Forest species diversity reduces disease risk in a generalist plant pathogen invasion

Empirical evidence suggests that biodiversity loss can increase disease transmission, yet our understanding of the 'diversity-disease hypothesis' for generalist pathogens in natural ecosystems is limited. We used a landscape epidemiological approach to examine two scenarios regarding diversity effects on the emerging plant pathogen Phytophthora ramorum across a broad, heterogeneous ecoregion: (1) an amplification effect exists where disease risk is greater in areas with higher plant diversity due to the pathogen's wide host range, or (2) a dilution effect where risk is reduced with increasing diversity due to lower competency of alternative hosts. We found evidence for pathogen dilution, whereby disease risk was lower in sites with higher species diversity, after accounting for potentially confounding effects of host density and landscape heterogeneity. Our results suggest that although nearly all plants in the ecosystem are hosts, alternative hosts may dilute disease transmission by competent hosts, thereby buffering forest health from infectious disease.     

Effects of Inoculum Density and Wounding on Stem Infection of Three Eastern US Forest Species by Phytophthora ramorum

Seedlings of three Eastern US forest species Quercus rubra (northern red oak), Quercus prinus (chestnut oak) and Acer rubrum (red maple) were inoculated by applying Phytophthora ramorum sporangia to stems at different inoculum densities with and without wounding. Disease occurred in all treatments involving wounds, and no disease was observed in unwounded treatments. Younger seedlings (2–3 years old) did not differ significantly from older seedlings (5–6 years old) in disease incidence, but older seedlings sustained smaller lesions compared with younger seedlings. For both old and young seedlings, disease on wounded stems was observed down to the lowest sporangia concentration utilized (500 sporangia/ml for old seedlings and 100 sporangia/ml for young seedlings). The results show that in the presence of wounding, even very low sporangia concentrations can result in disease, and further suggest that wounding caused by insects and other factors may play an important role in P. ramorum epidemiology in forest environments.     

Impact of sudden oak death on tree mortality in the Big Sur ecoregion of California

The Big Sur ecoregion in coastal California is a botanically and ecologically diverse area that has recently experienced substantial mortality of oak (Quercus spp.) and tanoak (Lithocarpus densiflorus) trees due to the emerging forest disease sudden oak death, caused by the invasive pathogen Phytophthora ramorum. In response to the urgent need to examine environmental impacts and create management response strategies, we quantified the impact of P. ramorum invasion on tree mortality across the Big Sur ecoregion using high-resolution aircraft imagery and field data. Using the imagery, we mapped all detectable oak and tanoak trees possibly killed by P. ramorum infection within redwood-tanoak forests and mixed oak woodlands. To validate and improve our remote assessment, we quantified the number, size, and infection status of host trees in 77 field plots (0.25 ha). The field data showed that our remote assessment underestimated mortality due to the occurrence of dead trees in the forest understory. For each forest type, we developed regression models that adjusted our remote assessments of tree mortality in relation to field observations of mortality and local habitat variables. The models significantly improved remote assessment of oak mortality, but relationships were stronger for mixed oak woodlands (r ² = 0.77) than redwood-tanoak forests (r ² = 0.66). Using the field data, we also modeled the amount of dead tree basal area (m²) in relation to the density of mapped dead trees in mixed oak woodlands (r ² = 0.73) and redwood-tanoak forests (r ² = 0.54). Application of the regression models in a GIS estimated 235,678 standing dead trees in 2005 and 12,650 m² of tree basal area removed from the ecoregion, with 63% of mortality occurring in redwood-tanoak forests and 37% in mixed oak woodlands. Integration of the remote assessment with population estimates of host abundance, obtained from an independent network of 175 field plots (0.05 ha each), indicated similar prevalence of mortality in redwood-tanoak forests (20.0%) and mixed oak woodlands (20.5%) at this time. This is the first study to quantify a realistic number of dead trees impacted by P. ramorum over a defined ecological region. Ecosystem impacts of such widespread mortality will likely be significant.

