重金属污染区耕地轮作休耕治理农户参与意愿实证研究

  目的  研究我国农村重金属污染区耕地轮作休耕治理农户参与意愿,分析影响农户参与重金属污染区耕地轮作休耕治理影响因素,为我国重金属污染耕地长期治理的有效实施提供参考依据。  方法  基于343户的调查数据,构建累积logistic回归模型,探究我国重金属污染区耕地轮作休耕治理农户参与意愿及其影响因素。  结果  相比于男性,女性更愿意参与重金属污染轮作休耕治理（?0.1341）;农户参与意愿与受教育程度（?0.098）、家庭收入（0.2591）正相关,但与年龄（0.2036）负相关;农户参与意愿与轮作休耕治理政策了解程度（0.3049）、治理过程评价（0.0985）正相关,参与意愿受亲朋好友（?0.1110）影响较大,由于信任度原因现阶段农村基层组织政策宣传对农户参与意愿影响较小;农户参与意愿与轮作休耕后家庭收入变化（0.4851）正相关;农户参与意愿与自有耕地污染程度（?0.3995）负相关,与农户对环境关注度（?0.1953）呈负相关。  结论  农户个体特征及基本情况、参与后的家庭收入变化、耕地污染特征及对环境感知、政策宣讲及实施过程对农户参与意愿具备实质性影响。因此,要提高基层村组在政策宣讲和政策执行过程在农户心中的信任度;提高农业从业人员的受教育水平,降低农业从业人员平均年龄;增加农户家庭收入,拓宽农户收入来源渠道;从环境保护和收入层面加强治理的预期效应宣传,逐步消除农户污染治理与自身收入平衡的矛盾心理。     

认知对农户参与农业文化遗产保护行为的影响——以福建安溪铁观音茶文化系统为例

农户作为农业文化遗产保护的主体和直接参与者,对遗产保护的认知影响着参与保护的积极性,进而影响遗产系统的可持续性,是保护与发展措施实施的信息反馈,也是政策制定和改进的出发点和落脚点。本文以中国重要农业文化遗产——福建安溪铁观音茶文化系统为例,在计划行为理论的框架下,采用结构方程模型实证分析了农户认知对其参与农业文化遗产保护行为的影响。结果表明:1)农户遗产保护认知的行为态度对其参与遗产保护意愿的正向影响不显著,但农户遗产保护认知的主观规范、控制认知对其参与遗产保护意愿的正向影响显著,从而通过参与遗产保护意愿的中介作用对参与遗产保护行为产生间接的正向影响,间接影响效应分别为0.292、0.442。2)参与遗产保护的能力和遗产保护的制度环境是影响农户是否愿意参与遗产保护的关键因素。3)农户遗产保护认知的3个维度即行为态度、主观规范和控制认知两两存在显著地相互正向影响,其中行为态度与控制认知的相互影响最大,影响系数达到0.652。基于此研究结果,提出关于加大宣传力度、完善保护制度、落实激励政策等方面的政策建议,以此深入推动农业文化遗产的保护与发展。     

资源禀赋对农户生态耕种行为决策的影响分析

在农户资源禀赋日益分化的社会背景下,探究资源禀赋对农户生态耕种行为决策影响的规律性,对于制定耕地生态保护政策具有重要参考价值。在对江西省2 068户农户进行实地调查的基础上,运用Tobit模型实证分析了资源禀赋对农户生态耕种行为决策的影响。结果表明资源禀赋显著影响农户生态耕种行为决策,其中农户受教育程度、家庭人口、常年在家务农人口、加入合作社、被认定为家庭农场、耕地收入占家庭收入比重、耕地面积表现出显著的正向影响,劳动力人口则为显著的负向影响。在此基础上,提出加强农户耕地生态保护知识、技能培训,提高农民科学文化素质;大发展农业专业合作社,提高农户的组织化程度;培育家庭农场,发展现代化生态农业;在"三权分置"的基础上,推进承包地经营权流转,实现适度规模经营。     

