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Graphical abstract Highlights • Whole Tree Harvesting can impact temperate forest soil macrofauna communities. • Responses of soil macrofaunal community were studied on 4 sites with 2 tree species. • Organic matter export lead to a decrease of total abundance of soil macrofauna. • Four macrofaunal bioindicators of organic matter export were highlighted. Abstract Numerous studies predict a short-term important decrease in fossil resources and stress the need to develop alternative renewable energies, thus European countries aim at increasing biomass production for energetic purposes. One such source of bioenergy could be obtained from forest biomass pools by exporting logging residues, yet this practice would have strong impacts on forest ecosystems (e.g. disturbance of soil biodiversity and chemical properties). Most studies on biomass removal effects focused on boreal forests but responses in temperate forests are still scarcely studied. Soil macrofauna is involved in forest ecosystem functioning through numerous chemical, physical and biological processes and multiple interactions with other organisms. A disturbance of the soil macrofauna community can thus lead to a response of the forest ecosystem as a whole. Experimental plots were set up in 6 northern France forests (either dominated by oak or beech), with a treatment corresponding to Whole Tree Harvesting (WTH) practices compared to control, in order to characterize the response of soil macrofaunal communities to organic matter (OM) export. Our study showed that OM export leads to a short-term loss of abundance in macrofaunal communities in temperate deciduous forest soils that can also lead to an alteration of soil OM cycle, and revealed that the breadth of this negative impact is modulated by tree species and faunal trophic groups. Furthermore, some results of community responses were directly applicable to forest management as marked responses of several taxa revealed four bioindicators of OM disturbance. Therefore, the level of disturbance related to new forest management practices, such as WTH to increase forest biofuel yields, (i) could be characterized by surveying either total soil macrofauna or using tools such as bioindicator taxa and (ii) should be assessed regarding tree stand identity. [ABSTRACT FROM AUTHOR]

Most forest ecosystems grow on acid and nutrient poor soils. In many cases, a slow degradation of forest soil chemical fertility due to increasing external pressures (decreasing atmospheric inputs, intensification of biomass harvesting and silvicultural practices) has been observed and is a growing concern in the international forest community. When the pressure endured by low fertility forest ecosystems is too intense, nutrient losses and ecosystem function losses may occur, forest decline being the ultimate stage of this process. In such cases, forest liming with a carbonate product is a solution to restore soil fertility and reduce soil acidity, globally improve the ecosystem functioning and compensate for nutrient losses caused by biomass harvest and exportation. However, the effects of liming on ecosystem processes and the biogeochemical cycling of nutrients in forest ecosystems are still unclear. We studied the dynamics of magnesium and calcium originating from the dissolution of liming products in the different compartments (organic and mineral soil layers and, aboveground biomass) of five long-term (20 to 40 years) monitoring beech ( Fagus sylvatica L.) plots located in Northern France from ecosystem magnesium and calcium budgets. Compared to the control plots, soil exchangeable pools of Mg and Ca in the 0–15 cm mineral soil layer increased during the first decade after liming but these differences rapidly decreased after 20–30 years. The effect of liming on foliar concentrations and tree growth was still observed after 40 years, most probably because the biological cycling of these elements was more dynamic in the limed plots. Liming increased the decomposition rate of the soil organic layer but the pools of Mg and Ca in this layer remained relatively stable over time, probably because Mg and Ca concentrations in foliage and litterfall increased after the liming. Liming effects varied between sites depending on the liming product and amount, and the initial chemical fertility level of the soil. Although liming operations may help improve forest soil fertility, they may also generate nutrient deficiencies and/or imbalances for nutrients that are poorly available in the soil. The planning of liming operations therefore necessitates a thorough soil chemical fertility diagnosis. [ABSTRACT FROM AUTHOR]

