Spatial and temporal patterns at small scale in Austrocedrus chilensis diseased forests and their effect on disease progression

Austrocedrus chilensis is an endemic conifer of Patagonia that suffers a widespread mortality whose causes are a topic of discussion. Since Phytophthora austrocedrae is the most probable cause, we proposed that the spatial and temporal patterns of disease at small scale should reflect pathogen behavior. We aimed at characterizing the spatial and temporal patterns of diseased trees in different soil types and the effect of microsite variability on diseased trees spatial pattern. The spatial pattern of disease was influenced by soil type and tree density. In clay soils with low disease incidence (ca. 25%), the spatial pattern was random and not influenced by abiotic microsite conditions. When disease incidence increased (ca. 70%), concurring with denser plots, the spatial pattern was clustered, as a result of an infection process, and it was independent of microsite variability. In soils with better drainage conditions, that is, alluvial soils with volcanic ash input and coarse textured volcanic soils, the disease was clustered and associated with flat microtopographies. The progression of the disease at small scale was influenced by soil, precipitation and tree density. The spatial and temporal patterns of disease progression were associated with a contagion process and with environmental variables that affect drainage, coinciding with Phytophthora biology and requirements. Our results concur in pointing at Phytophthora as the cause of A. chilensis disease in the study area. Management practices should be urgently applied in order to minimize the spread of the inoculum.     

Modelling the management of fragmented forests: Is it possible to recover the original tree composition?: The case of the Maulino forest in Central Chile

In the fragmented Maulino forest (in Central Chile), differences in the relative frequencies of species between seedlings and mature trees are strong indicators of a changing replacement dynamics in the community. Stationary Markov chain models predict that the future tree composition such Maulino forest fragments will differ from that of continuous, intact forest. We found that the persistence probability was highest for Aristotelia chilensis and lowest for Nothofagus glauca. These two tree species are the most affected by fragmentation, and changes in their abundances appear to be the main drivers of the long-term change in stand composition. The aim of our study was to test if the management of just these two species would be sufficient to avoid long-term changes in the composition of forest fragments or would recover their composition toward a state more similar to the continuous forest. For this purpose, we constructed a Markov matrix model from published information, and calculated the future stable stand composition under different management simulations: (1) reduction of A. chilensis recruitment, (2) increased recruitment of N. glauca, and (3) a combined treatment. To evaluate the effectiveness of management treatments, the future composition of fragments was compared with the composition expected for continuous (i.e., undisturbed) Maulino forest. We performed a sensitivity analysis of the stable composition in order to assess the intensity of changes in the future composition driven by the treatments, and to determine to what extend the recruitment of other coexisting species contributes to changes in relative frequencies of A. chilensis and N. glauca.     

Stand development patterns as a consequence of the mortality in Austrocedrus chilensis forests

The forests of Austrocedrus chilensis (D. Don) Pic. Sern. et Bizarri in Argentina suffer decline and mortality throughout their natural distribution known as ‘mal del ciprés’. While several aspects of this, to date, temporally unpredictable process of overstory tree mortality have been the focus of detailed studies, there has been little research on tree growth and stand dynamics in symptomatic forests nor stand development patterns and prediction of future stand structure. We studied 12 stands in northern Patagonia (Province of Río Negro) using stand reconstruction studies to examine the changes in stand structure over time as a consequence of overstory mortality and the implications of these structural changes on the establishment and growth of the residual overstory. Dendrochronological analyses were used to reconstruct stand establishment and structure over time, and to study past diameter growth patterns. Mortality in A. chilensis forests was variable in time among stands. As expected, overstory mortality led to the successful establishment of trees in the understory in all stands; however, the response of residual overstory trees was variable. Understory establishment was low in some stands and high in others depending on the density of the overstory. While overstory trees in almost all stands released after the onset of the mortality, the pattern was not distinctive, varying in time, number and magnitude. In some stands, growth releases occurred after single or multiple tree deaths suggesting a relationship between processes, while in others this was not the case. Even when the patterns of recruitment in the understory and the overstory response varied greatly among stands, when examined together, some general patterns emerged. This study is the first to intensively explore the dynamics of A. chilensis forests affected by ‘mal del ciprés’. Additionally, this study showed that arbitrarily categorizing disturbances as discrete or chronic masks the true process of release of growing space and the resulting stand dynamics.     