Evaluation of several commercial biocontrol products on European and North American populations of Phytophthora ramorum

Five commercially available biological control products were tested in vitro with seven isolates of Phytophthora ramorum from North American (NA1, NA2), and European (EU1) populations. The in vitro tests included dual culture methods and detached leaf assays on wounded Rhododendron and Camellia leaves. Variability in response to biocontrol agents among isolates of P. ramorum from North American and European populations was examined. In dual culture tests, both Bacillus subtilis products (Companion® and Serenade®) resulted in better inhibition of the NA1 group than NA2 and EU1. Actinovate® (Streptomyces lydicus) was the least effective of the three bacterial biocontrol agents and there was no difference in percent inhibition among P. ramorum lineages. Two products containing Trichoderma spp. were tested: Plant Helper® (T. atroviride) caused 100% inhibition of all lineages of P. ramorum, while SoilGard? (T. virens) was only about 30% effective. There was great variability among P. ramorum isolates in their response to biocontrol agents. All treatments reduced P. ramorum lesion size on both Rhododendron and Camellia. Combined treatments of Actinovate® with one other BCA did not perform as well as either treatment used individually. Best results were obtained with Serenade® on Rhododendron and Camellia foliage, especially against the NA1 group. Lack of a linear relationship between percent inhibition of P. ramorum by BCAs in vitro and foliar treatments on detached Rhododendron and Camellia leaves indicates that in vitro testing is a poor predictor of BCA performance on plant material.     

Temperature Effects on the Onset of Sporulation by Phytophthora ramorum on Rhododendron ‘Cunningham's White’

The effect of temperature and moist period on the onset of sporangia production by Phytophthora ramorum on Rhododendron ‘Cunningham's White’ was examined with misted detached leaves held in humid chambers. Following wound inoculation with sporangia, leaves were pre‐incubated at 20°C for either 24 or 72 h prior to placement at six different temperatures (4, 10, 15, 20, 25 and 30°C). The overall mean moist period required for first occurrence of sporulation over all six temperatures was 3.24 days with the 24‐h pre‐incubation time, compared with 1.49 days for the 72‐h pre‐incubation time. Following 24 h pre‐incubation at 20°C and at an incubation temperature of 15°C, sporangia were first collected from leaves following a 24 h incubation. At 10 and 20°C, sporangia were first collected after 48 h, whereas at 4, 25 and 30°C, sporangia were first collected after 3 days. Following 72 h pre‐incubation at 20°C, sporulation generally occurred within 1 day, even at temperatures such at 4 and 30°C that are suboptimal for sporulation. The highest levels of P. ramorum sporulation were observed at 20°C. P. ramorum formed sporangia on host tissue under moist conditions within the same time frame reported for P. phaseoli, P. palmivora and P. nicotianae, but substantially more slowly than certain other species such as P. infestans. Quantifying moisture and temperature conditions for initiation of sporangia production provides knowledge which leads to a greater understanding of the epidemic potential of P. ramorum.     

基于最小费用模型的景观连接度评价

作为物种扩散的重要影响因子,景观连接度反映了景观促进或阻碍生物体在资源斑块间运动的程度,它也是区域土地可持续利用和生物保护领域的主要指标.最小费用模型起源于图论,其结合了景观中的详细地理信息和生物体的行为特征,通过费用距离分析可直观形象地描绘出物种在异质景观中的连接度,且可在GIS程序包中实现简便运算和适度的数据需求量,使其在大尺度景观连接度评价中受到广泛关注.本文结合当前的景观连接度研究,详细阐述了最小费用模型评价景观连接度的意义、原理及运算过程,并探讨了该模型应用中存在的问题,以期为进一步开展相关研究及生物多样性保护提供依据.     

漫湾库区景观破碎化对区域生境质量的影响

水利工程的建设不仅改变了库区的景观格局,还会导致区域生物生境质量的变化。以澜沧江漫湾库区为例,在综合海拔高度、植被类型和水源地距离生境因子的基础上,考虑生物扩散过程,研究了建坝前后整个库区以及典型研究小区(库首、库中、库尾、对照)的重要生境斑块空间分布变化。结果表明:漫湾水电站建成后库区的猕猴总体生境破碎化程度增加,景观连接度减少且重要生境斑块的比例也有所降低,生境质量整体下降;4个研究小区的景观格局变化情况同整个库区相一致。空间上,生境质量明显退化的地区主要分布在库区的西部和南部,尤其是库尾地区,其生境斑块数量相较于建坝前增长了9倍,而景观连接度指数下降了81.48%。回归分析结果表明景观连接度指数与占景观面积百分比指数(PLAND)呈显著正相关(R~2=0.973),与斑块数(NP)呈显著负相关(R~2=-0.611);肯德尔系数表明斑块数(NP)、最大斑块指数(LPI)、占景观百分比指数(PLAND)、相似邻近百分比指数(PLADJ)、连通度指数(CONNECT)和香农多样性指数(SHDI)7个景观格局指数与景观连接度指数均表现出显著一致性。由此看出,库区景观破碎化越严重、区域景观连接度越低生境质量退化越明显;而提高生境主要植被类型的覆盖率、保护连接度贡献大的重要斑块和建设生态廊道,可以有效恢复库区生物生境质量。     

