Genetic structure of the green oak leaf roller (Tortrix viridana L.) and one of its hosts, Quercus robur L.

An herbivorous insect, the green oak leaf roller (Tortrix viridana) and one of its host species, pedunculate oak (Quercus robur), were investigated for their genetic variation within and among populations on the basis of mitochondrial, chloroplast, and anonymous markers. Oaks and green oak leaf rollers from 10 oak stands in North Rhine-Westphalia (North-Western Germany) were examined. The genetic variation of pedunculate oaks is much lower within than among populations when assessed using chloroplast gene markers and higher among populations when assessed using anonymous markers. When using mitochondrial and AFLP markers, the genetic variation of the green oak leaf roller populations was higher within than among the populations, which suggests a high gene flow between the populations. Mantel tests on the gene diversities of oaks and the green oak leaf roller yielded a significant negative correlation for both marker types. To sum up, the reasons for the differences in the spatial patterns of the genetic variation of the host and herbivorous insect may be found in their different generation times, mechanisms and capacities for dispersal.The results for the green oak leaf roller revealed a higher migration rate than assumed before which has consequences for the prediction of the dynamics of future outbreak events.     

Impacts of burial and insect infection on germination and seedling growth of acorns of Quercus variabilis

Rodents usually exert important role, through their scatter seed hoarding behavior, on plant regeneration in the field. To investigate the effects of burial and insects infection on germination and seedling growth of acorns of Quercus variabilis, perfect and infected acorns were buried in the soil among four depths, 0 cm, 4 cm, 8 cm and 12 cm, to simulate the seed hoarding behavior by rodents in the field. The results showed that (1) the germination rate were both high, under 4 cm burial depth, for perfect and infected acorns (92% and 53% separately), and decreased significantly with increased burial depth; (2) perfect acorns germinated better in 4 cm burial depth group by autumn of first year; (3) there 32% (perfect) and 26% (infected) acorns with 0 cm burial depth, on the soil surface, germinated successfully; for infected acorns, the 4 cm depth group had the best germination or seedling recruitment in both the first year and the second year; (4) acorns of Q. variabilis exhibited dormancy period ca 7 months; (5) burial, infection, and the interaction between these two factors influenced several aspects including stem height, leaf weight, Tannic acid, and biomass within seedling growth; (6) the results from this study suggest that proper burial would be helpful for the germination and seedling growth, and seedlings of shallow buried acorns had an advantage in their early development; and (7) infection by insects will not inevitably influence seedling early development.     

Pedunculate oak (Quercus robur L.) silviculture in natural stands of NW Spain: Environmental conditioners

Forest management is often carried out in different ways, without any appropriate environmental restrictions. Stands of pedunculate oak (Quercus robur L.) in Galicia (NW Spain) have been harvested by alternating high forest and, mainly, coppice forest. However, some totally inappropriate silvicultural treatments have been used, such as thinning of the best trees and inadequate pruning. The objective of the present study was to analyse how environmental characteristics affect the management of oak forests in Galicia. For this, a botanical inventory was carried out in 39 selected stands of Q. robur and a total of 42 parameters were measured, 4 of which were physiographical, 12 climatic, 19 edaphic and 7 silvicultural. In order to analyse the possible relationships among these variables, the silvicultural data were compared with the other data, by canonical correlation analysis. All parameters were correlated with the silvicultural regime, although the correlation was weak for the floristic data. It is therefore evident that the environmental conditions affect how forest stands should be managed, although this does not imply that more profitable use of the stands cannot be achieved than at present, and alternative silvicultural methods must be found to enable appropriate management and conservation of oak stands.     

