Warming counteracts defoliation‐induced mismatch by increasing herbivore‐plant phenological synchrony

Climate change is altering phenology; however, the magnitude of this change varies among taxa. Compared with phenological mismatch between plants and herbivores, synchronization due to climate has been less explored, despite its potential implications for trophic interactions. The earlier budburst induced by defoliation is a phenological strategy for plants against herbivores. Here, we tested whether warming can counteract defoliation‐induced mismatch by increasing herbivore‐plant phenological synchrony. We compared the larval phenology of spruce budworm and budburst in balsam fir, black spruce, and white spruce saplings subjected to defoliation in a controlled environment at temperatures of 12, 17, and 22°C. Budburst in defoliated saplings occurred 6–24 days earlier than in the controls, thus mismatching needle development from larval feeding. This mismatch decreased to only 3–7 days, however, when temperatures warmed by 5 and 10°C, leading to a resynchronization of the host with spruce budworm larvae. The increasing synchrony under warming counteracts the defoliation‐induced mismatch, disrupting trophic interactions and energy flow between forest ecosystem and insect populations. Our results suggest that the predicted warming may improve food quality and provide better growth conditions for larval development, thus promoting longer or more intense insect outbreaks in the future.     

Oviposition and feeding on red pine by jack pine budworm at a previously unrecorded scale

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Spruce budworm (Choristoneura spp.) biotype reactions to forest and climate characteristics

The spruce budworm (Choristoneura fumiferana) is the most destructive insect defoliator of forests in North America. Climatic influences on this species' life history are considered a major factor in restricting the extent and intensity of outbreaks. We examine the life history traits of the spruce budworm and related Choristoneura populations with respect to forecasting the conifer‐feeding responses of these insects in changing environments. Analysis of the evolutionary relationships between Choristoneura entities, including their hybridization, genetic distances, and their degree of sympatry leads us to distinguish 15 possible Choristoneura‘biotypes’. Population trend has been associated with recruitment to the feeding stage, and two indicators of recruitment, egg weights and phenological development, are both ‘biotype’ and climate dependent. Among Abietoid feeding ‘biotypes’ and among spruce budworm populations, those from locations with extreme winters tend to have heavier eggs than those from the more benign environments. In spruce budworm, this genetically based adaptation allows populations to increase their potential recruitment substantially where winters are mild. All biotypes feed on the newly developed shoots of their host trees in spring, and are thus vulnerable to the uncertain timing of budbreak. Genetic control of spring emergence is weak so larvae from a single family typically exit from hibernacula over a prolonged period. This guarantees some synchronization with budburst. However, hybrid populations have high heritabilities. This allows rapid adaptation to new conditions (e.g. mixed host‐species stands). Geographic variation in phenological development after establishing feeding sites is largely genetically controlled. The importance of variation in these traits is examined with respect to competing population dynamics theories to evaluate their utility in forecasting future trends in defoliation. We finish with a plea for jointly using alternative approaches in forecasting spatiotemporal patterns of defoliation.     

Heritability of life‐history traits in the spruce budworm

The heritability of life‐history traits is of particular importance for insects that are very dependent on host conditions. Severe defoliation caused by the spruce budworm negatively impacts its food source, which in turn imposes environmental constraints on the insect. The heritability of those traits can help elucidate this species' evolutionary process. Heritability also helps identify which traits exhibit significant additive variance and can be key to understanding natural selection effects. Individuals were reared under laboratory conditions over three generations on an artificial diet. Heritability was estimated by parent–offspring regression. Fertility and fecundity demonstrated significant heritability followed by larval development, while pupal mass showed minimal heritable variation. These results suggest an important percent of additive variance in life‐history traits. This study contributes to our understanding of the relationship of this forest pest to its environmental conditions. This study also reveals an important genetic architectural structure of life‐history traits in the spruce budworm.     

