Pierre Trichet

Allometric relationships for branch and tree woody biomass of Maritime pine (Pinus pinaster Aı̈t.)

Modelling biomass repartition in a tree is either done using theories regarding carbon transfer and allocation or through empirical repartition coefficients. The latter can be derived from the study of the allometric relationships inside a tree, which reflect the equilibrium between tree structure and biomass. In order to quantify the biomasses of the main aerial compartments (needles, stem wood, stem bark, branch wood and buds) of a Maritime pine tree (Pinus pinaster Ait.) and to assess their relationships with tree structure, we undertook some destructive measurements of architecture and biomass. The study of leaf area was presented in a specific paper [Porte et al., Ann. For. Sci. 57 (1) (2000) 73], and the present paper is dealing with the woody compartments (branch wood, stem bark and wood). We collected biomass samples on thirty 5-year-old, sixteen 26-year-old and ten 32-year-old Maritime pines. Allometric equations were developed per site to estimate branch wood biomass. It depended only on the branch basal diameter and the models were very satisfying. Using these equations, we estimated the total branch wood biomass of each sampled tree. A single relationship for all sites was found to model crown or trunk biomass. A power function of tree diameter at breast height (DBH) and the inverse of tree age was fitted to the branch wood data. A power function of DBH and tree age was used for the stem wood and bark models, which takes into account the differences in vitality with different ages. All models performed quite well. Input variables were easy to measure so that the models could be applied to estimate the aerial biomass of a whole stand, per compartment, over a 20-year-long period. The allometric relationships presented here can be derived to be used as biomass repartition laws, for a 5–30-year-old Maritime pine stand in humid Lande.

Structural root architecture of 5-year-old Pinus pinaster measured by 3D digitising and analysed with AMAPmod

Pinus pinaster (Ait.) is a high yielding forest tree, producing nearly a fourth of French marketed timber essentially from intensively managed stands located in southwestern France, in the Landes Forest. This species has generally a poor stem straightness, especially when it grows in poor sandy podzol of the Landes Forest, affected by summer droughts and winter floods. Above- and below-ground architecture and biomass as well as stem straightness were measured on twenty-nine 5-year-old planted trees uprooted by pulling with a lumbering crane. A very precise numeric representation of the geometry and topology of structural root architecture was gained using a low-magnetic-field digitising device (Danjon et al., 1998; Sinoquet and Rivet, 1997). Data were analysed with AMAPmod, a database software designed to analyse plant topological structures (Godin et al., 1997). Several characteristics of root architecture were extracted by queries including root number, length, diameter, volume, spatial position, ramification order, branching angle and inter-laterals length. Differences between root systems originated from their dimensions, but also from the proportion of deep roots and the taproot size, which represented 8% of the total root volume. The proportion of root volume in the zone of rapid taper was negatively correlated with the proportion of root volume in the taproot indicating a compensation between taproot and main lateral root volume. Among all studied root characteristics the maximal rooting depth, the proportion of deep roots and the root partitioning coefficient were correlated with stem straightness.

Adaptation of fine roots to annual fertilization and irrigation in a 13-year-old Pinus pinaster stand

