Lamto Structure, Functioning, and Dynamics of a Savanna Ecosystem
Known as "a dream place for scientists," the Lamto savannas, located on the edge of the Cote d'Ivoire rain forests, are one of the only savannas in the world where ongoing ecological research has endured for more than forty years. Drawing from and synthes
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7.1 Introduction Monitoring grass aboveground biomass has been one of the favorite field surveys done at Lamto since its foundation in December 1961, partly because most of the work done at Lamto during the 70s was funded by the IBP (see Chap. 1), and later because most ecological surveys needed these data as a preliminary input. Abundant data thus exist on grass biomass cycles, from 1962 to 2003, fully covering more than 25 different seasonal cycles; tree biomass cycles have also been studied, although less regularly. From the initial consideration of grass as a homogenous cover, studies progressively paid more and more attention to species composition and small scale spatial heterogeneity of the grass layer, both in modeling and field sampling. The main questions addressed in this chapter are as follows: 1. the average production level of savannas relative to other biomes, and in particular the relative contributions of the tree and grass components, 2. the interannual variability in biomass cycle and production, and 3. the spatial variability of these patterns along the topographic sequence. We use the classical ecological terminology, with biomass for green plant parts, necromass for dead plant parts and phytomass for the total (biomass + necromass).
7.2 The aboveground phytomass cycle Aboveground grass phytomass dynamics has been surveyed for various purposes in 1962 [22], 1963 [15], 1969 [3], 1970 to 1972, 1977 to 1980 [4], 1981-82 [1], 1984-86 (Fournier and Abbadie, unpublished data), 1986-87 [21], 1989 [17, 18], 1991 to 1993 [10] and 1999 (Simioni, unpublished data). Most of these surveys covered the whole cycle with usually a sampling point per month (Table 7.1), and some concerned a fairly large number of plots (Table 7.2).
Year 1962
1963
1963
1965
196972; 1977-80
1969-73
1981-82
Survey Grass cycle
Grass regrowth after fire
Tree allometry
Palm tree allometry
Productivity of grasslands
Tree primary production
Grass nitrogen dynamics
10 m2 s., dry weight
Cutting trees (n>160), basal ∅ inc., leaf surface
4 m2 s. × 4
Cutting trees - fresh weight
Cutting trees - fresh weight
Aboveground 16/100 m2 s., fresh weight 12 m2 s., contact point sampling
Sampling methods for phytomass variables
Bl. 25 ×25 cm to 50 cm dp. × 4; cores 8 cm ∅ to 50 cm dp. ×10; dry sorting of roots on 1 mm sieves
Bl. 20 × 20 cm to 70 cm dp. by 10 cm strata, w./2mm sieve Digging out main roots
—
Excavating 1 m2 to 20 cm dp., sorting roots Digging out main roots
Belowground1 — Aboveground Biomass, necromass Biomass, necromass, cover Biomass of branches, trunk, leaves, fruits p.i. Biomass of trunk, leaves, fruits p.i. Biomass, necromass, water content - p.sp. Biomass of trunk, fruits, leaves, branches; crown maps, leaf area p.i. Biomass, necromass, nitrogen content
Variables recorded
Monthly, 12 mths.
Once (biomass); May 1969, 70, 73 (∅ inc.)
Large root biomass, maps of main roots, rooting depth p.i. Fine root (2 mm in diameter) were manually sorted out.
1 m2 s. ×4, contact point
19992000
1
4 m2 s. ×4
1991-93
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