Simple isolation of functional RNA from woody stems of gymnosperms

Stems of woody conifers contain high levels of polysaccharides and phenolic compounds that complicate the isolation of functional RNA from this highly lignified tissue. These difficulties were overcome by pulverizing the frozen tissue with a stainless-steel mortar and by effectively sequestering interfering phenolic compounds with vinylpyrrolidone polymers, thereby minimizing damage to nucleic acids during extraction. RNases were inhibited by aurintricarboxylic acid, and gelatinous polysaccharides were removed by inclusion of a 10% ethanol precipitation step. RNA was then isolated by precipitation with 33% isopropanol and ultracentrifugation onto a cushion of 5.7 M CsCl. Yields of 10 to 20 μg RNA/g FW were obtained from woody stems of several different gymnosperm species, including grand fir (Abies grandis), lodgepole pine (Pinus contorta), loblolly pine (Pinus taeda), Douglas fir (Pseudotsuga menziesii) and Pacific yew (Taxus brevifolia). The high quality of the RNA obtained was determined by UV-spectrophotometry, denaturing agarose gel electrophoresis, andin-vitro translation, and this material was used to construct cDNA libraries.     

Seasonal differences between moose and roe deer in ability to digest browse

The digestive capacity of free-living moose Alces alces (L.) and roe deer Capreolus capreolus (L.) for four plant species was studied with in vitro technique. Moose were found to digest all species better than roe deer. Individual variations were also smaller for moose. In moose the level of digestibility was the same both summer and winter, while roe deer shot in winter digested winter samples of bilberry Vaccinium myrtillus L. and to some extent Scots pine Pinus silvestris L. better than did summer roe deer. This was taken as evidence for a seasonal adaptation in the roe deer rumen. Digestibility of the plant material studied showed a strong negative correlation to the fiber content. The results are discussed in relation to winter problems for roe deer and possible food competition between moose and roe deer.     

Primary attraction and kairomonal host discrimination in three species of Dendroctonus (Coleoptera: Scolytidae)

Abstract 1 Synthetic blends of bole and foliage volatiles of four sympatric species of conifers were released from pheromone‐baited multiple‐funnel traps to determine if three species of tree‐killing bark beetles (Coleoptera: Scolytidae): (i) exhibited primary attraction to volatiles of their hosts and (ii) discriminated among volatiles of four sympatric species of host and nonhost conifers. 2 Bole and foliage volatiles from Douglas‐fir, Pseudotsuga menziesii (Mirb.) Franco, increased the attraction of coastal and interior Douglas‐fir beetles, Dendroctonus pseudotsugae Hopkins, to pheromone‐baited traps. Primary attraction to bole volatiles was observed in interior D. pseudotsugae. Beetles were significantly less attracted to the pheromone bait when it was combined with volatiles of lodgepole pine, Pinus contorta var. latifolia Engelm. or interior fir, Abies lasiocarpa × bifolia. 3 The monoterpene myrcene synergized attraction of mountain pine beetles, Dendroctonus ponderosae Hopkins, to their aggregation pheromones, but there was no evidence of primary attraction to host volatiles or discrimination among volatiles from the four conifers. 4 There was significant primary attraction of the spruce beetle, Dendroctonus rufipennis Kirby, to bole and foliage volatiles of interior spruce, Picea engelmannii × glauca, but beetles did not discriminate among volatiles of four sympatric conifers when they were combined with pheromone baits. 5 Our results indicate that host volatiles act as kairomones to aid pioneer Douglas‐fir beetles and spruce beetles in host location by primary attraction, and that their role as synergists to aggregation pheromones is significant. For the mountain pine beetle, we conclude that random landing and close range acceptance or rejection of potential hosts would occur in the absence of aggregation pheromones emanating from a tree under attack.     