Effect of defoliation on tracheid production and the level of indole-3-acetic acid in Abies balsamea shoots

To simulate feeding by the spruce budworm ( Choristoneura fumiferana Clem.), the apical current-year shoots on 1-year-old branches in the uppermost whorl of 6-year-old balsam fir [ Abies balsamea (L.) Mill.] trees were either removed completely by debudding before the start of the growing season or defoliated 0, 50, 90 or 100% shortly after budbreak. Debudded branches were treated at the apical end with 0, 0.1 or 1.0 mg of indole-3-acetic acid (IAA) (g lanolin)⁻¹. Ninety % of the 1-year-old needles were also removed from some of the experimental branches. After ca 4 weeks of growth, the radial width of new xylem and the level of IAA were determined in the 1-year-old internode. The IAA content was measured by radioimmunoassay.
The removal or defoliation of current-year shoots inhibited tracheid production and decreased the IAA level. Exogenous IAA stimulated tracheid production and increased the IAA level in debudded branches. Current-year shoot defoliation also inhibited current-year shoot elongation. The inhibitory effect of current-year needle removal on all parameters generally increased with increasing intensity of defoliation. The removal of 1-year-old needles did not affect the IAA level or current-year shoot elongation, nor did it influence tracheid production in branches with current-year shoots. However, removal of 1-year-old needles inhibited tracheid production in debudded branches supplied with exogenous IAA. The results indicate that (1) IAA is involved in the control of tracheid production in the 1-year-old internode, (2) IAA is supplied primarily by current-year shoots, and (3) defoliation by the spruce budworm inhibits tracheid production partly by decreasing the supply of IAA.     

Tolerance responses to herbivory: implications for future management strategies in potato

Tolerance is a plant response to herbivory that allows plants to sustain defoliation without any fitness consequences. In agriculture, the maximum amount of defoliation that crops can experience without yield loss is defined as the damage threshold. Damage thresholds can be used to develop tolerance‐based management strategies, which would offer guidelines for farmers for when pest control should be enacted to minimise pesticide use while maintaining yield. Damage thresholds for many varieties of potatoes, Solanum tuberosum, have been documented, but not consolidated into a general framework. We aggregated data from published studies and quantified the effects of variety, maturity group, life stage and defoliation mechanisms on damage thresholds to inform a tolerance‐based management strategy for potato. Late maturing varieties did not have different damage thresholds than early maturing varieties. Damage thresholds were greater than 60% defoliation at emergence and post‐bloom and less than 40% defoliation pre‐bloom and during bloom. If the stems were damaged, emergence and post‐bloom damage thresholds were reduced from 60% defoliation without stem damage to 35% and 52% defoliation with stem damage. Likewise, the damage thresholds during bloom were reduced to 20% defoliation when stems were damaged. We propose using action thresholds based on defoliation as a baseline to develop a tolerance‐based management strategy for potatoes.     

Spatial scale and the detection of density dependence in spruce budworm outbreaks in eastern North America

Using two tests for direct density dependence and standard techniques of time series analysis, we identified density dependence in defoliation time series of the spruce budworm across its outbreak range in eastern North America over the years 1945–1988. We carried out analyses for the entire region and for grid cells of defoliation maps at five spatial scales created by aggregating the smallest grid cells. The rate of detection of direct density dependence, as assessed by two previously published methods, decreased with increasing spatial scale. Using both methods, density dependence was detected more frequently at the periphery of the outbreak range, where defoliation rate was lower. This result suggested that density-dependent regulation may be stronger in those areas. The first order autoregressive process was the basic model for defoliation dynamics overall and the most common model across spatial scales. Second-order processes were encountered much less frequently, and those commonly identified as resulting from delayed density dependence generally occurred across spatial scales at a rate expected by chance alone. Our results were similar to those of other published studies, which have found the detection of density dependence to decrease at larger spatial scales. The results also reinforced the importance of considering spatial scale when diagnosing population processes using time series of abundance for single species. Received: 26 December 1999 / Accepted: 17 March 2000     

Incorporating zoning and socioeconomic costs in planning for bird conservation

New systematic conservation approaches have high potential in evaluation of different conservation scenarios and can be used as decision support tools for managers and planners with multiple goals. The present study focused on two major issues in conservation planning including socioeconomic costs and zoning procedure. The goal was to prioritize and identify representative areas for bird conservation, while minimizing the economic cost for the silvicultural sector and resolve conflicts with recreational activities. The study was conducted in forest areas of Golestan Province as part of Hyrcanian mixed forests, located along the southern coasts of the Caspian Sea and northern slopes of the Alborz Mountains, northern Iran. We used systematic conservation software Marxan with Zones to select candidate areas for conservation. Two types of conservation networks were defined, one with high and partial protection zones and the other with high protection zones only. We focused on four conservation scenarios varying in targets, costs, and multiple zones. The results showed that incorporation of socioeconomic costs significantly decreases the potential impacts on the silvicultural and recreational sectors without significant change in the area of protection zones. Furthermore, we found that design of multiple zone conservation areas facilitates evaluation of a wider range of conservation scenarios that can reduce potential socioeconomic impacts on other interests.     

