秦岭南坡北桑寄生生态危害状况评价

为了探明北桑寄生在秦岭南坡林区的分布式样及危害状况,对陕西省宝鸡市凤县林区进行全面踏查及典型样地调查。结果表明,北桑寄生在凤县林区主要寄主为锐齿栎,在锐齿栎林中呈中心辐射状分布,多寄生于成过熟林木上,树龄在40～50年的锐齿栎被侵染的数量最大。被侵染植株总数为样地内各树种总株数的29.03%,被侵染的锐齿栎为样地内锐齿栎总数的36.90%。受害锐齿栎一级分枝平均感染率为49.53%,被寄生枝干呈明显衰退趋势,分枝末端甚至死亡。受害严重寄主生长状况较差。单丛寄生植株最大直径达160 cm,多寄生于寄主冠部偏南。寄生植株平均最大直径与寄主年龄呈线性正相关。北桑寄生目前未对凤县林区造成严重危害,但对部分寄主个体的生存造成威胁。近年来随着“天保工程”的实施,秦岭南坡锐齿栎种群密度及其种子主要传播者种群数量逐渐增加,北桑寄生的种群数量有可能随之增加,由此带来对森林的潜在危害。     

桑寄生植物在从江的主要寄主调查初报

2011年8月至2012年8月期间,通过对从江县境内桑寄生植物的主要寄主植物种类、分布及受害状况的定期、不定期调查(观察),共发现并鉴定出桑寄生的11科18属18种主要寄主植物,同时也大致摸清了其分布及受害状况。     

日本菟丝子对园林植物危害度及适应性生长的研究

通过对日本菟丝子危害范围和增加率的调查，确定偶发、常见和主要寄主园林植物，测定主要的发病率和受害度，分析日本菟丝子与主要寄主植物的相互适应性生长关系。结果表明：日本菟丝子的危害范围不断扩大，乔木、灌木和地被受害率差异显著，但均逐年增加（P<0.05）。日本菟丝子入侵28科35属的41种植物，偶发寄主为12种、常见寄主为19种、主要寄主为10种（3种乔木、2种草本和5种灌木）。主要寄主发病率和受害度在种间和年份间均有显著差异（P<0.05），不同寄主的症状和伴生病害显著不同。日本菟丝子对不同寄主植物叶片和幼茎生长及新枝形成的影响差异显著，寄主种类对日本菟丝子生长和生殖有显著影响，日本菟丝子和寄主植物有显著的适应性生长关系。     

杨干象对12种植物挥发物的电生理及行为反应

【目的】从12种植物挥发物中筛选出对杨干象成虫具有显著驱避、引诱作用的挥发性物质,并为生产制备驱避引诱剂提供依据,为有效控制杨干象种群奠定基础。【方法】利用EAG技术对12种植物挥发物质进行触角电生理反应,筛选出与对照差异显著的植物挥发物,再进行浓度梯度筛选。进而,进行Y型嗅觉仪和风洞生物测定。【结果】糠醛、苯甲酸、丁香酚、橙花醇、香茅醇、香柏油6种植物挥发物在1mol·L-1浓度下均能引起雌雄成虫较强的EAG反应(P0.05);行为反应测试表明:Y型嗅觉仪生测中1mol·L-1寄主植物挥发物糠醛对杨干象雌虫有明显引诱作用(P0.01),引诱率达71.59%;1mol·L-1非寄主植物挥发物橙花醇对杨干象雌虫具有较强的驱避作用(P0.01),驱避率高达81.5%。风洞生测中1mol·L-1寄主植物挥发物苯甲酸对杨干象雌虫具有明显驱避作用,驱避率达74.68%。1 mol·L-1非寄主植物挥发物香柏油对杨干象雄虫具有驱避作用(P0.01),驱避率达78.75%。【结论】在所选择的挥发物中,非寄主植物挥发物对杨干象成虫的行为影响略高于寄主植物;杨干象雌虫较雄虫对植物源挥发物更敏感;Y型嗅觉仪和风洞生测都获得了比较理想的试验结果。     