Impacts of forest fragmentation on species composition and forest structure in the temperate landscape of southern Chile

Aim Few studies have explicitly examined the influence of spatial attributes of forest fragments when examining the impacts of fragmentation on woody species. The aim of this study was to assess the diverse impacts of fragmentation on forest habitats by integrating landscape‐level and species‐level approaches. Location The investigation was undertaken in temperate rain forests located in southern Chile. This ecosystem is characterized by high endemism and by intensive recent changes in land use. Method Measures of diversity, richness, species composition, forest structure and anthropogenic disturbances were related to spatial attributes of the landscape (size, shape, connectivity, isolation and interior forest area) of forest fragments using generalized linear models. A total of 63 sampling plots distributed in 51 forest fragments with different spatial attributes were sampled. Results Patch size was the most important attribute influencing different measures of species composition, stand structure and anthropogenic disturbances. The abundance of tree and shrub species associated with interior and edge habitats was significantly related to variation in patch size. Basal area, a measure of forest structure, significantly declined with decreasing patch size, suggesting that fragmentation is affecting successional processes in the remaining forests. Small patches also displayed a greater number of stumps, animal trails and cow pats, and lower values of canopy cover as a result of selective logging and livestock grazing in relatively accessible fragments. However, tree richness and β‐diversity of tree species were not significantly related to fragmentation. Main conclusions This study demonstrates that progressive fragmentation by logging and clearance is associated with dramatic changes in the structure and composition of the temperate forests in southern Chile. If this fragmentation process continues, the ability of the remnant forests to maintain their original biodiversity and ecological processes will be significantly reduced.     

Ancient isolation and independent evolution of the three clonal lineages of the exotic sudden oak death pathogen Phytophthora ramorum

The genus Phytophthora includes some of the most destructive plant pathogens affecting agricultural and native ecosystems and is responsible for a number of recent emerging and re-emerging infectious diseases of plants. Sudden oak death, caused by the exotic pathogen P. ramorum , has caused extensive mortality of oaks and tanoaks in Northern California, and has brought economic losses to US and European nurseries as well due to its infection of common ornamental plants. In its known range, P. ramorum occurs as three distinct clonal lineages. We inferred the evolutionary history of P. ramorum from nuclear sequence data using coalescent-based approaches. We found that the three lineages have been diverging for at least 11% of their history, an evolutionarily significant amount of time estimated to be on the order of 165 000 to 500 000 years. There was also strong evidence for historical recombination between the lineages, indicating that the ancestors of the P. ramorum lineages were members of a sexually reproducing population. Due to this recombination, the ages of the lineages varied within and between loci, but coalescent analyses suggested that the European lineage may be older than the North American lineages. The divergence of the three clonal lineages of P. ramorum supports a scenario in which the three lineages originated from different geographic locations that were sufficiently isolated from each other to allow independent evolution prior to introduction to North America and Europe. It is thus probable that the emergence of P. ramorum in North America and Europe was the result of three independent migration events.     

Investigating the distribution of prairie dogs in an urban landscape

Habitat fragmentation is a prevalent threat to biological diversity, and urbanization is a primary agent of fragmentation and a leading cause of species endangerment. Landscape biogeographic and local habitat characteristics can be important determinants of the distribution of species in habitat patches in urban landscapes. However, the specifics of which characteristics are most critical to maintaining biological diversity are not fully known for prairie ecosystems, especially in fragmented urban habitat. This study focuses on black-tailed prairie dogs along an urban gradient in Denver, CO. Prairie dogs have declined precipitously throughout the region and are an essential part of the prairie ecosystem, making them excellent study subjects. We identified a series of habitat fragments along a gradient of urbanization in the fully urbanized areas and south suburbs of Denver, CO, both containing and not containing prairie dogs. Local characteristics, including fragment slope and vegetative cover, and landscape characteristics, including fragment size, age and connectivity, were measured on each fragment. We used likelihood-based methods to explore which variables most accurately predicted prairie dog occurrence within our study area. Multiple factors influenced the distribution of prairie dogs in urban settings, with colony connectivity the strongest predictor of occupancy. Large and recently isolated fragments near other prairie dog colonies, flat areas and those with high graminoid cover were most likely to support prairie dog populations. Our study provides the first attempt to model prairie dog occurrence in highly fragmented urban habitat and has important implications for the management and conservation of prairie dogs.     

