Rainfall interception by an isolated evergreen oak tree in a Mediterranean savannah

Redistribution of ground‐level rainfall and interception loss by an isolated Quercus ilex tree were measured over 2 years in a Mediterranean oak savannah. Stemflow, meteorological variables and sap flow were also monitored. Rainfall at ground level was measured by a set of rain‐gauges located in a radial layout centred on the tree trunk and extending beyond the crown limits. Interception loss was computed as the difference between the volume of rainwater that would reach the ground in the absence of the tree and the volume of water that actually fell on the ground sampling area (stemflow included). This procedure provided correct interception loss estimates, irrespective of rainfall inclination. Results have shown a clear non‐random spatial distribution of ground‐level rainfall, with rainwater concentrations upwind beneath the crown and rain‐shadows downwind. Interception loss amounted to 22% of gross rainfall, per unit of crown‐projected area. Stand interception loss, per unit of ground area, was only 8% of gross rainfall and 28% of tree evapotranspiration. These values reflect the low crown cover fraction of the stand (0·39) and the specific features of the Mediterranean rainfall regime (predominantly with few large storms). Nevertheless, it still is an important component of the water balance of these Mediterranean ecosystems. Copyright © 2005 John Wiley & Sons, Ltd.     

Leaf litter decomposition in remote oceanic islands: The role of macroinvertebrates vs. microbial decomposition of native vs. exotic plant species

Freshwater communities on remote oceanic islands can be depauperate due to the influence of biogeographic processes that operate over a range of spatial scales, influencing the colonization of organisms, and events that shape local freshwater assemblages. The consequences of this paucity in organism diversity for the functioning of these ecosystems are, however, not well understood.Here, we examine the relative decomposition rate of leaf litter of native vs. exotic origin by aquatic macroinvertebrates and microbial communities in an isolated and depauperate oceanic environment.Bags containing a standard amount of leaf litter of each of 10 tree species (5 native and 5 non-native species) were deployed on two streams. Two types of bags differing in mesh size were used to allow or prevent the access of leaf litter to macroinvertebrates, respectively. Over a period of 28 days, mass loss of leaf litter was similar in the two bag types suggesting that macroinvertebrates had little influence on the break down of leaf litter in this system. In addition, there was no difference in mass loss of leaf litter of native and exotic origin. Decomposition rates were highly species-specific suggesting that decomposition rates were related to inhibitory substance specific of each leaf species. Our results add to the wider literature by showing that in depauperate and isolated ecosystems, and in contrast to temperate continental ecosystems, decomposition of plant litter by aquatic macroinvertebrates is negligible.     

贡嘎山亚高山演替林林冠截留特征与模拟

通过对贡嘎山亚高山峨眉冷杉与冬瓜杨演替林连续两年林下降水与树干径流的实验观测,分析研究了演替林林下降水、树干径流、林冠截留的变化特征,并验证了Gash(1995)模型模拟该区林冠截留的适用性.结果显示,2008年和2009年贡嘎山亚高山演替林林下降水分别占降水量的76.4%和77.0%,树干径流量较小,可以忽略不计,林...     

太行山地区不同植被林冠截留降水的研究

通过穿透降雨和树干径流自动采集系统,对油松、侧柏、刺槐三种植被截留实验数据进行了分析。结果表明,三种植被林内穿透降雨与林外天然降雨都具极显著的正相关线性关系,林冠截留量与林外降雨量呈幂函数关系,平均截留率大小关系为油松>侧柏>刺槐。相同林外降雨量下产生的树干径流量大小关系为刺槐>侧柏>油松。     

Hydrological characteristics of betel nut plantations on slopelands in central Taiwan / Caractéristiques hydrologiques de plantations de noix de bétel sur des versants du centre Taïwan

Abstract

Betel nut or betel palm (Areca catechu Linn.) has become a major cash crop in southern and central Taiwan since the mid-1980s. Many slopeland fruit orchards and forests have been converted to betel nut plantations. The total area of betel nut plantations has increased over the past 30 years, reaching a peak of 56 542 ha in 1997. The public and conservation groups frequently express great concern over the potential negative hydrological impacts of betel nut plantations on steep slopes. This investigation in central Taiwan examines the effects of hillslope betel nut plantations on hydrological processes. Differences in hydrological characteristics between plots planted with betel nut trees and those with other ground cover types were evaluated at two study sites. The tall, single-layer canopy and wide spacing between planted betel nut trees led to low interception losses, high throughfall and high net rainfall. Plots planted with betel nut trees had lower infiltration, higher surface runoff and higher erosion than forested sites. These hydrological characteristics can be related to factors such as crown cover, soil organic content and soil porosity in betel nut plantations. Streamflow data from three gauged watersheds with different proportions of total area planted with betel nut showed that where greater proportions of total area were planted with betel nut trees, there were higher annual streamflow/rainfall ratios, higher specific peak flows, steeper recessions and higher peak flow/baseflow ratios. The results from this study suggest that, in general, betel nut trees are less desirable from the soil and water conservation viewpoints than natural forests.     