粮食生产核心区不同类型农户耕地保护的认知与行为

[目的]剖析粮食生产核心区内不同类型农户参与耕地保护的认知与行为差异,为制定相关差异化政策,引导农户加强对耕地的监督和保护提供支持。[方法]选择粮食生产核心区河南省周口市为样本点,采用分层随机抽样与乡村参与性评估法(PRA)对各类农户参与耕地保护的认知与行为进行调查,运用Logistic回归模型进行影响因素分析。[结果](1)随着受教育程度的提高和兼业程度的加深,各类农户对耕地重要性和多功能性的认识、时间投入偏好、对耕地保护前景的信心、对农业污染的防范都呈现出:缺失型(Ⅰ)基本型(Ⅱ)自然资产型(Ⅲ)人力资产型(Ⅳ),得到补偿后参与意愿、追加补偿到耕地的意愿、定期施用有机肥或采用过测土配方施肥、制止他人破坏耕地的比例都呈现出缺失型(Ⅰ)基本型(Ⅱ)自然资产型(Ⅲ)人力资产型(Ⅳ)。(2)影响各类农户耕地保护行为的因素既存在相同之处也存在各自差异。相同因素包括户主文化程度、投入偏好、补偿意愿。户均年龄高,家庭劳动力少的缺失型农户影响因素还包括户主年龄、务农人数、补偿方式;专门从事农业生产的基本型农户影响因素还包括家庭毛收入、经营土地面积、耕地破碎度;从事短期兼业且非农收入较高的自然资产型农户影响因素还包括非农收入比、粮食种植经济效益、农户兼业;长期居住城镇,较少参与农业生产的人力资产型农户的影响因素还包括耕地经济区位、当期粮食价、政策性补偿方式。[结论]农户作为耕地保护的直接参与者,其认知与行为很大程度决定着耕地保护的成效。     

农户参与保护农田生态环境意愿的影响因素实证分析

利用对武汉市农户的实地调查数据,以农户＂是否愿意减少化肥农药的施用量＂来衡量农户参与保护农田生态环境意愿的指标,运用Logistic模型对影响农户参与意愿的因素进行了计量分析。研究结果表明：（1）愿意参与保护农田生态环境的农户具有以下特征：女性居多,家庭农业收入比例较高,家庭人口数较少,农田质量高,灌溉设施好,区位条件优,对环境关注程度高,认为施用化肥对环境造成危害和迫切希望尽快治理环境。（2）农户参与农田生态环境保护的意愿与性别、农业收入比例、环境满意度呈显著正相关,与家庭人口数、灌溉条件、土地区位、施用化肥状况对环境有害认知呈显著负相关。提出加大农田生态环境的宣传力度,开展农田整治工作和改善农田生态环境等措施,增强农户参与保护农田生态环境的意愿。     

资本禀赋对农户绿色生产行为影响研究进展

为促进农户绿色生产,实现农业绿色转型和增强农业可持续发展,理清并掌握资本禀赋与农户绿色生产行为之间的影响关系,增强研究成果对行为决策的辅助作用,在农业生产污染的现实背景下,系统整理了绿色生产行为的内涵以及影响因素、资本禀赋的内涵及分类、资本禀赋中各要素指标对绿色生产行为的影响,并对未来的研究提出展望,进一步促进我国农民参与绿色生产和提升农业绿色发展。     

环境规制下农户感知对参与农业废弃物资源化利用意愿的影响

为提高农户农业废弃物资源化利用意愿,改善农村生态环境,顺应农民对美好人居环境的期待,本文基于河南、山东、四川、黑龙江4省693个农户的调研数据,建立多元有序Logistics模型,研究农户农业废弃物资源化利用价值与技能感知、成本收益感知与市场回收条件感知对其参与意愿的影响,并引入环境规制政策作为调节变量,分析了环境规制政策对农户农业废弃物资源化利用感知-参与意愿关系的调节效应。结果表明：1）农户农业废弃物资源化利用技能感知、成本感知、与回收渠道间的距离感知、回收渠道稳定性感知,均显著地影响其参与意愿;其中,农户技能感知和回收渠道稳定性感知对其参与意愿具有显著的正向影响。2）引导型规制对农户农业废弃物资源化利用前景感知与技能感知-参与意愿关系存在显著的正向调节效应;约束型规制对农户农业废弃物回收利用重要性感知、回收渠道稳定性感知-参与意愿关系存在显著的正向调节效应;激励型规制对农户农业废弃物资源化利用前景感知与技能感知、收益感知、回收渠道稳定性感知-参与意愿关系存在显著的正向调节效应,对与回收渠道间的距离感知-参与意愿关系存在显著负向调节效应。建议加强技术培训、增设更多补贴款项、健全农业废弃物回收机制,提高农户参与意愿,充分发挥3种规制政策的互补作用,不断调整优化农业废弃物资源化利用政策,持续推进农业农村绿色发展。     

