Tree-ring analysis of larch sawfly (Pristiphora erichsonii (Hartig)) defoliation events and hydrological growth suppression in a peatland

Insect defoliation events are a major forest disturbance in the boreal forest in Canada. Reconstructing previous events are crucial to understanding natural factors that lead to insect defoliation periods, improving our ability to predict future infestations and increasing the reliability of forest management plans and pest control programs. Researchers have often been limited in their ability to draw accurate conclusions regarding the history of larch sawfly (Pristiphora erichsonii (Hartig)) infestation events in North America. It is well known that floods can affect survival of larch sawfly populations, as well as suppress radial growth of eastern larch (Larix laricina (Du Roi) K. Koch) trees. Eastern larch often inhabits peatlands where high water-table levels can lead to a decrease in tree-ring widths. Water-table level increases result in similar radial-growth patterns to when trees are defoliated by larch sawfly, making accurate diagnoses of larch sawfly events a challenge. This fact becomes more accentuated when non-host species used for standard dendroecological analyses (often black spruce (Picea mariana (Mill.) Britton) present an opposite relationship to water-table variability, enhancing chances of drawing erroneous conclusions when using program OUTBREAK.This paper introduces a novel case study to advance the understanding of the complex landscapes where these larch sawfly events are taking place. It stresses the necessity of using upland sites less influenced by the hydrological regime to accurately reconstruct larch sawfly defoliation events. We found that where investigations are taking place solely in peatlands or lowlands, and where they are heavily influenced by hydrological conditions, the use of other lines of evidence such as pale rings and long-term hydrological records are crucial to understand the dynamics in the system. In our case study, program OUTBREAK identified five defoliation events in a peatland and upland site; however, hydrological data and pale ring evidence indicated that the last event identified in the peatland site by the host/non-host analysis was confounded by hydrological growth suppression.     

Dendroentomological and forest management implications in the Interior Douglas-fir zone of British Columbia, Canada

Douglas-fir (Pseudotsuga menziesii var. glauca Mirb. Franco) forests in the Interior of British Columbia, Canada, show periodic defoliation due to western spruce budworm (WSB) (Choristoneura occidentalis Freeman) outbreaks. Tree defoliation causes a reduction in radial growth and is therefore visible in tree rings. In this paper, we identify WSB defoliation history, and critically examine the potential for using dendrochronological analysis by comparing tree-ring estimates with insect surveys. WSB defoliation history was investigated using cores from Douglas-fir growing in the Lac du Bois region of the Kamloops Forest District. Years with an abrupt decrease in radial growth were considered as negative pointer years that potentially reflected WSB outbreaks. The comparison with ponderosa pine (Pinus ponderosa Dougl., ex P. & C. Laws.) (a non-host species) permitted differentiation between growth reductions in Douglas-fir due to climatic effects and those due to defoliation by WSB. The dendrochronological data were matched with information reporting visible damage in Forest Insect Disease Survey (FIDS) and British Columbia Ministry of Forest records. Our objective-based method using ring-width measurements from host and non-host chronologies was compared with qualitative techniques based on the software program OUTBREAK. We were able to distinguish seven distinct outbreak events in 300 years of record.     

Dendroentomological and forest management implications in the Interior Douglas-fir zone of British Columbia,Canada

Douglas-fir (Pseudotsuga menziesii var. glauca Mirb. Franco) forests in the Interior of British Columbia, Canada, show periodic defoliation due to western spruce budworm (WSB) (Choristoneura occidentalis Freeman) outbreaks. Tree defoliation causes a reduction in radial growth and is therefore visible in tree rings. In this paper, we identify WSB defoliation history, and critically examine the potential for using dendrochronological analysis by comparing tree-ring estimates with insect surveys. WSB defoliation history was investigated using cores from Douglas-fir growing in the Lac du Bois region of the Kamloops Forest District. Years with an abrupt decrease in radial growth were considered as negative pointer years that potentially reflected WSB outbreaks. The comparison with ponderosa pine (Pinus ponderosa Dougl., ex P. & C. Laws.) (a non-host species) permitted differentiation between growth reductions in Douglas-fir due to climatic effects and those due to defoliation by WSB. The dendrochronological data were matched with information reporting visible damage in Forest Insect Disease Survey (FIDS) and British Columbia Ministry of Forest records. Our objective-based method using ring-width measurements from host and non-host chronologies was compared with qualitative techniques based on the software program OUTBREAK. We were able to distinguish seven distinct outbreak events in 300 years of record.     

