Tree Spatial Structure,Host Composition and Resource Availability Influence Mirid Density or Black Pod Prevalence in Cacao Agroforests in Cameroon

Combining crop plants with other plant species in agro-ecosystems is one way to enhance ecological pest and disease regulation mechanisms. Resource availability and microclimatic variation mechanisms affect processes related to pest and pathogen life cycles. These mechanisms are supported both by empirical research and by epidemiological models, yet their relative importance in a real complex agro-ecosystem is still not known. Our aim was thus to assess the independent effects and the relative importance of different variables related to resource availability and microclimatic variation that explain pest and disease occurrence at the plot scale in real complex agro-ecosystems. The study was conducted in cacao (Theobroma cacao) agroforests in Cameroon, where cocoa production is mainly impacted by the mirid bug, Sahlbergella singularis, and black pod disease, caused by Phytophthora megakarya. Vegetation composition and spatial structure, resource availability and pest and disease occurrence were characterized in 20 real agroforest plots. Hierarchical partitioning was used to identify the causal variables that explain mirid density and black pod prevalence. The results of this study show that cacao agroforests can be differentiated on the basis of vegetation composition and spatial structure. This original approach revealed that mirid density decreased when a minimum number of randomly distributed forest trees were present compared with the aggregated distribution of forest trees, or when forest tree density was low. Moreover, a decrease in mirid density was also related to decreased availability of sensitive tissue, independently of the effect of forest tree structure. Contrary to expectations, black pod prevalence decreased with increasing cacao tree abundance. By revealing the effects of vegetation composition and spatial structure on mirids and black pod, this study opens new perspectives for the joint agro-ecological management of cacao pests and diseases at the plot scale, through the optimization of the spatial structure and composition of the vegetation.     

不同区域典型树木的空间分布格局及关联性

以温带长白山(CBS)、暖温带关帝山(GDS)、亚热带黑石顶(HSD)样地监测数据为基础,采用成对相关函数g(r)分析了3个样地共有的3科(松科、壳斗科、蔷薇科)树木的空间分布格局及其关联性.结果表明:不同样地3科树木分布数量及结构特征存在差异.松科在GDS分布数量较多,呈双峰型径级结构,在CBS和HSD分布数量少,径级结构近似正态分布;壳斗科在CBS和GDS分布数量少,分别呈双峰型和偏正态径级结构,在HSD分布数量多,呈倒"J"型径级分布;蔷薇科在GDS分布数量多,呈"L"型径级分布,在CBS和HSD分布相对较少,径级结构分别呈倒"J"型和"L"型分布.3科树木空间分布格局在不同样地表现也不同,松科的大径级个体在CBS和GDS小尺度上呈均匀分布,在HSD呈聚集分布,中、小径级在3个样地均呈聚集分布;壳斗科在CBS以大径级个体为主,呈近似随机分布,在GDS和HSD以中、小径级为主,呈聚集性分布格局;蔷薇科在3个样地均为聚集分布.3科树木的聚集程度均随尺度增加而降低.大径级的壳斗科个体在CBS和HSD与松科呈不相关或小尺度负相关关系,中、小径级的壳斗科在CBS和GDS与松科呈负相关关系,但在HSD与松科表现为正相关;松科与蔷薇科在3个样地均表现为负相关;中、小径级的壳斗科与蔷薇科在CBS和GDS呈正相关关系,但在HSD呈负相关关系.总之,3科树木空间分布格局及关联性随径级、尺度而变化且在不同样地内有不同表现.     