Unlike Eucalyptus monocultures, nitrogen fixing trees are likely to improve the soil nutrient status through the decomposition of N-enriched litter. The Home Field Advantage (HFA) hypothesis states that plants can create conditions that increase the decomposition rates of their own litter. However, there may not be any HFA when most of the decomposers are generalists. A reciprocal transplant decomposition experiment of fine roots and leaves of Acacia mangium and Eucalyptus grandis was undertaken in monocultures of these two species to test the HFA hypothesis using a complete randomized design with three blocks. Three litterbags containing leaf or fine root residues of each species were collected every 3 months from each plot over 12 months for fine roots and 24 months for leaves. The litter mass and C, N and P concentrations were measured at each sampling date. The concentrations of C-compounds were measured 0, 12 and 24 months from the start of the experiment. There was no evidence of HFA for either the leaves or the fine roots of either species. The decomposition rates were slower for Acacia litter than for Eucalyptus litter even though initial N concentrations were 1.9–2.9 times higher and P concentrations were 1.5–3.3 times higher in the Acacia residues. N:P ratios were greater than 20–30 for the residues of both species, with the highest values for Acacia . Litter decomposition depended partly on the C quality of the litter, primarily in terms of water soluble compounds and lignin content. As shown recently in tropical rainforests, these results suggest that the activity of decomposers is limited by energy starvation in tropical planted forests. Decomposer activity may also have been limited by P availability which may not have been directly related to the P concentrations or C:P ratios in the residues. [ABSTRACT FROM AUTHOR]

Climate-mitigation strategies encourage the use of forest products and wood energy. This will likely increase the risk of soil depletion through nutrient exportation. Given the high variability in nutrient concentrations within and between trees, it is crucial to better understand the biochemical patterns of nutrient distribution and the related driving factors. Thus, predictions of nutrient concentrations can be improved, and used for assessing nutrient exportation through roundwood exploitation and for developing forest-management rules to maintain soil fertility. Our aims were to better determine (1) the shapes of the relationships between the total concentrations of different nutrients (N, S, P, K, Ca, Mg, Mn) in roundwood and roundwood diameter; (2) the variation of these relationships between different tissues (wood, bark); and (3) potential effects of site conditions and/or stand age on nutrient concentrations. We therefore developed a new modelling approach that relied on empirical and mechanistic relationships, and allowed for sound predictions of both concentrations in individual tissues and in total. We applied the approach to Fagus sylvatica using 134 trees from 11 plots that covered large ranges of ecological conditions in terms of geographic region (from the northwest to the northeast of France), site index (from <25 m to >35 m), stand age (form 10 years to 159 years), and roundwood diameter with nutrient concentrations being measured separately for wood and bark tissues partly up to a minimum diameter of 1 cm. Relationships between total nutrient concentrations and roundwood diameter showed several different shapes: a reverse-J-shape for N, S and P; a U-shape for K; and no clear, more complex shapes for Ca, Mg and Mn. These shapes were related to concentration changes with roundwood diameter in both wood and bark for N, S and P (but with low goodness of fit for the models of N and S in the bark), while they were only related to concentration change in the wood for K, and in the bark for Ca and Mn (but with low goodness of fit for the model of Mn in the bark). Moreover, shifts of concentration-diameter curves (additive effect) were likely related to site conditions (chemical fertility), as assessed based on foliar nutrient concentrations. An additional effect of stand age could not be excluded, but so far it appeared difficult to clearly distinguish between influences of site and age. We argue that our modelling approach is particularly suitable to further tackle the issue of site and age effects, by combing data from several studies on the same species and/or on other species (genericness). Comprehensive forest-management rules based on silvicultural scenario simulation and assessment may finally be developed by coupling nutrient, biomass and site-sensitive tree-growth models. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this study was to model the volume expansion factor (VEF), defined as being the ratio between the total aboveground woody volume and the stem merchantable volume of a tree, as a function of tree height and diameter at breast height. A large database (dataset #1) of detailed stem and branches volume measurements, constituted by 8192 felled trees from 19 temperate tree species, was used for calibrating the models. In addition, an independent dataset (dataset #2), constituted by 176 felled trees from 13 species, was collected for validating the models. From dataset #1, the RMSE for the prediction of the total volume varied from 0.005 to 0.476m3, depending on the diameter class, and the corresponding relative RMSE varied from 8.0% to 13.7%, depending on the diameter class. A 10-fold cross-validation on dataset #1 gave an average RMSE of 0.136 for the prediction of the VEF and of 0.150m3 for the prediction of the total volume, which was in the same order as average RMSE obtained from the whole dataset #1. Validation on dataset #2 gave satisfactory results, even for the application of VEF to other tree species: RMSE obtained for the different tree species were in the same order as RMSE obtained from calibration dataset #1, except for some particular cases. The largest errors were obtained when the model was clearly used in extrapolation, e.g., for five large-size Fraxinus (whereas dataset #1 included smaller trees) and several Quercus and Fagus from coppice-with-standards stands (whereas dataset #1 included mainly pure even-aged high-forest trees). The observed differences between species seemed consistent with the general knowledge about species-specific traits. For a given diameter at breast height, angiosperms were found to have a much larger volume of branches in comparison with the corresponding stem volume than gymnosperms. For a tree of 30cm in diameter, the lowest values of VEF were obtained for Picea and Abies (VEF <1.1) and the highest ones for Fraxinus and Carpinus (VEF >1.3). The methodology that was developed, based on nonlinear mixed-effects modeling, is easily applicable to other definitions of VEF or biomass expansion factors. [Copyright &y& Elsevier]

