Saproxylic insect assemblages associated with burned forests are generally abundant and species rich, consisting of a mix of pyrophilous and secondary, opportunistic species depending on time elapsed since disturbance. Life-history traits associated with each group suggest that they may respond differentially to habitat fragmentation caused by salvage logging, with pyrophilous species having a much higher dispersal potential. In a 2-year-old burn highly fragmented by pre- and post-fire logging, we sampled saproxylic beetles in coniferous and broadleaf burned residual stands along a gradient of spatial context including intensity of fragmentation and isolation from source habitat using Lindgren multiple-funnels traps. Beetle assemblages differed in composition between coniferous and broadleaf burned stands, with secondary users dominating the latter. Pyrophilous species increased in abundance with distance from the edge and avoided unburned patches within the fire. Secondary users did not respond negatively to fragmentation or isolation of burned habitats, with one exception, the alleculid Isomira quadristriata (Couper), being overall diverse and abundant throughout the study area regardless of salvage logging prevalence. No deleterious effects of isolation were thus detected in the occurrence patterns of secondary users, even up to 8 km from the edge. Our results suggest that older burns, especially those having some broadleaf cover, are intensively used by non-pyrophilous saproxylic species usually associated with dead wood in green forests and may contribute to maintain broader saproxylic assemblages than originally thought, especially when considering the importance of dead wood volume pulses associated with fire in boreal forests. © 2012 The Royal Entomological Society.

Fire severity can vary greatly within and among burns, even in the Canadian boreal forest where fire regimes consist mostly of stand-replacing fires. We investigated the effects of fire severity on the long-term occupancy of burns by (i) saproxylic insects and (ii) three wood-foraging birds. Based on observations made 6 to 11 years after fire in burned conifer forests that varied in fire severity in Quebec, Canada, our results indicate that low-severity portions of the burns likely provided snag conditions suitable for the long-term presence of deadwood-associated insects and birds. The black-backed woodpecker, a post-fire forest specialist, was still abundant 6 and 8 years after fire. This pattern was likely explained by the persistence of several saproxylic insect species that are associated with recently dead trees and by the positive effect of lower fire severity on the abundance of Arhopalus foveicollis, a cerambycid with a long life cycle in dead wood. The American three-toed woodpecker and the brown creeper, and their associated prey (Scolytinae beetles), were more abundant in burned stands of lower v. higher severity. We conclude that less severely burned snags and stands within high-severity burns may favour the long-term presence of trophic webs that involve saproxylic insects and wood-foraging birds in burned boreal forests.

Fire has been part of the North American boreal and cordilleran ecosystems for thousands of years. Because fire and harvesting compete directly for the same wood supply, and provinces have, within the last few decades, tended to reach their annual allowable cut, salvage logging has emerged as a practice to minimize the impact of fire on long-term wood supply. In most parts of the boreal and cordilleran forests, fire-killed boles rapidly degrade after their death, as wood-boring insects, stain, wood-decay fungi and checking lead to significant loss of grade or volume in the months following the fire. Because of this impending degradation, salvage operations are often hurried and other considerations, including the potential ecological impacts of salvage logging, have seldom been taken into consideration when defining harvesting strategies. The ecological consequences of rapid salvage have been widely studied only in the last 5 years, and it is now clear that salvage logging can have negative impacts on natural regeneration by seed, water quality, and fire-associated animal species. In this paper, we review both industrial and ecological constraints to salvage logging and discuss how both can be integrated in salvage plans. In particular, we focus on the issues of salvage timing and retention. At this point, some type of retention of merchantable stands, even if only for a few years, appears to be the only way to alleviate the negative ecological impacts of post-fire logging. On-site operational constraints, e.g., stands that cannot be harvested due to lack of accessibility, represent an important starting point for any retention strategy.

We examined landing patterns of phloeophagous and xylophagous Coleoptera among trees and snags of different physiological and decay states in a pure open-canopy black spruce stand in boreal Canada to study prelanding host selection mechanisms in the absence of nonhost volatiles. Sticky traps were used to capture insects landing oil high- and low-density natural snags (i.e., wood density), girdled trees, living trees, and stovepipe controls. Patterns were generally weak, with high within-group variability in species composition and landing rates. Within-group variability differed between groups, with highest variations in living trees and recent snags. Despite this evidence of frequent landing oil Suboptimal or inappropriate hosts, affinities were detected in most common taxa. Cerambycidae showed preferences for girdled trees. Common species of Scolytinae showed divergent preferences, because Crypturgus borealis Swaine and Dryocoetes autographus (Ratzeburg) were captured more often on high-density natural snags, Polygraphus rufipennis (Kirby) oil girdled trees, and Orthotomicus latidens (LeConte) oil living trees. These observed landing patterns are broadly consistent with current knowledge oil the ecology of these species. Although preferences, and thus prelanding assessment of hosts based oil volatiles, were detected in several species, the numerous landings observed on inappropriate hosts suggest that random landing at close range may be as common in pure stands as what was previously observed in mixed stands.

