Novel forest decline triggered by multiple interactions among climate,an introduced pathogen and bark beetles

Novel forest decline is increasing due to global environmental change, yet the causal factors and their interactions remain poorly understood. Using tree ring analyses, we show how climate and multiple biotic factors caused the decline of whitebark pine (Pinus albicaulis) in 16 stands in the southern Canadian Rockies. In our study area, 72% of whitebark pines were dead and 18% had partially dead crowns. Tree mortality peaked in the 1970s; however, the annual basal area increment of disturbed trees began to decline significantly in the late 1940s. Growth decline persisted up to 30 years before trees died from mountain pine beetle (Dendroctonus ponderosae), Ips spp. bark beetles or non‐native blister rust pathogen (Cronartium ribicola). Climate–growth relations varied over time and differed among the healthy and disturbed subpopulations of whitebark pine. Prior to the 1940s, cool temperatures limited the growth of all subpopulations. Growth of live, healthy trees became limited by drought during the cool phase (1947 –1976) of the Pacific Decadal Oscillation (PDO) and then reverted to positive correlations with temperature during the subsequent warm PDO phase. In the 1940s, the climate–growth relations of the disturbed subpopulations diverged from the live, healthy trees with trees ultimately killed by mountain pine beetle diverging the most. We propose that multiple factors interacted over several decades to cause unprecedented rates of whitebark pine mortality. Climatic variation during the cool PDO phase caused drought stress that may have predisposed trees to blister rust. Subsequent decline in snowpack and warming temperatures likely incited further climatic stress and with blister rust reduced tree resistance to bark beetles. Ultimately, bark beetles and blister rust contributed to tree death. Our findings suggest the complexity of whitebark pine decline and the importance of considering multiway drought–disease–insect interactions over various timescales when interpreting forest decline.     

Radial growth response of trees to seasonal soil humidity in a subtropical forest

Tree growth is the most important factor in determining the carbon sequestration processes of forest ecosystems. However, the growth phenology (seasonal growth pattern) and responses of tree growth to climatic variables vary considerably among different species, especially between deciduous and evergreen species. Thus, it is crucial to explore the seasonal growth patterns of different tree species in relation to climate to better understand the responses of tree physiology to climate changes, especially in mixed-species forest stands. In this study, we monitored the daily basal area increments of 220 individuals belonging to 15 common broadleaved tree species, nine deciduous and six evergreen species, in mixed-species experimental stands in subtropical China and analysed the relationships between radial stem growth and seasonal climate at a high-temporal resolution. We fitted daily increments of stem diameters with four frequently used nonlinear models and chose the best model for each species. The results showed that the evergreen trees grew faster than the deciduous trees, both annually and within the growing season. The tested nonlinear models (Korf, Weibull, logistic and Gompertz) produced good fits for the growth patterns of all species. Overall, the evergreen species began stem growth earlier and finished later during the growing season than that of the deciduous species. Within the growing season, the radial growth of trees in mixed stands containing both types of species was strongly positively correlated with humidity. In spring, increases in both temperature and moisture increased the daily relative basal area increment of all species. Maximum growth rates occurred when the soil water content reached its highest level and gradually decreased when the soil water content decreased. In summer, high temperatures combined with low amounts of precipitation led to heat-induced summer drought, to which the evergreen trees appeared to be more tolerant than the deciduous trees, which was reflected in the reduced stem growth of the latter. These results indicate the different climate-dependent seasonal growth strategies of evergreen and deciduous trees related to the trade-off described by the leaf economics spectrum, i.e., short-lived leaves with higher assimilation rates in deciduous and longer-lived leaves with a greater drought tolerance in evergreen species.     