马尾松毛虫寄生天敌与寄主数量关系的研究

1987～1988年,对湖南省洞口县马尾松毛虫种群密度及天敌寄生情况进行调查,发现寄生性天敌昆虫27种,重寄生者14种。据此,构造了松毛虫—寄生者系统食物网及营养级数量金字塔,对系统的稳定性进行初步分析表明,各代松毛虫的寄生天敌种类和寄生率均存在着差异。寄生率以第2代为最高;害虫种群变动趋势与天敌种类有关;寄生数量与寄主密度成正比;赤眼蜂、平腹小蜂的寄生率与卵块密度呈微弱负相关或无关,卵总寄生率与卵块密度呈轻微负相关,幼虫和蛹的寄生率与寄主密度无关。     

幼虫取食不同寄主树种的云斑白条天牛成虫种群分化

【目的】基于幼虫取食不同寄主树种云斑白条天牛的成虫补充营养行为、形态特征及遗传特性的比较,探讨不同寄主对成虫行为的影响及其机制。【方法】比较幼虫取食毛白杨和美国红木岑2种寄主树种的云斑白条天牛成虫外形特征及雄性生殖器结构差异,利用选择性取食试验,观测这2类云斑白条天牛成虫对美国红木岑、野蔷薇、美国山核桃、日本珊瑚树及毛白杨5种寄主植物嫩枝的取食行为及交配行为,最后基于COI基因分析二者间遗传多样性差异及系统发育关系。【结果】1)幼虫取食美国红木岑的云斑白条天牛和幼虫取食毛白杨的云斑白条天牛外部特征存在明显差异。幼虫取食美国红木岑的云斑白条天牛雄虫腹部末端窄,呈钝角内凹状,毛稀疏,雌虫腹部末端呈弧形内凹,底部中央缺刻不明显,而幼虫取食毛白杨的云斑白条天牛雄虫腹部末端宽,呈弧形内凹状,密被毛,雌虫腹部末端呈平截状,底部中央具有明显缺刻;两者生殖器差异不明显; 2)幼虫取食美国红木岑的云斑白条天牛成虫仅取食美国红木岑嫩枝,而幼虫取食毛白杨的云斑白条天牛可取食野蔷薇、美国山核桃和日本珊瑚树3种植物嫩枝,偏好顺序为野蔷薇美国山核桃日本珊瑚树; 3) 2个种群的天牛雌、雄成虫之间可相互交配,平均交配次数较同类群间存在差异但不显著(P0.05); 4) 2个不同寄主源的天牛种群存在明显遗传分化,分化指数Fst=0.814(P0.001),变异分化主要来源于种群间(83.19%)。【结论】幼虫的取食经历(取食不同寄主植物)和生境异质性可能对云斑白条天牛成虫补充营养行为及种群遗传分化产生显著影响。     

铜鼓岭热带常绿季雨矮林5种蒲桃属植物的种群结构及空间格局

【目的】分析海南岛文昌市铜鼓岭自然保护区5种蒲桃属植物的种群结构、分布格局及种间关联性,以期了解该地区蒲桃属植物种群的现状、分布状况及发展动态,为该属植物的保护工作提供依据。【方法】在热带常绿季雨矮林建立2.56 hm2固定样地,采用种群结构和空间格局常用的种群径级结构分析、种群静态生命表和绘制种群存活曲线研究方法,结合点格局分析中的Ripley’s K函数和SPSS软件,对5种蒲桃属植物种群的空间格局、种间关联性以及种群聚集规模与种群优势度的关系进行研究。【结果】种群死亡率随龄级的增加而增大,生命期望值ex与此趋势相反,但方枝蒲桃、赤楠和肖蒲桃3个种群中的ex值会出现明显的小波动,说明这3个种群内部经历了密度调节过程,使种群密度达到适合个体生长的最佳状态;方枝蒲桃种群具有最多的个体数目(1 950株),并集中于幼苗和幼树,表明该种群更新良好,存活曲线随着龄级增大逐渐趋于Deevey-Ⅱ型,说明种群将长期保持稳定的种群死亡率并更新繁衍下去;其他4个种群的总个体数相差不大(假赤楠374株、赤楠390株、子凌蒲桃393株、肖蒲桃282株),尽管它们的存活曲线最终都趋于Deevey-Ⅰ型,但存在差异,假赤楠的幼苗、幼树数量较少(共82株),虽然其更新木一般都可以生长到生理寿命(Deevey-Ⅰ型),但过少的数量也可能会影响种群的正常繁衍,其他3个种群都具有一定规模的幼苗和幼树,种群更新能力上虽不及方枝蒲桃,但在群落中也具有相当大的生存潜力;总体上,5个种群的空间分布都符合种群普遍格局分布规律,即由小尺度的聚集分布到大尺度上的随机乃至于均匀分布,但假赤楠、子凌蒲桃和肖蒲桃在某些尺度范围内出现了规则分布,说明在这些尺度上可能存在其他种群带来的竞争压力;5个种群的聚集规模和聚集范围都随着种群优势度的降低而减小,其中,种群的聚集规模与优势度呈显著线性相关,二者的回归方程为y=58.531x-132.33(R2=0.958,P=0.004<0.01),肖蒲桃与假赤楠和赤楠在一些尺度上负相关,其他4个种群在任何尺度上均可以共存。【结论】生长在热带常绿季雨矮林中的蒲桃属植物发育良好,都具有一定的更新能力,但假赤楠种群不仅更新幼苗较少,而且在较大尺度上还存在其他种群(如肖蒲桃)对其的竞争压力,所以在天然次生林各种群的科学管控过程中应加以适当侧重保护。     