ABSTRACT

Extensive even-aged management of the boreal forest and its consequences on the loss of late-seral stages (>100 years) is raising concerns about the future of organisms associated with standing deadwood. The considerable reduction of deadwood not only at the stand but at the landscape level is considered to be one of the principal causes of biodiversity loss in managed forest ecosystems worldwide. Ecosystem-oriented management approaches propose a fundamental change in forestry practices whereby live and dead tree retention becomes an important consideration in forest harvesting. We use woodpecker assemblages and their association with standing deadwood for both nesting and foraging to emphasize the importance of the entire range of snag degradation stages for maintenance of key ecological processes in habitat remnants of managed landscapes. We argue that bridging foraging and nesting knowledge of woodpecker’s snag requirements can refine conservation objectives for deadwood retention in the boreal forest.

RÉSUMÉ

L’aménagement équien de la forêt boréale transforme le couvert forestier notamment en réduisant la proportion de forêts âgées (>100 ans). Cette diminution des forêts âgées s’accompagne d’une baisse considérable du bois mort à l’échelle des peuplements et des paysages, ce qui est considérée comme l’une des principales causes de perte de diversité biologique dans les forêts aménagées à l’échelle mondiale. Les approches écosystémiques proposent un changement fondamental en foresterie, soit que la rétention des arbres vivants et morts dans les forêts aménagées devient une considération importante en aménagement forestier. Dans cet article, nous utilisons les assemblages de pics et leurs relations avec le bois mort sur pied pour statuer sur l’importance de conserver le spectre complet de stades de dégradation du bois mort dans les habitats résiduels des territoires aménagés pour maintenir les fonctions écologiques des pics, un groupe d’espèces clés dans les forêts âgées. Nous considérons l’importance de faire les liens entre les besoins d’alimentation et de reproduction des pics pour raffiner les objectifs de conservation du bois mort en forêt boréale.

Saproxylic Coleoptera are diverse insects that depend on dead wood in some or all of their life stages. In even-aged boreal forest management, remnant habitats left as strips and patches contain most of the dead wood available in managed landscapes and are expected to act as refuges for mature forest species during the regeneration phase. However, use of remnant habitats by the saproxylic fauna has rarely been investigated. Our objective was to characterize the saproxylic beetle assemblages using clearcuts and forest remnants in western Québec, Canada, and to explore the effects of forest remnant stand characteristics on saproxylic beetle assemblages. We sampled both beetle adults and larvae, using Lindgren funnels and snag dissection, in five habitat locations (clearcuts, forest interiors of large patches, edges of large patches, small patches and cut-block separators) from three distinct landscapes. Adult saproxylic beetles (all feeding guilds combined) had significantly higher species richness and catch rates in small patches compared to forest interiors of large patches; the phloeophagous/xylophagous group had significantly higher species richness only. Small patches, cut-block separators and edges of large patches also had the highest snag density and basal area, increasing habitat for many saproxylic beetles. No significant differences in density of saproxylic larvae were found between habitat patches, but snag dissection nevertheless suggests that snags in forest remnants are used by comparable densities of insects. Saproxylic beetles appear to readily use habitat remnants in even-aged managed landscapes suggesting that forest remnants can insure the local persistence of these species, at least in the timeframe investigated in our study.

1. Determinants of host-use patterns in plant-feeding insects have been extensively studied, usually within the framework of optimality theory. Comparatively, factors driving host selection in saprophagous insects have received little attention.

2. In this study, mechanisms creating occurrence peaks of saprophagous wood-borers (Cerambycidae: Coleoptera) in standing dead aspen in the middle and late stages of decay were investigated by correlating insect occurrence with variations in substrate-related nutritional and physical parameters. Twenty-four snags at four decay stages were dissected from a mature stand in western Quebec, Canada. Wood samples were taken to measure levels of nitrogen, non-structural carbohydrates, phenols, wood density, water content and snag age.

