天然林演替为人工林对林地水量平衡及土壤水影响作用机制

Heat and water resources in South China are relatively abundant, it’s suitable for planting eucalyptus in South China. Large areas of development of eucalyptus plantation in South China effectively alleviate the pressure of the timber shortage in our country and increase the local farmers' income. However, effects and mechanisms of the forest succession from natural forest to eucalyptus plantation on ecological hydrological cycle characteristics is not clear. There are still a lot of controversy about large area of eucalyptus plantation at present. The project is based on the existing problems during eucalyptus plantation in South China, by the means of the positioning observation test in field artificial runoff plots, dividing the forest succession into different stages based on the stand structure, fully considering the time-scale effects of ecological hydrology factors in woodlands, studies change rules of surface runoff in individual rainfall event and soil evapotranspiration at different stages, analyze the variation trend of deep soil moisture at different stages, illuminates the change features of the water dynamics blance and soil water in woodlands at different stages, finally reveals the effect and mechanism of the forest succession on the water blance and soil water in woodlands. The study can provide important basis and reference for reasonable large area development of eucalyptus plantation in South China and the efficient management and utilization of soiil water in woodlands.

我国华南地区水热资源较为丰沛，是桉树人工林大面积种植的天然优良场地。该区域桉树人工林大面积发展在缓解我国木材短缺的同时也增加了当地农民收入。但由于天然林演替为桉树人工林对林地生态水文循环特征影响作用机制尚不够明晰，导致目前桉树人工林大面积发展仍存在诸多争议。本项目立足于华南地区桉树人工林发展中现存问题，采用野外人工径流小区定位观测试验方法，以林分为主导因子将演替过程划分为不同阶段，充分考虑林地生态水文要素时间尺度效应，研究不同林分演替阶段林地次降雨产流及土壤蒸散发变化规律，分析不同林分演替阶段深层土壤水分变化趋势，阐明不同林分演替阶段多时间尺度下林地水量动态平衡及土壤水变化特征，揭示林分演替对林地水量平衡及土壤水影响作用机制。该研究可为华南地区合理大面积发展桉树人工林及林地土壤水分高效管理利用提供重要依据和参考。

如何解决和回答天然林大面积演替为桉树人工林对土壤水影响作用这一科学问题，是保证林分演替后土壤水“消耗－补给”动态平衡、实现桉树人工林大面积发展经济与生态效益协同提高的重要途径。本研究采用对比研究的方法，基于野外定位观测试验，以林地降雨水循环各水文要素变化特征为研究对象，揭示不同林分林地水量平衡及土壤水动态变化规律，为桉树人工林发展及其林地土壤水管理与高效利用提供科学依据。获得如下研究结论：（1）雨季（4～9月份）植被冠层截留量约占全年总和的80%～85%。观测期内EUP、MEM和MPN处理植被冠层截留量均值无显著性差异（p>0.05）。（2）各处理雨季月径流量占径流总量的88.37%～89.15%。方差分析结果表明各处理间月径流量存在无显著性差异（p=0.4702>0.05）、月径流系数存在显著差异（p=0.0038<0.05）。（3）观测期内EUP、MEM和MPN处理月土壤入渗量均值无显著性差异存在（p=0.6463>0.05）。各处理雨季月土壤入渗量为旱季的3.76～4.11倍。各处理不同土层深度含水量在一年观测周期内呈现单峰变化趋势。雨季3个试验处理在0～50 cm、150～200 cm和200～250 cm三个土层深度含水量间存在显著或极显著差异（p<0.05）。（4）各处理雨季林地月蒸腾量和土壤蒸发量是旱季的1.46～1.58倍和1.47～1.57倍。方差分析结果表明雨季、旱季和全观测期内3个处理林地月蒸腾量、土壤蒸发量间均存在显著性差异。（5）观测期内各试验处理植被冠层截留量占降雨量的10%～18.4%，树干径流量占1.6%～2.3%，径流量占21.2%～37.4%，入渗量35.5%～48.6%，土壤蒸发量占3%～4.3%，林木蒸腾量5.6%～8.7%，深层渗漏等损失水量占1.6%～1.7%。