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The ongoing loss of red‐listed coastal heathlands is a threat to biodiversity and cultural heritage legacies throughout the Atlantic coastal regions of Europe. It is possible to restore degraded and afforested heathlands, but restoration interventions are often labour‐intensive and costly, and the outcome of specific restoration actions are not well documented. We assess the efficiency of restoring coastal heathlands through natural succession (i.e. 'passive restoration') after removal of Sitka spruce Picea sitchensis (Bong.) Carr. plantations. The study was replicated on two neighbouring islands in a nature reserve in Western Norway. Low‐intensity free‐range sheep grazing was implemented as part of the reserve management plan. Furthermore, we tested the effect of leaving the clear‐felled woody material as chips on site, this being a cost‐efficient strategy on islands. Succession was monitored 1, 2, 4/5 and 8 years after clear‐felling, and revegetation of vascular plants and bryophytes was compared to target heathland vegetation. Surprisingly, we found different successional trajectories on the two islands. Species composition on one island approached target heathland vegetation during succession, but not on the other. Wood chips reduced species richness and slowed the restoration process, but these negative effects were only short‐term (<8 years). Differences in seed bank composition and soil conditions due to land use may explain the deviating successional trajectories on the two islands. We also found that management actions beyond clear‐felling and introducing sheep grazing are necessary due to the rapid seed regeneration of the Sitka spruce. [ABSTRACT FROM AUTHOR]

Sitka spruce (Picea sitchensis) needles contain a variety of bioactive compounds including phenolic compounds and flavonoids, many of which have been used in the cosmetic, pharmaceutical, and food industries. This study aimed to investigate the effects of novel extraction techniques, including ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE) and simultaneous ultrasound-microwave-assisted extraction (UMAE) on the recovery of phenolic, flavonoids and associated antioxidant and anti-cancer properties from Sitka spruce (Picea sitchensis) needles. The ferric reducing antioxidant power (FRAP) assay was used to evaluate the antioxidant capacity, and the Alamar Blue assay using the human brain glioblastoma cancer cellline (U-251 MG) was used to evaluate the cytotoxicity activity. Results showed that US-probe accomplished the highest recovery of phenolic and flavonoids at 38 W cm-2 for 10 min (106.3 f 2.5 mg GAE g-1 DW and 63.2 i 3.8 mg QE g-1 DW, respectively). Hence, the highest cytotoxicity activity of IC5O (0.0114% w/v) was achieved by US-probe at 19 W cm-2 for 10 min. However, the antioxidant capacity of (2591.3 f 92.5 mM TE g-1 DUO was achieved under UMAE at ultrasound intensity of 38 W cm-2, microwave power of 302.4 W for 10 min. This study emphasised the potential application of UAE and MAE in the extraction of bioactive as an environmentally friendly method to be used in the valorisation of by-products in food and agro-industries. This supports the use of renewable natural resources in an efficient way to produce high-value compounds therefore it is in line with the new era of bioeconomy and its new biorefinery concepts. [ABSTRACT FROM AUTHOR]

In UK forestry, the synthetic pyrethroid insecticides alpha-cypermethrin and cypermethrin have been used for many years to provide protection for young trees from damage by the large pine weevil, Hylobius abietis L. However, concerns over the toxicity of these insecticides has led to a search for alternatives. In our work, applications of 0.037 g.a.i.stem–1 acetamiprid provided high levels of protection from Hylobius browsing, comparable to alpha-cypermethrin or cypermethrin, and without causing phytotoxicity. However, re-application is likely to be required in the second growing season after planting. Our research identified that acetamiprid treated trees can be safely cold stored as part of normal nursery practice. Acetamiprid is less toxic than synthetic pyrethroids. We also found that pre-treating trees with 0.016 g.a.i.stem–1 chlorantraniliprole, a relatively low toxicity insecticide, can be equally effective in protecting trees, and that dye markers can be safely used to help target spays. Our testing of physical barriers such as MultiPro®, and to a lesser extent Kvaae® wax, suggests they may have a role as a partial substitute for the use of insecticides in some circumstances in the UK and Ireland, but only as part of an integrated approach where on-site populations of Hylobius are predicted to be low. [ABSTRACT FROM AUTHOR]

The hypothesis that similar processes govern interannual dynamics of green spruce aphid in the UK and France, is generally supported by the application of a general discrete model. A simple model based on relatively few parameters was able to closely characterise interannual population dynamics from completely independent aerial and arboreal samples of aphids. Long‐term field population estimates of the green spruce aphid Elatobium abietinum (Walker) in France have provided the opportunity to select and evaluate the generality of a model, which was developed in the UK to explain the year‐to‐year variations in peak abundance of the aphid. The objective was to observe the influence of the local climates and disturbing climate factors on the population densities of the insect in two regions of France. The model uses climate variables and aphid population data from regular samples in the two regions that were investigated. A general discrete model was used to predict aphid population densities. The model performed well in tracking the interannual patterns of population but was less likely to predict absolute population density. To improve predictions, further account would need to be taken of additional site‐specific climate variables and the strength of overcompensating density dependence. Nevertheless, it is clear that broadly similar processes are at work in the population dynamics of this insect across its biogeographical range. [ABSTRACT FROM AUTHOR]

Context: Western Olympic valley bottoms, disturbed by alluvial processes, are dominated by Picea sitchensis and isolated cohorts of Pseudotsuga menziesii, while upland contexts, disturbed by wind and fire, are dominated by P. menziesii. These forests have distinct structure and produce large trees with habitat for endangered birds. Objectives: Describe how disturbance and forest development create landscape forest patterns and distribution of large trees in valley bottom and upland forests. Methods: LiDAR data of ~ 9700 ha within Olympic National Park, USA was classified based on vegetation height and percent cover to contrast valley bottom and upland forests. Within-crown structure from 36 P. sitchensis and 12 P. menziesii was then used to predict locations of the largest and most complex trees. Results: Valley bottoms comprise small patches of dense tall (11%), medium-height trees (19%), and gaps (7%) embedded in open-canopy forest with scattered tall trees (63%). Upland forests comprise larger patches of tall (16%), medium (58%), and open-canopy forest (25%) with few gaps (1%). The largest trees are more abundant in valley bottoms (0.05 tree ha−1) than upland (0.02 tree ha−1) due to small patches of tall trees within open-canopy forest. Conclusions: Alluvial disturbance, fungi-wind interaction, and dominance of late-successional fast-growing P. sitchensis create open-canopy forest with more large trees, while severe fire and wind interacting with P. menziesii create patchy closed-canopy forest with fewer large trees. Management for large habitat trees should use aggregated retention with P. menziesii, multi-aged selection techniques with P. sitchensis, and indefinitely retain a low density of large trees. [ABSTRACT FROM AUTHOR]