Optimizing mirid control on cocoa farms through complementary monitoring systems

Mirids (Sahlbergella singularis and Distantiella theobroma) are the most important insect pests affecting cocoa production across West Africa. Understanding the population dynamics of mirids is key to their management; however, the current recommended hand‐height assessment method is labour intensive. The objective of the study was to compare recently developed mirid sex pheromone trapping and visual hand‐height assessment methods as monitoring tools on cocoa farms and to consider implications for a decision support system. Ten farms from the Eastern and Ashanti regions of Ghana were used for the study. Mirid numbers and damage were assessed fortnightly on twenty trees per farm, using both methods, from January 2012 to April 2013. The mirid population increased rapidly in June, reached a peak in September and began to decline in October. There was a significant linear relationship between numbers of mirids sampled to hand‐height and mirid damage. High numbers of male mirids were recorded in pheromone traps between January and April 2012 after which there was a gradual decline. There was a significant inverse relationship between numbers of trapped adult mirids and mirids sampled to hand‐height (predominantly nymphs). Higher temperatures and lower relative humidities in the first half of the year were associated with fewer mirids at hand‐height, but larger numbers of adult males were caught in pheromone traps. The study showed that relying solely on one method is not sufficient to provide accurate information on mirid population dynamics and a combination of the two methods is necessary.     

Sources of variation in the incidence of ant–aphid mutualism in boreal forests

• 1 The mutualism between wood ants of the Formica rufa group and aphids living in the canopy of trees is a widespread phenomenon in boreal forests, and it can affect tree growth. However, not all trees in the forest are involved in this interaction.
• 2 To assess the incidence of host trees involved in this ant–aphid mutualism and its spatial distribution in boreal forests, we inventoried sample plots with a radius of 10–15 m around wood ant mounds in 12 forest stands of two age classes (5–12‐year‐old sapling stands and 30–45‐year‐old pole stands) and two dominant tree species (Scots pine and silver birch) in Eastern Finland from 2007 to 2009.
• 3 The proportion of trees visited by ants out of all trees on the individual study plots were in the range 4–62%, and 1.5–39% of the trees on the plots were consistently visited by ants during all 3 years. The percentage of host trees increased with the ant mound base area on the plots. Trees visited by ants were larger and closer to the mound than trees not visited by ants. Within the group of visited trees, more ants were found on bigger trees and on trees close to the ant mounds.
• 4 Extrapolated from plot to stand level, we estimated that 0.5–6.6% of the trees were host trees in at least one of the three study years, and that only 0.01–2.3% of all the trees were consistently visited by ants during all 3 years. It is concluded that ant–aphid mutualism is a minor occurrence at the stand level.

     

Influence of shaded systems on Xylosandrus compactus infestation in Robusta coffee along a rainfall gradient in Uganda

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Sprouting as a survival strategy for non-coniferous trees: Relation to population structure and spatial pattern of Emmenopterys henryi (Rubiales)

To improve the management and protection strategies of Emmenopterys henryi, the effect of sprouting on the population and spatial distribution pattern was explored. Environmental conditions of the community, tree diameter at breast height (DBH), and height of each individual tree were obtained using a contiguous grid quadrate method in four plots of deciduous and evergreen broad-leaved forests in Dapan Mountain National Nature Research in Zhejiang, China with the largest distribution area of E. henryi. The principal components analysis (PCA) showed that the sprouting ability of E. henryi is strongly related to the degrees of rock bareness, altitude, and slope. The analysis of the population structures showed that the population of group A only with parental trees was in decline due to a lack of seedlings and saplings, whereas the population of group B with both parental trees and sprouts (group B) was increasing. Groups A and B differed in their spatial distribution patterns in the plot 2, with group A showing a random distribution and group B displaying an aggregated distribution. Because the optimum block scale was between 16?m² and 32?m², analyses of the spatial pattern and dynamics of the spatial pattern at 25?m² could accurately reflect the true distribution. The population of E. henryi is small, and the spatial patterns of the population indicated an aggregated distribution with the exception of plot 2 of group A. Plot 2 showed significant environmental deterioration from nearby rocks and ravines, and as a result, a number of small trees died from root exposure, which led to a random distribution of plot 2. The effects of sprouting should be considered when studying the population and spatial patterns of plants.     

