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Plants are enormously diverse in their traits and ecological adaptation, even within given ecosystems, such as tropical rainforests. Accounting for this diversity in vegetation models poses serious challenges. Global plant functional trait databases have highlighted general trait correlations across species that have considerably advanced this research program. However, it remains unclear whether trait correlations found globally hold within communities, and whether they extend to drought tolerance traits.For 134 individual plants spanning a range of sizes and life forms (tree, liana, understorey species) within an Amazonian forest, we measured leaf drought tolerance (leaf water potential at turgor loss point, πtlp), together with 17 leaf traits related to various functions, including leaf economics traits and nutrient composition (leaf mass per area, LMA; and concentrations of C, N, P, K, Ca and Mg per leaf mass and area), leaf area, water‐use efficiency (carbon isotope ratio), and time‐integrated stomatal conductance and carbon assimilation rate per leaf mass and area. We tested trait coordination and the ability to estimate πtlp from the other traits through model selection. Performance and transferability of the best predictive model were assessed through cross‐validation.Here πtlp was positively correlated with leaf area, and with N, P and K concentrations per leaf mass, but not with LMA or any other studied trait. Five axes were needed to account for >80% of trait variation, but only three of them explained more variance than expected at random. The best model explained only 30% of the variation in πtlp, and out‐sample predictive performance was variable across life forms or canopy strata, suggesting a limited transferability of the model.Synthesis. We found a weak correlation among leaf drought tolerance and other leaf traits within a forest community. We conclude that higher trait dimensionality than assumed under the leaf economics spectrum may operate among leaves within plant communities, with important implications for species coexistence and responses to changing environmental conditions, and also for the representation of community diversity in vegetation models. [ABSTRACT FROM AUTHOR]

* Background and Aims In mountain ecosystems, predicting root density in three dimensions (3-D) is highly challenging due to the spatial heterogeneity of forest communities. This study presents a simple and semi-mechanistic model, named ChaMRoots, that predicts root interception density (RID, number of roots m-2). ChaMRoots hypothesizes that RID at a given point is affected by the presence of roots from surrounding trees forming a polygon shape. * Methods The model comprises three sub-models for predicting: (1) the spatial heterogeneity - RID of the finest roots in the top soil layer as a function of tree basal area at breast height, and the distance between the tree and a given point; (2) the diameter spectrum -- the distribution of RID as a function of root diameter up to 50mm thick; and (3) the vertical profile -- the distribution of RID as a function of soil depth. The RID data used for fitting in the model were measured in two uneven-aged mountain forest ecosystems in the French Alps. These sites differ in tree density and species composition. * Key Results In general, the validation of each sub-model indicated that all sub-models of ChaMRoots had good fits. The model achieved a highly satisfactory compromise between the number of aerial input parameters and the fit to the observed data. * Conclusions The semi-mechanistic ChaMRoots model focuses on the spatial distribution of root density at the tree cluster scale, in contrast to the majority of published root models, which function at the level of the individual. Based on easy-to-measure characteristics, simple forest inventory protocols and three sub-models, it achieves a good compromise between the complexity of the case study area and that of the global model structure. ChaMRoots can be easily coupled with spatially explicit individual-based forest dynamics models and thus provides a highly transferable approach for modelling 3-D root spatial distribution in complex forest ecosystems. [ABSTRACT FROM AUTHOR]

Abstract: Vegetation is increasingly used to protect artificial and natural slopes against shallow landslides. Mechanically, plant roots reinforce soil along a slope by providing cohesion (cr). cr is usually estimated using either of two models: a Wu and Waldron''s Model (WWM) or a Fiber Bundle Model (FBM). The WWM assumes that all fine and medium roots break simultaneously during shearing, whereas the FBM assumes progressive breakage of these roots. Both models are based on measurements of root density (RD), root tensile strength (Tr) and root orientation (Rf). RD is highly variable and influences cr significantly more than the other variables. We investigated RD in a mixed forest stand dominated by Fagus sylvatica and Abies alba growing at an altitude of 1400m and a mixed stand of Abies alba and Picea abies located at 1700m. We assumed that our sites were composed of different plant functional groups, i.e. (1) only trees and shrubs were present and (2) trees, shrubs and herbaceous plants coexisted within the same site. Results showed that RD was significantly influenced by soil depth, tree spatial density and species composition. cr was then estimated by the WWM and three different FBMs; each FBM differed in the manner that load was apportioned to the roots (as a function of root cross-sectional area (CSA), root diameter or number of intact roots). Results showed that c r values differed significantly depending on the model used: cr (FBM, root number)

