Marcel Darveau

Riparian forest strips as habitat for breeding birds in Boreal forests

Riparian forest strips are usually protected from logging for their buffer effect on aquatic habitats. However, their value to terrestrial wildlife is unknown. From 1989 to 1992, we compared bird abundance and species composition in 5 experimental riparian forest strips (20-m, 40-m, 60-m, and control [>300 m wide], intact strips, and 20-m-wide thinned strips), in boreal balsam fir (Abies balsamea) stands, for 3 years following clear-cutting. Bird densities increased 30-70% (P 0.05) thereafter to approximately pretreatment levels. The 20- and 40-m-wide riparian strips had highest mean bird densities, but also the fastest (P < 0.05) decreases thereafter. By the third year after clear-cutting, forest-dwelling species were less (P = 0.01) abundant than ubiquitous species in the 20-m strips. The golden-crowned kinglet (Regulus satrapa), Swainsons thrush (Catharus ustulatus), blackpoll warbler (Dendroica striata), and black-throated green warbler (D. virens) became nearly absent in 20-m strips. The removal of 33% of the trees in some 20-m strips resulted in a <20% decline of bird densities, a moderate effect that combined with the greater effect of strip narrowness. There was evidence that 60-m-wide strips are required for forest-dwelling birds. Bird populations may continue to decline in strips before regeneration of adjacent clear-cuts provides suitable habitat for forest-dwelling species

FORESTRY PRACTICES AND THE RISK OF BIRD NEST PREDATION IN A BOREAL CONIFEROUS FOREST

Reconciling tree harvesting with the maintenance of forest bird populations is a major concern of integrated management. Because bird nest predation causes >50% of the nest losses in passerines and is known to vary according to habitat characteristics, we explored some aspects of avian nest predation in relation to forestry practices in a boreal coniferous landscape managed primarily for timber production in Quebec. Using artificial tree and ground nests with Common Quail (Coturnix coturnix) and plasticine eggs, we compared the risk of nest predation (1) in experimental riparian forest strips of different widths (20-m, 40-m, and 60-m unthinned strips; >300-m control strips; and 20-m thinned strips) and (2) in clearcuts experimentally subjected to different regeneration practices (plantations with chemical and mechanical weeding, and naturally regenerated clearcuts) between 1992 and 1995. The risk of ground nest predation was lower in naturally regenerated clearcuts (5% daily probability of predation) than...

Short term response of small mammals and forest birds to silvicultural practices differing in tree retention in irregular boreal forests.

Abstract: The effects of logging on wildlife have been evaluated mainly in landscapes dominated by even-aged forest stands, leaving the impacts of harvesting on wildlife in irregularly structured stands less documented. We assessed the response of small mammals and birds to 4 silvicultural treatments with different levels of tree retention (from < 10% to 73%) in old-growth boreal forests of eastern Canada, where approximately 70% of stands have irregular structure. The experimental design controlled for local variation in the abundance of forest birds and small mammals by pairing each experimental harvested stand with an uncut stand. We found that species richness of small mammals and birds did not vary according to tree retention. Moss cover and vertical cover influenced small mammal community composition, whereas forest bird assemblages responded to conifer basal area, vertical cover, and snag availability. Species associated with silvicultural practices entailing retention levels > 55% included those that prefer closed canopy, such as the brown creeper (Certhia americana), ruby-crowned kinglet (Regulus calendula), and red-backed vole (Myodes gapperi). Our study demonstrates that silvicultural practices with retention levels > 55% are the most suitable for mitigating the impact of logging on animal communities in old-growth irregularly structured stands.

A landscape perspective of bird nest predation in a managed boreal black spruce forest.

Abstract Several landscape level studies have reported that bird nest predation increases as forest cover decreases. These studies have mainly been conducted in agricultural or urban regions. However, few studies have explored relationships between forest cover and nest predation in boreal forests managed for timber harvesting. In 1997 and 1998, we evaluated bird nest predation in a mosaic of clearcuts and forest remnants dominated by black spruce (Picea mariana [Mill.] B.S.P.) and located north of Lake Saint-Jean, Québec. We used a 7 km × 9 km grid of sampling points to determine nest predation at four landscape scales (local vegetation, and 250 m, 500 m, and 1000 m radii around sampling points). Artificial nests (ground and arboreal) containing a common quail (Coturnix coturnix L.) egg and a plasticine egg were used to calculate predation pressure and to identify nest predators. Nest predation was high over the entire study area. Dominant predators were the gray jay (Perisoreus canadensis L.) and the red squirrel (Tamiasciurus hudsonicus Erxleben). Depredation by squirrels was influenced by local variables in 1997 and by landscape variables in 1998. In the latter case, depredation by squirrels increased as spruce cover increased. Depredation by gray jays was positively related to water body area and jack pine (Pinus banksiana Lamb.) cover. Squirrels preyed more on ground nests than on arboreal nests, while gray jays preyed almost exclusively on arboreal nests. We conclude that these predators probably impose different threats to different songbird species in boreal black spruce forests. Our results show that, in the short term, timber harvesting did not seem to increase predation in a boreal black spruce forest.