沙丘不同部位中间锦鸡儿人工林土壤养分特性及植物群落特征

以青海共和盆地沙丘上12年生的中间锦鸡儿人工林为研究对象,并以流动沙丘为对照,探讨在沙丘上建立中间锦鸡儿人工林后,沙丘部位对土壤养分含量以及植物群落的影响。在中间锦鸡儿人工林内沙丘的迎风坡中部、坡顶、背风坡中部和流动沙丘采集土壤样品,深度为0 5,5 10,10 20和20 50 cm。结果表明:与流动沙丘相比,沙丘3个部位中间锦鸡儿人工林0 20 cm的有机质、0 50 cm的全氮和全磷含量得到显著提高。迎风坡中间锦鸡儿人工林0 5 cm深度的土壤有机质和全氮、0 20 cm深度的全磷含量显著高于坡顶和背风坡。在沙丘上建立中间锦鸡儿人工林后,草本植物种类、数量和植被盖度增加,迎风坡草本植物盖度明显高于坡顶和背风坡。     

Coupling of vegetation layers and environmental influences in a mature, second-growth Central Hardwood forest landscape

Forest communities across the landscape of the Central Hardwood Forest Region are experiencing a transition from dominance by oak (Quercus) and hickory (Carya) to maple (Acer) driven largely by a prolonged period of fire suppression. In many cases, this shift in community composition, structure, and function is considered undesirable as oak-hickory forests are valued for timber, wildlife habitat, and natural heritage. Considerable management and restoration efforts target the restoration of oak-hickory forest communities, yet treatments have yielded varying degrees of success. In some cases, difficulties in meeting targets may be due to ecological thresholds created by complex vegetation-environment interactions that maintain the maple-dominated community state. We examined direct and indirect interactions among vegetation layers and environmental gradients for the mature, second-growth forest communities of the Ironton Unit of the Wayne National Forest (WNF) in southeastern Ohio. Using a stratified random approach, we identified 72 study communities with trees at least 70 years old and without evidence of recent disturbance. Within these communities, we sampled all overstory vegetation on two-four 500 m² plots and recorded saplings and ground-flora species in nested sub-plots. At each plot, we also collected soil samples for physical and chemical analyses and recorded physiographic variables. Our first objective was to describe the Ironton forest landscape, where communities were likely transitioning from oak to maple. To identify such patterns, we used ordination analyses that relate species occurrence to implied environmental gradients. Our second objective was to use the relationships to develop a structural equation model (SEM) to quantify the strength of pathways among the canopy, sapling, and ground-flora vegetation layers and environmental factors (e.g., soil chemistry and physiographic position). Our results indicate that the forest landscape of the Ironton Unit of the WNF is at a transition point with communities dominated by either oak or maple, and a sapling layer dominated by maple. Maple may be most likely to replace oak and hickory in the canopies of communities at mid- and lower-slope positions with intermediate soil moisture. This transition will likely have cascading effects throughout the sapling and ground-flora layers, which SEM demonstrates are directly influenced by the canopy. We believe the simultaneous consideration of direct and indirect interactions shaping vegetation structure and composition using techniques such as SEM will advance understanding of the current transition from an oak-hickory to a maple-dominated forest landscape. This information will contribute to the continued improvement of appropriate forest management and ecosystem restoration techniques for the Central Hardwood Forest Region, including those designed to shift the dominance of forest communities from maple to oak.     

