Melampsora rust species on biomass willows in central and north-eastern Germany

Melampsora willow rusts are the most important fungal pathogens in short rotation coppices of biomass willows. In the past, breeding programmes for rust resistant biomass willows concentrated on the distinction of races within the forma specialis Melampsora larici-epitea f. sp. larici-epitea typica that colonized Salix viminalis and related clones. In a new breeding program that is based on a wider range of willow species it is necessary to identify further Melampsora species and formae specialis that are pathogens of willow species other than S. viminalis. Therefore, three stock collections with Salix daphnoides, Salix purpurea, and other shrub willow species (including S. viminalis) species were sampled in north-eastern Germany. A fourth stock collection in central Germany contributed rusts of tree willows (Salix fragilis and Salix alba) and the large shrub Salix caprea. Out of 156 rust samples, 149 were successfully sequenced for ITS rDNA. A phylogenetic analysis combining Neighbour-Joining, Maximum-Likelihood and Bayesian analysis revealed six species: Melampsora ribesii-purpureae, Melampsora allii-salicis-albae, Melampsora sp. aff. allii-fragilis, Melampsora larici-pentandrae, Melampsora larici-caprearum, and Melampsora larici-epitea. The first four species were found exclusively on the expected hosts. Melampsora larici-caprearum had a wider host range comprising S. caprea and S. viminalis hybrids. Melampsora larici-epitea can be further differentiated into two formae speciales. The forma specialis larici-epitea typica (59 samples) colonized Salix viminalis clones, Salix purpurea, Salix×dasyclados, and Salix×aquatica. In contrast to this relatively broad host range, f. sp. larici-daphnoides (65 samples) was found exclusively on Salix daphnoides. With the distinction and identification of the rust species/formae speciales it is now possible to test for race-specific resistances in a more targeted manner within the determined pairings of rust and willow species.     

Correspondence of ectomycorrhizal diversity and colonisation of willows (Salix spp.) grown in short rotation coppice on arable sites and adjacent natural stands

Willows (Salix spp.) are mycorrhizal tree species sometimes cultivated as short rotation coppice (SRC) on arable sites for energy purposes; they are also among the earliest plants colonising primary successional sites in natural stands. The objective of this study was to analyse the degree of colonisation and diversity of ectomycorrhizal (EM) communities on willows grown as SRC in arable soils and their adjacent natural or naturalized stands. Arable sites usually lack ectomycorrhizal host plants before the establishment of SRC, and adjacent natural or naturalized willow stands were hypothesized to be a leading source of ectomycorrhizal inoculum for the SRC. Three test sites including SRC stands (Salix viminalis, Salix dasyclados, and Salix schwerinii) and adjacent natural or naturalized (Salix caprea, Salix fragilis, and Salix?×?mollissima) stands in central Sweden were investigated on EM colonisation and morphotypes, and the fungal partners of 36 of the total 49 EM fungi morphotypes were identified using molecular tools. The frequency of mycorrhizas in the natural/naturalized stands was higher (two sites) or lower (one site) than in the corresponding cultivated stands. Correspondence analysis revealed that some EM taxa (e.g. Agaricales) were mostly associated with cultivated willows, while others (e.g. Thelephorales) were mostly found in natural/naturalized stands. In conclusion, we found strong effects of sites and willow genotype on EM fungi formation, but poor correspondence between the EM fungi abundance and diversity in SRC and their adjacent natural/naturalized stands. The underlying mechanism might be selective promotion of some EM fungi species by more effective spore dispersal.     

Potential of Salix as phytoextractor for Cd on moderately contaminated soils

Biomass production and Cd uptake in Salix (willow) is generally high. The aim of this study was to quantify the amounts of Cd in different plant and soil compartments in commercial Salix stands grown on different soil types and to use these data for estimation of the long-term effects of Cd removal by Salix at stem harvest on the soil Cd content by calculating Cd balances. Ten commercial short rotation willow coppice stands, planted with clone 78183 of Salix viminalis (L.) were investigated in order to include three different soil types with respect to pH. Stands with high stem biomass production generally had lower Cd concentrations in the plant and grew on more alkaline soils with low Cd availability when compared to stands with low stem biomass production. The highest output of Cd by Salix is therefore not necessarily achieved by stands with the highest yields or the highest Cd concentrations, as both these parameters have to be considered. The net removal of Cd from the plough layer by the Salix crop under different conditions varied between 2.6 and 16.5 g Cd ha^–1 year^–1. The long-term effects of Salix cultivation on soil Cd content, i.e. after 6–7 cutting cycles (25 years), were calculated and we reached the conclusion that there is a high potential in Salix to remove significant amounts of Cd at stem harvest. Salix can therefore presumably be used to counteract Cd pollution of agricultural soils in Sweden provided that the Cd in furnace ashes is taken care of.     

