Ecology of Armillaria species on conifers in Japan

Distribution, host preference and pathogenicity of Japanese Armillaria species on conifers were investigated on the basis of field collections of 65 isolates. We identified seven Armillaria species from 19 conifer species including six major Japanese plantation conifers using mating tests and sequences of the translation elongation‐1 α gene. Armillaria mellea, Armillaria ostoyae, Armillaria cepistipes and Armillaria sinapina were frequently collected, whereas Armillaria nabsnona, Armillaria tabescens and a biological species Nagasawa’s E were rare. On the basis of host condition when the isolates were collected, A. mellea, A. ostoyae, A. cepistipes and A. tabescens are considered as moderate to aggressive pathogens of conifers in Japan.     

Effects of some ecological variables on carabid communities in native and non native forests in the Ibaizabal basin (Basque Country: Spain)

? Carabid beetles were investigated at five different forest types in the Ibaizabal basin (northern Spain). The landscape is characterized by the presence of remnants of native forest surrounded by conifer plantations.

? Carabids were trapped in 52 stands of mixed forest, beech forest, holm oak forest, mixed pine and Monterey pine plantations in 2005 and 2006. The main objectives of the study were: compare carabid diversity, recognise the characteristic species, and study the effects of ecological variables on carabid assemblages in the different forest types.

? No significative differences in species abundance, richness and diversity were found among the studied forests. Most of the trapped beetles were identified as forest generalists, nevertheless some native and non-native forest specialist species were also found. Distribution of carabid communities overlapped and, except for beech forest, no specific communities were distinguished. Altitude, percentage of grass coverage and temperature were the main variables influencing species distribution.

? The results suggest high habitat homogeneity, caused by regeneration in pine plantations of the indigenous understorey, and by poor habitat quality in native forest (patchy remnants enclosed in conifer plantations). This situation could explain the similar carabid diversity.

     

Diversity of woody plant seedling banks under closed canopy in fragmented coppice forests

? Seedling banks of woody species established under closed canopy have received little consideration in coppice forests despite their potential importance for natural regeneration.

? This study aimed to evaluate the influences of canopy composition and of distance from the nearest forest edge on the abundance and species richness of the seedling bank, for different ecological groups of seedlings (age, successional status and dispersal vector) in 68 fragmented coppice stands.

? Seedlings were found in 67 stands, with 19 species identified. Eight species present as older seedlings were lacking as first-year old seedlings, suggesting temporal variability of species recruitment. Seedling abundances of species with low-dispersal ability were positively correlated with the abundances of their conspecific adults. Seedling abundance of mid-successional species was negatively correlated with the distance from the nearest forest edge, while mid-to-late successional species seedling abundance presented the opposite pattern.

? Our results showed that woody species were able to establish frequently under closed canopy in these fragmented coppices and form a seedling bank which may be used for natural regeneration.

     

Productivity of temperate broad-leaved forest stands differing in tree species diversity

? Understanding the effects of tree species diversity on biomass and production of forests is fundamental for carbon sequestration strategies, particularly in the perspective of the current climate change. However, the diversity-productivity relationship in old-growth forests is not well understood.

? We quantified biomass and above-ground production in nine forest stands with increasing tree species diversity from monocultures of beech to stands consisting of up to five deciduous tree species (Fagus sylvatica, Fraxinus excelsior, Tilia spp., Carpinus betulus, Acer spp.) to examine (a) if mixed stands are more productive than monospecific stands, (b) how tree species differ in the productivity of stem wood, leaves and fruits, and (c) if beech productivity increases with tree diversity due to lower intraspecific competition and complementary resource use.

? Total above-ground biomass and wood production decreased with increasing tree species diversity. In Fagus and Fraxinus, the basal area-related wood productivity exceeded those of the co-occurring tree species, while Tilia had the highest leaf productivity. Fagus trees showed no elevated production per basal area in the mixed stands.

? We found no evidence of complementary resource use associated with biomass production. We conclude that above-ground productivity of old-growth temperate deciduous forests depend more on tree species-specific traits than on tree diversity itself.

     

Comparing volume growth in pure and mixed stands of Pinus sylvestris and Quercus pyrenaica

? In Mediterranean forestry, it is important to improve knowledge about mixed stands dynamics, including their productivity. Previous studies have focused on the interactions between different species (competition, reduction of competition and facilitation) depending on site, species composition and structure.

? At the centre of this research are the possible differences between pure and mixed stands of Pinus sylvestris and Quercus pyrenaica in terms of density-growth relationships and volume growth per species.