Red pine harvest debris as a potential source of inoculum of Diplodia shoot blight pathogens

A high incidence of Diplodia shoot blight (site means ranging 85-100%) was observed on recently planted red pine (Pinus resinosa) seedlings where mature red pine stands previously had been clearcut. An investigation of the potential of harvest debris as a source of inoculum of Diplodia pathogens then was conducted. Cones, bark, needles, stems from shoots bearing needles, and stems from shoots not bearing needles (both suspended above the soil and in soil contact) were collected from harvest debris left at sites where clearcutting occurred. Conidia were quantified, and their germination rate was assessed, and Diplodia species were identified using PCR. Conidia of Diplodia species were found at all study sites and conidia counts increased from samples collected from 6 to 18 months after harvest. Germinable conidia were obtained from debris collected 6 months to 5 years after harvest. Fewer conidia were obtained from debris collected at intervals of up to 4-5 years after harvest and the percentage of germinable conidia was lower after longer intervals following harvest. More conidia were obtained and a greater percentage germinated from debris collected above the soil than from debris in soil contact. The host substrate also influenced the number of conidia and the percentage that germinated. Planting red pine seedlings next to debris infested with Diplodia pathogens could provide a persistent source of inoculum. Results should prompt further consideration by land managers and researchers of the potential forest health risks, in addition to benefits, that may be associated with harvest debris.     

Soil changes induced by Acacia mangium plantation establishment: Comparison with secondary forest and Imperata cylindrica grassland soils in South Sumatra,Indonesia

Acacia plantation establishment might cause soil acidification in strongly weathered soils in the wet tropics because the base cations in the soil are translocated rapidly to plant biomass during Acacia growth. We examined whether soils under an Acacia plantation were acidified, as well as the factors causing soil acidification. We compared soils from 10 stands of 8-year-old Acacia mangium plantations with soils from 10 secondary forests and eight Imperata cylindrica grasslands, which were transformed into Acacia plantations. Soil samples were collected every 5–30 cm in depth, and pH and related soil properties were analyzed. Soil pH was significantly lower in Acacia plantations and secondary forests than in Imperata grasslands at every soil depth. The difference was about 1.0 pH unit at 0–5 cm and 0.5 pH unit at 25–30 cm. A significant positive correlation between pH and base saturation at 0–20 cm depth indicated that the low pH under forest vegetation was associated with exchangeable cation status. Using analysis of covariance (ANCOVA), with clay content as the covariate, exchangeable Ca (Ex-Ca) and Mg (Ex-Mg) stocks were significantly lower in forested areas than in Imperata grasslands at any clay content which was strongly related to exchangeable cation stock. The adjusted average Ex-Ca stock calculated by ANCOVA was 249 kg ha⁻¹ in Acacia plantations, 200 kg ha⁻¹ in secondary forests, and 756 kg ha⁻¹ in Imperata grasslands at 0–30 cm. Based on a comparison of estimated nutrient stocks in biomass and soil among the vegetation types, the translocation of base cations from soil to plant biomass might cause a decrease in exchangeable cations and soil acidification in Acacia plantations.     

Applying cost-distance analysis for forest disease risk mapping: Phytophthora austrocedrae as an example

Cost-distance model analyzes the relative difficulty in reaching each spot of the landscape for the object or species under study. It calculates the effective distance, which is the Euclidian distance modified by the friction to movement through different landscape elements. This work deals with the application of cost-distance analysis in forest pathology, considering Austrocedrus chilensis root rot caused by Phytophthora austrocedrae as an example. In this case, cost-distance analysis was used to determine the relative difficulty for the pathogen to reach healthy forest patches from the patches that are presently diseased. Friction values were assigned on the basis of abiotic conditions, biological characteristics of the pathogen and host presence. Since cattle may be a vehicle for Phytophthora dispersion, three hypothetical situations of ranching were considered. Cost-distance application resulted useful to define minimum risk areas for conservation purposes. In the study case, minimum risk area strongly varied in response to cattle presence. This study provided valuable information for A. chilensis disease management and showed one of the broad applications of cost-distance analysis in forestry.     

