Embryonal Development of Siberian Pine (Pinus sibirica Du Tour) with the Annual Cycle of Ovulate Cone Development in the Western Sayan Mountains

Morphological and cytoembryological studies of unique forms of Siberian pine (Pinus sibirica Du Tour) with the annual cycle of ovulate cone development were carried out. The morphogenesis of female shoots in these anomalous trees with the annual cycle of development was shown to provide for an accelerated development and very rapid growth of megastrobili and accelerated formation of reproductive structures. Cytoembryological studies of ovules in these trees showed significant shortening of the free-nuclear stage of gametophyte development (up to 3 weeks instead of one year) and ultra-early formation of archegonia and egg cells. However, no fertilization of egg cells and the development of embryos occur in the anomalous forms; the egg-cell nucleus divides in the haploid state. Developing seeds are formed without embryo. The author hypothesizes that the acceleration of embryo development in the anomalous pine trees is caused by enhanced hormonal, carbohydrate, and nitrogen metabolism in ovule tissues.     

Pathogenicity of Bursaphelenchus xylophilus on Pines in Minnesota and Wisconsin

The pinewood nematode, Bursaphelenchus xylophilus, was inoculated into established native jack and red pines (Pinus banksiana and P. resinosa) and exotic Austrian pine (P. nigra) in Minnesota and Wisconsin forests during summer 1981. The nematode isolates did not kill established nonstressed pine trees growing in the forest. However, the same nematode isolates killed pine seedlings under greenhouse conditions. Girdling the main stem of some trees to induce stress resulted in the death of the majority of inoculated and noninoculated branches of Austrian and jack pines, but no branch death was observed on red pine. Greater numbers of nematodes were extracted from branches of inoculated, girdled trees than from nongirdled trees. The mean number of nematodes extracted from branches of inoculated, nongirdled trees was 0.3 - 14 nematodes per gram of wood.     

不同干扰措施对松材线虫入侵松林内物种多样性的影响

经野外调查发现:松材线虫入侵松林后,对原先林型相同的两块染病松林而言,经过人为伐除和保留受害木这两种干扰措施后,任其自然恢复更新,后恢复的林型会大不相同,即对受害木采取不同的干扰措施会对染病松林内林下植被的更新产生不同的影响.基于以上出发点,以松材线虫入侵后采取不同伐除干扰措施的2个马尾松受害群落为研究对象,针对受害木移除和保留两种处理方式,选择α多样性指数函数Rényi指数为测量单位,探讨了不同受害木处理方式下植物多样性的变化规律.结果表明:受害木及时移走的松林内林下灌草多样性比受害木保留的要高.     

Occurrence of Bursaphelenchus mucronatus (Nematoda: Aphelenchoididae) and the microhabitat distribution of fungi in declining pine trees in a locale in Korea

A total of 33 pine trees with symptoms of decline were collected in Jeonnam Province, South Korea, and were examined for the presence of nematodes. About 20% of the trees sampled were positive with Bursaphelenchus species. All Bursaphelenchus species were found in recently dead or dying trees. Based on morphological observations, the nematode extracted from the declining pine trees was identified as B. mucronatus. The highly pathogenic pine wood nematode B. xylophilus was not found in any pine trees sampled. B. mucronatus was easily reared on fungus Botrytis cinerea. Twenty one fungal isolates were isolated from dead trees, fallen twigs, and healthy pine trees. The fungal isolates belonged to Trichoderma genus and were dominant in the wood of partially declining pines. The blue‐stain fungi transmitted by the Monochamus beetle were not detected. The B. mucronatus population decreased markedly on Auxarthron reticulatum DY‐2 isolated from soils. The number of nematodes also reduced on Verticillium saksenae A‐1, a nematophagous fungus, and Beauveria bassiana, an entomopathogenic fungus. This observation suggested the fungal production of nematicidal activity against B. mucronatus. When the fungal culture filtrates were also used for nematicidal activity on B. mucronatus, the culture filtrates of A‐1, DY‐2 and B. bassiana showed over 50% mortality within 48 h exposure. The fungi BC4, BC5 and BC6 isolated from declining pine trees inhibited the reproduction of B. mucronatus, and their culture filtrates also expressed nematicidal activity, indicating a possible interaction between the fungi in pine trees and nematodes at microhabitat level.     