Summer temperature dependency of larch budmoth outbreaks revealed by Alpine tree-ring isotope chronologies

Larch budmoth (LBM, Zeiraphera diniana Gn.) outbreaks cause discernable physical alteration of cell growth in tree rings of host subalpine larch (Larix decidua Mill.) in the European Alps. However, it is not clear if these outbreaks also impact isotopic signatures in tree-ring cellulose, thereby masking climatic signals. We compared LBM outbreak events in stable carbon and oxygen isotope chronologies of larch and their corresponding tree-ring widths from two high-elevation sites (1800–2200 m a.s.l.) in the Swiss Alps for the period AD 1900–2004 against isotope data obtained from non-host spruce (Picea abies). At each site, two age classes of tree individuals (150–250 and 450–550 years old) were sampled. Inclusion of the latter age class enabled one chronology to be extended back to AD 1650, and a comparison with long-term monthly resolved temperature data. Within the constraints of this local study, we found that: (1) isotopic ratios in tree rings of larch provide a strong and consistent climatic signal of temperature; (2) at all sites the isotope signatures were not disturbed by LBM outbreaks, as shown, for example, by exceptionally high significant correlations between non-host spruce and host larch chronologies; (3) below-average July to August temperatures and LBM defoliation events have been coupled for more than three centuries. Dampening of Alps-wide LBM cyclicity since the 1980s and the coincidence of recently absent cool summers in the European Alps reinforce the assumption of a strong coherence between summer temperatures and LBM defoliation events. Our results demonstrate that stable isotopes in tree-ring cellulose of larch are an excellent climate proxy enabling the analysis of climate-driven changes of LBM cycles in the long term.     

The potential for using Larix decidua ring widths in reconstructions of larch budmoth (Zeiraphera diniana) outbreak history: dendrochronological estimates compared with insect surveys

In the Alps, larch (Larix decidua Mill.) forests show periodic discolouration due to larch budmoth (LBM) outbreaks (Zeiraphera diniana Guénée, Lepidoptera: Tortricidae). Tree defoliation causes severe reductions in radial growth, visible in tree rings. This paper aims at reconstructing LBM outbreak history, and critically examining the potential for using dendrochronological data by comparing tree-ring estimates with insect surveys. The occurrence of LBM outbreaks was investigated using 249 cores from larch growing near the timberline in three regions of the French Alps (Briançonnais, Maurienne, and Tarentaise). Years with an abrupt decrease in radial growth (-40%) were considered as negative pointer years reflecting the potential impact of LBM. The comparison with three non-host conifers (Norway spruce, stone and mountain pines) permitted us to distinguish growth reductions in larch due to climatic effects from those due to defoliation by LBM. The dendrochronological data were matched with information reporting conspicuous discolouration in old forestry reports or recovered from systematic field observations. Twenty-two outbreaks are discernible within the period 1800-1983. A peak reduction in larch growth occurred at intervals of 8.86ǃ.01 years in the following years: 1801, 1811, 1820, 1830, 1838, 1846, 1857, 1867, 1875, 1884, 1892, 1901, 1909, 1918, 1926, 1936, 1945, 1953, 1963, 1972, 1980, and 1987. Our objective method based on ring measurements and comparison with non-host trees was compared with qualitative techniques based on the visual detection of conspicuous latewood anomalies. Larch in the Briançonnais (which experiences a continental climate) are infested first, whereas the Tarentaise region exhibits a much weaker impact of LBM. Complete tree recovery was observable 3 years after outbreak peaks.     

