• Energy Research

Understanding the capacity of forests to adapt to climate change is of pivotal importance for conservation science, yet this is still widely unknown. This knowledge gap is particularly acute in high-biodiversity tropical forests. Here, we examined how tropical forests of the Americas have shifted community trait composition in recent decades as a response to changes in climate. Based on historical trait-climate relationships, we found that, overall, the studied functional traits show shifts of less than 8% of what would be expected given the observed changes in climate. However, the recruit assemblage shows shifts of 21% relative to climate change expectation. The most diverse forests on Earth are changing in functional trait composition but at a rate that is fundamentally insufficient to track climate change.

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.

AbstractForest biomass is an essential indicator for monitoring the Earth’s ecosystems and climate. It is a critical input to greenhouse gas accounting, estimation of carbon losses and forest degradation, assessment of renewable energy potential, and for developing climate change mitigation policies such as REDD+, among others. Wall-to-wall mapping of aboveground biomass (AGB) is now possible with satellite remote sensing (RS). However, RS methods require extant, up-to-date, reliable, representative and comparable in situ data for calibration and validation. Here, we present the Forest Observation System (FOS) initiative, an international cooperation to establish and maintain a global in situ forest biomass database. AGB and canopy height estimates with their associated uncertainties are derived at a 0.25 ha scale from field measurements made in permanent research plots across the world’s forests. All plot estimates are geolocated and have a size that allows for direct comparison with many RS measurements. The FOS offers the potential to improve the accuracy of RS-based biomass products while developing new synergies between the RS and ground-based ecosystem research communities.

Impacts of climate change on the future dynamics of Central African forests are still largely unknown, despite the acuteness of the expected climate changes and the extent of these forests. The high diversity of species and the potentially equivalent diversity of responses to climate modifications are major difficulties encountered when using predictive models to evaluate these impacts. In this study, we applied a mixture of inhomogeneous matrix models to a long-term experimental site located in M’Baïki forests, in the Central African Republic. This model allows the clustering of tree species into processes-based groups while simultaneously selecting explanatory climate and stand variables at the group-level. Using downscaled outputs of 10 general circulation models (G cm ), we projected the future forest dynamics up to the end of the century, under constant climate and Representative Concentration Pathways 4.5 and 8.5. Through comparative analyses across G cm versions, we identified tree species meta-groups, which are more adapted than ecological guilds to describe the diversity of tree species dynamics and their responses to climate change. Projections under constant climate were consistent with a forest ageing phenomenon, with a slowdown in tree growth and a reduction of the relative abundance of short-lived pioneers. Projections under climate change showed a general increase in growth, mortality and recruitment. This acceleration in forest dynamics led to a strong natural thinning effect, with different magnitudes across species. These differences caused a compositional shift in favour of long-lived pioneers, at the detriment of shade-bearers. Consistent with other field studies and projections, our results show the importance of elucidating the diversity of tree species responses when considering the general sensitivity of Central African forests dynamics to climate change.

Abstract Background Natural disturbance is a fundamental component of the functioning of tropical rainforests let to natural dynamics, with tree mortality the driving force of forest renewal. With ongoing global (i.e. land-use and climate) changes, tropical forests are currently facing deep and rapid modifications in disturbance regimes that may hamper their recovering capacity so that developing robust predictive model able to predict ecosystem resilience and recovery becomes of primary importance for decision-making: (i) Do regenerating forests recover faster than mature forests given the same level of disturbance? (ii) Is the local topography an important predictor of the post-disturbance forest trajectories? (iii) Is the community functional composition, assessed with community weighted-mean functional traits, a good predictor of carbon stock recovery? (iv) How important is the climate stress (seasonal drought and/or soil water saturation) in shaping the recovery trajectory? Methods Paracou is a large scale forest disturbance experiment set up in 1984 with nine 6.25 ha plots spanning on a large disturbance gradient where 15 to 60% of the initial forest ecosystem biomass were removed. More than 70,000 trees belonging to ca. 700 tree species have then been censused every 2 years up today. Using this unique dataset, we aim at deciphering the endogenous (forest structure and composition) and exogenous (local environment and climate stress) drivers of ecosystem recovery in time. To do so, we disentangle carbon recovery into demographic processes (recruitment, growth, mortality fluxes) and cohorts (recruited trees, survivors). Results Variations in the pre-disturbance forest structure or in local environment do not shape significantly the ecosystem recovery rates. Variations in the pre-disturbance forest composition and in the post-disturbance climate significantly change the forest recovery trajectory. Pioneer-rich forests have slower recovery rates than assemblages of late-successional species. Soil water saturation during the wet season strongly impedes ecosystem recovery but not seasonal drought. From a sensitivity analysis, we highlight the pre-disturbance forest composition and the post-disturbance climate conditions as the primary factors controlling the recovery trajectory. Conclusions Highly-disturbed forests and secondary forests because they are composed of a lot of pioneer species will be less able to cope with new disturbance. In the context of increasing tree mortality due to both (i) severe droughts imputable to climate change and (ii) human-induced perturbations, tropical forest management should focus on reducing disturbances by developing Reduced Impact Logging techniques.