农户耕地保护意愿及影响因素研究——以甘肃省会宁县翟家所乡为例

合理利用和保护耕地是我国经济社会和谐发展的重要基础。农户是耕地利用的组织者和耕地保护的执行者,他们的保护意愿和行为选择是影响耕地保护的重要因素。以甘肃省会宁县翟家所乡为例,从农户角度出发,通过相关性分析,运用Logistic回归模型分析法对影响该乡农户耕地保护意愿的因素进行了分析与研究,最后结合回归系数分析得出,农户成员的年龄、文化水平、非农就业技能,以及耕地的社会效益和耕地的破碎度5个因素对农户的耕地保护意愿呈现不同程度的正影响,家庭人口数、农户对耕地产权的认知和耕地附近的道路状况这3个因素对农户的耕地保护意愿呈现不同程度的负影响。基于此提出如下建议:开展有关耕地利用和保护的宣传活动,增强农户保护耕地的主动性和积极性;大力发展农村服务业,为农户养老提供保障,也为农户参与耕地保护提供强大的经济支撑;做好区域内的土地利用规划,改善农业基础设施,提高耕作的机械化水平和耕地利用集约度,减轻区位因素对农户耕地保护意愿的制约。     

基于条件价值评估法的农业生态补偿意愿及支付水平评估——以甘肃省永登县为例

[目的]揭示甘肃省永登县农户对农业生态补偿的意愿及支付水平,为政府未来进行相关农业生态建设提供依据。[方法]在问卷调查的基础上,采用条件价值评估法(CVM)对永登县的农业生态补偿农户意愿和支付水平进行分析。[结果](1)永登县农户生态认知和补偿意愿较好。(2)农户愿意进行补偿的人数达到调查总人数的87.76%,农业生态补偿支付水平均值达到人均52.11元/a。(3)影响农户进行农业生态补偿支付意愿的重要性程度依次为:受教育程度人均年纯收入生态环境的重要程度对自己的影响程度外出打工天数环境关注度是否治理年龄地理区位。[结论]永登县农户的农业生态补偿意愿强烈,支付水平符合实际情况,受个人认知和人均收入影响明显。     

耕地土壤质量保护中农户认知行为影响因素研究——基于结构方程模型的估计

探讨耕地土壤质量保护中农户认知行为的影响因素,可以在深化已经研究基础上,为政府制定引导农户合理利用和保护耕地土壤质量的政策提供依据。本研究采用结构方程模型,利用辽宁省沈阳市沈北新区233户农户调查数据进行实证分析。研究结果表明:(1)社会经济因素特征、农户自身条件特征和耕地自然条件特征这3类外源潜变量对农户耕地质量土壤质量保护认知均有显著的正向影响,农户自身条件特征是影响耕地土壤质量保护中农户认知行为的主要因素,其特征每提高一个单位,农户耕地土壤质量保护认知程度会提高0.877个单位;(2)可观测变量对3类外源潜变量的解释能力均较强,且显著水平、影响程度和作用方向存在明显的差异,其中农产品价格、户主受教育程度和典型地块面积分别对这3类外源潜变量的解释能力相对较好。基于以上的研究结果,本研究认为提高农业生产的比较效益、稳定的农村土地经营权和将土地向以农业收入为主的农户流转实现规模经营,并针对这种类型的农户进行农业生产和耕地土壤质量保护方面的技术服务和培训,是未来政策制定和实施的重要方向。     