Effects of fertilization and irrigation on fine roots and fungal hyphae were studied in 13-year-old maritime pine (Pinus pinaster Aït. in Soland), 7 years after the initiation of the treatments. The fertilization trials consisted of a phosphorus treatment, a complete fertilizer treatment (N, P, K, Ca and Mg), and an unfertilized treatment (control). Fertilizers were applied annually and were adjusted according to foliar target values. Two irrigation regimes (no irrigation and irrigation of a set amount each day) were applied from May to October. Root samples to depths of 120 cm were collected in summer of 2005, and the biomass of small roots (diameter 2-20 mm) and fine roots (diameter </= 2 mm) and fine root morphology were assessed. Biomass and length of hyphae were studied by a mesh ingrowth bag technique. Total fine root biomass in the litter and in the 0-120 cm soil profile ranged between 111 and 296 g m(-2). Results derived from the measurements of biomass and root length, or root area, showed that both fertilizer treatments reduced the size of the fine root system, especially in the top soil layers, but did not affect small roots. Compared with control treatments, fine root morphology was affected by both fertilizer treatments with the fine roots having increased specific root length/area, and irrigation tended to reinforce this finer morphology. The amount of hyphae in the mesh ingrowth bags was higher in the fertilization and irrigation treatments than in the controls, suggesting further extension of the root system (ectomycorrhizal infection) and thus of the uptake system. Irrigation had no significant effect on the size of the fine root system, but resulted in a shallower rooting system. Total root to shoot ratios were unaffected by the treatments, but fine root mass:needle mass and fine root area index:leaf area index ratios decreased with increasing nutrient supply. Overall, compared with the control fine roots, increased nutrient supply resulted in a lower fine root biomass but the dynamic fraction of the finest roots was greater. Irrigation had only limited effects on fine root size, distribution and morphology.

Manipulating nutrient and water availability in a maritime pine plantation: effects on growth, production, and biomass allocation at canopy closure

Abstract• We present here the results of a water and nutrient manipulation experiment in a five-year-old plantation of maritime pine in south-western France.• Water and nutrient levels were manipulated in a factorial design with two levels of irrigation (control receiving only rainfall (C) and irrigated (I)) and three levels of fertilisation (control with no added nutrients (C), P-only (P) and annual addition of a complete nutrient mix (F)) in order to quantify growth limitations of plantation forest in this particular area.• The treatments applied during five years increased aboveground biomass annual increment by 4% (I) to 58% (IF) with respect to the control (C). The fertilised plots had a slightly non-significant lower root-to-shoot ratio. The effect of irrigation was maximal in 2002, resulting in 6%, 7% and 12% higher growth rate on the F, C and P plots, respectively. A windstorm disturbed the experiment in 1999 and has affected preferentially the fertilised plots, with IF plots displaying 60% damage.• The higher growth rate of fertilised and irrigated plots was attributed to both an increase (estimated at 5 to 15%) in the amount of light absorbed by the canopy, and an increase (estimated at 26% for IF plots) in the amount of above-ground biomass produced annually per unit leaf area.Résumé• Dans l’objectif de quantifier l’impact des facteurs limitant de la croissance du pin maritime dans le sud-ouest de la France, les apports d’eau et d’éléments minéraux sont manipulés selon un schéma expérimental factoriel à deux niveaux d’alimentation en eau (témoin recevant uniquement les pluies et irrigué) et à trois niveaux d’alimentation minérale (témoin, apport annuel de phosphore, apport annuel d’un mélange minéral complet).• Les traitements appliqués pendant cinq ans ont entrainé une augmentation de l’accroissement annuel en biomasse aérienne allant de +4 % (I) à + 58 % (IF). Les arbres fertilisés ont un rapport biomasse aérienne sur racinaire légèrement mais non significativement supérieur à celui des arbres témoins. L’effet de l’irrigation a été maximal en 2002, avec des accroissements en biomasse aérienne plus élevés de 6 %, 7 %, 12 % pour les arbres fertilisés, témoins et fertilisés en P. Une tempête a endommagé le dispositif en 1999, affectant préférentiellement les arbres fertilisés avec 60 % des arbres touchés, contre 13 % pour les témoins.• La plus forte croissance observée pour les placeaux fertilisés et irrigués a été attribuée à une augmentation d’une part de +5 à +15 % de la quantité de rayonnement absorbé par la canopée, et d’autre part de +26 % de la quantité de biomasse aérienne produite annuellement par unité d’indice foliaire.