Do life history traits predict responses to defoliation in co‐occurring prairie grasses?

Abstract. This study examines whether competition between the unpalatable grass Hilaria mutica and three co‐occurring, palatable grasses in a Texan mixed prairie is altered by non‐selective or selective defoliation. In this four‐year study, plants were grown in monoculture or in combination with the unpalatable Hilaria in a replacement design. Under no defoliation, the unpalatable Hilaria had a lower growth potential than Bouteloua curtipendula and Nassella leucotricha that were of equal stature, and produced only as much as the shorter grass, Buchloe dactyloides. Bouteloua had the highest growth potential under no‐defoliation and was defoliation tolerant, except when defoliated at ground level. Nassella was more productive than the unpalatable Hilaria, since the ability to grow earlier in the year enabled it to compete successfully with Hilaria. These results indicate that with adequate deferment Bouteloua and Nassella should compete successfully with Hilaria and Buchloe should be able to maintain itself in the presence of Hilaria. Under non‐selective defoliation, Hilaria was able to compete successfully only with Buchloe. Hilaria was sensitive to defoliation, despite being rhizomatous, and competed less successfully with Buchloe after non‐selective defoliation than it did when not defoliated. This indicates that the management practice of burning and stocking heavily with livestock until Hilaria is avoided, resulting in non‐selective defoliation, will not cause Hilaria to be more competitive with the more palatable Bouteloua, Buchloe or Nassella. Hilaria was able to compete most successfully under selective defoliation when it was not defoliated. Under selective defoliation, by avoiding herbivory, Hilaria is able to compete strongly with at least Buchloe and Nassella. The reaction of Nassella and Buchloe to selective defoliation indicates that they may have been displaced by Hilaria in the past. In contrast, under the short‐term and non‐limiting growth conditions of this study, Bouteloua competed successfully with Hilaria even under selective defoliation. These results do not rule out the possibility that, through selective defoliation, Hilaria may have displaced other grasses including Bouteloua in the past.     

Can hyperparasitoids cause large‐scale outbreaks of insect herbivores?

Synchronous population fluctuations occur in many species and have large economic impacts, but remain poorly understood. Dispersal, climate and natural enemies have been hypothesized to cause synchronous population fluctuations across large areas. For example, insect herbivores cause extensive forest defoliation and have many natural enemies, such as parasitoids, that may cause landscape‐scale changes in density. Between outbreaks, parasitoid‐caused mortality of hosts/herbivores is high, but it drops substantially during outbreak episodes. Because of their essential role in regulating herbivore populations, we need to include parasitoids in spatial modelling approaches to more effectively manage insect defoliation. However, classic host‐parasitoid population models predict parasitoid density, and parasitoid density is difficult to relate to host‐level observations of parasitoid‐caused mortality. We constructed a novel model to study how parasitoids affect insect outbreaks at the landscape scale. The model represents metacommunity dynamics, in which herbivore regulation, colonisation and extinction are driven by interactions with the forest, primary parasitoids and hyperparasitoids. The model suggests that parasitoid spatial dynamics can produce landscape‐scale outbreaks. Our results propose the testable prediction that hyperparasitoid prevalence should increase just before the onset of an outbreak because of hyperparasitoid overexploitation. If verified empirically, hyperparasitoid distribution could provide a biotic indicator that an outbreak will occur.     

Taste receptor activity and feeding behaviour reveal mechanisms of white spruce natural resistance to Eastern spruce budworm Choristoneura fumiferana

The pattern of feeding of Eastern spruce budworm Choristoneura fumiferana (Clem.) (Lepidoptera, Tortricidae) is compared on foliage from white spruce Picea glauca (Moench) Voss. (Pinaceae) trees previously determined to be susceptible and resistant to defoliation by budworm. No differences are observed in electrophysiological responses from taste sensilla to aqueous extracts of the two foliage types, nor is there a preference for either extract type in a choice test. Acetone extracts from the two foliage types are both preferred to a control sucrose solution, although neither elicits a preference relative to the other. These results suggest that there is no difference in phagostimulatory power of internal leaf contents of the two foliage types. Longer‐term observation of feeding behaviour in a no‐choice situation shows no difference in meal duration, confirming the lack of difference in phagostimulatory power. However, on average, intermeal intervals are twice as long on the resistant foliage, leading to an overall lower food consumption during the assay. This result suggests an anti‐digestive or toxic effect of the resistant foliage that slows behaviour and limits food intake. Previous research has shown that waxes of the resistant foliage deter initiation of feeding by the spruce budworm and that this foliage contains higher levels of tannins and monoterpenes. The data suggest that the resistant foliage contains a post‐ingestive second line of defence against the spruce budworm.     

