A host monoterpene influences Ips typographus (Coleoptera: Curculionidae,Scolytinae) responses to its aggregation pheromone

1 Host tree terpenes can influence attraction of conifer‐infesting bark beetles to their aggregation pheromones, and both synergistic and inhibitory effects have been reported. 2 We tested a gradient of ratios of (–)‐α‐pinene, the predominant monoterpene in Norway spruce, to the pheromone of Ips typographus, a major pest of Norway spruce. 3 Attraction of I. typographus increased as the release rate of (–)‐α‐pinene increased. The two highest (–)‐α‐pinene : pheromone ratios (526 : 1 and 2595 : 1) attracted twice as many I. typographus as pheromone alone, whereas low to intermediate ratios (56 : 1, 274 : 1) did not differ from pheromone alone. 4 Our results are in agreement with a proposed model, which suggests that bark beetles display unique response profiles to host terpenes depending on the physiological condition of the host trees that they typically colonize. Ips typographus, which is an aggressive species capable of colonizing and killing healthy trees, showed an increased attraction to monoterpene : pheromone ratios, and this may be high enough to inhibit attraction of less aggressive beetle species typically colonizing dead, dying or stressed trees. 5 Attraction of associates of I. typographus was also modified by (–)‐α‐pinene. Ips duplicatus, a competitor of I. typographus, showed increased attraction to the pheromone of I. typographus across all concentrations of (–)‐α‐pinene.     

Divergent growth responses of healthy and declining spruce trees to climatic stress: A case study from the Western Carpathians

Long-lived tree species optimize resource allocation processes, and there are likely trade-offs between the growth and response to environmental stressful conditions. The study aims to investigate the growth of healthy and declining Norway spruce trees using dendrochronological analysis. We have selected a natural high mountain spruce population and established 27 sampling plots in Poľana Mts. We measured 270 trees, from which we visually evaluated 133 individuals. Moreover, 51 trees were sampled for increment cores. Our study reveals thatspecific extreme combination of winter, spring and summer temperatures and precipitation sums within the particular year 1974 induced long-term growth divergence of neighboring spruce trees of comparable age and size and differentiated between healthy and declining (highly defoliated) trees. This period accounts for a decrease in size of relativized increments by 30.2% in declining trees compared to visually healthy individuals. Trees with a low ability to recover from climatic stress compensate the response to environmental conditions by lower growth rates. In high mountain temperate forests, the long-term growth decline of spruce trees last about 40 years. The single-tree selection silvicultural system should be preferred in high mountain conditions, where frequent small-scale, low-intensity disturbances drive stand dynamics. Trees showing low growth resilience to revealed combination of weather conditions should be preferentially removed from stands , especially within the transformation of even-aged spruce monocultures using selective cuttings.     

Ocular estimates of understory vegetation structure in a closed Picea glauca/Betula papyrifera forest

Abstract. Horizontal/vertical profiling is a method used to assess vegetation space occupancy. This study investigated consistency and repeatability of measurements made on plots designed to describe forest understory vegetation structure. 20 circular, 100‐m² plots were measured by six independent observers, three times during the summer of 1997. The plots, located in south‐central Alaska, were established in a closed Picea glauca (white spruce)/Betula papyrifera (paper birch) forest. Consistency and repeatability of measurements were evaluated by examining components of variance. Response variables were absolute and relative canopy cover. Results indicate that observers were not consistent relative to each other estimating vegetative cover from one plot to the next and from one measurement period to the next, making measurements unrepeatable.     

Picturing local adaptation: Spectral and structural traits from drone remote sensing reveal clinal responses to climate transfer in common-garden trials of interior spruce (Picea engelmannii × glauca)

Common-garden trials of forest trees provide phenotype data used to assess growth and local adaptation; this information is foundational to tree breeding programs, genecology, and gene conservation. As jurisdictions consider assisted migration strategies to match populations to suitable climates, in situ progeny and provenance trials provide experimental evidence of adaptive responses to climate change. We used drone technology, multispectral imaging, and digital aerial photogrammetry to quantify spectral traits related to stress, photosynthesis, and carotenoids, and structural traits describing crown height, size, and complexity at six climatically disparate common-garden trials of interior spruce (Picea engelmannii × glauca) in western Canada. Through principal component analysis, we identified key components of climate related to temperature, moisture, and elevational gradients. Phenotypic clines in remotely sensed traits were analyzed as trait correlations with provenance climate transfer distances along principal components (PCs). We used traits showing clinal variation to model best linear unbiased predictions for tree height (R² = .98–.99, root mean square error [RMSE] = 0.06–0.10 m) and diameter at breast height (DBH, R² = .71–.97, RMSE = 2.57–3.80 mm) and generated multivariate climate transfer functions with the model predictions. Significant (p < .05) clines were present for spectral traits at all sites along all PCs. Spectral traits showed stronger clinal variation than structural traits along temperature and elevational gradients and along moisture gradients at wet, coastal sites, but not at dry, interior sites. Spectral traits may capture patterns of local adaptation to temperature and montane growing seasons which are distinct from moisture-limited patterns in stem growth. This work demonstrates that multispectral indices improve the assessment of local adaptation and that spectral and structural traits from drone remote sensing produce reliable proxies for ground-measured height and DBH. This phenotyping framework contributes to the analysis of common-garden trials towards a mechanistic understanding of local adaptation to climate.     

