title: Allocation strategies of savanna and forest tree seedlings in response to fire and shading: outcomes of a field experiment.
abstract: The forest-savanna ecotone may be very sharp in fire-prone areas. Fire and competition for light play key roles in its maintenance, as forest and savanna tree seedlings are quickly excluded from the other ecosystem. We hypothesized a tradeoff between seedling traits linked to fire resistance and to competition for light to explain these exclusions. We compared growth- and survival-related traits of two savanna and two forest species in response to shading and fire in a field experiment. To interpret the results, we decomposed our broad hypothesis into elementary tradeoffs linked to three constraints, biomass allocation, plant architecture, and shade tolerance, that characterize both savanna and adjacent forest ecosystems. All seedlings reached similar biomasses, but forest seedlings grew taller. Savanna seedlings better survived fire after topkill and required ten times less biomass than forest seedlings to survive. Finally, only savanna seedlings responded to shading. Although results were consistent with the classification of our species as mostly adapted to shade tolerance, competition for light in the open, and fire tolerance, they raised new questions: how could savanna seedlings survive better with a 10-times lower biomass than forest seedlings? Is their shade intolerance sufficient to exclude them from forest understory?
authors.affiliation: Institute of Ecology and Environmental Sciences. UMR 7618 (UPMC-CNRS), 4 Place Jussieu, 75005 Paris, France.
authors.forename: Jacques
authors.initials: J
authors.lastname: Gignoux
authors.affiliation: Research Pole on Environment and Sustainable Development. University Nangui Abrogoua, UFR-SN. 02 BP 801 Abidjan 02, Côte d'Ivoire.
authors.forename: Souleymane
authors.initials: S
authors.lastname: Konaté
authors.affiliation: Institute of Ecology and Environmental Sciences. UMR 7618 (UPMC-CNRS), 4 Place Jussieu, 75005 Paris, France.
authors.forename: Gaëlle
authors.initials: G
authors.lastname: Lahoreau
authors.affiliation: Ecologie Microbienne, INRA, CNRS, Université Lyon 1. UMR 5557, Université Claude Bernard Lyon I 43, Boulevard du 11 Novembre 1918, 69622 Villeurbanne cedex, France.
authors.forename: Xavier
authors.initials: X
authors.lastname: Le Roux
authors.affiliation: INRA, Ecologie des Forêts Mediterranéennes (UR629). Domaine Saint Paul, Site Agroparc, 84914 Avignon Cedex 9, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Simioni