杉木与马褂木混交效果分析

采用标准地调查、树干解析等方法对安溪白濑国有林场10年生的马褂木纯林及马褂木、杉木混交林(9杉1马、8杉2马、7杉3马)的树高、胸径、蓄积量等进行对比分析,结果表明:4种林分的树高、胸径、蓄积量间有显著或极显著差异;在相似的郁闭度下,林分蓄积量大小排序为7杉3马>8杉2马>9杉1马>马褂木纯林;不同混交比例对土壤肥力有较大影响,随着林分中马褂木树种数量增加,林地土壤的有机质含量、全N、水溶性N、速效P等土壤肥力指标显著提高。综合分析结果表明,7杉3马为杉木、马褂木混交的最佳比例。     

丽水山区竹子害虫种类调查与为害评估

在不同时间对竹林中不同虫态的害虫进行调查。结合室内饲养观察，共采集各种标本5000余号，经整理鉴定（包括资料摘录），丽水山区竹子害虫种类有11目72科177属244种。其中一字竹笋象、刚竹毒蛾、卵圆蝽、竹织叶野螟、竹蝗、德清真片胸叶蜂、竹莫小叶蝉、南京裂爪螨等为害较严重。     

A size-based stock assessment model for invasive blue catfish in a Chesapeake Bay sub-estuary during 2001–2016

Stock assessment modeling provides a means to estimate the population dynamics of invasive fishes and may do so despite data limitations. Blue catfish (Ictalurus furcatus) were introduced to the Chesapeake Bay watershed to support recreational fisheries but also consume species of conservation need and economic importance. To assess management tradeoffs, managers need to understand the current status of the population and anticipate future population abundance and trends. A Bayesian size-based stock assessment model was used to estimate blue catfish abundance, fishing mortality, and size structure over time (2001–2016) in the tidal James River. The model estimated population size increases until around 2006, with declines in total abundance after 2011 and large blue catfish (≥80 cm total length) after 2001. These first estimates of blue catfish population dynamics in the Chesapeake Bay region provide inputs for projection models to evaluate prospective management actions and identify monitoring needs.     

基于辐射和温度的ET0模型在吐鲁番地区的比较与修正

利用吐鲁番地区3个气象站2000—2015年逐日气象资料,以FAO-56 Penman-Monteith(FAO-56 PM)模型为标准,对6种ET_0模型(M-A模型、P-T模型、M-H模型、H-S模型、Traj模型和B-H模型)进行评价并修正,采用均方根误差(RMSE)、绝对平均误差(MAE)、平均相对误差(MRE)评价指标和Wilcoxon非参数检验法比较年、月尺度上各模型修正前后的估算精度,以筛选适用吐鲁番地区ET_0简化估算模型。结果表明:吐鲁番地区ET_0的主要影响因子是R_s(太阳辐射),其次是e_s(饱和水汽压)和R_n(作物表面净辐射);修正前,年尺度上,M-H模型的估算精度最高;月尺度上,各模型误差较大且与FAO-56 PM模型存在显著差异,适用性较差;修正后,各模型在年、月尺度上的精度均有明显提高,无显著差异,其中修正后的P-T、M-H和B-H模型估算精度最高,可作为吐鲁番地区ET_0简化估算模型。     

辽宁省主要地区农田生态系统氮负荷的研究

利用辽宁省统计年鉴以及文献相关数据,通过农田养分收支平衡的计算,使用GIS工具,探讨辽宁省各地区农田生态系统的氮平衡变化.结果表明,辽宁省2007-2009年的平均总氮输入量是1.40E+ 09kg/a,平均总氮输出量是9.28E +08kg/a,平均总氮负荷是4.68E +08kg/a;其中,由使用化肥所产生的氮输入占总氮输入量的56.75％,有机肥氮占总氮输入量的18.73％.平均单位面积的氮输入量为358.94kg/(hm2·a),平均单位面积的氮输出量为240.37kg/(hm2·a),平均氮负荷为118.57kg/(hm2·a).通过对辽宁省14个地区农田生态系统的氮负荷研究,可以预测出不同地区的农田氮负荷对辽河流域水环境以及地下水的潜在威胁,对农田非点源污染的管理与预防具有重大意义.     