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)

Abstract: The objectives of this study were: (i) to test whether near infrared reflectance spectroscopy (NIRS) can be used to assess site fertility in sandy and ferralitic soils of the Congo; (ii) to evaluate the comparative advantages of this methodology with respect to classical regressions with chemical and physical analysis of soils; and (iii) to assess the ability of NIRS to predict concentrations of individual nutrients. Sixty-two plots were sampled in 20 selected forest stands with varying wood production. Site indices (Hlim) were estimated from the measured dominant height in the plots. Soil samples (N =353) were analysed by NIRS, while physical and chemical analyses were carried out on 210 subsamples. Partial Least Squares regression (PLS) was used to model the site index from NIRS, while Variable Importance in Projection (VIP) allowed relating the main explicative frequencies to nutrient availability. A validation was performed based on an independent field trial (not used in the calibration set) in which soils were collected and analysed by NIRS. The measured dominant height growth was compared with the dominant height growth simulated from the site indices predicted using NIR spectra. Multiple regressions between site indices (Hlim) and soil properties failed to explain the variability in Hlim (R 2 =0.36). This variability was better predicted by NIR spectra, with an R 2 =0.64 and a predicted Root Mean Square Error of 7% for the mean value of Hlim. Based on analysis of VIP frequencies, the most important factors determining the site indices were organic matter, phosphorus, CEC, clay content, and pH. The comparison between measured and simulated dominant height in the validation set gave similar R 2 (0.61) than in the calibration set. These results demonstrate that mapping of site indices could be performed at an affordable cost in this region. The methodology developed here, which links PLS and VIP to assess the main factors determining soil fertility, is not specific to this study and could be used elsewhere. [Copyright &y& Elsevier]