Phase-dependent outbreak dynamics of geometrid moth linked to host plant phenology

Climatically driven Moran effects have often been invoked as the most likely cause of regionally synchronized outbreaks of insect herbivores without identifying the exact mechanism. However, the degree of match between host plant and larval phenology is crucial for the growth and survival of many spring-feeding pest insects, suggesting that a phenological match/mismatch-driven Moran effect may act as a synchronizing agent.We analyse the phase-dependent spatial dynamics of defoliation caused by cyclically outbreaking geometrid moths in northern boreal birch forest in Fennoscandia through the most recent massive outbreak (2000–2008). We use satellite-derived time series of the prevalence of moth defoliation and the onset of the growing season for the entire region to investigate the link between the patterns of defoliation and outbreak spread. In addition, we examine whether a phase-dependent coherence in the pattern of spatial synchrony exists between defoliation and onset of the growing season, in order to evaluate if the degree of matching phenology between the moth and their host plant could be the mechanism behind a Moran effect.The strength of regional spatial synchrony in defoliation and the pattern of defoliation spread were both highly phase-dependent. The incipient phase of the outbreak was characterized by high regional synchrony in defoliation and long spread distances, compared with the epidemic and crash phase. Defoliation spread was best described using a two-scale stratified spread model, suggesting that defoliation spread is governed by two processes operating at different spatial scale. The pattern of phase-dependent spatial synchrony was coherent in both defoliation and onset of the growing season. This suggests that the timing of spring phenology plays a role in the large-scale synchronization of birch forest moth outbreaks.     

A lagged, density-dependent relationship between jack pine budworm Choristoneura pinus pinus and its host tree Pinus banksiana

Abstract. 1. Survival of newly emerged jack pine budworm Choristoneura pinus pinus is related to the density of available pollen cones (microsporangiate strobili) produced by its host tree, jack pine Pinus banksiana. 2. A 7‐year time series of observations from a plot network in Ontario, Canada, compared the propensity of jack pine to produce pollen cones, τ, on trees that were either defoliated or undisturbed by the jack pine budworm. 3. Non‐defoliated jack pine trees have a high propensity to produce pollen cones. More than one‐third of these trees produced pollen cones in every year of the series. Propensity varied significantly among plots and trees. Temporal patterns in propensity were also highly variable but within a plot propensity was often autocorrelated in time. 4. Defoliation by the jack pine budworm was associated with forest plots composed of the oldest and the largest trees and with the fewest trees per hectare. Within a plot, outbreaks lasted 3 or 4 years although individual trees were only defoliated in 1 or 2 years. 5. The propensity to produce pollen cones in jack pine was reduced in the years after defoliation. The most pronounced reductions in propensity occurred where defoliation was most severe. 6. The reduction in propensity to produce pollen cones resulting from previous defoliation, coupled with the dependence of jack pine budworm survival on the availability of pollen cones, induces a lagged, negative feedback between the density of the consumer and that of its resource. 7. The lagged, density‐dependent relationship between jack pine budworm and its jack pine host contributes to oscillatory dynamics of the jack pine budworm. Comparison of the outbreak behaviour of jack pine budworm with that of the closely related eastern spruce budworm C. fumiferana suggests that differences in the strength of the host‐plant interaction may account for differences in the relative frequency of outbreaks in the respective systems.     

Extensive gypsy moth defoliation in Southern New England characterized using Landsat satellite observations

Southern New England is currently experiencing the first major gypsy moth (Lymantria dispar) defoliation event in nearly 30 years. Using a novel approach based on time series of Landsat satellite observations, we generated consistent maps of gypsy moth defoliation for 2015 (first year of the outbreak), 2016 (second year of outbreak), and 2017 (third year of outbreak). Our mapped results demonstrate that the defoliation event continued through the 2017 growing season. Moreover, the affected area more than doubled in extent each year and expanded radially to encompass 4386 km² of forested area in Rhode Island, eastern Connecticut, and central Massachusetts. The current gypsy moth outbreak is believed to be the result of a series of unusually dry springs in 2014, 2015, and 2016, which suppressed Entomophaga maimaiga, a fungal mortality agent that has historically reduced gypsy moth impacts in this region. The continuation and marked expansion of the outbreak in 2017 despite average spring rainfall suggests that caterpillars were active early in the growing season, and mortality from the fungus likely peaked after significant defoliation had already occurred. Our Landsat time series approach represents an important new source of data on spatial and temporal patterns in gypsy moth defoliation, and continued satellite-based monitoring will be essential for tracking the progress of this and other gypsy moth outbreaks.     