Drought alters timing, quantity, and quality of wood formation in Scots pine

Drought has been frequently discussed as a trigger for forest decline. Today, large-scale Scots pine decline is observed in many dry inner-Alpine valleys, with drought discussed as the main causative factor. This study aimed to analyse the impact of drought on wood formation and wood structure. To study tree growth under contrasting water supply, an irrigation experiment was installed in a mature Scots pine (Pinus sylvestris L.) forest at a xeric site in a dry inner-Alpine valley. Inter- and intra-annual radial increments as well as intra-annual variations in wood structure of pine trees were studied. It was found that non-irrigated trees had a noticeably shorter period of wood formation and showed a significantly lower increment. The water conduction cells were significantly enlarged and had significantly thinner cell walls compared with irrigated trees. It is concluded that pine trees under drought stress build a more effective water-conducting system (larger tracheids) at the cost of a probably higher vulnerability to cavitation (larger tracheids with thinner cell walls) but without losing their capability to recover. The significant shortening of the growth period in control trees indicated that the period where wood formation actually takes place can be much shorter under drought than the 'potential' period, meaning the phenological growth period.     

Armillaria mellea as a cause of oak decline in Hatam-baigh forest of Iran

A200 ha forest of "Hatam-baig" is located in Ardebil Province on the Northwest of Iran. Oak trees (Quercus macranthera Fisch & Mey) in this forest have been faced with declining and extinction since 1991, that has destructed about one third of the forest trees until now. This disorder was expressed in various symptoms including wilting, defoliation and decline. In order to identify factors causing decline, a study was managed from 1998 to 2001. Samples were taken from roots, trunks, crowns and soil beneath the canopy and were cultured on different culture media subsequently. Armillaria mellea (Vahl) P. Kumm., Phytophthora cryptogea Pethybr. & Laff., Dematophora sp., Pythium aphanidermatum (Edson) Fitzp. and Fusarium spp. were the most common isolated fungi. A. mellea appeared to be the essential causal agent of the decline according to the studies made on oak tress decline around the world and based on brown rot observed beneath mycelial fans in the cross section prepared from the trunk and characteristics of the isolated fungi. The fungus activity had been favored by physiological weakness and stresses in oak rootstocks caused by brown- tail moth (Euproctis chrysorhoea L.) and drought stress in infected trees. The biological species of this fungus was identified as Armillaria mellea, using hybridization tests and application of haploid test strains. The fungi such as Phytophthora sp., Pythium sp., and Dematophora sp. can not be infective in this forest due to being hydrophylous. In the southern part of the forest with remarked steepness, the severity of the decline appears to be more than that in the smoothly northern part. The decline of Q. macranthera is reported as matrix nova. The report of the isolated fungi from this oak species is also universally new.     

北京地区侧柏人工林密度效应

密度是影响森林尤其是人工林生长的重要因素,林冠层是森林生态系统与其他系统进行能量和物质交换的重要场所,树木及树冠生长对林分密度的响应关系可以看作是生物对环境变化产生的适应性现象。林分密度效应是生态学和森林培育学的重要研究内容之一。以23块8种不同密度梯度的北京山区侧柏人工幼龄林林分为研究对象分析其树木生长及树冠生长对密度的响应关系,其中树冠指标使用了参照了美国林务局(USDA)的树冠调查指标。研究结果表明:(1)林分平均胸径、平均树高和平均冠幅生长均随密度增大而减小,林分密度大于3000株/hm2时各指标减小的趋势变缓,使用异速生长模型可以很好地拟合这种变化关系;(2)随密度增加,树冠水平方向和垂直方向生长均到显著地抑制作用,树冠外形表现出由饱满冠型向狭长冠型变化的适应性现象;(3)使用树冠二维、三维指标与密度进行相关性分析可知树冠长度、树冠率等指标与林分密度呈负相关关系,树冠圆满度及树冠生产效率与密度表现出极显著正相关关系;(4)采用枝解析的方法研究了树枝长度、材积的平均生长量、连年生长量与密度的关系,结果表明幼龄期各生长量差异不大;(5)在建立冠幅模型时考虑了自变量间的多重共线性问题,所建的胸径单自变量二次方模型能够很好地预测侧柏人工幼龄林冠幅生长过程,模型相关系数R2为0.961。     

