中亚热带4种森林凋落物量、组成、动态及其周转期

为研究亚热带次生林保护对森林生态系统养分循环等功能过程的影响。采用凋落物直接收集法,比较湘中丘陵区3种次生林(马尾松+石栎针阔混交林、南酸枣落叶阔叶林、石栎+青冈常绿阔叶林)和杉木人工林的凋落物量、组成特征及其周转期。结果表明:4种林分年凋落物量在414.4—818.2 g m-2a-1之间,3种次生林显著高于杉木人工林,3种次生林两两之间差异不显著,落叶对林分凋落物量的贡献最大,占林分凋落物量的59.9%—66.6%。杉木人工林和南酸枣落叶阔叶林的凋落物量月动态变化呈"双峰型",马尾松+石栎针阔混交林、石栎+青冈常绿阔叶林呈"不规则型"。优势树种的凋落物量对其林分凋落物量的贡献随林分树种多样性的增加而下降,杉木、马尾松凋落物量的月动态与其林分凋落物量的月动态基本呈一致变化趋势,但南酸枣、青冈、石栎没有一致的变化趋势。杉木人工林凋落物分解率最低(0.31),周转期最长(3.2 a),南酸枣落叶阔叶林分解率最高(0.45),周转期最低(2.2 a),凋落物的分解速率和周转随林分树种多样性增加而加快。可见,次生林凋落物量大,且分解快,周转期短,有利于养分归还和具有良好地力维持的能力。

Litter production and turnover in four types of subtropical forests in China

Aboveground litter production (leaves, twigs, fruits, flowers) is an important component of the nutrient cycling in forests. In order to quantify annual litter production of subtropical forests and to better understanding of the effects of secondary forests on nutrient cycling in forest ecosystems, litter production, composition and turnover were investigated in four dominant subtropical forest types in Hunan Province, China. The four forest types included 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 a Cunninghamia lanceolata plantation forest. The results showed that mean annual litter productions in the four forests ranged from 414.40 g m^-2 a^-1 to 818.22 g m^-2 a^-1, with the maximum in P. massonana and L. glaber mixed forest (818.22 g m^-2 a^-1), followed by C. axillaries deciduous broadleaved forest (794.56 g m^-2 a^-1) and L. glaber and C. glauca evergreen broadleaved forest (723.67 g m^-2 a^-1), and the minimum in C. lanceolata plantation forest (414.40 g m^-2 a^-1). Leaf litter was the dominant component in the total litter and contributed about 59.92%) to 66.62% in total litter production. Monthly changes in litterfall pattern showed two peaks in both C. lanceolata plantation forest and C. axillaries deciduous broadleaved forest, while no obvious litterfall pattern was found for P. massonana and L. glaber mixed forest and C. glauca and L. glaber evergreen broadleaved forest. The contribution of dominant tree species toward annual litter production became less important with increasing of the tree species richness in the studied forests. 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.