The impact of simulated moose densities on conifer aphids along a productivity gradient

Large herbivores have a significant impact on boreal forest ecosystems. The modification of resources through their feeding induces changes in trophic dynamics and affects the direction of interactions in a community. Moose Alces alces may decrease the available plant biomass for herbivorous insects on one of their main winter forage species in Fennoscandia, Scots pine Pinus sylvestris, and indirectly alter the abundance of invertebrates through exploitative competition. Moose browsing can also induce chemical, morphological, and phenological changes in plants, changing their nutritive value to insect herbivores such as aphids. Habitat productivity may further modify the responses of aphids to moose browsing. We studied the responses of the gray pine aphid Schizolachnus pineti to different moose densities, and their relations to habitat productivity by sampling pine branches and measuring the number of aphids on pine needles. The experimental setup consisted of 8 exclosures along a productivity gradient, where the feeding, defecation, and urination of 4 densities of moose had been simulated for 7 yr. We here show that high levels of simulated browsing decrease the amount of gray pine aphids in areas with high productivity. In areas with low productivity, however, simulated browsing had no such effect. Habitat productivity should therefore be considered as an important factor that may determine the strength of an areas buffering capacity to high moose densities. Low resource environments appear to be favourable to specialist conifer aphids on pines under high browsing pressure, but the performance of generalist insect herbivores might be lowered.     

Environmental variation and moose Alces alces density as determinants of spatio-temporal heterogeneity in browsing

Understanding temporal variation in habitat selection and browsing intensity by large herbivores is fundamental because of their large impact on the ecosystems. I studied the annual variation in winter browsing pressure on young trees and habitat selection by moose Alces alces over a ten year period. Specifically, the relationships between browsing pressure on Scots pine Pinus sylvestris and two birch species ( Betula ssp.) and three explanatory variables – 1) availability of forage, 2) moose density (estimated by pellet group counts) and 3) snow cover was studied. At a larger spatial scale (forest stand level) the relationship between moose habitat selection between three different habitat types (forest <30 yr, forest>30 yr and mire) and two explanatory variables, 1) snow condition and 2) moose density, were studied. Browsing pressure on Scots pine, the dominating food plant, was related to forage availability, moose density and snow condition. No significant relationships between any of the three explanatory variables and browsing pressure on the two birch species were found. Moose selection for certain habitats varied between years and was affected by number of days with >0.10 m of snow.
Habitat selection was not significantly related to moose density and the relationship between overall moose density and habitat specific moose densities was proportional within the studied density range. These findings have implications for understanding varying browsing patterns – and will affect both the ability to predict herbivores' effect on the forest ecosystem. A snow dependent browsing pattern also indicates that one can expect a long term decrease in browsing pressure on the tree and shrub layer as a consequence of the ongoing large-scale climate change.     

Food-plant effects on larval performance do not translate into differences in fitness between populations of Panolis flammea (Lepidoptera: Noctuidae)

In the UK, Panolis flammea (Denis & Schiffermüller) is a pest of monocultures of non-native lodgepole pine Pinus contorta Douglas, but not of the indigenous host Scots pine P. sylvestrisL. This difference in population dynamics may be due to the adaptation of P. flammea populations to the phenology, chemical composition and natural enemy complement of lodgepole pine. To ascertain if there was local adaptation of P. flammea populations to lodgepole pine, this study tested for improved performance of both larvae and adults on the host plant species from which they were sourced, compared with their performance on the alternative host plant species. No difference was found in the relative mean performance of populations sourced from Scots pine or lodgepole pine plantations, when fed on Scots or lodgepole pine foliage. Larvae grew faster on Scots pine but this difference did not translate into differences in pupal weight, female body weight or fecundity. Indeed, those insects that had fed on lodgepole pine had a longer lifespan than those that had fed on Scots pine, which, if translated into greater probability of mating or higher fecundity, could contribute to the observed outbreak dynamics in the field. The prediction that the observed outbreak dynamics of P. flammea can be explained by the existence of populations locally adapted to lodgepole pine was not supported. These results cast doubt on the use of larval growth parameters as surrogates of fitness in Lepidoptera.     