Models to predict the distribution and abundance of breeding ducks in Canada

Detailed knowledge of waterfowl abundance and distribution across Canada is lacking, which limits our ability to effectively conserve and manage their populations. We used 15 years of data from an aerial transect survey to model the abundance of 17 species or species groups of ducks within southern and boreal Canada. We included 78 climatic, hydrological, and landscape variables in Boosted Regression Tree models, allowing flexible response curves and multiway interactions among variables. We assessed predictive performance of the models using four metrics and calculated uncertainty as the coefficient of variation of predictions across 20 replicate models. Maps of predicted relative abundance were generated from resulting models, and they largely match spatial patterns evident in the transect data. We observed two main distribution patterns: a concentrated prairie-parkland distribution and a more dispersed pan-Canadian distribution. These patterns were congruent with the relative importance of predictor variables and model evaluation statistics among the two groups of distributions. Most species had a hydrological variable as the most important predictor, although the specific hydrological variable differed somewhat among species. In some cases, important variables had clear ecological interpretations, but in some instances, e.g., topographic roughness, they may simply reflect chance correlations between species distributions and environmental variables identified by the model-building process. Given the performance of our models, we suggest that the resulting prediction maps can be used in future research and to guide conservation activities, particularly within the bounds of the survey area. Des modèles pour prédire la répartition et l’abondance des canards nichant au Canada RÉSUMÉ. Le manque de connaissances détaillées sur l’abondance et la répartition des espèces de sauvagine dans l’ensemble du Canada limite notre capacité à conserver et à gérer leurs populations de façon efficace. Au moyen de 15 années de données provenant d’inventaires aériens réalisés par transects, nous avons modélisé l’abondance de 17 espèces ou groupes d’espèces de canards dans les parties méridionale et boréale du Canada. Nous avons inclus 78 variables relatives au climat, à l’hydrologie et au paysage dans des modèles amplifiés d’arbres de régression, pour lesquels des courbes de réponse flexibles et les interactions multidimensionnelles entre les variables ont pu être examinées. Nous avons évalué la capacité de prédiction des modèles à l’aide de quatre paramètres et avons estimé l’incertitude en calculant le coefficient de variation des prédictions d’un jeu de 20 répétitions de modèles. Des cartes de l’abondance relative prédite ont été produites à partir des modèles et elles correspondent bien au profil spatial des données récoltées dans les transects. Nous avons observé deux tendances principales dans la répartition : l’une centrée sur les Prairies et les forêts-parcs, l’autre plus dispersée à la grandeur du Canada. Ces tendances coïncidaient avec l’importance relative des variables explicatives et les statistiques d’évaluation des modèles pour les deux groupes de répartition. Les variables qui expliquaient le mieux la répartition de la majorité des espèces avaient trait à l’hydrologie, bien que plus spécifiquement, elles différaient quelque peu d’une espèce à l’autre. Pour certaines variables importantes d’après les modèles, nous avons pu établir des liens clairs entre celles-ci et la répartition des espèces, tandis que pour d’autres, par exemple l’irrégularité du relief, nous pensons qu’elles pourraient simplement être le fruit de corrélations, attribuables au hasard, entre la répartition des espèces et les variables environnementales retenues lors du processus de consolidation des modèles. Considérant les performances de nos modèles, nous proposons que les cartes de répartition prédite soient utilisées dans le cadre de recherches futures et à des fins d’orientation des activités de conservation, surtout à l’intérieur des limites de notre aire d’étude.

Site complementarity between biodiversity and ecosystem services in conservation planning of sparsely-populated regions.

The consequences of considering ecosystem services (ES) in conservation assessment are still widely debated. The degree of success depends on the extent to which biodiversity and ES can be secured under joint conservation actions. Unlike biodiversity, ES conservation is inseparably linked to human beneficiaries. Reconciling biodiversity with ES and conservation can be particularly challenging in sparsely populated areas. This study, in a sparsely-populated region of eastern Canada, focused on freshwater wetland biodiversity and ten ES provided by wetlands. Within a given maximal total area, the results showed that planning for biodiversity underrepresented local flow ES supply by 57% and demand by 61% in conservation networks. Planning for ES alone underrepresented wetland biodiversity surrogates by an average of 34%. Considering both biodiversity and ES simultaneously, all of the biodiversity and ES targets were achieved with only a 6% mean increase in area. Achieving all conservation targets starting from a network that was primarily built for either ES or biodiversity features alone was two to five times less efficient than considering both ES and biodiversity simultaneously in conservation assessment. A better framework is required to translate these spatial synergies into effective joint conservation actions.

