• Energy Research

AbstractTropical forests face increasing climate risk1,2, yet our ability to predict their response to climate change is limited by poor understanding of their resistance to water stress. Although xylem embolism resistance thresholds (for example, $$\varPsi $$ Ψ 50) and hydraulic safety margins (for example, HSM50) are important predictors of drought-induced mortality risk3–5, little is known about how these vary across Earth’s largest tropical forest. Here, we present a pan-Amazon, fully standardized hydraulic traits dataset and use it to assess regional variation in drought sensitivity and hydraulic trait ability to predict species distributions and long-term forest biomass accumulation. Parameters $$\varPsi $$ Ψ 50 and HSM50 vary markedly across the Amazon and are related to average long-term rainfall characteristics. Both $$\varPsi $$ Ψ 50 and HSM50 influence the biogeographical distribution of Amazon tree species. However, HSM50 was the only significant predictor of observed decadal-scale changes in forest biomass. Old-growth forests with wide HSM50 are gaining more biomass than are low HSM50 forests. We propose that this may be associated with a growth–mortality trade-off whereby trees in forests consisting of fast-growing species take greater hydraulic risks and face greater mortality risk. Moreover, in regions of more pronounced climatic change, we find evidence that forests are losing biomass, suggesting that species in these regions may be operating beyond their hydraulic limits. Continued climate change is likely to further reduce HSM50 in the Amazon6,7, with strong implications for the Amazon carbon sink.

Andean tropical montane forests (TMF) are hotspots of biodiversity that provide fundamental hydrological services as well as carbon sequestration and storage. Agroforestry systems occupy large areas in the Andes but climatic pressures, market volatility and diseases may result inagroforest abandonment, promoting secondary succession. Secondary forests are well-adapted and efficient carbon sinks whose conservation is vital to mitigate and adapt to climate change and to support biodiversity. Little is known, however, about how secondary TMF recover their aboveground biomass (AGB) and composition after abandonment. We established a 1.5 ha plot at 1780 masl on a 30-year old abandoned agroforest and compared it against two control forest plots at similar elevations. Agroforestry legacies influenced AGB leading to far lower stocks (42.3 ± 5.4–59.6 ± 7.9 Mg ha−1 using allometric equations) than those expected after 30 years (106 ± 33 Mg ha−1) based on IPCC standard growth rates for secondary montane forests. This suggests a regional overestimation of mitigation potentials when using IPCC standards. Satellite-derived AGB largely overestimated our plot values (179 ± 27.3 Mg ha−1). Secondary growth rates (1.41–2.0 Mg ha−1 yr−1 for DBH ≥ 10 cm) indicate recovery times of ca. 69 to 97 years to reach average control AGB values (137 ± 12.3 Mg ha−1). This is 26 years above the average residence time of montane forests at our elevation (71 ± 1.91 years) suggesting a non-recovery or far slower recovery to control AGB values. Three variables appear to define this outcome compared to the control plots: lower DBH (15.8 ± 5.9 cm vs 19.8 ± 11.0 cm), lower basal area (12.67 ± 0.7 vs 28.03 ± 1.5 m2 ha−1) and higher abundance of lighter-wood tree genera (0.46 ± 0.10 vs 0.57 ± 0.11 gr cm3) such as Inga, a common shade-tree in Andean agroforests. With 3.2 million hectares committed to restoration, Peru needs to target currently neglected TMF recovery schemes to support biodiversity, water and carbon storage and fulfill its international commitments.

AbstractNon-structural carbohydrates (NSC) are major substrates for plant metabolism and have been implicated in mediating drought-induced tree mortality. Despite their significance, NSC dynamics in tropical forests remain little studied. We present leaf and branch NSC data for 82 Amazon canopy tree species in six sites spanning a broad precipitation gradient. During the wet season, total NSC (NSCT) concentrations in both organs were remarkably similar across communities. However, NSCT and its soluble sugar (SS) and starch components varied much more across sites during the dry season. Notably, the proportion of leaf NSCT in the form of SS (SS:NSCT) increased greatly in the dry season in almost all species in the driest sites, implying an important role of SS in mediating water stress in these sites. This adjustment of leaf NSC balance was not observed in tree species less-adapted to water deficit, even under exceptionally dry conditions. Thus, leaf carbon metabolism may help to explain floristic sorting across water availability gradients in Amazonia and enable better prediction of forest responses to future climate change.