Effects of defoliation on the resistance and tolerance of rice,Oryza sativa,to root injury by the rice water weevil,Lissorhoptrus oryzophilus

Understanding plant‐mediated interactions in agricultural systems may facilitate the development of novel and improved management practices, which is important, as management of these insects is currently heavily reliant on insecticides. The fall armyworm, Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae, Prodeniini), is a sporadic pest of rice fields in the southern USA. In southwestern Louisiana, this defoliating insect typically attacks rice early in the growth season, before fields are flooded. Defoliation by fall armyworm larvae may trigger increased expression of plant defenses, which may result in increased resistance to subsequent herbivores. The rice water weevil (RWW), Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae, Stenopelmini), enters rice fields as an adult both before and after flooding, but oviposition and larval infestation occur only after fields are flooded. RWW may be affected by changes in plant resistance caused by fall armyworm defoliation before flooding. The objectives of this study were to investigate the plant‐mediated effects of natural and artificial defoliation on population densities of RWW larvae after flooding and on the ability of rice plants to compensate for root injury by RWW larvae. In the 2015 season, fall armyworm defoliation before flooding resulted in reduced RWW densities after flooding. However, in 2016 no significant effects of fall armyworm defoliation on densities of RWW larvae were detected. Similarly, mechanical defoliation of rice before flooding did not affect RWW densities after flooding. Although lowest yields were observed in plots subjected to both root injury and defoliation, there was little evidence of a greater than additive reduction in yields from simultaneous injury. These results suggest a lack of plant‐mediated interactions among these two pests in rice in the southern USA.     

Effects of defoliation intensity on soil food-web properties in an experimental grassland community

We established a greenhouse experiment based on replicated mini‐ecosystems to evaluate the effects of defoliation intensity on soil food‐web properties in grasslands. Plant communities, composed of white clover (Trifolium repens), perennial ryegrass (Lolium perenne) and plantain (Plantago lanceolata) with well‐established root and shoot systems, were subjected to five defoliation intensity treatments: no trimming (defoliation intensity 0, or DI 0), and trimming of all plant material to 35 cm (DI 1), 25 cm (DI 2), 15 cm (DI 3) and 10 cm (DI 4) above soil surface every second week for 14 weeks. Intensification of defoliation reduced shoot production and standing shoot and root mass of plant communities but increased their root to shoot ratio. Soil microbial activity and biomass decreased with intensification of defoliation. Concentrations of NO₃–N in soil steadily increased with intensifying defoliation, whereas NH₄–N concentrations did not vary between treatments. Numbers of microbi‐detritivorous enchytraeids, bacterial‐feeding rotifers and bacterial‐feeding nematodes steadily increased with intensifying defoliation, while the abundance of fungal‐feeding nematodes was significantly enhanced only in DI 3 and DI 4 relative to DI 0. The abundance of herbivorous nematodes per unit soil mass was lower in DI 3 and DI 4 than in DI 0, DI 1 and DI 2, but when calculated per unit root mass, their abundance tended to increase with defoliation intensity. The abundance of omnivorous and predatory nematodes appeared to be highest in the most intensely defoliated systems. The ratio of abundance of fungal‐feeding nematodes to that of bacterial‐feeding nematodes was not significantly affected by defoliation intensity. The results infer that defoliation intensity may significantly alter the structure of soil food webs in grasslands, and that defoliation per se is able to induce patterns observed in grazing studies in the field. The results did not support hypotheses that defoliation per se would cause a shift between the bacterial‐based and fungal‐based energy channels in the decomposer food web, or that herbivore and detritivore densities in soil would be highest under intermediate defoliation. Furthermore, our data for microbes and microbial feeders implies that the effects of defoliation intensity on soil food‐web structure may depend on the duration of defoliation and are therefore likely to be dynamic rather than constant in nature.     