The Importance of Geology, Climate and Anthropogenic Disturbances in Shaping Boreal Wetland and Aquatic Landscape Types

Abstract: Boreal wetlands are recognized as important wildlife habitats, especially as breeding and staging grounds for a large number of waterfowl. The main objectives of this study were to quantify the distribution of wetland and aquatic wildlife-habitat landscape types within boreal Quebec and to determine how such recognizable wildlife habitats vary among climatic regimes and landforms. A total of 456 forest maps systematically distributed within a 540000 km2 area were used to classify 12 wetland and 5 different aquatic habitat types. Habitat types belonging to wetland and aquatic classes respectively covered 10.3 % and 11.7 % of the study area. Spatial heterogeneity was confirmed using a hierarchical cluster analysis by identification of 6 wetland landscape types further categorized into 3 groups: wet, dry, and anthropogenic. The last emphasizes the magnitude of human alteration of aquatic habitats, with reservoirs representing 26% of total water coverage. Partial redundancy analyses showed that landform data alone had better explanatory power (28%) than climatic data (19%) to account for the variation in wetland coverage. These results suggest that terrestrial ecozones based on landform (rather than climate) could serve as indicators for wetland conservation planning and facilitate wetland conservation and management decisions.

Bot fly parasitism of the red-backed vole: host survival, infection risk, and population growth

Parasites can play an important role in the dynamics of host populations, but empirical evidence remains sparse. We investigated the role of bot fly (Cuterebra spp.) parasitism in red-backed voles (Myodes gapperi) by first assessing the impacts of the parasite on the probability of vole survival under stressful conditions as well as on the reproductive activity of females. We then identified the main factors driving both the individual risk of infection and the abundance of bot flies inside red-backed voles. Finally, we evaluated the impacts of bot fly prevalence on the growth rate of vole populations between mid-July and mid-August. Thirty-six populations of red-backed voles were sampled in the boreal forest of Québec, Canada. The presence and the abundance of parasites in voles, two host life history traits (sex and body condition), three indices of habitat complexity (tree basal area, sapling basal area, coarse woody debris volume), and vole abundance were considered in models evaluating the effects of bot flies on host populations. We found that the probability of survival of red-backed voles in live traps decreased with bot fly infection. Both the individual risk of infection and the abundance of bot flies in red-backed voles were driven mainly by vole abundance rather than by the two host life history traits or the three variables of habitat complexity. Parasitism had population consequences: bot fly prevalence was linked to a decrease in short-term growth rate of vole populations over the summer. We found that bot flies have the potential to reduce survival of red-backed voles, an effect that may apply to large portions of populations.

Modeling distribution and abundance of multiple species: Different pooling strategies produce similar results

Quantifications of spatial distribution and abundance of animals are essential to identifying key landscape characteristics and targeting locations for conservation action. Since conservation decisions often focus on multiple species aggregated in groups, e.g., guild-level, rather than individual species, predictions of species group abundance are of central importance. However, areas chosen for conservation action may differ if results from various modeling strategies also differ. Therefore, we compared three different strategies for modeling species group distribution and abundance: predict first, assemble later (PA); assemble first, predict later (AP); and the combined assemble, predict, then assemble (APA). All strategies were performed using Boosted Regression Trees (BRTs), which were fit to individual species data and then grouped after modeling, or fit to datasets that were grouped before modeling. Modeling strategies produced very similar results in terms of statistical performance assessed throug...

North American Beaver (Castor canadensis Kuhl) key habitat characteristics: review of the relative effects of geomorphology, food availability and anthropogenic infrastructure

ABSTRACT The North American beaver is considered a keystone species because its behaviour leads to profound changes in the wetland systems within forested landscapes. Such changes influence species composition and their interactions. However, in some cases, beavers are considered as an important source of disturbance and conflict with anthropogenic activities. In this paper, we reviewed regional studies using geomorphology, food availability and anthropogenic infrastructure on spatial modelling of beaver habitat. Even though all studies used different sets of variables and methodologies, important factors affecting beaver occurrence or abundance are mainly stream gradient, watershed size and hardwood cover that is adjacent to the streams. However, the identification of key habitat indicators often varies between studies depending upon the object being modelled (colonies vs. dams), the geomorphological characteristics of the region, and the scale of the study area. Recent developments in geomatics and improved data quality now allow spatial modelling of beaver habitat across larger areas, and make models using at least stream gradient and forest cover types more accessible to managers. Such large-scale predictive beaver habitat models could have valuable applications for the prevention of infrastructure damage and related costs, and for managing wildlife species that rely upon beaver ponds.