Abstract: Tropical plantation forests are meeting an increasing proportion of global wood demand and comprehensive studies assessing the impact of silvicultural practices on tree and soil functioning are required to achieve sustainable yields. The objectives of our study were: (1) to quantify the effects of contrasting organic residue (OR) retention methods on tree growth and soil nutrient pools over a full Eucalyptus rotation and (2) to assess the potential of soil analyses to predict yields of fast-growing plantations established on tropical sandy soils. An experiment was set up in the Congo at the harvesting of the first rotation after afforestation of a native herbaceous savanna. Six treatments were set up in 0.26ha plots and replicated in 4 blocks, with OR mass at planting ranging from 0 to 46.5Mgha−1. Tree growth over the whole rotation was highly dependent on OR management at planting. Over-bark trunk volume 7 years after planting ranged from 96m3 ha−1 in the treatment with forest floor and harvest residue removal at planting to 164m3 ha−1 in the treatment with the largest amount of OR. A comparison of nutrient stocks within the ecosystem at planting and at the end of the rotation suggested that nutrient contents in OR were largely involved in the different response observed between treatments. OR management treatments did not significantly modify most of the nutrient concentrations in the upper layers of the mineral soil. Conventional soil analyses performed before planting and at ages 1 and 3 years were unable to detect differences between treatments despite large differences in tree growth. In contrast, linear regressions between stand aboveground biomass at harvesting and OR mass at planting (independent variable) showed that OR mass was an excellent predictor of stand yield (R 2 =0.99). A large share of soil fertility comes from organic material above the mineral soil in highly weathered sandy soils and OR mass at planting might be used in conjunction with soil analyses to assess the potential of these soils to support forest plantations. [Copyright &y& Elsevier]

Abstract: Specific leaf area (SLA; m2 leaf kg−1 leaf) is a key ecophysiological parameter influencing leaf physiology, photosynthesis, and whole plant carbon gain. Both individual tree-based models and other forest process-based models are generally highly sensitive to this parameter, but information on its temporal or within-stand variability is still scarce. In a 2–4-year-old Eucalyptus plantation in Congo, prone to seasonal drought, the within-stand and seasonal variability in SLA were investigated by means of destructive sampling carried out at 2-month intervals, over a 2-year period. Within-crown vertical gradients of SLA were small. Highly significant relationships were found between tree-average SLA (SLA t) and tree size (tree height, H t, or diameter at breast height, DBH): SLA t ranged from about 9m2 kg−1 for dominant trees to about 14–15m2 kg−1 for the smallest trees. The decrease in SLA t with increasing tree size was accurately predicted from DBH using power functions. Stand-average SLA varied by about 20% during the year, with lowest values at the end of the 5-month dry season, and highest values about 2–3 months after the onset of the wet season. Variability in leaf water status according to tree size and season is discussed as a possible determinant of both the within-stand and seasonal variations in SLA. [Copyright &y& Elsevier]

Abstract: Contrasting responses of Eucalyptus trees to K fertilizer applications have been reported on soils with low K contents. A complete randomized block experiment was set up in Brazil to test the hypothesis that large atmospheric deposits of NaCl in coastal regions might lead to a partial substitution of K by Na in Eucalyptus physiology and enhance tree growth. Treatments with application of 1.5, 3.0, 4.5kmolKha−1 (K1.5, K3.0, K4.5, respectively) as KCl, 3.0kmolKha−1 applied as K2SO4, 3.0kmolNaha−1 (Na3.0) as NaCl commercialized for cattle feeding, and a mixture of 1.5kmolK+1.5kmolNaha−1 (K1.5 +Na1.5) were compared to a control treatment (C) with no K and Na applications. All the plots were fertilized with large amounts of the other nutrients. A positive effect of NaCl applications on the growth of E. grandis trees was observed. NaCl and KCl additions in treatments Na3.0 and K3.0 increased above-ground biomass by 56% and 130% three years after planting, respectively, in comparison with the C treatment. By contrast, accumulated litterfall up to age 3 years was not significantly modified. NaCl applications in the Na3.0 treatment significantly increased Na accumulation in above-ground tree components but did not modify K accumulation, whatever the sampling age. A partial substitution of K by Na in tree physiology, as observed for various agricultural crops, might explain this behaviour. Our results suggest the possibility of applying inexpensive K fertilizers, which are less purified in Na, and explain why high yields are achieved without K fertilizer applications in areas with large dry depositions of marine aerosols. Further investigations are necessary to identify the processes involving Na in Eucalyptus tree physiology. [Copyright &y& Elsevier]