Soil warming (0–5.5 °C above controls) effects on ectomycorrhizal growth, carbon sequestration and community composition were examined in a Picea sitchensis forest spanning a geothermal gradient in Iceland. Fungal communities were assayed with sand-filled ingrowth meshbags incubated in the soil for 5 months. Meshbags amended with compost made from maize leaves (a C4 plant enriched in 13C) were incubated for 5 or 12 months and used to estimate C sequestration by the fungal community. Despite increases in tree growth, moderate warming only slightly reduced or had no effect on mycelial growth and had no effect on fungal carbon sequestration or overall ectomycorrhizal community composition. Warming was associated with increased abundance of ascomycetes, particularly pyronemataceous ectomycorrhizal fungi, and altered saprotrophic community composition. Increased nitrate availability and root turnover may explain the lack of a positive ectomycorrhizal growth response to increased tree growth and observed shifts in community composition with warming. [ABSTRACT FROM AUTHOR]

Summary: Tree species in the northern hemisphere are currently subject to rapid anthropogenic climate change and are shifting their ranges in response. This prompts questions about the mechanisms allowing tree populations to respond quickly to selection pressures when establishing into new areas. Focusing on the northern expanding range edge of Picea sitchensis, a widespread conifer of western North America, we ask how genetic structure and diversity develop during colonization, and assess the role of demographic history in shaping the evolutionary trajectory of an establishing population.We combined 500 yr of tree‐ring and genotyping‐by‐sequencing data in 639 trees at the expansion front on the Kodiak Archipelago.We show that alleles accumulated rapidly during an increase in recruitment rate in the early 1700s. A shift from foreign to local pollen flow subsequently homogenized genetic structure at the expansion front.Taking advantage of the exceptional longevity of conifers, we highlight the major role of long‐distance pollen dispersal in the rapid but incomplete recovery of genetic diversity during the initial stages of colonization. We also warn that slow initial population growth as well as long‐lasting dominance of local gene flow by early founders could increase evolutionary load under a rapidly changing climate. [ABSTRACT FROM AUTHOR]

Global warming is predicted to impact high-latitude and high-altitude forests severely, jeopardizing their overall functioning and carbon storage, both of which depend on the warming response of tree fine root systems. This paper investigates the effect of soil warming on the biomass, morphology and colonizing ectomycorrhizal community of spruce fine and absorptive fine roots. We compare the responses of spruce roots growing at a man-made long-term soil warming (+ 4°C) experiment to results obtained from a geothermal soil temperature gradient (+ 1 to + 14°C) extending to the forest die-off edge, to shed light on the generalizability of the warming response and reveal any thresholds in acclimation ability. Trees in warmer soils formed longer and less-branched absorptive roots with higher specific root length and area, and lower root tissue density in both spruce stands, irrespective of warming method and location. Soil warming at the experimental warming site also supported the occurrence of a more varied EcM community and an increase in the abundance of Tomentella spp., indicating a shift in nutrient foraging. Fine and absorptive fine root biomass decreased toward warmer soil, with a sharp reduction occurring between + 4 and + 6°C from the ambient and leading to the collapse of the fine root system at the geothermal gradient. At the experimental warming site, the applied + 4°C warming had no effect on fine and absorptive fine root biomass. The similar fine root responses at the two warming sites suggest that the observations possibly reflect general acclimation patterns in spruce forests to global warming. [ABSTRACT FROM AUTHOR]

Preserving biodiversity in remaining old-growth forests is a high priority for many land managers. To this end, we inventoried the diversity, abundance, and distribution of epiphyte species in one 318-year-old, 86 m tall Picea sitchensis tree on the north coast of California. In 39 plots, we recorded species present and mean percent cover for each species. Our findings include the following: 1) 68 epiphyte species were found in this one tree; 2) epiphyte diversity increased with height; 3) lichens had the highest diversity of all epiphyte classes; and 4) mosses had the highest percent cover of all epiphyte classes. These findings highlight the capacity for old trees to serve as reservoirs of biodiversity in younger forests. [ABSTRACT FROM AUTHOR]

Summary: Conifers depend on complex defense systems against herbivores. Stone cells (SC) and oleoresin are physical and chemical defenses of Sitka spruce that have been separately studied in previous work.Weevil oviposit at the tip of the previous year's apical shoot (PYAS). We investigated interactions between weevil larvae and trees in controlled oviposition experiments with resistant (R) and susceptible (S) Sitka spruce. R trees have an abundance of SC in the PYAS cortex. SC are mostly absent in S trees. R trees and S trees also differ in the composition of oleoresin terpenes. Transcriptomes of R and S trees revealed differences in long‐term weevil‐induced responses.Performance of larvae was significantly reduced on R trees compared with S trees under experimental conditions that mimicked natural oviposition behavior at apical shoot tips and may be attributed to the effects of SC. In oviposition experiments designed for larvae to feed below the area of highest SC abundance, larvae showed an unusual feeding behavior and oleoresin appeared to function as the major defense.The results support a role for both SC and oleoresin terpenes and possible synergies between these traits in the defense syndrome of weevil‐resistant Sitka spruce. [ABSTRACT FROM AUTHOR]

Premise of the study: Leaves are the sites of greatest water stress in trees and a key means of acclimation to the environment. We considered phenotypic plasticity of Pseudotsuga menziesii leaves in their ecological context, exploring responsiveness to natural gradients in water stress (indicated by sample height) and light availability (measured from hemispherical photos) to understand how leaf structure is controlled by abiotic factors in tall tree crowns. Methods: After measuring anatomy, morphology, and carbon isotope composition (δ13C) of leaves throughout crowns of P. menziesii >90 m tall, we compared structural plasticity of leaves among the three tallest conifer species using equivalent data from past work on Sequoia sempervirens and Picea sitchensis. Key results: Leaf mass per projected area (LMA) and δ13C increased and mesoporosity (airspace/area) decreased along the water‐stress gradient, while light did not play a detectable role in leaf development. Overall, leaves of P. menziesii were far less phenotypically responsive to within‐crown abiotic gradients than either P. sitchensis, whose leaves responded strongly to light availability, or S. sempervirens, whose leaves responded equally strongly to water stress. Conclusions: P. menziesii maintain remarkably consistent leaf structure despite pronounced vertical gradients in abiotic factors. Contrasting patterns of leaf structural plasticity underlie divergent ecological strategies of the three tallest conifer species, which coexist in Californian rainforests. [ABSTRACT FROM AUTHOR]

