连续年龄序列桉树林蒸腾耗水及其环境控制机制与生态影响研究

The tropical sub-humid and semi-arid West Hainan presents itself as a special habitat and is an important Eucalyptus planting area in China. Planting Eucalyptus trees has brought significant economic benefits, while a series of relevant ecological problems have become topics of academic arguments. Previous studies showed that the difference in soil water content was not obvious between Eucalyptus plantations aged more than 20 years and surrounding woodlands, while there was a lower soil water content for short-rotation and continuously planted Eucalyptus trees. In order to further clarify the ecological and environmental effects of short-rotation Eucalyptus trees on soil moisture, Danzhou, which lies in West Hainan and where large-scale Eucalyptus plantations are present, is chosen as the target study area. Based on the long-term continuous experimental observation on sap flow, temperature, humidity, precipitation, soil moisture and other environmental factors, the research is to: (1) Measure stand-scale water consumption and its change with age in a scientific approach; (2) Analyze the relationships between water consumption and such environmental factors as solar radiation and soil water content, in a bid to find the transpiration mechanisms of Eucalyptus forests; (3) Reveal the law of temporal change of soil moisture in short-rotation and its coupling relationship with transpiration water consumption of age-sequence Eucalyptus forests; and (4) Answer the soil eco-hydrological influence of Eucalyptus planting, providing an effective basis for the ecological management and sustainable development of Eucalyptus forests.

海南中西部为我国热带半湿润、半干旱特殊生境区，也是我国重要的桉树浆纸林栽植区之一。速生桉树林虽带来良好的经济效益，但质疑其会对周边水土产生负面生态影响的争论也从未间断。研究表明，20a桉树林土壤水分与周边其他林地差异不明显，而短伐连栽桉树林的土壤水分则较低。厘清短伐连栽桉树林与土壤水分之间的生态关系，是回答上述科学争论和生产实践均应解决的突出科学问题。本研究拟选择海南西部儋州连片种植的桉树林为研究靶区，基于对树干液流和光照、气温、湿度、降水、土壤水分等环境因子的长期连续观测，科学测算林分尺度桉树林蒸腾耗水量及其年龄变化；分析桉树林蒸腾耗水与光照、气温、湿度、降水、土壤水分等环境因子的关系，弄清环境因子对桉树林蒸腾耗水的影响机制；揭示短伐连栽桉树林土壤水分变化规律，探明短伐连栽桉树林蒸腾耗水与其土壤水分变化之间的耦合关系；为科学回答桉树林的水生态影响及桉树林持续发展提供科学依据。

桉树林蒸腾耗水及其产生的土壤水生态影响备受关注。海南中西部为热带半湿润、半干旱特殊生境区，也是重要的桉树林栽植区。海南桉树林地土壤水生态研究滞后，缺少桉树蒸腾耗水研究数据。以海南儋州林场连片种植的桉树林为研究靶区，开展桉树林地土壤水分定位监测，研究土壤水分时间变化；开展桉树林植株生长和植株胸径系统监测，测算单木—林分尺度边材面积及其实时变化；基于监测数据，测算林分尺度蒸腾耗水，并分析光照、气温、降水、湿度、土壤水分等环境因子对桉树蒸腾耗水的影响。.桉树林地1~4月0-150 cm深的土壤水分持续减少，5~6月土壤水分波动较大，7~10月土壤水分最高，11~12月土壤水分降低，但仍处于年内较高水平。短伐桉树林地土壤多年平均体积含水量最低（9.85%），而20a桉树林地（12.27%）较对照椰林地（11.50%）的土壤水分略高或相似。.2014年6月3a桉树平均胸径为85.46 mm，2014~2017年年底分别增长到90.10、93.95、98.25和103.22 mm；桉树胸径生长第一个高峰出现6-7月，第二个生长高峰出现在11-12月，而3-5月生长缓慢，甚至停滞。.晴天（雨季）的桉树茎流密度日平均最大峰值、日均值分别是阴天的2.27倍、1.50倍，是雨天的7.0倍、3.74倍；旱季桉树晴、阴、雨天茎流密度的峰值均值和日均值分别是雨季的0.67、0.27、0.06倍和0.50、0.26、0.15倍。.4a、5a、6a短伐桉树林年蒸腾耗水350 mm左右，雨季蒸腾耗水约占同期降水量的20-30%，旱季占同期降水量的60-100%，甚至更高；随林龄增加蒸腾耗水呈增大趋势，但不同年份趋势不同。长时间尺度（年）桉树林蒸腾耗水不仅受林龄影响，还与年降水量密切相关；短时间尺度（日、月）桉树林蒸腾耗水主要受太阳辐射影响，降水、土壤水分与蒸腾耗水之间关系比较复杂。.与乡土椰林、非短伐20a桉树林相比，短伐连栽桉树林对土壤水分产生一定负面影响；但从多年监测结果来看，短伐桉树林的土壤水分并未出现持续下降，即短伐桉树林生长对土壤水生态的负面影响未见“累积效应”，其影响总体可控。研究结论为科学评估短伐连栽桉树林的土壤水生态影响及其生态管理提供科学依据。