© 2004 Heron Publishing—Victoria, Canada
Spatial and temporal variations in leaf area index, specific leaf area and leaf nitrogen of two co-occurring savanna tree
species
Guillaume Simioni (1, 2, 3), Jacques Gignoux (1), Xavier Le Roux (4, 5), Raphaëlle Appé (1) and Daniele Benest (1)
1. Laboratoire Fonctionnement et Evolution des Systèmes Ecologiques, CNRS-ENS-Paris 6, 46 rue d’Ulm, 75230 Paris cedex 05, France / 2. CSIRO Forestry and Forest Products and CRC for Greenhouse Accounting, P.O. Box E4008, Kingston, ACT 2604, Australia / 3. Author to whom correspondence should be addressed (guillaume.simioni@csiro.au) / 4. UMR PIAF Tree Physiology (INRA-University Blaise Pascal), 234 avenue du Brezet, 63039 Clermont Ferrand, France / 5. Laboratoire d’Ecologie Microbienne, UMR CNRS 5557, bât. Gregor Mendel, 43 bd du 11 Novembre 1918, 69622 Villeurbanne cedex,
France / Received February 24, 2003; accepted May 24, 2003; published online December 15, 2003
Summary
Foliage growth, mass- and area-based leaf nitrogen concentrations (Nm and Na) and specific leaf area (SLA) were surveyed during a complete vegetation cycle for two co-occurring savanna tree species:
Crossopteryx febrifuga (Afzel. ex G. Don) Benth. and Cussonia arborea A. Rich. The study was conducted in the natural reserve of Lamto, Ivory Coast, on isolated and clumped trees. Leaf flush
occurred before the beginning of the rainy season. Maximum leaf area index (LAI), computed on a projected canopy basis for
individual trees, was similar (mean of about 4) for both species. Seasonal courses of the ratio of actual to maximum LAI were
similar for individuals of the same species, but differed between species. For C. febrifuga, clumped trees reached their maximum LAI before isolated trees. The LAI of C. arborea trees did not differ between clumped and isolated individuals, but maximum LAI was reached about 2 months later than for
C. febrifuga. Leaf fall was associated with decreasing soil water content for C. arborea. For C. febrifuga, leaf fall started before the end of the rainy period and was independent of changes in soil water content. These features
lead to a partial niche separation in time for light resource acquisition between the two species. Although Nm, Na and SLA decreased with time, SLA and Na decreased later in the vegetation cycle for C. arborea than for C. febrifuga. For both species, Na decreased and SLA increased with decreasing leaf irradiance within the canopy, although effects of light on leaf characteristics
did not differ between isolated and clumped trees. Given relationships between Na and photosynthetic capacities previously reported for these species, our results show that C. arborea exhibits higher photosynthetic capacity than C. febrifuga during most of the vegetation cycle and at all irradiances.
Keywords:
Crossopteryx febrifuga, Cussonia arborea, LAI, Lamto, phenology, shading, SLA.
