are more important than soil richness. Although site type, expressed as a combination of surface deposit and moisture regime class, may be more detailed than needed, it provided an adequate prediction of potential jack pine productivity.

The growth and yield of jack pine (Pinusbanksiana Lamb.) was studied in even-aged stands of three types: pure jack pine, jack pine mixed with paper birch (Betulapapyrifera Marsh.), and jack pine mixed with trembling aspen (Populustremuloides Michx.) growing on moderately well-drained glaciolacustrine clay soils in the southern tip of the Clay Belt of northwestern Quebec. Site index, average DBH, and average height of jack pine, and the availability of nutrients in the forest floor were compared among stand types. No differences were found in the height growth of jack pine among stand types. However, diameters of jack pine in mixtures with paper birch were significantly greater than in either pure stands or in mixtures with aspen despite the fact that both mixed stand types showed higher forest floor pH and greater concentrations of exchangeable calcium and magnesium than the pure stands. These results, together with the pattern of height growth of the three species, suggest that the beneficial effect of paper birch on the diameter growth of jack pine is caused mainly by a reduction in the competition for light among individual jack pine trees. The silvicultural implications of the results are discussed.

Natural regeneration in jack pine (Pinus banksiana Lamb.) stands in Quebec is only sufficient 4% of the time and up to only 33% of the time in mixed stands. This study evaluates the usefulness of forest ecological types as defined by the Quebec Ministry of Forests in predicting abundance of advanced growth in pure and mixed jack pine stands of the Abitibi region, in north-western Quebec. Trees above 1.3 m in height and up to 5 cm DBH were tallied in 102 quadrats of 20 × 20 metres to evaluate advanced growth densities. No significant difference in advanced growth densities was observed between the two main types of surficial geological deposit in the region, lacustrine clays and glacial tills. Only shallow till and organic deposits over bedrock and fluvio-glacial sands showed significantly higher advanced growth densities. Prediction can be improved by using ecological variables such as soil texture, moisture regime, distance from a seed source and stand composition. Abundance of black spruce (Picea mariana (Mill.) B.S.P.) regeneration is positively associated with the proportion of sand in the soil profile and with drier sites; advanced growth of balsam fir (Abies balsamea (L.) Mill.) and white spruce (Picea glauca (Moench) Voss.) is weakly associated with the distance to a fire-preserved zone containing seed trees. Abundance of pin cherry (Prunus pensylvanica L.f.), probably associated with canopy openings, is positively linked with abundance of balsam fir and white spruce advanced growth. Jack pine regeneration by means of advanced growth occurs almost exclusively in jack pine stands on sand; higher proportions of hardwoods in the overstory appear to be negatively linked to jack pine advanced growth. Although the site variables studied showed some significant relationships with advanced growth abundance (maximum R2 = 0.32) which were slightly improved with stand composition variables (maximum R2 = 0.38), no satisfactory predictive model could be implemented. Key words: jack pine, advanced growth, ecological classification

The Quebec Ministry of Forests has developed an approach to ecological cartography designed to complement its traditional forest inventory and delimit homogeneous land units for forest management. The methodology consists of field work, map analysis and photointerpretation. Within the hierarchical classification, ecological regions reflecting regional climate are mapped at the 1:1 250 000 scale. Major physiographic ensembles and ecological districts, mapped at 1:250 000, express patterns of physiography, geology and geomorphology and ecological types (1:20 000) characterize surface deposits, drainage class, slope and potential climax forest. Using information drawn from ecological classification work in northwestern Quebec and applying the Ministry's standards, an ecological framework for two townships was developed. In addition to maps of each classification level, the framework includes interpretative documents such as schematic cross-sections of ecosystems and descriptive texts. Examples of management interpretations (natural regeneration potential and site preparation effect on competition) are presented. The classification approach and its future are evaluated.

Spiralization is a developmental deformation in winter greenhouse produced black spruce seedlings characterized by a drooping stem or portion of stem. During lignification, the seedling redresses but maintains part of its deformation. The objective of this study is to evaluate the long-term effect of spiralization on the growth, survival and morphology of black spruce seedlings in order to determine to what degree the rejection of spiralized seedlings is justified. Field evaluation was undertaken on 2304 black spruce seedlings planted on three sites with different soil conditions in Abitibi, Québec. The seedlings were divided in the greenhouse into six stem deformation classes of varying intensities, including a control, and laid out on a randomized complete block design. From 1986, the year of plantation, to 1990, spiralization had little effect on height and diameter growth. However, severely deformed seedlings planted on a heavy-textured site suffered sufficiently high mortality rates to justify their rejection. Moreover, these seedlings developed a higher proportion of double leaders. The study suggests that systematic rejection of all classes of deformed seedlings, especially those in the less severe classes, is probably not justified. Key words: Spiralization, stem deformation, seedlings, planting, black spruce, greenhouse, early growth, mortality.

The role of the World's forests in climate regulation is now widely recognised and mechanisms are in place to use forests in influencing the carbon cycle. The scale of the phenomenon has made the estimation and mapping of forest parameters a global/national level priority. Remote sensing is the only effective means available to provide the needed information at the relevant scales. The objective of this research is to explore the potential of CHRIS/Proba imagery directional resolution in improving tree biomass mapping accuracy in savannas. The study preliminary results presented here focus on evidence of correlation between tree biomass and Bidirectional Reflectance Factor (BRF) fields computed from CHRIS data.

