• Energy Research

Forest dynamics and demography Tropical forest succession has been viewed mostly by considering trees in categories of early-, mid-, and late-successional species, corresponding to a fast–slow continuum of life history strategies. Rüger et al. now show that the fast–slow continuum does not capture the demographic strategy of the long-lived pioneer species, an important component of many tropical forests (see the Perspective by Bugmann). They developed a forest model that allows for objective predictions of tropical forest dynamics and validated the model's predictions against independent data. These findings should advance our understanding of tropical forest dynamics and facilitate sustainable tropical forest management. Science , this issue p. 165 ; see also p. 128

In the tropics, seasonally flooded forests (SFF) harbor fewer tree species than terra firme (i.e. non-flooded) forests. The low species diversity of tropical flooded forests has been ascribed to the paucity of species with adaptations to tolerate flooding. To test the hypothesis that flooding is the only factor restricting most species from SFF, we compared plant morphological and physiological responses to flooding in 2-month old seedlings of 6 species common to SFF and 12 species common to terra firme forests. Although flooding impaired growth, total biomass, maximum root length and stomatal conductance in most species, responses varied greatly and were species-specific. For example, after 90 days, flooding reduced leaf area growth by 10-50% in all species, except in Tabebuia, a common species from non-flooded habitats. Similarly, flooding had a 5-45% negative effect on total biomass for all species, except in 1 SFF and 1 terra firme species both of which had more biomass under flooding. A principal component analysis, using the above responses to flooding, provided no evidence that SFF and terra firme species differed in their responses to flooding. Flooding also caused reductions in root growth for most species. Rooting depth and root: shoot ratios were significantly less affected by flooding in SFF than in terra firme species. Although flood tolerance is critical for survival in flooded habitats, we hypothesize that responses to post-flooding events such as drought might be equally important in seasonal habitats. Therefore, we suggest that the ability to grow roots under anoxia might be critical in predicting success in inundated habitats that also experience a strong dry season.

1 IntroducciónDada la apremiante necesidad de cuantificar los flujos de carbono asociados con la dinámica de la vegetación terrestre, un número creciente de investigadores ha tratado de mejorar las estimaciones del volumen de árboles,la biomasa y las reservas de carbono. Las ecuaciones alométricas de árboles son herramientas críticas para tal propósito y tienen el potencial de mejorar nuestra comprensión sobre el secuestro de carbono en la vegetación boscosa, para apoyar la implementación de políticas y mecanismos diseñados para mitigar el cambio climático (por ejemplo, CDM y REDD+; Agrawal et al. 2011), para calcular los costos y beneficios asociados con los proyectos de carbono forestal, y para mejorar los sistemas de bioenergía y la gestión forestal sostenible (Henry et al. 2013). 1 Introduction Étant donné le besoin urgent de quantifier les flux de carbone associés à la dynamique de la végétation terrestre, un nombre croissant de chercheurs ont cherché à améliorer les estimations du volume des arbres, de la biomasse et des stocks de carbone. Les équations allométriques des arbres sont des outils essentiels à cette fin et ont le potentiel d'améliorer notre compréhension de la séquestration du carbone dans la végétation ligneuse, de soutenir la mise en œuvre de politiques et de mécanismes conçus pour atténuer le changement climatique (par exemple, CDM et REDD+ ; Agrawal et al. 2011), de calculer les coûts et les avantages associés aux projets de carbone forestier, et d'améliorer les systèmes de bioénergie et la gestion durable des forêts (Henry et al. 2013). 1 IntroductionGiven the pressing need to quantify carbon fluxes associatedwith terrestrial vegetation dynamics, an increasing number ofresearchers have sought to improve estimates of tree volume,biomass, and carbon stocks. Tree allometric equations arecritical tools for such purpose and have the potential toimprove our understanding about carbon sequestration inwoody vegetation, to support the implementation of policiesand mechanisms designed to mitigate climate change (e.g.CDM and REDD+; Agrawal et al. 2011), to calculate costsand benefits associated with forest carbon projects, and toimprove bioenergy systems and sustainable forest manage-ment (Henry et al. 2013). 1 المقدمة بالنظر إلى الحاجة الملحة لقياس تدفقات الكربون المرتبطة بديناميكيات الغطاء النباتي الأرضي، سعى عدد متزايد من الباحثين إلى تحسين تقديرات حجم الأشجار والكتلة الحيوية ومخزونات الكربون. تعد المعادلات المتجانسة للأشجار أدوات حاسمة لهذا الغرض ولديها القدرة على تحسين فهمنا لعزل الكربون في الغطاء النباتي الخشبي، لدعم تنفيذ السياسات والآليات المصممة للتخفيف من تغير المناخ (مثل CDM و REDD+؛ Agrawal et al. 2011)، لحساب التكاليف والفوائد المرتبطة بمشاريع كربون الغابات، وتحسين أنظمة الطاقة الحيوية والإدارة المستدامة للغابات (Henry et al. 2013).