Abstract: The European spruce bark beetle Ips typographus is a damaging pest on spruce in Europe. Beetle interactions with tree species originating outside the natural range of the beetle are largely unknown and may be unpredictable because trees without a co‐evolutionary history with the beetle may lack effective defences. The terpenoid composition and breeding suitability for I. typographus of the historic host Norway spruce Picea abies were compared with two evolutionary naïve spruces of North American origin that are extensively planted in North‐West Europe: Sitka spruce Picea sitchensis and Lutz spruce Picea glauca x lutzii. The bark of all three species had a similar chemical composition and similar levels of total constitutive terpenoids, although Norway spruce had higher total induced terpenoid levels. Beetles tunnelling in the three spruce species produced similar amounts of aggregation pheromone. Controlled breeding experiments showed that I. typographus could produce offspring in all three species, with a similar offspring length and weight across species. However, total offspring production was much lower in Sitka and Lutz spruce. Overall, the results of the present study suggest that I. typographus will be able to colonize Sitka and Lutz spruce in European plantations and in native spruce forests in North America if introduced there. [ABSTRACT FROM AUTHOR]

A wide range of Sitka spruce breeding material ( Picea sitchensis (Bong.) Carr.) was assessed for its ability to respond to somatic embryogenesis (SE) and cryo-preservation methods, with 765 cell lines being established from seeds taken from the UK's breeding population for testing with the relevant methodologies. Cell lines were most readily established from immature seeds (63%) on a proliferation medium originally developed for white spruce ( P. glauca) with agar as the gelling agent. However, it was also found that 48% of the zygotic embryos taken from freshly harvested mature seed were also able to establish cell lines on the same medium, as were 20% of seeds that had been stored at −20 °C for up to 8 years. Most of the cell lines tested (57%) produced significant numbers of somatic embryos, but the rate at which they could be germinated into plants capable of surviving the transfer to nursery conditions varied considerably from 67 to 8% between years for reasons that were not clear. The ability of the cell lines to survive cryo-preservation was also assessed, and out of 199 cell lines tested, 45 cell lines from 21 breeding families were successfully established in a cryo-storage facility. The best rates of recovery were obtained when Phytagel was used in the medium for growing the samples before and after they were cryo-preserved. [ABSTRACT FROM AUTHOR]

The impact of bark-stripping by red deer on an 1825 ha plantation ofPicea sitchensisis reported. Monitoring began in 1978 with initially 6500 trees at 37 sites; by 2014, only 10 sites remained due to felling. Sites became vulnerable to bark-stripping once the trees reached 7 years’ age, and from then until felling at age c. 45 years, incidence rates averaged 1% of the trees damaged yearly. Intense damage at a site in a year (>2% trees damaged) was often followed by intense damage next year, but, on average, 53% of sites were undamaged in a year. Many trees suffered repeat wounding, which reduced final impact by c. 30% compared to the theoretical impact calculated from annual damage and damage duration. The trees bark-stripped were on average smaller than plot mean girths once these means exceeded 20 cm; this had only a minor effect on the final impact since bark-stripped small trees had similar mortality to undamaged small trees. Most wounds (>90%) were small (<180 cm2) and healed quickly, so were unlikely to develop decay. Larger wounds never healed in less than 8 years, but the proportion healed increased progressively from 10 to 20 years after wounding. [ABSTRACT FROM AUTHOR]

White pine weevil (Pissodes strobi, Peck.) is a native forest insect pest in the Pacific Northwest of North America that attacks species of spruce (Picea spp.) and pine (Pinus spp.). Young Sitka spruce [Picea sitchensis (Bong.) Carr.] trees are particularly susceptible to weevil attack. Pockets of naturally occurring Sitka spruce resistance have been identified in high weevil hazard areas in coastal British Columbia. In this study, we characterize behavioral, physiological and reproductive responses of weevils to an extremely resistant Sitka spruce genotype (H898) in comparison to a highly susceptible genotype (Q903). The experiments relied on a large number of three-year-old clonally propagated trees and were therefore restricted to two contrasting Sitka spruce genotypes. When exposed to resistant trees, both male and female weevils were deterred during host selection and mating, females showed delayed or reduced ovary development, and successful reproduction of weevils was prevented on resistant trees.

• Invertebrate predators were sampled below and in the canopy of Sitka spruce. • Predators varied in their response to stand management. • Total predator abundance was similar in clear-cut and continuous cover stands. • Species richness and H' diversity were higher in continuous cover stands. Invertebrate predators of aphids were sampled at ground level and in the canopy in 13 even-aged Sitka spruce Picea sitchensis forest stands managed by clear-cutting and replanting, and in 11 Sitka spruce stands managed as continuous cover forestry using either shelterwood or group selection silvicultural systems. The expectation was that stands managed using shelterwood or group selection systems would support a greater abundance and diversity of invertebrate predators, because of their more complex internal structure, but results were mixed. Hoverflies (Syrphidae), predatory bugs (Hemiptera), ladybird beetles (Coccinellidae) and spiders (Araneae) were more abundant in shelterwood and group selection stands, but soldier beetles (Cantharidae), lacewings (Neuroptera) and harvestmen (Opiliones) were more abundant in mid-rotation and mature even-aged stands, and vespid wasps (Vespidae) showed a similar abundance across all stand types. In contrast, species richness and diversity of the insect predator groups were higher in shelterwood and group selection stands, even for groups that were less abundant in those stands. It was not clear, however, whether the greater species richness of insect predators in shelterwood and group selection was the result of these stands supporting breeding populations of a wider range of species, including less common species, or was because the more open structure of these stands allowed introgression of species from other habitats within the forest. [ABSTRACT FROM AUTHOR]

Climate change in the UK is predicted to cause an increase in summer drought events. Elatobium abietinum is an important pest of Sitka spruce (Picea sitchensis), causing defoliation of trees, and is predicted to become more abundant in response to climatic change, reducing spruce productivity. Populations are also moderated by invertebrate predators, though the extent to which this might be modified under a changing climate is unclear. Elatobium abietinum is preyed upon by the coccinellid species Aphidecta obliterata (a spruce specialist) and Adalia bipunctata (a generalist), populations of which naturally occur in spruce plantations. This study sought to investigate the effect of different intensities and frequencies of drought on the consumption rate of the aphids by the two coccinellids. In Petri dish trials, severe drought stress increased the consumption rates of 3rd instar aphids by both adult and larval coccinellids. Moderate intermittent stress tended to result in a reduced consumption rate for larval coccinellids only, suggesting an age-dependent response. The findings of this study suggest that, under drought conditions, a prey-mediated effect on predator consumption, and, therefore, biocontrol efficacy, is likely, with drought intensity and frequency playing an important role in determining the nature of the response. [ABSTRACT FROM AUTHOR]