旋流排沙渠道排沙特性试验

旋流排沙渠道是基于旋转水流的特点提出的一种水沙分离新技术,为明确不同来流条件对旋流排沙渠道排沙特性的影响,该研究通过物理模型试验探究了来流流量、来流流速、泥沙级配及下游渠道水力条件下旋流排沙渠道的排沙、余沙及淤沙特性,分析了其截沙率变化规律。结果表明,当来流条件改变时,旋流排沙渠道的排沙特性发生规律性变化,在来流流量增加或流速增加或来沙中值粒径减小情况下,旋流排沙渠道的排沙量减小,余沙量增加,其中改变来流流量对截沙率的影响最为明显,最大变幅为16.3%。不同水沙条件下0.075～0.315 mm细颗粒泥沙的排沙量及余沙量均存在较大差异,且下游渠道余沙均以该粒径区间的泥沙为主,而粒径>0.315～3.0 mm泥沙的排除效果受水沙条件改变的影响极小。排沙洞内泥沙淤沙量随来流量和泥沙中值粒径的增加而增加,而随流速的增加而减少,但各水沙条件下最大淤沙量仅为来沙量的2.6%。在渠道下游设置挡水板后,旋流排沙渠道的排沙性能得到进一步提升,提高了粒径>0.16～0.315 mm泥沙的排除效果,与不设挡水板相比截沙率增加了4.6个百分点,也改善了排沙洞内的泥沙淤积问题。旋流排沙渠道具有良好的泥沙分选效果,能有效排除高含沙水流中的粗颗粒泥沙（在不同水沙条件下最小截沙率为76.9%）,从而减少了泥沙对渠道下游设施的影响,因此工程中可通过优化流量、流速、下游水力条件等提升旋流排沙渠道的排沙特性。研究明确了不同水沙条件下旋流排沙渠道的适用性,成果可为其在工程中的设计和应用提供参考。     

Changes in soil biological and biochemical characteristics in a long-term field trial on a sub-tropical inceptisol

Soil organic carbon (SOC), microbial biomass carbon (MBC), their ratio (MBC/SOC) which is also known as microbial quotient, soil respiration, dehydrogenase and phosphatase activities were evaluated in a long-term (31 years) field experiment involving fertility treatments (manure and inorganic fertilizers) and a maize (Zea mays L.)-wheat (Triticum aestivum L.)-cowpea (Vigna unguiculata L.) rotation at the Indian Agricultural Research Institute near New Delhi, India. Applying farmyard manure (FYM) plus NPK fertilizer significantly increased SOC (4.5-7.5 g kg⁻¹), microbial biomass (124-291 mg kg⁻¹) and microbial quotient from 2.88 to 3.87. Soil respiration, dehydrogenase and phosphatase activities were also increased by FYM applications. The MBC response to FYM+100% NPK compared to 100% NPK (193 vs. 291 mg kg⁻¹) was much greater than that for soil respiration (6.24 vs. 6.93 μl O₂ g⁻¹ h⁻¹) indicating a considerable portion of MBC in FYM plots was inactive. Dehydrogenase activity increased slightly as NPK rates were increased from 50% to 100%, but excessive fertilization (150% NPK) decreased it. Acid phosphatase activity (31.1 vs. 51.8 μg PNP g⁻¹ h⁻¹) was much lower than alkali phosphatase activity (289 vs. 366 μg PNP g⁻¹ h⁻¹) in all treatments. Phosphatase activity was influenced more by season or crop (e.g. tilling wheat residue) than fertilizer treatment, although both MBC and phosphatase activity were increased with optimum or balanced fertilization. SOC, MBC, soil respiration and acid phosphatase activity in control (no NPK, no manure) treatment was lower than uncultivated reference soil, and soil respiration was limiting at N alone or NP alone treatments.     

Effects of livestock grazing on pollination on a steppe in eastern Mongolia

Widespread degradation of Mongolian grasslands by overgrazing is of global concern. The objective of this study was to reveal the effects of grazing on pollination as an example of interaction biodiversity in Mongolian grasslands. We established three plots according to grazing intensity on the eastern steppe of Mongolia. In each plot, we recorded the numbers of insect-pollinated plants and observed the foraging behavior of pollinators in June and August. The richness of insect-pollinated species was high and these species were most abundant in lightly grazed plots, and formed complex relations with diverse pollinators. But, frequency of flower visitation and pollination index were greater in heavily grazed plots. All pollination properties were poorest in intermediately grazed plots. These results suggest that the forb-biased foraging of sheep and goats reduces the floral diversity of insect-pollinated species, and consequently reduces pollinators in the intermediately grazed plots. In the heavily grazed plots, only limited ruderal species could survive under heavy cattle grazing, and such simple vegetation formed unbalanced but strong bonds with pollinators. Removal simulation showed that the mutual network was more fragile with respect to the extinction of certain species.     

