Leaf traits, litter decomposability and forest floor dynamics in an evergreen- and a deciduous-broadleaved forest in warm temperate Japan

There is a consistent relationship between the litter quality, litter decay rates in litter bags and forest floor dynamics of coniferous forests and deciduous broadleaved forests (DBFs) in boreal-to-cool temperate regions. We examined whether there was a similar relationship between an evergreen broadleaved forest (EBF) and a DBF in warm temperate Japan. The leaf toughness and leaf mass per leaf area was significantly higher, and initial decomposability, in terms of mass loss rate and CO2 emission rate, of the litter in litter bags was significantly lower for Quercus acuta, an evergreen oak that is dominant in EBF than for Carpinus laxiflora, Prunus yamasakura and Quercus serrata, three deciduous species that are co-dominant in DBF, respectively. Nevertheless, the CO2 emission rate of the A(0)-layer tended to be higher in EBF than in DBF, and litter turnover rate did not differ between them. The discrepancy between the initial litter decomposability and the forest floor dynamics across the two functional types was ascribed to activities of microorganisms and surface-living earthworms that were affected by the water content of the A(0)-layer. We concluded that due to the crucial effect of moisture on decomposition, the power of substrate quality for predicting forest floor dynamics in EBF and DBF was smaller than that in coniferous forests and DBFs in boreal-to-cool temperate regions where temperature is a major factor controlling decomposition.