Six juvenile Sitka spruce ( Picea sitchensis (Bong.) Carr) clones were grown in monoclonal (pure) and polyclonal mixtures (mixed) in a field experiment to assess effects of clonal diversity on above- and below-ground growth, biomass partitioning and fine root morphology. Shoot height and root collar diameter were measured twice annually and after the second year 48 clones were destructively harvested. Fine roots were divided into 10 diameter classes, for each of which morphological characteristics were calculated from digitized images. Competitive interactions arising from deployment type were found to significantly increase fine root surface area in mixed plots and fine root length in pure plots for two fine root diameter classes for some clones. Competitive interactions were also found to significantly alter relationships between above- and below-ground variables and reduce the strength and significance of relationships among root traits in mixed plots. Significant inter-clonal variation for many above- and below-ground parameters was also observed. The two most productive clones, in terms of height and diameter growth, differed significantly in biomass partitioning suggesting that a high degree of variation occurs among Sitka spruce clones, which may affect stand productivity and uniformity. [ABSTRACT FROM AUTHOR]

Temperate forest 15N isotope trace experiments find nitrogen (N) addition-driven carbon (C) uptake is modest as little additional N is acquired by trees; however, several correlations of ambient N deposition against forest productivity imply a greater effect of atmospheric nitrogen deposition than these studies. We asked whether N deposition experiments adequately represent all processes found in ambient conditions. In particular, experiments typically apply 15N to directly to forest floors, assuming uptake of nitrogen intercepted by canopies ( CNU) is minimal. Additionally, conventional 15N additions typically trace mineral 15N additions rather than litter N recycling and may increase total N inputs above ambient levels. To test the importance of CNU and recycled N to tree nutrition, we conducted a mesocosm experiment, applying 54 g N/15N ha−1 yr−1 to Sitka spruce saplings. We compared tree and soil 15N recovery among treatments where enrichment was due to either (1) a 15N-enriched litter layer, or mineral 15N additions to (2) the soil or (3) the canopy. We found that 60% of 15N applied to the canopy was recovered above ground (in needles, stem and branches) while only 21% of 15N applied to the soil was found in these pools. 15N recovery from litter was low and highly variable. 15N partitioning among biomass pools and age classes also differed among treatments, with twice as much 15N found in woody biomass when deposited on the canopy than soil. Stoichiometrically calculated N effect on C uptake from 15N applied to the soil, scaled to real-world conditions, was 43 kg C kg N−1, similar to manipulation studies. The effect from the canopy treatment was 114 kg C kg N−1. Canopy treatments may be critical to accurately represent N deposition in the field and may address the discrepancy between manipulative and correlative studies. [ABSTRACT FROM AUTHOR]

• Monospecific stands were more resilient than intimate mixtures to spring drought. • P. sylvestris was more resistant and resilient than P. sitchensis to spring drought. • Neighbourhood competition was not associated with drought resistance, recovery or resilience. Understanding how we can increase the resilience of forest systems to future extreme drought events is increasingly important as these events become more frequent and intense. Diversifying production forests using intimate mixtures of trees with complementary functional traits is considered as one promising silvicultural approach that may increase drought resilience. However, the direction and magnitude of the drought response of mixed-species stands relative to monospecific stands of the same species can vary with species identity, relative abundance and levels of competition in a focal tree's immediate neighbourhood. Using a long-term experiment where tree-level mortality and the neighbourhood composition of each tree was known, we assessed the radial growth response of 24-year-old Scots pine (Pinus sylvestris) and Sitka spruce (Picea sitchensis) trees in intimately mixed and monospecific stands to a short-duration, high-intensity spring drought in Scotland. Mixing proportions included 25:75, 50:50 and 75:25 of P. sylvestris and P. sitchensis. At the species level, Scots pine was more drought resistant and resilient than Sitka spruce, while Sitka spruce showed higher recovery. Surprisingly, neither pre-drought tree size nor neighbourhood competition were significantly associated with resistance or resilience to drought, and trees of both species within monospecific stands showed higher recovery and resilience than trees growing in mixed stands. Our study suggests intimate mixtures of these two species may not be an effective way to mitigate the negative impacts of future extreme spring drought events. Given that these two species comprise almost 70% of coniferous forests in the UK, our results highlight the pressing need to better understand their vulnerability to drought and the conditions under which intimate mixtures of these species could be beneficial or detrimental. Such knowledge is essential if we are to enable forest managers to effectively plan how to adapt these forests to the challenges of a changing climate. [ABSTRACT FROM AUTHOR]

Elatobium abietinum (Walker) is the most important defoliating pest of Sitka spruce Picea sitchensis (Bong.) Carr. Climate change in the U.K. is predicted to increase incidences of spring-summer drought events, with the aphid expected to respond to these changes. This will have serious implications for damage levels and growth of infested Sitka spruce, as well as control of the aphid pest., Under controlled laboratory conditions, nymphal survival rate, lifespan and generation time of E. abietinum were examined in time-staggered trials during the spring and autumn periods of population growth, using five levels of drought with differing frequencies and magnitude., Survivorship and lifespan were unaffected by drought stress compared with a well-watered control. Generation time, however, was increased under severe continuous and high amplitude intermittent drought stress. Advancement of Sitka spruce dormancy was not supported as no differences between the autumn trials were observed for the three parameters., The findings of the present study suggest that, under severe water deficit, populations of E. abietinum may be reduced as a result of a reduced period of time available for reproduction. This has implications for the population development of E. abietinum and, consequently, damage levels and growth reductions of host Sitka spruce under altered climatic conditions. [ABSTRACT FROM AUTHOR]