Abstract: The sustainability of fast-growing tropical Eucalyptus plantations is of concern in a context of rising fertilizer costs, since large amounts of nutrients are removed with biomass every 6–7 years from highly weathered soils. A better understanding of the dynamics of tree requirements is required to match fertilization regimes to the availability of each nutrient in the soil. The nutrition of Eucalyptus plantations has been intensively investigated and many studies have focused on specific fluxes in the biogeochemical cycles of nutrients. However, studies dealing with complete cycles are scarce for the Tropics. The objective of this paper was to compare these cycles for Eucalyptus plantations in Congo and Brazil, with contrasting climates, soil properties, and management practices. The main features were similar in the two situations. Most nutrient fluxes were driven by crown establishment the two first years after planting and total biomass production thereafter. These forests were characterized by huge nutrient requirements: 155, 10, 52, 55 and 23kgha−1 of N, P, K, Ca and Mg the first year after planting at the Brazilian study site, respectively. High growth rates the first months after planting were essential to take advantage of the large amounts of nutrients released into the soil solutions by organic matter mineralization after harvesting. This study highlighted the predominant role of biological and biochemical cycles over the geochemical cycle of nutrients in tropical Eucalyptus plantations and indicated the prime importance of carefully managing organic matter in these soils. Limited nutrient losses through deep drainage after clear-cutting in the sandy soils of the two study sites showed the remarkable efficiency of Eucalyptus trees in keeping limited nutrient pools within the ecosystem, even after major disturbances. Nutrient input–output budgets suggested that Eucalyptus plantations take advantage of soil fertility inherited from previous land uses and that long-term sustainability will require an increase in the inputs of certain nutrients. [Copyright &y& Elsevier]

Abstract: Studies on stem profile of teak (Tectona grandis) hardly exist. This can be possibly attributed to the occurrence of forks that is prevalent on teak trees. Stem profile model was therefore developed for teak in West Africa, which took into account the occurrence of forks. Trees were destructively sampled from Moist Evergreen Forest (MEF), Moist Semi-deciduous Forest (MSDF), Dry Semi-deciduous Forest (DSDF) and Savannah ecological zones in both Ghana and Côte d’Ivoire for the study. A single set of parameters could be used explicitly to predict stem profile of any teak tree, irrespective of country, eco-climatic zone, edaphic variables, site index, tree age, stand density and tree competition. The model efficiency and root mean square error (in relative diameter) were calculated to be 0.97 and 0.053, respectively. The relative position of the forks along the stem bole, with respect to total tree height, was highly variable and did not follow any particular trend, except higher value for the first fork in the Moist Evergreen Forest zone. However, average tree height to the first fork decreased along the ecological gradient from MEF, MSDF and DSDF to Savannah. The extent of diameter reduction due to the forks could be predicted. Relative tree form for zero-forked, one-forked and two-forked trees was calculated to be 0.39, 0.36 and 0.33, respectively. Relative loss of stem volume due to one fork and two forks was estimated to be 6.5 and 13.9%, respectively. The measured stem volume when related to the corresponding predicted value yielded coefficient and intercept not significantly different from unity and zero, respectively, with an r 2 value of 0.97. [Copyright &y& Elsevier]

Abstract: Eucalyptus plantations have been introduced since 1978 on savannah soils of the coastal plains of Congo, but there is still little information on the effect of silvicultural practices on soil organic carbon dynamics after afforestation on these savannahs. The objectives of this study were to assess the effects of two experimental site preparation treatments on soil CO2 efflux, tree growth and soil carbon balance during the first year following plantation establishment. One treatment involved mechanical soil disturbance with disk harrowing (D), whereas in the second treatment (H), savannah grasses were killed by herbicide application before planting, without mechanical soil disturbance. Soil respiration and soil water content were monitored for 1 year following treatment application, at 2-week intervals. We hypothesized that mechanical soil disturbance would increase soil CO2 efflux, but the results did not support this hypothesis. The cumulated soil CO2 efflux over 1 year was not significantly different in the two treatments and averaged 658gCm−2. In contrast, tree growth was significantly increased by disk harrowing, maybe as a result of decreased soil penetration resistance. Carbon inputs to the soil from savannah residues (428gCm−2) were outweighed by the annual carbon outputs through heterotrophic respiration (505 and 456gCm−2 in the H and D treatments, respectively) leading to a slightly negative soil carbon budget in both treatments 1 year after afforestation. [Copyright &y& Elsevier]