Short-term Effects of a Partial Drawdown on Fish Condition in a Eutrophic Reservoir

Prescribed or natural drawdowns occur frequently in reservoirs but their effects on fish populations have been barely studied. As a consequence of a severe drought and the need to optimize water quality, a partial drawdown was prescribed in autumn 2005 to a eutrophic reservoir that provides water supply to a large metropolitan area (Barcelona, Spain). In order to avoid a potential massive fish kill given the reduced oxygen availability and high fish abundance, preventive purse seine fisheries were performed to reduce the fish stock. The fisheries had little effect on the fish assemblage because final population size structure and species composition did not change significantly. The species composition of the purse seine catches varied significantly during the drawdown with higher proportion of bleak (Alburnus alburnus) in pelagic water during the days of worst water quality, confirming that bleak is more tolerant than roach (Rutilus rutilus) to poor water quality and a potential good indicator of water pollution. The weight–length relationship (i.e. condition) of roach and bleak also varied significantly during the drawdown following the same tendency in both species, losing and recovering their weight (4.99% in roach and 5.96% in bleak) in only 16 days. The close relationship found between water quality and fish condition demonstrates that fish condition can be a good metric of the well being of fish, even for extreme short-term changes.     

某水电站库区一大型滑坡的形成机制与环境影响评价

通过对某水电站库区一大型滑坡的边界条件、内部结构特征、赋存环境等的详细调查和系统分析,运用地质历史的方法和观点,反演论证了该滑坡的生成机制和演化过程,在此基础上,计算了滑坡不同部位在各种情况下的稳定性,分析预测了其未来的主要破坏方式及可能造成的社会危害和环境影响。     

The effects of human disturbance on a stingless bee community in a tropical rainforest

Human disturbance of tropical rainforests may change pollinator communities indirectly as a result of changes in resource availability. We studied the mechanisms by which human disturbance affects a community of major pollinators, stingless bees, in Sarawak, Malaysia. We surveyed forest structure and flowering activity, and conducted a nest census and a bait-trap survey of stingless bees, both in primary forests and in forests disturbed by logging and shifting cultivation. The densities of late successional trees and large trees (diameter at breast height >50 cm) were higher in the primary forests than in the disturbed forests. The density of flowering trees was lower one year after logging, but recovered in old disturbed forests because of the active flowering of pioneer trees that became established after the disturbance. Stingless bees nest only in large trees, and nest density was positively correlated with the density of large trees. However, we found no relationship between the numbers of foragers and floristic parameters. Some species preferred nesting in dipterocarps, while others preferred dead trees. The results of the bait-trap survey also indicated that some species were abundant in the primary forests, whereas other species were abundant in the disturbed forests. These results suggest that human disturbance alters the species composition of the stingless bee community. Such changes in the bee community may affect the reproductive success of plants, and ultimately forest composition.     

Effects of a plastic cover on soil moisture change in a Mediterranean climatic regime

Water deficit is a serious problem for most agricultural crops, especially in arid–semiarid regions, and limits sustainable development. Production can be improved by reducing evapotranspiration and loss of infiltrated water by the use of a plastic cover. We monitored soil moisture fortnightly over 1 yr using a neutron probe near four trees in an olive grove (Olea europaea, var. Arbequina), two of which had a plastic cover buried in the topsoil around them. These trees were monitored using three neutron probe access tubes per tree to compare the behaviour of soil moisture over time with two other identically instrumented and nearby trees with no cover. Analysis was based on the resultant moisture profiles. The plastic cover retained moisture and increased soil water residence time. During the dry season, the amount of water retained in the plots was at most 15–20% greater in the mid‐season and at least 5–6% greater at the end of season than in the central part of the plots near the trunk. The plastic cover was effective to ca. 50 cm with maximum water content near the soil surface. During the wet season, the cover did not affect soil water. Soil moisture was greater near the tree trunk as a result of stemflow and throughfall.     