Modelling jay (Garrulus glandarius) abundance and distribution for oak regeneration assessment in Mediterranean landscapes

Because natural regeneration of oak is strongly dependent on jay abundance and distribution, we need to understand the determinants of jay abundance and occurrence as a first step to assess oak regeneration. In this paper we modelled the jay population distribution and abundance in a Mediterranean landscape mosaic of the eastern Iberian Peninsula (Valencia, east Spain). The methodology was based on assessing landscape attributes (habitat composition and configuration variables) on seven 9-km² sites and registering jay fledgling locations. Using a stepwise regression model we determined the variables that best explained the jay density. The probability of occurrence of jay nests within each site was assessed by comparing the landscape attributes of jay and non-jay areas within each site. Results were validated by predicting each site on the basis of data from the remaining six sites and then calculating the deviation between the predicted and the observed values in the field. The results suggest that jay density correlates positively with forest cover and landscape heterogeneity variables, and negatively with shrubland cover. Validation of the results showed that the model is reasonably effective in predicting both jay abundance and distribution at the extent and resolution used.     

Effects of treeshelters and polyethylene mulch sheets on survival and growth of cork oak (Quercus suber L.) seedlings planted in northwestern Tunisia

Success of plantation establishment depends on the ability of seedlings to withstand animal browsing and competition from vegetation. This study in northwestern Tunisia examined the influence of browsing protection and vegetation control on seedling mortality, diameter, and height growth components of an evergreen sclerophyllous oak species, cork oak (Quercus suber L.) for the first 2 years after planting (2005 and 2006). Browsing protection was controlled by varying both treeshelter type (non-vented, vented, and control) and height (1.2-m and 1.8-m tall). Competing vegetation was controlled through increasing sizes of square-shaped black polyethylene mulch sheets: 0 m, 0.7 m, 1 m and 1.3 m large. Seedling mortality rate was relatively low during the first year (9%) and was not affected by any of the studied factors. During the following year, mortality was lower for seedlings in both types (non-vented and vented) of 1.2-m tall treeshelters than for unsheltered ones. Mortality was only slightly higher for 1.8-m tall shelters than for 1.2-m shelters. Compared to unsheltered seedlings, basal diameter was reduced during both seasons for seedlings inside non-vented treeshelters (1.2-m and 1.8-m tall), whereas for vented shelters it was reduced during the first year and then increased during the second year. Height growth was positively affected by tree shelters during both years. Seedlings inside non-vented 1.8-m tall shelters were the tallest having an average height of up to 140 cm at the end of the second year, while the unsheltered seedlings had only an average height of up to 42 cm. The greater height of the sheltered seedlings was attributed to the increase of: (1) the number of shoot flushes yearly established on the main stem (up to three), and (2) the length of all the growth units produced during each flush. Seedlings inside vented shelters had balanced growth with a low proportion of seedlings unable to support themselves without a stake (7%). However, non-vented shelters had unbalanced height and diameter growths resulting in both a higher height-to-diameter ratio and in a higher proportion of seedlings having stability problems (47%). Polyethylene mulch sheets did not affect early survival, seedling basal diameter, or number of shoot flushes established yearly, but did slightly improve seedling height at the end of the second season, mostly due to the significant improvement in shoot elongation of the first flush. Results suggest that both 1.8 m treeshelters and plastic mulches may enhance the growth of cork oak seedlings planted on harsh sites in northwestern Tunisia.     

Understorey plant community characteristics and natural hardwood regeneration under three partial harvest treatments applied in a northern red oak (Quercus rubra L.) stand in the Great Lakes-St. Lawrence forest region of Canada

