Litter production, composition and turnover in four different subtropical forests in China
Aboveground litter production, components (leaves, twigs, fruits, flowers) and turnover rate are of importance for carbon release and nutrient cycling in forests. In order to quantify annual litter production of subtropical forests and to better assess the effects of secondary forests differing in successional stages and species richness on nutrient cycling in forest ecosystems, litter production, composition and turnover were investigated in four dominant subtropical forest types differing in dominant species and successional stages in southern China, including three types of secondary forests (i.e. a Pinus massoniana and Lithocarpus glaber mixed forest, a Choerospondias axillaries deciduous broadleaved forest, and a L. glaber and Cyclobalanopsis glauca evergreen broadleaved forest) and one Cunninghamia lanceolata plantation forest.
The mean annual litter productions in the four forests ranged from 414.40 g m-2·yr-1 to 818.22 g m-2·yr-1, with the maximum in P. massonana and L. glaber mixed forest (818.22 g m-2·yr-1), followed by C. axillaries deciduous broadleaved forest (794.56 g m-2·yr-1) and L. glaber and C. glauca evergreen broadleaved forest (723.67 g m-2·yr-1), and the minimum in C. lanceolata plantation forest (414.40 g m-2·yr-1). Leaf litter was the dominant component in the total litter and contributed about 59.92%) to 66.62% in total litter production.
In the study site, C. lanceolata and P. massonana contributed significantly great amount of litterfall to monthly litter production in their corresponding forested stands, and therefore, control the seasonal variations in litterfall in the forests. However, the tree species of C. axillaries, L.glaber and C. glauca did not exhibit such dominance in the seasonal change patterns. Among the four forest types, C. lanceolata plantation forest had the lowest decomposition rate (0.31) and the longest turnover time (3.2 years), while C. axillaries deciduous broadleaved forest had the highest decomposition rate (0.45) and the lowest turnover time (2.2 years). It was found that the decomposition rate and turnover time of litterfall were accelerated with increasing in the tree species richness in the studied forests.
Our results indicated that the secondary forests had relative high annual litter production, high decay rate and short turnover time, which provided benefits for nutrient return and maintaining site fertility in forest lands.