Root respiration consumes an important part of the daily assimilated carbon but the magnitude of this component of forest net ecosystem exchange and its partitioning among the different energy demanding processes in roots are still poorly documented. 5-month old Eucalyptus cuttings were grown in a greenhouse in pot filled with coarse sand. They were fertilized with three different amounts of a slow-release fertilizer with the doses of 8, 24 and 48 g of nitrogen per plant. Root respiration was measured using an infrared gas analyser by perfusing air through the pot on 9 plants per treatment on three dates 14 days apart. Measure of root respiration of the three treatments over time was made in order to obtain a large range of growth and nutrient uptake. Root respiration normalized at 22°C ranged from 0.09 to 0.23 gC d−1 for the three treatments during all the experiment. It was well predicted with a model that includes root growth rate and root nitrogen content.The nitrogen related maintenance coefficient was negatively correlated to the root nitrogen concentration suggesting a decrease in protein turnover with increasing fertility. Growth rate of fine root in a virtual stand was simulated using age-related allometric equations and further used to estimate root respiration in the field. Simulated root respiration increased over time from 0.39 to 3.14 gC m−2 d−1 between 6 and 126 months assuming a turnover of 2 yr−1 for fine roots. The major fraction of simulated root respiration in the field (78–92%) was used for the maintenance of the existing biomass. [ABSTRACT FROM AUTHOR]

In timber production, there is a need to select the right log for a given end-product. To achieve this objective, individual tree characteristics (total height, diameter at breast height and age) and external measurements made on the log shape were combined. In this study, three possible methods are analyzed to assess the number of annual rings for a given Picea abies (L.) Karst. log using modelling. The first method consists of finding a link between the number of rings and the size, the taper and the location of the log in the tree. The second one is based on the log location in the tree and the use of an height-age growth model. The third involves the whorl location inside the log and the use of an individual height-age growth model. The three methods are compared on the basis of the amount of data required by each and error analysis. [ABSTRACT FROM AUTHOR]

In forest ecosystems, the specific influence of soil resources on stand productivity is difficult to assess because many other ecological variables also affect tree growth. In this study, we took advantage of a natural soil gradient, from shallow calcic soil to deep acidic soil, all with similar climate, atmospheric depositions, species composition and management, to determine the relationship between soil nutritive resources and the growth and mineral nutrition of a beech ( Fagus sylvatica ) mature forest of Northeastern France. Soil resources were assessed through the quantification of the stocks of available water and mineral nutrients (Ca, Mg, K and P 2 O 5 ). Beech stand growth and mineral nutrition were determined through the use of several indicators, i.e., standing aboveground biomass and annual biomass production, potential growth index (prediction of the height of dominant trees at 100 years) and foliar nutrient content. We observed a gradient of nutritive resources in soils as well as a gradient of stand growth on the study site: the current aboveground biomass was highest on the calci-brunisol which presented the highest water and nutrient stocks while it was lowest on the rendisol, characterized by a very low water holding capacity and a very low stock of available K. However, the growth of beech trees on the rendisol was equivalent to the highest growth classes of beech trees in France, and K nutrition was optimal. Observations on the study site suggest that, in favorable climate conditions, some biological adaptation processes, such as an efficient root colonization as well as an efficient nutrient cycling may allow to maintain stand growth and nutrition on soils with low water and nutrient reserves. The fertility of forest soils has thus to be assessed in a dynamic way by integrating nutrient fluxes as well as the adaptations of trees to environmental constraints. The biological processes become an increasingly important part in the conservation of soil fertility, notably in the perspective of global changes. [ABSTRACT FROM AUTHOR]

Many forest soils are acidic and have very low plant-available pools of magnesium. Past and present sylvicultural, nutritional and/or climatic pressures endured by forest ecosystems can result in net losses of nutrients and ecosystem function losses. Liming with a carbonate product is an alternative to counteract these degradations but the effects of liming on the biogeochemical cycling of nutrients over time and the dynamics of Mg released from liming products are still unclear. We studied the Mg isotopes composition in four paired-treatment experimental beech forest ecosystems in northern France. At the sites where dolomitic lime was applied, the variation in exchangeable and foliar δ26Mg demonstrated the direct contribution of dolomite-derived Mg to the replenishment of topsoil exchangeable pools and to tree nutrition improvement: dolomite-derived Mg was incorporated into the biological cycling which allows its retention on the mid to long term in the soil–plant system. At the sites limed with calcium carbonate, the changes in exchangeable and foliar Mg contents and δ26Mg observed on the long term suggest that the applied product contained a small amount of Mg and/or that Mg cycling changed after liming, to cope in particular with the low Mg availability. Lastly, our results highlight the high δ26Mg of the organic layer (humus): fractionation processes occurring within this layer (mineralization/ageing of organic matter, preferential retention of 26 Mg) could explain these singular signatures that could greatly influence the topsoil Mg exchangeable pools. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