The most important defoliating pest of Sitka spruce Picea sitchensis in the U.K. is the green spruce aphid Elatobium abietinum. This aphid species is expected to respond to a predicted increase in the incidence of spring-summer drought events, with serious implications for growth of infested spruce plants and control of the pest., Growth rate, adult weight and nymph weight of E. abietinum were assessed under controlled laboratory conditions, using five levels of spring-summer drought of differing intensities and frequencies. Trials were time-staggered to investigate changes through season., Growth rate, adult weight and nymph weight were consistently increased under low amplitude intermittent drought stress, suggesting improved host nutritional quality through the year and increased fecundity., A complex response under severe and low amplitude intermittent drought stress was also observed, mediated by season. Although an overall reduction in host quality was typically observed, continuous severe stress improved host quality during the autumn. Despite this, the onset of dormancy was unaffected., The findings of the present study have implications for E. abietinum population development, Sitka spruce growth and biological control of the species under climate change and increased drought frequency. [ABSTRACT FROM AUTHOR]

Picea sitchensis (Bong.) Carrière (one- and two-year-old needles) and Pinus sylvestris L. (one-year-old needles), were tested for their capacity to accumulate particulate matter (PM) on the leaf surface or in waxes on the leaf surface. Element accumulation on needle surfaces was also analyzed. Sampling was carried out at four distances from a heavily trafficked road in South Western Norway in October 2012. P. sitchensis accumulated a higher quantity of coarse PM compared to P. sylvestris. Deposition of all fractions of PM increased with time, with largest amounts on two-year-old as compared to one-year-old needles of P. sitchensis . Surface content of 14 out of 25 analyzed elements were highest in P. sitchensis compared to P. sylvestris . A higher accumulation of coarse PM and elements therein (in 14 of 25 elements), was observed in samples taken closest to the road as compared to those from greater distances. [ABSTRACT FROM AUTHOR]

Climate change in the UK is predicted to cause an increase in summer drought events. Elatobium abietinum is an important pest of Sitka spruce (Picea sitchensis), causing defoliation of trees, and is predicted to become more abundant in response to climatic change, reducing spruce productivity. Populations are also moderated by invertebrate predators, though the extent to which this might be modified under a changing climate is unclear. Elatobium abietinum is preyed upon by the coccinellid species Aphidecta obliterata (a spruce specialist) and Adalia bipunctata (a generalist), populations of which naturally occur in spruce plantations. This study sought to investigate the effect of different intensities and frequencies of drought on the consumption rate of the aphids by the two coccinellids. In Petri dish trials, severe drought stress increased the consumption rates of 3rd instar aphids by both adult and larval coccinellids. Moderate intermittent stress tended to result in a reduced consumption rate for larval coccinellids only, suggesting an age-dependent response. The findings of this study suggest that, under drought conditions, a prey-mediated effect on predator consumption, and, therefore, biocontrol efficacy, is likely, with drought intensity and frequency playing an important role in determining the nature of the response.

Pine plantations are prone to stem breakage due to high cyclic stress levels associated with hurricane force winds. Stress analytical and finite element simulation models were constructed of a representative profile of a (Sitka) Picea sitchensis tree. The profile surface stress (S) was determined due to the combined load of tree self-weight and hurricane wind speed. The results were complemented by reference to two other studies by other researchers that investigated the impact of fatigue cycles on failure (N) of pine wood and tree sway cycles to present a stem fatigue life prediction. The position of maximum surface profile stress and trunk fracture initiation location was ascertained from a non-uniform stress response. No stress uniformity along the trunk profile was observed for any wind-load case examined. The analytical model and finite element analysis of the P. sitchensis tree trunk profile revealed a statically adequate strength reserve factor of 1.4, which suggested another mode of failure was responsible. Fatigue life failure prediction was examined under cyclic and same-stress amplitude related to the hurricane wind speed of 33 m s-1. Predicted trunk fracture occurred in 2.6 hours, which dramatically reduced to two minutes with an increase in wind speed of only 1 m s-1. The calculated exposure time was similar to that recorded during Hurricane Hugo's transit in 1989. The time-to-failure prediction obtained by the method of analysis provided in this study seemed plausible, and that the profile associated with the P. sitchensis tree would suffer trunk breakage by low cycle fatigue failure. [ABSTRACT FROM AUTHOR]

The green spruce aphid, Elatobium abietinum, is the most important defoliating pest of Sitka spruce, Picea sitchensis, in the UK. Populations are expected to increase in response to predicted climate change, therefore placing Sitka spruce under increased risk of widespread and severe defoliation. The effect of spring-summer drought stress on E. abietinum population dynamics and development over multiple years was assessed in a field experiment under five different drought treatments with differing intensities and frequencies. The impact on host tolerance, in terms of needle retention, was also investigated. No differences in the length of time taken to reach peak population size were observed. Despite this, E. abietinum populations were found to respond positively to low amplitude intermittent stress, with high densities maintained for longer after the peak. Spring peak densities of aphids did not differ among drought levels, although an autumn peak was observed consistently over 2 years on trees subjected to continuous severe drought. This suggested advancement in the onset of Sitka spruce dormancy. Aphid infestation significantly increased percentage needle loss under all drought treatments, although no differences were observed between drought levels. An interaction between aphid presence and drought treatment was, however, observed during a second year of drought where no aphids were present. The study herein presented has contributed to the understanding of E. abietinum population responses under a changing climate. The implications for damage to host Sitka spruce are of relevance to forest management strategies, as an increase in drought events are predicted in the UK. [ABSTRACT FROM AUTHOR]

Invasion by non-native conifers may pose a threat to local biodiversity, but knowledge about introduced conifer effects on Northern Hemisphere ecosystems is scarce. The coastal heathlands of north-west Europe are threatened by invasion of native and introduced tree species. We assess how spread of the introduced conifer Sitka spruce ( Picea sitchensis (Bong.) Carr.) into European coastal heathlands affect two major functional groups; vascular plants and bryophytes, and how these effects relate to the environmental changes imposed by the developing tree canopies. We compared the impact of introduced Sitka spruce and native Scots pine ( Pinus sylvestris L.) by analysing effects on species richness and turnover of vascular plants and bryophytes along fine-scale transects from individual tree stems into open heathland vegetation. Environmental impacts were assessed by measured environmental variables, and the responses of the two species groups were assessed by calculating changes in their respective mean Ellenberg indicator values. Species richness decreased beneath both conifers, related to decreased light and increased nitrogen and pH. Whereas vascular plants responded negatively to poor light conditions beneath dense and low Sitka spruce canopies, bryophytes were more negatively affected by the warmer and drier microclimates beneath Scots pine. Introduced Sitka spruce impacts the sub-canopy environment differently from the native Scots pine, and the two functional plant groups responded differently to these impacts. This suggests that future forests are likely to differ in species richness and composition, depending on whether succession is based on native or introduced coniferous trees. [ABSTRACT FROM AUTHOR]