内蒙古东北段森林衰退现状及种群竞争对其生长的影响

随着气候变化加剧,中国半干旱区东段发现大量森林衰退现象,威胁到社会生产和环境保护的可持续发展。种群竞争是森林动态的内在驱动因子,当前对该区域森林种群竞争与森林衰退关系的研究尚缺乏足够的依据。选取内蒙古大兴安岭典型森林作为研究对象,依据Hegyi单木竞争指数模型计算个体水平上和样地水平上的竞争指数,利用树木个体树轮指数(TRI)年表作为个体水平上的衰退指标,利用样地年表(TRI)和胸高断面积增量(BAI)来分析样地水平上的衰退指标,探讨不同尺度上森林衰退状况。探讨个体水平上和样地水平上竞争指数与不同尺度上森林衰退指标之间的关系,分析研究区森林衰退的内因特征。主要结论如下：第一,样地年表与树木个体年表所指示的衰退时段基本一致,结合两者的重合结果,可以得出各样地的衰退年份。不同样地的生长衰退时段有重合的现象,个体年表中超过阈值50%的样地的严重衰退时期年份基本在2001-2005年间,而在样地年表中,样地五岔沟林场(L-WCG1)、五岔沟林场大样地(L-WCG2)、乌尔根(L-WRG)在1989年至1997年都出现生长衰退,样地军达盖林场(L-HDG)、L-WCG1、L-WCG2、L-WRG和s根河(L-GH1)衰退重合期在1998-2003年期间。这是由于这一阶段研究区发生了大规模的干旱事件,导致不同地点的树木生长都受到抑制。第二,各样地中树木个体的五年平均相对胸高断面积增量(rBAI₅)与个体竞争指数相关的显著性最高,两者的关系可用指数函数方程表达,即rBAI₅随着个体水平竞争指数的上升而下降。这说明了竞争指数对于树木生长存在显著的影响。而样地竞争指数与近2年、5年和10年内样地胸高断面积均值(BAI₂、BAI₅、BAI₁₀)之间的关系不明显。从种群竞争方面研究中国半干旱区东段的森林衰退影响因素,旨在为森林衰退机理研究提供依据,为半干旱区森林资源可持续发展提供支持。     

Presence of natural genetic resistance in Fraxinus excelsior (Oleraceae) to Chalara fraxinea (Ascomycota): an emerging infectious disease

Fraxinus excelsior, common ash native to Europe, is threatened by a recently identified pathogenic fungus Chalara fraxinea, which causes extensive damage on ash trees across Europe. In Denmark, most stands are severely affected leaving many trees with dead crowns. However, single trees show notably fewer symptoms. In this study, the impact of the emerging infectious disease on native Danish ash trees is assessed by estimating presence of inherent resistance in natural populations. Disease symptoms were assessed from 2007 to 2009 at two different sites with grafted ramets of 39 selected clones representing native F. excelsior trees. A strong genetic variation in susceptibility to C. fraxinea infections was observed. No genetic or geographic structure can explain the differences, but strong genetic correlations to leaf senescence were observed. The results suggest that a small fraction of trees in the Danish population of ash possess substantial resistance against the damage. Though this fraction is probably too low to avoid population collapse in most natural or managed ash forests, the observed presence of putative resistance against the emerging infectious disease in natural stands is likely to be of evolutionary importance. This provides prospects of future maintenance of the species through natural or artificial selection in favour of remaining healthy individuals.     