Abstract Understanding tropical secondary forest canopy greenness and responses to climatic conditions is important for climate change mitigation, particularly in the tropics where secondary forest growth is a substantial carbon sink and a promoted natural climate solution. We here test three hypotheses: (a) forest canopy greenness is higher in younger, secondary forests than in older, primary or mature forests, (b) secondary forests are more vulnerable to climatic pressures and (c) there are significant differences between forest types regarding primary–secondary canopy greenness and their differential responses to drought anomalies. To explore these relationships, we monitored wet and dry seasonal greenness from 2001 to 2020, estimated through the enhanced vegetation index (EVI), of Peruvian tropical dry, montane and lowland secondary forests and compared it to nearby primary forests. We developed predictive models of seasonal EVI using remotely sensed variables, including land surface temperature (LST), evapotranspiration (ET), potential evapotranspiration (PET), ratio of ET and PET (ETn), and the standard precipitation index (SPI). Overall, there was a higher change in annual and seasonal EVI for secondary forests compared to primary forests. However, primary forests maintained relatively stable EVI levels during the wet season despite drought anomalies. When decoupling forest type canopy greenness and drought response, primary forest greenness in dry and lowland ecosystems were temporally more stable. Secondary montane had a lower increase in greenness when drought anomalies held during different seasons. Stepwise multiple linear regression models indicated that LST and ETn, a plant water use index, were the most significant factors to predict greening fluctuations in dry and montane forest types. ET and SPI mostly drove wet season mean EVI across all forest types. Predictors of dry season mean EVI varied, but mostly including water availability. Our results suggest that tropical secondary forests are more productive overall yet more vulnerable to prolonged drought.

