title: Carbon dioxide fluxes from a degraded woodland in West Africa and their responses to main environmental factors.
abstract: BACKGROUND
  In West Africa, natural ecosystems such as woodlands are the main source for energy, building poles and livestock fodder. They probably behave like net carbon sinks, but there are only few studies focusing on their carbon exchange with the atmosphere. Here, we have analyzed CO2fluxes measured for 17 months by an eddy-covariance system over a degraded woodland in northern Benin. Specially, temporal evolution of the fluxes and their relationships with the main environmental factors were investigated between the seasons.
  
  
  RESULTS
  This study shows a clear response of CO2absorption to photosynthetic photon flux density (Qp), but it varies according to the seasons. After a significant and long dry period, the ecosystem respiration (R) has increased immediately to the first significant rains. No clear dependency of ecosystem respiration on temperature has been observed. The degraded woodlands are probably the "carbon neutral" at the annual scale. The net ecosystem exchange (NEE) was negative during wet season and positive during dry season, and its annual accumulation was equal to +29 ± 16 g C m-2. The ecosystem appears to be more efficient in the morning and during the wet season than in the afternoon and during the dry season.
  
  
  CONCLUSIONS
  This study shows diurnal and seasonal contrasted variations in the CO2fluxes in relation to the alternation between dry and wet seasons. The Nangatchori site is close to the equilibrium state according to its carbon exchanges with the atmosphere. The length of the observation period was too short to justify the hypothesis about the "carbon neutrality" of the degraded woodlands at the annual scale in West Africa. Besides, the annual net ecosystem exchange depends on the intensity of disturbances due to the site management system. Further research works are needed to define a woodland management policy that might keep these ecosystems as carbon sinks.
authors.affiliation: Axe Exchange Ecosystems-Atmosphere, Department of Biosystem Engineering (BIOSE), University of Liege, Gembloux Agro Bio Tech, 8, Avenue de la Faculté, 5030 Gembloux, Belgium ; Laboratoire d'Hydraulique et de Maîtrise de l'Eau, Faculté des Sciences Agronomiques (FSA), Université d'Abomey-Calavi (UAC), BP 2819, Cotonou, Benin.
authors.forename: Expedit Evariste
authors.initials: EE
authors.lastname: Ago
authors.affiliation: Laboratoire d'Aérologie, UMR CNRS 5560, Université Paul Sabatier, Toulouse, France.
authors.forename: Dominique
authors.initials: D
authors.lastname: Serça
authors.affiliation: Laboratoire d'Hydraulique et de Maîtrise de l'Eau, Faculté des Sciences Agronomiques (FSA), Université d'Abomey-Calavi (UAC), BP 2819, Cotonou, Benin.
authors.forename: Euloge Kossi
authors.initials: EK
authors.lastname: Agbossou
authors.affiliation: Univ. Grenoble Alpes, LTHE, 38000 Grenoble, France ; CNRS LTHE, 38000 Grenoble, France ; IRD, LTHE, 38000 Grenoble, France.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Galle
authors.affiliation: Axe Exchange Ecosystems-Atmosphere, Department of Biosystem Engineering (BIOSE), University of Liege, Gembloux Agro Bio Tech, 8, Avenue de la Faculté, 5030 Gembloux, Belgium.
authors.forename: Marc
authors.initials: M
authors.lastname: Aubinet
keywords: Annual NEE; Benin; Eddy-covariance; Net ecosystem exchange; Sudanian climate; West Africa; Woodland