Variation in the uptake of Arsenic, Cadmium, Lead, and Zinc by different species of willows Salix spp. grown in contaminated soils

The experiment assessed the variability of in seven clones of willow plants of high biomass production (Salix smithiana S-218, Salix smithiana S-150, Salix viminalis S-519, Salix alba S-464, Salix ’Pyramidalis’ S-141, Salix dasyclados S-406, Salix rubens S-391). They were planted in a pots for three vegetation periods in three soils differing in the total content of risk elements. Comparing the calculated relative decrease of total metal contents in soils, the phytoextraction potential of willows was obtained for cadmium (Cd) and zinc (Zn), moderately contaminated Cambisol and uncontaminated Chernozem, where aboveground biomass removed about 30% Cd and 5% Zn of the total element content, respectively. The clones showed variability in removing Cd and Zn, depending on soil type and contamination level: S. smithiana (S-150) and S. rubens (S-391) demonstrated the highest phytoextraction effect for Cd and Zn. For lead (Pb) and arsenic (As), the ability to accumulate the aboveground biomass of willows was found to be negligible in both soils. The results confirmed that willow plants show promising results for several elements, mainly for mobile ones like cadmium and zinc in moderate levels of contamination. The differences in accumulation among the clones seemed to be affected more by the properties of clones, not by the soil element concentrations or soil properties. However, confirmation and verification of the results in field conditions as well as more detailed investigation of the mechanisms of cadmium uptake in rhizosphere of willow plants will be determined by further research.     

Biomass Harvest from Natural Willow Rings around Prairie Wetlands

The study followed the harvest of natural willow from three wetlands using a prototype modified agricultural round baler nicknamed a Bio-Baler. The study reports fuel characteristics and combustion testing of biomass harvested from natural willow rings. Composition of native willow species in the harvested willow rings was determined. We specifically measured regrowth of the biomass and number of regenerated stems per stump 1 year after harvest to determine how different willow species responded to mechanical biomass cutting with the Bio-Baler. The results of combustion testing for the natural willow were essentially similar to those with “conventional” wood chips or planted willows. The ash content was approximately 1.65%, slightly lower than for planted willow plantations. The calorific value of the natural willow was 19.6 MJ kg^?1 (dry basis) similar to what is expected for wood and planted willow. Four Salix species (Salix bebbiana Sarg., Salix petiolaris Sm., Salix eriocephala Michx., and Salix discolor Muhl) were identified in the willow rings. Stem biomass increased for all species except S. bebbiana after willow was harvested with the Bio-Baler. Overall, willow regeneration was not affected by mechanical harvesting compared to hand cutting. Regenerated stem density was 93 stems per square meter for mechanically harvested stumps compared to 105 stems per square meter for hand-pruned stumps. Based on the results, biomass harvested from natural willow rings has acceptable fuel characteristics when compared to purpose-grown willows and mechanical harvest with a Bio-Baler does not have a negative effect on willow regeneration.     

Fine root dynamic characteristics and effect on plantation’s carbon sequestration of three Salix shrub plantations in Tibetan Plateau alpine sandy land

