渭北黄土塬区地埂花椒林的水保作用与生态经济效益调查研究

渭北黄土塬区地埂花椒林的水保作用与生态经济效益调查研究王忠林，薛智德（西北林学院，陕西杨陵７１２１００）渭北黄土塬区现有梯田和台田面积８．４４万ｈｍ２，农田地埂占梯田和台田面积的０．５％～１％。地埂上营造花椒林，既充分利用了这部分空地，解决了林粮争地...     

水土保持是改善库区环境、安置三峡移民的根本

三峡库区的现有环境已成失衡态势，三峡工程上马后对库区环境影响较大的是随淹没而来的移民和搬迁。改善库区环境状况、解决移民安置的根本出路为搞好水土保持，扩大环境容量，抓好预防监督保护和以坡改梯及经济林果、林草建设为重点的水土保持综合治理。当前应紧紧抓住三峡工程开工这个机遇，在已有的“长治”工程基础上加优、扩大开发性防治，再辅之以其它政策性措施，库区环境和移民安置可以得到根本解决。     

How does litter quality and site heterogeneity interact on decomposer food webs of a semi-natural forest?

The relative importance of litter quality and site heterogeneity on population dynamics of decomposer food webs was investigated in a semi-natural mixed deciduous forest in Denmark. Litterbags containing beech or ash leaves were placed in four plots. Plots were located within gaps and under closed canopies at two topographically different sites, above and below a slope, respectively, to cover variable environmental conditions. Litter was collected after 2, 4 and 9 months of decomposition. Extensive decay prevented analysis of ash after 9 months. Density of bacteria (CFU), active fungal mycelium (FDA), protozoa (MPN) and nematodes were 4-15-fold higher in ash leaves than in beech leaves in accordance with the higher resource quality of ash. Similar effects of site on density of decomposers were evident in both litter types: with some exceptions, decomposers were higher at the low site and stimulated in gaps. Taxonomic diversity of nematodes increased during decomposition and functional diversity of nematodes followed a pattern often encountered, i.e. opportunistic bacterial-feeders were gradually replaced by fungal-feeders and slower growing bacterial-feeders while predators and omnivors peaked at the end of the study period. At the first sampling, where bacterial activity prevailed, the relative abundance of the two dominant bacterial-feeders, Rhabditidae (fast growing) and Plectus spp. (slower growing), depended more on site than litter type. At the second sampling where fungal activity became more important, the proportions of bacterial and fungal-feeding nematodes also depended more on site than on litter type. At the third sampling individual nematode taxa responded differently to site. In summary, we conclude that although litter quality had a major influence on the density of organisms in the decomposer food web, site effects were also detected and nematode functional groups responded more to site than to litter quality early on in the decomposition process.     

Carbohydrate dynamics in particle-size fractions of sandy spodosols following forest conversion to maize cropping

In southwest France, much of the forested land on sandy spodosols has been converted to continuous maize cropping in the last few decades. To evaluate the impacts of this change on soil organic matter properties, we compared total organic C and neutral and amino sugars content in whole soil and particle size separates of two forested, and five related sites that had been either clear-cut for 12 and 18 mo, or cultivated to maize for 4-22 yr. Soil carbohydrates accounted for 4-7% of the total organic C across all sites. Soil organic C contents of clear-cut and cultivated sites were only 57-79% of the average value measured in forested sites. Accordingly, carbohydrate content of clear-cut and cultivated sites were only 35-66% of the value in forested sites. Ordering the sites in a chronosequence indicated that both total organic C and carbohydrate contents decreased with an increase in time elapsed since clear-cutting and maize cultivation. The only exception was a partial recovery of carbohydrate content in the site that had been under continuous maize for 22 yr. The clay+silt fraction (0-50 μm) was enriched in carbohydrates, mainly of microbial origin, whereas the sand size fractions (50-200 and 200-2000 μm) contained fewer carbohydrates which were mainly of plant origin. Monosaccharide analysis of particle size separates revealed significant differences in carbohydrate composition between sites. Relative to forested sites, the coarse and fine sand fractions in clear-cut and cultivated sites were depleted in carbohydrates and were relatively enriched in plant-derived carbohydrates. Carbohydrate content of the clay+silt fraction drastically decreased upon clear-cutting. Amino sugar content was consistently lower in clear-cut and cultivated sites than in forested sites, indicating that microbial populations were negatively affected by clear-cutting and cultivation. The fungal population appeared more sensitive than bacteria to these land-use changes as indicated by a greater decline in glucosamine than in muramic acid contents.     

播种造林种基盘基质的改良研究

 为提高干旱半干旱地区植被恢复中的种子发芽率、成活率和初期生长量,提出了局部改善植物生长环境的技术,即播种造林的种基盘绿化技术。实验研究了添加物对种基盘基质水分特性的影响和使用种基盘绿化技术对植物生长的影响。结果表明:通过添加土壤活性改良剂,可以提高种基盘基质的透水性和吸水速率,降低其表面蒸发量,并能促进植物的地上部生长;添加土壤侵蚀防止剂,对种基盘基质的透水性及植物的生长没有显著的影响,但对于维持种基盘形状、提高施工效果很有帮助;通过种基盘进行播种造林,可以增加根的生长粗度,并能促进植物根系向土壤深处发展,从而有利于提高苗木的抗旱能力。     