Cavitation fatigue in conifers: a study on eight European species

After drought-induced embolism and repair, tree xylem may be weakened against future drought events (cavitation fatigue). As there are few data on cavitation fatigue in conifers available, we quantified vulnerability curves (VCs) after embolism/repair cycles on eight European conifer species. We induced 50% and 100% loss of conductivity (LC) with a cavitron, and analyzed VCs. Embolism repair was obtained by vacuum infiltration. All species demonstrated complete embolism repair and a lack of any cavitation fatigue after 50% LC . After 100% LC, European larch (Larix decidua), stone pine (Pinus cembra), Norway spruce (Picea abies), and silver fir (Abies alba) remained unaffected, while mountain pine (Pinus mugo), yew (Taxus baccata), and common juniper (Juniperus communis) exhibited 0.4–0.9 MPa higher vulnerability to embolism. A small cavitation fatigue observed in Scots pine (Pinus sylvestris) was probably biased by incomplete embolism repair, as indicated by a correlation of vulnerability shifts and conductivity restoration. Our data demonstrate that cavitation fatigue in conifers is species-specific and depends on the intensity of preceding LC. The lack of fatigue effects after moderate LC, and relevant effects in only three species after high LC, indicate that conifers are relatively resistant against cavitation fatigue. This is remarkable considering the complex and delicate conifer pit architecture and may be important considering climate change projections.     

Temptations of weevil: feeding and ovipositional behaviour of Hylobius warreni Wood on host and nonhost bark in laboratory bioassays

• 1 Warren root collar weevil Hylobius warreni Wood (Coleoptera: Curculionidae) is a long‐lived, flightless insect native to coniferous forests across northern North America. Girdling by larval feeding causes significant mortality on young trees. The insect poses considerable challenges to reforestation.
• 2 Adult weevils feed on all life stages of a variety of coniferous hosts prior to oviposition. Their relative feeding preferences, however, have not been quantified. Moreover, it is not known whether host bark influences oviposition behaviour.
• 3 Feeding preferences of adult weevils were tested in both choice and no‐choice laboratory bioassays using small branches from three conifers (lodgepole pine Pinus contorta var. latifolia, interior hybrid spruce Picea glauca×engelmannii, and Douglas‐fir Pseudotsuga menziesii) and one deciduous tree (trembling aspen Populus tremuloides). Measurements included the surface area of bark consumed, rate of consumption, the number of days of feeding, and, in the no‐choice assay, the number of eggs oviposited.
• 4 Bark consumption was greatest on pine and Douglas‐fir, followed by spruce. Little to no feeding occurred on aspen. Consumption did not vary between male versus female insects for any of the feeding metrics quantified.
• 5 The presence of aspen branches did not inhibit feeding on any of the other species in the choice bioassays.
• 6 The number of eggs laid by female insects did not differ significantly among tree species in the no‐choice assay. Eggs were laid indiscriminately in the presence of all four host types.
• 7 Results and opportunities for future research are discussed in the context of formulating new integrated pest management strategies for this insect, which is increasingly important in the period of reforestation subsequent to the mountain pine beetle epidemic in western Canada.

     

Photosynthesis and Photoprotection in Overwintering Plants

Abstract: Seasonal differences in the capacity of photosynthetic electron transport, leaf pigment composition, xanthophyll cycle characteristics and chlorophyll fluorescence emission were investigated in two biennial mesophytes ( Malva neglecta and Verbascum thapsus ) that grow in full sunlight, and in leaves/needles of sun and shade populations of several broad-leafed evergreens and conifers (Vinca minor, Euonymus kiautschovicus, Mahonia repens, Pseudotsuga menziesii [Douglas fir], and Pinus ponderosa). Both mesophytic species maintained or upregulated photosynthetic capacity in the winter and exhibited no upregulation of photoprotection. In contrast, photosynthetic capacity was downregulated in sun leaves/needles of V. minor, Douglas fir, and Ponderosa pine, and even in shade needles of Douglas fir. Interestingly, photosynthetic capacity was upregulated during the winter in shade leaves/needles of V. minor, Ponderosa pine and Euonymus kiautschovicus. Nocturnal retention of zeaxanthin and antheraxanthin, and their sustained engagement in a state primed for energy dissipation, were observed largely in the leaves/needles of sun-exposed evergreen species during winter. Factors that may contribute to these differing responses to winter stress, including chloroplast redox state, the relative levels of source and sink activity at the whole plant level, and apoplastic versus symplastic phloem loading, are discussed.     