3. Several nutritional and physical parameters varied significantly along the decay gradient and were correlated with insect occurrence, but all significant parameters were also strongly correlated with snag age and wood density. Model selection using Akaike’s second order information criteria was used to rank the different models; the model including snag age only performed best, with a wi of 0.873.

4. This importance of snag age gives support to a proposed hypothesis of host selection in which temporal autocorrelation in probability of insect occurrence explains peaks observed in the middle and late stages of decay. However, further studies will be needed to confirm the prevalence of such neutral mechanisms over active selection in the determination of host-use patterns in decaying aspen.

Several boreal insect species respond to smoke and heat generated by forest fires and use recent burns to reproduce in high numbers. Some of these species are rare or uncommon in undisturbed forests, and the contribution of recently burned habitats to their population dynamics has been deemed crucial by some to their long-term persistence. Consequently, the severe decline seen in some species in Fennoscandia has been frequently linked with fire suppression. In this paper, we explore some aspects of the spatial dynamics of pyrophilous insect populations in relation to the expected relative contribution of burned and unburned habitats to their global population dynamics. Forest fires are, throughout the boreal forest biome, generally highly aggregated in some years while rare in most other years. The low connectivity between fire events and the typical life cycle seen in these species make it improbable that recent burns act as significant population sources. This leads us to suggest that populations of pyrophilous species may be more limited by the adequacy of the unburned matrix than by the occurrence of fire events. Moreover, by combining an age-class distribution model and a dead wood availability model, we show that the quality of the unburned matrix increases in landscapes with longer fire cycles, in which pyrophilous insects should persist at higher population levels. We conclude that the degradation of the unburned habitat better explains the decline of pyrophilous insects than fire suppression alone.

1 Most plant-feeding insects show some degree of specialization and use a variety of cues to locate their host. Two main mechanisms of host location, primary attraction and random landing, have been investigated for such insects.

2 Research has led to contradictory conclusions about those hypotheses, especially for wood-feeding insects; however, recent studies suggest that both mechanisms may take place in a single taxon but at different scales.

3 We developed a field experiment to test the hypothesis that primary attraction occurs at larger scale and random landing at finer scale in wood-feeding insects. Landing rates, measured using sticky traps, were compared first between patches and then between individual trees according to their distance to a baited central tree.

4 Polynomial functions describing landing rate to distance relationships were compared with a function produced by a null model describing what should occur under the random landing hypothesis. Scolytidae and Cerambycidae (Coleoptera) responded to volatiles at the patch scale, supporting the primary attraction hypothesis, but the landing patterns of some groups at finer scale matched closely the predictions of our null model, giving support to the random landing hypothesis.

5 Our results show that the primary attraction and random landing hypotheses are not mutually exclusive and that prelanding use of host-produced volatile is scale-dependant. Scale considerations should thus be included in the study of prelanding host-selection of wood-feeding insects.

Some currently used tree-scale sampling techniques targeting saproxylic insects capture individuals that are attracted to or landing on speciÞc potential hosts. The success of such techniques is entirely dependent on strong primary attraction in targeted insects. However, up to this point, Þeld experiments testing the primary attraction hypothesis have produced contradictory results. To test the efÞciency of such techniques, and consequently, the strength of primary attraction for saproxylic Coleoptera, we sampled insects landing on contrasting snag types including new and old snags of Þve different tree species using sticky traps in a single mixed 135-yr-old boreal stand in Western Quebec, Canada. Ordination analyses showed homogenous assemblages among the different snag types and stovepipe controls, when considering either all species captured or only targeted functional groups, and very few species showed strong afÞnities to speciÞc snag types. Species composition of assemblages was in several cases correlated with the species and status of trees neighboring the sampling units, which suggest that prelanding host selection mechanisms do not allow insects to single out a potential host while in ßight. Our results suggest that primary attraction may play a role at larger spatial scales and help insects identify potential habitat patches, while selection of a single host at the local scale is done by trial-and-error through random landing. In such a context, future studies aiming at describing precise host-use patterns of saproxylic insects should rely on methods targeting larvae or emerging adults such as wood dissection and rearing.