Throughout eastern North America, stands of northern red oak (Quercus rubra L.) are undergoing successional replacement by shade-tolerant competitors. In the Great Lakes-St. Lawrence (GLSL) forest region, Q. rubra approaches the northern limit of its distribution, and ecosystem-specific silvicultural directives are needed to promote regeneration. We used an inductive, ordination-based approach to explore patterns in understorey plant community composition and microenvironment under different partial harvest treatments applied in a GLSL hardwood stand, and related these to characteristics of natural seedlings of Q. rubra and its competitors Acer rubrum and Acer saccharum.Two years after harvest, we established 2 m × 2 m plots in a stratified random design under 70% (n = 20) and 50% (n = 19) crown closure uniform shelterwood, group selection (n = 15), and uncut upper slope (n = 10) and lower slope (n = 10) areas. Percent cover of understorey vascular plant species, and a suite of microclimatic and edaphic variables were measured in each plot. Density, mean diameter and mean height of seedlings in the understorey (height <1 m) were determined in each plot for Q. rubra, A. rubrum and A. saccharum.Correspondence analysis (CA) ordination extracted two major axes explaining 21.6% of the total inertia in the species cover by plot matrix. Axis one separated uncut plots from the 50% shelterwood along a gradient of canopy cover associated with partial harvest treatments. Plot scores on axis one (13.2%) reflected a shift in dominance of the understorey from shade-tolerant Acer spp. to shade-intolerant colonizers, Rubus idaeus and Carex spp. Plot scores on axis one were directly (p < 0.05) associated with total understorey plant cover, litter depth, soil temperature and pH, but not with measures of plant diversity. Axis two (8.4%) separated plots from upper slope and lower slope areas, and plot scores were inversely associated (p < 0.05) with soil pH, phosphorus and nitrogen levels. Along axis two there was a shift in dominance from competitive (e.g. A. saccharum) to stress-tolerant (e.g. A. rubrum) species as soil fertility declined. Stepwise linear regression indicated seedling diameter in Q. rubra, A. rubrum and A. saccharum was inversely related to canopy cover. This suggests all three species benefited from partial harvest, although the relationship was strongest in Q. rubra. Patterns in understorey composition, microenvironment and seedling characteristics provide the basis to identify the main competitors of Q. rubra seedlings and adjust regeneration efforts along gradients of canopy closure and soil fertility under partial harvest systems within the GLSL forest region.     

Gene flow pattern and mating system in a small population of Quercus semiserrata Roxb. (Fagaceae)

Pollen flow from external sources is important for the conservation of tree species in fragmented forests or small populations, because it can be sufficient to prevent differentiation among them, and appears to be able to prevent the loss of their genetic diversity through genetic drift. In this study, we examined the genetic heterogeneity of pollen pools accepted by each Quercus semiserrata seed parent at the Khun Wang Royal Agriculture Research Center, Thailand, both within and among two mast fruiting years (2005 and 2007), using paternity analysis and analysis of molecular variance (AMOVA). The mating systems of the trees were also examined using the multilocus mating system model (MLTR), after determining the genotypes at eight microsatellite loci of 26 seed-trees and 435 seeds from 8 seed-trees in the 2 mast fruiting years. The average distance of effective pollen flow within the plot was estimated to be 52.4 m, and 95% of effective pollen was dispersed within 200 m, indicating that effective pollen flow is highly localized and that most effective pollen is contributed by near-neighbor trees. The proportion of effective pollen that immigrated from external sources was estimated to be 26.2%. The AMOVA analysis based on the pollen haplotypes showed that the pollen pools, both total and for each reproductive year, significantly genetically differed among the seed parents. Using a mixed mating model, the estimate of biparental inbreeding for the total population (t_m − t_s) was 0.013, indicating that a low proportion of mating occurred among close relatives. The effective number of pollen donors (N_ep) was estimated to be 9.987 using the TwoGener model, or 10.989 using the mixed mating model. The effective number of pollen donors of seeds was higher in the mast fruiting year 2005 than in the other examined year, 2007. Consequently the allelic richness and genetic diversity of seeds produced in 2005 were higher than those produced in 2007. Overall, the results show that high outcrossing rates, high levels of gene flow from other populations and heterogeneity in the pollen received by an individual may enhance the ability of populations to maintain effective population sizes. Therefore, these processes may be sufficient to prevent loss of genetic diversity through genetic drift of Q. semiserrata at this study site.     