Climate‐diameter growth relationships of black spruce and jack pine trees in boreal Ontario,Canada

To predict the long‐term effects of climate change – global warming and changes in precipitation – on the diameter (radial) growth of jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana [Mill.] B.S.P.) trees in boreal Ontario, we modified an existing diameter growth model to include climate variables. Diameter chronologies of 927 jack pine and 1173 black spruce trees, growing in the area from 47°N to 50°N and 80°W to 92°W, were used to develop diameter growth models in a nonlinear mixed‐effects approach. Our results showed that the variables long‐term average of mean growing season temperature, precipitation during wettest quarter, and total precipitation during growing season were significant (alpha = 0.05) in explaining variation in diameter growth of the sample trees. Model results indicated that higher temperatures during the growing season would increase the diameter growth of jack pine trees, but decrease that of black spruce trees. More precipitation during the wettest quarter would favor the diameter growth of both species. On the other hand, a wetter growing season, which may decrease radiation inputs, increase nutrient leaching, and reduce the decomposition rate, would reduce the diameter growth of both species. Moreover, our results indicated that future (2041–2070) diameter growth rate may differ from current (1971–2000) growth rates for both species, with conditions being more favorable for jack pine than black spruce trees. Expected future changes in the growth rate of boreal trees need to be considered in forest management decisions. We recommend that knowledge of climate–growth relationships, as represented by models, be combined with learning from adaptive management to reduce the risks and uncertainties associated with forest management decisions.     

Using the nematophagous fungus Esteya vermicola to control the disastrous pine wilt disease

The present study evaluated the protective effects of the nematophagous fungus Esteya vermicola on the large pine trees of Mt. Wora, Jinju, South Korea for six years. When pine trees were treated with E. vermicola 110 days before artificial normal pinewood nematode (PWN) infection, 30–50% of the trees survived for six years. When pine trees were treated with E. vermicola one week after artificial normal PWN infection, 40% of the trees were saved. In contrast, all of the control trees were killed by pine wilt disease in the first year. Although it has been more than six years since the beginning of this experiment, the existence of E. vermicola inside the treated pine trees was successfully detected using a PCR method with two pairs of specific primers for E. vermicola. These results suggest that E. vermicola possesses great potential as a biocontrol agent to combat the disastrous pine wilt disease. This is the first report of using nematophagous fungi to control pine wilt disease in the field for a duration of over five years.     

Postpollination drop production in hybrid larch is not related to the diurnal pattern of xylem water potential

The hourly production of postpollination drops in the ovules of three hybrid larch trees (Larix x. marschlinsii Coaz) was examined and compared with the measured diurnal pattern of xylem water potential of the same trees under non-stressed conditions during two reproductive seasons. There was no consistent relationship between xylem water potential and ovular drop production in hybrid larch. Individual trees that showed a diurnal drop production in one year did not follow a similar pattern the other year. One tree produced drops in over half of its ovules hourly, regardless of the measured xylem water potential. Variation in number of drops produced per ovule and drop mass was observed between the three trees both years, and between years for two of the trees. This variation was not in response to xylem water potential or environmental conditions. Here we report the first simultaneous measurements of branch water status and the production of ovular secretions for any conifer. We conclude that the postpollination drop production of hybrid larch is not regulated by a tree's overall water status, but is under the control of localized structures such as the cone or the ovule.     

红松阔叶林倒木贮量动态的研究

在森林倒木研究的基础上探讨长白山红松阔叶林倒木贮量的动态,涉及红松阔叶林倒木分解及其贮量的动态规律。研究表明,倒木分解,除心腐木外,均由表及里进行;倒木分解速率在其它生态条件相同时因树种、直径和部位而异。红松阔叶林倒木贮量动态包括现有倒木贮量和倒木年输入量两个分解动态过程,现有倒木贮量在头100年其干重迅速减少,其中椴树比红松尤速,前者分解91%,后者为72%.林地倒木贮量动态与倒木年输入量分解动态相似,但前者在分解初期贮量增加较大,因为部分现有倒木未完全分解;100年后趋于一致,并恒定于16～17t·hm^-2,直至群落的顶极阶段结束.     