Desertification land in Gonghe Basin of Tibetan Plateau, China accounts for 91.9% of the total land area. Vegetation restoration and reconstruction with desert shrubs in degraded ecosystem are effective ways to prevent and control desertification. However, the evaluation studies of fine root dynamic characteristics of desert shrubs and their contribution to carbon sequestration of plantation are limited. To gain a better understanding of vegetation restoration, the vertical distribution of fine root biomass, fine root decomposition, fine root turnover was investigated, as well as their coupling effect on carbon sequestration of plantation in three desert vegetation. The results estimated that the total decomposition time of fine roots of Salix cheilophila (S. cheilophila), Salix psammophila (S. psammophila), and Salix microstachya (S. microstachya) are 39.00, 27.99 and 35.95 years. Biomass carbon density for three Salix plantations ranged from 1.42 to 2.39 t/hm², which showed that three Salix plantations in alpine sandy land are an important carbon pool. In addition, fine root biomass carbon density for the three shrub plantations varied significantly. Fine root biomass carbon density for S. psammophila reached the largest among the three plantations, which was 1.48 t/hm², accounting for the ratio of 62% of the plantation total biomass carbon density. The results indicated that the root system of S. psammophila, especially the fine roots, was very developed, which was conducive to soil water transportation and carbon sequestration. Therefore, S. psammophila might be a better species for carbon sequestration of plantation in alpine sandy areas. The carbon input from the fine roots of the three shrub plantations through decomposition and turnover into the plantations accounts for 11.5% to 15.5% of total carbon sequestration of plantations. Therefore, the fine roots dynamics must be considered for long‐term carbon pool estimations in three Salix plantations, otherwise the total carbon sequestration of plantations would be underestimated.     

Changes in the Rooting and Growth of Willows and Poplars Induced by Cadmium

Growth parameters of six fast growing trees showed that the roots responded to Cd treatment more sensitively than the shoots. Cd-treatment suppressed rooting and root growth (length and biomass production) as well as its development in all tested species. Root systems of Salix cinerea, Salix alba, and Populus cv. Robusta were more tolerant to Cd stress than the root system of the other studied species. Shoot growth parameters of Salix species were significantly reduced unlike Populus species, which were not affected by Cd treatment.     

Impact of arbuscular mycorrhizal fungi (AMF) and atmospheric CO2 concentration on the biomass production and partitioning in the forage legume alfalfa

The influence of mycorrhizal symbiosis, atmospheric CO₂ concentration and the interaction between both factors on biomass production and partitioning were assessed in nodulated alfalfa (Medicago sativa L.) associated or not with arbuscular mycorrhizal fungi (AMF) and grown in greenhouse at either ambient (392 μmol?mol^?1) or elevated (700 μmol?mol^?1) CO₂ air concentrations. Measurements were performed at three stages of the vegetative period of plants. Shoot and root biomass achieved by plants at the end of their vegetative period were highly correlated to the photosynthetic rates reached at earlier stages, and there was a significant relationship between CO₂ exchange rates and total nodule biomass per plant. In non-mycorrhizal alfalfa, the production of leaves, stems and nodules biomass significantly increased when plants had been exposed to elevated CO₂ concentration in the atmosphere for 4 weeks. Regardless CO₂ concentration at which alfalfa were cultivated, mycorrhizal symbiosis improved photosynthetic rates and growth of alfalfa at early stages of the vegetative period and then photosynthesis decreased, which suggests that AMF shortened the vegetative period of the host plants. At final stages of the vegetative period, AMF enhanced both area and biomass of leaves as well as the leaves to stems ratio when alfalfa plants were cultivated at ambient CO₂. The interaction of AMF with elevated CO₂ improved root biomass and slightly increased the leaves to stems ratio at the end of the vegetative growth. Therefore, AMF may favor both the forage quality of alfalfa when grown at ambient CO₂ and its perennity for next cutting regrowth cycle when grown under elevated CO₂. Nevertheless, this hypothesis needs to be checked under natural conditions in field.     

Assessment of Genotype Ranking in Long-term Biomass Production of Salix Based on Juvenile Plant Traits: Breeding Implications

Willow (Salix spp.) is among the most promising energy crops to be grown on agricultural land and breeding research to increase biomass yield of this perennial crop is performed in Europe and North America. Biomass willows are grown in short rotation and harvests are performed every 3 to 5 years (i.e., at 3- to 5-year cutting cycles) for a period of up to 25 years. However, breeding programs to improve long-term biomass yield are often relying on the results of short-term screening studies performed on juvenile plants. A pre-requisite for successful breeding of perennial energy crops is thus the identification of relevant juvenile plant traits indicative of long-term plant performance under field conditions. In this study a number of juvenile plant traits, measured at various Salix genotypes grown in a short-term experiment were evaluated in terms of their capacity to predict the long-term performance in biomass production after the first and second cutting cycle. The objective was to develop a simple model linking juvenile plant traits such as shoot biomass, total leaf area and leaf nitrogen (N) concentration to the long-term biomass productivity of field-grown plants. A two-component regression model combining juvenile shoot biomass and leaf N concentration provided the highest prediction accuracy (coefficients of determination around 0.8). The model based on two easy-to-measure juvenile plant traits clearly has implications for willow breeding programs. The implications for breeding are discussed in the light of the possibilities and limitations associated with the chosen approach.     