6个栓皮栎种源种子形态及其幼苗生长的比较

[Objective]To compare the differences of seed morphological characters among provinces of Quercus variabilis Bl.,and explore the adaptive growth status of seedlings growing in the central distribution area. [Method]The seeds of 6 Q. variabilis provenances from six provinceswerecollected, and the seedlings were cultivated and transplanted to experimental field in the centre of natural distribution range (Wuhan Jiufeng National Forest Park), then the seed morphology and one-year seedling growth traitswere surveyed. [Result](1)There were significantor extremely significantdifferences among provenances in seed length, seed width, seed length/width ratio and 100-seed mass, the order of seed length among provenances was Beijing Provenance (22.28 mm),Hubei Provenance (22.10 mm), He'nan Provenance (20.80 mm), Shaanxi Provenance (19.57 mm), Yunnan Provenance (18.93 mm)and Liaoning Provenance (18.81 mm), the seed width of Beijing Provenance (19.71 mm) and Hubei Provenance (19.16 mm) was higher than that of the others, the seed length/width ratio of He'nan Provenance (1.38) was extremely significantly higher than that of the others; (2)There were significant or extremely significant differences among provenances in seedling height, ground diameter, leaf number, branching number and seedling height/ground diameter, the Beijing Provenance and Hubei Provenance were better in seedling height and leaf number, which were respectively 19.54 cm and 20.26 cm, 8.32 leaves and 9.50 leaves; (3)A decreasing trend with time for seedling growth traits among provenances was found; (4)There was a positive relationship between seed morphological characters and seedling growth traits except seed length/width ratio; the leaf number was significantly related to ground diameter and branching number and the seedling height and leaf number were closely related to the seed morphological characters; (5)It showed a decreasing trend with the growth time in the relationship between seedling growth traits and 100-seed mass. [Conclusion]The seedlings of Beijing Provenance and Hubei Provenance grew better in the experimental field which might be related to their larger seed mass, and the Yunnan Provenance in the south margin and the Liaoning Provenance in the north margin of distribution area of Q. variabilis grew weaker than the provenances in the centre of distribution area.With the effect of climate change, provenances in the margin of distribution area may lose in the community competition in the seedling stage if it cannot take advantage of its dispersal and settlement and affected by the disadvantage of growth and competition, so that the distribution and population renewal would surely be affected.     

五道峡自然保护区锐齿槲栎群落物种组成与群落特征研究

锐齿槲栎是广泛分布于我国暖温带和亚热带山地中海拔地段的主要优势种,以五道峡国家级自然保护区内的锐齿槲栎群落为研究对象,通过种群年龄结构及数量动态变化,生活型谱及生长模型方面的研究,分析五道峡国家级自然保护区锐齿槲栎群落特征。结果表明,锐齿槲栎龄级结构中,个体数量在Ⅲ~Ⅵ龄级占比最大,种群中低龄个体数量充足;种群数量动态指数显示锐齿槲栎种群呈现增长趋势,但种群稳定性差且抗干扰能力较弱;生活型谱分析发现,占比最高的属于高位芽植物,且呈随海拔升高占比逐渐降低的趋势,植物生活型谱大致呈现“L”型;生长模型的研究表明,三次函数模型的决定系数R2达到最大值,且经过T检验,表明三次函数模型可以很好地用来拟合锐齿槲栎胸径—树高的关系。建议在原地保护的基础上进行科学的管理,并充分调动群众的积极性,为种群营造稳定的生存环境,促进种群的长期发展。     