Isolation and characterization of microsatellite markers in Phytophthora ramorum,the causal agent of sudden oak death

We describe specific primers and conditions to amplify two dinucleotide and five trinucleotide microsatellite DNA loci isolated from the oomycete Phytophthora ramorum, the causal agent of sudden oak death. The primer sets were tested on 14–30 isolates from North America and Europe. Seven of 14 loci differentiated between A1 and A2 mating types. All seven loci successfully amplified DNA isolated from infected plant tissue. Four loci may be useful for the diagnosis of P. ramorum because they do not amplify closely related Phytophthora species.     

新疆额河河谷林区景观格局对杨树植食性昆虫危害的影响

开展森林景观格局与植食性昆虫危害关系的研究,是构建景观生态安全格局和实现有害生物生态调控的重要理论依据。在额河河谷林区开展实地调查获取杨树植食性昆虫危害数据,基于遥感数据提取景观格局相关指数,使用线性混合效应模型（Linear Mixed-Effects Models）分别从景观水平和景观类型水平上分析了林区景观格局与林地、耕地、草地和荒地的景观格局对两种植食性昆虫危害的影响。结果表明在额河河谷林区中,景观破碎化是造成两种植食性昆虫危害加重的关键,但食叶率和潜叶蛾虫口密度对景观格局的响应不完全一致;景观水平下,景观丰富度和景观连接度越高,食叶率越高,平均斑块面积与潜叶蛾虫口密度呈显著负相关;景观类型水平下,林地的斑块数量越多,额河河谷林区受到的植食性昆虫危害越严重,耕地面积的增加导致潜叶蛾虫口密度上升,荒地的景观凝聚力指数和草地的平均斑块分维数与食叶率呈显著正相关。因此在优化景观格局时,合理规划景观组成并减少景观破碎化有助于维持经济发展和生态保护的平衡,促进森林的可持续发展。     

森林所有制对景观格局和动物生境的影响研究进展

在欧美等地区的林业发达国家,多种森林所有制长期并存,至今,多种所有制影响下森林景观和生境格局的变化以及与动物保护之间的关系成为研究热点和重点.本文首先阐述了森林所有制对森林景观格局和动物生境的影响,以及林权分散和林权流转的加剧带来的生态后果,包括提供多样化的生境和导致原有大面积生境的破碎化;其次,总结了林业发达国家解决林权分散与生物保护之间矛盾的两个理论途径--改变所有制格局和相对统一各所有制的管理行为,分析现多采用后一种途径的原因,并指出目前森林所有制研究中模拟方法的局限;最后,论述我国的研究现状以及面临的机遇和挑战,提出近期发展建议.     

景观空间异质性对生态系统服务形成与供给的影响

景观空间异质性与生态系统服务的关系极为密切,适当调整景观空间异质性有助于生态系统服务的持续形成与稳定供给。研究景观空间异质性和生态系统服务形成与供给之间的相互影响作用及响应机制具有重要的理论与现实意义,是保护生物多样性、管理生态系统服务与优化景观空间配置的基础。现有研究大多在不同尺度上探讨了景观格局与生态过程或生态系统服务间的相互影响关系,而缺乏景观格局-生态过程-生态系统服务三者间有效联结等方面的研究。景观空间异质性是怎样直接或间接地作用于生态系统服务形成与供给的,目前还没有一个较为明确的解释。因此,通过分析国内外文献,回顾了景观格局或景观空间异质性与生态系统服务之间关系的研究进展、研究内容和研究方法;从景观组成、景观构型的变化入手,讨论了景观空间异质性对生态系统服务形成与供给的影响及其强度,并认为景观组成异质性变化能够直接影响生态系统服务,而景观构型异质性变化会通过改变生态过程而间接影响生态系统服务;阐述了景观空间异质性在影响生态系统服务形成与供给的同时,也使生态系统服务在空间上产生了异质性分布,并从自然因素和人为因素两个方面对其进行解释;强调了尺度问题在景观空间异质性与生态系统服务研究中的重要性;最后,明确了对生态系统服务形成与供给的景观空间异质性影响研究不仅有助于生态系统服务的维持与调节,也能更深层次地揭示其中的生态学意义。     