Successional changes in ectomycorrhizal fungi associated with the polar willow Salix polaris in a deglaciated area in the High Arctic, Svalbard

Polar willow (Salix polaris Wahlenb.), a mycorrhizal dwarf shrub, colonizes recently deglaciated areas in the High Arctic, Svalbard. To clarify successional changes in ECM fungi associated with S. polaris after glacier retreat, we examined the diversity and density of ECM fungi in culture and field conditions. Plant and soil samples were collected from three sites of different successional stages in the deglaciated area of Austre Br?ggerbreen, near Ny-?lesund, Svalbard. The successional stages were early stage with newly exposed bare ground (site I), transient stage with scattered colonization of Salix (sites IIa and IIb), and late stage with well-developed vegetation (site III). No ECM colonization on Salix was observed in soils collected from bare ground in early and transient stages (sites I and IIa). However, most Salix individuals showed ECM colonization in soils collected from sites close to Salix colonies in transient and late stages (sites IIb and III). Based on molecular analyses and operational taxonomic unit (OTU: >95% ITS sequence similarity) delimitations, we identified 15 OTUs/species in eight genera. The dominant OTU/species of ECM fungi identified in the transient and late stages was Geopora sp.1 and Cenococcum sp.1, respectively. In the culture experiment, ECM diversity was greater in late stage (eight OTUs/species) than in transient stage (three OTUs/species). This pattern was consistent with field observations, i.e., late-stage sites contained more OTUs/species of ECM fungi. These results indicate that species diversity of ECM fungi increases and the dominant species changes with the progress of succession after glacier retreat in the High Arctic.     

Effects of Sewage Sludge Application on Biomass Production and Concentrations of Cd,Pb and Zn in Shoots of <Emphasis Type="Italic">Salix</Emphasis> and <Emphasis Type="Italic">Populus</Emphasis> Clones: Improvement of Phytoremediation Efficiency in Contaminated Soils

Fast-growing clones of Salix and Populus species have been studied for phytoremediation of soils contaminated by risk elements (REs) using short-rotation coppice plantations. Biomass yield, accumulation and removal of RE (Cd, Pb and Zn) by highly productive willow (S1—(Salix schwerinii × Salix viminalis) × S. viminalis, S2—Salix × smithiana) and poplar (P1—Populus maximowiczii × Populus nigra, P2—P. nigra) clones were investigated with and without sewage sludge (SS) application. The precise field experiment was established in April 2008 on moderately Cd-, Pb- and Zn-contaminated soil. Initially, shoots were harvested after four seasons in February 2012 and then after two more seasons in February 2014. The application of SS limited plant growth during the first years of the experiment in the majority of treatments, mainly due to weed competition and higher concentrations of available soil nutrients causing lower yields than those of control (C) treatments. Well-developed roots were able to take advantage of SS applications, and shoot yield was mainly higher in SS treatments in the second harvest, reaching up to 15 t dry matter (DM)?ha^?1. Willows performed better than poplars. Application of SS reduced RE shoot concentrations compared to the C treatment. The removal of RE was significantly higher in the second harvest for all clones and elements (except the P2 clone), and the biomass yield was the major driving force for the amount of RE removed by shoots. Well-developed plantations of fast-growing trees showed better suitability for the phytoextraction of moderately contaminated soils for Cd and partly for Zn but not for Pb, which was less available to plants. From the four tested clones, S2 showed the best removal of Cd (up to 0.94 %) and Zn (up to 0.34 %) of the total soil element content, respectively, and this clone is a good candidate for phytoextraction. SS can be a suitable source of nutrients for Salix clones without any threat to the food chain in terms of biomass contamination, but its application to the soil can result in an increased incidence of some weeds during the first years of plantation.     