Alors que les forêts tropicales subissent une transformation rapide en raison des impacts humains directs, de nombreuses zones déboisées reviennent à la forêt par le biais d'une régénération naturelle ou assistée par l'homme. Cette situation offre une fenêtre d'opportunité pour mettre en œuvre des stratégies de gestion forestière afin d'atteindre les objectifs environnementaux tout en promouvant le développement social et en contribuant aux moyens de subsistance locaux. Cependant, une politique de gestion forestière réussie dépend de la façon dont nous pouvons évaluer les conséquences environnementales ainsi que de la valeur des services écosystémiques fournis par ces forêts en repousse. Ici, nous passons en revue la littérature publiée pour synthétiser les services écosystémiques fournis par trois types de transitions forestières : les forêts secondaires naturellement régénérées, les systèmes agroforestiers et les plantations d'arbres, dans les régions côtières, andines et amazoniennes du Pérou. Nous discutons ensuite du potentiel de ces forêts en repousse en tant que solutions basées sur la nature qui peuvent aider à l'adoption de politiques qui favorisent leur utilisation durable et leur conservation. Notre analyse documentaire révèle que les transitions forestières fournissent des services importants pour compenser les émissions de carbone, fournir des habitats pour la biodiversité et réguler les services hydrologiques. Cependant, la quantité et l'importance des services écosystémiques varient en fonction de la transition forestière type.Les forêts secondaires offrent de multiples services, représentant une stratégie peu coûteuse, immédiate et très efficace pour atténuer les crises climatiques et de biodiversité et, en fin de compte, fournir des services écosystémiques vitaux à la société, tels que l'approvisionnement en eau. En revanche, les plantations d'arbres exotiques ont des effets négatifs sur les services de régulation de l'eau. Nous soulignons le potentiel des forêts secondaires pour la gestion des terres qui soutient de multiples initiatives environnementales intégrées. Ce cadre peut guider les décisions politiques pour choisir les options appropriées sur les types de transition forestière les plus appropriés pour atteindre des objectifs finaux spécifiques à l'échelle locale et régionale, en tenant compte à la fois des services écosystémiques et des services pour éviter les compromis dans lesquels la réalisation d'un objectif est préjudiciable à un autre. Si bien los bosques tropicales están experimentando una rápida transformación como resultado de los impactos humanos directos, muchas áreas deforestadas están volviendo a los bosques a través de la regeneración natural o asistida por el hombre. Esta situación brinda una ventana de oportunidad para implementar estrategias de manejo forestal para lograr objetivos ambientales al tiempo que promueve el desarrollo social y contribuye a los medios de vida locales. Sin embargo, la política de manejo forestal exitosa depende de qué tan bien podemos evaluar las consecuencias ambientales, así como del valor de los servicios ecosistémicos que brindan estos bosques en crecimiento. Aquí, revisamos la literatura publicada para sintetizar los servicios ecosistémicos proporcionados por tres tipos de transiciones forestales: bosques secundarios regenerados naturalmente, sistemas agroforestales y plantaciones de árboles, en las regiones costeras, andinas y amazónicas del Perú. Luego discutimos el potencial de estos bosques en crecimiento como soluciones basadas en la naturaleza que pueden ayudar en la adopción de políticas que promuevan su uso y conservación sostenibles. Nuestro análisis de la literatura revela que las transiciones forestales brindan servicios significativos para compensar las emisiones de carbono, proporcionar hábitats para la biodiversidad y regular los servicios hidrológicos. Sin embargo, la cantidad y la importancia de los servicios ecosistémicos varían dependiendo de la transición forestal tipo. Los bosques secundarios ofrecen múltiples servicios, lo que representa una estrategia de bajo costo, inmediata y altamente efectiva para mitigar las crisis climáticas y de biodiversidad y, en última instancia, proporcionar servicios ecosistémicos vitales a la sociedad, como la provisión de agua. En contraste, las plantaciones de árboles exóticos tienen efectos negativos en los servicios de regulación del agua. Destacamos el potencial de los bosques secundarios para la gestión de la tierra que apoya iniciativas ambientales múltiples e integradas. Este marco puede guiar las decisiones políticas para elegir las opciones apropiadas sobre los tipos de transición forestal más adecuados para lograr objetivos finales específicos a escala local y regional, considerando tanto los servicios ecosistémicos como los diservicios para evitar compensaciones en las que el logro de un objetivo es perjudicial para otro. While tropical forests are undergoing rapid transformation as a result of direct human impacts, many deforested areas are reverting to forest through natural or human-assisted regeneration.This situation provides a window of opportunity to implement forest management strategies to achieve environmental objectives while promoting social development and contributing to local livelihoods.Successful forest management policy, however, depends on how well we can appraise environmental consequences as well as on the value of ecosystem services that these regrowing forests provide.Here, we review the published literature to synthesize the ecosystem services provided by three types of forest transitions: naturally-regenerated secondary forests, agroforestry systems, and tree plantations, in the coastal, Andean, and Amazonian regions of Peru.We then discuss the potential of these regrowing forests as naturebased solutions that can help in the adoption of policies that promote their sustainable use and conservation.Our literature analysis reveals that forest transitions provide significant services in offsetting carbon emissions, providing habitats for biodiversity, and regulating hydrological services.However, the amount and importance of ecosystem services vary depending on the forest transition type.Secondary forests offer multiple services, representing a low-cost, immediate, and highly effective strategy in mitigating the climate and biodiversity crises and ultimately providing vital ecosystem services to society, such as water provision.In contrast, exotic tree plantations have negative effects on water regulation services.We highlight the potential of secondary forests for land management that supports multiple and integrated environmental initiatives.This framework can guide policy decisions to choose appropriate options on forest transition types most suitable to achieve specific end goals at local and regional scales, considering both ecosystem services and disservices to avoid trade-offs in which the achievement of one goal is detrimental to another. في حين أن الغابات الاستوائية تمر بتحول سريع نتيجة للتأثيرات البشرية المباشرة، فإن العديد من المناطق التي أزيلت منها الغابات تعود إلى الغابات من خلال التجديد الطبيعي أو بمساعدة الإنسان. يوفر هذا الوضع فرصة لتنفيذ استراتيجيات إدارة الغابات لتحقيق الأهداف البيئية مع تعزيز التنمية الاجتماعية والمساهمة في سبل العيش المحلية. ومع ذلك، تعتمد سياسة إدارة الغابات الناجحة على مدى قدرتنا على تقييم العواقب البيئية وكذلك على قيمة خدمات النظام الإيكولوجي التي توفرها هذه الغابات التي تعيد نموها. هنا، نراجع الأدبيات المنشورة توليف خدمات النظام الإيكولوجي التي توفرها ثلاثة أنواع من التحولات الحرجية: الغابات الثانوية المتجددة طبيعياً، وأنظمة الحراجة الزراعية، ومزارع الأشجار، في المناطق الساحلية والأنديز والأمازون في بيرو. ثم نناقش إمكانات إعادة زراعة هذه الغابات كحلول قائمة على الطبيعة يمكن أن تساعد في اعتماد سياسات تعزز استخدامها المستدام والحفاظ عليها. يكشف تحليلنا الأدبي أن التحولات الحرجية توفر خدمات مهمة في تعويض انبعاثات الكربون، وتوفير الموائل للتنوع البيولوجي، وتنظيم الخدمات الهيدرولوجية. ومع ذلك، فإن كمية وأهمية خدمات النظام الإيكولوجي تختلف باختلاف انتقال الغابات النوع. تقدم الغابات الثانوية خدمات متعددة، تمثل استراتيجية منخفضة التكلفة وفورية وفعالة للغاية في التخفيف من أزمات المناخ والتنوع البيولوجي، وفي نهاية المطاف توفر خدمات النظام الإيكولوجي الحيوية للمجتمع، مثل توفير المياه. وعلى النقيض من ذلك، فإن مزارع الأشجار الغريبة لها آثار سلبية على خدمات تنظيم المياه. نسلط الضوء على إمكانات الغابات الثانوية لإدارة الأراضي التي تدعم مبادرات بيئية متعددة ومتكاملة. يمكن أن يوجه هذا الإطار قرارات السياسة لاختيار الخيارات المناسبة لأنواع انتقال الغابات الأكثر ملاءمة لتحقيق أهداف نهائية محددة على المستويين المحلي والإقليمي، مع مراعاة كل من خدمات النظام الإيكولوجي والخدمات لتجنب المفاضلات التي يكون فيها تحقيق هدف ما ضارًا بآخر.