- Vegetation changes in a Sahelian valley system in Burkina Faso - 245 Proceedings IAVS Symposium, pp. 245-248, 2000 © IAVS; Opulus Press Uppsala. Printed in Sweden Abstract. Sahelian valley systems (‘bas-fonds’) are key stone ecosystems in the sense that they harbour dense, species-rich vegetation in an otherwise dry environment. Many of the woody valley species are highly appreciated by local people, because they provide construction-wood, fruits, medicine, and livestock fodder. In this study two methods, interviews with elderly local people and vegeta- tion sampling are used to gain information about vegeta- tion changes of the woody vegetation in a valley system in northern Burkina Faso, West Africa. According to local Fulani people (former nomads) the valley vegetation is highly degraded today, the vegetation used to be dense a few decades ago, but it is now open and lacks regeneration; many species are declining, and some have become locally extinct. Vegetation data support the local information; size class distributions reveal that most woody species have few young individuals and weak rejuvenation, and many of the locally appreciated species are rare. Through interviews and vegetation studies it is possible to assess the state of most of the ca. 60 woody species that grow in the area which is important for the planning of natural management strategies. Keywords: Degradation; Fulani people; Sahel. Nomenclature: Lebrun & Stork (1991-1997). Introduction The Sahel is well-known for its environmental problems as degradation and desertification in the Sahel have been frequently debated political issues. The degradation prob- lems concern both soil, herbaceous vegetation, and woody vegetation. This study, however, focuses on the woody vegetation, an extremely important element of the Sahelian ecosystems that has been particularly affected by thinning and compositional changes during the last decades (e.g. Geerling 1985; Sinclair & Fryxell 1985; Cross & Barker 1991; Breman 1992; Stiles 1995a). A degradation of the woody vegetation affects local societies directly as woody plants serve essential functions by providing livestock fodder (Le Houérou 1989), by sustaining and ameliorating soil and grass components of the ecosystem (Dunham 1991; Solbrig 1993; Belsky & Canham 1994), and by providing a variety of daily used products such as food, medicine, Vegetation changes in a Sahelian valley system in Burkina Faso Lykke, Anne Mette Department of Systematic Botany, University of Aarhus, Nordlandsvej 68, 8240 Risskov, Denmark; Fax +45 8942 4747; E-mail lykke@biology.au.dk firewood, and construction materials (e.g. von Maydell 1990). Despite the fact that trees and shrubs are both severely declining and extremely useful to local people in the Sahel, management of the woody vegetation has received little attention in west African arid and semi-arid areas (von Maydell 1995). Also the newest theories for rangeland management in disequilibrium systems (e.g. Behnke et al. 1993; Scoones 1996) largely ignore problems concerning assessment and management of woody resources. The aim of this study is therefore to specify floristic changes of woody plants in order to provide data that can be used as a basis for management strategies. Species level infor- mation on vegetation changes can be gained from vegeta- tion investigations and from local knowledge, which to- day is a widely recognized source for information on natural resource questions (Gadgil et al. 1993; Meffe & Carroll 1994; Stiles 1995b). The field studies took place in a typical Sahelian area and included (1) interviews with elderly local people and (2) vegetation sampling with focus on valley systems (‘bas- fonds’). Valley systems are key stone ecosystems in the Sahel as they are relatively humid with a comparatively dense, tall, species-rich, and productive vegetation in an otherwise dry environment. Valley systems are highly im- portant for maintaining biodiversity in the Sahel, and they are recognized by local people as the most important veg- etation type for extraction of wild products (Lykke 1998). Study site The study took place in the region of Gorom Gorom, Oudalan province, in northern Burkina Faso (Fig. 1). The landscape is characterized by large stretches of planes interrupted by valley and dune systems. The word ‘valley’ is used in a broad sense to include floodplains and banks of seasonal streams with a vegetation that is clearly different from that of the neighbouring plane. The planes are cov- ered by grassland and shrubland vegetation, the dunes are dominated by grasslands and open spaces, and the valleys hold vegetation types ranging from forest to grassland. The rainy season lasts about three months (June-Sep- tember) with irregular, sporadic, and unpredictable pre- cipitation, as is typical for the Sahel. From 1958 to 1996 average precipitation in Gorom Gorom was 403 mm/yr. Two major droughts occurred in this period, one in the early 1970s and one during the 1980s. The area is mainly inhabited by people from the ethnic groups of Fulani (Peulh/Rimaibe), Bella, Touaregs and Sonrai. Following the tradition in the Sahel, rangelands are communal lands. During the last 30 yr many nomadic pastoralists have settled down in order to supplement their income by agriculture, and today most people live as agro-pasturalists (Reenberg & Fog 1995). Many families, though, supple- ment their income by migratory work.