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To develop rehabilitation planting techniques in tropical degraded forests, we investigated (1) basic soil characteristics and light conditions; (2) growth and survival of seven dipterocarp seedlings over 81 months; and (3) the effect of environmental factors on the survival of seedlings grown in three degraded vegetations (grassland, secondary forest, and logged forest) in Sarawak, Malaysia. The soil was weakly acidic, and kaolin minerals dominated. The amount of exchangeable bases in surface soils, soil temperature (>35°C), and relative light intensity were all highest in the grassland. Seedling growth was also highest in the grassland, whereas many seedlings died there over 81 months. Growth and survivability were very similar in secondary and logged forests. The death of the seedlings in the grassland was attributable to an extremely high light intensity for all species. In contrast, the seedling growth rate in all species was also enhanced by light intensity. In conclusion, dipterocarp seedlings can be planted on highly degraded land such as grassland, although high light intensity limits their survival. Planting under nurse trees such as regenerated pioneer trees may be an effective method to enhance seedling survival under open conditions such as grassland.

Data capturing multiple axes of tree size and shape, such as a tree's stem diameter, height and crown size, underpin a wide range of ecological research-from developing and testing theory on forest structure and dynamics, to estimating forest carbon stocks and their uncertainties, and integrating remote sensing imagery into forest monitoring programmes. However, these data can be surprisingly hard to come by, particularly for certain regions of the world and for specific taxonomic groups, posing a real barrier to progress in these fields. To overcome this challenge, we developed the Tallo database, a collection of 498,838 georeferenced and taxonomically standardized records of individual trees for which stem diameter, height and/or crown radius have been measured. These data were collected at 61,856 globally distributed sites, spanning all major forested and non-forested biomes. The majority of trees in the database are identified to species (88%), and collectively Tallo includes data for 5163 species distributed across 1453 genera and 187 plant families. The database is publicly archived under a CC-BY 4.0 licence and can be access from: https://doi.org/10.5281/zenodo.6637599. To demonstrate its value, here we present three case studies that highlight how the Tallo database can be used to address a range of theoretical and applied questions in ecology-from testing the predictions of metabolic scaling theory, to exploring the limits of tree allometric plasticity along environmental gradients and modelling global variation in maximum attainable tree height. In doing so, we provide a key resource for field ecologists, remote sensing researchers and the modelling community working together to better understand the role that trees play in regulating the terrestrial carbon cycle.

Tropical forests take up more carbon (C) from the atmosphere per annum by photosynthesis than any other type of vegetation. Phosphorus (P) limitations to C uptake are paramount for tropical and subtropical forests around the globe. Yet the generality of photosynthesis-P relationships underlying these limitations are in question, and hence are not represented well in terrestrial biosphere models. Here we demonstrate the dependence of photosynthesis and underlying processes on both leaf N and P concentrations. The regulation of photosynthetic capacity by P was similar across four continents. Implementing P constraints in the ORCHIDEE-CNP model, gross photosynthesis was reduced by 36% across the tropics and subtropics relative to traditional N constraints and unlimiting leaf P. Our results provide a quantitative relationship for the P dependence for photosynthesis for the front-end of global terrestrial C models that is consistent with canopy leaf measurements.