Linking increasing drought stress to Scots pine mortality and bark beetle infestations

In the dry Swiss Rhone Valley, Scots pine forests have experienced increased mortality in recent years. It has commonly been assumed that drought events and bark beetles fostered the decline, however, whether bark beetle outbreaks increased in recent years and whether they can be linked to drought stress or increasing temperature has never been studied. In our study, we correlated time series of drought indices from long-term climate stations, 11-year mortality trends from a long-term research plot, and mortality probabilities modeled from tree rings (as an indicator of tree vitality) with documented occurrences of various bark beetle species and a buprestid beetle, using regional Forest Service reports from 1902 to 2003 and advisory cases of the Swiss Forest Protection Service (SFPS) from 1984 to 2005. We compared the historical findings with measured beetle emergence from a 4-year tree felling and breeding chamber experiment. The documented beetle-related pine mortality cases increased dramatically in the 1990s, both in the forest reports and the advisory cases. The incidents of beetle-related pine mortality correlated positively with spring and summer temperature, and with the tree-ring based mortality index, but not with the drought index. The number of advisory cases, on the other hand, correlated slightly with summer drought index and temperature, but very highly with tree-ring-based mortality index. The tree-ring-based mortality index and observed tree mortality increased in years following drought. This was confirmed by the beetle emergences from felled trees. Following dry summers, more than twice as many trees were colonized by beetles than following wet summers. We conclude that increased temperatures in the Swiss Rhone Valley have likely weakened Scots pines and favored phloeophagous beetle population growth. Beetles contributed to the increased pine mortality following summer drought. Among the factors not addressed in this study, changed forest use may have also contributed to increased beetle populations and Scots pine mortality, whereas air pollution seems to be of lesser importance.     

Production of Seeds and Cones and Consequences for Wood Radial Increment in Norway Spruce (Picea Abies (L.) Karst.)

Abstract

The presence of a trade–off between growth and reproduction was tested in four sites in a subalpine Norway spruce (Picea abies (L.) Karst.) forest by measuring annual stem diameter increments at breast height and seed and cone productions during the periods 1962–1985 and 1983–1990, respectively. Trees growing in forest stands near the timber line (about 1900 m above sea level) had the greatest reduction in annual stem diameter increment during mast years; while trees growing at about 1300–1500 m above sea level did not show any reduction. Trees growing at about 1700 m showed only a limited reduction. At the same elevation, trees growing within closed forest stands suffered a greater reduction in stem growth when compared with trees growing at the edge of a cutting.     

Forest Structure and Primary Productivity in a Bornean Heath Forest

Aboveground forest structure, biomass, and primary productivity in a tropical heath forest in Central Kalimantan (Indonesian Borneo) were examined using data from 1-ha plots and stand-level allometric equations developed from harvested tree samples. The study site experienced a severe drought in 1997–1998 associated with the El Niño Southern Oscillation event. The drought effect on heath forest productivity was also assessed by evaluating changes in wood mass increment rates. Allometric relationships suggested that heath forest trees had leaves with smaller specific leaf area (SLA), and large heath forest trees allocate more to leaf mass compared to mixed dipterocarp forest trees. Aboveground biomass (for trees ≥ 4.8 cm DBH) in two 1-ha plots, P1 and P4, totaled 244.8 and 232.0 Mg/ha. Aboveground wood mass increment rate was –0.1 and 4.7 Mg/ha/yr in P1 and P4 during the drought period (from February to August 1998), while it quickly recovered to 8.1 and 8.5 Mg/ha/yr during the post-drought period (from August 1998 to August 1999 for P1 and from August 1998 to November 1999 for P4). This suggests a severe impact of the drought on heath forest productivity. Leaf characteristics of heath forest such as small SLA and long-lived leaves probably play a significant role in effective assimilation and maintenance of heath forest productivity under stressful conditions.     

Association of the coprophilous fungus <Emphasis Type="Italic">Pirella circinans</Emphasis> with an indigenous beetle on the sub-Antarctic Bird Island

The zygomycete fungus Pirella circinans was isolated from cadavers of the beetle Hydromedion sparsutum from diverse sites on the sub-Antarctic Bird Island and was found to be the dominant or sole fungal coloniser during the primary degradation of cadavers. The fungus was observed to grow and colonise cadavers from discrete areas of the beetle carapace, some of which were not affected by alcohol surface sterilisation. The fungus is commonly reported from the dung of rodents and other small mammals, both of which are absent from Bird Island. Recovery of P. circinans as the only fungus from beetle cadavers is unusual and may indicate a close association between the beetle and the fungus.     

