• Energy Research

The palm Euterpe oleracea is a dominant and promising species in flood plains of the Atrato river, Choco region of Colombia. We assessed the population dynamics of this species through growth rates, mortality and recruitment patterns for a period of two and a half years. Dynamic rates were compared between mixed and pure flood plain palm forests. These forests types were associated to different flooding regimes. Trees and palms were thinned in a portion for each forest type, the rest was left undisturbed. We used projection matrices to follow population trends. Thinning increased the transition probability of smaller individuals, but decreased it for larger individuals, as is typical of light demanding species. Thinning also increased mortality rates in almost all size classes, but did not affect recruitment rates. Under natural conditions, the E. oleracea populations are in equilibrium in pure and mixed forests. Thinning increased population growth in both forest types, suggesting the role played by density-dependent processes on the population size of this species. The palm Euterpe oleracea is a dominant and promising species in flood plains of the Atrato river, Choco region of Colombia. We assessed the population dynamics of this species through growth rates, mortality and recruitment patterns for a period of two and a half years. Dynamic rates were compared among mixed and pure flood plain palm forests. These forests types were associated to different flooding regimes. Trees and palms were thinned in a portion for each forest type, the rest was left undisturbed. We used projection matrices to follow population trends. Thinning increased the transition probability of smaller individuals, but decreased it for larger individuals, as is typical of light demanding species. Thinning also increased mortality rates in almost all size classes, but did not affect recruitment rates. Under natural conditions, the E. oleracea populations are in equilibrium in pure and mixed forests. Thinning increased population growth in both forest types, suggesting the role played by density-dependent processes on the population size of this species. The palm Euterpe oleracea is a dominant and promising species in flood plains of the Atrato river, Choco region of Colombia. We assessed the population dynamics of this species through growth rates, mortality and recruitment patterns for a period of two and a half years. Dynamic rates were compared among mixed and pure flood plain palm forests. These forests types were associated to different flooding regimes. Trees and palms were thinned in a portion for each forest type, the rest was left undisturbed. We used projection matrices to follow population trends. Thinning increased the transition probability of smaller individuals, but decreased it for larger individuals, as is typical of light demanding species. Thinning also increased mortality rates in almost all size classes, but did not affect recruitment rates. Under natural conditions, the E. oleracea populations are in equilibrium in pure and mixed forests. Thinning increased population growth in both forest types, suggesting the role played by density-dependent processes on the population size of this species. نخيل يوتيربي أوليراسيا هو نوع مهيمن وواعد في سهول الفيضانات في نهر أتراتو، منطقة تشوكو في كولومبيا. قمنا بتقييم الديناميكيات السكانية لهذا النوع من خلال معدلات النمو والوفيات وأنماط التجنيد لمدة عامين ونصف العام. تمت مقارنة المعدلات الديناميكية بين غابات النخيل السهلية المختلطة والنقية. ارتبطت هذه الأنواع من الغابات بأنظمة فيضانات مختلفة. تم ترقق الأشجار والنخيل في جزء لكل نوع غابة، وترك الباقي دون عائق. استخدمنا مصفوفات الإسقاط لمتابعة الاتجاهات السكانية. زاد الترقق من احتمالية انتقال الأفراد الأصغر، لكنه قللها بالنسبة للأفراد الأكبر، كما هو الحال بالنسبة للأنواع التي تتطلب الضوء. كما أدى التخفيف إلى زيادة معدلات الوفيات في جميع فئات الحجم تقريبًا، لكنه لم يؤثر على معدلات التجنيد. في ظل الظروف الطبيعية، تكون مجموعات E. oleracea في حالة توازن في الغابات النقية والمختلطة. ترقق النمو السكاني المتزايد في كلا نوعي الغابات، مما يشير إلى الدور الذي تلعبه العمليات المعتمدة على الكثافة في حجم سكان هذا النوع.

Abstract Wood density is a critical control on tree biomass, so poor understanding of its spatial variation can lead to large and systematic errors in forest biomass estimates and carbon maps. The need to understand how and why wood density varies is especially critical in tropical America where forests have exceptional species diversity and spatial turnover in composition. As tree identity and forest composition are challenging to estimate remotely, ground surveys are essential to know the wood density of trees, whether measured directly or inferred from their identity. Here, we assemble an extensive dataset of variation in wood density across the most forested and tree-diverse continent, examine how it relates to spatial and environmental variables, and use these relationships to predict spatial variation in wood density over tropical and sub-tropical South America. Our analysis refines previously identified east-west Amazon gradients in wood density, improves them by revealing fine-scale variation, and extends predictions into Andean, dry, and Atlantic forests. The results halve biomass prediction errors compared to a naïve scenario with no knowledge of spatial variation in wood density. Our findings will help improve remote sensing-based estimates of aboveground biomass carbon stocks across tropical South America.

