Sustainable biomass production in eucalypt plantations under climate changes: insights from a throughfall exclusion experiment

The frequency of drought periods should increase under climate changes in many tropical regions. A large-scale throughfall exclusion experiment was set up in Brazil to study the interaction between water status and potassium (K) or sodium (Na) availability on the ecophysiology of Eucalyptus trees. Across the water supply regimes, the stemwood biomass at the harvest age was 2.7 and 1.6 times higher in trees fertilized with KCl and NaCl, respectively, than in trees with no K and Na addition. Excluding 1/3 of the rainfall reduced stemwood production only for trees fertilized with K, as a result of low water requirements of K-deficient trees. Gas exchange water used efficiency (WUE) estimates were not correlated with WUE for wood production. The allocation pattern in response to nutrient and water supply appeared to be a major driver of WUE for stemwood production. Phloem sap and leaf ä13C were not valuable proxies of WUE for wood production, which suggests a weak interest for breeding programs. The strong interaction between water and nutrient availabilities on tree functioning in this study suggests that a slight decrease in fertilization rates could help reduce the risks of mortality of Eucalyptus trees under conditions of extreme water deficit. (Résumé d'auteur

Insights into management from forest ecology

Comprehensive studies of forest ecology improve our understanding of how forest ecosystems function and our ability to design sustainable silvicultural practices that maximize the ecosystem services provided by forest ecosystems. Three case studies are presented to show sustainable management practices derived from studies dealing with forest ecology. In tropical regions, large amounts of fertilizers are needed to sustain the productivity of eucalypt plantations. Improved understanding of rooting patterns in deep soil layers as well as the nutrient demands of trees and the geochemical processes controlling the fluxes of nutrients in gravitational soil solutions made it possible to reduce the cost of fertilization at large scale in Brazil by refining the timing of application needed. In coastal rainforests of British Columbia, ecological studies of old-growth forests elucidated the proximate and ultimate causes of growth check and poor nutrient supply in regenerating forests. As a result, silvicultural interventions can be focused on the causes rather than the symptoms of the regeneration problem. In temperate forests of North America, ecologists have demonstrated the importance of early successional forest habitat for sustaining biodiversity, while also incorporating legacy structures that provide habitat for other species. (Texte intégral

Inventaire d'exploitation du massif forestier de Neboueba

Par convention n° 5937/90, la Province Nord de la Nouvelle-Calédonie a confié au Centre Technique Forestier Tropical, la réalisation de l'inventaire forestier d'exploitation du massif de NEBOUEBA. Les travaux de terrain ont été réalisés en Mai et Juin 1990, à partir d'un plan de sondage mis au point par une mission biométrie du CTFT/Siège. Ce dernier s'est chargé des dépouillements informatiques mais la rédaction du rapport a été effectuée par le CTFT/NC. Les résultats de l'inventaire montrent que l'accessibilité de la forêt est moyenne. Les essences les plus recherchées sont cantonnées dans les parties les plus hautes du massif : le Nord de la réserve de NEBOUEBA et la zone domaniale. La surface de cet ensemble représente 300 à 400 ha. Les volumes commercialisables atteignent 4500 m3 de houps et 7200 m3 de tamanous, bois qui ne présentent pas de difficultés d'écoulement sur le marché local. Malgré l'absence de kaoris, le volume de houps disponible semble juste suffisant pour justifier la création d'une entreprise d'exploitation forestière dans les tribus de NEBOUEBA et de SAINT-YVES. Toutefois, l'exploitation du massif, nécessite un accord entre les 2 tribus et la vente des bois à une scierie existante, pour que l'investissement reste modéré. De très forts volumes d'essences principales semblent cependant disponibles en zone domaniale, à l'Ouest du massif inventorié ; en particulier dans la vallée de NA GODEA. (Résumé d'auteur

Is there a niche complementarity for nitrate uptake among savannah shrub and tree species in a very deep Brazilian soil?