Influence of plot characteristics and surrounding vegetation on the intra-plot spatial distribution of Empoasca vitis

• 1 Spatial distributions of adults and nymphs of Empoasca vitis were assessed during 3 years inside two adjacent vine plots having considerable intra‐plot variability, diversified natural ground cover and surrounding vegetation, and no insecticide application.
• 2 Geostatistical analysis confirmed that, in spite of repeated adult migrations, spatial distributions of summer populations were highly aggregated, similar every year and similar between adults and nymphs. Comparison of insect distribution with intra‐plot characteristics, such as vine plant vigour (leaf density and leaf chlorophyll concentration) and phenology, plot topography and surrounding vegetation, revealed that E. vitis clearly aggregates in areas with the most vigorous vine plants.
• 3 Even though the presence of natural enemies in the surrounding vegetation was confirmed by specific observations, we did not observe significant population decrease at the contiguous plot edges. Natural ground cover, together with the absence of insecticide, might allow the spreading and perennial conservation of E. vitis natural enemies inside the plots.
• 4 Clear adult aggregations observed along downwind woodlands suggest that this vegetation acts as a barrier and intercepts the adults flying passively across the plot. However, this surrounding vegetation could also serve as an alternative refuge when vine water deficit and vine foliage temperature increase.

     

Proximity is not a proxy for parentage in an animal-dispersed Neotropical canopy palm

We used parentage analysis to estimate seedling recruitment distances and genetic composition of seedling patches centred around reproductive trees of the animal-dispersed Neotropical canopy palm Iriartea deltoidea in two 0.5 ha plots within second-growth forest and one 0.5 ha plot in adjacent old-growth forest at La Selva Biological Field Station in north-eastern Costa Rica. Seedlings were significantly spatially aggregated in all plots, but this pattern was not due to dispersal limitation. More than 70 per cent of seedlings were dispersed at least 50 m from parent trees. Few seedlings were offspring of the closest reproductive trees. Seedling patches observed beneath reproductive trees originate from dozens of parental trees. Observed patterns of seedling distribution and spatial genetic structure are largely determined by the behaviour of vertebrate seed dispersers rather than by spatial proximity to parental trees.     

Beech forest management does not affect the infestation rate of the beech scale Cryptococcus fagisuga across three regions in Germany

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Abundance and mortality of leaf miners on artificially shaded Emory oak

ABSTRACT.

• 1 We measured solar radiation reaching ten Quercus emoryi Torr. trees and recorded densities of four leaf-mining insect species on these trees from June until September 1982.
• 2 The measurements showed that densities of two leaf miner species were negatively correlated with solar radiation.
• 3 In a field experiment, polypropylene shade fabric was suspended 1.3 m above four experimental trees to test for effects of reduced sunlight.
• 4 Leaves of experimentally-shaded trees were heavier and contained lower percentages of proteins and gallotannins than leaves of control, sun trees, while per cent foliar monomeric, polymeric, and total phenols, and water content did not differ between sun and shaded trees.
• 5 Two of four leaf miner species had greater densities on experimentally-shaded trees than sun trees. One of these two species experienced lower survivorship on sun trees owing to high levels of death from unknown causes on sun trees.
• 6 Two leaf miner species had greater densities on sun trees. One of these species had higher survivorship on shaded trees owing to high levels of parasitism on sun trees.
• 7 We conclude that even subtle differences in shading influences leaf miner density and mortality; however, the effects of shading vary from positive to negative among leaf miner species.

