海南西部桉树人工林土壤水分变化特征及其对林龄的响应

在海南西部儋州林场选取空间相邻、自然环境相似、不同林龄与连栽代次的桉树林样地和椰树林对照样地,通过2010—2012年连续3a定点取样,研究桉树林土壤水分变化特征及其对林龄的响应,分析桉树林种植对林地土壤水分的影响。结果表明:(1)1—4月土壤含水量持续减少,5—6月波动较大,7—10月增加到年内极大值,11—12月降低,但处于年内较高水平。(2)短伐桉树林(二代5年桉树林、三代1年桉树林、三代4年桉树林)、20a桉树林以及10a椰树林5个样地的月均土壤含水量存在显著或极显著差异。二代5年桉树林与三代1年桉树林之间以及20a桉树林与10a椰树林之间的土壤含水量差异均不显著;其余各林地之间土壤含水量差异显著或极显著。(3)随着土壤深度增加,短伐桉树林与20a桉树林、10a椰树林之间的土壤含水量差异增大。表层0—30 cm短伐桉树林年均土壤含水量为6.08%,20a桉树林为7.53%,10a椰树林为6.93%;80 cm以下则分别为8.10%、11.72%和11.95%。与10a椰树林、20a桉树林相比,短伐桉树林对土壤深层水分有较大负面影响。(4)短伐桉树林、20a桉树林和10a椰树林土壤含水量的变异系数由表层到深层逐渐递减,其中林龄较大的短伐桉树林变异系数较大,且变异系数较大的土层也较深厚。与20a桉树林、10a椰树林相比,林龄较大的短伐桉树林对深层土壤水分的消耗较多。(5)连栽代次愈多,林龄越大,土壤含水量愈少;采伐之后1a桉树林的土壤含水量明显增加,有利于桉树后期生长。

Variation of soil moisture content for Eucalyptus forests and its response to stand ages in Western Hainan

Danzhou, which lies in western Hainan and where large-scale Eucalyptus plantations are present, was chosen as the target study area. We selected 1-to-5-year-old short-rotation Eucalyptus trees, 20-year-old Eucalyptus trees and 10-year-old Cocos trees with adjacent space and similar natural conditions as our experimental plots. After 3 years of continuous sampling, from 2010 to 2012, in fixed sites, we analyzed the variation of soil moisture content for Eucalyptus forests and its response to plantation ages. The results showed that: (1) Soil moisture content decreased continuously from January to April, fluctuated in May and June, increased to the annual maximum between July and October, and descended slightly during the remaining months. (2) There were significant or highly significant differences in mean monthly soil moisture content among the short-rotation Eucalyptus plantations (including a second-generation 5-year-old short-rotation Eucalyptus plantation, a third-generation 1-year-old short-rotation Eucalyptus plantation and a third-generation 4-year-old short-rotation Eucalyptus plantation), 20-year-old Eucalyptus plantation and 10-year-old Cocos plantation, except between the second-generation 5-year-old short-rotation Eucalyptus plantation and the third-generation 1-year-old short-rotation Eucalyptus plantation and between the 20-year-old Eucalyptus plantation and the 10-year-old Cocos plantation. (3) Differences in soil moisture content increased with soil depth between the short-rotation Eucalyptus plantations and 20-year-old Eucalyptus plantation, 10-year-old Cocos plantation. In the 0-30 cm soil layer, the average moisture contents for the short-rotation Eucalyptus plantations, non-short-rotation Eucalyptus plantation and Cocos plantation were 6.08%, 7.53% and 6.93%, respectively, while, in soil layers deeper than 80 cm, values were 8.10%, 11.72% and 11.95%, respectively. The phenomenon that increases in soil depth enlarge differences in soil moisture content reveals that short-rotation Eucalyptus forests consumed more water in the deep soil, compared with the Cocos forest and non-short-rotation Eucalyptus forest. (4) The variation coefficient of soil moisture content gradually declined from top to deep soil layers for the short-rotation Eucalyptus plantations, 20-year-old Eucalyptus plantation and 10-year-old Cocos plantation. In addition, the coefficient was larger for the elder short-rotation Eucalyptus forests and under deeper soil layers, which indicated that compared to the Cocos forest and non-short-rotation Eucalyptus forest, the elder short-rotation Eucalyptus forests consumed more deep soil water. (5) More continuous planting and greater stand age minified soil moisture content. The soil moisture of the 1-year-old Eucalyptus plantation was in a recovery phase and exhibited a higher content, which would improve the soil water environment and the growth of Eucalyptus trees.