Impact of sawfly defoliation on growth of Scots pine Pinus sylvestris (Pinaceae) and associated economic losses

Needle defoliation by diprionid sawflies decreases the increment and timber yield of Scots pine Pinus sylvestris L. The aim of this study was to provide approximate estimates of this decrease and preliminary estimates of the economic value of growth losses and tree mortality. Growth loss after needle damage by Diprion pini (Linnaeus) was studied in western Finland. Increment cores were sampled for radial growth measurements from trees subjected to slight, moderate and heavy defoliation. A literature survey was carried out to estimate radial growth losses after defoliation by Neodiprion sertifer (Geoffroy). Calculations for economic consequences were based on previous estimates and on the ongoing 9th Finnish National Forest Inventory. Moderate defoliation by N. sertifer and D. pini reduced volume growth by 21% and 86% and heavy defoliation by 38% and 94%, respectively. Tree mortality in defoliated stands was recorded as approximately 4% after an outbreak of N. sertifer and 30% after an outbreak of D. pini. The estimated average economic value of the losses due to reduced growth and tree mortality reached $40 ha-1 after a single-year outbreak of N. sertifer and $310 ha-1 in the case of D. pini. These preliminary estimates of economic losses indicate a much higher impact of pine sawflies than those revealed by the few earlier studies in Europe.     

Defoliation increases risk of carbon starvation in root systems of mature aspen

Large trees are noted to decline and die over several years after defoliation or extended periods of drought. The underlying mechanisms of this decline are thought to be driven by moisture limitations to photosynthesis, but alternative considerations also suggest carbon storage limitations as a driver. This research assesses the non-structural carbohydrate reserves in crowns and roots tissues during and after defoliation by insects in trembling aspen. We monitored the non-structural carbon reserves of nine tall mature aspen forest stands over 8 years, including two defoliation events. We report on the carbohydrate dynamics in root and crown tissues during and after defoliation. Following defoliation, branch reserves recovered to levels of undefoliated control trees within the same season, while roots took up to 2 years to recover. We argue that in large trees, tissues closest to the foliage are the first sinks to access C in the phloem stream, while roots, which are more distal and separated by a long bole, will only receive adequate supplies of C when the other more proximate sinks are sated. These results support the hypothesis that in times of limited carbon assimilation, root tissues in mature trees experience the longest reduction in carbon reserves, which likely plays a critical role in tree decline and mortality.     

Linking aerial survey data of forest insect defoliation and tree ring data to estimate forest level growth losses

Aerial surveys provide valuable information on the scale and severity of defoliation and mortality caused by forest insects. However, methods to estimate the losses in growth using aerial survey data are not available. This study presents a method to link aerial survey data of location and severity of insect defoliation to tree ring series of radial growth in order to quantify potential growth losses due to defoliation. The method includes estimation of potentially confounding effects of climate. As an example we used aerial surveys of hemlock looper defoliation in the Mt. Revelstoke region of British Columbia, and tree ring series of radial growth of 351 western hemlock trees located in 22 plots and exposed to various levels of periodic defoliation. An autoregressive conditional heteroskedasticity time-series model (ARCH) of standardized growth indices identified significant direct and lagged effects of climate and defoliation on radial growth between 1930 and 2005. Defoliation effects were statistically significant in all plots (P < 0.05). The variation in both timing and strength of estimated growth reductions varied considerably among plots. During years of observed defoliation the radial growth was reduced by an average of 10%. Growth reductions attributed to defoliation were most pronounced in the second and third year of a looper outbreak. Our modelling approach linked tree ring data to aerial survey data of defoliation through a logistic distance dependent threshold function and affords a quantitative estimation of regional growth losses.     