Abstract

The general objectives of this thesis project were to describe and to understand the dynamics creating occurrence patterns of saproxylic wood-feeding Coleoptera in snags (i.e., standing dead trees) of black spruce and aspen along the decay gradient. The first part of this thesis focuses on pre-landing host-selection behaviours in coniferophagous species, i.e. the use of host-produced volatiles to locate potential hosts. Results presented suggest that most saproxylic wood-feeding beetles studied herein use volatiles to orient towards potential habitat patches but that olfactive information does not allow the identification of suitable hosts at close range prior to landing. The second part of the thesis focuses on the occurrence patterns themselves and on underlying mechanisms. Sampling was conducted using snag dissection, a novel method allowing a better characterization of larval stage wood-feeding assemblages. Opposite patterns were observed between the two host species studied, as abundance and species richness were highest in early stages of decay in spruce, and in middle to late stages of decay in aspen. In aspen, numerous nutritional and physical parameters of dead wood correlated significantly with wood-borer occurrence. However, most of these parameters were strongly auto-correlated, and the explanatory model most highly ranked by model selection consisted of only a snag age term. Also, a simple neutral model based on temporal autocorrelation in occurrence probability produced patterns similar to those observed through sampling. In the last original paper presented, results suggest that wood-boring larvae select for specific types of substrate in highly variable aspen snags. This selection on the part of the larvae likely decreases the impact of the oviposition site on subsequent larval performance, and could explain the lack of strong selection seen on the part of the mother. My results suggest very different host-selection dynamics in black spruce and aspen, as assemblages of the former were dominated by early-decay species with volatiles-driven colonization dynamics, while middle- to late-decay species dominated the later, seemingly through mostly neutral colonization mechanisms. Some of my findings suggest that patterns observed in black spruce and aspen could be extrapolated to a coniferous/deciduous host dichotomy in colonization dynamics of woodfeeding species, based on divergent secondary chemistry and wood structure.

Résumé

Les objectifs de cette thèse consistaient à décrire et comprendre les méchanismes créant les patrons d’utilisation d’hôte chez les coléoptères saproxylophages utilisant l’épinette et le peuplier au long du gradient de décomposition. La première partie étudie l’utilisation des volatiles relâchés par l’hôte dans le processus de sélection d’hôte de ces insectes. Les résultats obtenus suggèrent que les insectes saproxylophages utilisent ces volatiles pour identifier une parcelle contenant un hôte potentiel, mais qu’ils ne peuvent être utilisés pour localiser un hôte en particulier à courte distance. La deuxième partie se concentre sur les patrons d’occurrence et les méchanismes sous-jacents. L’échantillonnage s’est effectué par dissection, méthode originale permettant une meilleure caractérisation des assemblages d’espèces saproxylophages, en particulier de stade larvaire. Des patrons opposés ont été observés entre les deux espèces d’arbre, les insectes étant concentrés en début de décomposition chez l’épinette, et davantage en fin de gradient chez le tremble. Chez le tremble, plusieurs paramètres nutritionels et physiques du bois étaient corrélés avec l’occurrence d’insectes. Cependant, la plupart de ces paramètres étaient corrélés entre eux, et le modèle le plus performant identifié ne comprenait que l’âge des chicots. Aussi, les patrons observés ont pu être re-créés par un simple modèle neutre basé sur l’autocorrelation temporelle dans la probabilité d’occurrence. Les résultats du dernier article suggèrent que les larves saproxylophages effectuent une sélection pour des types de substrats spécifiques au sein de chicots de tremble hautement variables. Cette sélection larvaire diminue l’impact du site d’oviposition originel sur la performance des larves, et pourrait expliquer le faible degré de sélection observé chez les espèces se développant dans le tremble. Mes résultats suggèrent des dynamiques de sélection d’hôte très différentes entre l’épinette et le tremble, les assemblages étant dominés chez l’épinette par des espèces de début de décomposition ayant des comportements de sélection axés sur les volatiles relâchés par leur hôte, et par des espèces de décomposition avancée aux dynamiques en apparence plutôt neutres chez le tremble. Ces divergences pourraient s’extrapoler à une dichotomie conifères/feuillus plus large basée sur les différences au niveau de la chimie secondaire et de la structure du xylème. © 2006 McGill tous droits réservés.