松材线虫病取样技术简介

松材线虫病(Buraphelenchus sylopilus)又称松材线虫萎蔫病,是松材线虫寄生在松树体内所引起的一种毁灭性流行病。该病危害的毁灭性在于:病原适生范围广,致病力强,寄主死亡速度快;寄主植物种类多,病害传播蔓延迅速,常常猝不及防;危害严重,防治难度大,被称作松树的“癌症”,为国     

海南省油茶及其他寄主植物果生刺盘孢菌群体遗传结构分析

【目的】研究海南省油茶树及其他寄主植物炭疽病菌果生刺盘孢菌群体遗传结构、群体遗传多样性及单倍型地理分布,探索海南地区不同寄主植物炭疽病菌的分子遗传变异规律。【方法】利用单孢分离法对采集自海南省南圣镇、通什镇、枫木林场和澄迈林场4个地区9种不同寄主植物的炭疽病病叶进行炭疽菌分离,并对每个菌株ITS,CAL和GAPDH 3个基因进行PCR扩增和测序,按顺序对3个基因的序列进行拼接,然后采用Gen ALEx6,Dna SP 5.0,TCS1.21和MEGA6.0软件分别对数据进行分析。【结果】分离、鉴定共获得12个病菌种群的108个果生刺盘孢菌病菌样品,可推导出18种单倍体型(haplotype),其中单倍型Haplotype11共70个菌株,为优势单倍型,在每个病菌种群中均有分布;单倍型网络结构分析表明,病原菌以单倍型Haplotype11为辐射中心,呈现出1个比较典型星状发散图,推测Haplotype11为原始单倍型;108株病菌表现出丰富的遗传多样性;AMOVA分析显示,种群间和种群内的遗传变异分别占总变异的3%和97%,变异主要存在种群内,而种群间的差异小,说明不同的寄主植物未对病菌交流造成隔离障碍;遗传分化和基因流分析发现,12个病菌种群间遗传分化小,种群间基因交流频繁;另外,油茶种群之间以及油茶与鲫鱼胆、葛根和山矾等植物种群之间的果生刺盘孢菌存在遗传重组现象;系统发育分析表明,来自同一个果生刺盘孢菌种群的单倍型未能聚在一起,而是散乱的分布在系统树中,没有显示出明显的寄主植物分布族群;核苷酸不配对分析表明病菌种群历史上并没有发生显著的种群扩张。【结论】海南省果生刺盘孢菌遗传多样性丰富,不同地区和不同寄主植物病菌种群之间存在有效基因流,揭示该病菌可以在油茶树及其他寄主植物之间迁移,这为整体考虑海南省油茶及其他寄主植物制定可持续控制油茶炭疽病策略提供重要的理论依据。     