Tracing the influence of larch-bud-moth insect outbreaks and weather conditions on larch tree-ring growth in Engadine (Switzerland).

Tree-ring analysis of insect-defoliated trees has so far been used for detecting past insect outbreaks only. We hypothesize that the impact of the larch-bud-moth (LBM) Zeiraphera dinian outbreaks on the growth of larch Larix decidua in the Engadine (Switzerland) is closely coupled to the spatial development of the outbreak and the ecological characteristics of the respective sites and weather conditions. We tested this hypothesis by reviewing data sets available in the literature and by analysing original data. We monitored LBM population densities and the needle phenology, growth and defoliation of larch over 28 years, i.e. over four outbreak cycles. In addition, information on defoliation patterns covering six earlier outbreaks over 50 years was matched with tree-ring information. Tree-ring chronologies of 18 larch stands were analysed with regard to abrupt growth changes and latewood events. Defoliation induces an immediate reduction in latewood, followed by a reduction in needle length and a significant decrease in radial growth in the subsequent year. We have called this tree-ring pattern the "larch-bud-moth syndrome". A careful analysis of the various parameters of the LBM syndrome for two specific population cycles enabled us to define different interaction patterns between weather conditions and tree growth. These can then be included in climate change models to help disentangle the impact of insect defoliation from that of adverse climatic conditions.     

Determinants of mountain birch growth in situ: effects of temperature and herbivory

Variation in in situ growth performance of the mountain birch as indicated by the widths of annual rings was analysed and related mainly to temperature and herbivory using ring width series from five heath forest sites in the Lake Torneträsk area, northern Sweden. Climate explained 48–64% of the variation in age-corrected mean ring width series. In general, the effect of current year July followed by June temperature was most important at all sites. A warm May resulted in wider rings due to an earlier budburst. Short-term (inter-annual) responses to increased temperature were in most cases not reflected into long-term responses (decades). A large proportion of the variation in stem mean ring width was due to variation among stems within trees (81%) in these polycormic trees, while variation among sites was marginal (0.4%). Within trees, main stems grew faster and were more responsive to climate variation than subordinate stems. No effect of insect herbivory on ring width was found at low defoliation levels (≤12%). At a defoliation level of ca 84% a one-year reduction in stem growth was observed while the growth reduction (ca 50% reduction in ring width) lasted for 4 yr after ca 93% defoliation. After outbreaks resulting in complete defoliation and some stem mortality, ring widths of surviving stems mainly responded with increased growth. Basal sprouts, emerging just after a severe insect outbreak with a high mortality of old stems, grew faster than sprouts occurring during other periods. It is concluded that the mountain birch is well adapted to recover from Epirrita outbreaks; the ability to produce basal sprouts, that can benefit from an existing root system for fast initial growth, is one important mechanism for this.     

The effect of previous defoliation of pole-stage lodgepole pine on plant chemistry,and on the growth and survival of pine beauty moth (Panolis flammea) larvae

Summary A study of the effects of defoliation by insects on the chemistry of lodgepole pine (Pinus contorta), and on the performance of Panolis flammea (Lepidoptera; Noctuidae) larvae, was carried out in a forest in northwest Scotland I year after a severe outbreak of P. flammea had caused extensive defoliation. Larval weight and survival were not significantly different on trees that had experienced different levels of defoliation in 1986. The nitrogen and tannin content of current and previous years' pine needles was not significantly affected by defoliation (although both were slightly greater in the foliage of defoliated trees). Phosphorus content of young pine foliage was lower (but not significantly lower except on one occasion) on heavily defoliated trees. On all sampling occasions, however, the nitrogen: phosphorus ratio was significantly higher on heavily defoliated trees. There were large differences in monoterpene composition of the previous year's shoots associated with defoliation intensity, but these differences had largely disappeared in the new growth. The results are discussed in relation to other studies on the effects of insect damage on plant chemistry and insect performance and in relation to the abundance of P. flammea in Scotland.     