Abstract: Conversion of native vegetation into fast-growing tree plantations is known to affect soil organic matter (SOM): soil carbon (C) and nitrogen (N) content and their distribution in particle-size fractions can be modified in various ways depending on numerous factors, such as soil properties, SOM levels prior to conversion, climatic conditions, silvicultural practices and fire occurrence. Since 1978, 43,000ha of clonal eucalyptus plantations have been established on sandy coastal plains under savannas near Pointe-Noire, Congo. We investigated the effects of afforestation on topsoil (0–10cm) C and N through the analysis of their distribution in particle-size fractions using a pairwise experimental design that compared adjacent savannas and plantations. The studied plantations were of different ages (2–30-year-old stands) and differently affected by accidental fires. No significant difference in total topsoil C, N or C/N was observed between young plantations and savanna. In old plantations that had not been affected by fire, total topsoil C content was twice as high as in savanna (), on average, mostly involving fractions 50 m. By contrast, total topsoil N did not differ significantly at these sites. In old plantations affected by fire, total topsoil C content did not differ significantly from that in savanna, but total topsoil N was 26 lower in plantations than in savanna (), on average, and the decrease affected fractions 200 m especially. Whatever the fire occurrence, total topsoil C/N was higher in old plantations than in savanna, in fractions 20 m especially. [Copyright &y& Elsevier]

Abstract: Clonal plantations of Eucalyptus have been introduced since 1978 on savanna soils of the coastal plains of Congo. Atmospheric deposition, canopy exchange and transfer through the soil were estimated on the whole rooting depth (6m) over 3 years, in an experimental design installed in a native savanna and an adjacent 6-year-old Eucalyptus plantation. Complementary measurements after planting the experimental savanna made it possible to establish input–output budgets of nutrients for the whole Eucalyptus rotation and to compare them with the native savanna ecosystem. In this highly-weathered soil, atmospheric deposits and symbiotic N fixation by a legume species balanced the nutrient budgets in savanna, despite large losses during annual burnings. After afforestation, weeding in the Eucalyptus stands eliminated the leguminous species responsible for a N input by symbiotic fixation of about 20kgha−1 year−1. Whereas the budgets of P, K, Ca and Mg were roughly balanced, the current silviculture led to a deficit of about 140kgNha−1 in the soil, throughout a 7-year rotation. This deficit was large relative to the pool of total N in the upper soil layer (0–50cm), which was about 2tha−1. Therefore, the sustainability of Congolese plantations will require an increase in N fertilizer inputs over successive rotations to balance the N budget. These results were consistent with field trials of fertilization. Practical consequences of these budgets were identified, in order to: (i) direct field trials of fertilization, (ii) select appropriate methods of soil preparation, weed control and harvest, (iii) highlight the importance of fire prevention in this area, and (iv) support the implementation of field trials aiming at introducing a biological nitrogen fixing understorey in Eucalyptus stands. [Copyright &y& Elsevier]

Abstract: A complete set of equations for below- and above-ground biomass of a natural Eucalyptus hybrid in Congo was constructed. Heteroscedasticity of data was taken into account by fitting weighted non-linear regressions using maximum likelihood estimates. Stand age was introduced as a complementary variable in the equations for a majority of above-ground compartments and led to improved estimates of biomass. Because of the limited number of sampled trees for below-ground parts, it was not possible to develop the same kind of equations. Simple allometric relationships were then fitted for these components (stumps, large, medium, and fine roots). Additivity was verified and showed no significant deviation except for the youngest stand, where the sum of below- and above-ground biomass equations was preferable to the sum of component equations or to the total biomass equation. This set of equations will now be used to evaluate both the mean and the interval of confidence of biomass content and partitioning within the stands. [Copyright &y& Elsevier]

