南方红壤区马尾松林冠对降雨雨滴特性的影响

Influence of Masson pine canopy on characteristics of raindrops in red soil region of southern China

降雨是土壤侵蚀的主要影响因素,降雨动能是土壤侵蚀最重要的动力来源。降雨经过林冠层后,由于受到林冠的再分配作用,雨滴特性（雨滴大小、雨滴终点速度和雨滴动能）发生改变,进而改变林下土壤侵蚀特征。为探讨南方红壤区典型树种马尾松林冠对林下土壤侵蚀的影响机制,于2014年5—6月期间在福建长汀县观测了5场有代表性的天然降雨,采用滤纸色斑法对马尾松林内外的降雨雨滴同时进行观测,并汇总分析不同降雨条件下林内外的降雨雨谱,研究结果表明：1）与林外雨滴相比,林内雨滴数量增多,分布范围变大。林外雨滴数量为1 346个,林内雨滴数量为1 608个,比林外多19.5%;林外雨滴直径的大小分布范围是0.6~5.7 mm,林内雨滴直径的大小分布范围是0.4~6.1 mm。2）马尾松林下不同大小雨滴的分布呈双峰曲线,2个峰值对应的直径分别是1.5、3.6 mm,林外不同大小雨滴的分布呈单峰曲线,峰值对应的直径为1.8 mm,林内雨滴中数直径（3.2 mm）比林外（2.0 mm）高60.0%。3）雨滴直径（d）〈2.0 mm时,林内外雨滴终点速度相似,d≥2.0 mm后,林内雨滴的终点速度开始低于林外,且二者间的差异随雨滴直径的增加由0.6%逐渐增加到2.0%。4）人工马尾松林是南方红壤区植被恢复与重建的一种可行途径,降雨经林冠层后,受林冠截留和林冠高度的影响,降雨动能减少了21.8%。该研究可为南方红壤区马尾松林下土壤侵蚀机理的研究提供科学依据。

Rainfall is the main factor influencing soil erosion,and rainfall kinetic energy is the most important source of power to soil erosion. After passing through forest canopy,characteristics of raindrops（ raindrop size,terminal velocity and kinetic energy） change due to the redistribution of canopy and as a result,the characteristics of soil erosion on forest floor change. To explore the effect of canopy of Masson pine（ Pinus massoniana）,a typical tree species in red soil region of southern China,on soil erosion on forest floor,we observed five representative natural rainfall events at Changting County in Fujian Province,southern China,from May to June in 2014. Raindrop size was simultaneously measured by using filter paper method inside and outside the Masson pine forest,and raindrops inside and outside forest under different rainfall conditions were analyzed. The results showed that： 1） Raindrops inside forest were larger in number and wider in distribution range than those outside forest. The number of raindrops inside forest was 1 608,19. 5% more than that outside forest（ 1 346）. Raindrop size distribution outside forest ranged from 0. 6 to 5. 7 mm,while that inside forest varied from 0. 4 to 6. 1 mm. 2） There was a clear difference in drop size distribution between inside and outside forest. Raindrop size inside forestconformed to a bimodal distribution,with the first peak around 1. 5 mm in diameter and the second peak3. 6 mm. In contrast,raindrop size outside forest followed a unimodal distribution,with the peak around1. 8 mm in diameter. The median diameter of raindrops inside forest was 3. 2 mm,60. 0% higher than that outside forest,which was 2. 0 mm. 3） Terminal velocity of raindrops inside forest was similar to that outside forest when they were smaller than 2 mm in size; however,it was smaller inside than outside forest when drops were larger than 2 mm in size and the difference gradually increased from 0. 6% to2. 0%. 4） Masson pine plantation was an applicable approach for vegetation restoration in red soil region of southern China. Rainfall kinetic energy was reduced by 21. 8% after passing through canopy,mainly due to the canopy interception and canopy height. The results of our study could provide a reasonable basis for revealing soil erosion mechanism under Masson pine plantation in red soil region of southern China.