Delayed induced changes in the biochemical composition of host plant leaves during an insect outbreak

In birch, Betula pubescens, herbivore-induced delayed induced resistance (DIR) of defoliated trees may cause a strong reduction in the potential fecundity of a geometrid folivore Epirrita autumnata. In this study, we examined the biochemical basis of DIR in birch leaves during a natural outbreak of E. autumnata. A set of experimental trees was defoliated at four sites by wild larvae in the peak year of the outbreak, whereas control trees were protected from defoliation by spraying with an insecticide. The biochemical composition of leaves was analysed in the following year and, although the DIR response was weak during this outbreak, causing less than a 20% reduction in the potential fecundity of E. autumnata, some consistent relationships between defoliation, biochemistry and pupal mass of E. autumnata suggested a general biochemical basis for the defoliation-induced responses in birch leaves. Total concentrations of nitrogen, sugars and acetone-insoluble residue (e.g. cell wall polysaccharides, cell-wall-bound phenolics, protein, starch, lignin and hemicellulose) were consistently lower, and total concentrations of phenolics, especially of gallotannins and soluble proanthocyanidins, were higher in the leaves of trees defoliated in the previous year than in those protected from defoliation. The capacity of tannins to precipitate proteins correlated with contents of gallotannins, and was highest in defoliated trees. The pupal mass of E. autumnata showed a strong, positive correlation with concentrations of nitrogen and sugars, and a negative correlation with the acetone-insoluble residue and gallotannins in foliage. Correlations with other measured biochemical traits were weak. The correlation coefficients between biochemical traits and pupal mass consistently had similar signs for both defoliated and insecticide–sprayed trees, suggesting that variation in leaf quality due to defoliation in the previous year was based on similar biochemical traits as variation for other reasons. We suggest that DIR is associated with reduced growth activity of leaves, and may be seen as a delay in the biochemical maturation of leaves in defoliated trees. This explains the high concentration of gallotannins in defoliated trees, a characteristic feature of young leaves. However, the lower content of nitrogen and the higher content of soluble proanthocyanidins in defoliated trees are traits usually characterising mature, not young, leaves, indicating defoliation-induced changes in chemistry in addition to modified leaf age. Our results emphasise the importance of understanding the natural changes in chemistry during leaf maturation when interpreting defoliation-induced changes in leaf biochemistry. Received: 26 January 1998 / Accepted: 10 April 1998     

Additive and synergistic integration of multimodal cues of both hosts and non-hosts during host selection by woodboring insects

Host selection by herbivorous insects is primarily thought to depend on attraction to olfactory cues emitted from the host species. However, the discrimination of these hosts from non-host species may also arise from the adaptive detection and avoidance of non-host cues, including visual characteristics. Many generalist, conifer-colonising beetles, for example, use characteristic volatiles to identify and discriminate against non-host angiosperm trees such as aspens and birches while flying. These trees also differ in bark reflectance characteristics, which could also mediate host/non-host discrimination by interacting with semiochemicals. We tested this hypothesis by evaluating the responses of eight species of polyphagous woodboring beetles to traps which simulated the visual appearance of coniferous hosts (black) and angiosperm non-hosts (white), and which were baited with host or non-host volatiles. As predicted, three species of large woodboring beetle and a woodboring wasp all avoided white, non-host-simulating traps that were baited with attractive kairomones, and preferred black, host-simulating traps. Conversely, three ambrosia beetle species demonstrated weaker visual preferences, possibly because they preferentially colonise fallen hosts that would transmit less accurate visual information. However, the ambrosia beetle Trypodendron lineatum did show a greater preference for host-coloured traps when these released host-associated kairomones in addition to their pheromone, and also avoided white non-host traps, but only when these released non-host volatiles. To our knowledge, this is the first evidence that multiple non-host cues could synergistically mediate the adaptive discrimination of hosts and non-hosts. Our results suggest that successful host location by generalists arises from the complex integration of cues in multiple sensory modes, and that foraging herbivores evaluate both hosts and non-hosts during their search.     