? Using data from the second and third Spanish National Forest Inventory (606 plots), volume increment models for these species were fitted. Both species displayed a similar density-growth pattern for pure and mixed stands, with a maximum volume growth at maximum density. Volume increment per occupied area was also found to be greater in mixed stands as opposed to pure stands, suggesting a species interaction with reduced levels of competition in the former. However, the total volume growth was generally lower in mixed stands since the growth rate of oak is much lower.

? The results highlight the expedience of favouring P. sylvestris-Q. pyrenaica mixed stands with higher proportions of pine trees in order to gain the benefits of a more complex forest whilst retaining an acceptable level of wood production.

     

Species variables or environmental variables as indicators of forest biodiversity: a case study using saproxylic beetles in Maritime pine plantations

? To assess the sustainability of plantation forest management we compare two types of biodiversity indicators. We used the species richness of saproxylic beetles as a case study to test the “species” and “environmental” indicator approaches. We compared single species abundance or occurrence and deadwood volume or diversity as predictor variables.

? Beetles were sampled with flight interception traps in 40 Maritime pine plantation stands. The volume and diversity of deadwood was estimated with line intersect and plot sampling in the same stands. Predictive models of species richness were built with simple linear or Partial Least Square regressions.

? Deadwood variables appeared to be good predictors of saproxylic beetle richness at the stand-scale with at least 75% of variance explained. Deadwood diversity variables consistently provided better predictive models than volume variables. The best environmental indicator was the diversity of deadwood elements larger than 15 cm in diameter.

? By contrast, the use of “species variables” appeared to be less relevant. To reach the quality of prediction obtained with “environmental variables”, the abundance or occurrence of 6 to 7 species — some of which are difficult to identify — had to be used to build the indicator.

     

Root elongation in tropical Eucalyptus plantations: effect of soil water content

? Sustainability of Eucalyptus plantations is often questioned in resource-limited environments, especially in areas characterized by soils with poor nutrient and water holding capacities. Yet, field-based observations of fine root dynamics in relation with the seasonality of rainfall are lacking.

? This study was undertaken on two Eucalyptus stands planted in the Kouilou Region (south-western Congo), which is characterized by a four-month-long dry season. Fine root (less than 2 mm in diameter) dynamics were studied using rhizotron observations of root elongation in the field.

? Fine root elongation rates displayed a seasonal variation in the two stands, with higher elongation rates during the rainy season than during the dry season. Positive and significant correlations were found between fine root elongation rates and soil water content at all depths, but a better correlation was found with soil water content in the deep soil horizon than in the superficial horizons.

? These results suggest that the temporal variations in fine root elongation were related to the seasonality of rainfall, and they were probably associated with seasonal changes in tree water status, carbon assimilation and belowground allocation.

     

Forest liming durably impact the communities of ectomycorrhizas and fungal epigeous fruiting bodies

? Liming is a forestry practice used to counteract forest decline in acidic soils. It consists of direct Ca and Mg input to forest soil, which restores tree mineral nutrition, but also modifies microbial communities in soil. The aim of this study was to assess the effects of liming on both belowground (ectomycorrhizal root tips) and aboveground (epigeous sporocarps) fungal communities.

? Results showed that the modification of soil chemical properties (pH, and Ca-Mg contents versus total free Al and Fe concentrations) was a stronger factor of ECM community structuring than tree host. The species appearing in limed plots were ubiquist or known as good competitors and replaced acidophilic and stress species.

? At the sporocarp level, tree host was a stronger factor of community structuring than soil chemical properties associated with liming. On the whole, there was a shift in the community composition from a typical acidophilic forest fungal community of medium altitude in the untreated plots to a less typical one, with the reduced dominance of acidophilic fungi while many late-stage forest species appeared.

? We finally suggest a marker species (Russula ochroleuca) to assess both above and belowground effects of liming on ectomycorrhizal communities.

     

Which factors most influence heartwood distribution and radial growth in plantation teak?

? To investigate the effect of climate on radial growth in young plantation grown teak (Tectona grandis L.), growth ring width was measured in 105 trees and correlated to precipitation and temperature data.

? The social status of trees within the stand was also determined and cross-sectional area (CSA) for the trunk correlated to the proportion of heartwood (HW) within the tree. HW develops asymmetrically in leaning stems of some conifer species, but it is not known if this phenomenon also occurs in broadleaf species. Therefore, we measured HW proportion in leaning and straight stems, along with the number of growth rings in the HW.