Harvest residue management is a key issue for the sustainability of Eucalyptus plantations established on poor soils. Soil microbial communities contribute to soil fertility by the decomposition of the organic matter (OM), but little is known about the effect of whole-tree harvesting (WTH) in comparison to stem only harvesting (SOH) on soil microbial functional diversity in Eucalyptus plantations. We studied the effects of harvest residue management (branches, leaves, bark) of Eucalyptus grandis trees on soil enzymatic activities and community-level physiological profiles in a Brazilian plantation. We measured soil microbial enzymatic activities involved in OM decomposition and we compared the community level physiological profiles (CLPP) of the soil microbes in WTH and SOH plots. WTH decreased enzyme activities and catabolic potential of the soil microbial community. Furthermore, these negative effects on soil functional diversity were mainly observed below the 0–5 cm layer (5–10 and 10–20 cm), suggesting that WTH can be harmful to the soil health in these plantations. [ABSTRACT FROM AUTHOR]

Abstract A growing demand for renewable carbon (C) has led to intensified forest management resulting in the use of forest residues (e.g. canopy, bark or litter layer) as energy sources with potential modifications of soil properties and tree productivity. Because microbes mediate the recycling of C and nutrients sequestered in organic matter, we investigated the effects of organic matter (OM) removal on soil properties, root surfaces, microbial functions and abundance using a new observational forest network. We compared leaf litter and logging residue removal plots to reference plots in six beech forests located in the northern half of France. After three consecutive years of OM removal, C and nitrogen (N) pools were not affected, but OM exportation decreased the cation exchange capacity and available phosphorus (P) pool by respectively 12% and 30% in the topsoil (0–5 cm depth). Fine root surface area significantly increased by 21% in the subsoil (5–10 cm depth) in response to OM removal. Enzymatic activities involved in N and P mobilisation decreased from 12 to 38% with the manipulation of OM. Community-level profiling (CLPP) based on BIOLOG approach revealed that the metabolic potential of the microbial community strongly decreased in response to OM removal. Our results indicated that intensive forestry could affect microbial functions implicated in nutrients mobilisation. We demonstrated that soil organic matter (SOM) content is a predictor of microbial functions resistance to forest residue removal. We recommend that intensive forestry should be reduced or limited in beech forests characterised by low soil OM contents. Highlights • Soil microbial functions change in the short term in response to organic matter removal. • Organic matter removal leads to a decrease in the microbial activities involved in nitrogen and phosphorus mobilisation. • The initial soil organic matter content is a predictor of microbial function sensitivity to organic matter removal. [ABSTRACT FROM AUTHOR]

Summary: Fungal succession in rotting wood shows a surprising abundance of ectomycorrhizal (EM) fungi during the late decomposition stages. To better understand the links between EM fungi and saprotrophic fungi, we investigated the potential capacities of the EM fungus Paxillus involutus to mobilize nutrients from necromass of Postia placenta, a wood rot fungus, and to transfer these elements to its host tree. In this aim, we used pure cultures of P. involutus in the presence of labelled Postia necromass (15N/13C) as nutrient source, and a monoxenic mycorrhized pine experiment composed of labelled Postia necromass and P. involutus culture in interaction with pine seedlings. The isotopic labelling was measured in both experiments. In pure culture, P. involutus was able to mobilize N, but C as well, from the Postia necromass. In the symbiotic interaction experiment, we measured high 15N enrichments in all plant and fungal compartments. Interestingly, 13C remains mainly in the mycelium and mycorrhizas, demonstrating that the EM fungus transferred essentially N from the necromass to the tree. These observations reveal that fungal organic matter could represent a significant N source for EM fungi and trees, but also a C source for mycorrhizal fungi, including in symbiotic lifestyle. [ABSTRACT FROM AUTHOR]

The relationship between forest productivity and tree species diversity has been described in detail, but the underlying processes have yet to be identified. One important issue is to understand which processes are at the origin of observed aboveground overyielding in some mixed forests. We used a beech-maple plantation exhibiting aboveground overyielding to test whether belowground processes could explain this pattern. Soil cores were collected to determine fine root (FR) biomass and vertical distribution. Correlograms were used to detect spatial arrangement. Near-infrared reflectance spectroscopy was used to identify the tree species proportion in the FR samples and spatial root segregation. An isotopic approach was used to identify water acquisition patterns. The structure and the composition of the ectomycorrhizal fungal community were determined by high-throughput sequencing of DNA in the soil samples. We found no spatial pattern for FR biomass or for its vertical distribution along the gradients. No vertical root segregation was found, as FR density for both species decreased with depth in a similar way. The two species displayed similar vertical water acquisition profiles as well, mainly absorbing water from shallow soil layers; hence, niche differentiation for water acquisition was not highlighted here. Significant alterations in the fungal community compositions were detected in function of the percentage of maple in the vicinity of beech. Our findings do not support the commonly suggested drivers of aboveground overyielding in species-diverse forests and suggest that competition reduction or between-species facilitation of belowground resource acquisition may not explain the observed aboveground overyielding. [ABSTRACT FROM AUTHOR]