AbstractIt is largely unknown how South America’s Andean forests affect the global carbon cycle, and thus regulate climate change. Here, we measure aboveground carbon dynamics over the past two decades in 119 monitoring plots spanning a range of >3000 m elevation across the subtropical and tropical Andes. Our results show that Andean forests act as strong sinks for aboveground carbon (0.67 ± 0.08 Mg C ha−1y−1) and have a high potential to serve as future carbon refuges. Aboveground carbon dynamics of Andean forests are driven by abiotic and biotic factors, such as climate and size-dependent mortality of trees. The increasing aboveground carbon stocks offset the estimated C emissions due to deforestation between 2003 and 2014, resulting in a net total uptake of 0.027 Pg C y−1. Reducing deforestation will increase Andean aboveground carbon stocks, facilitate upward species migrations, and allow for recovery of biomass losses due to climate change.

Summary The relative importance of tree mortality risk factors remains unknown, especially in diverse tropical forests where species may vary widely in their responses to particular conditions. We present a new framework for quantifying the importance of mortality risk factors and apply it to compare 19 risks on 31 203 trees (1977 species) in 14 one‐year periods in six tropical forests. We defined a condition as a risk factor for a species if it was associated with at least a doubling of mortality rate in univariate analyses. For each risk, we estimated prevalence (frequency), lethality (difference in mortality between trees with and without the risk) and impact (‘excess mortality’ associated with the risk, relative to stand‐level mortality). The most impactful risk factors were light limitation and crown/trunk loss; the most prevalent were light limitation and small size; the most lethal were leaf damage and wounds. Modes of death (standing, broken and uprooted) had limited links with previous conditions and mortality risk factors. We provide the first ranking of importance of tree‐level mortality risk factors in tropical forests. Future research should focus on the links between these risks, their climatic drivers and the physiological processes to enable mechanistic predictions of future tree mortality.

AbstractAccurate estimates of forest biomass stocks and fluxes are needed to quantify global carbon budgets and assess the response of forests to climate change. However, most forest inventories consider tree mortality as the only aboveground biomass (AGB) loss without accounting for losses via damage to living trees: branchfall, trunk breakage, and wood decay. Here, we use ~151,000 annual records of tree survival and structural completeness to compare AGB loss via damage to living trees to total AGB loss (mortality + damage) in seven tropical forests widely distributed across environmental conditions. We find that 42% (3.62 Mg ha−1 year−1; 95% confidence interval [CI] 2.36–5.25) of total AGB loss (8.72 Mg ha−1 year−1; CI 5.57–12.86) is due to damage to living trees. Total AGB loss was highly variable among forests, but these differences were mainly caused by site variability in damage‐related AGB losses rather than by mortality‐related AGB losses. We show that conventional forest inventories overestimate stand‐level AGB stocks by 4% (1%–17% range across forests) because assume structurally complete trees, underestimate total AGB loss by 29% (6%–57% range across forests) due to overlooked damage‐related AGB losses, and overestimate AGB loss via mortality by 22% (7%–80% range across forests) because of the assumption that trees are undamaged before dying. Our results indicate that forest carbon fluxes are higher than previously thought. Damage on living trees is an underappreciated component of the forest carbon cycle that is likely to become even more important as the frequency and severity of forest disturbances increase.