Tree community structure, dynamics, and diversity partitioning in a Bornean tropical forested landscape

Human-modified forested landscapes are prevalent in the tropics, and the role of complex mosaics of diverse vegetation types in biodiversity conservation remains poorly understood. Demographic traits and the spatial pattern of biodiversity are essential information when considering proper forest management and land use strategies. We compared the tree community structure (stem density, basal area, tree diversity, abundance of rare, endemic, and upper-layer trees, and species composition) and the forest dynamics (mortality, recruitment rate, and increments of basal area, and above- and below-ground biomass) of 39–46 plots among five dominant forest types: young and old fallows, rubber plantations, and fragmented and old-growth forests in Sarawak, Malaysia. We also explored how tree diversity was distributed across different spatial scales using additive partitioning of diversity. Swidden cultivation and rubber plantations showed decreased stem density, basal area, tree diversity, abundance of rare, endemic, and upper-layer trees, and increments of above- and below-ground biomass, which affected tree mortality, dominant trees, and species composition. Little distinction in species composition was observed among young and old fallows and rubber plantations, indicating a relatively quick recovery of the tree community in the early stages. The highest diversity was found among forest types, indicating that the whole forested landscape comprises a suitable scale for tree biodiversity conservation in the region. Our results suggest that although fragmented and old-growth forests have an irreplaceable role and a high priority in conserving biodiversity and sustaining the function of the forest ecosystem, secondary forests may also have a reinforcing role in maintaining tree diversity in the region, especially under the current circumstances in which a large portion of the landscape is human-modified and faces an increasing threat from the expansion of oil palm plantations.     

Spruce beetle outbreak was not driven by drought stress: Evidence from a tree‐ring iso‐demographic approach indicates temperatures were more important

Climate change has amplified eruptive bark beetle outbreaks over recent decades, including spruce beetle (Dendroctonus rufipennis). However, for projecting future bark beetle dynamics there is a critical lack of evidence to differentiate how outbreaks have been promoted by direct effects of warmer temperatures on beetle life cycles versus indirect effects of drought on host susceptibility. To diagnose whether drought‐induced host‐weakening was important to beetle attack success we used an iso‐demographic approach in Engelmann spruce (Picea engelmannii) forests that experienced widespread mortality caused by spruce beetle outbreaks in the 1990s, during a prolonged drought across the central and southern Rocky Mountain region. We determined tree death date demography during this outbreak to differentiate early‐ and late‐dying trees in stands distributed across a landscape within this larger regional mortality event. To directly test for a role of drought stress during outbreak initiation we determined whether early‐dying trees had greater sensitivity of tree‐ring carbon isotope discrimination (?¹³C) to drought compared to late‐dying trees. Rather, evidence indicated the abundance and size of host trees may have modified ?¹³C responses to drought. ?¹³C sensitivity to drought did not differ among early‐ versus late‐dying trees, which runs contrary to previously proposed links between spruce beetle outbreaks and drought. Overall, our results provide strong support for the view that irruptive spruce beetle outbreaks across North America have primarily been driven by warming‐amplified beetle life cycles whereas drought‐weakened host defenses appear to have been a distant secondary driver of these major disturbance events.     