基于CFD模型的大跨度温室自然通风热环境模拟

大跨度温室作为一种新型南北走向的钢骨架覆膜温室,解决了传统日光温室土地利用率低、空间狭小的问题。为了研究在自然通风条件下大跨度温室的温度和气流场的分布规律,以及不同室外风速条件下通风口开度对大跨度温室温度和气流场的影响,利用计算流体力学(computational fluid dynamics,CFD)软件构建三维稳态大跨度温室模型,模拟自然通风条件下大跨度温室内的温度场和气流场,并采集典型晴天下通风口开启50%时大跨度温室内13个测点的温度,将各测点的测量值与模拟值进行比较,最后利用已验证模型模拟分析通风口开度(25%、50%、75%、100%)在不同室外风速(1、2、3、4 m·s~(-1))条件下的大跨度温室温度和气流场。验证结果表明:模型模拟值与实测值的绝对误差在0.2~2.8℃,均方根误差为1.6℃,最大相对误差为9.9%,平均相对误差为4.1%,表明模拟值与实测值吻合良好。模拟结果显示,温室顶部温度高,底部温度低;室外冷空气从西侧通风口进入,温室内西侧温度低于东侧;温室内平均风速从南到北逐渐减小;温室中部风速明显小于东西两侧。大跨度温室上通风口及侧通风口全开时,温室内温度分布较均匀。温室通风口开度一定时,温室内通风率与室外风速呈显著线性正相关。考虑温室内温度及风速对作物的影响,以降温为主要目的时,建议通风口开度取75%~100%,若室外风速大于3m·s-1且室内温度能满足作物生长,则建议通风口开度75%。     

Carbon partitioning in a wet and a semiwet subarctic mire ecosystem based on in situ C pulse-labelling

In this study we quantify the partitioning of recent assimilates to above- and below-ground carbon (C) pools in two subarctic mire ecosystems - wet minerotrophic and semiwet ombrotrophic mire - using in situ ¹⁴C pulse-labelling. Ecosystem C partitioning to rhizomes, coarse roots, fine roots, dissolved organic carbon (DOC) and microbes were quantified twice  during the growing season at three different soil depths. Finally the ¹⁴C-partitioning data from this and a previous study were combined to estimate the overall C partitioning of the three main vegetation types of a Scandinavian subarctic mire in early and late summer.The semiwet ombrotrophic ecosystem hosted a much larger root biomass on an area basis compared to the wet minerotrophic ecosystem which might be due to differences in the soil nutrient level. Microbial C was found to be the largest C-pool in both ecosystems. Ecosystem ¹⁴C partitioning was poorly related to plant biomass for the semiwet and the wet ecosystem. Overall a higher partitioning of recent assimilates to below-ground compartments was apparent in August-September compared to June-July, while the opposite was found for the above-ground C-pools. In the semiwet ecosystem twice as much ¹⁴C was found in DOC compared to the wet ecosystem, where root density, litter and above-ground biomass were important controls of the ¹⁴C-recovery in DOC. Plant-derived DOC was estimated to be 15.4 versus 12.9 mg C m⁻² d⁻¹ in the semiwet and wet ecosystem, respectively.Graminoid dominated and dwarf shrub dominated vegetation types of the subarctic mire Stordalen differ with respect to the relative amount of recently assimilated C partitioned to C-pools with “slow” versus “fast” decomposition rate. The capacity for sequestration of recently fixed C within “slow” C-pools might affect the ecosystem C balance (NEE) and C-storage. The potential for vegetation changes might therefore be an important factor to consider in studies of response of ecosystem C-dynamics to global change factors in subarctic mires.     

Impact of a Semi-experimental increase in recreation intensity on the densities of birds in groves and hedges on a lake shore in The Netherlands

The possibility of disturbance of birds by outdoor recreation is often mentioned, but has rarely been studied. This article presents the results of a disturbance field experiment which took place during three breeding seasons and was conducted along a 4·5 km long lake shore with hedges and groves. Parts of this area have probably undergone an increase in visitor numbers since 1979 as a result of the construction and opening of a car park nearby. The recreation intensity in other parts further away from the car park has probably not increased.Visitors and the breeding birds were counted during the breeding seasons in 1977 and 1978 (before the car park was opened) and in the breeding season in 1980 (after the car park had been opened). All but one (Phylloscopus trochilus) of the 12 (most abundant) species showed a negative difference between experimental units and control units, indicating a disturbance effect. However, no significance was reached with regard to the following bird species analysed: Columba palumbus, Troglodytes troglodytes, Prunella modularis, Turdus philomelos, Turdus merula, Hippolais icterina, Sylvia atricapilla, Sylvia borin, Sylvia communis, Sylvia curruca, Phylloscopus trochilis, Phylloscopus collybita.The number of 11 negative differences out of 12, on the contrary, is highly significant using a sign test (p = 0·003).Interpreting the results as a recreation effect is also supported by the fact that species show negative correlations between recreation intensity and density in 1980 (p = 0·033; sign test). These correlations were significant for Hippolais icterina and Sylvia borin.Such correlations were not found for 1977 or 1978.