不同能源柳无性系对土壤镉污染的抗性研究

运为了比较不同能源柳无性系对土壤镉抗性的差异,采用盆栽方法,设置土壤镉含量5个梯度(0、10、20、40、80 mg·kg^-1),以乡土旱柳为对照,对能柳1、能柳2、能柳E、能柳C的扦插幼苗对土壤镉污染的生理生态反应进行了系统测定,分析了不同无性系的抗性。结果显示,低浓度处理（≤20 mg·kg^-1）促进苗木生长,其中能柳2在10 mg·kg^-1处理下根和单株生物量增幅最大,可达到对照的132.0%和120.0%;随着镉浓度的增加,生长量下降,在最高浓度处理下,能柳C生长量降低最少,根、枝、叶和单株生物量分别为对照的86.1%、85.3%、82.9%、84.9%,旱柳的枝、叶生物量降低最多,为对照（无镉）的43.8%、45.0%,而能柳1的根、单株生物量降低最多,仅为对照的36.1%、44.4%;随着镉浓度的增加,不同能源柳无性系叶片的SOD、POD、CAT活性和根系活力基本呈现先升后降的趋势,其中,CAT活性变化较为平缓;关于SOD活性和根系活力,能柳1、能柳2在20 mg·kg^-1时已显著下降,旱柳在40 mg·kg^-1时显著下降,而能柳E、能柳C在40 mg·kg^-1时才显著下降。采用隶属函数对5个无性系在镉胁迫条件下的生长和酶指标进行综合分析,不同无性系对土壤镉污染的抗性顺序为能柳C>能柳2>能柳1>旱柳>能柳E。不同无性系对镉均有抗性,都可在镉污染区推广种植,栽培中,应根据土壤污染和绿化目标,做出适当选择。     

Differential establishment and survival of species in deciduous and evergreen shrub patches and on bare ground,Mt. Koma,Hokkaido, Japan

The effects of patches formed by a deciduous shrub (Salix reinii) and an evergreen shrub (Gaultheria miqueliana) on cohabitants were examined on an active volcano Mt. Koma, northern Japan, using bareground as a comparative baseline (control). Species richness increased with increasing the areas of three habitats (Salix patches, Gaultheria patches and bareground), but significantly slowed in Gaultheria patches where the shoot densities of cohabitants also decreased. Calamagrostis hakonensis and Spiranthes sinensis were 2–3 times more likely to establish in Salix patches than in bareground, Anaphalis margaritacea var. angustior and Campanula lasiocarpa were 4–5 times more likely to establish on bareground than in Salix patches. Cohabitants was fewer with Gaultheria. Light intensities of the two patch types were ca 1/3 of that on bareground. Light intensity on Gaultheria was ca 88% of that on Salix patch and decreased with increasing patch size, because the differences in stem and leaf architectures and phenology between the two patch-forming species. Moisture and total nitrogen in volcanic deposits were 2–3 times higher in the patches than in bareground. In the patches, low light intensity restricted seed germination, in particular, for the plants characteristic of bareground, e.g., Anaphalis, while high soil moisture increased the survival rates of Calamagrostis. In Gaultheria patches, despite high moisture, the reduced light intensity influenced seed germination and inhibited the establishment of most species. Seedbanks estimated by a lab-experiment indicated that Salix patches trapped more seeds. As a consequence, Salix patches act as facilitator, in particular, for Calamagrostis, by improving moisture and nutrients status of volcanic deposits, moderating light intensity and seed trapping. Deciduous shrub patches, such as Salix reinii, have an improving role in accelerating rates of succession in harsh environments, while evergreen shrub patches slow plant establishment. Nomenclature: Ohwi and Kitagawa (1983)     

A taxonomic study of Salix section Longifoliae (Salicaceae)

Salix section Longifoliae occurs from Alaska to Guatemala and from the Atlantic to the Pacific. Nine taxa are here accepted as five species with one of the species including two subspecies and four varieties. the holotype of Salix taxifolia Humb., Bonpl. & Kunth represents the same taxon as the lectotype of Salix microphylla Schltdl. & Cham. Material recently called S. taxifolia is given a new name. Salix exilifolia Dorn. The name Salix fluviatilis Nutt is considered to be synonymous with S. melanopsis Nutt. One new variety is described and two new combinations are made under Salix exigua Nutt.     