     

Spatio‐temporal dynamics of an Ips acuminatus outbreak and implications for management

• 1 Understanding spatio‐temporal processes of bark beetle infestations is crucial for predicting beetle behaviour and aiding management decisions aiming to prevent or mitigate tree mortality. We recorded the spatial and temporal distribution of killed trees during the 5‐year period of an Ips acuminatus outbreak.
• 2 Killed trees were always grouped in well‐defined patches (infestation spots). In years of high population density, infestation spots were large and aggregated, whereas, in years of low density, infestation spots were small and weakly aggregated or randomly distributed within the study area.
• 3 Most trees were killed in the spring by beetles that had hibernated but, in some years, trees were also killed in the summer by new‐generation beetles originating from spring attacks. Spring‐killed trees always formed new infestation spots at new locations (i.e. spot proliferation). By contrast, summer‐killed trees always occurred at the edge of active spots established in the spring, thus resulting in spot growth.
• 4 With regard to management strategies, the results obtained in the present study suggest that areas located in close proximity to infestations of the previous year should be prioritized for risk assessment. Because large spots account for most of the observed tree mortality, the cut‐and‐remove method should be focused on these spots as soon as crown discoloration appears in the summer. If applied timely, this strategy will remove the new‐generation beetles originating from the spring attacks before they emerge and also reduce the risk of spot growth.

     

Spider web guilds in cacao agroforestry – comparing tree,plot and landscape‐scale management

Aim Owing to their role as insect predators, web‐building spiders can be important biological control agents within agricultural systems. In complex tropical agroecosystems such as agroforests, management determines plant architecture, vegetation composition and associated ant density, but little is known on how these attributes, together with landscape context, determine spider web density. We hypothesized that all three spatial scales and the presence of Philidris ants significantly contribute to the explanation of spider web density with web types being differently affected. Location In 42 differently managed cacao agroforestry systems in Sulawesi, Indonesia. Methods We surveyed the distribution of five spider‐web types on 420 cacao trees to determine how these relate to habitat variables and a numerically dominant ant species at three different spatial scales, comparing tree, plot and landscape features. We fitted linear mixed‐effects model, selected the best model subset using information‐theoretic criteria and calculated the model‐averaged estimates. We used non‐metric multidimensional scaling (NMDS) to determine and visualize guild level responses to the effects of the tree, plot and landscape‐scale variables. Results The five spider guilds preferred different features of cacao tree architecture. Most frequently recorded webs belonged to the line‐ and orb‐web type. At the tree scale, overall web density was positively related to canopy openness. At the plot scale, a higher number of shade trees was related to a higher web density. At the landscape scale, the altitude determined the distribution patterns of web‐building spiders. Presence of Philidris ants was positively associated with density of orb webs, while no pattern was found for other web types. Main conclusions Results suggest spider web density could be increased by pruning of cacao trees while keeping shade trees at high density in cacao plots. The results emphasize the need to consider scale dependency of crop management and web‐guild‐specific responses that may be related to different functional roles of spiders as a high‐density predator group in agroforestry.     

贵州特有植物红花瘤果茶种群空间格局及数量动态研究

红花瘤果茶(Camellia rubituberculata)为地理分布狭窄的贵州特有植物,颇具经济价值。为查清其分布特征和评估其濒危状况,该文在红花瘤果茶的集中分布区设置三个典型样地进行调查,采用空间点格局及多元点格局分析法分析种群空间分布格局,利用种群动态量化指数分析预测种群数量动态规律。结果表明:(1)兴仁县新寨村大皮坡1号样地幼龄树的小尺度呈集群分布、大尺度呈随机分布,中龄树和老龄树均呈随机分布; 兴仁县新寨村槽子土2号样地的幼龄树均呈集群分布,中龄树和老龄树均呈随机分布; 晴隆县紫马乡龙头村上捧碧林区3号样地幼龄树、中龄树和老龄树均呈随机分布。(2)不同发育阶段的空间关联主要表现为1号样地幼龄树和中龄树均为负相关,幼龄树和老龄树在中小尺度上为负相关,在大尺度上为无相关,中龄树和老龄树均为无相关。2号样地幼龄树和中龄树在小尺度上为负相关,中大尺度上为无相关; 幼龄树和老龄树在中小尺度上为负相关,中大尺度上为无相关; 中龄树和老龄树均为无相关。3号样地的幼龄树和中龄树均为正相关; 幼龄树与老龄树在小尺度上为负相关,中尺度上为无相关,大尺度上为正相关; 中龄树和老龄树均为无相关。(3)种群数量动态分析表明3个样地中幼苗补充充裕,种群结构为增长型,但易受外界环境干扰、生态脆弱。(4)红花瘤果茶的生境异质性及其种内种间关系相互作用的结果是影响种群数量扩大和物种散布的主要因素。     