Defoliation of a grass is mediated by the positive effect of dung deposition,moss removal and enhanced soil nutrient contents: results from a reindeer grazing simulation experiment

Herbivory is one of the key drivers shaping plant community dynamics. Herbivores can strongly influence plant productivity directly through defoliation and the return of nutrients in the form of dung and urine, but also indirectly by reducing the abundance of neighbouring plants and inducing changes in soil processes. However, the relative importance of these processes is poorly understood. We, therefore, established a common garden experiment to study plant responses to defoliation, dung addition, moss cover, and the soil legacy of reindeer grazing. We used an arctic tundra grazed by reindeer as our study system, and Festuca ovina, a common grazing‐tolerant grass species as the model species. The soil legacy of reindeer grazing had the strongest effect on plants, and resulted in higher growth in soils originating from previously heavily‐grazed sites. Defoliation also had a strong effect and reduced shoot and root growth and nutrient uptake. Plants did not fully compensate for the tissue lost due to defoliation, even when nutrient availability was high. In contrast, defoliation enhanced plant nitrogen concentrations. Dung addition increased plant production, nitrogen concentrations and nutrient uptake, although the effect was fairly small. Mosses also had a positive effect on aboveground plant production as long as the plants were not defoliated. The presence of a thick moss layer reduced plant growth following defoliation. This study demonstrates that grasses, even though they suffer from defoliation, can tolerate high densities of herbivores when all aspects of herbivores on ecosystems are taken into account. Our results further show that the positive effect of herbivores on plant growth via changes in soil properties is essential for plants to cope with a high grazing pressure. The strong effect of the soil legacy of reindeer grazing reveals that herbivores can have long‐lasting effects on plant productivity and ecosystem functioning after grazing has ceased.     

Linking above-ground and below-ground effects in autotrophic microcosms: effects of shading and defoliation on plant and soil properties

Although factors affecting plant growth and plant carbon/nutrient balance – e.g., light availability and defoliation by herbivores – may also propagate changes in below‐ground food webs, few studies have aimed at linking the above‐ground and below‐ground effects. We established a 29‐week laboratory experiment (～one growing season) using autotrophic microcosms to study the effects of light and defoliation on plant growth, plant carbon/nutrient balance, soil inorganic N content, and microbial activity and biomass in soil. Each microcosm contained three substrate layers – mineral soil, humus and plant litter – and one Nothofagus solandri var. cliffortioides seedling. The experiment constituted of the presence or absence of two treatments in a full factorial design: shading (50% decrease in light) and artificial defoliation (approximately 50% decrease in leaf area in the beginning of the growing season). At the end of the experiment a range of above‐ground and below‐ground properties were measured. The shading treatment reduced root and shoot mass, root/shoot ratio and leaf production of the seedlings, while the defoliation treatment significantly decreased leaf mass only. Leaf C and N content were not affected by either treatment. Shading increased NO ₃–N concentration and decreased microbial biomass in humus, while defoliation did not significantly affect inorganic N or microbes in humus. The results show that plant responses to above‐ground treatments have effects which propagate below ground, and that rather straightforward mechanisms may link above‐ground and below‐ground effects. The shading treatment, which reduced overall seedling growth and thus below‐ground N use and C allocation, also led to changes in humus N content and microbial biomass, whereas defoliation, which did not affect overall growth, did not influence these below‐ground properties. The study also shows the carbon/nutrient balance of N. solandri var. cliffortioides seedlings to be highly invariant to both shading and defoliation.     

Cell growth analysis during steady and non-steady growth in leaves of perennial ryegrass (Lolium perenne L.) subject to defoliation

The effect of defoliation on leaf elongation rate (LER) and on the spatial distribution of epidermal cell lengths in the leaf growth zone was studied in vegetative main tillers of perennial ryegrass (Lolium perenne L. cv Modus) grown in a controlled environment. A new material approach was used to analyse the responses of epidermal cell expansion and production during the initial, non‐steady growth phase following defoliation. The analysis involved assigning an identity to individual expanding cells, assessing the displacement and estimating the expansion of cells with assigned identity during day 1 and day 2 after defoliation. LER decreased by 34% during the first 2 d after defoliation and did not recover to the pre‐defoliation rate within the 14 day regrowth period. Decreased LER on day 1 and day 2 after defoliation was associated with (i) a decrease in the length of the leaf growth zone; (ii) a decrease in the length at which epidermal cells stopped expanding; (iii) a reduced expansion of cells at intermediate growth stages; and (iv) a reduction in cell production (i.e. division) and an associated decrease in the number of expanding cells in the growth zone. However, defoliation had no effect on the expansion of cells located in the proximal part of the growth zone. Reduced LER at 14 d after defoliation was associated with a reduced cell production rate (27% lower than the pre‐defoliation rate) and decreased final cell size ( ? 28%).     