Seasonal changes of pinosylvin distribution in the sapwood/heartwood boundary of Pinus sylvestris

Changes in pinosylvin concentration and distribution across the sapwood/heartwood boundary were studied on Scots pine (Pinus sylvestris L.) tree stems to detect seasonal activity in heartwood formation. Pinosylvin concentrations were measured with FT-(NIR) Raman spectroscopy for a total of 96 trees equally distributed on 16 different sampling occasions. In another experiment, cores were sampled every month from six individual Scots pine trees from June to October and analysed for pinosylvin. There was a great between-tree variation in concentration and spatial distribution of pinosylvin. No seasonal trend in the distribution pattern or concentration of pinosylvin was found. Therefore, the results indicate that there is no specific period during the year when heartwood is formed. Received: 12 February 1998 / Accepted: 3 May 1999     

DNA methylation during sexual embryogenesis and implications on the induction of somatic embryogenesis in Castanea sativa Miller

From anthesis to mature seed formation, burrs from cross-pollinated adult Castanea sativa Miller trees were characterized and seven developmental stages defined based on macro and micromorphological traits. In order to get an insight into the involvement of epigenetic mechanisms in sexual embryogenesis and to define somatic embryogenesis induction capability, global DNA methylation and the somatic embryogenic competence were quantified. On cross-pollinated trees once fertilization takes place, at least one ovule per ovary becomes dominant, and transient DNA demethylation occurs coinciding with the start of the sexual embryogenic programme. Unfertilized ovules from the same cluster, which maintain their prior size, increase their methylation level and undergo degeneration. These results were validated using non-cross-pollinated trees and the asynchrony of flower receptivity. When testing in vitro somatic embryogenesis response of isolated dominant ovules and axes from zygotic embryos under cross-pollinated conditions, the highest competence was found for reaching seed maturity. Thus, a “developmental window” of somatic embryogenesis in chestnut has been characterized. It includes from fertilization to embryo maturity, and a transient decrease in methylation is necessary after fertilization for the development of the somatic embryogenesis response.     

多样化松林中昆虫群落多样性特征

马尾松和湿地松是我国南方的2种主要松树。通过对6种不同林分结构下的马尾松林和湿地松林内昆虫群落调查与多样性指数分析,表明2种松树内的昆虫种类和数量无显著差异,混交林中的昆虫群落的种类和数量比纯林多,尤其以捕食天敌类群的种类和数量更为明显。整个昆虫群落和植食类群多样性指数以湿地松林内较大,而天敌(捕食类群和寄生类群)多样性指数则以马尾松林较高。从不同林分结构下昆虫多样性的比较来看,混交林内昆虫群落多样性指数波动较小,明显地高于纯林。但不同林分结构下昆虫多样性随水平分布和垂直分层格局而变化,松树北面和东面各样地之间的昆虫群落多样性指数差异显著,而南、西面之间差异较小;树冠层各样地之间的差异达极显著水平,而枯枝落叶层和树干层之间差异不显著。由此,还进一步讨论了混交林中昆虫群落稳定性问题。     

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.     

Attack dynamics of the pine shoot beetle, Tomicus piniperda (Col.; Scolytinae) in Scots pine stands defoliated by Bupalus piniaria (Lep.; Geometridae)

Abstract 1 After a 1‐year, extensive pine looper (Bupalus piniaria) outbreak, plots were laid out to study tree susceptibility to attack, and performance of Tomicus piniperda in pine trees suffering from varying levels of defoliation. 2 Tomicus piniperda was the dominating stem‐attacking species among the primary stem colonizers, and 82% of all trees that died had been colonized by T. piniperda. 3 Beetle attacks primarily struck severely defoliated trees, i.e. trees that suffered from 90% to 100% defoliation. 4 Beetle attacks peaked in the second year after cessation of the outbreak, and suppressed trees were both more frequently attacked and more susceptible to beetle attack than intermediate and dominant trees. 5 Trees surviving beetle attacks carried more foliage than trees that did not survive the attacks. 6 A single year of severe defoliation is enough to render pine trees susceptible to secondary pests, such as T. piniperda.     