In agroforestry systems, shade trees strongly affect the physiology of the undergrown crop. However, a major paradigm is that the reduction in absorbed photosynthetically active radiation is, to a certain extent, compensated by an increase in light-use efficiency, thereby reducing the difference in net primary productivity between shaded and non-shaded plants. Due to the large spatial heterogeneity in agroforestry systems and the lack of appropriate tools, the combined effects of such variables have seldom been analysed, even though they may help understand physiological processes underlying yield dynamics. In this study, we monitored net primary productivity, during two years, on scales ranging from individual coffee plants to the entire plot. Absorbed radiation was mapped with a 3D model (MAESPA). Light-use efficiency and net assimilation rate were derived for each coffee plant individually. We found that although irradiance was reduced by 60% below crowns of shade trees, coffee light-use efficiency increased by 50%, leaving net primary productivity fairly stable across all shade levels. Variability of aboveground net primary productivity of coffee plants was caused primarily by the age of the plants and by intraspecific competition among them (drivers usually overlooked in the agroforestry literature) rather than by the presence of shade trees. [ABSTRACT FROM AUTHOR]

The growing demand for renewable materials and energy leads to intensified forest management practices. Therefore, combining high forest productivity and soil carbon storage capacity with lower quantities of organic matter (OM) left on the ground to decompose represents a major challenge. Although microbial communities drive processes responsible for organic carbon stabilization in soil, we have limited knowledge of how the inputs of superficial OM affect the richness and composition of soil microbial communities. This study determined the impacts of OM removal on soil bacteria and fungi at six sites across French temperate forests using high-throughput amplicon sequencing. After three years of OM manipulation, we measured an alteration of the bacterial copiotrophic and fungal saprotrophic abundance and richness. Furthermore, aboveground OM removal reshaped microbial communities toward bacterial oligotrophic and fungal ectomycorrhizal-dominated populations, which are less efficient for OM decomposition. Finally, we proposed that understanding the response of soil microbial communities to variations in OM inputs should help anticipate future functional changes in forest ecosystems submitted to the intensification of silvicultural practices. • Organic matter removal changed the taxonomic composition of soil bacterial and fungal communities. • Organic matter removal increased the bacterial oligotroph:copiotroph OTU richness and abundance ratios. • Organic matter removal increased the fungal ectomycorrhizal:saprotroph OTU richness and abundance ratios • Organic matter removal reduced fungal association network complexity. [ABSTRACT FROM AUTHOR]

The compilation of GHG inventories has become a common practice to support environmental decision- and policy-making, for example in the context of the UNFCCC. To estimate GHG emissions, simulation models present viable alternatives to measured data. In order to make an informed decision on model selection, clear information on the purpose and applicability of a particular model is needed. This article discusses model requirements with respect to the suitability of estimating the carbon balance of dead wood and litter (dead organic matter; DOM) and soil in forests with a particular focus on policy needs under international processes such as the UNFCCC. Based on criteria established for GHG reporting under the UNFCCC including transparency, consistency, comparability, completeness and accuracy, this paper presents an approach to classify commonly used simulation models for estimating C budgets of DOM and soil in European forests. Among the six discussed models, the authors found a clear trend toward models for providing quantitatively precise, site-specific estimates. To meet reporting needs for national GHG inventories, the authors conclude that there is a need for models producing qualitative realistic and unbiased estimates at larger scales in a transparent and comparable manner. [ABSTRACT FROM PUBLISHER]

Recent developments in the field of airborne laser scanning offer new possibilities to map different forest attributes and improve forest inventory accuracy. In this work, two methods of LiDAR point clouds segmentation were used to obtain new variables and assess the gain in accuracy to estimate dominant height, basal area and volume, in three contrasted forest stands. The originality of this approach is to combined segmentation methods and standards metrics based on height distribution summarized at the "plot" level. The information obtained using the segmentation variables were compared to those obtained by the "standard" method initially proposed by Næsset (1997). The results confirm the advantage of combining the two methods. For basal area and volume, R² of 0.92 and 0.95, and mean square errors of 4.6 m²/ha (16%) and 72.4 m³/ha (17%) were obtained respectively. For dominant height, model error is in the range of field measurement error (estimated to be less than 1 m). So, it seems that segmentation allows an improvement of forest attributes estimations. The robustness of these findings remains to be evaluated on a larger number of stands and varied configurations of LiDAR acquisitions. [ABSTRACT FROM AUTHOR]