Questions What are the effects of conifer invasion on plant species composition and richness of coastal heathlands; do effects differ between heathlands invaded by introduced or native coniferous tree species? Location Threatened coastal Calluna heathlands, western Norway. Methods We compared the effects of invasion by introduced Sitka spruce ( Picea sitchensis (Bong.) Carr.) and native Scots pine ( Pinus sylvestris L.) on heathland plant communities by focusing on the local impacts of single coniferous tree canopies. For each of 58 target coniferous trees (2-4-m tall), 2-m transects were laid out in a north and south orientation from the tree stem to beyond the tree canopy, and control transects were laid out in open heathland adjacent to the target trees. Vascular plants and bryophytes were recorded within 0.0625 m2 contiguous quadrats along the transects. Principal response curves ( PRC) and generalized linear mixed models ( GLMMs) were used to investigate tree canopy effects on species composition and richness. Results Invasion by coniferous trees induced considerable changes in the coastal heathland vegetation: distinct microcommunitites developed beneath the canopies of relatively young, single coniferous trees in the heathlands. There was a marked difference in subcanopy species composition under the introduced Sitka spruce relative to the native Scots pine; forest floor species had colonized to a greater extent under Sitka spruce, replacing the light-demanding species characteristic of the coastal heathland vegetation. Conclusion Our study showed that conifer invasion induces considerable and rapid changes in heathland vegetation, and that the effects were stronger under the introduced conifer. This suggests that Sitka spruce invasion may pose a more immediate threat to the characteristic coastal heathland vegetation and flora than succession based on native conifers. The open coastal heathlands along the Atlantic coast of Western Europe are a threatened landscape of high conservation value, and our results suggest that the spread of Sitka spruce into these landscapes should be controlled, especially in heathlands that are targeted for conservation. [ABSTRACT FROM AUTHOR]

We examined yearly rings from increment cores of conifers on two seabird nesting islands (one in the Lucy Islands and one in the Rankine Islands, British Columbia), to determine whether trees contained signatures of historical activity of seabirds. Ten conifers (primarily Sitka Spruce, Picea sitchensis), ranging from 56 cm to 127 cm diameter (average 90 cm) and ranging from 70 to 232 years in age (average 132 years of age), were cored across a 200-m gradient in densities of seabird burrows. At the site in the Lucy Islands, annual growth was highest (8-14 mm) in the trees with the highest seabird burrow densities and highest in the earliest rings (-1930), which were followed by a fluctuating reduction down to ~2 mm/year in the year 2000, but with a secondary elevated growth period in the 1970s. Adjacent control trees without seabird burrows had a growth rate of ~2 mm/year throughout the same period. At the site in the Rankine Islands, growth rates were also variable and exhibited a 10-15 year non-synchronous periodicity, with the highest growths in the location with high seabird burrow density. Nitrogen isotope signatures (ô15N), which are greatly elevated in seabird guano, ranged from minus 3.9% to 17.4% among tree rings (n = 245 rings) and were positively correlated to percentage nitrogen in rings, average ring growth, and burrow densities. Using these methods, we infer from our tree ring data that seabird activity declined on the Lucy Islands over a 70-year period and that the combination of growth, nitrogen isotopic signatures, and percentage nitrogen in tree rings as well a more detailed sampling grid of target and adjacent control trees will provide seabird biologists with additional tools for evaluating spatial and historical trends in seabird activity on forested islands. [ABSTRACT FROM AUTHOR]

Background:The mechanism by which water transport, tree growth and heartwood formation are balanced is poorly understood. Aims:To test the hypothesis that xylem formation drives heartwood production through changes in water transport to regulate sapwood area. Methods:We measured changes in sap flux at multiple depths across the sapwood to heartwood boundary in Sitka spruce (Picea sitchensis) from May 2009–October 2010 using the Heat Field Deformation method. Results:The radial sap flux profile was peaked with maximum flux occurring 1–2 cm below bark before reducing to the heartwood boundary (tail). Changes occurred in two stages. The depth of peak sap flux (D) extended outwards as new xylem formed during the growing season, giving an annual increment (AI). Water transport reduced in the tail sometime during dormancy, from November to March. The correlation betweenAIandDwas good however, these variables and the increase in sapwood area correlated poorly with the extent of heartwood formed. Conclusions:Heartwood formed during the dormant period in Sitka spruce in Great Britain. Xylem formation did not directly drive heartwood production; however, changes in specific conductivity need consideration. Reduced transport in the inner sapwood could provide a temporal signal for heartwood formation in pre-conditioned cells. [ABSTRACT FROM PUBLISHER]

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Trends in the incidence of multi-trunking at 21 sites in Glenbranter Forest in western Scotland are reported. Monitoring began in 1978 and continued for 30 years except at five sites that were felled. Incidence varied greatly between sites, from 9% up to 67% of trees multi-trunked at age 15–16 years, but rates declined slowly at nearly all sites after this peak. Decline was partly due to trunk singling and partly to multi-trunked tree death; in generalised linear mixed model analyses, we found that singling showed a highly significant relationship to the girths of the main and second-ranked trunks, respectively positive and negative, and mortality showed a highly significant relationship to the difference between the main-trunk girth and plot mean girth. From observations at older sites monitored to felling, we predicted the final incidences of multi-trunking at three sites monitored since planting; for these sites, the trees predicted to remain multi-trunked had suffered substantially more leader browsing from deer when young than trees predicted to be finally single trunked. Sites planted in the 1970s are forecast to have final incidences of multi-trunking from 3 to 40%, with most expected to be in the range 20–30% multi-trunking. Hence appreciable losses in crop value are likely, and measures to combat multi-trunking are discussed. [ABSTRACT FROM AUTHOR]

This investigation sought to examine if there was a difference between the ectomycorrhizal (ECM) communities in plots of native oak and introduced Scots pine and Sitka spruce forest. The ECM communities in four plots of each forest type were described, from five soil cores collected in each plot, by morphotyping, internal transcribed spacer (ITS)-restriction fragment length polymorphism matching of mycorrhizas and sporocarps and ITS sequencing. Fifty-one distinct taxa were distinguished; 25 were identified to species level, 11 to genus and 15 remained unidentified. Seventy-one ECM species were recorded as sporocarps from the forest plots; most (43 species) were found in the Sitka spruce plots. The below-ground ECM communities of the different forest types did not differ significantly with respect to species richness of taxa on roots, but differed in species composition. Multivariate analysis produced a clear separation of the communities of the different forest types using below-ground data, but the above-ground sporocarp data did not separate the forest types. Moreover, results of a Mantel test found no relationship between the above- and below-ground similarity matrices. The oak plots had the most distinctive ECM community, with Laccaria amethystina and Elaphomyces granulatus being frequent. The Sitka spruce plots showed the lowest intra-forest type similarity and were often dominated by 'nursery type' ectomycorrhizas. There was only 10% similarity between the above- and below-ground ECM species in these plots, different colonisation methods of ectomycorrhizal taxa and insufficient below-ground sampling being possible reasons for this disparity. Our results indicate that plantations of non-native Sitka spruce can support similar levels of ECM diversity as native forests. [ABSTRACT FROM AUTHOR]

