海南岛霸王岭热带季雨林树木的死亡率

Mortality of woody plants in tropical monsoon rainforests of Bawangling National Nature Reserve on Hainan Island,South China

树木死亡是调节群落组成和结构的一种方式,在森林生态系统动态中发挥着重要作用。该文在对海南岛霸王岭热带季雨林群落大量调查和树种功能群划分研究的基础上,探索了热带季雨林群落及其不同功能群树木的死亡率及其随径级和环境条件的变化规律。结果表明:海南岛霸王岭热带季雨林群落内树木死亡率的变化范围为3.42%–18.71%,平均值为7.60%。按照功能群比较,乔木死亡率显著高于灌木,落叶树种死亡率高于常绿树种,但具刺树种死亡率显著低于无刺树种。按照树木径级划分,5–30cm径级范围的死亡率均超过10%,最高值出现在5–10cm径级范围,在相同径级范围内比较时,落叶树种在胸径(DBH)<5cm时的死亡率显著高于常绿树种,而在其他径级范围内,二者之间无显著差异,具刺和无刺树种的死亡率在所有径级范围内均无显著差异。乔木死亡率与群落距河流距离具有显著的相关性,距离河流越远死亡率越高;落叶树种和无刺树种则与坡位存在显著的相关性,坡上部的死亡率显著高于坡中部。热带季雨林内树木的死亡率与其所处的群落生境有关,较干旱的生境是导致树木死亡率较高的重要原因。

Aims We examined the mortality of woody plants in different functional groups,different diameter classes and different site conditions to understand the status and variation of woody plant mortality in the tropical monsoon rainforest （TMRF） communities on Hainan Island. Methods We established 15 plots （50 m × 50 m） in old-growth TMRF in Bawangling Nature Reserve of Hainan Island. Each plot was divided into 10 m × 10 m subplots to measure the height,diameter at breast height （DBH） of individuals with DBH ≥ 1.0 cm and live or dead status by species. Site conditions,such as slope gradient,slope aspect,slope position and distance to the rivers were recorded. We categorized woody plants into different functional groups,and stems into different diameter classes. Important findings Overall mortality rate of woody plants ranged from 3.42% to 18.71% （mean of 7.60%）. The mortality rate was higher for trees than shrubs,for deciduous species than evergreen species and for unarmed species than spinescent species. The mortality rate of the TMRF community was 〉10% for 5-30 cm DBH and was highest for 5-10 cm DBH. Within the 1-5 cm same diameter class,mortality of deciduous species was higher than evergreen species,and no significant differences were found in other diameter classes. No significant difference was found between mortality of spinescent and unarmed species in any diameter class. Tree mortality rate and distance to the rivers were directly correlated. Mortalities of deciduous species and unarmed species were correlated with slope position,with the mortality rates on upper slope position higher than at mid-slope position. The closest relationships were between mortality rate and community habitats,and drought was one of important causes of mortality.