Hypothesis

1. Organic matter breakdown is strongly affected in plantations compared to secondary and primary forests
(FLO > SEC > POC, POA)

2. This negative effect can be minimized by improving the biotic and abiotic conditions for the soil fauna

Methods

Regular assessment of litterfall and litter standing crop during 2 years

Assessment of soil fauna by soil core sampling and extracting every 3 months

Two litterbag experiments filled with leaves of Vismia sp.
(7 dates; 10 bags per date )

Analyses of litter quality (C/N-ration, Cations)
Soil respiration measurements

Test of rapid assessment methods (minicontainers, bait lamina)

Litter bags with different mesh sizes and the bait lamina test in the SEC plot

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Results

Summary of results:

OM breakdown rates in plantations (including the secondary forest) reach between 25 and 60 % of the primary forest

However, even at the site with the strongest inhibition (POA), the litter stock is not significantly enhanced compared to the primary forest (FLO).

Macrofauna determines decomposition rates in all systems

The plantation plots shelter an abundant and functional soil fauna, probably promoted by the layer litter from the secondary vegetation

Soil fauna structure in the plantations is different from the primary forest

to get a detailed list of the results click here

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Conclusions

Functional tests are useful for the evaluation of land-use changes, but must be assessed together with biotic and abiotic conditions.

The "ecosystem service" decomposition seems optimizable through promotion of the soil fauna

This has to be done indirectly, through melioration of microclimatic conditions by planting cover or alley crops or toleration of secondary vegetation and a more even supply with plant residues (mulching)

Through the positive effects of the soil fauna on nutrient cycling and soil structure should land use systems become sustainable without high nutrient inputs by mineral fertilization

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Outlook

We have started a new project in 2000 focussing on the "semi-farm" scale

"Managment of plant residues and its effect on macrofauna and decomposition in Amazonian agro-ecosystems (SHIFT ENV 52-2)"

structured in four modules:

field studies with different mulch quantities and qualities

microcosm experiments

screening of macrofauna and decomposition in various plantation types

ecotoxicological studies ( laboratory tests, microcosm, field studies )

For more details on the SHIFT ENV 52-2 project click here

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