Developmental plasticity in birch leaves: defoliation causes a shift from glandular to nonglandular trichomes

The structures on leaf surfaces, e.g. trichomes, can act as effective antiherbivory mechanisms as chemical repellents. Structural defences usually represent constitutive resistance, but there are also a few cases of inducible morphological defences. We tested whether defoliation may induce changes in trichome production in white birch (Betula pubescens). The studied birches were either 0, 50 or 100% defoliated during the previous or current summer, and we measured the alterations in the production of glandular vs. nonglandular leaf trichomes, developmental instability (fluctuating asymmetry, FA) and leaf and shoot growth. We detected a clear shift from glandular to nonglandular leaf trichomes following previous‐year defoliation but not after current‐year defoliation. Furthermore, the density of nonglandular trichomes around the mid‐vein of leaves increased following previous‐year defoliation but decreased after current‐year defoliation. While leaf and shoot growth showed a distinct decrease in response to defoliation, FA turned out to be less sensitive. Consequently, previous‐year defoliation can induce the production of nonglandular trichomes in birch leaves. Because this response was accompanied by a reduction in glandular trichomes, the present results may suggest a trade‐off between the different trichome types of birch leaves.     

Restoring planted ancient woodland sites — Assessment,silviculture and monitoring

Summary

This paper deals with three aspects of the process of restoring planted ancient woodland sites(PAWS) to semi-natural conditions. Firstly, we describe a baseline assessment of botanical interest within a PAWS. This survey has been undertaken to determine the impact of clearfelling, particularly on lower plants and the subsequent colonisation of ground vegetation into areas currently dominated by needle litter. Secondly, we discuss some of the main considerations when undertaking restoration through alternative silvicultural systems to clearfell. Finally, we describe the main requirement for successful site monitoring for management purposes.

The last decade has seen considerable attention given to the benefits of restoring plantations on ancient woodland sites (PAWS) to semi-natural conditions. The survival of species and communities associated with ancient woodland through the process of conversion will be a critical measure of success for restoration practice. It is generally assumed that a gradual approach will improve the chances of such success.

Glencripesdale National Nature Reserve (NNR) is a heterogeneous area of semi-natural open ground, ancient woodland and Sitka spruce plantation. The plantation blocks contain occasional discrete elements of semi-natural vegetation, including some veteran trees. Because of difficult access and poor stability, silvicultural options are limited and clear felling is the only practical option. We describe a simple method of monitoring changes to cryptogamic communities and ground layer vegetation prior to and following clearfelling of the plantation matrix. Baseline data are presented.

In more stable and accessible stands, there are a number of alternative silvicultural approaches to consider when gradually restoring a PAWS. This paper addresses the question of how to secure ancient woodland remnants. We outline some of the initial silvicultural considerations such as stability, thinning/felling pattern and light requirements of native tree species. An approach to site monitoring is presented to allow managers to assess whether conditions are improving or declining and whether they are delivering objectives.     

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.     

Effects of leaf beetle damage on stem wood production in coppicing willow

1 The effect of defoliation by larvae of the leaf beetle Phratora vulgatissima on current‐year stem wood production of resprouting Salix viminalis was investigated for two years. Adjacent subplots with varying levels of defoliation within one large willow plantation in south Sweden were studied in the two years. 2 High defoliation levels reduced stem wood production by an average of 32 and 39% in the two years, respectively. 3 Medium defoliation levels reduced stem wood production by 16% in one year. In the other year, the stem wood production of medium‐defoliated stools did not differ significantly from stools exposed to low defoliation, i.e. there was full compensatory growth. 4 The main difference between the year with compensatory growth and the one without was that overall productivity was higher in the year with compensation. This finding forms the basis for a mechanistic model by which compensation could be accomplished. We propose that the major contribution to full compensation comes from an increased growth among intermediate‐sized shoots of medium‐defoliated stools relative to the corresponding shoots in stools exposed to low defoliation.