对退耕还林还草有关问题的进一步思考

阐述了“一退双还”政策措施提出的意义和实施情况,提出应进一步明确“一退双还”的目的,从思想和政策上解决重林木轻草灌的倾向,力戒形式主义和表面文章、讲求实绩实效,“以林为主”的绿化方针值得进一步深思和商榷,“一退双还”的责任制和利益机制需进一步完善等一系列问题,值得进一步深入思考和认真解决,以保证“一退双还”和国土绿化工作的持续和健康发展。     

Scale dependence of tree abundance and richness in a tropical rain forest,Malaysia

Abundance and richness are the two fundamental components of speciesdiversity. They represent two distinct types of variables of which the formerisadditive when aggregated across scales while the latter is nonadditive. Thisstudy investigated the changes in the spatial patterns of abundance andrichnessof tree species across multiple scales in a tropical rain forest of Malaysiaandtheir variations in different regions of the study area. The results showedthatfrom fine to coarse scales abundance had a gradual and systematic change inpattern, whereas the change in richness was much less predictable and ahotspot in richness at one scale may become acoldspot at another. The study also demonstrated that differentmeasures of diversity variation (e.g., variance and coefficient of variation)can result in different or even contradictory results which further complicatedthe interpretation of diversity patterns. Because of scale effect the commonlyused measure of species diversity in terms of unit area (e.g.,species/m²) is misleading and of little use in comparing speciesdiversitybetween different ecosystems. Extra care must be taken if management andconservation of species diversity have to be based on information gathered at asingle scale.This revised version was published online in May 2005 with corrections to the Cover Date.     

内蒙古黄河上中游天然林资源保护工程区立地条件分析

文章通过对自治区黄河上中游“天保”工程区的自然条件分析和立地类型划分 ,提出了恢复植被 ,控制水土流失 ,减轻风沙危害的具体措施。根据工程区不同的立地类型 ,采取乔、灌、草相结合的不同模式 ,最大限度的增加植被盖度 ,从而达到改善生态环境的目的。     

内蒙古森林资源动态分析与评价

根据全国森林资源清查统计数据,对内蒙古森林资源的面积、蓄积量及质量在50年间的动态变化进行了综合分析与评价,得出如下结论:自20世纪70年代以来,内蒙古森林面积和蓄积量持续增长,森林覆盖率不断提高,林分结构渐趋合理,森林质量有所改善,林业发展后劲充足;但亦存在着森林资源总量不足、分布不均,林龄及树种结构不尽合理,林地生产力较低且流失严重,整体生态形势依然严峻以及经营管理不善等诸多问题与潜在危机。为此,继续加快林业生态建设步伐,采取有效措施实现跨越式发展是自治区林业发展和生态建设的根本途径。     

黄土坡面土壤性质随退耕时间的动态变化研究

退耕还林还草是控制水土流失和防治土壤退化的关键措施,黄土高原退耕还林还草从试验到推广已有几十年历史。该文通过对黄土高原地区退耕区的实地调查,测定不同地区不同退耕年限植被恢复区表层土壤的理化性质,分析黄土坡面土壤理化性质随退耕时间的动态变化规律。结果表明:随着退耕植被恢复时间的增长,土壤物理结构将日趋改善,土壤养分含量水平将逐渐的提高,并主要集中在植被恢复10~20年期间,20年后,尤其是30年后,土壤理化性质较为稳定,而且,植被维护的好坏往往影响其稳定性。同时,水热条件较好的安塞地区土壤理化性质随退耕时间的改善程度更明显,而水热条件较差的皇甫川流域土壤理化性质随植被类型和植被恢复程度的影响更为显著。结果可为退耕的环境影响评价预测以及土地利用的调控提供科学依据。     

The potential of nonpathogenic Fusarium oxysporum and other biological control organisms for suppressing fusarium wilt of banana

The aim of this study was to evaluate the ability of nonpathogenic F. oxysporum and Trichoderma isolates from suppressive soils in South Africa to suppress fusarium wilt of banana in the glasshouse. Several biological control agents and commercial biological control products were included in the study. The isolates were first screened in vitro on potato dextrose agar. In glasshouse evaluations, the fungal and bacterial isolates were established on banana roots before they were replanted in pathogen-infested soil, while the commercial biocontrol agents were applied as directed by the supplier. Banana plantlets were evaluated for disease development after 7 weeks. In vitro tests showed none of the nonpathogenic isolates suppressed Fusarium oxysporum f.sp. cubense ( Foc ), while slight suppression was observed with the two Trichoderma isolates. Results of the glasshouse evaluations revealed that two of the nonpathogenic F. oxysporum isolates, CAV 255 and CAV 241, reduced fusarium wilt incidence by 87·4 and 75·0%, respectively. The known biological control agent Fo47 did not suppress Foc significantly. Pseudomonas fluorescens strain WCS 417, known for its ability to suppress other fusarium wilt diseases (WCS 417), reduced disease incidence by 87·4%. These isolates should be further evaluated for potential application in the field, independently and in combination.     