Aims: Tropical plantations are likely to supply a growing share of the increasing world demand for forest products. We aimed to gain insight into the role of the nitrogen (N) contained in harvest residues (HR) for tree growth and soil N stocks. Methods: We used 15N-labeled harvest residues to (1) study the dynamic of N release throughout decomposition, (2) determine the vertical transport pathways of N from the forest floor to the upper soil layers, and (3) quantifying the contributions of HR to soil N stocks and the supply of N to young Eucalyptus trees. Results: Almost all of the 15N initially contained in the HR was recovered 27 months after deposition, with 21 % remaining in HR, 38 % being transferred to the underlying O layer, 21 % being transferred to the 0-15 cm soil layer, and approximately 15 % accumulating in the tree biomass. Our results supported the presence of two pathways of N transfers from the O layer to the mineral soil: (1) the leaching of dissolved 15N from fresh litter during the first year after planting which actively contributed to Eucalyptus N nutrition and (2) the transport of particulate organic matter in percolating water which contributed to maintain N stocks in the first 15 cm of the soil. Approximately 40 % of the N content in 2-year-old Eucalyptus trees was derived from the labeled HR. Conclusions: The sustainability of fast-growing Eucalyptus trees established on N-poor sandy tropical soils largely relies on organic residues, as an early source of mineral N for tree and as a source of organic N in the top soil. [ABSTRACT FROM AUTHOR]

GlobAllomeTree is an international platform for tree allometric equations. It is the first worldwide web platform designed to facilitate the access of the tree allometric equation and to facilitate the assessment of the tree biometric characteristics for commercial volume, bio-energy or carbon cycling. The webplatform presents a database containing tree allometric equations, a software called Fantallomatrik, to facilitate the comparison and selection of the equations, and documentation to facilitate the development of new tree allometric models, improve the evaluation of tree and forest resources and improve knowledge on tree allometric equations. In the Fantallometrik software, equations can be selected by country, ecological zones, input parameters, tree species, statistic parameters and outputs. The continuously updated database currently contains over 5000 tree allometric equations classified according to 73 fields. The software Fantallometrik can be also used to compare equations, insert new data and estimate the selected output variables using field inventory. The GlobAllomeTree products are freely available at the URL: http://globallometree. org for a range of users including foresters, project developers, scientist, student and government staff. [ABSTRACT FROM AUTHOR]

Background:Quantifying the dynamics of root growth is vital when characterising the role of vegetation in carbon cycling. Aims:We examined the temporal dynamics of root growth and responses to spatial (altitude, forest patchiness and soil depth) and biological factors (root diameter and root topology) in mid-montane and upper montane coniferous forest ecosystems. Methods:Using rhizotrons, two indicators were investigated: occurrence, i.e. the proportion of roots which had elongated since the previous measurement of root elongation (%), and daily root elongation speed (mm d−1) once the elongation occurred. Results:Spatial factors had a limited effect on root growth. Roots in the same diameter class possessed different elongation speeds and this was related to topological ranking, reflecting a disparity in physiological activity. Temporally, the occurrence of root elongation reached a peak in May–October (up to 90%) and sharply dropped after October 2010. The maximum root elongation speed (mean: 3.0 mm d−1) was measured in July–August. Root growth was the most inactive in February 2011 but some roots still exhibited positive elongation speeds (mean: 0.5 mm d−1). Occurrence and speed of elongation reacted differently with regard to environmental and biological factors. Conclusions:Temporal and biological factors contributed more towards explaining the variability of root growth than spatial factors. In future studies, both occurrence and speed of elongation should be used to characterise root growth. [ABSTRACT FROM AUTHOR]