Belowground niche complementarity between deep-rooted and shallow-rooted species in mixed forests may result in a more complete exploitation of soil resources than in monocultures. Our study aimed to assess 1) the maximum distance (horizontally and vertically) where the fine roots from common Cerrado species take up mobile nutrients in deep Ferralsols. and 2) whether there is a niche complementarity in nitrate uptake between some Cerrado species. Our study was carried out in a closed-canopy forest with dense woody understory (cerradão) at Bauru (Sao Paulo State); 15N-NO,- was injected at the onset of dry and rainy seasons at 6 depths (0.1. 1.5, 3. 6. 9 and 12 m) with 3 plots per depth and a distance> 50 m between each injection depth Leaves were sampled 4 months after tracer injection in 3 frequent species in each plot located at 4 intervals of distance from the tracer injection point (0-2 m; 3-6 m; 7-10 m; >12 m) and 15N atom% was determined. Great differences in 15N tracer uptake between the studied species showed a niche complementarity in this native savannah. Xylopia aromatica exhibited a strong 15N uptake at 6 m of depth, irrespective of the season. This species seems to exploit a much larger soil volume than the others, both vertically and horizontally (15N taken up at 5 m from the injection point). Miconia albicans and Coussarea hydrangeifolia showed similar behaviours, with a strong 15N uptake in the topsoil and down to 1.5 m depth. within 2 m from the injection point

Inventaire d'exploitation du massif forestier d'ATEOU

Par convention n°5937/90, la Province Nord de la Nouvelle Calédonie a confié au Centre Technique Forestier Tropical, la réalisation de l'inventaire forestier d'exploitation du massif d'ATEOU (2428 ha). Dès la mise en place du plan de sondage par une mission biométrie du CTFT/Siège, les travaux ont pu démarrer. Ils ont été réalisés en deux phases (defin1990 à début 1991). La phase de terrain s'est déroulée dans d'excellentes conditions météorologiques. L'embauche de cinq ouvriers à la tribu permis de constituer les équipes de layonnage et de comptage. La rédaction du rapport a été réalisée au CTFT/NC, mais le CTFT/Siège s'est chargé des dépouillements informatiques. Les résultats montrent que la forêt doit être subdivisée en trois unités : La zone Ouest qui couvre 817ha, entre 300 et 600 mètres d'altitude. Elle est difficilement accessible et pauvre en essences principales. Elle porte une forêt en cours de reconstitution, qui semble inexploitable dans le contexte actuel. Le versant Est s'étendant sur 954 ha, entre 300 et 1000 mètres d'altitude. L'accessibilité et la richesse en bois recherchés sont moyennes à faibles. La forêt dans sa composition définitive est en place mais encore en mélange avec les espèces pionnières. Seule la partie supérieure à 600m d'altitude (couvrant 500 ha) pourrait éventuellement être exploitée, Le "plateau" côte Ouest représentant 657 ha, entre 600 et 1000 mètres d'altitude. Il est riche en gros bois et très facilement accessible à partir de la tribu. Il porte une forêt dense humide classique. Cependant, les hêtres et les ralias constituent l'essentiel du volume des essences principales. Même dans cette zone les houps, les kaoris et les tamanous sont très rares. Le volume brut moyen sur l'ensemble du massif, des arbres de plus de 40cm de diamètre, représente 174 m3/ha et il augmente avec l'altitude. Il est très fort pour ce type de forêts en Nouvelle-Calédonie. Le volume commercial est de 119 m3/ ha, sur l'ensemble du massif. Au vu de ces résultats, le "Plateau" est la zone la plus intéressante même si la rareté de houps, kaoris et tamanous constitue un obstacle à l'exploitation. La zone exploitable peut éventuellement être portée à 1160 ha, en incluant le haut du versant Est sensiblement moins riche et moins accessible que le plateau. (Résumé d'auteur

Competition for light and light use efficiency for Acacia mangium and Eucalyptus grandis trees in mono-specific and mixed-species plantations in Brazil

