TOYI Sêwanoudé Scholastique Mireille (2012). Analysis of the impact of teak distribution (Tectona grandis L.f.) on landscape structure in the Atlantic Department (Southern Benin). University of Abomey-Calavi, Benin. 216 pages.
Thesis supervisors: Prof. Dr. Ir. Brice SINSIN (University of Abomey-Calavi, Benin) & Prof. Dr. Ir. Jan BOGAERT (University of Liege – Gembloux Agro Bio Tech, Belgium).
ABSTRACT: The landscape of Atlantic Department (southern Benin) is facing deep changes due to increasing anthropogenic pressures (extension of agricultural lands, inappropriate agricultural practices and wood extraction, urbanization and population growth) which has not been really quantified so far. Reforestation mainly based on teak (Tectona grandis L.f.), was undertaken in order to reduce this alarming degradation and to secure wood supplies. The monitoring and the quantification of land cover dynamics in the study area are therefore necessary to draw attention on these landscapes highly dependent on traditional extensive farming. The impact of teak (Tectona grandis L.f.) diffusion on landscape structure in southern Benin was analyzed. The study was intended to quantify the spatiotemporal land cover dynamic using diachronic data (geo data maps from 1972, 1986 and 2005) and landscape ecology techniques; and to assess the reforestation efforts in order to determine the roles played by these tree plantations in landscape components improvement. These consisted in, determining the dynamics and the evolution trend of land cover classes as well as the main spatial transformation processes in these classes; elaborating the suitable bases to inventory teak plantations through the analysis of their spectral signatures, analyzing the edge effects on teak timber productivity and finally, determining the role of teak plantations in the connectivity of landscape elements. Remote sensing and GIS (Geographic Information System) permitted to assess the spatiotemporal dynamic of the studied landscape between 1972 and 2005, based on multi-dates and multi-sources data. Landsat Multi-Spectral Scanner (MSS), Landsat Thematic Mapper (TM) and Landsat
Enhanced Thematic Mapper plus (ETM+) images were processed to generate land cover maps. Transition matrixes and the “decision tree algorithm” were used to capture differently the observed dynamics while modelling techniques based on the first order Markov chain permitted to simulate future trends up to 2025. The spectral signature of teak plantations was approached through the classification of the 2010 SPOT 5 image combined with field works. The productivity and ecological functions of teak plantation were essentially studied based on indexes specific to landscape ecology. It emerged that the landscape of Atlantic Department was submitted to a progressive degradation from 1972 to 2005 with a drastic regression of natural woody areas (forests and various types of savannas) as confirmed by the spatial processes of fragmentation and suppression, while agricultural lands significantly increased because of creation and enlargement processes. The area of tree plantations as well as settlements (especially in the south of the study area) increased noticeably as shown by land cover maps. In the short and medium terms, the trends observed could not be reversed regarding wooded areas. Agricultural areas will increase and tree plantations would not be able to compensate the losses of natural vegetation and the related services. The mapping of teak plantations through their spectral signatures analysis enabled to locate the regions of wide concentration of teak, but the accurate area could not be estimated. The edge effect, far from being a factor of wood downgrading, had a positive impact on the productivity of private teak plantations which are targeted to the production of poles (timber with diameter ranging from 5 to 15 cm) and by-products to satisfy consumers’ needs in service wood and firewood. The ecological function of teak plantations was explored by considering corridor network scenarios to reduce the patch isolation of surviving forests in the landscape and to protect the specific species of these forests. These network scenarios must be tested for an optimum use of teak plantations. The sustainable management of teak plantations, natural vegetation and the related biodiversity must take into account a suitable institutional framework, the respect of landscape ecological functions, an appropriate technical base, the improvement of the livelihoods and income of the rural population. The integration of these various factors in designing the management plans of municipalities in the Atlantic Department must be the top priority of decision makers. This thesis built on a fast and cheap methodology for investigating and monitoring landscape which is well suited to the context of developing countries such as Benin.