Abstract :
[en] In most of the cases, logging companies in Central Africa are now legally obliged to integrate a game management plan in their global management plans. The number of fauna inventories has increased rapidly. Fauna inventories make it possible to evaluate the relative abundance of animal species and their distribution, in order to define particularly valuable areas that should obtain a protected area status. However, logging companies often do not ensure a reliable coverage of their concessions. Moreover, inventory methods are not always reliable, which leads to a lack of precision and low representativeness of the results. It is absolutely necessary
to use a pragmatic low cost methodology for fauna inventories, which considers the particular context of logging companies and which is able to guarantee a quite precise estimation of fauna densities.
Line transect sampling methods are currently considered as the best to monitor large and medium-size game species living within rain forests. Two methods make it possible to evaluate the abundance of fauna.
The so-called distance sampling method is used to estimate absolute density figures. Indicators of animal presence (observation of individuals for small primates, dung piles for duikers and elephants or nests within the case of gorillas) within sampling units well knowing that not all the animals will be counted. Distances between the indicators of animal presence and the transect line are measured. The distribution of the observations using distance classes makes it possible to draw a detection curve and to calculate an absolute animal density. The particularly critical stage in this method appears to be the moment when dung piles and nest densities have to be
converted into animal density figures. Indeed, conversion factors such as production rates and degradation time of dung and nests are not exactly known and can vary a lot. This means that it is impossible to evaluate animal densities in a precise way. The Index of Kilometric Abundance method calculates the number of inventoried observations over a certain distance without measuring the distance between the transect and indicators of animal presence. This method is easier to apply, but neglects the decreasing detection probability of objects in relation with the distance from the transect. It is possible to balance the Index of Kilometric Abundance obtained using a visibility coefficient. Some authors have shown that the IKA method is a reliable tool to monitor relative abundance of animal populations in rain forests. It allows to collect maximum amounts of data in a cheap and easy way.
Considering the fact that the main goal of fauna inventories within forest concessions is to define the most valuable zones for animal species in order to choose the areas that should be protected, it is not necessary to estimate an absolute density. It is even not justified to do this, as it costs a lot to open new transects. Moreover, opening new transects should be avoided as much as possible, as they attract hunters. Fauna inventories make it possible to define the most interesting areas for fauna conservation. While defining these areas in order to protect them, the following parameters should be considered: global fauna densities; densities of threatened or vulnerable species; the importance of human activities (hunting in particular).
It is necessary to standardize these parameters in order to give them the same weight. For each inventory plot, values for animal abundance and densities of threatened species have to be added up. Afterwards, the value for hunting has to be subtracted from the sum of the first values. The index obtained is called “conservation potential”. Using software such as ArcView and its extension Spatial Analyst makes it possible to extrapolate the results obtained and to apply them to the whole forest concession. The botanical interest of the inventoried plots should also be considered through different parameters (species richness, diversity, vulnerable species, chorology) in order to produce a global index. Fauna inventories do not stand alone, but have to be considered as a basic tool to set up a sustainable game management. They have to be used to develop actions to preserve animal species, such as the creation of a protected area. They can also make it possible to monitor animal populations in order to evaluate the effectiveness of developed actions dedicated to reduce pressure on fauna.