Black spruce (Picea mariana (Mill.) B.S.P.) is a dominant species on north-facing slopes located on the permafrost in the Alaskan Interior, where tree growth rates vary significantly across slope gradients. To better understand the effects of nitrogen (N) and mycorrhizal associations on plant growth, we investigated the relationships between tree growth and isotope ratios of nitrogen (δ[sup.15]N) in foliage and roots, because plant δ[sup.15]N values reflect tree dependencies on N uptake by mycorrhizae. We established two transects (one along a slope gradient, and a second on a north-to-east axis at a fixed elevation) and four plots on the slope gradient transect. We measured current shoot growth of saplings on transects and aboveground biomass (AGB) in the plots. We collected foliage and fine root samples and measured their δ[sup.15]N signatures and N concentrations. The AGB and shoot growth varied widely across the gradient: values were higher at high elevations and at the east-northeast aspect. Foliage δ[sup.15]N values and N concentrations were positively correlated with tree growth, but growth rate was negatively correlated with the dependency on mycorrhizae for N uptake. Thus, black spruce had a reduced dependency on mycorrhizae for N uptake on the upper slope, where conditions were N-rich. On the lower slope, where the soil active layer was shallow, black spruce growth was limited and had an elevated dependency on mycorrhizae for N uptake. Key words: ectomycorrhizal, ericoid mycorrhizal fungi, nitrogen isotope, nitrogen uptake, Picea mariana. L'epinette noire (Picea mariana (Mill.) B.S.P.) est une espece dominante sur les pentes exposees au nord situees sur le pergelisol a l'interieur de l'Alaska, lal ou le taux de croissance des arbres varie de facon significative suivant l'inclinaison de la pente. Pour mieux comprendre les effets de l'azote (N) et des associations mycorhiziennes sur la croissance des plantes, nous avons etudies les relations entre la croissance des arbres et les rapports isotopiques de l'azote (δ[sup.15]N) dans le feuillage et les racines etant donne que les valeurs de δ[sup.15]N indiquent dans quelle mesure les arbres dependent de l'absorption de N par les mycorhizes. Nous avons etabli deux transects (le premier suivant l'inclinaison de la pente et l'autre suivant un axe est-nord-est a une altitude fixe) et quatre places echantillons sur le transect le long l'inclinaison de la pente. Nous avons mesure la croissance courante des pousses des gaules le long des transects ainsi que la biomasse aerienne (BA) dans les places echantillons. Nous avons preleve des echantillons du feuillage et des racines fines et mesure leur signature isotopique δ[sup.15]N ainsi que leur concentration en N. La croissance des pousses et de la BA variait beaucoup le long de la pente : les valeurs etaient plus elevees a haute altitude et pour l'exposition est-nord-est. Les concentrations de N et les valeurs de δ[sup.15]N etaient positivement correlees avec la croissance des arbres mais le taux de croissance etait negativement correle avec la dependance envers les mycorhizes pour l'absorption de N. Par consequent, l'epinette noire avait une moins forte dependance envers les mycorhizes pour l'absorption de N dans le haut de la pente ou N etait abondant. Dans le bas de la pente ou la couche active de sol etait peu profonde, la croissance de l'epinette noire etait limitee et fortement dependante des mycorhizes pour l'absorption de N. [Traduit par la Redaction] Mots-cles: ectomycorhize, champignons mycorhiziens ericoides, isotope d'azote, absorption de l'azote, Picea mariana., Introduction Carbon (C) stock accumulation and tree growth rates in boreal forests are generally limited by nitrogen (N) availability (Shaver and Chapin 1980). Low temperatures, water logging, and high soil [...]

The morphological and physicochemical traits of leaves are important in terms of plant adaptation to various growth environments, because such traits play central roles in various functions including photosynthesis. We measured the toughness, mass per unit area (LMA), nitrogen content, and S15N levels of the leaves of different life-forms of 39 broadleaf woody plants in interior Alaska. The plants were divided into three life-forms based on the maximum height of adult plants: understory ( Key words: δ[sup.15]N, heterobaric leaf, LMA, nitrogen, leaf toughness. Les traits morphologiques et physicochimiques des feuilles sont importants pour l'adaptation des plantes a divers environnements de croissance parce qu'ils jouent un role central dans diverses fonctions, incluant la photosynthese. Nous avons mesure la coriacite, la masse par unite de surface (MFS), la teneur en azote et le niveau de δ[sup.15]N des feuilles de differents types biologiques de 39 plantes ligneuses feuillues du centre de l'Alaska. Les plantes ont ete divisees en trois types biologiques en fonction de la hauteur maximale des plantes adultes : sous- etage ( Mots-cles: δ[sup.15]N, feuille heterobarique, masse foliaire par unite de surface foliaire, azote, coriacite., Introduction The morphological and physicochemical traits of leaves are important in terms of plant adaptation to growth environments, because such traits play central roles in various functions including photosynthesis and [...]