Phenylpropanoids in mycorrhizas of the Pinaceae

Tissue-specific accumulation of phenylpropanoids was studied in mycorrhizas of the conifers, silver fir (Abies alba Mill.), Norway spruce [Picea abies (L.) Karst.], white pine (Pinus strobus L.), Scots pine (Pinus silvestris L.), and Douglas fir [Pseudotsuga menziesii (Mirbel) Franco], using high-performance liquid chromatography and histochemical methods. The compounds identified were soluble flavanols (catechin and epicatechin), proanthocyanidins (mainly dimeric catechins and/or epicatechins), stilbene glucosides (astringin and isorhapontin), one dihydroflavonol glucoside (taxifolin 3′-O-glucopyranoside), and a hydroxycinnamate derivative (unknown ferulate conjugate). In addition, a cell wall-bound hydroxycinnamate (ferulate) and a hydroxybenzaldehyde (vanillin) were analysed. Colonisation of the root by the fungal symbiont correlated with the distribution pattern of the above phenylpropanoids in mycorrhizas suggesting that these compounds play an essential role in restricting fungal growth. The levels of flavanols and cell wall-bound ferulate within the cortex were high in the apical part and decreased to the proximal side of the mycorrhizas. In both Douglas fir and silver fir, which allowed separation of inner and outer parts of the cortical tissues, a characteristic transversal distribution of these compounds was found: high levels in the inner non-colonised part of the cortex and low levels in the outer part where the Hartig net is formed. Restriction of fungal growth to the outer cortex may also be achieved by characteristic cell wall thickening of the inner cortex which exhibited flavanolic wall infusions in Douglas fir mycorrhizas. Long and short roots of conifers from natural stands showed similar distribution patterns of phenylpropanoids and cell wall thickening compared to the respective mycorrhizas. These results are discussed with respect to co-evolutionary adaptation of both symbiotic partners regarding root structure (anatomy) and root chemistry. Received: 25 May 1998 / Accepted: 6 November 1998     

Comparative Space Use and Habitat Selection of Moose Around Feeding Stations

ABSTRACT The practice of feeding cervids in winter, either as a supplement to enhance nutritional status or to divert animals away from roads, railways, or vulnerable habitats, is rising noticeably. Moose (Alces alces) densities in Scandinavia are currently at historically high levels, resulting in amplified damage to economically important young Scots pine (Pinus sylvestris) forest stands. Nevertheless, there is limited information as to how diversionary feeding affects herbivore space use and habitat selection. We followed 32 female moose marked with Global Positioning System collars to evaluate 1) if feeding stations serve as attraction points to the extent that habitat-selection patterns resemble those of central-place foragers (i.e., high usage and more uniform selection close to the attraction point), and 2) if moose using feeding sites select young pine stands less than those not using feeding sites. Moose that used diversionary forage concentrated their space use around feeding stations and selected habitats as predicted for a central-place forager with a decreasing probability of using areas away from feeding sites and a low degree of habitat selectivity close to feeding sites. However, moose that used feeding sites continued to select young pine stands to the same extent as moose that did not use feeding sites. Feeding sites were, therefore, not successful in diverting moose away from valuable natural browse, so we recommend wildlife managers establish feeding sites in sacrifice areas where moose browsing is permissible and, if possible, >1 km from young pine plantations.     