Pioneer trees in Amazonian floodplains: Three key species form monospecific stands in different habitats

Three pioneer tree species —Salix humboldtiana, Cecropia latiloba, Senna reticulata — form monospecific stands in the Central Amazonian white-water flood plain. In contrast toterra firma forests where species composition is unpredictable even for pioneer species, in Central Amazonianvárzea the occurrence of the main colonizing species seems to be predictable. This predictability is linked to characteristic habitat conditions and the low number of pioneer species. This preference for different habitats is reflected by different germination and early growth, by the structural and physiological characteristics, as well as by the reproductive and morphological adaptations of the three main species. The germination rate was above 90% in all species, and the duration until germination ranged between one day inSalix and 14 days inCecropia. Stem elongation was more than 10 cm per month inSalix andCecropia, and about 50 cm per month inSenna. Wood specific gravity ranged from 0.33 g cm⁻³ inCecropia to 0.45 g cm⁻³ inSenna. The annual wood increment increased by 1.20 (Cecropia), 1.23 (Salix) to 2.14 cm per year (Senna). All species produced adventitious roots, lenticels and/or stem hypertrophy. Leaf photosynthesis was between 17 and 20 μmol m⁻²s⁻¹, and reached a maximum of 30 μmol m⁻²s⁻¹ inSenna. Flowering and fruiting inSalix occurred throughout the year, whereas inCecropia andSenna they were concentrated in the flooded period.Salix humboldtiana occurs mainly at low sites subjected to long periods of inundation and high sedimentation rates. OnceSalix has formed dense forest stands, sedimentation and water currents are reduced at these sites andCecropia latiloba may take over. This species grows on low to middle elevations in the flooding gradient at sites with lower current and sedimentation rates.Senna reticulata does not tolerate submergence and colonizes habitats that may have strong currents and high sedimentation on higher levels in the flooding gradient.     

Herbarium records in Arctic dwarf shrub dendrochronology: Methodological approach and perspectives

Our work aims to investigate whether herbaria resources can be used for the extension of Arctic dwarf shrub chronologies. The current use of herbaria reaches far beyond their initially aims; among the new applications, phenology observations and conservation biology can be mentioned. However, to this date, no studies on the use of herbarium specimens for dendrochronological research have been published. Examples of perennial plants from herbarium sheets that could potentially be used for such studies are dwarf shrubs, samples of which often consist of whole specimens, including the root system, the root collar and branches. Here, we present a protocol for the selection and processing of historical material. Based on the collections from Kew and Copenhagen, which are among of the largest herbaria with Arctic plants, a database of 25 areas from the Atlantic sector of the Arctic was created. Material from the following most common species was collected: grey willow (Salix glauca L.), polar willow (Salix polaris Wahlenb.), dwarf willow (Salix herbacea L.), net-leaved willow (Salix reticulata L.), arctic willow (Salix arctica Pall.), mountain avens (Dryas octopetala L.), dwarf birch (Betula nana L.). We present the preliminary results of a case study using historical samples of Salix arctica from the Thule (Qaanaaq) area, NW Greenland. Dwarf shrubs can commonly reach the age of 80–100 years or beyond, while herbaria resources may allow the extension of such series over the last centuries. Therewith, these resources may provide an excellent proxy data source on the changing natural environment beyond the northern and upper tree limits, where well-replicated proxy time-series remain sparse.     

Factors influencing forage selection by the North American beaver (Castor canadensis)

Across their range, a large number of biotic and abiotic factors are known to influence the choice of browse plant and the foraging behaviour of the North American beaver (Castor canadensis). We used generalized linear mixed-effects models to investigate sets of variables that may influence the foraging choices of beaver: forage species, distance of forage from water, forage density, and site. Communities across the study sites in central British Columbia, Canada, were dominated by Salix sitchensis, Salix lucida, and Alnus spp. Density had no impact on forage selection, while site, distance from water, and species identity all influenced the foraging decisions of beaver. We postulated that these factors may be ordered hierarchically: large-scale factors, such as site, followed by the medium-scale distance from water, and species of plant at the finest scale. Forage items in some sites had a higher probability of being browsed than in others, while in all sites the probability of being browsed decreased with increasing distance from water. Beaver appeared to be foraging as “picky” generalists; of the 9 plant species examined, 3 species of Salix (S. scouleriana, S. drummondiana and S. sitchensis) were selected by beaver, Salix bebbiana was avoided, and 5 species were neither selected for nor against. Browse selection within the genus Salix implied that beaver were able to differentiate among closely related species. Detailed information on forage selection is a crucial first step in designing and interpreting models that predict large-scale distributional patterns of beaver.     