Confessions of solitary oaks: We grow fast but we fear the drought

Competition effects and management related disturbances can contribute to strong non-climatic signals in ring-width trends of trees from closed canopy forests. Removing this noise comes at the price of losing a considerable amount of (climatic) information on decadal and centennial time scales. Alternatively, open grown solitary trees, which never competed for light or other resources could function as less biased climate proxies. To explore this potential we analysed individual growth trends and climate-growth relationships of solitary oaks, potentially representative of former, open forests, and compared it to those of trees growing in adjacent closed canopy forests. Solitary oaks show differing tree allometry with bigger crowns and lower absolute heights. Their radial growth was significantly higher compared to forest trees. Contrary to our expectations, these solitary oaks show highly individualistic decadal growth trends. Their inter-annual variations are nevertheless in good agreement between individuals and stronger compared to trees from closed canopy forests. Climate –growth analysis revealed a significantly higher drought sensitivity of solitary oaks. Given the typical open medieval forest structure of large trees with extensive crowns growing in a mosaic of grazed woodlands and grasslands, it is likely that these trees contribute to the historical part of tree-ring collections. When trees from today’s denser forests forming the recent parts of the collections are used to calibrate reconstruction models, the differing drought sensitivity might therefore lead to an overestimation of historical droughts.     

Drought effects on damage by forest insects and pathogens: a meta‐analysis

In the context of climate change, the effects of prolonged or more severe droughts on pest and pathogen damage are a major concern for forest ecosystems. To date, there is great uncertainty about the direction, magnitude and sources of variation in responses to drought by insects and fungi. We report the outcomes of a meta‐analysis of 100 pairwise comparisons of insect pest or pathogen damage to water‐stressed and control trees from 40 publications. The type of feeding substrate for insects and fungi and the water stress severity emerged as the main factors influencing the level of damage in water‐stressed trees. Overall, primary damaging agents living in wood caused significantly lower damage to the water‐stressed trees compared with the control, whereas primary pests and pathogens living on foliage caused more damage to water‐stressed trees, in all cases irrespective of stress severity. In contrast, damage by secondary agents increased with stress severity, which was best estimated by the ratio between the predawn leaf water potential in stressed trees and the xylem pressure inducing 50% loss in hydraulic conductance due to cavitation, a species‐specific index of drought tolerance. Insect and fungus feeding behaviour, affected tree part, and water stress severity are therefore proposed as three important predictors of forest damage in drought conditions.     

Role of stressed mango host conditions in attraction of and colonization by the mango bark beetle Hypocryphalus mangiferae Stebbing (Coleoptera: Curculionidae: Scolytinae) and in the symptom development of quick decline of mango trees in Pakistan

The mango sudden death syndrome has become a serious threat to the mango industry and caused significant decline in mango production worldwide. The bark beetle Hypocryphalus mangiferae (Stebbing) (Coleoptera: Curculionidae: Scolytinae) has been suggested as a potential vector of the disease based primarily on field observations with little or no supporting empirical data. In this study, we investigated the role of infected mango trees in host attraction and colonization by H. mangiferae to determine if beetle attack and colonization contributes to the disease progression on mango trees. Initially, the role of various stress factors on beetle attraction and disease progression was assessed under lathe house conditions from 2008 to 2009. Results suggest that symptomatic or recently inoculated mango trees (without any obvious symptoms) are preferentially colonized by H. mangiferae. Although not significant, high numbers of beetles attacked stressed or wounded mango trees, compared to healthy or dead mango trees. Disease symptoms after beetle colonization, such as bark splitting, wilting and oozing, were further evaluated. These symptoms showed positive correlation with the degree of disease severity and host plant condition. Furthermore, two fungi, Ceratocystis fimbriata and Lasiodiplodia theobromae, were frequently isolated from the beetle and beetle-colonized trees. Based on these findings, they suggests that H. mangiferae can vector multiple fungi associated with mango sudden decline disease and play a significant role in outbreaks of this disease.     

