Christian Hébert

Landscape-Scale Habitat Selection Patterns of Monochamus scutellatus (Coleoptera: Cerambycidae) in a Recently Burned Black Spruce Forest

Abstract The host selection process of most phytophagous insects can be described as a sequence of behaviors leading from landscape-scale habitat location to host-plant scale, microsite selection. For the whitespotted sawyer, Monochamus scutellatus (Say), a fire-associated xylophagous cerambycid, host location and acceptance patterns have been relatively well described, whereas landscape-scale distribution patterns in recently disturbed areas have received virtually no attention. In a 5,097-ha recently burned black spruce forest of Quebec, Canada, we evaluated the variability of larval density of 569 trees in 114 plots, by using entry hole counts. This variability was then related to environmental variables ranging from tree- to landscape-scale. Both diameter at breast height (positive relationship) and fire severity (negative relationship) were significant at explaining larval density at tree scale. At larger scales, altitude had a negative effect on larval density, whereas plots having a higher percentage of unburned forest in a 500-m radius were more intensely colonized. The importance of the proximity of unburned stands could be linked to the feeding requirements of the adults, which should show preference for stands offering both egg-laying and feeding substrata, because several species of Monochamus have been shown to feed while being reproductively active. In our models, large-scale variables explained more variability in entry hole counts than did tree-scale variables. Thus, our results suggest that large-scale habitat location mechanisms may play an important role in the host selection process of the whitespotted sawyer. RÉSUMÉ (FRENCH). La sélection d’hôte des insectes phytophages comporte plusieurs étapes allant de la localisation d’un habitat à l’échelle du paysage jusqu’à la sélection d’un microsite de ponte à l’échelle de la plante hôte. La localisation et l’acceptation d’hôte ont été relativement bien décrites pour le longicorne noir Monochamus scutellatus (Say); cependant, la localisation d’habitat à grande échelle a retenu peu d’attention. Dans un feu ayant eu lieu en pessière noire au Canada, nous avons évalué la densité de larves dans 569 arbres de 114 parcelles d’échantillonnage par décompte de trous d’entrée. Ces densités ont été confrontées à des variables environnementales à échelles multiples. À l’échelle de l’arbre, la densité de larves était liée au diamètre de l’arbre et à la sévérité du feu. À plus grande échelle, l’altitude a eu un effet négatif sur la densité de larves, alors que les peuplements ayant davantage de forêt verte dans un rayon de 500 mètres ont été plus intensément colonisés. L’importance de la proximité de massifs verts peut être liée aux éxigences nutritionelles des adultes, qui devraient préférenciellement coloniser des peuplements comportant à la fois des sites d’oviposition et d’alimentation, puisque plusieurs espèces de Monochamus continuent de s’alimenter lorsque sexuellement actifs. Les variables à grande échelle ont expliqué plus de variabilité dans nos modèles que les variables à l’échelle de l’arbre. Il semble donc que les mécanismes de localisation d’habitat à grande échelle jouent un rôle important dans le processus de sélection d’hôte chez le longicorne noir.

Community structures of Collembola in sugar maple forests: relations to humus type and seasonal trends

Summary Community structures of Collembola and their seasonal fluctuations were studied in eight southern Quebec sugar maple ( Acer saccharum Marsh.) forests growing on mull, moder and mor humus types. Endogeic species were extracted from soil cores using Berlese-Tullgren funnels while epigeic species were collected using pit-light traps (Luminoc®). Comparisons of species presence, abundance, and dominance among sites and seasons were done using Sorensens similarity coefficients and CANOCO. A total of 92 species from 7 families and 35 genera were identified. Species dominance and community structure differed according to humus types. Two groups of endogeic species were identified. The mor/mor-moder type group included Folsomia penicula, Hypogastrura (Ceratophysella) spp. Que., Micrisotoma achromata, Onychiurus (Protaphorura)? parvicornis, Onychiurus (Onychiurus) sp. A Que. And Onychiurus (Onychiurus) sp. B Que. The mull/mull-moder type group included Isotoma (Desoria) notabilis, Tullbergia (Tullbergia) silvicola, Tullbergia (Tullbergia) clavata , and Pseudosinella alba. Such clear humus type relationships were not found among the epigeic species, but important seasonal changes in community structures were found for these species. Spring species were Sminthurinus (Katiannina) macgillivrayi, Hypogastrura (Ceratophysella) maheuxi, Hypogastrura (Hypogastrura) sp. A Que. and Sminthurinus (Sminthurinus) latimaculosus. Tomocerus (Pogonognathellus) flavescens, Sminthurinus (Sminthurinus) henshawi , and Orchesella hexfasciata appeared in the summer samples while Dicyrtoma (Dicyrtoma) aurata was found only in fall samples where it was dominant in most sites along with either Sminthurides (Sminthurides) lepus or Sminthurinus (Sminthurinus) quadrimaculatus. No strong seasonal trends were found among the dominant endogeic species.