盲蝽类害虫种群密度与危害的调查方法

盲蝽是棉花、果树等作物上的一类重要害虫。盲蝽的卵产在植物组织中,若虫活动性和隐蔽性强,成虫善于飞行扩散。针对盲蝽各个虫态的习性,发展了田间种群发生与危害调查技术,为其种群监测提供了科学支撑。     

Within‐field spatial distribution patterns of corn planthopper,Peregrinus maidis,and severity of hopperburn and Maize mosaic virus symptoms as influenced by sunn hemp intercropping

Habitat management (e.g., intercropping) may alter within‐field spatial distribution patterns of herbivores, from a typical pattern as observed in a monoculture, and may influence patterns of crop injury. Field trials were conducted to study the effect of intercropping maize, Zea mays L. (Poaceae), with sunn hemp, Crotalaria juncea L. (Fabaceae) strips on within‐field spatial distribution patterns of corn planthopper, Peregrinus maidis (Ashmead) (Hemiptera: Delphacidae), and combined severity of hopperburn and Maize mosaic virus (MMV) (Rhabdoviridae: Nucleorhabdovirus) symptoms. In each field trial, spatially explicit data on P. maidis counts and ratings of severity of symptoms were obtained by sampling maize plants at weekly intervals. These data were used to examine the spatial patterns of P. maidis and severity of symptoms in maize‐intercropped and monoculture plots with Spatial Analysis for Distance IndicEs (SADIE) methodology. Spatial aggregation patterns of P. maidis in each treatment plot were not consistent among the field trials and tended to be mediated by their population densities. Interpolation of local cluster indices showed that P. maidis were more often aggregated at the field edges, irrespective of treatment. At times of MMV incidence in field trials (fall 2010 and spring 2011), the patch clusters of P. maidis and symptomatic plants were located at the field edges, but were spatially unassociated in both treatment plots. The results provided an approximation of the unpredictability of P. maidis spatial patterns at different population densities and their association with severity of symptoms in two maize‐cropping systems. However, the gap clusters of symptomatic plants were primarily located at the field interiors and were larger in intercropped than in monoculture plots. Such spatial pattern of symptomatic plants resulted in the reduced incidence of MMV in the intercropped plot compared with the monoculture plot, suggesting intercropping sunn hemp can be a useful tool in the management of MMV in maize fields.     

Agroforestry management and phytoseiid communities in vineyards in the South of France

This study deals with the long-term effect of agroforestry management (trees within vine crops) on communities of phytoseiid mites. Several plots were considered: vineyards co-planted with Sorbus domestica or Pinus pinea, monocultures of vines and monocultures of S. domestica or P. pinea. All vine plots included two vine cultivars, Syrah and Grenache. Phytoseiid mites have been surveyed in these plots during several years within the previous 10 years. In 2010, samplings were again carried out in these same plots, from May to September, twice a month. Significantly higher densities of Phytoseiidae were observed on the cultivar Syrah (0.85 phytoseiids per leaf) than on Grenache (0.26 phytoseiids per leaf). Furthermore, significantly higher phytoseiid mite densities were observed in the monocultural grapevine plot than in the two co-planted ones. The main species found was Typhlodromus (Typhlodromus) exhilaratus in all vine plots considered. However, Kampimodromus aberrans was observed in the grapevine plots co-planted with the two trees, but never in the monocultural vine plot. Surprisingly, this phytoseiid species was not found on the co-planted trees, nor in the neighbouring uncultivated vegetation. Several hypotheses are discussed to explain such an unexpected distribution. Furthermore, contrary to what has been observed previously, agroforestry management did not seem to favour phytoseiid mite development, especially on the Grenache cultivar. Again, some hypotheses are developed to explain such observations and density modifications.     

