闽北闽粤栲天然林林隙特征及干扰状况

研究林隙结构对天然林更新演替具有重要意义,以闽北闽粤栲天然林林隙的基本特征及干扰状况为研究对象,通过对闽北闽粤栲天然林中的28个林隙进行调查,进而分析其林隙大小结构、年龄结构、形成方式、形成木特征及干扰规律.结果表明,在闽北闽粤栲天然林中,冠林隙中10-20 m2所占的数量比例和面积比例都是最大的.扩展林隙个数以＜50 m2所占的数量比例最大,以50-100 m2所占的面积比例最大.林隙年龄以10-15 a所占的数量比例最大.林隙形成方式主要是折干与掘根风倒共同作用,占总株数的57.14％.林隙多由1-4株形成木形成的,平均每个林隙有4.04株形成木,形成木的径级以10、20cm为主,占与82.30％.林隙的线状密度为12.84个·km-1,冠林隙和扩展林隙的形成速率分别为2.08和7.02 m·km-1·a-1.林隙干扰的周期为476.19 a     

Gap-, stand-, and landscape-scale factors contribute to poor sugar maple regeneration after timber harvest

Natural regeneration in canopy gaps is a key process affecting long-term dynamics of many forests, including northern hardwood forests. The density and composition of regenerating trees are often highly variable, reflecting sensitivity to a suite of driving factors operating at different scales (e.g., harvest gap to regional landscape), including production of seeds, physical characteristics of gaps and stands, competition with non-tree vegetation, and browsing by animals. Multivariate analyses over broad geographic areas provide insights into the relative effects of these factors and permit exploration of spatial patterns in regeneration. We examined the effects of gap-, stand-, and landscape-scale factors on densities of tree seedlings (<1 m tall) and saplings (1-2 m tall) in 59 selection-harvested northern hardwood stands located across a 4500 km² region of Michigan's Upper Peninsula. We used Bayesian multilevel modeling to account for the hierarchical structure of the data and assess uncertainty in parameter estimates. Sugar maple (Acer saccharum) saplings were absent from 61% of 154 m² plots centered in harvest gaps (n = 347) despite its high shade tolerance and overstory dominance, but densities were high in other gaps. Densities of sugar maple seedlings and/or saplings were negatively associated with a combination of greater stand-scale densities of white-tailed deer (Odocoileus virginianus), greater gap-scale cover of non-tree vegetation, and lower gap-scale light availability, with deer density having the greatest effect. Densities of unpalatable and commercially less valuable ironwood (Ostrya virginiana), the second most common regeneration species, were positively related to gap-scale seed-production potential but were unrelated to factors affecting sugar maple. Ironwood tended to replace sugar maple saplings in areas with high deer density. At the landscape scale, densities of sugar maple seedlings and saplings decreased with decreasing latitude and snow depth and increasing winter deer densities. These inverse spatial patterns suggest that deer herbivory can lead to landscape-scale variation in regeneration success. However, the spatial distribution of habitat types (a proxy for soil moisture and nutrient conditions) confound this observation, with higher densities of sugar maple generally located on stands with less nutrient-rich habitat types. Results demonstrate that combinations of factors operating at different scales, and with different relative magnitudes of impact, contribute to high variation in regeneration composition and density following timber harvest. Selection silvicultural practices, as currently applied, do not ensure regeneration of desirable species; practices might require modifications in general (e.g., increasing gap size) and to match them to regionally varying factors like deer density.     

The effect of small gaps in California annual grassland on above‐ground biomass production

Small gaps and clumped species distributions are common in grasslands. In California annual grasslands, patches of Lolium multiflorum Lam. and Bromus hordeaceus L. are often separated by gaps. These gaps potentially limit the productivity and associated resource use of these grasslands. The effect that differences in spatial aggregation, gap distribution and species mixing on 20‐cm‐diameter plots has on overall forage production by these two grasses was tested. There were three levels of aggregation: whole plots planted; half planted/half empty; two opposing quarters planted/two empty. Each species was planted in each distribution, and they were combined as mixed, half L. multiflorum/half B. hordeaceus and two quarters L. multiflorum/two quarters B. hordeaceus (nine treatments). Plant aggregation had no significant effect on above‐ground production of whole plots, but individual tillers near gaps were significantly larger than others. Plasticity in the growth of individual annual grasses effectively buffered against variation in average productivity resulting from variations in plant distribution. There were significant (P < 0·001) differences in forage production as a result of the species the plots contained. Plots containing only L. multiflorum produced 4053 kg of dry matter (DM) ha^–1, B. hordeaceus plots produced 2448 kg of DM ha^–1, and plots containing both species produced 4712 kg of DM ha^–1. At small scales, spatial distribution was less important than species composition in determining annual grassland productivity.     

Editorial

No abstract available for this article.     

Initial Response of Understory Vegetation to Three Alternative Thinning Treatments

This study compares initial understory vegetation response among three thinning treatments and a control in 30- to 50-year-old even-aged Pseudotsuga menziesii (Mirbel) Franco (Douglas-fir) stands. It was conducted on four sites on the western slope of the central Oregon Cascades. Treatments included a control (no thinning), a light thinning, and two treatments designed to encourage development of understory vegetation: a light thinning with gap creation and a heavy thinning. Vegetation response was measured during the first post-treatment growing season and 5–7 years later. At a treatment-scale, vegetation structure and composition differed between thinned and unthinned stands but varied little among thinning treatments. Thinnings resulted in initial declines of bryophytes, tall shrubs, and low shrubs followed by subsequent recovery and growth. Herbs displayed little initial response, but a release of early-seral species was evident in thinned stands by 5–7 years posttreatment. The addition of gaps resulted in differentiation of plant composition across the gradient from gap center to the thinned forest matrix, but this was only statistically detectable at a within-treatment scale. The causal mechanisms driving initial post-thinning response are discussed to better understand long-term implications and potential roles of thinning in managing for understory vegetation.     