Effects of habitat characteristics and interspecific interactions on co-occurrence patterns of saproxylic beetles breeding in tree boles after forest fire: null model analyses

It is often suggested that habitat attributes and interspecific interactions can cause non-random species co-occurrence patterns, but quantifying their contributions can be difficult. Null models that systematically exclude and include habitat effects can give information on the contribution of these factors to community assembly. In the boreal forest, saproxylic beetles are known to be attracted to recently burned forests where they breed in dead and dying trees. We examined whether species co-occurrences of saproxylic beetles that develop in, and emerge from, boles of recently burned trees show non-random patterns. We also estimated the extent to which both the post-fire habitat attributes and interspecific interactions among beetles contribute to such patterns. We sampled tree boles encompassing key attributes (tree species, tree size/dbh and burn severity) that are thought to characterize species–habitat associations of saproxylic beetles, a proposition that we tested using indicator species analysis. Two null models with no habitat constraints (“unconstrained”) indicated that a total of 29.4% of the species pairs tested had significant co-occurrence patterns. Habitat-constrained null models indicated that most of the detected species aggregations (72%) and segregations (59%) can be explained by shared and distinct species–habitat relationships, respectively. The assembly pattern was also driven by interspecific interactions, of which some were modulated by habitat; for example, predator and prey species tended to co-occur in large-sized trees (a proxy of available bark/wood food resource primarily for the prey). In addition, some species segregation suggesting antagonistic, competitive, or prey–predator interactions were evident after accounting for the species’ affinities for the same tree species. Overall, our results suggest that an intimate link between habitat and interspecific interactions can have important roles for community assembly of saproxylic assemblages even following disturbance by fire. We also show that a systematic application of null models can offer insight into the mechanisms behind the assembly of ecological communities.

Saproxylic Beetles in Disturbed Boreal Forests: Temporal Dynamics, Habitat Associations, and Community Structure

Abstract: Early postfire habitats harbour numerous saproxylic species. Some are opportunistic feeders, while others are closely associated with burned forests. This distinction is important for developing sound postfire forest management aimed at conserving biodiversity, as concerns should be mostly directed towards burn-associated saproxylic beetles rather than opportunistic species. Here, we examine species-habitat associations, temporal dynamics, and community structure of saproxylic beetles in black spruce and jack pine stands disturbed by wildfire and by a “non-fire” disturbance generated by girdling trees to mimic the small-scale gap dynamics characterizing old-growth boreal forests in Canada. We used flightinterception traps and reared logs to compare abundance, species richness, and species composition of saproxylic beetles among treatments. We found that over 30% of saproxylic beetles had an affinity with jack pine or black spruce affected by either fire or girdling. Assemblages consistently differed between disturbance types over the 3 y of the study. We found that successional changes in species composition were more pronounced in burned sites than those with the girdling treatment, which indicates that the contribution of fire-generated habitats to regional diversity increases over time. While postfire forests are notable for their early-colonizing saproxylic species, our results show that they can also have substantial value for supporting mid-successional species such as Acmaeops pratensis, which is already on European red lists. This forewarns us about long-term negative consequences that postfire salvage logging could have for certain species.

Relationships between soil chemistry, microbial biomass and the collembolan fauna of southern Québec sugar maple stands.

