Savafor: determining the productivity of savannahs

Wood is the main energy source in the Sahel. In order to plan for changes in stocks, it is essential to be able to produce a common estimate of the productivity of savannahs in all the countries concerned. This is the aim of the Savafor network, which was founded recently.

Wood and charcoal cover a substantial part of domestic energy requirements in Sahel countries: from 47% of requirements in Senegal to 96% in Chad, according to a 1986 FAO study. Wooded formations, primarily dry savannahs, are thus under substantial logging pressure, particularly around towns. The FAO has put the annual rate of forest shrinkage in Sahelo-Sudanian Africa at 0.72% (2001).

As a result of this loss of resources, traders in Bamako, Mali, are now having to bring in supplies from as far away as 200 km from the city. This reduction in forest cover could be slowed through plans to develop village forests, in the hope of balancing the volumes logged and natural renewal of stocks. However, such an operation means determining wood stock growth rates more precisely.

Several summaries of the information available on savannah productivity have been produced since the 1980s. However, these studies have never been coordinated, and a consensus has never been reached on the value of savannah productivity, or on the ways of estimating that prioductivity. An effort thus needs to be made to coordinate operations so as to capitalize on the research already done on savannah productivity on a regional scale. This gave rise to the recent creation of a regional scientific network, Savafor.

It includes some twenty researchers from West and Central Africa, representing twelve research institutes or organizations, including CIRAD. Three questions in particular are at the heart of their work: How can we estimate productivity? What experimental designs and types of measurements are required? How can we build a sustainable skills network on this issue? The first necessity is to standardize measurement methods. This will be followed by joint analyses on a regional scale, based on data obtained from the existing installations in North Cameroon, Mali and Burkina Faso.

The problem is that for a given rainfall level, productivity estimates may vary by a factor of one to six, depending on the study. These variations can primarily be put down to a lack of harmonization of the various measurement protocols in terms of the tree components taken into account when defining firewood. The appropriateness of the very concept of productivity also needs to be reviewed.

Productivity is a dynamic concept, which varies in line with the stage of stand development. Determining it on an overall level, on the scale of a forest, is of no relevance except with a view to the exclusive exploitation of a single resource, occasionally and by clear cutting. However, local populations in fact use savannahs in a more subtle way: many species are used and satisfy many different needs, with fuelwood being just one in a range of uses. Moreover, the logging practises used do not correspond to clear cutting, but rather to a selection system. The productivity concept should thus move more towards one of forest dynamics, so as to take account of this type of use.