Background and aims: Plant roots provide mechanical cohesion ( c) to soil on slopes which are prone to shallow landslides. c varies in heterogeneous natural forests due to the spatial, inter- and intra-annual dynamics of root demography. Characterizing root initiation density and mortality, as well as how root growth is influenced by abiotic and biotic factors is essential for exploring a root system's capacity to reinforce soil. Methods: In this study, root demography data were monitored using field rhizotrons during 1.5 years in two naturally regenerated mixed forests in the French Alps. These forests are composed of trees growing in groups (tree islands) with large gaps between the islands. Three categories of driving variables were measured: (i) spatial factors: altitude (1,400 m, 1,700 m), ecological patch (gap, tree island), soil depth (0.0-1.0 m divided into five layers of 0.2 m); (ii) temporal factors: month (12 months from March 2010 to February 2011), winter (winter of 2009-2010 and 2010-2011); (iii) biological factors: root diameter classes (]0, 1] mm, ]1, 2] mm, ]2, 5] mm (according to the international standard ISO 31-11, ] x, y] denotes a left half-open interval from x (excluded) to y (included)). Two types of two-part models, a Hurdle model (H) and a Zero-inflated model (ZI) were used to fit root data with a high zero population, i.e. if root initiation or mortality was zero during a given time period, or if roots were not present at all points throughout a soil profile. Results: Root initiation quantity decreased with increasing soil depth, as well as being lower in tree islands. Both soil depth and ecological patch interacted strongly with altitude. Root dynamics were significantly less active with a lower net production and c increment in winter and spring than in summer and autumn. Roots which were ]1, 2] mm in diameter contributed the most to c compared to other diameter classes, as they had a high production but a low mortality. With regard to model selection, both H and ZI demonstrated similar outcomes and underestimated extreme values of root demography data. Conclusion: All factors contributed towards explaining the variability of root demography and c. We suggest taking into consideration the seasonality of root dynamics when studying root reinforcement. [ABSTRACT FROM AUTHOR]

Land use changes such as savannah afforestation with eucalypts impact the soil carbon (C) balance, therefore affecting soil CO efflux ( F), a major flux in the global C cycle. We tested the hypothesis that F increases with stand age after afforestation, due to an increasing input of fresh organic matter to the forest floor. In a Eucalyptus plantation established on coastal savannahs in Congo, bimonthly measurements of F were carried out for 1 year on three adjacent stands aged 0.9, 4.4 and 13.7 years and presenting similar growth patterns. Litterfall and litter accumulation on the forest floor were quantified over a chronosequence. Equations were derived to estimate the contribution of litter decomposition to F throughout the rotation. Litterfall increased with stand age after savannah afforestation. F, that was strongly correlated on a seasonal basis with soil water content (SWC) in all stands, decreased between ages 0.9 year and 4.4 years due to savannah residue depletion, and increased between ages 4.4 years and 13.7 years, mainly because of an increasing amount of decomposing eucalypt litter. The aboveground litter layer therefore appeared as a major source of CO, whose contribution to F in old stands was estimated to be about four times higher than that of the eucalypt-derived soil organic C pool. The high litter contribution to F in older stands might explain why 13.7 years-old stand F was limited by moisture all year round whereas SWC did not limit F for large parts of the year in the youngest stands. [ABSTRACT FROM AUTHOR]

Background and Aims Despite their importance for plant production, estimations of below-ground biomass and its distribution in the soil are still difficult and time consuming, and no single reliable methodology is available for different root types. To identify the best method for root biomass estimations, four different methods, with labour requirements, were tested at the same location. Methods The four methods, applied in a 6-year-old Eucalyptus plantation in Congo, were based on different soil sampling volumes: auger (8 cm in diameter), monolith (25 × 25 cm quadrate), half Voronoi trench (1·5 m3) and a full Voronoi trench (3 m3), chosen as the reference method. Key Results With the reference method (0–1m deep), fine-root biomass (FRB, diameter <2 mm) was estimated at 1·8 t ha−1, medium-root biomass (MRB diameter 2–10 mm) at 2·0 t ha−1, coarse-root biomass (CRB, diameter >10 mm) at 5·6 t ha−1 and stump biomass at 6·8 t ha−1. Total below-ground biomass was estimated at 16·2 t ha−1 (root : shoot ratio equal to 0·23) for this 800 tree ha−1 eucalypt plantation density. The density of FRB was very high (0·56 t ha−1) in the top soil horizon (0–3 cm layer) and decreased greatly (0·3 t ha−1) with depth (50–100 cm). Without labour requirement considerations, no significant differences were found between the four methods for FRB and MRB; however, CRB was better estimated by the half and full Voronoi trenches. When labour requirements were considered, the most effective method was auger coring for FRB, whereas the half and full Voronoi trenches were the most appropriate methods for MRB and CRB, respectively. Conclusions As CRB combined with stumps amounted to 78 % of total below-ground biomass, a full Voronoi trench is strongly recommended when estimating total standing root biomass. Conversely, for FRB estimation, auger coring is recommended with a design pattern accounting for the spatial variability of fine-root distribution. [ABSTRACT FROM AUTHOR]

