【作者】 万雪琴；

【导师】 胡庭兴；

【作者基本信息】 四川农业大学 ， 森林培育学， 2003， 硕士

【摘要】 本研究首先从景观生态学和恢复生态学角度论述了坡耕地退化生态系统的特征；再以坡耕地、退耕地和有林地的植被群落状况和土壤理化性质差异为基础，探讨了坡耕地退耕还林后，植被恢复的特点及其改土效应。结果表明： 1．坡耕地的出现总是伴随着森林景观的退化，它属于退化生态系统的范畴。其退化主要表现在森林景观破碎化及景观格局的变化，系统结构简单化及功能衰退，土壤退化，生物多样性下降等。 2．植被恢复伴随着退化森林景观的恢复；植物群落由简单到复杂；生物多样性显著增大，物种以多年生草本为主。群落演替的大致方向是：1年生草本→乔木+多年生草本→乔木+灌木+多年生草本→自然混交林。生态系统的水土保持和水源涵养功能增强。 3．植被恢复的改土效应主要表现出以下特点： (1)容重：土壤容重在短期(3年)内的变化主要决定于土壤质地和植被恢复模式。具体表现有增大、减小和基本不变三种。容重在中长期(＞15年)的变化主要决定于林分郁闭后林下活地被物的丰富程度。具体表现有降低和升高两种，即退耕还林后，林下始终保持丰富的活地被物，容重会降低，否则会升高。 (2)土壤孔隙和水分：退耕还林后，土壤孔隙的数量、组成及土壤水分特征均发生明显变化。土壤质地和植被恢复模式的不同，使这种变化很复杂。在短期内，石砾化严重，质地轻的土壤总孔隙、毛管孔隙、最大持水量、毛管持水量、最小持水量均显著提高，土壤持蓄水能力增强；而质地重的土壤总孔隙、非毛管孔隙、最大持水量、毛管持水量、最小持水量均有所下降，土壤持蓄水能力下降。在较长时期内土壤总孔隙增大，非毛管孔隙依林下植被的发育情况而异：林下植被始终丰富的，则增多；否则，减少。退耕还林后经过一定时期，最大持水量和最大贮水量接近或达到，甚至超过农耕地水平，毛管贮水量显著高于农耕地水平，土壤的水土保持和水源涵养分功能增强。 (3)土壤养分：在退耕还林初期，土壤有机质含量增加，速效N、P、K明显下降；随着植被群落的恢复速效N能较快地恢复和提高，而有效P和速效K则需经过一个较长的下降过程后，才能逐渐得到恢复和提高。土壤全量养分在退耕还林后略有下降，但趋势不明显。 (4)水土保持机制:退耕还林初期(3年)，耕作侵蚀停止和植被群落恢复是降低水土流失最主要的因素和机制。在一些情况下，该期土壤本身的蓄水保水能力较坡耕地有所降低。土壤本身在防治水土流失中的作用会随着植被群落的发育而逐渐增强，因此从长期来看，植被层、凋落物层和土壤本身在水土流失防治和水源涵养中都起着重要的作用。 4从水土保持和退耕还林工程对生态环境建设的基本要求来说，目前四川省主要发展的生态林、经济林、竹林、工业原料林和林草模式均能起到良好的恢复森林景观，保持水土，改善生态环境的作用。但不同的植被恢复模式，其植被恢复的特点，植被群落结构和相应的生态、经济效益的大小和人们关注的侧重点是有所不同的。更多还原

【Abstract】 The study expounded the degraded characteristics of hillside fields as a kind of degraded ecosystem from landscape ecology and restoration ecology, furthermore probed into the characteristics of vegetation restoration and its effects on soil. The results indicate:First, hillside fields always come along with the forest landscape degradation. Hillside fields ecosystems are products of extremely degraded forest ecosystem, and they themselves are seriously degraded ecosystems. The degraded characteristics mainly are forest landscape fragmentation, landscape pattern degradation, ecosystem structure oversimplification, ecosystem functions decline, soil degradation, productivity dropping and biodiversity decreasing, and so on.Second, vegetation communities developed from simply to complicatedly after converting hillside fields to forest. Simultaneously degraded forest landscapes are restored and improved by certain degrees. Biodiversity of communities drastically increased, and the dominant populations are perennial herbs. Pathway of vegetation succession approximately is from annual herbs to shrubs (they are breedings of cultivar) plus perennial herbs to trees plus shrubs and herbs, finally to natural mixed forests. In the process, both capacities of soil and water conservation and productivities of ecosystems will be enhanced.Third, effects of vegetation restoration on soil mainly are as following:(1) Change of volume weight is based on both soil properties and models of vegetational restoration in short-term (about 3 years). It may rise, reduce or approximately unchange. In long period (about more than 15 years), volume weight may increase or decrease, which depends on richness of ground vegetation and litter in stands. Namely it will decrease if there is plenty of ground vegetation and litter in stand, otherwise it will increase.(2) Remarkable changes happended to soil porosities and moisture contents, which were complicated both by defferent soil textures and vegetation retoration models. In short-term, water and soil conservation benefit of lithosols is greatly strengthened with improvement of total porosity, capillary porosity, and saturated water retaining cpacity, capillary moisture capacity, and field moisture capacity. However, the changes of loam and clay soil are just the contrary of lithosols except capillary porosity replaced by noncapillary porosity. Total porosity always enlarges; noncapillary porosity may increase or decrease in long period, which depend on ground vegetation. Namely it will increase provided plenty of ground vegetation, if not will decrease. Saturated water retaining capacity and field capacity will approximate to, even overtake the level of ploughs after a period. So capability of the waterand soil conservation will strengthen in long period.(3) In early days of converting hillside fields to forest, soil organic substance increased, while available nitrogen, phosphate and potassium had remarkablely decreased. With vegetations restoring, available nitrogen could rapidly recover, but available phosphate and potassium could only recover little by little after a long period of decreased process. The total soil nutrient slightly decreased, but its tendency was not definite.(4) Cease of tillage and restored vegetations are the most important contributors to effectivelyt cut down run-off and soil erosion, because soil itself was negative for water and soil conservation at beginning of cease tillage on hillside fileds. However the capacity of soil and water conservation of soil itself could be gradually strengthened with vegetations restoring. Therefore vegetaion, litter and soil all play important roles in conservating water and soil.Fourth, the several main vegetation restoration models such as public welfare forest, non-timber product forest, bamboo forest, industrial material forest plantation and tree plus forage grass, which have been developed in large scale in Sichuan province, can effectively restore forest landscape, cut down run-off and soil erosion, imp更多还原