辽东山区次生林不同大小林窗土壤养分特征

以辽东山区天然次生林中3种(大、中、小)林窗为对象,通过对林窗内土壤养分质量分数的监测,探讨了林窗形成早期对土壤养分状况的影响.结果表明:与非林窗(对照林分)相比,3种林窗对土壤有机碳、全氮和全磷的质量分数无显著影响;而土壤铵态氮、硝态氮、速效磷和微生物生物量磷的质量分数则显著增加(P相似文献   

作物产量差研究进展

随着人口的增加以及生活水平的提高,人们对粮食的需求不断增加,因此增加粮食产量、确保粮食安全仍是未来永恒不变的课题。近年来随着育秧、覆膜等技术的应用,灌溉、施肥技术措施的提高以及作物品种的更替和技术的进步等使得农作物产量呈现增加的趋势。即便如此,作物实际产量与其潜在产量间仍然存在较大差距,而这种现象广泛存在于世界各国的农业生产中。文章在阐述产量差内涵的基础上,对目前国内外产量差的研究方法及主要研究进展等方面进行了综述,并对未来产量差的研究做了展望,以期为进一步开展产量差研究提供科学参考。产量差概念发展至今,虽然众多学者都对其做了不同的定义及阐述,但总体而言,作物的最大产量水平为潜在产量,实际产量与潜在产量之间的产量差为该作物的总产量差。造成作物产量差的原因主要包括不可能应用到田间的技术和环境因子、生物因素（品种、病虫害等）和经济因素（投入产出比）、政策、文化水平及传统观念等。为了进一步解析作物产量差,前人根据研究目的的不同,划分了不同等级的产量差。目前国内外产量差的研究方法主要有试验调查统计分析法和作物模拟模型法。前者概念简单,可操作性强,但是要求足够的试验数据,试验费用大,周期长;后者可以设置更多的情景和处理,但难以精确定量实际生产中的所有管理措施。因此,在实际进行产量差研究中,可综合利用统计方法、作物模拟模型及遥感方法,充分发挥各种方法的优势。世界各地主要作物产量差的研究结果显示,发达国家因栽培管理水平相对较高,作物产量提升空间较小。虽然各地学者对当地不同作物产量差进行了详细的研究,为提升该地区产量、缩小作物产量差提供了科学依据和参考。然而,由于产量估算方法不同,使得研究结果之间差异较大,可比性差。同时因数据和方法的限制,大多集中在解析农业生产过程中的气候、土壤、品种、栽培管理措施等因素对产量的限制程度,而往往忽略了在产量形成过程中农民意愿、政策和经济等因素的影响。总之,未来的产量差研究重点应包括准确计算各区域主要作物产量潜力上限,明确针对不同产量差计算方法,综合考虑气候、土壤、品种和栽培技术以及社会经济因素,解析产量差限制程度。     

中国农村金融生态环境问题研究

摘要：农村金融生态环境的优劣评判依据是农村区域经济的发展和稳定程度,金融法律法规的完善程度及其在农村的执行状况,农村信用环境的健全程度,以及地方政府对农村金融活动的管理方式和介入程度。当前,我国农村金融生态环境面临农村宏观经济的形势严峻,农村金融缺口严重,行政力量对农村金融活动干预失当,且农村金融的市场化程度低,法制环境缺失,社会信用意识淡薄,征信体系建设滞后。因而,要改善农村金融生态环境的现状就必须统筹城乡经济社会发展,消除“二元结构”,促进农村经济发展;规范地方政府行为,建立地方治理与农村金融活动良性互动的关系,同时建立良好的法律和执法体系,为农村金融生态营造良好的法制环境,全面推进信用体系建设,规范农村金融生态的信用秩序。     

Bird use of logging gaps in a subtropical mountain forest: The influence of habitat structure and resource abundance in the Yungas of Argentina

Selective logging is one of the main economical activities in tropical and subtropical forests. While most of the effects of this activity on bird communities have been studied by comparing exploited vs. non-exploited areas; the use of human-created treefall gaps by birds is relatively unknown. We studied habitat structure, resource abundance (fruits, flowers and arthropods) and bird activity in logging gaps of different age (1-year-old and 10- to 20-year-old) in a mountain forest (Yungas) of northwest Argentina in both dry and wet seasons. In less than a year after creation, short herbs colonize logging gaps increasing the abundance of arthropods in the ground and the activity of understory insectivores. During dry seasons recently created gaps become an important source of resources for understory frugivores-insectivores. Later on in succession logging gaps are invaded by exotic graminoid vegetation and tall herbs (dispersed through extraction tracks) which can impede the colonization and development of pioneer trees and natural regeneration. Probably as a consequence of a high abundance of fruits and flowers in the understory and a very low abundance of these resources in the canopy, old gaps were mainly used by understory frugivores-insectivores while arboreal frugivores were rare. Because arboreal frugivores disperse most tree seeds in tropical and subtropical forests, the low activity of this guild in logging gaps contribute to the low observed regeneration. Sustainable timber harvest in tropical and subtropical forests should include gap and logging track management to minimize the invasion by exotic graminoid vegetation and facilitate natural succession.