International audience; - The dynamics of pure jack pine (Pinus banksiana) stands and of those also comprising a component of white birch (Betula papyrifera) and trembling aspen (Populus tremuloides) was assessed in natural post-fire stands on clay soils of eastern Canada boreal mixed woods in order to shed some light on mechanisms controlling composition. Age structures indicated that the presence of birch or aspen merely shortened the establishment of jack pine. Basal area structures of jack pine showed lower skewness coefficients in mixtures with birch than in pure jack pine stands or when mixed with aspen indicating that birch is probably a weaker competitor. Its effect on mean pine diameter probably reflects the lower pine stem density when mixed with birch. Inter-specific competition however had no effect on pine diameter at the tree level. Competition between birch, aspen and pine is avoided by species spatial exclusion measured by Ripley's statistic and reflects the reproductive strategies of the species and history of the site.; - Structure, distribution spatiale et compétition dans les peuplements mélangés et purs de pin gris (Pinus banksiana) sur argile dans l'est canadien. Nous avons étudié la dynamique des peuplements de pin gris purs (Pinus banksiana) et mélangés au bouleau à papier (Betula papyrifera) et au peuplier faux-tremble (Populus tremuloides), établis naturellement après un incendie sur sol argileux en forêt boréale mixte de l'est canadien dans le but de mieux comprendre ce qui contrôle leur composition. Les structures d'âge indiquent peu de différence dans le délai d'établissement du pin gris selon la composition. Les surfaces terrières des pins gris montrent de plus faibles coefficients d'asymétrie en mélange avec le bouleau qu'avec le peuplier, ce qui laisse à penser que le bouleau est un plus faible compétiteur. L'effet du bouleau sur le diamètre moyen du pin reflète la plus faible densité du pin en peuplements mélangés à du bouleau. La compétition interspécifique n'a cependant pas affecté le diamètre du pin à l'échelle de l'arbre. La compétition interspécifique est évitée par l'exclusion spatiale des espèces mise en évidence par la statistique de Ripley, ce qui reflète leur stratégies reproductives et l'historique du site.

Terrestrial LiDAR scanners have been shown to hold great potential for estimating and mapping three dimensional (3-D) leaf area distribution in forested environments. This is made possible by the capacity of LiDAR scanners to record the 3-D position of every laser pulse intercepted by plant material. The laser pulses emitted by a LiDAR scanner can be regarded as light probes whose transmission and interception may be used to derive leaf area density at different spatial scales using the Beer–Lambert law or Warren Wilson's contact frequency method among others. Segmenting the canopy into cubic volumes –or voxels- provides a convenient means to compute light transmission statistics and describe the spatial distribution of foliage area in tree crowns. In this paper, we investigate the optimal voxel dimensions for estimating the spatial distribution of within crown leaf area density. We analyzed LiDAR measurements from two field sites, located in Mali and in California, with trees having different leaf sizes during periods with and without leaves. We found that there is a range of voxel sizes, which satisfy three important conditions. The first condition is related to clumping and requires voxels small enough to exclude large gaps between crowns and branches. The second condition requires a voxel size large enough for the conditions postulated by the Poisson law to be valid, i.e., a turbid medium with randomly positioned leaves. And, the third condition relates to the appropriate voxel size to pinpoint the location of those volumes within the canopy which were insufficiently sampled by the LiDAR instrument to derive reliable statistics (occlusion effects). Here, we show that these requirements are a function of leaf size, branching structure, and the predominance of occlusion effects. The results presented provide guiding principles for using voxel volumes in the retrieval of leaf area distributions from terrestrial LiDAR measurements.

Tropical forests are considered important stocks of carbon and biodiversity. LiDAR is a technology that quantifies forest biomass in large areas. The estimation of aboveground biomass depends on the estimation of height which is itself influenced by the density of points acquired by aerial LiDAR. The mathematical model of this study evaluates the accuracy of estimating the maximum height of the canopy according to point density. This essay shows that the bias in height estimation is less in tropical forest than in boreal forest in northern Canada. This is certainly due to the different shape of the canopy, since the forest in northern Canada contains triangular conifers, while the Brazilian rainforest presents a rather flat canopy. This study then shows the effect of height estimation on forest biomass in Brazil. The underestimation is on average 50 Mg / ha for density data of 1 point / m², but from 3 points / m² the underestimation is almost negligible. However, the bias of aboveground biomass estimation does not appear to be important on low density data. Therefore, this study shows that it is not necessary to acquire high-density data on the Atlantic forest of Brazil for a biomass study based on height estimation.; Les forêts tropicales sont considérées comme des stocks de carbone et biodiversité importants. Le LiDAR est une technologie qui permet de quantifier la biomasse forestière sur de grands territoires. L’estimation de la biomasse aérienne dépend de l’estimation de la hauteur qui est elle-même influencée par la densité de points acquis par LiDAR aérien. Le modèle mathématique de cette étude permet d’évaluer la précision de l’estimation de la hauteur maximale de la canopée en fonction de la densité de points. Ce mémoire montre que le biais de l’estimation de la hauteur est moins important en forêt tropicale qu’en forêt boréale du Nord du Canada. Ce phénomène est certainement dû à la forme de la canopée qui diffère puisque la forêt du nord du Canada contient des conifères de forme triangulaire, alors que la forêt tropicale du Brésil présente une canopée plutôt plate. Cette étude montre ensuite l’effet de l’estimation de la hauteur sur la biomasse forestière du Brésil. La sous-estimation est en moyenne 50 Mg / ha pour les données de densité de 1 point / m², mais à partir de 3 points / m² la sous-estimation est quasiment négligeable. Le biais de l’estimation de la biomasse aérienne ne parait donc peu important sur des données à faible densité. Cette étude démontre qu’il n’est donc pas nécessaire d’acquérir de données à haute densité sur la forêt Atlantique du Brésil pour une étude de biomasse basé sur l’estimation de la hauteur.