Regional above-ground biomass estimates for tropical moist forests remain highly inaccurate mostly because they are based on extrapolations from a few plots scattered across a limited range of soils and other environmental conditions. When such conditions impact biomass, the estimation is biased. The effect of soil types on biomass has especially yielded controversial results. We investigated the relationship between above-ground biomass and soil type in undisturbed moist forests in the Central African Republic. We tested the effects of soil texture, as a surrogate for soil resources availability and physical constraints (soil depth and hydromorphy) on biomass. Forest inventory data were collected for trees ≥20 cm stem diameter in 2754 0.5 ha plots scattered over 4888 km. The plots contained 224 taxons, of which 209 were identified to species. Soil types were characterized from a 1:1 000 000 scale soil map. Species-specific values for wood density were extracted from the CIRAD's data base of wood technological properties. We found that basal area and biomass differ in their responses to soil type, ranging from 17.8 m ha (217.5 t ha) to 22.3 m ha (273.3 t ha). While shallow and hydromorphic soils support forests with both low stem basal area and low biomass, forests on deep resource-poor soils are typically low in basal area but as high in biomass as forests on deep resource-rich soils. We demonstrated that the environmental filtering of slow growing dense-wooded species on resource-poor soils compensates for the low basal area, and we discuss whether this filtering effect is due to low fertility or to low water reserve. Synthesis. We showed that soil physical conditions constrained the amount of biomass stored in tropical moist forests. Contrary to previous reports, our results suggest that biomass is similar on resource-poor and resource-rich soils. This finding highlights both the importance of taking into account soil characteristics and species wood density when trying to predict regional patterns of biomass. Our findings have implications for the evaluation of biomass stocks in tropical forests, in the context of the international negotiations on climate change. [ABSTRACT FROM AUTHOR]

Abstract: A nitrogen budget study of a highly fertilized coffee plantation growing on an Acrisol (Ultisol: Ustic Paleohumult) in Southern Costa Rica provided clear evidence of low nitrate (NO3 −) leaching to groundwater, in spite of a large annual rainfall and fairly high soil permeability. In this study, conducted at the same site, we measured soil properties in relation to nitrate adsorption. The clay content and proportion of kaolinite were high in the 80–200cm layer and decreased below, whereas the proportion of gibbsite and to a lesser extent of iron oxi-hydroxides increased below 200cm. Nitrate adsorption isotherms were measured. Nitrate adsorption maxima [coefficient a (N max ) of the Langmuir equation] ranged from 1.9 to 1.6cmolc kg−1 between 80 and 200cm depth and decreased below to reach a value of 0.9cmolc kg−1 at 380cm depth. Anion exchange capacity and nitrate adsorption maxima were positively correlated with the clay and kaolinite contents, and negatively with gibbsite content and the net charge, assessed from the difference between soil pH in KCl and in distilled water. Nevertheless, the sorption affinity of NO3 − to mineral surfaces, (coefficient b of the Langmuir equation), was highly correlated with the net charge and with the occurrence of gibbsite and iron oxi-hydroxides. We measured in the field a large NO3 −–N accumulation in the sub-soil (up to 1570kg of NO3 −–Nha−1 retained between 80 and 380cm depth). In the layer 80–200cm, where the clay size fraction was dominated by kaolinite, 55 to 75% of the stored NO3 − could be extracted by shaking soil in distilled water. In this soil layer, the NO3 − content was positively related to the net positive charge. In the layer 200–380cm, where the clay size fraction was dominated by gibbsite, the proportion of NO3 − extractable in distilled water was lower (45%) than above. Using adsorption coefficients obtained from batch experiments, we computed retardation factors for NO3 − leaching up to 16 pore volumes in deep layers. Therefore, NO3 − adsorption has already delayed and may further delay groundwater contamination over decades in these tropical Acrisols. Deep rooting perennial species may take advantage of this subsoil NO3 −, either after abandoning agriculture, or in agroforestry systems. [Copyright &y& Elsevier]

Soil organic matter is a key factor in the global carbon cycle, but the magnitude and the direction of the change in soil carbon after afforestation with Eucalyptus in the tropics is still a matter of controversy. The objective of this work was to understand the dynamics of soil carbon in intensively managed Eucalyptus plantations after the afforestation of a native savannah. The isotopic composition ( δ) of soil carbon (C) and soil CO2 efflux ( F) were measured on a four-age chronosequence of Eucalyptus and on an adjacent savannah. δF was used to partition F between a C3 component and a C4 component, the latter corresponding to the decomposition of a labile pool of savannah-derived soil carbon ( CSL). The mean residence time of CSL was 4.6 years. This further allowed us to partition the savannah-derived soil carbon into a labile and a stable ( CSS) carbon pool. CSL accounted for 30% of soil carbon in the top soil of the savannah (0–5 cm), and only 12% when the entire 0–45 cm soil layer was considered. The decrease in CSL with time after plantation was more than compensated by an increase in Eucalyptus-derived carbon, and half of the newly incorporated Eucalyptus-derived carbon in the top soil was associated with the clay and fine silt fractions in the 14-year-old. stand. Increment in soil carbon after afforestation of tropical savannah with Eucalyptus is therefore expected despite a rapid disappearance of the labile savannah-derived carbon because a large fraction of savannah-derived carbon is stable. [ABSTRACT FROM AUTHOR]