? Annual ring width depended strongly on mean monthly temperature during the rainy season and the most significant relationships were found corresponding to the months of June and July. With regard to the weaker relationship between precipitation and radial growth, correlations were highest during the period of bud-break at the beginning of the rainy season.

? The very high stand density affected radial growth, particularly in suppressed trees, which responded little to thinning operations. HW formation was greatest in dominant trees, and was highly regressed with stem CSA.

? Therefore, rapid growth of young stands should be encouraged by reducing stand density. Asymmetric HW formation occurred in both leaning and straight trees, and was significantly greater along the upper sides of leaning stems. It is probable that this eccentric HW formation is linked to mechanical loading on the tree.

     

Spring frost and decay fungi are implicated in suppressing aspen re-growth following partial cleaning in juvenile stands

? Aspen (Populus tremuloides Michx.) regenerates at high densities following manual cleaning.

? Ten-year-old stands located near Lac La Biche and Peace River, Alberta were manually cleaned to three densities (0, 500 or 1 500 stems ha^?1) at three times (bud set, dormancy or bud flush) to test the hypothesis that maintaining residual aspen reduces regeneration.

? At Lac La Biche up to 98% of the aspen regeneration died in the partially-cleaned plots compared to 67% at Peace River five years post-treatment. A spring frost in the second growing season at Lac La Biche is hypothesized to be the inciting factor predisposing the stump sprouts to infection by decay fungi such as Armillaria root rot, resulting in reduced density and height of the aspen regeneration at Lac La Biche relative to Peace River. Drought and ungulate herbivory provided additional stresses. The high mortality of aspen regeneration at Lac La Biche shifted the understory regeneration from aspen to balsam poplar (Populus balsamifera L.).

? These results indicate that maintaining 1 500 stems ha^?1 of residual aspen will not effectively control the re-sprouting of aspen; however, the vulnerability of aspen regeneration to spring frost and other stressors can nearly eradicate the re-growth of aspen.

     

Comparison of the virulence of Armillaria cepistipes and Armillaria ostoyae on four Norway spruce provenances

The basidiomycetes Armillaria cepistipes and Armillaria ostoyae frequently occur in the same forest stand. In this study, we determined the virulence of 20 isolates of A. cepistipes and 16 isolates of A. ostoyae on four different provenances of 2‐year‐old Norway spruce (Picea abies). Within 30 months after inoculation, 1.1 and 19.1% of the seedlings inoculated with A. cepistipes and A. ostoyae, respectively, had died or were dying. The incidence of dead and dying seedlings varied between 3 and 49% among the A. ostoyae isolates. The virulence of an isolate was positively correlated to its ability to produce rhizomorphs. One Norway spruce provenance showed significantly lower susceptibility to A. ostoyae than the other three. Rhizomorphs of both Armillaria species were attached to the root surface. The attached rhizomorphs of A. ostoyae, however, were associated with significantly more lesions. The virulence of the isolates was not correlated with their wood‐degrading capability for either of the Armillaria species.     

Climate-growth variability in Quercus ilex L. west Iberian open woodlands of different stand density

? We present the longest tree-ring chronology (141 y) of Quercus ilex L. (holm oak), and discuss the species climate-growth relationships and the influence of stand density on tree sensitivity to climate.

? Similarly to Quercus suber L., the most influential climatic variables upon holm oak growth were late spring and early summer precipitation, which enhanced growth, and high temperatures in the previous August and current July, which negatively affected growth.

? High density stands responded to similar climatic factors as low density stands, but their response was generally weaker. Holm oak sensitivity to climate has increased in recent decades, which might be related to increasing temperatures in the region. Sensitivity was higher in low density stands. Additionally, the effect of summer stress on growth seems to have increased during the same period, similarly to other species in the Iberian Peninsula, suggesting that trees are more vulnerable to climatic changes.

? Stand density could buffer the response to climate by smoothing climatic extremes. Nevertheless, the effect of competition might reverse this positive effect at the individual tree level. Precautions should be taken before providing management guidelines regarding the effect of climate change and stand density on holm oak.

     

Fuel and stand conditions in an isolated, unmanaged forest landscape in central Oregon

? Mature, unmanaged forests in western North America provide important reference conditions for managers, yet little is known about fuel composition and the factors that influence fuel accumulation in such stands. Our objectives were to characterize fuels in a passively managed landscape of dry forests in central Oregon and identify environmental factors influencing fuel accumulation.