For thousands of years, fire has been the main stand-replacing disturbance in the boreal forest but is now being supplemented by logging over most of the biome's extant. Community response to such disturbances of different nature and severity has been extensively compared in plant, but rarely in animal communities. Effects of fire and logging on some groups, such as ground beetles, have been assessed but separately, in different regions and different time frames. In a single 250-km² spruce-dominated landscape in the province of Quebec, Canada, we sampled ground beetle assemblages from recently logged (n = 12), recently burned (n = 12) and control stands (n = 18) using pitfall traps. Our objective was to compare assemblages from recently disturbed areas of the same age and nested in the same matrix. Assemblages were not highly specific to single habitats, but diverged significantly between treatments in abundance and species dominance. Capture rates were highest in logged stands, and lowest in burned stands. Forest generalists, including Calathus ingratus Dejean and Pterostichus brevicornis (Kirby), dominated assemblages in logged stands. We suggest that the contrasting activity levels observed following these two types of disturbance and the dominance of forest generalist in logged stands may partly reflect initial mortality patterns caused by these disturbances, as fires as severe as the one sampled in this study generally result in a much higher mortality rate in soil invertebrates than logging. © 2005 Elsevier B.V. All rights reserved.

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.

Several insect groups have adapted to fire cycles in boreal forests, and can efficiently use new habitats created by fire. Our study aimed at producing a first characterization of post-fire Coleoptera assemblages of black spruce forests of eastern North America. For two years, we sampled Coleoptera using flight-interception traps in burned stands of contrasting age and structure in a 5097-ha wildfire and in neighbouring unburned mature stands. More than 40 species were exclusively captured in burned stands. Time elapsed since fire and proximity of unburned forests were the most significant parameters affecting Coleoptera assemblages. Stand age and structure had limited effects on assemblage structure; the Scolytid Polygraphus rufipennis Kirby was the only common species to clearly favor older stands. Fire-associated Coleoptera assemblages found in our study area were clearly distinct from those found in similar unburned stands; we should thus be conservative in our management approach concerning recently burned stands.

Plusieurs groupes d’insectes sont adaptés aux cycles de feu en forêt boréale, et peuvent exploiter efficacement les habitats créés par le feu. Cependant, leur dépendance au feu les rend vulnérables aux phénomènes raréfiant ou dégradant les habitats brûlés, comme la suppression des feux, les changements climatiques ou les coupes de récupération. Une meilleure connaissance des espèces pyrophiles nord-américaines est nécessaire, puisque les forêts boréales de l’Est du Canada seront de plus en plus assujetties à ces facteurs dans les années à venir. Le feu ayant eu lieu dans le parc provincial des Grands-Jardins au début de l’été 1999 a offert une occasion privilégiée d’étudier un brûlis qui ne fera pas l’objet de coupes de récupération. Cette étude avait pour objectifs de caractériser la structure et la composition des communautés de coléoptères pyrophiles de la forêt boréale de l’est de l’Amérique du Nord, et d’établir des liens entre diverses variables environnementales et le patron d’utilisation d’habitat de ce groupe d’insectes. Dans le premier chapitre de ce mémoire, quatre groupes de peuplements aux structures et aux âges contrastants ont été échantillonnés à l’aide de pièges à interception, soit des forêts âgées de 20, 50 et 80 ans ayant brûlées en 1999, et des forêts de 80 ans ayant été épargnées par les flammes. Le niveau d’activité, la richesse et la structure des communautés résultantes ont été comparés et mis en relation avec des variables de structure de peuplement et de contexte spatial au sein du paysage. De la quarantaine d’espèces qui ont présenté un patron de distribution pyrophile, la plupart sont soit dépendantes du bois mort ou effectuent leur développement larvaire dans le sol. Les communautés exploitant des peuplements de structures très différentes étaient étonnamment semblables. L’année d’échantillonnage et le pourcentage de forêt verte dans un rayon de 250 mètres autour de la parcelle d’échantillonnage sont les deux facteurs ayant le plus influencé les communautés échantillonnées. Au deuxième chapitre, 84 segments de troncs d’arbres (40 cm de longueur) tués par le feu ont été prélevés et mis en élevage au cours des étés 2000 et 2001. Les arbres ont été sélectionnés en fonction de critères de diamètre, de hauteur et de sévérité du feu. Les facteurs liés à l’arbre tel le diamètre, le degré de carbonisation de l’écorce et la vigueur de l’arbre avant sa mort par le feu étaient déterminant dans l’abondance d’insectes émergeant des bois brûlés. Cette étude met en évidence qu’on retrouve en forêt boréale québécoise une entomofaune riche spécialisée dans l’exploitation des forêts brûlées et qu’il serait possible de se baser sur l’écologie de ces organismes pour mettre sur pied des stratégies d’aménagement viables favorisant la conservation de la biodiversité favorisée par le feu. © 2003 UQAM tous droits réservés.