Partial exclusion of precipitation: throughfall, stemflow and canopy interception in Eucalyptus plantations in southern Brazil

Abstract Hydrological behavior in reforested watersheds is different from that under other forms of cover. The variation may be related to aspects intrinsic to species, planting density, physiological maturity, management system and climatic conditions. Periodically, climatic anomalies such as the case of La Ninã are observed, and these are responsible for the alteration of the rainfall regime and consequently generate water deficits in the southern region of Brazil. Water deficit is responsible for reducing growth and productivity for the Eucalyptus genus, in addition to causing changes in hydrological behavior in reforested watersheds. Accordingly, this study compared the partition of rainfall in throughfall, stemflow and canopy interception of eucalyptus trees submitted or not to partial exclusion of precipitation. In the open field, 3 rainfall collectors were installed, and in the stand, for each rain exclusion treatment, 9 throughfall collectors and 9 stemflow collectors were installed. Every two weeks for 12 months, the volume of the collectors was measured. The quantified precipitation was 1627 mm over a year. In the treatment without exclusion, 84.8, 2.9 and 12.3% referred to throughfall, stemflow and canopy interception, respectively, while in the treatment excluding rainfall 80.6, 2.3 and 17.2% referred to throughfall, stemflow and canopy interception. The regression adjustments for throughfall and stemflow showed satisfactory R2 coefficients.

摘要
人工恢复造林流域的水文特征与其他土地覆被类型下的水文特征存在显著差异，该差异可能与树种固有特性、种植密度、生理成熟度、经营管理体系及气候条件等因素相关。研究区域周期性出现拉尼娜（La Niña）等气候异常事件，此类事件会改变降雨格局，进而引发巴西南部地区的水资源短缺。水资源短缺不仅会改变人工造林流域的水文特征，还会抑制桉属（Eucalyptus）植物的生长与生产力。鉴于此，本研究针对设置与未设置降水部分截留处理的桉树人工林，对比了其降雨在穿透雨（throughfall）、茎流（stemflow）与林冠截留（canopy interception）三个分量间的分配格局。本研究在裸地对照区布设3个雨量收集器；在林分中，针对每个降水截留处理组，分别布设9个穿透雨收集器与9个茎流收集器。研究持续12个月，每两周对各收集器内的集水量进行一次测定。该年度实测总降雨量为1627毫米。在未截留降水的对照组中，穿透雨、茎流与林冠截留分别占总降雨量的84.8%、2.9%与12.3%；而在降水截留处理组中，三者占比分别为80.6%、2.3%与17.2%。针对穿透雨与茎流的回归拟合分析均得到了表现优异的决定系数（R²）。