Wildfire promotes broadleaves and species mixture in boreal forest

Postfire tree species compositions are predicted to be the same prior to fire according to the direct regeneration hypothesis (DRH). We studied 94 upland boreal forest stands between 5 and 18 years after fire in Ontario, Canada. Postfire species-specific regeneration density was positively related to prefire stand basal area for Pinus banksiana, Populus spp., Betula papyrifera and Picea mariana, but not for Picea glauca and Abies balsamea. In addition, seedling density of Populus spp., B. papyrifera, P. mariana, P. glauca and A. balsamea were positively affected by build up index and, except Populus spp., their density increased with age of burn. To facilitate testing the DRH, we introduced a term called compositional difference (CD) that is the difference in a species relative percentage between the postfire and prefire stand. The testable null hypothesis is CD = 0 for a given species. CD was not different from 0 for P. banksiana, was 19.8% for Populus spp., 10.4% for B. papyrifera, −17.9% for P. mariana, −14.6% for P. glauca, and −14.9% for A. balsamea, indicating fire increases broadleaves at the expenses of mid- and late-successional coniferous species. Compositional increases of Populus spp. and B. papyrifera in postfire stands occurred mostly where these species were a minor component prior to fire. In conclusion, the DRH was supported by the specific positive relationships between postfire regeneration densities and prefire basal area for P. banksiana, Populus spp., B. papyrifera and P. mariana. However, if the DRH is used for predicting postfire composition, P. banksiana is the only species that had the same composition between postfire and prefire stands. Nevertheless, CD for P. banksiana was negatively related to its prefire composition. Similarly, CD for other species was negatively related to their prefire compositions with varying effects of build up index and age of burn. Our results suggest, if fire occurrences increase with global change, the boreal landscape will be more dominated by hardwoods and mixtures of conifers and hardwoods.     

Predicting productivity of trembling aspen in the Boreal Shield ecozone of Quebec using different sources of soil and site information

Site quality index (SQI) of trembling aspen (Populus tremuloides Michx) in the Boreal Shield of Quebec was predicted using two sources of information: (1) mappable permanent site variables derived from permanent sampling plots and other sources and (2) measured soil and site properties including both biological and permanent site variables. General mappable information did not produce reasonable relationships (R² < 0.25) with SQI while measured variables were able to explain much of trembling aspen SQI variability. For the two parent material types found in our study, i.e. fluvial and till, there was no difference between median SQI values between groups. However, different soil and site variables were better at predicting trembling aspen productivity for the individual parent material types. As much as 60% of the variability in trembling aspen productivity was explained when both biological and permanent site variables were considered in stepwise regression models. When treated individually, models developed for fluvial sites better explained trembling aspen productivity compared to models developed for till sites. Moreover, the ability of the model to predict trembling aspen productivity on till sites when using permanent site variables alone, e.g. soil texture, elemental chemistry and elevation was decreased (R² < 0.3). This indicates that the inclusion of biological site variables such as overstory species composition and forest floor properties provide a major contribution to SQI prediction and are necessary to yield high R². Overall, the data indicate that the traditional mapping of landscape attributes such as drainage and deposit as well as inferred soil geochemistry do not contribute much to explaining SQI. At present, field measurements are needed to predict SQI with a reasonable degree of precision within a forest management unit.     

Preliminary operational genetic management units of a highly fragmented forest tree species of southern South America

The management of the genetic resources of any wild species requires the definition of genetically homogeneous units about which practical decisions can be taken. To this end, a structure analysis was performed on the Patagonian cypress Austrocedrus chilensis (D.Don) Pic. Ser. et Bizzarri. A total of 746 seed trees corresponding to 27 natural populations sampled across its entire Argentinean range were genotyped at 12 isozyme gene markers. Genetic structure was analyzed following four successive steps: (1) proposal of different population groupings according to (a) environmental features, (b) cluster and principal coordinate analyses on genetic distances, (c) Bayesian inference utilizing BAPS program and (d) maximally differentiated groups by the software SAMOVA. (2) Evaluation of the proposed groupings with AMOVA, considering that best groupings were those with a proportion of covariance component due to inter-group differences higher than that due to intra-group differences. (3) New grouping proposition after a synthetic analysis. (4) Evaluation and characterization of the final structure proposed. Mean values of diversity parameters revealed a generally low level of allelic diversity (A/L = 1.52; A_e = 1.163; r₁₈ = 1.436), with moderate expected and observed heterozygosities (H_e = 0.143; H_o = 0.135). Differentiation at species level was low (δ = 0.048 and F_ST = 0.060). Grouping according to precipitation regimes and glacial patterns proved not to be significant. Cluster and principal coordinate analyses did not reveal any geographical pattern. A six-group structure was proposed considering AMOVA results with intuitive adjustments based on biological facts. Three out of the six groups include most of the Argentinean range of the species. Since they are latitudinal groups, a latitudinal pattern is the basis of this structure, onto which other effects seem to superimpose. The three remaining groups would be related to the glacial history of the region. One of them is composed of populations outside the glaciated area but close to the ice sheet border, which are probably related to the re-colonization process after last deglaciation. Populations forming the fifth group are extremely isolated patches far beyond the glacial border. It is possible that those populations are the remnants of a pre-glaciation distribution of the species that managed to last to the present without any profound change. The sixth one is a rather atypical single-population group, most likely determined by drift processes. Each group of this structure serves as a preliminary operational genetic management unit (OGMU). The addition of complementary genetic data on adaptive traits is necessary to delineate definitive OGMUs.     

