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AbstractAimTropical forests account for a quarter of the global carbon storage and a third of the terrestrial productivity. Few studies have teased apart the relative importance of environmental factors and forest attributes for ecosystem functioning, especially for the tropics. This study aims to relate aboveground biomass (AGB) and biomass dynamics (i.e., net biomass productivity and its underlying demographic drivers: biomass recruitment, growth and mortality) to forest attributes (tree diversity, community‐mean traits and stand basal area) and environmental conditions (water availability, soil fertility and disturbance).LocationNeotropics.MethodsWe used data from 26 sites, 201 1‐ha plots and >92,000 trees distributed across the Neotropics. We quantified for each site water availability and soil total exchangeable bases and for each plot three key community‐weighted mean functional traits that are important for biomass stocks and productivity. We used structural equation models to test the hypothesis that all drivers have independent, positive effects on biomass stocks and dynamics.ResultsOf the relationships analysed, vegetation attributes were more frequently associated significantly with biomass stocks and dynamics than environmental conditions (in 67 vs. 33% of the relationships). High climatic water availability increased biomass growth and stocks, light disturbance increased biomass growth, and soil bases had no effect. Rarefied tree species richness had consistent positive relationships with biomass stocks and dynamics, probably because of niche complementarity, but was not related to net biomass productivity. Community‐mean traits were good predictors of biomass stocks and dynamics.Main conclusionsWater availability has a strong positive effect on biomass stocks and growth, and a future predicted increase in (atmospheric) drought might, therefore, potentially reduce carbon storage. Forest attributes, including species diversity and community‐weighted mean traits, have independent and important relationships with AGB stocks, dynamics and ecosystem functioning, not only in relatively simple temperate systems, but also in structurally complex hyper‐diverse tropical forests.

Models reveal the high carbon mitigation potential of tropical forest regeneration.

AbstractMost tropical forests outside protected areas have been or will be selectively logged so it is essential to maximize the conservation values of partially harvested areas. Here we examine the extent to which these forests sustain timber production, retain species, and conserve carbon stocks. We then describe some improvements in tropical forestry and how their implementation can be promoted. A simple meta‐analysis based on >100 publications revealed substantial variability but that: timber yields decline by about 46% after the first harvest but are subsequently sustained at that level; 76% of carbon is retained in once‐logged forests; and, 85–100% of species of mammals, birds, invertebrates, and plants remain after logging. Timber stocks will not regain primary‐forest levels within current harvest cycles, but yields increase if collateral damage is reduced and silvicultural treatments are applied. Given that selectively logged forests retain substantial biodiversity, carbon, and timber stocks, this “middle way” between deforestation and total protection deserves more attention from researchers, conservation organizations, and policy‐makers. Improvements in forest management are now likely if synergies are enhanced among initiatives to retain forest carbon stocks (REDD+), assure the legality of forest products, certify responsible management, and devolve control over forests to empowered local communities.