黄土半干旱区刺槐林地土壤蒸发特性研究

对黄土半干旱区刺槐林内的土壤蒸发状况,进行比较系统的试验研究。试验采用微型蒸发器（Micro-lysimeters,MLS）,人为控制土壤水分梯度,对不覆盖、枯枝落叶物覆盖和苔藓覆盖3种处理的林地土壤蒸发进行了分析。结果表明,在不同土壤水分条件下,利用枯落物覆盖减小林地土壤蒸发效果晴天好于多云天,枯落物覆盖、苔藓覆盖与无覆盖相比,分别减少了20.15%～52.46%和11.11%～36.72%的土壤蒸发,枯落物覆盖效果好于苔藓;林地土壤蒸发量随土壤水分的增加呈上升趋势,当土壤含水量增加到一定临界值以后,林地土壤蒸发量由上升变为下降,表现出土壤水分对林地土壤蒸发具有明显的阈值反应,土壤含水量的临界值分别为14.2%（枯落物覆盖）和16.8%（不覆盖）;基于林地土壤蒸发量（E1）与水面蒸发量（E0）的观测数据,利用STATISTICA软件统计分析,建立林地土壤蒸发模型,可用于林地土壤蒸发量的估算,为林地土壤水分管理提供理论依据。     

黄土丘陵林区开垦地土壤抗冲性的时间变化研究

以黄土丘陵林区 10a径流泥沙观测资料为基础 ,进行土壤抗冲试验 ,分析了林地及其开垦后不同年限土壤的抗冲性能。结果表明 ,林地具有很强的抗冲性能 ,一旦被开垦后 ,随侵蚀年限的增长 ,土壤的抗冲性呈减弱趋势 ,在 3L/min流量下 ,土壤冲刷量从侵蚀 1a的 4.0 1g/L增大到侵蚀 10a的 2 5 .5 1g/L ,加剧了土壤侵蚀发展。相关分析表明 ,土壤的抗剪强度对抗冲性影响最大 ,其次为水稳性团粒和有机质含量。因此 ,退耕还林、恢复和重建植被 ,改善土壤侵蚀环境 ,提高土壤抗冲性 ,能有效地防治土壤侵蚀。     

Modern forestry vehicles and their impacts on soil physical properties

“Close-to-nature forest stands” are one central key in the project “Future oriented Forest Management” financially supported by the German Ministry for Science and Research (BMBF). The determination of ecological as well as economical consequences of mechanized harvesting procedures during the transformation from pure spruce stands to close-to-nature mixed forest stands is one part of the “Southern Black Forest research cooperation”. Mechanical operations of several typical forest harvesting vehicles were analysed to examine the actual soil stresses and displacements in soil profiles and to reveal the changes in soil physical properties of the forest soils. Soil compaction stresses were determined by Stress State Transducer (SST) and displacement transducer system (DTS) at two depths: 20 and 40 cm. Complete harvesting and trunk logging processes accomplished during brief 9-min operations were observed at time resolutions of 20 readings per second. Maximum vertical stresses for all experiments always exceeded 200 kPa and at soil depths of 20 cm for some vehicles and sequences of harvesting operations approached ≥500 kPa. To evaluate the impacts of soil stresses on soil structure, internal soil strengths were determined by measuring precompression stresses. Precompression stress values of forest soils at the field sites ranged from 20 to 50 kPa at soil depths of 20 cm depth and from 25 to 60 kPa at soil depths of 40 cm, at a pore water pressure of −60 hPa. Data obtained for these measured soil stresses and their natural bearing capacities proved that sustainable wheeling is impossible, irrespective of the vehicle type and the working process. Re-occurring top and subsoil compaction, increases in precompression stress values in the various soil horizons, deep rut depths, vertical and horizontal soil displacements associated with shearing stresses, all affected the mechanical strengths of forest soils. In order to sustain naturally “unwheeled” soil areas with minimal compaction, it is recommended that smaller machines, having less mass, be used to complete forest harvesting in order to prevent or at least to maintain currently minimal-compacted forest soils. Additionally, if larger machines are required, permanent wheel and skid tracks must be established with the goal of their maximum usefulness for future forest operations. A first step towards accomplishing these permanent pathways requires comprehensive planning with the Federal State Baden-Württemberg. The new guideline for final opening with skid tracks (Landesforstverwaltung Baden-Württemberg, 2003) proposes a permanent skid track system with a width of 20–40 m.     

青海大通退耕还林生态功能综合评价

根据生态经济学原理,采用层次分析法(AHP),建立了黄河上游退耕还林还草综合生态效益评价指标体系和数学模型。以青海大通县为例,对天然云杉林、退耕林地、天然荒草地、天然灌丛等植被类型进行综合生态效益评价,与农田生态系统进行对比研究。评价结果表明:天然云杉林、退耕林地、天然灌丛等类型的生态效益指数均大于农田生态系统,其综合生态效益指数排列顺序为,天然云杉林>退耕林地>天然灌丛>农地>天然荒草地。这一研究结果可为黄河上游退耕还林生态工程建设提供参考。     

长白山森林土壤有机碳库大小及周转研究

主要分析不同森林植被下有机碳的分解动态和土壤碳库各组分大小、周转时间。结果表明：土壤样品培养90天，CO2累计释放量表层大致为1723～5065mg／kg、下层大致为178～642mg／kg。分解速率总的趋势是前期快，后期慢，表层明显大于下层。大小顺序为：冷杉林〉针阔混交林和阔叶林〉针叶林。在不同植被下的表层和下层土壤中，活性碳占总有机碳的0．54％～1．67％，0．45％～5．48％．平均驻留时间为11～56天、60～88天；缓效性碳占总有机碳的23．0％～63．3％，33．2％～72．2％，平均驻留时间为4～70年、24～161年；惰效性碳占总有机碳的35．5％～75．5％．26．0％～65．%。表层土壤的总有机碳、活性碳、缓效性碳和惰效性碳含量都明显大于下层。凋落物的化学组成主要决定活性碳库、缓效性碳库含量，土壤的粘粒含量等性质主要决定惰效性碳库含量。