Metabolite fingerprinting of Sitka spruce ( Picea sitchensis) bark and sapwood was carried out by H nuclear magnetic resonance after wounding and artificial inoculation with the white rot fungus Heterobasidion annosum sensu stricto. The aim was to determine whether metabolites would differ in clones showing differing levels of susceptibility to H. annosum, in the fungal as compared with the control treatment (wounding, no fungus) and the reference (healthy sample collected at 0 days), at two different locations on the host, and at different sampling times (3 and 43 days after treatment). The results suggested that different metabolic processes occur in bark and sapwood after wounding and fungal inoculation, compared with healthy samples collected before treatment: In bark, greater peaks were elicited in the aromatic region whereas, in sapwood, lower amounts of all metabolites were observed in inoculated samples, compared with healthy samples. Multivariate statistical analysis carried out with analysis of variance-principal component analysis showed highly significant effects of reference, location, and time (PC1), and significant effects of clone and fungus. Differences between clones were apparent in sapwood but not in bark and were due to peaks in the aliphatic and carbohydrate regions. Over time, in bark, there was a decrease in carbohydrate peaks, followed by an increase in aliphatic and aromatic peaks. Sapwood, by contrast, showed a decrease in all peaks, followed by an increase in carbohydrate and aliphatic peaks. Changes in carbohydrate levels were observed within the lesion compared with the more distal location in both bark and sapwood. [ABSTRACT FROM AUTHOR]

Gene flow and effective population size (Ne) should depend on a population's position within its range: those near the edges are expected to have smaller Ne and lower relative emigration rates, whereas those nearer the centre should have larger Ne and higher relative emigration rates. In species with continuous ranges, this phenomenon may limit the ability of peripheral populations to respond to divergent selection. Here, we employ Sitka spruce as a model to test these predictions. We previously genotyped 339 single nucleotide polymorphisms (SNPs) in 410 individuals from 13 populations, and used these data to identify putative targets of divergent selection, as well as to explore the extent to which central–peripheral structure may impede adaptation. Fourteen SNPs had outlier FST estimates suggestive of divergent selection, of which nine were previously associated with phenotypic variation in adaptive traits (timing of autumn budset and cold hardiness). Using coalescent simulations, we show that populations from near the centre of the range have higher effective populations sizes than those from the edges, and that central populations contribute more migrants to marginal populations than the reverse. Our results suggest that while divergent selection appears to have shaped allele frequencies among populations, asymmetrical movement of alleles from the centre to the edges of the species range may affect the adaptive capacity of peripheral populations. In southern peripheral populations, the movement of cold-adapted alleles from the north represents a significant impediment to adaptation under climate change, while in the north, movement of warm-adapted alleles from the south may enhance adaptation. [ABSTRACT FROM AUTHOR]

Background: Tree breeders continue to use visual assessments of stem shape and branching habit as part of their selection criteria because these are key features used by timber merchants in assessing stand value. However, it is not known how effective these assessments are in introducing real improvements in stem and branching traits to breeding and production populations of Sitka spruce. This study determined the genetic characteristics of several traits associated with stem straightness and branching, and examined whether these traits are suitable as future selection criteria. Methods: Trees were sampled from 33 families selected from a 20-year-old half-sibling progeny trial growing in northern Scotland and a control of directly imported material from Queen Charlotte Islands, Canada. Stem straightness and branching habit were 'scored' for quality in addition to direct measurements made on growth and branching characteristics. Results: Results indicate that heritability values for most external stem and branching properties evaluated visually are sufficiently strong to enable effective selection in tree improvement programmes. Estimated genetic correlations suggest that substantial improvements in branch and stem quality could be achieved without a reduction in growth rate. Conclusions: Visual scoring systems appear to successfully target families of good growth and small branch size relative to the control population. [ABSTRACT FROM AUTHOR]

• Context: The frequency, size, and insertion angle of primary branches are important determinants of wood quality and can be significantly influenced by silvicultural activities. • Aims: This study quantified the long-term influence of early re-spacing on the branching characteristics of mature Sitka spruce [ Picea sitchensis (Bong.) Carr.] trees growing in Northern Ireland, UK. The primary aim was to investigate whether any residual effect of stand density on branch attributes remained once the effect of changes in tree size variables had been considered, while a secondary objective was to test the performance of existing Sitka spruce branch models using the current dataset. • Methods: Re-spacing treatments had corresponding stand densities of 2,858, 1,452, 725, 477, and 320 stems ha. Twenty-four trees were sampled when the stand was 57 years old and branch frequency, size, and insertion angle were recorded for model development. • Results: Maximum branch diameter, insertion angle, and branch frequency were significantly influenced by re-spacing, while no effect was found for relative branch diameter distribution. Residual re-spacing effects were most noticeable on branch size, with only small differences between treatments for branch frequency and insertion angle. Existing models performed well despite the wider range of stand densities examined in the present study. • Conclusion: The results indicate that early re-spacing from 1.9 m to wider than 2.6 m will result in branch attributes that are detrimental to Sitka spruce sawn timber quality. [ABSTRACT FROM AUTHOR]