遮荫对弗吉尼亚栎苗木生长及光合-荧光参数的影响

[目的]揭示美国引进树种弗吉尼亚栎幼苗对光照强度的响应特征,为弗吉尼亚栎的引种驯化和高效栽培提供科学依据。[方法]采用人工遮荫法,研究3种光环境下(全光——100%自然光、中度遮荫——50%自然光和强度遮荫——25%自然光)弗吉尼亚栎苗木生长、光合作用以及叶绿素荧光参数的变化。[结果]表明:中度遮荫明显促进弗吉尼亚栎苗高生长(P0.05),但对地径生长影响不明显;而强度遮荫条件下,地径生长受到明显抑制(P0.05),苗高虽有所下降,但与对照相比差异不明显。对弗吉尼亚栎光响应曲线的观测表明:与全光条件相比,中度遮荫条件下,弗吉尼亚栎叶片暗呼吸速率(Rd)、光饱和点(LSP)以及光补偿点(LCP)均明显下降(P0.05),说明适度的遮荫有助于提高弗吉尼亚栎对光的利用效率,促进干物质的积累;而强度遮荫条件下,光补偿点和光饱和点明显上升,暗呼吸速率明显增加(P0.05)。遮荫并未对表观量子效率(α)和最大净光合速率(P_(max))产生明显的影响。进一步对叶绿素荧光参数分析发现,遮荫条件下,PSⅡ最大光化学量子产量(F_v/F_m)和实际光量子产量(Yield)有所增加,但均在正常范围,说明遮荫对PSⅡ活性并未产生胁迫。[结论]弗吉尼亚栎幼苗对遮荫均具有一定的耐受性,中度遮荫有利于苗高生长;而强度遮荫不利于干物质的积累。因此,建议在营林以及人工栽培过程中维持50%以上的自然光照。     

Pine weevil (Hylobius abietis) damage to cuttings and seedlings of Norway spruce

Damage caused by pine weevil (Hylobius abietus L.) to planted seedlings and cuttings of Norway spruce (Picea abies (L.) Karst.) was studied at five clearcut sites in south-eastern Sweden. The main objective was to compare the two types of stock in terms of attack frequency and mortality due to pine weevil feeding. Cuttings and seedlings with the same initial stem-base diameter (4 mm) were compared. Two sites were harvested and scarified shortly before planting, two were harvested shortly before planting, but were not scarified, and one was harvested 2 years before and scarified the autumn before planting. The total mortality 5 years after planting was highest, greater than 90%, at the new, non-scarified sites, and lowest, 23%, at the old, scarified site. More than 90% of the mortality was caused by pine weevil feeding. Attack frequency and pine weevil induced mortality were significantly higher among seedlings than among cuttings. Mortality due to pine weevil damage was 4–43% higher in seedlings than in cuttings after the fifth year. Of the cuttings and seedlings that were attacked in the first year, a significantly higher frequency of the seedlings were girdled. The higher resistance of cuttings to pine weevil damage may partly explain the more rapid growth of cuttings reported in other studies. However, the causes of their higher resistance need to be further investigated. The thicker bark and needles on the stem base of the cuttings could be important in this respect.     

A spatial distribution model of cork oak (Quercus suber) in southwestern Spain: A suitable tool for reforestation

Cork oak (Quercus suber) is an evergreen tree characterized by a thick bark, which grows in Mediterranean schlerophyllous forests. It is most prevalent in the southwestern Iberian Peninsula. Despite the potential of the province of Huelva (southwestern Spain) to maintain mature forests of cork oak, the tree has been severely depleted and most forests have either disappeared or are seriously threatened. This paper presents a spatial distribution model of cork oak for the province of Huelva with a view to determining the optimal areas for reforestation. The model draws on all available digital cartographic information with respect to cork oak distribution: topographic data (altitude, slope and orientation) were obtained from a Digital Terrain Model (20 m scale); rainfall, temperature and PET models were based on data collected from a network of meteorological stations; litologic data derive from the litologic map of Huelva (1:100,000). The result of this work is a mesh of points at a resolution of 100 m, sufficient to meet the needs of any kind of reforestation or management programmes in the area studied. Each point of this mesh contains the corresponding values for bioclimatic, topographic and litologic variables in a georeferenced data matrix. The independent variables responsible for cork oak distribution (binary dependent variables) were then identified by means of binary logistic regression analysis. North-facing slopes, abundant annual rainfall and litology were the main explaining variables. The spatial distribution model was produced by applying the formula obtained to spatial analysis software. This model is proposed as a basis for future reforestation plans, especially in those areas most affected by forest fires.     