心率减速力及连续心率减速力对冠心病心脏性猝死的预警价值

目的：通过心率减速力（DC）及连续心率减速力（DRs）检测技术对老年冠心病患者进行风险分层,探讨其对心脏性猝死的预警价值。方法：随机选择经冠状动脉造影（CAG）确诊为冠心病（CHD）的患者218例作为观察组,其中隐匿性CHD 55例,急性心肌梗死（AMI）56例,心绞痛（AP）53例,缺血性心力衰竭（IHF）54例。同期选取在本院进行健康体检者55例（对照组）,对各组患者行24 h动态心电图检查,应用软件系统分析并计算出DC值及DRs值进行统计分析。结果：CHD各亚组（AMI组、AP组、IHF组、隐匿性CHD组）的DC值及DRs值均明显降低,与正常组比较,差异有统计学意义（P < 0.01）;DC值与DRs值所提示CAD各亚组的危险分级明显高于正常组,差异有统计学意义（P < 0.01）;冠状动脉造影显示冠脉病变数量越多范围越大,病情越重,这与DC、DRs所提示CHD各亚组的危险分级相一致。结论：心率减速力和连续心率减速力能够测定分析迷走神经功能,对冠心病患者进行危险分级,对高危人群有较高的预警价值,可作为预警冠心病患者发生心脏性猝死的敏感指标。     

Effects of historic and projected climate change on the range and impacts of an emerging wildlife disease

The global trend of increasing environmental temperatures is often predicted to result in more severe disease epidemics. However, unambiguous evidence that temperature is a driver of epidemics is largely lacking, because it is demanding to demonstrate its role among the complex interactions between hosts, pathogens, and their shared environment. Here, we apply a three‐pronged approach to understand the effects of temperature on ranavirus epidemics in UK common frogs, combining in vitro, in vivo, and field studies. Each approach suggests that higher temperatures drive increasing severity of epidemics. In wild populations, ranavirosis incidents were more frequent and more severe at higher temperatures, and their frequency increased through a period of historic warming in the 1990s. Laboratory experiments using cell culture and whole animal models showed that higher temperature increased ranavirus propagation, disease incidence, and mortality rate. These results, combined with climate projections, predict severe ranavirosis outbreaks will occur over wider areas and an extended season, possibly affecting larval recruitment. Since ranaviruses affect a variety of ectothermic hosts (amphibians, reptiles, and fish), wider ecological damage could occur. Our three complementary lines of evidence present a clear case for direct environmental modulation of these epidemics and suggest management options to protect species from disease.     

生物结皮分布格局对坡面流水动力特征的影响

生物结皮的分布格局是影响坡面产流产沙的因素之一,但其格局对侵蚀动力的影响机理尚不明确,妨碍了进一步解析生物结皮影响坡面产流产沙的机制。本研究通过室内模拟降雨试验,采用景观生态学方法,对带状、棋盘和随机3种分布格局下生物结皮坡面景观指数和水力学参数的变化规律与裸土坡面进行对比研究。结果表明: 生物结皮显著影响坡面侵蚀动力,其分布格局是影响坡面侵蚀动力的因素之一。与裸土相比,生物结皮显著降低了坡面流速(54.6%)和弗劳德数(67.0%),显著增加了径流深(86.2%)和阻力系数(10.68倍),但对雷诺数和径流功率的影响较小;除径流深外,3种格局的生物结皮坡面的各水力学参数均存在显著差异,其中,随机格局对坡面侵蚀动力的影响最大。基于因子分析和聚类分析,筛选出斑块占景观面积比例、斑块密度、景观形状指数、斑块连结度和分离度5个指标作为描述生物结皮斑块分布特征的指标。其中,生物结皮斑块间的斑块连结度和分离度是影响坡面侵蚀动力的主要格局因子。随着生物结皮斑块间斑块连结度减小、分离度增大,坡面流速增加,阻力减小,坡面侵蚀加剧。