夏蜡梅种群结构与分布格局研究

在夏蜡梅(Sinocalycanthus chinensis)主要分布地设置11个代表性样地,研究了种群结构与空间分布格局,并对种群密度与主要环境因子进行相关性分析。结果表明,大多数夏蜡梅种群幼年阶段的个体较丰富,种群自然更新良好;样地群落夏蜡梅以集群分布为主;在透光率低、林分郁闭的群落中夏蜡梅聚集强度高,但种群更新不良、幼苗缺乏。因此,夏蜡梅适合在相对开敞的遮阴环境下生长,过于郁闭林地应采取适度间伐上层乔木、疏除过密灌木的抚育保护措施。     

The effect of stem density on the probability of attack by the ambrosia beetle Platypus quercivorus varies with spatial scale

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Landscape and farm scale management to enhance biodiversity conservation in the cocoa producing region of southern Bahia, Brazil

In southern Bahia, Brazil, large land areas are used for the production of cocoa (Theobroma cacao), which is predominantly grown under the shade of native trees in an agroforestry system locally known as cabruca. As a dominant forest-like landscape element of the cocoa region, the cabrucas play an important role in the conservation of the region’s biodiversity. The purpose of this review is to provide the scientific basis for an action plan to reconcile cocoa production and biodiversity conservation in southern Bahia. The available research collectively highlights the diversity of responses of different species and biological groups to both the habitat quality of the cabrucas themselves and to the general characteristics of the landscape, such as the relative extent and spatial configuration of different vegetation types within the landscape mosaic. We identify factors that influence directly or indirectly the occurrence of native species in the cabrucas and the wider landscape of the cocoa region and develop recommendations for their conservation management. We show that the current scientific knowledge already provides a good basis for a biodiversity friendly management of the cocoa region of southern Bahia, although more work is needed to refine some management recommendations, especially on shade canopy composition and density, and verify their economic viability. The implementation of our recommendations should be accompanied by appropriate biological and socioeconomic monitoring and the findings should inform a broad program of adaptive management of the cabrucas and the wider cocoa landscape.     

长白山蒙古栎次生林群落结构特征及优势树种空间分布格局

群落结构特征研究是揭示植物群落维持机制和演替动态的基础,是合理安排森林经营活动的基本前提.以吉林省汪清林业局2块1 hm²的蒙古栎阔叶混交林固定样地为对象,研究了长白山蒙古栎次生林的群落结构特征,并采用点格局O-ring统计法对群落内优势树种的空间分布格局进行分析.结果表明: 两块样地都是以蒙古栎为优势树种的群落类型,都具有明显的层次结构,主要伴生树种存在差异,样地Ⅰ以大青杨、白桦、红松为主,样地Ⅱ以红松、紫椴和色木槭为主.且样地Ⅰ的树种数量、Shannon多样性指数高于样地Ⅱ.两块样地中所有个体的径级分布呈倒“J”型,蒙古栎径级结构呈近似正态型,红松呈倒J型,其他主要伴生树种径级结构存在一定差异.两块样地0～50 m尺度上蒙古栎呈现小尺度聚集、中大尺度随机分布的格局,红松呈先聚集、后随机的分布格局,但样地Ⅰ内红松聚集的尺度和强度均大于样地Ⅱ.样地Ⅰ白桦和大青杨均在0～17 m尺度上呈聚集分布、且聚集强度显著高于其他树种,而在18～50 m尺度分别呈现随机分布和均匀-随机分布.样地Ⅱ中紫椴基本呈现随机分布,色木槭在中大尺度上呈随机或均匀分布,聚集分布集中在小尺度.两块样地处于演替早期阶段的不同发育阶段,相比样地Ⅰ,样地Ⅱ的演替阶段更高、群落相对更加稳定.