Optimal Gene Trees from Sequences and Species Trees Using a Soft Interpretation of Parsimony

Gene duplication and gene loss as well as other biological events can result in multiple copies of genes in a given species. Because of these gene duplication and loss dynamics, in addition to variation in sequence evolution and other sources of uncertainty, different gene trees ultimately present different evolutionary histories. All of this together results in gene trees that give different topologies from each other, making consensus species trees ambiguous in places. Other sources of data to generate species trees are also unable to provide completely resolved binary species trees. However, in addition to gene duplication events, speciation events have provided some underlying phylogenetic signal, enabling development of algorithms to characterize these processes. Therefore, a soft parsimony algorithm has been developed that enables the mapping of gene trees onto species trees and modification of uncertain or weakly supported branches based on minimizing the number of gene duplication and loss events implied by the tree. The algorithm also allows for rooting of unrooted trees and for removal of in-paralogues (lineage-specific duplicates and redundant sequences masquerading as such). The algorithm has also been made available for download as a software package, Softparsmap.     

Effects of warming climate on early-season carbon allocation and height growth of defoliated mountain birches

Tree carbohydrate reserves are usually compromised following insect outbreak, which results in a delay in leaf emergence and a reduction in growth, especially in cold environments. However, in recent times, severe defoliation of subarctic mountain birches (Betula pubescens ssp. czerepanovii) by the winter moth (Operophtera brumata) has not induced such responses. This may be the result of a warming climate stimulating plant primary metabolism. We examined if increasing thermal sum (sum of daily mean temperatures above +5 °C, d.d.) and complete foliage loss affected the concentrations of carbohydrates in sap, juvenile leaves, and fine roots of mountain birches in northern Finland and Norway. The sampling was conducted at the beginning of the growing season, two years after the insect outbreak. We also investigated the morphologic properties of mature leaves and the shoot growth of the trees. Our results showed that the carbohydrate concentrations in leaves and roots (averages 67.8 and 12.5 mg g^?1 DW, respectively) decreased in defoliated trees with increasing thermal sum (>400 d.d.), whereas the response in intact trees was the opposite. The carbohydrates in the sap were unaffected by defoliation or thermal sum accumulation. The leaf area of mature leaves and the height growth of long shoots were greater in trees at warmer sites, irrespective of defoliation. However, defoliation increased the leaf weight per area (SLW: specific leaf weight). We conclude that under warmer growing conditions, low early-season leaf and fine root carbohydrate concentrations of previously defoliated trees cannot be used as indicators of aboveground growth.     

Attack dynamics of the pine shoot beetle, Tomicus piniperda (Col.; Scolytinae) in Scots pine stands defoliated by Bupalus piniaria (Lep.; Geometridae)

Abstract 1 After a 1‐year, extensive pine looper (Bupalus piniaria) outbreak, plots were laid out to study tree susceptibility to attack, and performance of Tomicus piniperda in pine trees suffering from varying levels of defoliation. 2 Tomicus piniperda was the dominating stem‐attacking species among the primary stem colonizers, and 82% of all trees that died had been colonized by T. piniperda. 3 Beetle attacks primarily struck severely defoliated trees, i.e. trees that suffered from 90% to 100% defoliation. 4 Beetle attacks peaked in the second year after cessation of the outbreak, and suppressed trees were both more frequently attacked and more susceptible to beetle attack than intermediate and dominant trees. 5 Trees surviving beetle attacks carried more foliage than trees that did not survive the attacks. 6 A single year of severe defoliation is enough to render pine trees susceptible to secondary pests, such as T. piniperda.     

A Lepidopteran defoliator attack on Brazil nut trees (Bertholletia excelsa) in Central Amazonia, Brazil

This paper describes a severe outbreak of a Lepidopteran defoliator, Lusura altrix (Stoll 1782), on Brazil nut trees in Central Amazonia. The pest outbreak appeared to succeed abnormal weather conditions, and defoliation was sufficient to disrupt normal phenological patterns.