转抗虫基因107杨对主要节肢动物种群的影响

为研究转基因杨对主要节肢动物种群的影响,对转基因杨生态安全性及进一步推广与应用提供理论依据,以转基因107杨为研究对象,采用随机取样的调查方法,于2019年对转基因107杨树林与未转基因杨树林(对照)内主要节肢种群数量、种类以及动态进行研究。结果表明:调查所获得的节肢动物个体分属于昆虫纲和蛛形纲,共14 299头,分属2纲,11目,105种。主要靶标害虫美国白蛾、杨扇舟蛾、杨银潜叶蛾个体数量显著低于对照组(P0.05),杨小舟蛾个体数量少于对照组,但差异不显著(P0.05),各株系间主要靶标害虫个体数量不存在显著性差异,#2株系个体数量相对较少,表明转基因107杨可有效抑制靶标害虫种群发展;主要非靶标害虫叶蝉sp.、皱大球蚧、大青叶蝉个体数量与对照无明显差异(P0.05),白杨毛蚜个体数量低于对照(P0.05),各株系间叶蝉sp.个体数量存在一定差异,#3株系个体数量显著低于#1、#9株系(P0.05),各株系间皱大球蚧、白杨毛蚜、大青叶蝉个体数量差异不显著(P0.05);转基因107杨对主要天敌及中性昆虫未造成显著不利影响,部分株系异色瓢虫、狼蛛sp.、跳蛛sp.与家蝇个体数量相对于对照表现为一定程度的增多;主要节肢动物种群发生高峰期集中在5-6月、8-9月,杨白潜叶蛾、白杨毛蚜发生高峰期分别在7月与10月。     

Impact of mistletoes (Amyema miquelii) on host (Eucalyptus blakelyi and Eucalyptus melliodora) survival and growth in temperate Australia

The damaging effects of mistletoes Amyema spp. on host eucalypts in rural Australia concern many landholders, but few data are available to evaluate mistletoe impacts or formulate management strategies. We used an experimental disinfection approach to determine the effects of a putative pest mistletoe, Amyema miquelii, on its two principal hosts, Blakely's red gum (Eucalyptus blakelyi) and yellow box (Eucalyptus melliodora), on pastoral properties in northern New South Wales. For each host species, pairs of nearby trees were matched for heigth, diameter at breast height, level of mistletoe infestation and distance to neighbouring trees. One tree per pair was chosen at random and all the mistletoes pruned. After 33 months all treated trees were still alive, but among control trees seven of 29 red gums and one of 20 yellow box trees had died. The difference in survival between treated and control trees was significant for red gum. Among surviving pairs of trees, treated trees of both species had significantly greater diameter increments and significantly more foliage than untreated trees. After 33 months, the average increase in relative host foliage biomass attributable to removal of mistletoes was 22% in red gum and 24% in yellow box, compared with untreated controls. The average increase in radial growth attributable to mistletoe removal was 55% in red gum and 49% in yellow box. Diameter increment was negatively and linearly related to mistletoe infestation level in control trees of both species. The differences between infected and disinfected trees in this experiment may underestimate the impact of Amyema miquelii on host growth because small amounts of host biomass were unavoidably lost during disinfection. In a separate experiment, loss of host biomass had a significant negative impact on diameter increment. Although the results indicate that control of serious Amyema miquelii infestation of individual trees will be worthwhile in terms of immediate host survival and higher growth rate, prudent long-term management may well allow for the loss of small numbers of farm trees to mistletoes when planning tree recruitment and utilisation.     

Proximate and mineral components of Viscum album var. coloratum grown on eight different host tree species

Mistletoes are parasite plants growing on various tree species,taking nutrients from the host.Beneficial compounds of mistletoe were used in medicine and these mistletoes were commonly collected from oak species that were not well identified.We analyzed the nutritional value by measuring proximate and mineral components of Korean mistletoe(Viscum album var.coloratum)from various host trees.Carbohydrate was the most proximate component in both leaves and twigs followed crude protein,crude fiber,crude ash and crude fat.While the contents of the proximate components and minerals varied among hosts and between plant parts,leaves contained higher crude protein and ash,and more minerals except for magnesium than twigs,although no significant difference was found inmistletoe grown on Prunus mandshurica.There were significant differences of proximate and mineral contents depending on the host species.Mistletoe grown on Chaenomeles sinensis contained higher levels of carbohydrates,crude fat,crude ash,magnesium,calcium,sodium,iron,and zinc than mistletoe grown on other species.Mistletoe grown on P.mandshurica contained high mineral levels of potassium,copper and phosphorous.The nutritional value of mistletoes were greatly influenced by the host species but among the hosts,specific nutrients accumulated in leaves more than in twigs,and vice versa.Based on the analysis,Korean mistletoe contains relatively good quality of nutrients and has high potential for dietary supplements as well as for medicinal compounds.     