Our objectives were to quantify soil respiration in a 3-year-old Eucalyptus plantation in coastal Congo and to investigate both temporal and spatial variations of this major component of ecosystem respiration. Soil respiration exhibited pronounced seasonal variations that clearly reflected those of soil water content, with minimum values below 1.6μmolm-2s-1 at the end of the dry season in September and a maximum value of 5.6μmolm-2s-1 after re-wetting in December. An empirical model describing the relationship between soil respiration and soil water content predicts the seasonal variations in soil respiration reasonably well (R2 = 0.88), even if the effects of soil temperature and soil water content may be confounded since both factors co-vary across seasons. Spatial heterogeneity of soil respiration was clearly affected by management practices with higher respiration rate in slash inter-rows which received higher amounts of detritus at the logging stage, and lower respiration rate in haulage inter-rows used for heavy vehicle traffic. Higher values of soil respiration were also recorded in the vicinity of trunks than in the middle of the inter-rows. While soil water content is the main determinant of seasonal variation of soil respiration, it poorly accounts for its spatial variability over the experimental stand, except for days with low soil water content. Soil respiration was related neither to root biomass nor to soil carbon content, but was positively correlated with both leaf and total aboveground litter (i.e. leaf, bark and woody debris). Plots exhibiting the highest soil respiration also contained the highest amounts of aboveground litter. Microbial respiration associated with litter decomposition is likely a major component of soil respiration, and the spatial heterogeneity in litter fall probably accounts for most of its spatial variability in this Eucalyptus plantation. [Copyright &y& Elsevier]

Clonal Eucalyptus plantations in the Pointe-Noire region have been established on sandy and nutrient poor soils, and carry potential risk of depleting water and nutrient. To assess these risks, water and nutrient budgets should be calculated. However, the accuracy of hydrological models is strongly dependent on a realistic description of root distribution in soil. The spatial distribution of root systems in a chronosequence of clonal stands was then studied, using root intersect counting. The stands were 3 months, 6 months, 1 year, 2 years and 9 years old. For each stand we studied three vertical profiles perpendicular to the planting row at different spacing from a representative tree. The profiles were divided into square grid cells of 25 cm2, and the number of roots belonging to three diameter classes (between 0.1 and 1, 1 and 10 mm, and over 10 mm) were counted in each grid cell. The profiles were 2.50 m wide (half the distance between the planting rows) and 3 m deep, except for the two youngest stands (1.5 m deep). Spatial statistical analyses and analysis of variance were carried out to describe root distributions and their spatial and temporal changes. We observed that:(1)The trees quickly developed an extensive root system. One year after planting the root system extended to depth beyond 3 m deep and up to the middle of the inter-row.(2)Root density decreased sharply with depth, with most fine roots in the surface layers. The number of fine root intersects in the 0–25 cm surface soil layer represented 16–53% of the total throughout the profile depending on stand age and the type of profile.(3)The percentage of root intersects in surface layers increased with stand age: this may reflect the greater concentration of nutrients in surface layers.(4)High variability in root densities was observed in the surface soil layers but no gradient of decrease from the planting row to the middle of the inter-row could be underscored. However, the highest root densities were generally observed under the stump.These patterns of distribution allow rapid access to soil water and nutrients, reduce loss by deep drainage, and may partially explain the fairly high productivity of these plantations. [Copyright &y& Elsevier]