? Ordination techniques and analysis of variance revealed no statistical differences in total fuel loads across a wide range of environmental conditions.

? Individual fuel size classes, however, did vary by stand location and composition. Interior stands had more 1- to 100-h fuels and snags than stands at or near the edge, stands dominated by ponderosa pine had fewer small-diameter fuels and snags, lodgepole pine stands had more 1-h fuels and snags, and white fir stands had more 10-h fuels, duff, and snag basal area.

? Tree species, density and age, and years since last fire were the most important environmental variables, explaining 23% of the variation in fuels.

? Our results present further evidence that fuel composition is highly variable at many spatial and temporal scales. They also provide useful baseline information for managers of fire-prone western forests.

     

Litterfall production in forests located at the Pre-delta area of the Paraná River (Argentina)

? The objectives of this study were to measure litterfall production of the four floodplain forest types and to analyze the relationship between litterfall (forest type, dominant species, and organic fractions) and flood pulses.

? Litterfall production was measured in two mono-specific stands of Salix humboldtiana or Tessaria integrifolia, respectively, and two mixed forests dominated by A. inundata or Nectandra angustifolia, during 1998 and the 2000–2002 periods.

? Mono-specific stands presented similar productivities (6.8 and 6.5 Mg dry matter ha^?1 y^?1, respectively), but differed significantly from the two other. The highest litterfall production was obtained during the large flood that occurred during 1998, decreasing later throughout the study period. Leaves were the dominant fraction of litterfall, followed by branches, flowers, and fruits.

? Only S. humboldtiana, T. integrifolia and A. inundata forests showed distinct patterns of litterfall production, depending on the flooding pulse. N. angustifolia did not show a distinctive litterfall pattern.

? The forests studied here presented patterns of litter production associated with the flood pulse according to its location along a topographic gradient, that controls the litter productivity of these forests.

     

Potential use of pine plantations to restore native forests in a highly fragmented river basin

? In forests, the substitution of broadleaf species by conifers can reduce biodiversity because coniferous forests generally provide less diverse vascular understories than broadleaf forests. However, in some cases, former pine plantations might be useful for restoring native forests. We compared plant species composition on the plot scale in natural beech and mixed oak forests with that in plantations of Pinus radiata. Links between plant diversity and landscape parameters (patch size, fractal dimension and distance to the nearest patch of the same type) were investigated.

? The objective of this study was to evaluate the use of pine plantations for restoring native diversity in a zone where native forests are very fragmented.

? Similar to oak forests, plant diversity in pine plantations was high, mainly due to the presence of generalist species. Some species characteristic of oak forests also appeared in pine plantations, suggesting the onset of natural forest regeneration.

? These results suggest that pine plantations could be used to promote natural regeneration of original oak forests. Moreover, residual native stands should be conserved as important sources of native species and their seeds.

     

Rhizomorph production and stump colonization by co‐occurring Armillaria cepistipes and Armillaria ostoyae: an experimental study

In managed spruce forests, Armillaria cepistipes and A. ostoyae are efficient stump colonizers and may compete for these resources when they co‐occur at the same site. The aim of this experiment was to quantify the mutual competitive ability of the two Armillaria species in producing rhizomorphs and in colonizing Norway spruce (Picea abies) stumps. Five isolates of A. cepistipes and two isolates of A. ostoyae were simultaneously inoculated pair‐wise into pots containing a 4‐year‐old spruce seedling. For comparison, each isolate was also inoculated alone. One year after inoculation, stumps were created by cutting down the seedlings. Six months after creation of the stumps, rhizomorph production and stump colonization were assessed. Armillaria spp. were identified from 347 rhizomorphs and 48 colonized stumps. Armillaria cepistipes dominated both as rhizomorphs in the soil and on the stumps. Nevertheless, A. ostoyae was relatively more frequent on the stumps than in the soil and A. cepistipes was relatively more frequent in the soil than on the stumps. In both species, the ability to colonize the stumps in simultaneous inoculations was significantly reduced compared with single inoculations. In respect to rhizomorph production, simultaneous co‐inoculations had a slightly stimulatory effect on A. cepistipes and no significant effect on A. ostoyae. Our study suggests a rather neutralistic co‐existence of A. cepistipes and A. ostoyae as rhizomorphs in the soil. Concerning the ability to colonize stumps, the two species experience a mutual negative effect from the interaction, probably because of interspecific competition.     