Willow leaf traits affecting host use by the leaf-gall-forming sawfly

Gall-forming insects usually have very restricted host ranges, but plant traits affecting patterns of host use have rarely been examined. The sawfly Phyllocolpa sp. (Hymenoptera: Tenthredinidae) forms leaf-roll galls on three of seven Salix (Salicaceae) species that occur together on riverbanks in central Japan. We have attempted to explain this host-use pattern by invoking three plant traits: synchrony of leaf flush with the oviposition period of the sawfly, intrinsic leaf quality as a potential larval food, and leaf morphology. Two Salix species frequently used by the sawfly, Salix eriocarpa and Salix pierotii, had similar leaf traits suitable for larval survival. The third species, Salix serissaefolia, was used relatively less often and the sawfly frequently stopped laying eggs on the plant during oviposition, suggesting ovipositional selection. S. serissaefolia had the smallest leaves, and survival of sawfly larvae was lower on S. serissaefolia than on S. eriocarpa and S. pierotii, because of gall destruction, by other herbivorous insects, and leaf-size restrictions. Among the four unused species, Salix chaenomeloides had a late leaf-flush phenology, Salix gracilistyla had inferior leaf quality, and Salix gilgiana had linear leaves; these seemed to be critical factors for non-use. Salix subfragilis was also unused, but the reason for this could not be explained by the three leaf traits studied.     

Composition, Stand Structure, and Biomass Estimates of “Willow Rings” on the Canadian Prairies

Many small wetlands are scattered across the Canadian Prairies. These wetlands are often surrounded by a ring of phreatophytic shrubs, of which willows are the dominant genus. Even though many of these willow rings are currently degraded, due to the lack of disturbance factors such as prairie wild fires and bison herds, they are still of great value as a biomass resource without carbon debt. Our study had the objectives to (1) study the distribution of five native willows (Salix bebbiana, Salix discolor, Salix eriocephala, Salix interior, and Salix petiolaris) in 12 willow wetland communities in relation to a moisture gradient and (2)examine the effects of age of the willow ring on biomass potential, stand structure, and species distribution. Annual biomass production ranged from 1.9 to 16.2 odt ha^?1 year^?1 for the 12 sites that were between 9 and 34 years old. Current standing biomass for the 12 willow rings with a total area of 1.5 ha was estimated at 239.2 odt. With age, stand structure changed from multiple small-diameter stems to fewer large-diameter stems, and at the same time the species distribution shifted from one dominated by S. petiolaris to one being dominated by S. discolor. Additionally, the sympatric willows showed a distribution along a moisture gradient, with S. eriocephala, S. interior, and S. petiolaris in moist locations and S. bebbiana and S. discolor in drier locations.     

Plant-mediated effects of different Salix species on the performance of the braconid parasitoid Perilitus brevicollis

The blue willow beetle, Phratora vulgatissima, is considered to be the most damaging herbivorous pest in Salix short-rotation coppices throughout Europe. The braconid parasitoid Perilitus brevicollis is an important natural enemy of Phratora. As several different Salix species are used in coppices, I investigated the bottom-up (tritrophic) effects of Salix on the parasitoid. Three host plants were studied: the introduced fast-growing S. viminalis, which is highly susceptible to the beetle; S. dasyclados, which is introduced and moderately-resistant to the beetle; and the native slow-growing Salix cinerea, which is not currently used in coppices. The identity of the host-plant species had significant effects on parasitoid larval development time; parasitoids developed rapidly on the susceptible S. viminalis and slowly on the moderately resistant S. dasyclados. Increased development time resulted in reduced adult longevity. Host-plant species identity also affected larval survival; 57%, 64%, and 49% of the parasitoids successfully completed larval development in beetles fed S. viminalis, S. cinerea, and S. dasyclados, respectively. Parasitoid development was also correlated with the body size of their beetle host, but this effect was independent of the identity of the host-plant species. The results of this study suggest that the parasitoid has higher survival and growth rates when it parasitizes beetles feeding on the common coppice species S. viminalis, but the performance of the parasite is reduced when the beetle feeds on the moderately-resistant S. dasyclados. Conversely, the omnivorous biocontrol agents sometimes used in these systems appear to perform better on S. dasyclados compared to S. viminalis. The results of this study suggest that Perilitus parasitoids and omnivorous beetle predators may provide complementary protection to Salix and therefore be useful in coppice management.