Relationship between respiratory depletion of sugars and loss of cold hardiness in coniferous seedlings over-wintering at raised temperatures: indications of different sensitivities of spruce and pine

Long-term effects of elevated winter temperatures on cold hardiness were investigated for Norway spruce (Picea abies L. Karst.), lodgepole pine (Pinus contorta Dougl.) and Scots pine (Pinus sylvestris L.). Two-year-old seedlings with the same pre-history of growth and cold hardening in the field were maintained from early December to late March at two field sites in northern Sweden and in a cold room. The temperatures at these locations averaged –13·5, –8·9 and 5·5°C, respectively. Following treatments, carbohydrate contents and cold tolerances were assessed. Needle respiration was also analysed during the 5·5°C treatment. Cold tolerance of lodgepole pine and Scots pine was much reduced following the 5·5°C treatment. Cold tolerance was somewhat reduced in lodgepole pine following the –8·9 °C treatment, but was essentially maintained in spruce throughout all treatments. The cold tolerance of needles was strongly correlated with their soluble sugar contents. Spruce maintained cold hardiness by having larger reserves of sugars and lower rates of respiration which decreased more rapidly as sugars were depleted. Tolerance of lodgepole pine to frost desiccation was also much reduced following the 5·5°C treatment.     

Uniform versus Asymmetric Shading Mediates Crown Recession in Conifers

In this study we explore the impact of asymmetrical vs. uniform crown shading on the mortality and growth of upper and lower branches within tree crowns, for two conifer species: shade intolerant lodgepole pine (Pinus contorta) and shade tolerant white spruce (Picea glauca). We also explore xylem hydraulics, foliar nutrition, and carbohydrate status as drivers for growth and expansion of the lower and upper branches in various types of shading. This study was conducted over a two-year period across 10 regenerating forest sites dominated by lodgepole pine and white spruce, in the lower foothills of Alberta, Canada. Trees were assigned to one of four shading treatments: (1), complete uniform shading of the entire tree, (2) light asymmetric shading where the lower 1/4–1/3 of the tree crown was shaded, (3) heavy asymmetric shading as in (2) except with greater light reduction and (4) control in which no artificial shading occurred and most of the entire crown was exposed to full light. Asymmetrical shading of only the lower crown had a larger negative impact on the bud expansion and growth than did uniform shading, and the effect was stronger in pine relative to spruce. In addition, lower branches in pine also had lower carbon reserves, and reduced xylem-area specific conductivity compared to spruce. For both species, but particularly the pine, the needles of lower branches tended to store less C than upper branches in the asymmetric shade, which could suggest a movement of reserves away from the lower branches. The implications of these findings correspond with the inherent shade tolerance and self-pruning behavior of these conifers and supports a carbon based mechanism for branch mortality – mediated by an asymmetry in light exposure of the crown.     

Boreal forest titans do not clash: low overlap in winter habitat selection by moose (<Emphasis Type="Italic">Alces americanus</Emphasis>) and reintroduced bison (<Emphasis Type="Italic">Bison bison</Emphasis>)

Despite moose (Alces americanus) likely being both an ecological and cultural keystone species in the North American boreal forest, few studies have examined niche overlap between moose and other ungulates. In response to concerns from local people about the potential for competition for habitat between moose and reintroduced bison (Bison bison), and the potential for disturbance to moose by bison and bison hunters, we investigated overlap in winter habitat selection by these species in southwestern Yukon, Canada. We used available geo-referenced data of animal locations, and associated environmental covariates, to develop resource selection probability function (RSPF) models of early-winter and late-winter habitat selection by moose and bison. In early-winter, moose selected sub-alpine shrub-dominated habitats, whereas bison extensively selected wet sedge meadows in lowland valleys. Both species used a greater variety of habitats in late-winter, with moose selecting drainages above tree line or river valleys with deciduous forest cover, while bison selected either south-facing grassy slopes or wet sedge meadows. Given observed differences in seasonal habitat selection between moose and bison, these species are predicted to overlap on only 0.5 and 6.6% of our 12,818-km² study area during early-winter and late-winter, respectively. The lack of demonstrated winter habitat overlap between moose and reintroduced bison, coupled with low diet overlap, points to an overall low potential for competition for winter habitat between these species, or for disturbance to moose attributable to bison or bison hunters. Resource partitioning that facilitates coexistence on a shared landscape suggests that concern over the impact of reintroduced bison on resident populations of moose is likely unwarranted.     