Soil CO2 efflux in an Afromontane forest of Ethiopia as driven by seasonality and tree species

Variability of soil CO₂ efflux strongly depends on soil temperature, soil moisture and plant phenology. Separating the effects of these factors is critical to understand the belowground carbon dynamics of forest ecosystem. In Ethiopia with its unreliable seasonal rainfall, variability of soil CO₂ efflux may be particularly associated with seasonal variation. In this study, soil respiration was measured in nine plots under the canopies of three indigenous trees (Croton macrostachys, Podocarpus falcatus and Prunus africana) growing in an Afromontane forest of south-eastern Ethiopia. Our objectives were to investigate seasonal and diurnal variation in soil CO₂ flux rate as a function of soil temperature and soil moisture, and to investigate the impact of tree species composition on soil respiration. Results showed that soil respiration displayed strong seasonal patterns, being lower during dry periods and higher during wet periods. The dependence of soil respiration on soil moisture under the three tree species explained about 50% of the seasonal variability. The relation followed a Gaussian function, and indicated a decrease in soil respiration at soil volumetric water contents exceeding a threshold of about 30%. Under more moist conditions soil respiration is tentatively limited by low oxygen supply. On a diurnal basis temperature dependency was observed, but not during dry periods when plant and soil microbial activities were restrained by moisture deficiency. Tree species influenced soil respiration, and there was a significant interaction effect of tree species and soil moisture on soil CO₂ efflux variability. During wet (and cloudy) period, when shade tolerant late successional P. falcatus is having a physiological advantage, soil respiration under this tree species exceeded that under the other two species. In contrast, soil CO₂ efflux rates under light demanding pioneer C. macrostachys appeared to be least sensitive to dry (but sunny) conditions. This is probably related to the relatively higher carbon assimilation rates and associated root respiration. We conclude that besides the anticipated changes in precipitation pattern in Ethiopia any anthropogenic disturbance fostering the pioneer species may alter the future ecosystem carbon balance by its impact on soil respiration.     

坡位对灰木莲生长的影响

灰木莲(Manglietia glauca Blume)属木兰科(Magnoliaceae)常绿阔叶大乔木,树干通直,高大挺拔,材质优良,木材为散孔材,干材密度为0.611 g.cm-3,纹理细致,易加工,切面光滑美丽,干燥速度较     

Small mammal responses to forest management for oak regeneration in southern Indiana

We used a 5-decade chronosequence of harvest openings to characterize population and community-level responses of small mammals to forest management targeting oak regeneration in southern Indiana. Live-trapping at 42 different sites allowed modeling of occupancy and relative abundance using environmental covariates while incorporating imperfect detection. Species richness was higher in smaller openings on southwest-facing aspects. Similarity between species richness of different age classes decreased with increasing site age. Eastern chipmunk (Tamias striatus) relative abundance was greater in early seral stages, i.e., at young sites with low basal areas. Relative abundance of white-footed mice (Peromyscus leucopus) exhibited different responses to coarse woody debris on sites versus microsites. Pine voles (Microtus pinetorum) and short-tailed shrews (Blarina brevicauda) were more likely to occupy older sites. We observed a greater relative abundance of short-tailed shrews at sites with steep and northeast-facing slopes. Northeast-facing slopes also resulted in higher short-tailed shrew occupancy rates. Incorporating detection probability enabled us to derive more accurate estimates of relative abundance and, when coupled with a Bayesian framework, permitted the estimation of occupancy for uncommon species. Our estimated responses can be used by forest managers to determine the potential impacts of even-aged and uneven-aged oak management on small mammals, and the statistical methodology we used can be applied even more broadly to improve understanding of wildlife responses to forest management.     