Growth characteristics and reproductive output of dwarf mistletoe-infected Juniperus polycarpos in Iran

Dwarf mistletoes are parasitic flowering plants that infect conifers, resulting in substantial loss of growth and mortality. Recently, forest managers in Iran are contemplating whether infection of Juniperus polycarpos C. Koch forests by dwarf mistletoe, Arceuthobium oxycedri （DC.） M. Bieb, influences tree vigor and contributes to insuffieient natural regeneration. The present study aimed at assessing the severity of infection and its impact on growth and reproductive output of./., polycar- pos. Infected and uninfected trees （n =20 each） were selected for assess- ment of diameter, height, crown area, and crown volume as well as quantity and quality of cones and seeds. The severity of infection of trees was determined by Hawksworth＇s 6-class dwarf mistletoe rating （DMR） system. The DMR system revealed that 40% of the infected sample trees were lightly infected （DMR =1-2） and 60% were moderately infected （DMR =3--4）. Growth characteristics did not differ significantly （p 〉 0.05） between infected and uninfected trees. However, moderate infec- tion affected the reproductive output of./. polycarpos by significantly （p 〈0.05） reducing the mean number of cones per unit area of the crown, increasing the number of damaged seeds, and reducing seed size and seedgermination capacity. We conclude that reproductive output of J.. poly- carpos is more sensitive than growth characters to moderate infection by juniper dwarf mistletoe, and this might partly account for poor natural regeneration.     

Contrasting arthropod communities associated with dwarf mistletoes Arceuthobium globosum and A. vaginatum and their host Pinus hartwegii

Arthropod communities and epiphytic plants associated with tree canopies have been widely studied and have revealed a great diversity of organisms; however,the community hosted by parasitic plants,such as dwarf mistletoes,remains poorly known.In the coniferous forests of North America,dwarf mistletoe infection(Arceuthobium spp.) significantly damages the health of the forest,causing large financial losses for the forest industry,but it also positively affects diversity,especially of mammals and birds.This study examined the attributes of the arthropod communities associated with two species of dwarf mistletoe [Arceuthobium globosum Hawksw. Wiens and A.vaginatum(Humb. Bonpl.ex Willd.) J.Presl] and their host Pinus hartwegii Lindl.In 2010,in five sites located in Zoquiapan(Central Mexico),we collected plant tissue from the three species bimonthly.Arthropods were separated from the plant tissue and identified to the finest level possible.We collected 32,059 individuals,for which51 morphospecies were identified,belonging to 15 taxonomic orders; the most abundant orders for the three plants were Prostigmata,Thysanoptera and Homoptera.The community associated with P.hartwegii had the highest value of diversity(H'= 1.47; A.globosum,H'= 0.64; A.vaginatum,H'= 0.68) and species richness(S = 40; A.globosum,S = 30; A.vaginatum,S = 35); while abundance was significantly higher for the mistletoes(A.globosum,n = 407 individuals/sample; A.vaginatum,n = 536 individuals/sample; P.hartwegii,n = 134 individuals/sample).Species richness,abundance and diversity were significantly different for the three studied plants,as well for sampling month and the interaction of these two factors(except for diversity).The results suggest that the canopy of P.hartwegii is an important element in the ecosystem,providing a mosaic of resources and conditions to the associated fauna.We also propose that mistletoes are key species within the forest canopy,as they greatly influence the establishment of diverse organisms,particularly arthropods.     

Incidence,severity, and aggregation patterns of two sympatric dwarf mistletoe species (Arceuthobium spp.) in Central Mexico