Abstract: Sun-shade models proved to be simple, fast and reliable tools for estimating the fraction of absorbed PAR (fAPAR) and the photosynthesis of low and simple canopies (e.g. wheat). Applications on tall canopies, or non-ideal canopies (e.g. row-planting, azimuthal heterogeneity, clumping, non-spherical leaf angle distribution, large proportion of non-green elements) were limited so far. We attempted to apply the Sun-shade model proposed by de Pury and Farquhar [de Pury, D.G.G., Farquhar, G.D., 1997. Simple scaling of photosynthesis from leaves to canopies without the errors of big-leaf models. Plant Cell Environ. 20, 537–557] at the scale of the non-ideal canopy of adult coconut palms. The gap fractions of the whole cover, fraction of intercepted PAR (fIPAR), clumping index and leaf orientation derived from LAI-2000 (PCA) were closely matching the simulations of a reference 3D architectural model (3DM) used for cross-validation. Moreover, 3DM supplied a relationship for down-scaling the gap-fractions from the whole cover to green elements of the canopy. The derived Sun-shade simulations of fAPAR by green leaves agreed within 5% with 3DM, on a half-hourly time-step and for 1 year, confirming combined PCA and Sun-shade methods as a fast and reliable tool, even for tall or complex canopies. fIPAR and plant area index (PAI) were compared with the coconut literature and an empirical model was proposed for estimating fIPAR from age and planting density. The coefficient of extinction, K, was adjusted to 0.33 for the regular range of planting density. [Copyright &y& Elsevier]

Abstract: A multi-site and multi-age set of in situ 15N-labelled litter decomposition experiments was carried out in various European beech forests. The sites presented contrasted situations of climate and humus type that were representative of northern Europe temperate forests. 15N-labelled leaf litter was produced by urea spraying in an experimental beech plot, and was used in litter decomposition experiments over a 3–6-year period, depending on the site. Schemes of decomposition covered a wide range of situations, some of them not expected, like high decay rate on Moder humus forms or slow decomposition on Mull humus form. The objectives of this study were to determine how nitrogen release and/or incorporation rates could characterize litter decomposition dynamics. A carbon and nitrogen coupled model of decomposition based on the quality theory was used to fit the given data. High correlation coefficients and unbiased fitting were obtained both for carbon and nitrogen . The theoretical concept of quality was somewhat lightened and related to decomposer activity: low rates of quality decrease were associated with high decomposition rates, showing that when decomposers are sufficiently supplied with labile carbon from the humus they decompose litter more completely than when they are carbon limited. Provided that the degrading substrate stoichiometry was kept constant (i.e. C loss /N loss ratio), the same litter decomposition could be processed at different rates. Taking seasonal variations of the parameters into account is likely to improve our understanding, but further experiments at more frequent intervals are needed. [Copyright &y& Elsevier]

Abstract: For open canopies, the partitioning of energy and water fluxes between the upper canopy and the under-storey is key to understand the competition mechanisms between layers. We monitored stand evapo-transpiration by eddy-covariance (E), tree transpiration ( T ) by heat-dissipative sapflow, soil (G) and stand (J) heat storage during 3 years in a typical coconut palm row-plantation of the humid tropics, displaying a constant leaf area index (LAI=3) and a grass under-storey. A two-level flux experiment yielded cross-validation of the evapo-transpiration of the under-storey (E u) with E − T , through energy balance closure for E and sapflow calibration in the laboratory for T . On a yearly time step, E represented 40% of rainfall, the sensible heat flux (H) was 26% of net radiation and the Bowen ratio was 0.39, all indicating that water availability was close-to-optimum. T represented 68% of E, close to the 75% of soil coverage by palms. The inter-annual variability was low for potential evapo-transpiration (ET o), energy and water fluxes. The seasonal variability was more pronounced, driven by radiation and vapour pressure deficit (VPD). The canopy conductance of coconut palms appeared to be strongly controlled by VPD. Given its constant LAI, its continuous growth and its simple architecture, the coconut palm appears to be an ideal candidate for physiological work and agroforestry modelling. [Copyright &y& Elsevier]