Defining urban forestry – A comparative perspective of North America and Europe

Urban forestry is generally defined as the art, science and technology of managing trees and forest resources in and around urban community ecosystems for the physiological, sociological, economic, and aesthetic benefits trees provide society. First mentioned in the United States as early as in 1894, the concept underwent a revival during the 1960s as a comprehensive and interdisciplinary approach to the specific challenges related to growing trees in urban environments. Later, urban forestry evoked the interest of scientists and practitioners in other parts of the world. However, harmonization of urban forestry terminology has been complicated by, for example, the involvement of different disciplines and translation difficulties. In many European languages, for example, the direct translation of ‘urban forestry’ relates more to forest ecosystems than to street and park trees. Efforts in North America and Europe defining ‘urban forest’, ‘urban forestry’ and related terms are introduced. A comparative analysis of selected urban forestry terminology in both parts of the world shows that urban forestry has a longer history in North America, based on traditions of shade tree management. Moreover, urban forestry has become more institutionalized in North America. Urban forestry in Europe has built strongly on a century-long tradition of ‘town forestry’. In both parts of the world, definitions of urban forestry and urban forest have become more comprehensive, including all tree stands and individual trees in and around urban areas. Agreement also exists on the multifunctional and multidisciplinary character of urban forestry. These similarities offer opportunities for international harmonization of terminology.     

The socioeconomics and management of Santiago de Chile''s public urban forests

Santiago, Chile's semi-arid climate and urbanized environment poses a severe limitation for the establishment and maintenance of urban forests. Municipalities, or comunas, are the main stakeholders in the management of Santiago's public urban forests. A tenable hypothesis would be that as the socioeconomic level of a comuna increases, the better the condition of a comuna's urban forest. Unfortunately, there is little comprehensive information on management, public expenditure, and structure of Santiago's public and private urban forests. To examine this hypothesis, Santiago was divided into socioeconomic strata, then using air photo interpretation and stratified field sampling, urban forest structures were quantified by socioeconomic strata. In addition, interview surveys were used to determine municipal urban forest management and expenditures for different public urban forests based on socioeconomic strata. Urban forests in the high socioeconomic strata had fewer public trees, greater tree cover, tree and leaf area density, and leaf area index than lower socioeconomic strata. The percentage of total municipal budget allocated to public urban forest management was consistent among strata, but the total public urban forest budgets were greater in the high socioeconomic strata. Public urban forest structure is related to the socioeconomic strata of Santiago's different comunas.     

Identification of Landscape Elements Related to Local Declines of a Boreal Grey-sided Vole Population

Several studies indicate a long-term decline in numbers of different species of voles in northern Fennoscandia. In boreal Sweden, the long-term decline is most pronounced in the grey-sided vole (Clethrionomys rufocanus). Altered forest landscape structure has been suggested as a possible cause of the decline. However, habitat responses of grey-sided voles at the landscape scale have never been studied. We analyzed such responses of this species in lowland forests in Västerbotten, northern Sweden. Cumulated spring densities representing 22 local time series from 1980–1999 were obtained by a landscape sampling design and were related to the surrounding landscape structure of 2.5×2.5 km plots centred on each of the 22 1-ha trapping plots. In accordance with general knowledge on local habitat preferences of grey-sided voles, our study supported the importance of habitat variables such as boulder fields and old-growth pine forest at the landscape scale. Densities were negatively related to clear cuts. Habitat associations were primarily those of landscape structure related to habitat fragmentation, distance between habitat patches and patch interspersion rather than habitat patch type quantity. Local densities of the grey-sided vole were positively and exponentially correlated with spatial contiguity (measured with the fragmentation index) of old-growth pine forest, indicating critical forest fragmentation thresholds. Our results indicate that altered land use might be involved in the long-term decline of the grey-sided vole in managed forest areas of Fennoscandia. We propose two further approaches to reveal and test responses of this species to changes in landscape structure.     

Habitat Selection and Breeding Success in a Forest-nesting Alcid, the Marbled Murrelet, in Two Landscapes with Different Degrees of Forest Fragmentation

We studied habitat selection and breeding success in marked populations of a protected seabird (family Alcidae), the marbled murrelet (Brachyramphus marmoratus), in a relatively intact and a heavily logged old-growth forest landscape in south-western Canada. Murrelets used old-growth fragments either proportionately to their size frequency distribution (intact) or they tended to nest in disproportionately smaller fragments (logged). Multiple regression modelling showed that murrelet distribution could be explained by proximity of nests to landscape features producing biotic and abiotic edge effects. Streams, steeper slopes and lower elevations were selected in both landscapes, probably due to good nesting habitat conditions and easier access to nest sites. In the logged landscape, the murrelets nested closer to recent clearcuts than would be expected. Proximity to the ocean was favoured in the intact area. The models of habitat selection had satisfactory discriminatory ability in both landscapes. Breeding success (probability of nest survival to the middle of the chick rearing period), inferred from nest attendance patterns by radio-tagged parents, was modelled in the logged landscape. Survivorship was greater in areas with recent clearcuts and lower in areas with much regrowth, i.e. it was positively correlated with recent habitat fragmentation. We conclude that marbled murrelets can successfully breed in old-growth forests fragmented by logging.