松材线虫(Bursaphelenchus xylophilus)耐久型幼虫(LIV)携带的香茅醇假单胞杆菌(Pseudomonas citronellolis)分离与鉴定

[目的]目前有关松材线虫与伴生细菌的关系及伴生细菌的病原作用是松树枯萎病研究的重点。为了揭示松材线虫与伴生细菌之间存在的密切关系,作者对松材线虫L_IV幼虫携带的细菌进行了分离鉴定。[方法]根据培养性状和16S rDNA序列同源性以及系统发育学等方面进行分析鉴定。[结果]确定L_IV幼虫携带的是香茅醇假单胞杆菌（Pseudomonas citronellolis）,携带率为100%;每条L_IV幼虫携带量在1.4×10⁵~4.5×10⁵。L_IV幼虫生活在松褐天牛体内,是引起松材线虫病侵染流行的唯一虫态;新发现的香茅醇假单胞杆菌能分解纤维素及降解或合成萜烯和酚类化合物。[结论]L_IV幼虫携带香茅醇假单胞杆菌的发现,揭示了松树、松褐天牛、松材线虫、细菌同为一体的紧密关系,并为揭示松树枯萎病机制提供了一种新病原和重要的研究思路。     

卵巢线虫(Contortylenchus genitalicola)在中国松褐天牛上的分布与作用研究

[目的]日本学者Kosaka与Ogura发现松褐天牛成虫除携带松材线虫外,雌成虫卵巢内还携带有另一种线虫,他们将其命名为卵巢线虫,并认为这种线虫是松褐天牛成虫的寄生性线虫。我国对该种线虫的研究迄今未见报道。为了证明这种线虫在我国是否存在和分布,开展了本项研究。[方法]分期分批捕获刚羽化的松褐天牛雌雄成虫,采用解剖松褐天牛成虫松树木质部及感病的松褐天牛幼虫等方法,调查卵巢线虫的存在与分布。[结果]通过调查研究,发现我国的松褐天牛成虫体内有该卵巢线虫存在,分布于松褐天牛成虫、幼虫体内和松树木质部3个部位;在松褐天牛成虫体内的卵巢线虫通过松褐天牛雌成虫产卵而接种、进入寄主树木木质部中。同时,木质部的卵巢线虫也有一部分进入松褐天牛幼虫体内寄生,另一部分仍在木质部生活,当松褐天牛幼虫再次发育为成虫时,在木质部中的卵巢线虫和已被寄生的松褐天牛幼虫体内的卵巢线虫再次进入松褐天牛成虫体内,完成循环。卵巢线虫在松褐天牛雌、雄虫体内均有分布,携带率为44.4%,其中松褐天牛雌成虫携带率为43.8%,松褐天牛雄成虫携带率为45.0%,两者间无显著差异;每头松褐天牛成虫平均携带卵巢线虫574条,其中雌成虫平均携带816条,雄成虫平均携带308条,具显著差异。初步研究表明,卵巢线虫在松褐天牛成虫体内只能完成产卵到1~4龄的幼虫阶段,不能完成一个完整的世代;在松褐天牛幼虫体内寄生和在木质部生活的卵巢线虫能完成一个完整世代,但具体过程尚不清楚;调查中未观察到卵巢线虫对松褐天牛成虫有寄生致病或致死的现象,但对松褐天牛幼虫有寄生致死的能力;卵巢线虫常与松材线虫同时存在,而且侵入松树及离开松树的方式与松材线虫相同。[结论]我国松褐天牛体内也发现有卵巢线虫存在;目前尚不能证明该线虫对松褐天牛成虫具有寄生致死性,但对松褐天牛幼虫具有一定的寄生致死性;卵巢线虫的生活史与松材线虫相似,是否与松材线虫一样对松树具有危害性以及其病理作用还有待于进一步研究。     

Effect of management on the spatial spread of mountain pine beetle (Dendroctonus ponderosae) in Banff National Park