Dwarf mistletoes are widely studied because of their significant impact on host populations; however, few studies have focused on sympatric species. The understanding of their coexistence is important because it can provide useful knowledge for future management plans. We investigated the incidence, severity, and aggregation patterns of Arceuthobium vaginatum and A. globosum coexisting in Central Mexico. We estimated the correlation between both species incidences (N = 75 plots), the incidence–severity correlation (N = 47 plots) for each species, and the effect of biotic (host and non-host species abundance) and abiotic (altitude and slope) factors on the mistletoe incidence. In addition, we compared the hierarchical aggregation among and within plots of the two mistletoe species with a χ ² test. There is a clear dominance of A. vaginatum in the area, and both species incidences are negatively correlated with each other (r _s = ? 0.54, P < 0.05) and host abundance (r = ? 0.26, P < 0.05). The remaining factors were non-significant. Both species have a linear relationship between incidence and severity, i.e., they show a uniform increase in severity with incidence, which could help diagnose the degree of tree infection from incidence measurements. The species are aggregated within plots, but only A. globosum shows an aggregation among plots (χ ² = 82.25, P < 0.001); aggregation has not been shown previously for two sympatric dwarf mistletoe species. Our results can improve the scientific basis for forest management planning to control dwarf mistletoe and maintain biodiversity.     

The influence of prescribed crown fire on lodgepole pine dwarf mistletoe (Arceuthobium americanum) populations 33 years post‐fire

Dwarf mistletoes (Arceuthobium spp.) are a group of obligate, hemiparasitic plants that infect numerous species in the Pinaceae in North America. Wildland fire is considered to be the primary natural agent influencing the population and distribution of dwarf mistletoes across landscapes. Based on this understanding, prescribed fire has been suggested as a potential method for dwarf mistletoe sanitation and control; however, experimental work has primarily focused on prescribed surface fire. In this study, we report long‐term impacts of three experimental crown fires on dwarf mistletoe severity in infested lodgepole pine stands in Colorado 33 years post‐fire. The three fires achieved tree mortality rates ranging from 20% to 100%. Our results suggested a significant negative relationship between the amount of fire‐caused tree mortality and future dwarf mistletoe severity. These findings supported the presumed natural role of fire in altering dwarf mistletoe populations, which perhaps exhibits a linear relationship between fire‐caused host tree mortality and future dwarf mistletoe severity.     

Spatial and seasonal variation in amino compounds in the xylem sap of a mistletoe (Viscum album) and its hosts (Populus spp. and Abies alba)

In a field study, the composition and concentrations of amino compounds in the xylem sap of the mistletoe, Viscum album L., and in the xylem sap of two host species, an evergreen conifer (Abies alba Mill.) and a deciduous broad-leaved tree (Populus x euramericana), were analyzed. The xylem sap of both hosts and mistletoe contained large, but similar amounts of total organic nitrogen in low molecular weight amino compounds (TONLW). Nevertheless, individual amino compounds accumulated in the xylem sap of mistletoe relative to the host xylem sap, indicating selective uptake. In the xylem sap of Populus, major amino compounds (asparagine (Asn) and glutamine (Gln)) and the bulk parameters, TONLW and proteinogenic amino acids, showed significant seasonal variation. In Abies and in mistletoe on either host, variation of amino compounds in xylem sap was largely explained by inter-annual differences, not by seasonal variation. In both hosts, TONLW in the xylem sap was dominated by Gln. There was a steady decrease in relative abundance of Gln from the host xylem sap to the mistletoe xylem sap and to the stems and leaves of mistletoe. Simultaneously, the abundance of arginine (Arg) increased. Arginine was the predominant amino compound in the stems and leaves of mistletoe, occurring at concentrations previously observed only in leaves of trees exposed to excess nitrogen. We conclude that Gln (2 mol N mol(-1)) delivered by the host xylem sap is converted, in mistletoe, to Arg (4 mol N mol(-1)) and that the organic carbon liberated from Gln contributes significantly to the parasite's heterotrophic carbon gain. Statistical analyses of the data support this conclusion. Accumulation of Arg in mistletoe is an indication of excess N supply as a result of the uptake of amino compounds from the host xylem sap and a lack of phloem uploading.     

