• Energy Research

AbstractForests are a substantial terrestrial carbon sink, but anthropogenic changes in land use and climate have considerably reduced the scale of this system1. Remote-sensing estimates to quantify carbon losses from global forests2–5 are characterized by considerable uncertainty and we lack a comprehensive ground-sourced evaluation to benchmark these estimates. Here we combine several ground-sourced6 and satellite-derived approaches2,7,8 to evaluate the scale of the global forest carbon potential outside agricultural and urban lands. Despite regional variation, the predictions demonstrated remarkable consistency at a global scale, with only a 12% difference between the ground-sourced and satellite-derived estimates. At present, global forest carbon storage is markedly under the natural potential, with a total deficit of 226 Gt (model range = 151–363 Gt) in areas with low human footprint. Most (61%, 139 Gt C) of this potential is in areas with existing forests, in which ecosystem protection can allow forests to recover to maturity. The remaining 39% (87 Gt C) of potential lies in regions in which forests have been removed or fragmented. Although forests cannot be a substitute for emissions reductions, our results support the idea2,3,9 that the conservation, restoration and sustainable management of diverse forests offer valuable contributions to meeting global climate and biodiversity targets.

Abstract Species’ traits and environmental conditions determine the abundance of tree species across the globe. The extent to which traits of dominant and rare tree species differ remains untested across a broad environmental range, limiting our understanding of how species traits and the environment shape forest functional composition. We use a global dataset of tree composition of >22,000 forest plots and 11 traits of 1663 tree species to ask how locally dominant and rare species differ in their trait values, and how these differences are driven by climatic gradients in temperature and water availability in forest biomes across the globe. We find three consistent trait differences between locally dominant and rare species across all biomes; dominant species are taller, have softer wood and higher loading on the multivariate stem strategy axis (related to narrow tracheids and thick bark). The difference between traits of dominant and rare species is more strongly driven by temperature compared to water availability, as temperature might affect a larger number of traits. Therefore, climate change driven global temperature rise may have a strong effect on trait differences between dominant and rare tree species and may lead to changes in species abundances and therefore strong community reassembly.