To evaluate control measures, the spread of mountain pine beetles, Dendroctonus ponderosae, in management and monitoring regions in Banff National Park was analyzed for years 1997 to 2004. The Park allowed mountain pine beetles to follow their natural course in a monitoring zone (74,041 ha), whereas in a management zone (45,997 ha) an extensive eradication program was established in 2001 which included baiting mountain pine beetles and cutting and burning all colonized trees. We used data collected from an annual aerial survey and the geo-referenced location of trees that were cut and removed to assess if the area colonized and the spatial extent of mountain pine beetles differed between the two zones. After 4 years, the control measures did not significantly affect the area colonized by mountain pine beetles, and in 2004 mountain pine beetles were still expanding in both zones, although at a slow rate (1.23 ha per year). The spatial extent and the rate at which 500 m × 500 m cells (25 ha) were colonized were much reduced in the management zone. Thus, the management program appeared to have reduced the success of long distance movement as measured by colonizing new 25 ha cells, but short distance dispersal remained successful as indicated by the continued increase in area colonized. The effectiveness of control measures was probably limited by the number of colonized trees that were missed and by survival rates determined by other untested factors.     

In vitro antileishmanial, antiplasmodial and cytotoxic activities of phenolics and triterpenoids from Baccharis dracunculifolia D. C. (Asteraceae)

Baccharis dracunculifolia (Asteraceae), the most important plant source of the Brazilian green propolis (GPE), displayed in vitro activity against Leishmania donovani, with an IC₅₀ value of 45 µg/mL, while GPE presented an IC₅₀ value of 49 µg/mL. Among the isolated compounds of B. dracunculifolia, ursolic acid, and hautriwaic acid lactone showed IC₅₀ values of 3.7 µg/mL and 7.0 µg/mL, respectively. Uvaol, acacetin, and ermanin displayed moderate antileishmanial activity. Regarding the antiplasmodial assay against Plasmodium falciparum, BdE and GPE gave similar IC₅₀ values (about 20 µg/mL), while Hautriwaic acid lactone led to an IC₅₀ value of 0.8 µg/mL (D6 clone).     

寄主树木、寄主和环境因子对松褐天牛深沟茧蜂寄生率的影响研究

[目的]松材线虫病是我国对森林危害和威胁最严重的病害,控制其传播媒介昆虫松褐天牛是防治松材线虫病的主要手段。作者发现的松褐天牛深沟茧蜂(Iphiaulax monochamusi Yang)是寄生松褐天牛中老龄幼虫的重要天敌。为明确松褐天牛深沟茧蜂的寄生率与寄主树木、寄主和环境因子的关系,开展了本研究。[方法]通过解剖46株松褐天牛危害致死的马尾松,调查了松褐天牛深沟茧蜂寄生率与马尾松、松褐天牛和环境因子之间的关系。[结果]调查研究表明:寄主树木的高度、胸径和树龄对松褐天牛深沟茧蜂寄生率没有显著影响,松褐天牛的数量对松褐天牛深沟茧蜂寄生率亦没有显著影响,而松褐天牛幼虫龄期和松褐天牛幼虫在树干上的位置显著影响松褐天牛深沟茧蜂寄生率。松褐天牛深沟茧蜂寄生率与松褐天牛龄期呈显著正相关,其偏好寄生3~5龄幼虫;就天牛在其危害寄主树木上的位置而言,松褐天牛深沟茧蜂偏好寄生马尾松主干上部和在韧皮部危害的松褐天牛幼虫,其对位于马尾松树干上部的寄主幼虫寄生率最高,达27.38%,对在韧皮部生活、危害的寄主幼虫寄生率为20.18%,显著高于位于木质部生活的寄主幼虫寄生率(5.46%)。逐步回归分析表明:影响松褐天牛深沟茧蜂寄生率的关键环境因子是寄主树木的坡位和其它天敌寄生率,其中,坡位与松褐天牛深沟茧蜂呈显著正相关,其它天敌寄生率与松褐天牛深沟茧蜂寄生率呈显著负相关。[结论]以上研究初步明确了松褐天牛深沟茧蜂的寄生率与寄主树木、寄主害虫和天敌之间的关系,为今后利用该重要天敌控制松褐天牛打下了基础。     

Nutrient cycling and soil leaching in eighteen pure and mixed stands of beech (Fagus sylvatica) and spruce (Picea abies)