农地确权对小农户信贷可得性的影响——基于双稳健估计方法的平均处理效应分析

基于我国9省小农户调查数据,运用双稳健的平均处理效应模型,研究了农地确权对小农户信贷可得性的影响及其作用机理。结果表明:农地确权可以提升小农户信贷可得性。进一步研究发现,需求方面的影响路径是:确权提高了小农户的土地安全性,增加了农业长期投资,并提高了信贷意愿。供给方面的影响路径是:确权增加了小农户的财产权并使其拥有了可流转大额财产,传递了还款可能性增加的信号;而且可将农地作为抵押品获得农地抵押贷款,增加了金融机构的贷款供给。不过,农地的信号传递作用大于抵押作用,农地抵押作用的发挥需要进行进一步的制度和组织创新。     

基于环境水力学的产漂流性卵鱼类早期资源量估算方法改进

针对鱼类早期资源量估算方法误差大的问题,基于环境水力学,建立鱼卵移流扩散的瞬时点源二维模型,并对模型进行参数选取、守恒验证,分析了鱼类早期资源量传统估算方法的误差,提出一种新的基于环境水力学的产漂流性卵鱼类早期资源量估算方法。结果表明,中心产卵群体,从产卵点到下游约80 km范围内的断面,鱼卵密度呈钟形分布,由传统方法估算得到的早期资源量低于真实值,最大误差为17.5%;对于近岸产卵群体,从产卵点到下游约200 km范围内的断面,鱼卵密度随距离增加呈指数下降,由传统方法估算得到的资源量高于真实值,最大误差为-33.9%;当断面鱼卵密度均匀分布,即中心产卵和近岸产卵时,产卵场下游80 km和200 km后的断面鱼卵密度沿断面分布均匀,传统方法估算结果较为准确,不必进行校正。改进的估算方法可用于计算产漂流性鱼卵的鱼类早期资源量。     

Density‐ and species‐dependent errors in single‐pass timed electrofishing assessment of riverine salmonids

Electrofishing techniques are widely used for the estimation of the size of stream‐dwelling fish populations for both fishery management and scientific study. In contrast to multiple pass, population depletion methods, single‐pass catch‐per‐unit‐effort (CPUE) methods are less time‐consuming and labour‐intensive. A possible issue with the commonly used fixed total time CPUE protocol is that it does not differentiate between the time spent actively fishing and the time incurred while not actively fishing (e.g. removing fish from nets and navigating the site). This issue is likely related to fish density. This study compared two methods of CPUE electrofishing and tested the hypothesis that time spent handling fish and navigating a site can be a source of error in the commonly used fixed total time electrofishing method. Seventy‐one sites were sampled across three subcatchments in the Foyle catchment in Northern Ireland. We found a difference in the catch per unit time between the two methods and that this difference increased with fish density. The fixed‐time CPUE method also failed to detect a species presence in low‐density sites.     

The evolution of the prevalence of classical scrapie in sheep in Great Britain using surveillance data between 2005 and 2012

After the decline of the Bovine Spongiform Encephalopathy (BSE) epidemic in Great Britain (GB), scrapie remains the most prevalent animal Transmissible Spongiform Encephalopathy (TSE) present in GB. A number of control measures have been implemented for classical scrapie, and since 2005 there has been a large reduction in the number of observed cases. The objective of this study is to estimate two measures of disease frequency using up to date surveillance data collected during and after the implementation of different control measures established since 2004, and breeding for resistance schemes that ran from 2001 until 2009. This would enable an assessment of the effectiveness of both the breeding for resistance programme and the compulsory eradication measures in reducing the prevalence of scrapie in GB. Evaluation of the sensitivity of the rapid post-mortem test for scrapie indicated that it detected scrapie in the last 25% of the incubation period. A back-calculation model was developed to estimate the prevalence of infection at animal and flock-level. The results of the model indicated a mean drop of infection prevalence of 31% each year, leading to a 90% drop in infection prevalence between 2005, with an estimate of 5737 infected sheep in GB in 2012.     

A method for estimating fish density through the catches of gillnets

We propose a new method for estimating fish density using catches obtained by gillnets of given mesh size. This method builds on work for estimating the number of fish approaching a gillnet by modelling the fish movement that leads to a gillnet encounter. The theoretical framework is developed, and the method is tested on catch data for cod Gadus morhua and Dolly Varden Salvelinus malma to demonstrate how the method can be applied. The method relies on knowledge of geometric properties of the net, and morphological and behavioural properties of the fish, so we explore the sensitivity of the estimates to some of these parameters. Estimates are most sensitive to the morphological parameter of the angle the mouth is open while swimming and largely invariant to estimates of uncertain parameters like maximum number of fish that can be caught by the particular net.