L'une des questions les plus fondamentales en écologie est de savoir combien d'espèces habitent la Terre. Cependant, en raison des défis logistiques et financiers massifs et des difficultés taxonomiques liées à la définition du concept d'espèce, le nombre global d'espèces, y compris celles des formes de vie importantes et bien étudiées telles que les arbres, reste encore largement inconnu. Ici, sur la base de données mondiales provenant de sources terrestres, nous estimons la richesse totale des espèces d'arbres aux niveaux mondial, continental et du biome. Nos résultats indiquent qu'il y a environ73 000 espèces d'arbres dans le monde, parmi lesquelles environ9 000 espèces d'arbres n'ont pas encore été découvertes. Environ 40 % des espèces d'arbres non découvertes se trouvent en Amérique du Sud. En outre, près d'un tiers de toutes les espèces d'arbres à découvrir peuvent être rares, avec des populations très faibles et une répartition spatiale limitée (probablement dans les basses terres tropicales et les montagnes éloignées). Ces résultats mettent en évidence la vulnérabilité de la biodiversité forestière mondiale aux changements anthropiques dans l'utilisation des terres et le climat, qui menacent de manière disproportionnée les espèces rares et donc la richesse mondiale en arbres. Una de las preguntas más fundamentales en ecología es cuántas especies habitan la Tierra. Sin embargo, debido a los enormes desafíos logísticos y financieros y a las dificultades taxonómicas relacionadas con la definición del concepto de especie, el número global de especies, incluidas las de formas de vida importantes y bien estudiadas, como los árboles, sigue siendo en gran medida desconocido. Aquí, con base en datos globales de fuentes terrestres, estimamos la riqueza total de especies de árboles a nivel global, continental y de biomas. Nuestros resultados indican que hay ~73,000 especies de árboles a nivel mundial, entre las cuales ~9,000 especies de árboles aún no se han descubierto. Aproximadamente el 40% de las especies de árboles no descubiertas se encuentran en América del Sur. Además, casi un tercio de todas las especies de árboles por descubrir pueden ser raras, con poblaciones muy bajas y una distribución espacial limitada (probablemente en tierras bajas y montañas tropicales remotas). Estos hallazgos ponen de relieve la vulnerabilidad de la biodiversidad forestal mundial a los cambios antropogénicos en el uso de la tierra y el clima, que amenazan desproporcionadamente a las especies raras y, por lo tanto, a la riqueza arbórea mundial. One of the most fundamental questions in ecology is how many species inhabit the Earth. However, due to massive logistical and financial challenges and taxonomic difficulties connected to the species concept definition, the global numbers of species, including those of important and well-studied life forms such as trees, still remain largely unknown. Here, based on global ground-sourced data, we estimate the total tree species richness at global, continental, and biome levels. Our results indicate that there are ∼73,000 tree species globally, among which ∼9,000 tree species are yet to be discovered. Roughly 40% of undiscovered tree species are in South America. Moreover, almost one-third of all tree species to be discovered may be rare, with very low populations and limited spatial distribution (likely in remote tropical lowlands and mountains). These findings highlight the vulnerability of global forest biodiversity to anthropogenic changes in land use and climate, which disproportionately threaten rare species and thus, global tree richness. أحد أهم الأسئلة الأساسية في علم البيئة هو عدد الأنواع التي تعيش على الأرض. ومع ذلك، نظرًا للتحديات اللوجستية والمالية الهائلة والصعوبات التصنيفية المرتبطة بتعريف مفهوم الأنواع، لا تزال الأعداد العالمية للأنواع، بما في ذلك أشكال الحياة المهمة والمدروسة جيدًا مثل الأشجار، غير معروفة إلى حد كبير. هنا، استنادًا إلى البيانات العالمية من مصادر أرضية، نقدر إجمالي ثراء أنواع الأشجار على المستويات العالمية والقارية والبيولوجية. تشير نتائجنا إلى أن هناك 73000 نوع من الأشجار على مستوى العالم، من بينها 9000 نوع من الأشجار لم يتم اكتشافها بعد. يوجد ما يقرب من 40 ٪ من أنواع الأشجار غير المكتشفة في أمريكا الجنوبية. علاوة على ذلك، قد يكون ما يقرب من ثلث جميع أنواع الأشجار التي سيتم اكتشافها نادرًا، مع أعداد قليلة جدًا وتوزيع مكاني محدود (على الأرجح في الأراضي المنخفضة والجبال الاستوائية النائية). تسلط هذه النتائج الضوء على ضعف التنوع البيولوجي العالمي للغابات أمام التغيرات البشرية المنشأ في استخدام الأراضي والمناخ، والتي تهدد بشكل غير متناسب الأنواع النادرة وبالتالي ثراء الأشجار العالمي.

AbstractUnderstanding what controls global leaf type variation in trees is crucial for comprehending their role in terrestrial ecosystems, including carbon, water and nutrient dynamics. Yet our understanding of the factors influencing forest leaf types remains incomplete, leaving us uncertain about the global proportions of needle-leaved, broadleaved, evergreen and deciduous trees. To address these gaps, we conducted a global, ground-sourced assessment of forest leaf-type variation by integrating forest inventory data with comprehensive leaf form (broadleaf vs needle-leaf) and habit (evergreen vs deciduous) records. We found that global variation in leaf habit is primarily driven by isothermality and soil characteristics, while leaf form is predominantly driven by temperature. Given these relationships, we estimate that 38% of global tree individuals are needle-leaved evergreen, 29% are broadleaved evergreen, 27% are broadleaved deciduous and 5% are needle-leaved deciduous. The aboveground biomass distribution among these tree types is approximately 21% (126.4 Gt), 54% (335.7 Gt), 22% (136.2 Gt) and 3% (18.7 Gt), respectively. We further project that, depending on future emissions pathways, 17–34% of forested areas will experience climate conditions by the end of the century that currently support a different forest type, highlighting the intensification of climatic stress on existing forests. By quantifying the distribution of tree leaf types and their corresponding biomass, and identifying regions where climate change will exert greatest pressure on current leaf types, our results can help improve predictions of future terrestrial ecosystem functioning and carbon cycling.