Generalized biomass equations for the main aboveground biomass components of maritime pine across contrasting environments

Abstract• IntroductionIn order to predict the biomass of aerial components of maritime pine stands (Pinus pinaster Ait.), generalized allometric equations were developed using data collected from the southern and northern margins of its geographical area.• MethodsThe data comprised biomass values divided into foliage, branch, stem and minor components collected from 26 trees in Tunisia and 152 trees in France. Some trees were taken from plots receiving fertilisation and irrigation. The equation W = aDb, where W is the biomass, D the stem diameter and a and b are fitted parameters, explained 98% of the variations in the total aerial biomass. The addition of tree age reduced significantly the residual sum of squares for the foliage component. This model explains 79% of the variations in foliage biomass observed.• ResultsTo a lesser extent, the age variable also improved the stem and branch models that explain 98% and 71% of the observed sum of squares, respectively. Site variables such as the stocking density, stand basal area, fertilisation or annual precipitation did not reduce the residual sum of squares, suggesting that their putative effects are conveyed through tree growth rate.

Improving models of forest nutrient export with equations that predict the nutrient concentration of tree compartments

Abstract• The objective of this study was to explore the distribution of major nutrients (N, P, K, Ca and Mg) in the aboveground compartments of an intensively managed tree species (Pinus pinaster Ait.). A total of 53 trees were cut down in even-aged stands respectively 8, 16, 26, 32 and 40 years old. The nutrient concentrations of the aboveground compartments were analysed.• Nutrient concentrations of foliage did not vary with any of the variables used, except needle age. Nutrient concentrations of living branches, stem bark, stem sapwood, stem heartwood, stemwood and stem decreased with increasing branch diameter, bark thickness, sapwood thickness and heartwood thickness, respectively. Beyond a certain value of the predictive variable (stem diameter ≈ 15 cm; branch diameter ≈ 2.5 cm), the concentration of all the nutrients stabilised.• A 50 year-old pine stand was used to obtain a validation dataset for nitrogen concentration. For this nutrient, the regression relationships gave satisfactory estimates for most compartments (mean error = 12–25%) and particularly for the stem.• A procedure is proposed to estimate the nutrient exports associated with harvests of Pinus pinaster biomass.Résumé• L’objectif de cette étude est d’explorer la distribution des éléments majeurs (N, P, K, Ca, Mg) dans les compartiments aériens d’une essence gérée de manière intensive. Au total, 53 pins maritimes (Pinus pinaster Ait.) ont été abattus parmi des peuplements équiennes de 8, 16, 26, 32 et 40 ans.• Les concentrations en nutriments du feuillage ne varient pas pour une classe d’âge d’aiguilles donnée. Les concentrations des branches vivantes, de l’écorce, de l’aubier et du duramen décroissent lorsque le diamètre ou l’épaisseur du compartiment considéré augmente. La concentration de l’ensemble des nutriments devient constante lorsque la variable prédictive (diamètre ou épaisseur) atteint une valeur plateau.• Un jeu de données de validation pour les concentrations en azote, provenant d’un peuplement équienne de pins de 50 ans, permet de confirmer les performances satisfaisantes des modèles construits (erreur moyenne = 12–25 %) et en particulier pour le tronc.• Une procédure d’estimation des exportations de nutriments associées aux récoltes de biomasse de Pinus pinaster est présentée.

Growth and uptake of mineral elements in response to sodium chloride of three provenances of maritime pine 1

Abstract Effect of sodium chloride (NaCl) on the growth, mineral concentration, and net accumulation of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) was established in one‐year‐old seedlings (Iberique, Landais, Tamjoute provenances) grown in a regulated greenhouse in nutrient solutions. Increasing concentration of NaCl induces a reduced rate of growth and the Iberique provenance was most affected. Accumulation of Na is significantly more intense in the Tamjoute provenance irrespective of the growth response. Macronutrient concentration are markedly modified, as a result of salinity, by increases in the N and K concentrations and decreases in P, Ca and Mg concentrations in the root. The nutrient concentrations in the tissues did not appear to become deficient or toxic under these saline conditions. Total accumulation of most ions was reduced as a consequence of relative growth and provide a good indication of geographic provenance response. The results presente...