Studies on the combined effects of beech–spruce mixtures are very rare. Hence, forest nutrition (soil, foliage) and nutrient fluxes via throughfall and soil solution were measured in adjacent stands of pure spruce, mixed spruce–beech and pure beech on three nutrient rich sites (Flysch) and three nutrient poor sites (Molasse) over a 2-year period. At low deposition rates (highest throughfall fluxes: 17 kg N ha⁻¹ year⁻¹ and 5 kg S ha⁻¹ year⁻¹) there was hardly any linkage between nutrient inputs and outputs. Element outputs were rather driven by internal N (mineralization, nitrification) and S (net mineralization of organic S compounds, desorption of historically deposited S) sources. Nitrate and sulfate seepage losses of spruce–beech mixtures were higher than expected from the corresponding single-species stands due to an unfavorable combination of spruce-similar soil solution concentrations coupled with beech-similar water fluxes on Flysch, while most processes on Molasse showed linear responses. Our data show that nutrient leaching through the soil is not simply a “wash through” but is mediated by a complex set of reactions within the plant–soil system.     

Enrichment of logging gaps with moabi (Baillonella toxisperma Pierre) in a Central African rain forest

Studies of regeneration in African rain forests suggest that without silvicultural treatments, natural succession in logging gaps may not result in the establishment of timber species. In this paper we present the results of an experimental enrichment planting with moabi (Baillonella toxisperma Pierre), a valuable and important timber species harvested in Central Africa. Although forest gaps are generally considered as favourable for the regeneration of this species, a survey conducted in a forest concession in south-eastern Cameroon provided an estimate of only 12.7 seedlings ha⁻¹, suggesting that the species was, in fact, poorly represented in logging gaps within the study area. To further investigate the dynamics of the moabi in logging gaps, 795 seeds were sown in 15 logging gaps and 410 nursery-raised seedlings were planted in 15 other gaps. A biannual monitoring program over a 30-month period showed a lower survival rate for seedlings from sowing (75.9%) compared to that of nursery-raised seedlings (95.3%). Planted seedlings reached an average of 229.3 cm tall whereas seedlings from sowing were 167.5 cm tall, with the observed difference roughly corresponding to the average height of the nursery-raised seedlings at the time they were introduced to the logging gaps. After 30 months, the diameters of planted seedlings (16.8 mm) were also greater than those of the directly sown individuals (12.5 mm). Forest gap characteristics significantly influenced the growth of the plants. Factors accounting for the differences were total solar radiation, the soil content of coarse sand, the topographic position of the gap, the vegetation cover and the density of Macaranga spp. Whilst total solar radiation had a positive influence on growth, the remaining factors had impacted growth negatively. A streamlined technique was tested by planting 7 seedlings in 250 gaps. Without additional site maintenance, 29.3% of the moabi seedlings emerged naturally from the competing vegetation after 24 months. With biannual maintenance some 89.4% of seedlings became successfully established. Clearance operations had no significant influence on the height of plants whilst plant diameter was greater in cleared gaps. The total cost of the enrichment technique was 5.5 EUR per gap without maintenance and 7.5 EUR per gap with a single maintenance measure. Whilst long-term monitoring is needed, this study suggests a high survival rate of moabi introduced in logging gaps, and a growth rate 10 times higher than previously reported under canopy cover. These findings, combined with the low costs of the enrichment technique, support the use of silvicultural measures in logging gaps to restore the forest.     

桑天牛成虫生活习性的进一步研究

桑天牛成虫昼夜活动分为白天取食和晚上繁殖两个阶段。１头雌虫一生可产卵２３～２３４粒,平均１３０．３粒;平均每天１．６粒。经过交配的雌虫不再交配后,在１３～１４４ｄ内仍能产生授精卵,每头９～１７６粒,平均８９．７粒。成虫在构树上喜欢栖息于西北方向的枝条上取食,其数量占总数的４９．４％,高度在１．１～２．０ｍ的占总数的７５．４％。