东莞主要森林群落凋落物碳储量及其空间分布

基于2 km×2 km的UTM网格对东莞市不同的森林群落类型进行了详细调查,以研究森林凋落物的碳储量及其空间分布.研究结果表明,天然林凋落物碳储量显著高于人工林;不同森林类型的凋落物碳储量之间差异极显著,其碳密度大小依次为:湿地松-阔叶混交林>相思林>马尾松-杉木林>荷木林>桉树林>杉木-阔叶混交林>马尾松-阔叶混交林>荔枝-龙眼林>青皮竹林.针叶林的单位凋落物碳含量最大,占59%,大于阔叶林;相思林和荷木林单位凋落物碳含量仅次于马尾松-杉木针叶林.不同的经营措施对森林凋落物碳储量有显著的影响,经封山育林的林分凋落物碳储量最大.坡位对凋落物碳储量也有显著的影响,随着坡位的降低,森林凋落物现存量和碳密度随之降低.东莞市森林凋落物碳密度为4.25±0.15 t/hm2,凋落物碳储量总量为0.23±0.008 Mt.凋落物的碳储量动态直接关系到土壤碳储库,采取合适的经营措施,减少人为干扰造成的凋落物的流失,最终对于提高本地区森林生态系统碳库会有积极作用.     

三江平原小叶章湿地枯落物和根分解及其硫元素释放动态

在三江平原小叶章(Calamagrostis angustifolia)典型草甸湿地和小叶章沼泽化草甸湿地中,利用分解袋法研究了小叶章的枯落物和根的分解及其硫元素释放动态。结果表明,在两种类型湿地中,小叶章枯落物和根的分解模式相同,都为快、慢交替的变化模式;但它们的分解速率不同,其原因主要是两种湿地的微环境和分解袋的投放方式不同。经过450 d的分解之后,在小叶章典型草甸和小叶章沼泽化草甸湿地中,小叶章枯落物的干物质损失率分别为32.31%和36.10%,相应的分解速率分别为0.0005797 d-1和0.0006321 d-1,而小叶章根的干物质损失率分别为60.75%和33.68%,其相应的分解速率分别为0.00153 d-1和0.0006412 d-1。在两种类型湿地中,小叶章枯落物和根中的总硫含量都呈波动性变化,小叶章枯落物中硫的释放模式为淋溶、固持、释放,根中硫的释放模式为固持、释放,C/S比值是影响硫发生固持或释放的主要因素。     

典型喀斯特植被类型条件下绿水循环过程数值模拟

绿水对于喀斯特地区的生态恢复具有重要意义。从绿水循环过程入手,综合考虑冠层截留过程、土壤水分运动过程和植被蒸散发过程,建立典型喀斯特地区不同植被类型条件下的绿水循环过程模型。模型在小型人工模拟降雨实验和长时段监测数据的验证下,依托遥感和GIS手段,扩展到区域尺度,模拟了研究区2005年10月~2006年3月的绿水循环过程,结果表明:(1)研究区的绿水占了降雨量的87.4%,大部分降水通过冠层截留、蒸散发和入渗转化为绿水,供给生态用水。(2)典型喀斯特地区不同植被类型条件下绿水循环存在重要差异,随着喀斯特生态恢复和植被类型改变,生态系统把更多的降雨转化为绿水,即转化为生态用水。(3)模拟时段内的绿水贮存量呈增大趋势,不易发生干旱,是"春旱"和"夏旱"前绿水补充的重要时段。     

植物对降水截留的研究进展

降水资源是植物生长发育和产量形成的主要水分来源,植物通过吸收土壤中的水分维持正常生长发育,降水不仅影响自然植物物种分布,也影响植物生产力。由于未考虑植物冠层对降水的截留作用,在水资源评估和农田水分平衡研究中往往高估降水作用,因此,讨论降水截留在水文生态学和农业气象学中均有重要意义。该文系统介绍降水截留的观测方法,包括间接测量法中各分量测定方法、直接测量法详细过程及应用各种方法需注意的问题;系统回顾有关森林和农作物对降水截留的研究成果;探讨在植物对降水截留研究中存在的主要问题：对截留概念的理解不同导致截留测定结果差异显著,没有完善的方法导致测定结果准确性不足,植物种植密度不同导致截留差异,降水强度不同导致截留差异,风速、植物形态结构、叶片表面特性等因素也会影响降水截留的大小。降水过程中植物叶面蒸发问题、降雪的截留问题、风的影响、研究尺度、研究方法以及综合模拟模型将是未来研究的重点和难点。     

广西岩溶区灌木林地凋落物—土壤碳、氮、磷化学计量特征

文章对广西7个典型岩溶石山区（隆林各族自治县、凌云县、东兰县、河池市金城江区、罗城仫佬族自治县、融水苗族自治县和桂林市雁山区）、63个灌木林地样方土壤及环境因子进行取样和调查,研究典型岩溶区土壤和凋落物有机碳（C）、全氮（N）和全磷（P）的化学计量特征及其影响因素。结果表明：（1）研究区灌木林地0~40 cm土壤C、N、P平均值分别为31.90 g·kg⁻¹、3.95 g·kg⁻¹和2.65 g·kg⁻¹,变异系数分别为40.13%、41.46%、65.24%;C/N、C/P、N/P平均值分别为8.10、14.82、7.80,变异系数分别为14.88%、48.78%和41.33%;0~20 cm土壤C/N、C/P、N/P值略高于20~40 cm土壤;0~20 cm和20~40 cm土壤C/N、C/P和N/P组间均存在显著差异;（2）土壤养分元素含量之间均存在极显著相关性,土壤养分元素生态化学计量特征与凋落物N、P含量显著正相关,与凋落物C/N显著负相关;土壤P含量与海拔显著正相关,土壤C/N与年平均气温呈负相关关系;年平均降水量与土壤C、P呈中等负相关关系;年平均气温与土壤C、C/N、C/P呈负相关关系,与土壤N呈正相关关系。广西岩溶区土壤和凋落物均具有低碳高磷的特征,凋落物氮、磷是影响岩溶灌丛土壤养分化学计量特征的重要因子,年均温升高会促进土壤N增加,降低土壤C/N,年均降水量增加会降低土壤C、P含量。