Establishment of

We compared establishment of Douglas fir (Pseudotsuga menziesii) and Corsican pine (Pinus nigra) seedlings in kanuka (Kunzea ericoides) and manuka (Leptospermum scoparium) shrubland to test the hypothesis that Douglas fir, because of its greater shade tolerance, is better able to establish in woody communities than pine species. Seed of the conifer species was sown under a range of canopy covers at six sites, the cover being low-statured vegetation in openings between stands, stand edges, and moderate and dense canopies. After three growing seasons, survival of Corsican pine seedlings was greatest in the open and declined progressively as canopy cover increased. This contrasted with Douglas fir, where survival was greatest at the canopy edge. Survival of Douglas fir seedlings significantly exceeded that of Corscican pine seedlings under dense canopy positions. Seedling numbers of both species declined significantly with increasing leaf area index of manuka, but not kanuka stands, where seedling numbers were lower. Leaf area index of manuka stands accounted for substantially greater variation in number and survival of Corsican pine than Douglas fir seedlings. It is concluded that Douglas fir is better able to establish in shaded environments in woody communities than Corsican pine; however, further monitoring is required to confirm the long-term survival of both species under the moderate and dense canopy positions in this trial.     

The effect of shoot growth stage of Pinus contorta and Pinus sylvestris on the growth and survival of Panolis flammea larvae

Summary Young Panolis flammea (Lepidoptera: Noctuidae) larvae were unable to survive on the mature (one-year old) needles of Pinus contorta and Pinus sylvestris. Larval growth and survival on the current year's shoots of the 2 pine host plants first incresed, and then decreased as pine shoot development progressed, the effect on survival being more marked at 10° C that 18° C. The survival of larvae on lodgepole pine on field-grown plants transferred to 10° C rose from 26% in March to 87% in mid May, and rose from 3% to 82% on Scots pine in the same period. Larval survival exceeded 70% for about 8 weeks on lodgepole pine and about 6 weeks on Scots pine, this period starting and ending earlier on lodgepole than on Scots pine. The nitrogen, water and phosphorus contents of both pines were at a maximum in May and decline gradually thereafter; the soluble tannin content showed a more complex pattern. These results are discussed in relation to the possible importance of phenological coincidence on the population dynamics of P. flammea with emphasis on its greater abundance on lodgepole pine in Scotland.     

Mining conifers’ mega-genome using rapid and efficient multiplexed high-throughput genotyping-by-sequencing (GBS) SNP discovery platform

Next-generation sequencing (NGS) technologies are revolutionizing both medical and biological research through generation of massive SNP data sets for identifying heritable genome variation underlying key traits, from rare human diseases to important agronomic phenotypes in crop species. We evaluated the performance of genotyping-by-sequencing (GBS), one of the emerging NGS-based platforms, for genotyping two economically important conifer species, lodgepole pine (Pinus contorta) and white spruce (Picea glauca). Both species have very large genomes (>20,000 Mbp), are highly heterozygous, and lack reference sequences. From a small set (six accessions each) of independent replicated DNA samples and a 48-plex read depth, we obtained ~60,000 SNPs per species. After stringent filtering, we obtained 17,765 and 17,845 high-coverage SNPs without missing data for lodgepole pine and white spruce, respectively. Our results demonstrated that GBS is a robust and suitable method for genotyping conifers. The application of GBS to forest tree breeding and genomic selection is discussed.     