Effects of green tree retention and prescribed burning on the crown damage caused by the pine shoot beetles (Tomicus spp.) in pine-dominated timber harvest areas

Abstract: We explored how two recently introduced methods to promote biodiversity during the timber harvest in boreal forests – green tree retention and use of fire – may affect damages caused by pine shoot beetles (Tomicus piniperda and Tomicus minor; Col., Scolytinae) in the surrounding pine forests. The experimental design included 24 separate study sites, 3–5 ha each, which were assigned to different treatments according to factorial design. Retention levels included 0, 10, 50 m³/ha and uncut controls. Twelve of the sites were burned and thus there were three replicates of each treatment combination. Old and new fallen pine shoots were counted from transects in adjacent pine‐dominated forests 2 and 3 years after the treatments. Populations of Tomicus spp. in the sites were monitored using window traps before and after the treatments, and by examining felled sample trees. Numbers of fallen shoots returned to background levels around unburned and burned clearcuts with no retention trees in 3 years after the treatments, but remained still at increased level in burned harvested sites with 10 and 50 m³ of retained trees per hectare. Numbers of fallen shoots in burned uncut forests increased in one site only, where the fire was intense enough to kill large pine trees, but the damage did not extend outside the burned area. Shoot numbers remained at such low levels (<18 000 shoots/ha) in all treatment combinations that growth losses were not likely. Numbers of egg galleries of Tomicus spp. in trees killed by fire were low, indicating that burnings that take place after the swarming of Tomicus beetles create dead wood that is not optimal for the breeding of these pests. We conclude that green tree retention and prescribed use of fire do not automatically affect populations of Tomicus spp. more than traditional forestry operations (thinnings and clearcuttings) do.     

Changes in diversity and storage function of ectomycorrhiza and soil organoprofile dynamics after introduction of beech into Scots pine forests

Diversity and storage function of mycorrhiza as well as soil organoprofile formation were investigated in a chronosequence of a pure Scots pine (Pinus sylvestris L.) stand, of Scots pine stands that were underplanted with beech (Fagus sylvatica L.) and in three pure beech stands of different age. Mycorrhiza diversity was higher in the pure beech stands compared to the pure pine stand. Beech and pine trees in the mixed stands had similar dominant mycorrhiza morphotypes. However, trees in two of the three pure beech stands were mycorrhized with other types. Mycorrhizal abundance and nutrient amounts of mycorrhizae associated with beech trees were higher in the mixed and in the pure beech stands compared to pine mycorrhizae indicating that nutrient uptake was higher in older beech than in older pine trees. Humus quality varied from pine to beech stands. Plant litter storage in the humus layer was highest in the youngest mixed stand and lowest in the oldest beech stand. Humus forms changed from moder grass-type in the pure Scots pine stand to mor-like moder and moder rich in fine humus with increasing age of beeches in the mixed stands. The older beech stands were characterised by oligomull and mull-like moder as the dominating humus forms. The ecologically favourable humus forms, i.e., nutrient rich humus forms in the older beech stands correlate well with the higher mycorrhizal diversity and abundance as well as the higher nutrient storage of their mycorrhizae in these stands. The results are also discussed with regard to the 'base-pump effect' of beech trees.     

Pollen tube growth and early ovule development following self- and cross-pollination in<Emphasis Type="Italic"> Eucalyptus nitens</Emphasis>

Controlled self- and cross-pollinations were conducted on flowers of five mature Eucalyptus nitens trees. Levels of self-sterility of the trees ranged from 25.8 to 93.6%. Pollen tube numbers in styles and ovule penetration by pollen tubes was investigated 2 weeks after pollination by fluorescence microscopy. There were no significant differences between treatments in the number of pollen tubes present in styles or in the percentage of ovules penetrated by pollen tubes. Embryology of material harvested 2 and 4 weeks after pollination was investigated by bright-field microscopy. Fertilisation had taken place by 2 weeks after pollination with nearly every ovule showing evidence of fertilisation. Cross-pollination resulted in a greater proportion of healthy, developing ovules, at both 2 and 4 weeks after pollination, compared with self-pollination. The proportion of degenerating ovules increased from 2 to 4 weeks after pollination. The reduced ability of E. nitens to set self-pollinated seed compared with cross-pollinated seed appears to be controlled by a post-zygotic mechanism. Differences in ovule size may potentially assist in the identification of trees incapable of setting self-pollinated seed.     

