twoe: An R package for modelling tropical forest dynamics from permanent sample plots using a hierarchical Bayesian approach to capture species diversity

Permanent sample plots are commonly used in tropical forest ecology for conservation and management purposes. Longitudinal tree data can be used to estimate species demographic functions which can then be implemented in forest dynamics simulators to help decision. For tropical forests, with many species being rare species with few observations, the classical modelling approach assumes a restricted number of functional groups (pioneer, light-demanding and shade-tolerant species groups when light partitioning is supposed to be the main mechanism driving community, which is a frequent assumption). Although this simplified approach is convenient in practice, it relies on strong assumptions: i) that species can be grouped, ii) regarding a limited number of criteria, and it suffers from several pitfalls both on the theoretical and applied side. First, because of the principle of competitive exclusion and of the multidimensionality of the species niche, the functional group approach is likely to be biased and to lead to unrealistic simulations. Second, using functional groups impede conservation planning at the species level which should be the advised approach especially when considering rare species. In this study, we present the "twoe" (2e) software, available as a R package, which allows i) formatting the permanent sample plot data for demographic analysis, ii) estimating the parameters of growth, mortality and recruitment functions including a competition effect, iii) simulating forest dynamics with a forecast of the basal area (possibly carbon) and of the community composition. The modelling approach in the twoe software includes species random effects in a hierarchical Bayesian framework, allowing an independant dynamics for each species. The twoe software includes original MCMC algorithms to handle variable time-interval between census for the mortality and recruitment processes, is easy of use and product usefull objects (table with parameter estimates for each species, graphics) for ecological interpretations. (Résumé d'auteur

Quelle efficacité environnementale des plans d'aménagement des concessions forestières ?

Des débats sur l'efficacité environnementale des plans d'aménagement en Afrique centrale se sont fait jour récemment. Une première discussion porte sur le déboisement supplémentaire qui serait lié aux concessions aménagées par rapport aux concessions sans plan d'aménagement. Des résultats publiés début 2016 et allant dans ce sens ont été questionnés par d'autres chercheurs, lesquels ont mis en évidence l'arbitraire de certains choix et proposent d'autres manières de mesurer cette efficacité. Une autre discussion émerge sur la durabilité de l'exploitation sous aménagement. Le renouvellement de plusieurs espèces commerciales importantes ne semble pas assuré après plusieurs rotations, ce qui contredirait l'idée d'aménagement durable. Néanmoins, ce processus se déroulant sur plusieurs décennies, il faut prendre en compte l'évolution du marché, le progrès technique et les transformations possibles des modes d'utilisation des écosystèmes forestiers sur le très long terme. La durabilité reste une question ouverte. (Résumé d'auteur

What environmental effectiveness of forest concession's management plan?

The environmental effectiveness of Central African management plans has recently become a topic of debate. The first discussion focused on additional deforestation connected to concessions with a management plan, as opposed to concessions without. Conclusions of an article published in early 2016 that supported this debate were challenged by researchers who pointed out certain choices judged arbitrary and proposed other ways to measure effectiveness. The sustainability of managed exploitations also became a subject of debate. The uncertainty of the recovery of several major commercial species after several rotations challenges the idea of sustainable management. However, since this process requires several decades, due attention must be given to the evolution of the market, technical progress and possible changes in the method governing the very long-term use of the forest ecosystems. Sustainability is still an open, unresolved question. (Résumé d'auteur

Dynamique des forêts du bassin du Congo : harmoniser et fédérer les dispositifs de suivi à long terme [fiches de compétences forêts SIA 2011]

Afin de préserver les forêts à long terme, la réforme des codes forestiers des Etats d'Afrique centrale (1994-2002) a rendu obligatoire l'élaboration de plans d'aménagement. Ces plans définissent des règles de prélèvement durable de la ressource en bois en s'appuyant sur une double connaissance : l'état de la ressource à exploiter et sa dynamique prévisionnelle, l'enjeu étant de ne pas prélever davantage que ce qui peut être produit. Les dispositifs bien adaptés à la détermination des paramètres de dynamique forestière sont très peu nombreux dans le bassin du Congo. Le Cirad propose son appui pour harmoniser les protocoles, en collaboration étroite avec les opérateurs. (Résumé d'auteur

Scientifically based biodiversity management in timber concessions: contribution to conservation and sustainable use of biodiversity

During the past 25 years, forest laws in Central African countries have undergone major changes. Management plans were made mandatory: nearly 19 million hectares of timber concessions (38% of total granted concessions) were subject to a management plan in 2013 and the dynamics is currently underway. The management plan is based on a set of technical and scientific studies, including statistical surveys (management inventories) covering the whole concession and taking into account all timber species, large mammals and the main non timber forest products. These inventories allow, at concession level, to characterize ecosystems and to assess the forest conservation values, through floristic and faunal biodiversity indicators and by taking into account threats to the forest ecosystems, especially anthropogenic ones. Such management inventories are used especially for planning and forecasting harvests, while minimising environmental impacts on the forest structure and functioning, and retaining regeneration capacities of the timber species and the forest ecosystems. The knowledge gained on specific and ecosystemic biodiversity helps to define management rules to ensure the sustainability of different timber species' populations, noticeably the exploited ones. It is also used to design areas within the concessions were exploitation will not take place due to conservation interest (most biodiversity-rich areas, protection of rare or endangered species...). Such so-called “conservation series” therefore complement the protected areas network. Well-managed forest concessions can help conserve the regional forest ecosystems and maintain essential functions that they provide. However, management plans were up to now designed at the concession scale. Data acquired in forest concessions also significantly contribute to improve knowledge of the forest ecosystems and their functioning at the regional level. Using this data, the CoForChange Project (http://www.coforchange.eu) issued a map of the forest ecosystems developed in the "Sangha River Interval" region. This project suggested that those forest ecosystems could react differently to disturbance, and could need an adaptation of management methods to each ecosystem. Based on forest inventories, other initiatives are underway to map the forest types and the biomass stock at the scale of Central Africa, and might be of particular interest for policy decisions on forest ecosystems. (Texte intégral