Vertical distribution of epiphytic bryophytes in an Indonesian rainforest

We studied species richness, composition and vertical distribution of epiphytic bryophytes in submontane rainforest of Central Sulawesi. Bryophytes were sampled on eight canopy trees and on eight trees in the forest understorey. Microclimate was measured at trunk bases and at crown bases. The total recorded number of 146 epiphytic bryophyte species is among the highest ever reported for tropical forests and underlines the importance of the Malesian region as a global biodiversity hotspot. Species composition differed significantly between understorey trees and canopy tree trunks on the one hand, and the forest canopy on the other. Fourty-five percent of the bryophyte species were restricted to canopy tree crowns, 12% to the understorey. Dendroid and fan-like species mainly occurred in the forest understorey whereas tufts were most species rich in the tree crowns. The findings reflect the different microclimatic regimes and substrates found in the understorey and in the forest canopy. The results indicate that assessments of the bryophyte diversity of tropical forests are inadequate when understorey trees and tree crowns are excluded.     

Negative Feedbacks on Bark Beetle Outbreaks: Widespread and Severe Spruce Beetle Infestation Restricts Subsequent Infestation

Understanding disturbance interactions and their ecological consequences remains a major challenge for research on the response of forests to a changing climate. When, where, and how one disturbance may alter the severity, extent, or occurrence probability of a subsequent disturbance is encapsulated by the concept of linked disturbances. Here, we evaluated 1) how climate and forest habitat variables, including disturbance history, interact to drive 2000s spruce beetle (Dendroctonus rufipennis) infestation of Engelmann spruce (Picea engelmannii) across the Southern Rocky Mountains; and 2) how previous spruce beetle infestation affects subsequent infestation across the Flat Tops Wilderness in northwestern Colorado, which experienced a severe landscape-scale spruce beetle infestation in the 1940s. We hypothesized that drought and warm temperatures would promote infestation, whereas small diameter and non-host trees, which may reflect past disturbance by spruce beetles, would inhibit infestation. Across the Southern Rocky Mountains, we found that climate and forest structure interacted to drive the 2000s infestation. Within the Flat Tops study area we found that stands infested in the 1940s were composed of higher proportions of small diameter and non-host trees ca. 60 years later. In this area, the 2000s infestation was constrained by a paucity of large diameter host trees (> 23 cm at diameter breast height), not climate. This suggests that there has not been sufficient time for trees to grow large enough to become susceptible to infestation. Concordantly, we found no overlap between areas affected by the 1940s infestation and the current infestation. These results show a severe spruce beetle infestation, which results in the depletion of susceptible hosts, can create a landscape template reducing the potential for future infestations.     

昆明地区金龟虫霉的鉴定和流行

1978年在昆明温泉地区发生了金龟子的虫霉病大流行,病原菌经鉴定为金龟虫霉(Entomophthora brahmina Bose et Mehta)。本文对该菌的形态进行了观察,测定出每虫金龟(Heptophylla brevicollis Fair.)约产生休眠孢子76,800个;该菌在一块狭小的地段引起地方病,推测由于雨季的提前而使小面积的低频常在性感染向大面积流行性感染演变。     

Digital image analysis of different crown shape of Platycladus orientalis

Platycladus orientalis (L.) Franco is a beautifully crown-shaped evergreen tree species used for ornamental cultivation. These trees are also important afforestation plants at hill sites containing calcareous parent rocks and exhibit high tolerance to drought and barren sites. However, Platycladus orientalis trees with abnormal crowns, such as fusiform and torch-form, have been identified at sites with extreme drought and barren hills in Shandong, China, although the abnormal crowns does not reduce the ornamental value of these trees. In the present study, we used the RGB imaging and geographical statistical analyses through the construction of meteorological indices. The results indicate that variations of abnormal Platycladus orientalis crowns are associated with both the internal metabolism of these trees and the external environment. Crown shapes are strongly affected by the local dry, hot and windy meteorological environment, particularly individuals planted at poor hill site conditions. In response to extreme events of drought, high temperature and strong winds, the twigs and scale leaves of Platycladus orientalis typically wilt from the lower part to the upper part of the crown. The fusiform and torch-form crowns are formed through the wilting of partial twigs and scale leaves to avoid the entire wilt of the trees, thereby saving the life of the tree at the expense of partial twigs and scale leaves.