Mortality and growth of dwarf mistletoe‐infected red and white fir and the efficacy of thinning for reducing associated losses

In managed forests dominated by true fir (Abies) species, stands are often restocked using understory trees retained during timber harvest, making the effects of dwarf mistletoe (Arceuthobium spp.) infestation on small true fir a concern. This study examined the response of small red (A. magnifica) and white (A. concolor) fir and their dwarf mistletoes (A. abietinum f.sp. magnificae and A. abietinum f.sp. concoloris, respectively) to precommercial thinning treatments in fir‐dominated stands in the Sierra Nevada Mountains of California. Tree diameters and dwarf mistletoe ratings were monitored from 1981 to 2001, and mortality was observed from 1981 to 2006. Red and white fir survival and radial growth decreased significantly with greater mistletoe ratings and increased with larger diameters and live crown ratios. Thinning significantly increased survival and growth of white, but not red fir. Over the course of the study, mistletoe ratings for both fir species did not change significantly in unthinned stands, but increased in thinned stands. However, while statistically significant, increases in mistletoe ratings in thinned stands were gradual and mistletoe ratings did not statistically differ between treatments 20 years post‐thinning. Additionally, thinning did not significantly influence mistletoe spread to uninfected trees, indicating that precommercial thinning in lightly infested red and white fir stands will not likely result in substantial increases in dwarf mistletoe abundance over typical harvesting intervals. Overall, while severe dwarf mistletoe infection ratings reduced tree survival and growth, because ratings remained low, actual losses resulting from mistletoes during this study were minor and will not likely result in substantial economic losses over normal harvesting intervals. This finding indicates that precommercial thinning treatments designed specifically to compensate for mistletoe‐associated losses may not be necessary when managing red and white fir for timber production.     

‘华宁大砂壳核桃’不同树形冠层特性与其产量的相关性研究

【目的】探索适宜的‘华宁大砂壳核桃’高产树形,从而为该品种核桃高产树形的培养和整形修剪提供参考依据和技术指导。【方法】以10年生‘华宁大砂壳核桃’树为研究对象,利用HemiView数字植物冠层分析仪测定其冠层特性参数,对比研究了该品种主干分层形、开心形和自然圆头形3种树形的树体结构、冠层特性参数和单株产量的差异性,还分析了其冠层特性与单株产量间的相关性。【结果】主干分层形的总透光比为0.207,显著低于其他两种树形(P<0.05);主干分层形的叶面积指数为1.574,显著高于其他两种树形的(P<0.05);3种树形的综合光立地系数、直射光立地系数和散射光立地系数的大小顺序均为开心形>自然圆头形>主干分层形,且开心形树形的直射光立地系数和散射光立地系数与其他两种树形间均存在显著差异(P<0.05);主干分层形树冠层截获的总辐射能相比于开心形和自然圆头形的分别增加了9.9%和9.2%,其直射辐射能分别增加了10.2%和9.7%;单株平均产量,主干分层形的为110.90 kg,显著高于其他两种树形的(P<0.05)。相关性分析结果表明:冠层总透光比、散射光立地系数与单株产量均呈显著负相关(P<0.01);叶面积指数、冠层截获的总辐射能和单株产量均呈显著正相关(P<0.01),冠层截获的直接辐射能与单株产量呈显著正相关(P<0.05)。【结论】从单株产量来看,该地区大砂壳核桃的3种整形修剪树形中,主干分层形要高于自然圆头形和开心形树形。     

Factors influencing the dispersion of Arceuthobium oxycedri in Central Spain: evaluation with a new null model for marked point patterns

The dwarf mistletoe, Arceuthobium oxycedri, is found on populations of Juniperus oxycedrus, in central Spain. This species can have negative effects on the physiology of its host, including mortality. Understanding the mechanisms that control its distribution and dispersal is critical to assessing its potential for spread. We assessed dwarf mistletoe distribution within a population of J. oxycedrus, including infected and uninfected host individuals. A new null model of parasitic dispersion was built using two dispersal kernel forms that were simulated with lower and upper envelopes for second‐order functions to summarize a point pattern, such as Ripley's K, nearest‐neighbour distribution and pair correlation functions. Nine dispersal scenarios were constructed with half‐bandwidth kernels (10, 20, 30 m) and initial population of infected trees (P₀ = 05, 10 and 20). These scenarios were compared with the observed pattern and evaluated using the goodness‐of‐fit test. Significant differences at short distance (r < 10 m) were found between the observed pattern and simulated patterns, corresponding to the range of seed dispersal of the dwarf mistletoe. Interactions between infected and uninfected hosts patterns at all scales were identified, suggesting that A. oxycedri uses other mechanisms in addition to ballistic seed shooting as secondary dispersal agents to spread to distances greater than 20 m. Given that the seed characteristics facilitate dispersal by adhesion, we infer that spread between host individuals is amplified by seed transport by birds or small mammals.