Light availability and infestation by the green spruce aphid (Elatobium abietinum) are key factors affecting the growth of Sitka spruce (Picea sitchensis) seedlings under a mature tree canopy, but their combined effect on seedling growth has not previously been quantified. A controlled outdoor experiment in which light levels (high light (HL): 100%, intermediate light (IL): 24%) and aphid infestation (absence/presence) were manipulated was conducted over 2 years to look at the effects on seedling growth and biomass distribution patterns. Aphid population assessments showed a significantly increased population density under IL, with three to four times higher cumulative aphid densities than that under HL. Defoliation rates of infested seedlings were directly related to aphid density. Total seedling biomass was strongly reduced in IL, and aphid infestation caused additional reductions in the biomass of particular components of the seedlings. Dry weight (DW) of older (≥1-year-old) needles in infested trees was significantly decreased in both years. Total root DW at the end of the second year was significantly affected by aphid infestation, and the reduction (14–18%) was similar in IL and HL treatments despite large differences in aphid density. Biomass distribution patterns in infested trees were similar to that of uninfested trees within each light treatment, indicating that the relative decreases in root biomass were accompanied by similar reductions in distribution to the above-ground parts of the seedlings. Leader extension growth of infested seedlings was reduced by 15–17% compared with uninfested seedlings under IL, whereas only a 2–3% reduction in leader extension of infested seedlings under HL was observed. The results showed that the response of seedlings to E. abietinum were primarily dependent on the light environment. The significant reduction caused by aphids on the total DW of older needles and roots, and on leader extension growth, does suggest the potential for effects to accumulate over time. [ABSTRACT FROM AUTHOR]

Abstract: Conifers produce terpenoid-rich oleoresin in specialized resin ducts as a main line of defence against pests and pathogens. In spruce species (Picea spp.), axial resin ducts are either present constitutively in the cortex tissue (cortical resin ducts, CRDs) or are formed de novo as traumatic resin ducts (TRDs) in the cambial zone upon attack by insects, fungi or treatment with methyl jasmonate (MeJA). Using immunofluorescence localization we tested if previously formed CRDs respond to MeJA treatment with increased capacity for diterpenoid biosynthesis. We also tested the dynamics of diterpene synthase localization in the cambial zone. Immunofluorescence localization was performed using an antibody against a diterpene synthase, levopimaradiene/abietadiene synthase (LAS), in stem cross-sections of untreated and 0.1% MeJA-treated 4-year old Sitka spruce (P. sitchensis) trees. No fluorescence signal was observed in untreated stem cross-sections; however, signal was present 2days after treatment with MeJA exclusively in the epithelial cells of CRDs. Fluorescence steadily increased in the CRD epithelial cells 4 and 8days after treatment. At 8days, additional fluorescence was observed in developing epithelial cells of traumatic resin ducts TRDs in the cambial zone. These results confirm that resin duct epithelial cells are the main site of diterpene biosynthesis in Sitka spruce, diterpenoid biosynthesis is induced in CRD epithelial cells early upon treatment with MeJA, and immature developing TRD epithelial cells produce diterpene synthase enzyme. Overall, the results of this work improve our understanding of spatial and temporal patterns of induced diterpene resin acid biosynthesis in conifers. [Copyright &y& Elsevier]

Deviations of the site frequency spectrum of mutations (SFS) from neutral expectations may be caused by natural selection or by demographic processes such as population subdivision or temporal changes in population size. As most widespread temperate and boreal tree species have expanded from glacial refugia in the past 13 000 years, colonization bottlenecks associated with this migration may have left variable demographic signatures among geographic populations corresponding to distance from the refugia. To determine whether the signature of postglacial re-colonization has skewed the SFS in the widely distributed conifer Sitka spruce ( Picea sitchensis (Bong.) Carr.), we re-sequenced 153 nuclear genes in six populations from across the species range. We found that while the SFS for the pooled sample produced negative values for Tajima’s D and Fay and Wu’s H, these statistics exhibited strong clinal variation when populations were analysed separately ( R2 = 0.84, P = 0.007 for Tajima’s D and R2 = 0.65, P = 0.033 for Fay and Wu’s H). When historical bottlenecks of varying age were simulated using approximate Bayesian computation, distance of populations from the southern range limit explained most of the variation in bottleneck timing among populations ( R2 = 0.89, P = 0.003). These data suggest that sequential population bottlenecks during postglacial re-colonization have resulted in diverse among-population signatures within the contemporary SFS in Sitka spruce, with rare variants more common in the south, and medium-frequency variants more common in the north. Our results also emphasize the need to consider sampling strategy and to explore population-specific null demographic models in surveys of nucleotide variation in widely distributed species. [ABSTRACT FROM AUTHOR]

Novel or emergent ecosystems arising from human action present both threats and opportunities for biodiversity. It has been suggested that exotic species can "facilitate" or "inhibit" native biodiversity through habitat modification. In Britain, there is a discussion over the contribution to biodiversity of plantations of exotic conifer species as these are commonly thought to have little relevancy as a habitat for native biodiversity. To address this we compared the species richness of a range of different taxonomic groups (lichens, bryophytes, fungi, vascular plants, invertebrates and songbirds) in exotic and native forest stands of differing structural stages in northern and southern Britain. In terms of overall native species-richness there was no significant difference between the exotic and the native stands. In the north, six species groups showed higher values in the exotic Sitka spruce (Picea sitchensis) stands with the remaining six showing higher values in the native Scots pine (Pinus sylvestris) stands. Most notably, lichen species richness was much lower in the exotic stands compared to the native stands, whereas bryophyte and fungal species richness was proportionately higher in the exotic stands. In the south, five species groups (all invertebrate taxa) showed higher species richness in exotic Norway spruce (Picea abies) stands compared to native oak (Quercus robur) stands. Five species groups had higher species-richness in the oak stands, in particular lichens and fungi. It is concluded that emergent ecosystems of exotic conifer species are not irrelevant to biodiversity. Where already well-established they can provide habitat for native species particularly if native woodland is scarce and biodiversity restoration is an immediate priority. [ABSTRACT FROM AUTHOR]

Partial defoliation of spruce by the green spruce aphid Elatobium abietinum (Walker) is a recurrent event in European and, increasingly, North American forests. The patterns of insect abundance on trees have never been satisfactorily described by a numerical model despite considerable knowledge of endogenous and exogenous factors in the population dynamics of the species. Long-term field population estimates of the aphid on foliage provided the opportunity to evaluate such a model. Unlike comparable models for tree-dwelling aphids, this was also applicable to almost completely independent aphid field data derived from the Rothamsted Insect Survey’s nationwide network of suction traps. Although based on relatively few parameters, the model was robust in its predictions of alate aphids geographically remote from the forest in which the original population was estimated. The population maximum, which causes the greatest forest damage, is reached in early summer and can be predicted from knowledge of winter temperature (chill bouts), spring temperature (thermal sum), and interannual negative feedback (density dependence). The model provides confirmation that alate populations of spruce aphids, upon which a number of other extensive studies have been based, are ultimately influenced by similar endogenous and climatic factors and that they are a reasonable proxy for aphids on trees. [ABSTRACT FROM AUTHOR]