Los registros de dióxido de carbono atmosférico indican que la superficie terrestre ha actuado como un fuerte sumidero de carbono global en las últimas décadas, y una fracción sustancial de este sumidero probablemente se encuentra en los trópicos, particularmente en la Amazonía. Sin embargo, no está claro cómo evolucionará el sumidero de carbono terrestre a medida que el clima y la composición atmosférica continúen cambiando. Aquí analizamos la evolución histórica de la dinámica de la biomasa de la selva amazónica a lo largo de tres décadas utilizando una red distribuida de 321 parcelas. Si bien este análisis confirma que los bosques amazónicos han actuado como un sumidero neto de biomasa a largo plazo, encontramos una tendencia decreciente a largo plazo de la acumulación de carbono. Las tasas de aumento neto de la biomasa superficial disminuyeron en un tercio durante la última década en comparación con la década de 1990. Esto es consecuencia de que los aumentos de la tasa de crecimiento se estabilizaron recientemente, mientras que la mortalidad por biomasa aumentó persistentemente en todo momento, lo que llevó a un acortamiento de los tiempos de residencia del carbono. Los posibles impulsores del aumento de la mortalidad incluyen una mayor variabilidad climática y retroalimentaciones de un crecimiento más rápido de la mortalidad, lo que resulta en una menor longevidad de los árboles. La disminución observada del sumidero amazónico difiere notablemente del reciente aumento de la absorción de carbono terrestre a escala global, y es contraria a las expectativas basadas en modelos. Les enregistrements atmosphériques de dioxyde de carbone indiquent que la surface terrestre a agi comme un puissant puits de carbone mondial au cours des dernières décennies, une fraction substantielle de ce puits étant probablement située sous les tropiques, en particulier en Amazonie. Néanmoins, on ne sait pas comment le puits de carbone terrestre évoluera à mesure que le climat et la composition atmosphérique continueront de changer. Nous analysons ici l'évolution historique de la dynamique de la biomasse de la forêt amazonienne sur trois décennies à l'aide d'un réseau distribué de 321 parcelles. Bien que cette analyse confirme que les forêts amazoniennes ont agi comme un puits de biomasse net à long terme, nous constatons une tendance à la baisse à long terme de l'accumulation de carbone. Les taux d'augmentation nette de la biomasse aérienne ont diminué d'un tiers au cours de la dernière décennie par rapport aux années 1990. C'est une conséquence de la stabilisation récente de l'augmentation du taux de croissance, tandis que la mortalité liée à la biomasse a constamment augmenté, ce qui a entraîné une réduction des temps de résidence du carbone. Les facteurs potentiels de l'augmentation de la mortalité comprennent une plus grande variabilité du climat et des rétroactions d'une croissance plus rapide sur la mortalité, entraînant une réduction de la longévité des arbres. Le déclin observé du puits amazonien s'écarte nettement de la récente augmentation de l'absorption terrestre de carbone à l'échelle mondiale, et est contraire aux attentes basées sur des modèles. Atmospheric carbon dioxide records indicate that the land surface has acted as a strong global carbon sink over recent decades, with a substantial fraction of this sink probably located in the tropics, particularly in the Amazon. Nevertheless, it is unclear how the terrestrial carbon sink will evolve as climate and atmospheric composition continue to change. Here we analyse the historical evolution of the biomass dynamics of the Amazon rainforest over three decades using a distributed network of 321 plots. While this analysis confirms that Amazon forests have acted as a long-term net biomass sink, we find a long-term decreasing trend of carbon accumulation. Rates of net increase in above-ground biomass declined by one-third during the past decade compared to the 1990s. This is a consequence of growth rate increases levelling off recently, while biomass mortality persistently increased throughout, leading to a shortening of carbon residence times. Potential drivers for the mortality increase include greater climate variability, and feedbacks of faster growth on mortality, resulting in shortened tree longevity. The observed decline of the Amazon sink diverges markedly from the recent increase in terrestrial carbon uptake at the global scale, and is contrary to expectations based on models. تشير سجلات ثاني أكسيد الكربون في الغلاف الجوي إلى أن سطح الأرض كان بمثابة حوض كربون عالمي قوي على مدى العقود الأخيرة، وربما يقع جزء كبير من هذا الحوض في المناطق المدارية، لا سيما في الأمازون. ومع ذلك، من غير الواضح كيف ستتطور بالوعة الكربون الأرضية مع استمرار تغير المناخ وتكوين الغلاف الجوي. نحلل هنا التطور التاريخي لديناميكيات الكتلة الحيوية لغابات الأمازون المطيرة على مدى ثلاثة عقود باستخدام شبكة موزعة من 321 قطعة أرض. في حين يؤكد هذا التحليل أن غابات الأمازون كانت بمثابة بالوعة صافية طويلة الأجل للكتلة الحيوية، فإننا نجد اتجاهًا تنازليًا طويل الأجل لتراكم الكربون. انخفضت معدلات الزيادة الصافية في الكتلة الحيوية فوق الأرض بمقدار الثلث خلال العقد الماضي مقارنة بالتسعينيات. وهذا نتيجة لاستقرار زيادات معدل النمو في الآونة الأخيرة، في حين زادت وفيات الكتلة الحيوية باستمرار طوال الوقت، مما أدى إلى تقصير أوقات بقاء الكربون. وتشمل الدوافع المحتملة لزيادة الوفيات زيادة تقلب المناخ، وردود الفعل على النمو الأسرع للوفيات، مما يؤدي إلى تقصير عمر الأشجار. يختلف الانخفاض الملحوظ في حوض الأمازون بشكل ملحوظ عن الزيادة الأخيرة في امتصاص الكربون الأرضي على النطاق العالمي، ويتعارض مع التوقعات القائمة على النماذج.

AbstractTropical forests are global centres of biodiversity and carbon storage. Many tropical countries aspire to protect forest to fulfil biodiversity and climate mitigation policy targets, but the conservation strategies needed to achieve these two functions depend critically on the tropical forest tree diversity-carbon storage relationship. Assessing this relationship is challenging due to the scarcity of inventories where carbon stocks in aboveground biomass and species identifications have been simultaneously and robustly quantified. Here, we compile a unique pan-tropical dataset of 360 plots located in structurally intact old-growth closed-canopy forest, surveyed using standardised methods, allowing a multi-scale evaluation of diversity-carbon relationships in tropical forests. Diversity-carbon relationships among all plots at 1 ha scale across the tropics are absent, and within continents are either weak (Asia) or absent (Amazonia, Africa). A weak positive relationship is detectable within 1 ha plots, indicating that diversity effects in tropical forests may be scale dependent. The absence of clear diversity-carbon relationships at scales relevant to conservation planning means that carbon-centred conservation strategies will inevitably miss many high diversity ecosystems. As tropical forests can have any combination of tree diversity and carbon stocks both require explicit consideration when optimising policies to manage tropical carbon and biodiversity.