Mixed plantations with N-fixing species might be an attractive option for limiting the use of fertilizer in highly productive Eucalyptus plantations. A randomized block design was set up in southern Brazil, including a replacement series and an additive series design, as well as a nitrogen fertilization treatment, and conducted during a full 6 years rotation. The gradient of competition between Eucalyptus and Acacia in this design resulted in very different conditions of growth of Acacia, from totally dominated up to dominant canopies. We used the MAESTRA model to estimate the amount of absorbed photosynthetically active radiation (APAR) at tree level. This model requires the description of the scene and distinct structural variables of the two species, and their evolution with time. The competition for light is analysed by comparing the inter-specific values of APAR during a period of 2 years at the end of the rotation. APAR is further compared to the measured increment in stem wood biomass of the tree, and their ratio is an estimation of the light use efficiency for stemwood production at tree-scale. Variability of these LUE are analysed in respect to the species, the size of the tree, and at plot scale (competition level). Stemwood production was 3400, 3900 and 2400 gDM/m2 while APAR was 1640, 2280 and 2900 MJ/y for the pure Eucalyptus, pure Acacia and 50/50 mixed plantation, respectively, for an average LAI of 3.7, 3.3 and 4.5, respectively. Individual LUE for stemwood was estimated at an average value of 1.72 and 1.41 gDM/MJ/tree for Eucalyptus and Acacia, respectively, and at 0.92 and 0.40 gDM/MJ/tree when they were planted in mixed 50/50 plantations. LUE was highly dependant on tree size for both species. At the plot scale, LUE for stemwood were 2.1 gDM/MJ and 1.75 for Eucalyptus and Acacias, respectively, and 0.85 for the mixed 50/50 plantation. These results suggest that the mixed 50/50 plantation, which absorbed a higher amount of light, produce less stemwood since half of the canopy (Acacias) are dominated, and the other half does not benefit much in terms of tree growth compared to absorbed light. The eventual benefit of the nitrogen-fixing species is not visible in the mixture with 50% of each species. More attention has to be paid to introducing acacias in an additive series with the same density of eucalyptus trees as in the monospecific stands

Calibration of home-made heat dissipation probes for a full rotation of Eucalyptus grandis trees in Brazil

With the aim of proposing an appropriate calibration equation that could be used for Eucalyptus grandis of any size over a rotation of seven years, we carried out direct measurements of water consumption for 3 trees at 19, 45, 54 and 72 months after planting, and measured values of tree transpiration were compared with estimations from HDPs installed on the trunks. The trees used for direct measurements were cut and kept in situ, standing with the bottom inserted in a water tank. The accuracy of the calibration was checked by two independent methods: 1) directs measurements for other individual trees, and 2) through Eddy covariance measurements. We compared direct measurements for 3 trees of different size at the ages of 29 and 65 months with HDP. At the stand level, 15 trees selected to cover the range of sizes of one commercial plantation at the end of the rotation were monitored by HDP over 8 months. The comparison with eddy-covariance measurements was carried out during dry periods. Resulted showed that the calibration developed for these home-made probes can be used with great reliability at the tree and stand scales

Light use efficiency and productivity of 16 genotypes of Eucalyptus along a 6-year rotation in Brazil

Forest stemwood productivity depends on the amount of absorbed light and on the Light Use Efficiency (LUE), i.e. the amount of stemwood produced per amount of absorbed light. Other growth limiting factors than absorbed light are for instance water and nutrients, carbohydrates allocation processes, and management practices. In fertilized eucalyptus plantations in Brazil, a shift in the main factor limiting growth is expected, from light at the beginning of the rotation (not limited by water because soil has been recharged during the interval between rotation) to other factors such as water in the subsequent years. Changes of allocation patterns and foliar traits also occur along the rotation. These trends may differ between genotypes. These hypotheses were tested along a 6-year rotation, with 16 contrasted genotypes planted in 10 randomized repetitions in São Paulo Region, Brazil. Absorbed light was estimated using the MAESTRA 3D model precisely parameterized at tree scale for each plot. Stand growth was computed based on allometric relationships calibrated on regular destructive biomass measurements. Results at stand scale showed that 1) LUE increased with stand age for all genotypes, from 0.15 to 0.70 gdry_matter/MJ on average; 2) light was the main limiting factor during the first year of growth (R2 between 0.5 and 0.95). Subsequently, the variability of wood production explained by light was variable among genotypes (R2 of 0.25 on average; 3) The effect of genotype on stemwood production remains high and significant along the rotation. These results and their implications for plantation management are discussed