Water holdup capacity and residence time of red spruce and balsam fir branches

Summary This study examined the throughfall dynamics of high-elevation red spruce (Picea rubens Sarg.) and balsam fir [Abies balsamea (L.) Mill.] branches. A site was established at an elevation of 1160 m on Mt. Washington, New Hampshire, USA, and branches were collected from the canopies of mature trees. Throughfall water dynamics of branches collected in September 1988 and March 1989 were determined using a fluorescent tracer in an artificial precipitation apparatus. Water holdup capacities of spruce and fir branches from different canopy positions were similar. Spruce retained more water per unit area than fir. For rain, a three-compartment model that was used to analyze water dynamics showed that the bulk of water initially on the branch experienced very slow turnover, while intercepted water left the branch quickly. There did not appear to be any difference in throughfall dynamics between spruce and fir. Our results suggest that the initial composition of rain and mobilized dry deposition will influence the composition of water in contact with the branch for a relatively long time, as branch water composition will respond slowly to changes in precipitation composition. These predictions require field testing where sequential sampling of throughfall and precipitation occurs on a time scale equivalent to 0.1–0.2 mm of precipitation.     

Segregation analysis of random amplified polymorphic DNA (RAPD) markers in Picea abies Karst.

The reliability of arbitrarily primed amplification products was tested. The segregation analysis of 266 amplification products obtained using 17 different 10-mer oligonucleotides in 34 megagametophytes from a single tree of Picea abies was carried out. Fifty-four out of the 165 variable bands fit the 1:1 segregation ratio expected for Mendelian traits. The segregation ratio of a subset of six RAPD markers in five other individuals from the same population confirmed their genetic nature. Our results strengthen the evidence previously reported that RAPDs markers can be considered Mendelian traits useful in the detection of genetic variability among both different individuals and populations.     

Larval experience induces adult aversion to rearing host plants: a novel behaviour contrary to Hopkins' host selection principle

1. Hopkins' host selection principle (HSP) states that insects should prefer foliage from their rearing host plant over that of an alternative host. 2. The current study tested whether eastern spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), that were laid and developed on, respectively, resistant and susceptible white spruce Picea glauca (Moench) Voss, showed differences in their feeding and oviposition preferences for these two hosts. 3. The data revealed that previous experience of spruce budworm on a host tree type does not influence the host acceptance and feeding behaviour of later larval stages. However, adult budworm reared on resistant white spruce needles preferentially selected susceptible white spruce needles as the host for their progeny, whereas those reared on susceptible needles showed no preference. 4. To the authors' knowledge, this is the first report of an insect showing an oviposition preference for the non‐rearing host plant. This would tend to increase mixing between insects from susceptible and resistant trees. The present results thus argue against Hopkins' HSP and suggest that learned aversion to resistant foliage experienced by larvae is carried into the adult stage.     

Characterization of tree macroremains production in a recently burned conifer forest in northern Québec,Canada

The production of plant macroremains was studied in a conifer forest twomonths after it burned in 1996 in northern Québec. The proportions ofvarious types of charred and uncharred pieces (needles, cones andwood) produced by black spruce (Piceamariana) and jack pine (Pinusbanksiana) were determined by sampling around individual trees.Both species produced equivalent masses of charred material, but pieces of woodcharcoal from jack pine are generally larger that those of black spruce. Theproportion of charred versus uncharred needles is the bestindicator of the species dominance in the forest. Although the fall of uncharredneedles is delayed from the time of a fire, they contribute to more than half ofall remains produced. Jack pine cones remain on the tree for a long time after afire, while charred cones of black spruce are dehiscent (cones come off thebranches easily). Trees are poor wood charcoal producers compared toundergrowth shrubs. As a result, the macroremains assemblage associated with afire event is made up of large amount of uncharred material from trees and alarge proportion of charred pieces produced by undergrowth vegetation. Modernassemblages of plant macroremains indicate that in order to reconstruct pastvegetation associated with fire disturbance, it is important to distinguishbetween the various types of remains, because wood charcoal is mainly producedby material that is already dead.