Determinants of woody encroachment and cover in African savannas

Savanna ecosystems are an integral part of the African landscape and sustain the livelihoods of millions of people. Woody encroachment in savannas is a widespread phenomenon but its causes are widely debated. We review the extensive literature on woody encroachment to help improve understanding of the possible causes and to highlight where and how future scientific efforts to fully understand these causes should be focused. Rainfall is the most important determinant of maximum woody cover across Africa, but fire and herbivory interact to reduce woody cover below the maximum at many locations. We postulate that woody encroachment is most likely driven by CO2 enrichment and propose a two-system conceptual framework, whereby mechanisms of woody encroachment differ depending on whether the savanna is a wet or dry system. In dry savannas, the increased water-use efficiency in plants relaxes precipitation-driven constraints and increases woody growth. In wet savannas, the increase of carbon allocation to tree roots results in faster recovery rates after disturbance and a greater likelihood of reaching sexual maturity. Our proposed framework can be tested using a mixture of experimental and earth observational techniques. At a local level, changes in precipitation, burning regimes or herbivory could be driving woody encroachment, but are unlikely to be the explanation of this continent-wide phenomenon

The Effect of Carbon Credits on Savanna Land Management and Priorities for Biodiversity Conservation

Carbon finance offers the potential to change land management and conservation planning priorities. We develop a novel approach to planning for improved land management to conserve biodiversity while utilizing potential revenue from carbon biosequestration. We apply our approach in northern Australia's tropical savanna, a region of global significance for biodiversity and carbon storage, both of which are threatened by current fire and grazing regimes. Our approach aims to identify priority locations for protecting species and vegetation communities by retaining existing vegetation and managing fire and grazing regimes at a minimum cost. We explore the impact of accounting for potential carbon revenue (using a carbon price of US$14 per tonne of carbon dioxide equivalent) on priority areas for conservation and the impact of explicitly protecting carbon stocks in addition to biodiversity. Our results show that improved management can potentially raise approximately US$5 per hectare per year in carbon revenue and prevent the release of 1–2 billion tonnes of carbon dioxide equivalent over approximately 90 years. This revenue could be used to reduce the costs of improved land management by three quarters or double the number of biodiversity targets achieved and meet carbon storage targets for the same cost. These results are based on generalised cost and carbon data; more comprehensive applications will rely on fine scale, site-specific data and a supportive policy environment. Our research illustrates that the duel objective of conserving biodiversity and reducing the release of greenhouse gases offers important opportunities for cost-effective land management investments

Development of coffee associated with Eucalyptus deglupta or Terminalia ivorensis during the establishment phase

2 ilus. 1 tab. 7 ref.Se evalu? el efecto de Eucalyptus deglupta o Terminalia ivorensis sobre la arquitectura y producci?n de plantas de caf? (Coffea arabica var. Costa Rica) de dos a?os a diferentes distancias (0.5-3.5 m) del ?rbol. Comparados con caf? a pleno sol, caf? asociado con E. deglupta o T. ivorensis tuvo 15 a 22 por ciento menos frutos. La altura, el n?mero de nudos en el tallo principal y el n?mero de ramas primarias de los cafetos disminuy? con la cercan?a de los ?rboles. Adem?s, la cercan?a de T. ivorensis afect? el di?metro del tallo, di?metro de copa hacia las calles, la proyecci?n de copa, el n?mero de ramas productivas por planta, el promedio de frutos por nudo productivo y el n?mero de frutos por planta en el caf?. El n?mero de frutos en las plantas de caf? m?s cercanas a T. ivorensis disminuy? hasta un 75 por ciento. Las plantas de caf? asociadas con ?rboles maderables, presentaron hasta un 29 por ciento menos hojas en las ramas del estrato inferior, comparadas con plantas establecidas a pleno sol. El promedio de ?rea foliar en el estrato inferior de los cafetos, el promedio de nudos productivos en los estratos superior e intermedio y el promedio de frutos por rama para los tres estratos en las plantas de caf? fue reducido con la cercan?a de los ?rboles. The effect of Eucalyptus deglupta or Terminalia ivorensis on the architecture and production of two year old coffee plants established at different distances (0.5-3.5m) from the trees was evaluated. Coffee plants associated with E. deglupta or T. ivorensis, had 15 and 22 percent fewer fruits respectively, compared with coffee in full sun. The proximity of the trees significantly affected the height, the number of nodes on the main stem and the number of primary branches of the coffee plants. The proximity of T. ivorensis affected coffee stem diameter, crown diameter towards the alleys, crown projection, number of productive branches per plant, the average number of berries per productive node, and number of berries per plant. The number of coffee berries on plants closest to the T. ivorensis decreased up to 75 percent. Coffee plants associated with timber trees had up to 29 percent fewer leaves in the lower branches, compared to the same branches of coffee plants exposed to full sunlight. The proximity of the trees, significantly affected the average leaf area for the lower strata, the average number of productive nodes for the upper and middle strata and the average number of fruits per branch for all three strata

Agroecology, a Tool for the Realization of the Right to Food

Sustainable agriculture is a rapidly growing field aiming at producing food and energy in a sustainable way for humans and their children. Sustainable agriculture is a discipline that addresses current issues such as climate change, increasing food and fuel prices, poor-nation starvation, rich-nation obesity, water pollution, soil erosion, fertility loss, pest control, and biodiversity depletion. Novel, environmentally-friendly solutions are proposed based on integrated knowledge from sciences as diverse as agronomy, soil science, molecular biology, chemistry, toxicology, ecology, economy, and social sciences. Indeed, sustainable agriculture decipher mechanisms of processes that occur from the molecular level to the farming system to the global level at tim