Asynchrony in larval development of the pine beauty moth, Panolis flammea, on an introduced host plant may affect parasitoid efficacy

In the United Kingdom, Panolis flammea (Den. and Schiff.) (Lepidoptera: Noctuidae) is an important pest species of the introduced lodgepole pine but not of its natural host Scots pine. The timing of P. flammea larval growth must be synchronized with its host tree if the larvae are to succeed. We collected field data during 1990 which revealed that the phenological window starts earlier in Scots pine and is shorter than that observed in lodgepole pine. The larvae are found in the field earlier and within a narrower time frame within a Scots pine forest than in a lodgepole pine forest. The larval developmental period is significantly longer on lodgepole pine than on Scots pine. The synchrony/asynchrony of P. flammea to its natural host (Scots pine) and an introduced tree (lodgepole pine) results in the parasitoids having a different impact on the larvae of the two hosts. At any one time, the host plant, caterpillars and parasitoids are more synchronous on the ancestral Scots pine than on lodgepole pine, resulting in a higher percentage of larvae in the optimal instar for parasitism at that time. In lodgepole pine, the percentage of suitable instars available to parasitoids is lower at any given time. The information presented here furthers our understanding of the possible mechanisms for the observed differential population dynamics of the insect on Scots pine and lodgepole pine in the UK. Handling editor: Robert Glinwood.     

Reproductive development and maternal effects in the pine weevil Hylobius abietis

1. In a laboratory study of maturation feeding of female pine weevil Hylobius abietis on current and 1‐year‐old stem bark of transplants of Scots and Corsican pine, Norway and Sitka spruce, Douglas fir, and hybrid larch, the length of the pre‐oviposition period was influenced by the species on which weevils fed. The shortest pre‐oviposition period was on hybrid larch (11.8 days) and the longest on Douglas fir (15.5 days). 2. The species on which weevils fed also affected fecundity but there was evidence of a species–year interaction. Over a period of 36 days, most eggs were laid by weevils feeding on current stem of Norway spruce and Corsican and Scots pine and fewest on current stem of Sitka spruce. 3. Significant maternal effects on egg size were observed both in relation to female size and conifer species. The largest eggs were laid on Corsican pine and the smallest on Douglas fir, with no evidence of a trade‐off between number of eggs laid and their size. 4. There was a positive relationship between egg and larval size and between larval size and survival on logs of four conifer species. Residual resistance mechanisms in the bark of recently cut stumps and larval competition are discussed briefly in relation to the importance of the observed maternal effects on weevil population dynamics.     

What explains landscape patterns of tree mortality caused by bark beetle outbreaks in Greater Yellowstone?

Aim Bark beetle outbreaks have recently affected extensive areas of western North American forests, and factors explaining landscape patterns of tree mortality are poorly understood. The objective of this study was to determine the relative importance of stand structure, topography, soil characteristics, landscape context (the characteristics of the landscape surrounding the focal stand) and beetle pressure (the abundance of local beetle population eruptions around the focal stand a few years before the outbreak) to explain landscape patterns of tree mortality during outbreaks of three species: the mountain pine beetle, which attacks lodgepole pine and whitebark pine; the spruce beetle, which feeds on Engelmann spruce; and the Douglas‐fir beetle, which attacks Douglas‐fir. A second objective was to identify common variables that explain tree mortality among beetle–tree host pairings during outbreaks. Location Greater Yellowstone ecosystem, Wyoming, USA. Methods We used field surveys to quantify stand structure, soil characteristics and topography at the plot level in susceptible stands of each forest type showing different severities of infestation (0–98% mortality; n= 129 plots). We then used forest cover and beetle infestation maps derived from remote sensing to develop landscape context and beetle pressure metrics at different spatial scales. Plot‐level and landscape‐level variables were used to explain outbreak severity. Results Engelmann spruce and Douglas‐fir mortality were best predicted using landscape‐level variables alone. Lodgepole pine mortality was best predicted by both landscape‐level and plot‐level variables. Whitebark pine mortality was best – although poorly – predicted by plot‐level variables. Models including landscape context and beetle pressure were much better at predicting outbreak severity than models that only included plot‐level measures, except for whitebark pine. Main conclusions Landscape‐level variables, particularly beetle pressure, were the most consistent predictors of subsequent outbreak severity within susceptible stands of all four host species. These results may help forest managers identify vulnerable locations during ongoing outbreaks.