Abstract The relationships between the presence of endogeic and epigeic collembolan species and chemical and microbiological top soil parameters were examined for eight sugar maple forests. While the composition of the tree strata was similar among sites, the soil conditions varied widely and encompassed three regions of different geological origins as well as contrasting humus types. Endogeic species were extracted using Berlese-Tullgren equipment, whereas epigeic species were collected with pit-light traps (Luminoc®). In all, 92 species from 14 families and 36 genera were identified. The association between sampling locations and soil parameters was determined by principal component analysis (PCA), and the relationships between epigeic and endogeic collembolan communities and soil parameters were determined by canonical correspondence analysis (CCA and DCCA). The DCCA revealed that the distribution of endogeic species of the collembolan fauna was related to organic matter content, including pH, C, N, and C/N ratio. Sites were clustered according to humus types. Epigeic species were influenced by available P and exchangeable K and Mg. Sites were clustered according to geographical distribution, suggesting that for epigeic species, regional occurrence could be a stronger determinant of community composition than soil parameters.

Effect of temperature and host tree on cold hardiness of hemlock looper eggs along a latitudinal gradient.

The hemlock looper, Lambdina fiscellaria, is an economically important insect pest of Canadian forests which overwinters as eggs. Although the hemlock looper causes extensive damages, no information on the mechanisms related to its cold tolerance is known. The objective of this study was to determine the effect of temperature and exposure duration on hemlock looper winter survival but also to identify seasonal supercooling capacity and cryoprotectant levels of three populations along a latitudinal gradient. As host plant may contribute to offspring overwintering success, cold tolerance of hemlock looper eggs from parents whose larvae were fed on three different tree species was also measured. Mean supercooling point (SCP) of hemlock looper eggs was lower than -30 °C from October through the following spring with values being as low as -47 °C in February. Trehalose was the most abundant sugar found in hemlock looper eggs with a peak concentration of 0.3 μg mg⁻¹ DW⁻¹. Glycerol, a polyol, was more often absent in eggs of the different populations and tree species tested in the study. When exposed to different temperature regimes for various periods of time, significant mortality of hemlock looper eggs occurred at higher temperatures than the mean SCP. Thus, hemlock looper could be considered as a chill tolerant species. No clear pattern of population and host plant effects on SCP and cryoprotectants was detected in this study. However, when exposed to different winter temperatures and exposure duration, hemlock looper from higher latitudes survived better (survival rates ranging between 0 and 89% at -20 °C) than those from lower latitudes (survival rates ranging between 0 and 56% at -20 °C). Our results may contribute to a better understanding of hemlock looper winter biology and thus facilitate predictions of outbreaks and range expansion.

Oviposition Traps to Survey Eggs of Lambdina fiscellaria (Lepidoptera: Geometridae)

Abstract Outbreaks of the hemlock looper, Lambdina fiscellaria (Guenée), are characterized by rapid increase and patchy distribution over widespread areas, which make it difficult to detect impending outbreaks. This is a major problem with this insect. Population forecasting is based on tedious and expensive egg surveys in which eggs are extracted from 1-m branches; careful observation is needed to avoid counting old unhatched eggs of previous year populations. The efficacy of artificial substrates as oviposition traps to sample hemlock looper eggs was tested as a means of improving outbreak detection and population forecasting. A white polyurethane foam substrate (1,095 lb/ft3) used with the Luminoc insect trap, a portable light trap, was highly efficient in sampling eggs of the hemlock looper. Foam strips placed on tree trunks at breast height were less efficient but easier and less expensive to use for the establishment of extensive survey networks. Estimates based on oviposition traps were highly correlated with those obtained from the 1-m branch extraction method. The oviposition trap is a standard, inexpensive, easy, and robust method that can be used by nonspecialists. This technique makes it possible to sample higher numbers of plots in widespread monitoring networks, which is crucial for improving the management of hemlock looper populations.

Distribution Patterns of Three Long-Horned Beetles (Coleoptera: Cerambycidae) Shortly After Fire in Boreal Forest: Adults Colonizing Stands Versus Progeny Emerging from Trees