Site-related influences on cone-borne inoculum and asymptomatic persistence of Diplodia shoot blight fungi on or in mature red pines

The shoot blight and canker pathogens Diplodia pinea and D. scrobiculata sporulate abundantly on cones of many pine hosts. Variation in incidence and abundance of potential inoculum from cones and frequency of asymptomatic persistence on or in shoots was examined for mature red pines in sites differing in dominant presettlement vegetation and soil type in Bayfield and Douglas counties in northern Wisconsin. Collections were made in each county from 6 plantations, 3 each in areas historically vegetated with jack pine and soils mapped as sands and three in areas historically vegetated with red pine with soils mapped as loamy sands. At each site, 5 cones were collected from each of 5 red pines and 10 shoots were collected from up to 5 red pines. Conidia from cones were quantified with a water wash and filtration technique. Diplodia species were cultured from surface-disinfested asymptomatic shoots. A species-specific PCR assay was used to identify the Diplodia species from cones and shoots. Although cones and asymptomatic shoots from each county yielded D. pinea and D. scrobiculata, D. pinea was detected more frequently. More conidia were obtained from cones from Douglas Co., where there is a history of severe shoot blight damage, than cones from Bayfield Co. In Douglas Co., more conidia were obtained from cones from plantations in areas of more sandy soil and presettlement jack pine dominance than cones from plantations in areas of less sandy soil and presettlement red pine dominance. The numbers of conidia and frequencies of cultural detection of Diplodia species from asymptomatic shoots at a site were positively correlated. These results provide evidence for site-related influences on abundance of pathogen inoculum and asymptomatic persistence on or in red pine crowns that may contribute to differences in frequency and severity of damage from Diplodia shoot blight.     

兰花炭疽病拮抗细菌5A5-3菌株的初步筛选和鉴定

从毛乌素沙地采集的10份土样中共分离到细菌320株,将分离到的细菌菌株与兰花炭疽病病原菌胶胞炭疽菌进行生长对峙试验.初筛获得拮抗菌57株.复筛后得到筛选自毛乌素沙地土壤生物结皮样品的5A5-3对病原菌具有较高的抑菌活性.对其进行形态特征观察和生理生化试验及16S rDNA序列相似性分析,结果表明:菌株5A5-3与Bacillus velezensis标准菌株(CR-502,AY603658)的16S rDNA序列相似度达100％,最终将菌株5A5-3鉴定为Bacillus velezensis.     

Stand level estimation of root respiration for two subtropical plantations based on in situ measurement of specific root respiration

In this study, the stand level root respiration was estimated for two monoculture plantations: Acacia crassicarpa and Eucalyptus urophylla, based on in situ measurement of specific root respiration using simplified root chamber method. The respiration rates of fine roots (<5 mm) were significantly higher than those of coarse roots (>5 mm) for both A. crassicarpa and E. urophylla species. The root respiration of A. crassicarpa showed a clear seasonal pattern with a higher value in the wet season. For E. urophylla, the seasonal pattern was observed for fine roots but not for coarse roots. After determining the biomass of fine roots and coarse roots and their specific rates of respiration at different time points, root respiration at the stand level (R_a) was estimated using a direct up-scaling model. We found that the R_a accounted for 14% and 19% of total soil respiration (R_s) for A. crassicarpa and E. urophylla, respectively. The fine (R_Tf) and coarse (R_Tc) root respiration at the stand level accounted for about 47% and 53% of the R_a for A. crassicarpa, and accounted for 58% and 42% for E. urophylla. This suggests that coarse root respiration cannot be ignored when estimating the root respiration at the stand level. Our results showed that the Q₁₀ values were more accurate in representing the temperature dependence when the confounding effect of soil moisture was considered. This study introduces an alternative approach to estimate stand level root respiration, but its reliability is largely dependent on the accuracy of root biomass quantification.     