Les sols du massif forestier des Landes de Gascogne : Formation, histoire, propriétés et variabilité spatiale

The ‘Landes’ forest gives an impression of great homogeneity as it is mainly composed of even-aged, single species pine stands. This apparent uniformity is also visible from the geological point of view as the parent material is a flat, sandy and fairly homogeneous eolian deposit. In actual fact, upon closer scrutiny of the distribution of soils on various scales, their organisation turns out to be more complex under the combined effects of the water table, soil microrelief and the plant associations that are specific to them. This soil variability holds true across a range of scales and should be taken into account when studying or managing these soils.

Biomass and nutrients in tree root systems-sustainable harvesting of an intensively managed Pinus pinaster (Ait.) planted forest.

To develop sources of renewable energy and to reduce greenhouse gas emissions, increasing attention has been given to the extraction of forest biomass, especially in the form of harvest residues. However, increasing the removal of biomass, and hence nutrients, has raised concerns about the sustainability of site fertility and forest productivity. The environmental cost of harvesting belowground biomass is still not fully understood. The objectives of this study were to (i) estimate the stocks of belowground biomass that potentially can be collected; (ii) measure the nutrient (N, P, K, Ca, Mg) concentrations of the different root compartments (stumps, coarse and thin roots); and to (iii) quantify the biomass and nutrient exports under different scenarios, including harvests of above and belowground compartments. The study was carried out on Pinus pinaster stands located in south‐western France. Results showed that roots could be a significant fuelwood resource, particularly at forest clear cutting. Negative relationships between root diameter and root nutrient concentration were observed, independently of root function or tree age. Such relationships can be used to accurately simulate nutrient concentrations in roots as well as nutrient exports. Combining our original results on roots with previously published data on the aboveground compartments showed that nutrient losses were higher in canopy harvest scenarios than in root harvest scenarios. This was mainly due to high nutrient concentrations of needles. We concluded that stump and root harvest could be sustainable in our study context, conversely to foliage harvest. Because thin roots have higher nutrient concentrations than coarse roots and the proportion of thin roots increased with an increase in the distance from the tree, collecting roots only in the close vicinity of the stumps should limit nutrient exports (particularly N) without unnecessarily reducing fuelwood biomass.

Field effect of P fertilization on N2 fixation rate of Ulex europaeus

European gorse (Ulex europaeus L.) N2 fixation rate (%Ndfa) was studied in a maritime pine (Pinus pinaster Aït.) oligotrophic forest. Fertilization field trials were carried out on 5 sites with various inputs of phosphorus (0–240 kg P2O5·ha−1). Seven to ten years after pine planting, gorse were sampled to evaluate the effect of P fertilization on gorse %Ndfa, determined using the 15N natural abundance method. One of the prerequisites of this method is the existence of a significant difference between the 15N/14N ratios in the atmospheric N reference and in the stand soil N references. This prerequisite was satisfied for 80 of 120 cases. The average %Ndfa was high (70 ± 3%) but with high local variability. No significant difference in %Ndfa was detected among P treatments. Nitrogen concentration of gorse was significantly higher in the highest dose treatments compared to the control.RésuméLe taux de fixation de l’azote atmosphérique (%Ndfa) de l’ajonc d’Europe (Ulex europaeus L.) a été étudié dans une forêt oligotrophe de pins maritimes. Des essais de fertilisation ont été établis avec plusieurs niveaux d’apport en phosphore (0–240 kg P2O5·ha−1). Sept à dix ans après la plantation de pins, les ajoncs ont été échantillonnés afin d’évaluer l’effet de la fertilisation en phosphore sur le %Ndfa, calculé par la méthode de l’abondance naturelle en 15N. Cette méthode nécessite notamment une différence significative entre les rapports 15N/14N de la référence atmosphérique et de la référence du sol des peuplements. Cette condition était satisfaite dans 80 cas sur 120. Le %Ndfa moyen était élevé (70 ± 3 %) mais avec une grande variabilité locale. Aucune différence des %Ndfa n’a été détectée entre les traitements. Les teneurs en azote des ajoncs étaient significativement plus élevées pour les doses maximales que pour les témoins.