• A typology of nutritional functioning of forest ecosystems emerges from our study. • Forest productivity can be high even when pools of nutrients in soil are low. • Chemical fertility of forest ecosystems needs to encompass biogeochemical cycling. • Biological cycling becomes predominant when the soil nutrient reservoir is small. Many forest ecosystems are developed on acidic and nutrient-poor soils and it is not yet clearly understood how forests sustain their growth with low nutrient resources. In forestry, the soil chemical fertility is commonly defined, following concepts inherited from agronomy, as the pool of plant-available nutrients in the soil at a given time compared to the nutritional requirement of the tree species. In this two-part study, Part 1 (Hansson et al., 2020) showed, through the compiled dataset of 49 forest ecosystems in France, Brazil and Republic of Congo, the limits of this definition of soil chemical fertility in forest ecosystem contexts. In this study (Part 2), we investigated the nutrient pools and fluxes between the different ecosystem compartments at 11 of the 49 sites in order to better characterize the role of the biogeochemical cycling of nutrients in the chemical fertility of forest ecosystems, and in particular the roles of the biological and geochemical components of biogeochemical cycling. The analysis of our dataset shows different types of biogeochemical functioning. When the geochemical component (inputs through mineral weathering and/or atmospheric inputs, capillary rise) is predominant, sufficient nutrients are provided to the plant-soil system to ensure tree nutrition and growth. Conversely, when the geochemical component of the cycle brings too few nutrients to the plant-soil system, the biological component (litterfall, plant internal cycling) becomes predominant in tree nutrition and growth. In the latter case, forest production may be high even when pools of nutrients in the soil reservoir are low because small but active nutrient fluxes may continuously replenish the soil reservoir or may directly ensure tree nutrition by bypassing the soil reservoir. This study highlights the necessity to include biogeochemical cycling and recycling fluxes in the definition and diagnosis methods of soil chemical fertility in forest ecosystems. We show that the chemical fertility is not only supported by the soil in forest ecosystem but by the sum of all the ecosystem's compartments and fluxes between these pools. [ABSTRACT FROM AUTHOR]

• A unique dataset combining soil properties and stand productivity was compiled. • Common soil chemical properties were poor predictors of stand productivity. • Forest soils with low nutrient stocks sometimes exhibit high stand productivity. • Nutrient fluxes and cycling could better explain stand productivity. Forest soil fertility can be defined as a combination of physical, chemical and biological factors characterising the biomass production capacity of the soil. However, numerous ecological variables affect tree growth and the aim of the present study was to investigate the specific influence of soil chemical properties on tree productivity at 49 acidic forest sites. A standardized tree productivity index based on tree height expressed as dominant height of the studied stand divided by maximum tree height observed at the same age for the same species in the same climatic region was firstly computed at each site. This index is assumed to limit the influence of species, ages and climate. A soil database was also compiled with data on soil properties from 47 temperate (France) and two tropical (Congo, Brazil) sites. Data included seven tree species, varying in age from 1 to 175 years. Commonly used indicators such as C:N ratio, soil pH, as well as available and total pools of soil nutrients were compared to the standardized tree productivity index, to find the most reliable indicator(s). Nutrient pools at fixed mineral soil depths (down to 100 cm) were used, as well as (for 11 stands) the depth comprising 95% of fine roots. Our results show that none of the common soil chemical parameters tested in this paper could individually explain stand productivity. Combinations of different parameters were also tested using PCA and they could better explain the variability of the data set but without being able to separate the sites according to their standardized tree productivity index. Moreover, random Forests performed on our dataset were unable to properly predict the standardized tree productivity index. Our results reinforce the idea that the influence of the soil chemical fertility on stand productivity is complex and the soil chemical parameters alone (individually or combined) are poor predictors of tree productivity as assessed by the H 0 :H max index. In this paper we focused on static soil chemical indicator and more dynamic indictors, such as nutrient fluxes involved in the biogeochemical cycles, could better explain stand productivity. A companion paper (Legout et al., 2020) focuses on the connection between productivity and different components of the biogeochemical cycle, using data from 11 of the stands presented in this paper. [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]

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]

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]

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]