ABSTRACT We identified the factors that affect the early colonization of burned stands by adults and the progeny surviving in fire-killed black spruce trees for three cerambycid beetles: Acmaeops proteus proteus (Kirby), Acmaeops pratensis (Laicharting), and Monochamus scutellatus scutellatus (Say) (Coleoptera: Cerambycidae) in the northern Canadian boreal forest. Furthermore, we measured if progeny emerging from burned trees was related to patterns of adults captured in traps the same year as the fire. Fire severity at the stand and landscape scales were the most important predictors for colonizing adults. Except for A. pratensis, thick-barked and lightly burned trees positively influenced the occurrence of surviving progeny at the tree level. Last-instar larvae of A. pratensis emerged from burned trees more often in severely burned landscapes. This may result from biotic interactions with intraguild species or predators. With the exception of A. pratensis, variables affecting the postfire abundance and occurrence pattern of adults were strikingly different from progeny emerging after fire. Progeny emerging from burned trees was almost exclusively related to tree- or stand level characteristics, whereas colonizing adults were correlated with variables measured at various spatial scales, and most often at the landscape scale. Moreover, A. proteus proteus and M. scutellatus scutellatus adults were more common in severely burned landscapes, although their progeny emerged more often in lightly or moderately burned trees. Host selection behavior within stands (e.g., host acceptance) by colonizing adults or host suitability for the larvae might have caused this discrepancy.

Stand Composition and Structure as Indicators of Epixylic Diversity in Old-Growth Boreal Forests

Abstract: This study aims to evaluate the relative contribution to biodiversity of 4 dominant types of virgin black spruce (Picea mariana) forests found in a typical regional landscape of the black spruce—moss bioclimatic domain of central Québec: mature black spruce forests with a regular structure, old black spruce forests with a regular structure, old black spruce—fir (Abies balsamea) mixed forests with 2 stories, and mixed forests with irregular structure. A total of 16 stands covering these 4 forest types were sampled to characterize forest composition and structure as well as epixylic communities. Multivariate analyses of variance were performed to evaluate to what extent the epixylic community structure differed among the 4 forest types. Results show that the old two-story and irregular forest types sustain higher species richness of epixylics per unit area; therefore, these types may be key habitats for old-growth dependent species of bryophytes and lichens. The close association of epixylics with these forest types was mainly due to better moisture conditions and the presence of greater amounts of coarse woody debris in advanced decaying stages. We also demonstrated that forest compositional and structural attributes are good indicators of epixylic diversity. Finally, we suggest that maintaining old irregular black spruce—fir mixed forests should be the primary aim of conservation strategies for old-growth forests. Nomenclature: Brodo et al., 2001; Ley & Crowe, 1999; Crum & Anderson, 1980.

Differential Effects of Post-Fire Habitat Legacies on Beta Diversity Patterns of Saproxylic Beetles in the Boreal Forest

Abstract: Fire-generated mosaics of habitat legacies such as dead and dying trees are key structural components in boreal forest ecosystems that support diverse saproxylic beetles. Our study sought to elucidate the spatial pattern of community composition (beta diversity) of saproxylic beetles along gradients of post-fire habitat legacies (tree species composition, tree size [dbh], and burn severities) and geographical distance. For 2 y, we reared saproxylic beetles from 360 logs retrieved from 72 sites in burned forests. Tests were performed to explain the overall beta diversity (&bgr;sor) by partitioning it into its 2 components: the “species spatial turnover” due to species replacement (&bgr;sim) and the “richness-driven” beta diversity due to species richness differences (&bgr;rich)- Variations in tree species, tree size, and burn severity had significant effects on overall beta diversity (&bgr;sor) of saproxylic beetles; these effects varied according to the differential influence of these factors on the 2 distinct components of beta diversity. Tree composition had notable effects on species spatial turnover (&bgr;sim), for which saproxylic species composition differed between jack pine and black spruce, and it was more variable between jack pine sites than between black spruce sites. On the other hand, variation in tree size was primarily responsible for the richness-driven beta diversity component (&bgr;rich), which was highest between the smallest and largest dbh groups and lowest between largest and mid-sized trees. Similarly, richness-driven composition differed significantly across severity gradients and was highest across low to high severity and lowest between low-severity stands. Broader geographical distance per se did not affect compositional patterns of saproxylic beetles, yet the landscape context could have some effect. These results could have crucial implications for post-fire management, which also aims to efficiently conserve saproxylic beetles. The significant spatial turnover in saproxylic composition between black spruce and jack pine and the underlying host-tree specificity suggest that a mosaic of both tree species should be maintained in the landscape. The richness-driven beta diversity pattern along the tree size and severity gradients implies that it may be necessary to prioritize the most species-rich classes, such as larger trees with lower severity burns, but with qualifications to cater also for species displaying idiosyncratic distributions.