Sirex noctilio in North America: the effect of stem‐injection timing on the attractiveness and suitability of trap trees

• 1 Sirex noctilio Fabricius, an invasive woodwasp responsible for severe economic damage to pine industries in the southern hemisphere, is now established in the northeastern U.S.A. and portions of eastern Canada.
• 2 Parts of North America are considered to be high risk for S. noctilio invasion. Effective detection tools, including trap trees, are needed to monitor and survey S. noctilio populations.
• 3 The present study was conducted to determine the optimal time to chemically stress a tree when aiming to attract the most S. noctilio to the host substrate, as well as to determine which timing produced the most adult progeny. Both of these measures (host attraction and host suitability for development) support the main objectives of the study by offering improved methods for monitoring and management of S. noctilio.
• 4 Red pine (Pinus resinosa) and Scots pine (Pinus sylvestris) were treated with Dicamba at three time intervals. Multiple funnel lindgren traps were placed on these trees and, at the end of the flight season, the treatment trees were felled and brought into the laboratory. The number of S. noctilio caught in the traps (host attraction) and the number of S. noctilio emerged from the treated trees (host suitability) were determined.
• 5 Optimal timing of the chemical girdle was dependent on host species. Significantly more female S. noctilio were captured on trap trees prepared 1 month before flight (red pine and Scots pine) or prepared at flight (Scots pine) compared with other treatments. There were also significantly more females reared from Scots pine trap trees prepared at flight and red pine trap trees prepared 1 month before and/or at flight.
• 6 By the beginning of August, most (79%) of the S. noctilio for the flight season were caught in the traps at the trap trees. The sex ratio (males : females) was closer to 1 : 1 than previously reported in studies from other countries.
• 7 The results obtained in the present study demonstrate that timing is important when creating a trap tree with herbicide in North America, whether for the purpose of detection or as part of a biological control effort.

     

Bio-monitoring the genotoxicity of populations of Scots pine in the vicinity of a radioactive waste storage facility

Results of a long-term (1997-2002) study of the Scots pine populations growing in the vicinity of the radioactive waste storage facility ('Radon' LWPE) are presented. Cytogenetic disturbances in reproductive (seeds) and vegetative (needles) tissues sampled from Scots pine populations were studied to examine whether Scots pine trees have experienced environmental stress in areas with relatively low levels of pollution. The data clearly indicate the presence of mutagenic contaminants in the environment of the pine trees. An increased number of mitotic abnormalities, especially multipolar mitoses was found in the pine tree populations submitted to man-made exposure, which suggests that the cytogenetic damage is mainly caused by chemical contamination. A higher radioresistance of the Scots pine seeds from the impacted populations was shown by use of acute gamma-irradiation. During the observation period 1997-2002, pine trees exposed to anthropogenic pollution showed a steady increase of cytogenetic alterations in the root meristem cells.     

A review of factors affecting the population dynamics of jack pine budworm (Choristoneura pinus pinus Freeman)

Jack pine budworm (Choristoneura pinus pinus Free.) (Lepidoptera: Tortricidae) is a native insect that periodically defoliates areas of jack pine (Pinus banksiana Lamb.) in the subboreal forests of North America east of the Rocky Mountains. Outbreaks of jack pine budworm generally occur at 6- to 12-year intervals and collapse after 2–4 years. Periodicity of outbreaks varies and is associated with site-related factors. Survival of early-instar larvae during spring dispersal is tied to the abundance of pollen cones (microsporangiate strobili), which provide a refuge for larvae until current-year needles expand. Jack pine trees that have been heavily defoliated produce few pollen cones in the following year, often resulting in high mortality of early-stage larvae. A diverse guild of generalist parasitoids attack jack pine budworm, but only a few species account for most mortality in any area. Collapsing jack pine budworm populations are characterized by sharp declines in early instar survival, coupled with an increased rate of parasitism in the late larval and pupal stages. The reciprocal interaction between heavy defoliation and low pollen cone production, and increased parasitism of late-stage larvae or pupae, are consistent with second-order density dependence factors identified in analysis of a long-term population data set. Since the 1950s, several jack pine budworm outbreaks have been roughly synchronous over a large geographic area, suggesting that Moran effect processes, as well as moth dispersal or other factors, may be involved in jack pine budworm dynamics. Although the short duration of outbreaks enables most trees to recover, over time dead trees and top-killed trees accumulate in jack pine stands. Jack pine is well adapted to fire and when fires ignite, the accumulation of dead trees and woody debris often leads to intense wildfires followed by prolific regeneration. The three-way interaction of jack pine, jack pine budworm, and fire ultimately serves to maintain vigorous stands and ensures continued hosts for jack pine budworm. Received: October 1, 1999 / Accepted: September 22, 2000