Litter quantity controls soil macro-invertebrate biomass in warm temperate broad-leaved forests of Southwestern Japan

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The biomass distribution of soil macro-invertebrates across various biomes worldwide is an indispensable factor to be taken into account in predicting plant litter decomposition rates in a global perspective. In boreal to cool temperate regions, soil macro-invertebrate biomass is lower in coniferous forests than in deciduous broad-leaved forests, with the difference being attributed to tree species effects via litter quality. On the basis of a simplistic analogy with the litter quality-controlled differences in soil macro-invertebrate biomass between coniferous forests and deciduous broad-leaved forests, soil macro-invertebrate biomass is expected to be lower in evergreen broad-leaved forests that produce leaves with a longer lifespan of lower quality than in deciduous broad-leaved forests. In order to test this expectation, soil macro-invertebrate biomass, forest floor mass, an indicator of litter quantity, and litter pH, a possible index of litter quality were assessed in evergreen broad-leaved forests and deciduous broad-leaved forests under similar abiotic conditions in Southwestern Japan. The total biomass of the entire animal community was depended greatly on earthworms and was significantly higher in evergreen broad-leaved forests than in deciduous broad-leaved forests. The forest types were completely separated by a discriminant function combining the biomasses of twelve major taxa with a high stand-based frequency. Earthworms, spiders, and woodlice were the top three of contribution to the discrimination, the biomasses of all of which were significantly higher in evergreen broad-leaved forests than in deciduous broad-leaved forests. Multiple regression analysis and PCA revealed that the biomass differences in the three taxa between the forest types were predominantly influenced by forest floor mass without any indication of important effects of litter pH. Importance of “litter quantity control” over soil macro-invertebrate biomass in warm temperate forests of Southwestern Japan was concluded.