Les modèles généraux de dynamique forestière et de productivité dans les Andes sont mal caractérisés. Nous présentons ici la première étude à grande échelle de la dynamique des forêts andines à l'aide d'un ensemble de 63 parcelles forestières permanentes assemblées au cours des deux dernières décennies. Dans le centre-nord des Andes, le renouvellement des arbres (mortalité et recrutement) et la croissance des arbres ont diminué avec l'augmentation de l'altitude et la diminution de la température. De plus, la surface terrière a augmenté dans les forêts humides montagnardes inférieures, mais n'a pas changé dans les forêts humides montagnardes supérieures. Cependant, à des altitudes plus élevées, l'absence de changement net de la surface terrière et l'excès de mortalité par rapport au recrutement suggèrent des impacts environnementaux négatifs. Dans le nord-ouest de l'Argentine, la dynamique des forêts semble être influencée par l'histoire de l'utilisation des terres en plus des variations environnementales. Pris ensemble, nos résultats indiquent que les combinaisons de facteurs abiotiques et biotiques qui varient selon les gradients d'élévation sont des déterminants importants du renouvellement et de la productivité des arbres dans les Andes. Un suivi et des analyses plus approfondis et à plus long terme de la dynamique des forêts dans les parcelles permanentes seront nécessaires pour comprendre comment les processus démographiques et la biomasse ligneuse répondent aux conditions environnementales changeantes le long des gradients d'altitude tout au long de ce siècle. Los patrones generales de dinámica forestal y productividad en la Cordillera de los Andes están mal caracterizados. Aquí presentamos el primer estudio a gran escala de la dinámica forestal andina utilizando un conjunto de 63 parcelas forestales permanentes ensambladas en las últimas dos décadas. En los Andes centro-norte, la rotación de árboles (mortalidad y reclutamiento) y el crecimiento de los árboles disminuyeron con el aumento de la elevación y la disminución de la temperatura. Además, el área basal aumentó en los bosques húmedos montanos inferiores, pero no cambió en los bosques húmedos montanos superiores. Sin embargo, en altitudes más altas, la falta de cambio neto en el área basal y el exceso de mortalidad sobre el reclutamiento sugieren impactos ambientales negativos. En el noroeste de Argentina, la dinámica forestal parece estar influenciada por la historia del uso de la tierra, además de la variación ambiental. En conjunto, nuestros resultados indican que las combinaciones de factores abióticos y bióticos que varían según los gradientes de elevación son determinantes importantes de la rotación y la productividad de los árboles en los Andes. Será necesario un monitoreo y análisis más extenso y a más largo plazo de la dinámica forestal en parcelas permanentes para comprender cómo los procesos demográficos y la biomasa leñosa están respondiendo a las condiciones ambientales cambiantes a lo largo de los gradientes de elevación a lo largo de este siglo. General patterns of forest dynamics and productivity in the Andes Mountains are poorly characterized. Here we present the first large-scale study of Andean forest dynamics using a set of 63 permanent forest plots assembled over the past two decades. In the North-Central Andes tree turnover (mortality and recruitment) and tree growth declined with increasing elevation and decreasing temperature. In addition, basal area increased in Lower Montane Moist Forests but did not change in Higher Montane Humid Forests. However, at higher elevations the lack of net basal area change and excess of mortality over recruitment suggests negative environmental impacts. In North-Western Argentina, forest dynamics appear to be influenced by land use history in addition to environmental variation. Taken together, our results indicate that combinations of abiotic and biotic factors that vary across elevation gradients are important determinants of tree turnover and productivity in the Andes. More extensive and longer-term monitoring and analyses of forest dynamics in permanent plots will be necessary to understand how demographic processes and woody biomass are responding to changing environmental conditions along elevation gradients through this century. تتسم الأنماط العامة لديناميكيات الغابات والإنتاجية في جبال الأنديز بالضعف. نقدم هنا أول دراسة واسعة النطاق لديناميكيات غابات الأنديز باستخدام مجموعة من 63 قطعة أرض حرجية دائمة تم تجميعها على مدى العقدين الماضيين. في شمال وسط جبال الأنديز، انخفض معدل دوران الأشجار (الوفيات والتجنيد) ونمو الأشجار مع زيادة الارتفاع وانخفاض درجة الحرارة. بالإضافة إلى ذلك، زادت المساحة القاعدية في الغابات الرطبة الجبلية السفلى ولكنها لم تتغير في الغابات الرطبة الجبلية العليا. ومع ذلك، في المرتفعات المرتفعة، يشير الافتقار إلى صافي التغير في المنطقة القاعدية وزيادة الوفيات على التجنيد إلى آثار بيئية سلبية. في شمال غرب الأرجنتين، يبدو أن ديناميكيات الغابات تتأثر بتاريخ استخدام الأراضي بالإضافة إلى التباين البيئي. تشير نتائجنا مجتمعة إلى أن مجموعات العوامل اللاأحيائية والأحيائية التي تختلف عبر تدرجات الارتفاع هي محددات مهمة لدوران الأشجار والإنتاجية في جبال الأنديز. سيكون من الضروري إجراء عمليات رصد وتحليل أكثر شمولاً وأطول أجلاً لديناميكيات الغابات في قطع الأراضي الدائمة لفهم كيفية استجابة العمليات الديموغرافية والكتلة الحيوية الخشبية للظروف البيئية المتغيرة على طول تدرجات الارتفاع خلال هذا القرن.