Variation in the decay resistance of larch to fungi

? Decay resistance of larch (Larix sp.) to fungi was evaluated on heartwood samples belonging to 3 species (L. decidua, L. kaempferi and their hybrid), 3 races of European larch (polonica, sudetica and alpine), 13 wood lots (populations) and 313 trees.

? Larch wood appeared, on average, as moderately durable although a high variability was observed. At the sample level as well as at the mean individual tree level, durability ranged from class 1 to 5 according to EN 350-1 standard. At the population level, larch wood varied from ‘durable’ to ‘slightly durable’. Genetics played a major role in decay resistance at the species, provenance and tree levels. Environmental factors such as the position of heartwood samples and the age of trees were also identified as a source of variability.

? The most durable wood was not necessarily from old native alpine stands of European larch: some young larches from faster growing lowland origins also produced durable wood.

? Genetic improvement of larch wood durability appeared therefore likely by the selection of the best populations for decay resistance as well as from the selection of individuals.

     

Genetic variation in architectural seedling traits of Patagonian cypress natural populations from the extremes of a precipitation range

? Species distributed along wide environmental ranges are expected to be either plastic or adapted to local optima. The elucidation of which of these alternatives prevails, is crucial in planning breeding and conservation strategies for not yet domesticated species. Austrocedrus chilensis (Cupressaceae) is the most commercially important conifer of the temperate forests of Argentina and the target of a domestication program. A steep precipitation gradient characterizes its Argentinean range.

? Variation within and differentiation among four natural populations of this Patagonian cypress representative of two contrasting precipitation regimes (>1 300 and 330 mm per y) were assessed by analyzing several morpho/architectural traits in one-year-old seedlings grown in a greenhouse.

? Progenies from one of the two xeric populations did not differ from those corresponding to both humid-site populations. The two most variable populations in terms of additive genetic variance belonged to contrasting precipitation regimes. Differentiation among populations was low as measured by each and every variable (average Q _st = 0.088). Morphological traits related to the main axis size would have a dubious adaptive meaning.

? The results suggest that the Patagonian cypress would have not evolved genetic pools adapted to local optima, and thus it appears to be a phenotypically plastic species, at least regarding growth at juvenile age.

     

Genetic variation of isolated Picea balfouriana populations from the southeast of the Qinghai-Tibet Plateau

? The objective of this work is to estimate the level of genetic variation and pattern of genetic structure of isolated Picea balfouriana populations.

? Nine SSR markers and six STS markers were assayed in ten natural populations of P. balfouriana, which is a regionally distributed conifer species in the southeast of the Qinghai-Tibet Plateau.

? Expected heterozygosity ranged from 0.592 to 0.710 based on SSRs, and from 0.489 to 0.635 based on STS markers. The SSR and STS markers revealed that 11% and 12% of variation, respectively, was present among populations. However, the SSRs showed no deviation from the Hardy-Weinberg equilibrium (F _IS = ?0.030), unlike the STS markers (F _IS = 0.249). In addition, assignment methods showed that individuals from the same sampling site usually cluster together.

? Our results indicated that the distribution of genetic variation and population genetic structure of P. balfouriana may be attributed to habitat fragmentation and heterogeneous environments caused by the complex topographic environment in the Qinghai-Tibet Plateau. The population genetic information obtained in our study will benefit the development and utilization of appropriate conservation and breeding strategies for P. balfouriana.

     

Characteristics of a 20-year-old evergreen broad-leaved forest restocked by natural regeneration after clearcut-burning

? To elucidate the application of natural regeneration to the restocking of evergreen broad-leaved forests in the subtropics, the characteristics of a 20-year-old evergreen broad-leaved forest restocked by natural regeneration after clearcut-burning were studied in Okinawa, Japan. Within a 0.87 ha clearcut area with four 10 m × 10 m sampling plots, two burned and two unburned ones, the tree composition, tree species diversity and vegetation changes were investigated.

? The results showed that the species diversity, basal area and density of woody stems ? 1.0 m in height differed significantly among phanerophyte types, while they were not significantly different between the burned and unburned treatments. A vegetation census also revealed no obvious differences between the treatments.

? The primary dominant species, Castanopsis sieboldii, continued to dominate the secondary forest with a broad height distribution.

? The structural complexity and high tree species diversity of the regenerating forest after clearcut-burning provides no evidence of degeneration. We can predict that the regeneration forest may gradually develop into stands similar to pre-clearcut primary forest, and that natural regeneration may restore the high tree species diversity of the evergreen broad-leaved forests in Okinawa.