Relationship of site and stand characteristics to Armillaria root disease incidence on ponderosa pine in the Black Hills,South Dakota

Ponderosa pine (Pinus ponderosa) in the Black Hills National Forest, SD, USA, was surveyed for Armillaria root disease (ARD). The root pathogen Armillaria ostoyae occurred on ponderosa pine seedlings, saplings, pole‐size trees and large‐diameter trees. The mean incidence of aboveground disease symptoms by stem count was low (0.2%), but in certain areas, the incidence was higher, affecting the regeneration success and tree longevity. Symptomatic ponderosa pine were in areas characterized by having higher elevation, greater annual precipitation, more seedlings, bigger large‐diameter trees and greater odds of past harvesting activity than in areas without root disease. Stump density was positively spatially correlated with root disease incidence. No particular soil type was related to disease occurrence; though, in areas with symptomatic trees, soil available water holding capacity (AWC) was greater and soil permeability was less where root disease was present. Spatial analysis confirmed the relationships found in linear correlations, with soil AWC and stump density positively and soil permeability negatively correlated with per cent infected stems ha^?1 and basal area infected.     

The interaction between competition in interior Douglas-fir plantations and disease caused by Armillaria ostoyae in British Columbia

Interior Douglas-fir trees in plantations were assessed for size differences related to the level of diseased neighbours infected with Armillaria ostoyae. The four Douglas-fir stands studied ranged from 25- to 34-year-old, and represented the oldest accessible planted stands in the Interior Cedar Hemlock (ICH) ecosystem in British Columbia. Twenty-three to 25, 10-m radius plots were established in each stand. The spatial coordinates, total height, and diameter at breast height of all live and dead trees in the plots were recorded. Subject trees whose competitors were contained in the 10-m radius plots were also identified. Trees were pulled out of the soil using a mechanical excavator and the root systems were surveyed for evidence of infection by A. ostoyae. Stem disks were taken from each tree at 1.3 m above the ground for a determination of basal area. Increasing proportion of diseased trees in the plots resulted in less total plot basal area, but did not affect the mean basal area or height. Individual subject tree basal area was negatively related to the level of disease in surrounding competitors, opposite to expectations; however, diseased subject trees had reduced height and basal area compared to disease-free subject trees. Increasing competition reduced both the height and basal area of the trees, while regular distribution of all trees increased both total and mean plot basal area but not height. Disease incidence at the plot level and in individual subject trees was mainly affected by the neighbourhood conditions in which it grew, and was also related to disease intensity in the tree root systems. Although disease may alter resource partitioning among trees, the utilization of these resources is mostly limited by the increasing disease incidence as the stands age, the higher probability of larger trees being diseased with time, the occurrence of dead trees in clumps, and the high probability that dead trees will eventually infect live neighbours. The widespread belowground incidence of A. ostoyae in the ICH, its rapid colonization of stumps, and its wide host range can reduce site potential in managed stands.     

不同绿僵菌菌株对筛胸梳爪叩甲幼虫的毒力测定

竹林金针虫是南方竹林笋期最为重要的害虫之一,筛胸梳爪叩甲幼虫是竹林金针虫的优势种群,应用绿僵菌防治具有重要意义。测定了3株绿僵菌对筛胸梳爪叩甲幼虫的毒力,并比较了毒土法和毒饵法两种施菌方式对绿僵菌致病力的影响。结果表明,平沙绿僵菌WP08菌株和金龟子绿僵菌30104菌株对筛胸梳爪叩甲幼虫具有明显的致病效果,在30 d的试验期内,校正累计死亡率分别为90.0%和66.3%,半数致死时间（LT₅₀）分别为15.8 d和25.8 d;毒土法的校正累计死亡率略高于毒饵法,分别为60.1%和52.0%,LT₅₀分别为22.6 d和28.0 d。金龟子绿僵菌LRC112菌株对金针虫无致病力。