Résilience des sapinières aux surabondances des grands herbivores : le contrôle des densités permet-il le retour des composantes taxonomiques et fonctionnelles de l'écosystème?

Combiner des approches basées sur la composition en espèces et sur les traits fonctionnels a permis d’évaluer la réaction de l’écosystème forestier boréal à la suite de réductions de densités de cerfs, dans un contexte de surabondance. Un dispositif de broutement contrôlé a été instauré en 2001 à l’île d’Anticosti et a été suivi pendant 8 ans. Dans ce dispositif, la densité de cerfs était maintenue à 4 niveaux : 0, 7,5, 15 cerfs/km2 ainsi qu’à densité in situ (26-56 cerfs/km2). Avec l’approche taxonomique, 12 plantes, 11 papillons et 1 oiseau ont été identifiés comme indicateurs de 12 densités de cerfs. L’utilisation de combinaisons de deux ou trois espèces de plantes a ajouté des indicateurs pour 17 patrons de densités de cerfs augmentant ainsi la capacité d’estimation des densités. Ensuite, des syndromes fonctionnels à hautes densités et densités réduites de cerfs ont été identifiés grâce à l’analyse des traits fonctionnels des communautés. À haute densité de cerfs (> 15 cerfs/km²), les traits dominants chez les plantes, tels qu’une reproduction végétative et une pollinisation et dispersion abiotique, impliquaient peu d’interactions avec les animaux, ce qui pourrait nuire au maintien de la biodiversité. De plus, bien que les méthodes de réduction de cerfs ne permettent pas, en 8 ans, un retour de la composition en espèces d’une sapinière de référence, elles permettent une succession menant à une composition fonctionnelle similaire à cet écosystème de référence. Finalement, les indices fonctionnels (ex : Rao), sont plus révélateurs de la réaction de la végétation à différentes densités de cerfs que les indices spécifiques (ex : Shannon), notamment lorsqu’on considère la variance de certains traits, comme la reproduction végétative qui diminue à haute densité de cerfs. Une faible variance d’un trait peut affecter la résilience d’un écosystème à de nouvelles perturbations. Ces résultats permettent d’entrevoir le retour d’une sapinière fonctionnelle sur l’île d’Anticosti avec une réduction des densités de cerfs.We combined specific and functional approaches of biodiversity to capture the impact of deer densities on communities of Anticosti Island. With the specific approach, 12 plants, 11 moths and one bird have been identified as indicator of 12 specific patterns of deer densities. The use of plant combinations in comparison with single plant species added indicators for 17 deer density patterns and increased our capacity to estimate deer density. Then, functional syndromes at high and reduced deer densities were identified through analysis of functional traits of communities. For example, plants at high densities (> 15cerfs/km²) had a vegetative reproduction and abiotic pollination and dispersal. They are traits involving few interactions with animals, which could affect the maintenance of biodiversity. In addition, after eight years of succession, reduction of deer density on Anticosti did not allow the return of species composition similar to the one found in a reference stand of balsam fir forest. However, communities at reduced deer densities had similar composition of functional traits to the reference. Finally, the indices of species diversity (e.g. Shannon) did not change according to deer density but the indices of functional diversity (e.g. Rao) did. For example, the variance of some traits, such as vegetative reproduction, was reduced at high deer density. Low variance of a trait can affect the resilience of ecosystems to new disturbances. These results provide a glimpse for the return of afunctional Balsam fir forest on Anticosti Island when deer densities are controlled

Compositional and functional trajectories of herbaceous communities after deer density control in clear-cut boreal forests

Overabundant populations of large herbivores have strong persistent effects on forest composition, structure, and function. However, the mechanism through which plant communities recover their original composition and function after herbivore management remains poorly understood. We assessed the temporal trajectories of the herbaceous communities in Abies balsamea (L.) Mill. and Picea glauca (Moench) Voss stands on Anticosti Island (Quebec, Canada) over 8 years following clear-cutting and deer management. The impact of deer exclusion or reduction to 7.5 and 15 deer·km–2 was compared with benchmark in situ deer densities (27 and 56 deer·km–2). Effects of deer management treatments on plant species and functional trait assemblages over time were assessed using principal response curves. Although complete deer exclusion seemed necessary to modify species composition from that occurring under intense browsing, a reduced density of 7.5 deer·km–2 was sufficient to induce significant changes in functional trait assemblages of regenerating stands. For instance, reduced deer densities favored plants with brightly colored flowers and compound inflorescences pollinated by animals and producing large seeds and fleshy fruits dispersed by animals. We conclude that the boreal forest's herbaceous communities are resilient to chronic browsing when deer population reduction and forest clearcutting are applied in synergy.Les populations surabondantes de grands herbivores ont des effets majeurs et persistants sur la composition, la structure et le fonctionnement de la forêt. Toutefois, le mécanisme par lequel les communautés végétales retrouvent leur composition et leur fonctionnement originels en réponse au contrôle des herbivores demeure mal compris. Nous avons évalué les trajectoires temporelles des communautés herbacées dans des peuplements d'Abies balsamea (L.) Mill. et de Picea glauca (Moench) Voss à l'île d'Anticosti (Québec, Canada) pendant 8 années après avoir effectué une coupe à blanc et contrôlé les populations de cerfs. L'impact de l'exclusion du cerf ou d'une réduction de la densité à 7,5 ou 15 cerfs·km–2 a été comparé à des densités témoins in situ (27 et 56 cerfs·km–2). Les effets des traitements de gestion du cerf sur les espèces végétales et les assemblages de traits fonctionnels ont été évalués en fonction du temps au moyen de la méthode des courbes de réponses principales. Bien que l'exclusion complète du cerf ait semblé nécessaire pour modifier la composition spécifique par rapport à celle observée en conditions de broutage intense, une densité réduite à 7,5 cerfs·km–2 était suffisante pour induire des changements significatifs dans les assemblages de traits fonctionnels des peuplements en régénération. À titre d'exemple, des densités réduites de cerfs ont favorisé les plantes à fleurs de couleur vive et les plantes à fleurs composées pollinisées par les animaux et produisant de grosses graines et des fruits charnus dispersés par les animaux. Nous concluons que les communautés herbacées de la forêt boréale sont résilientes au broutage chronique quand une réduction des populations de cerfs et une coupe forestière à blanc sont appliquées en synergie

Dieta de Tapirus terrestris Linnaeus em um fragmento de Mata Atlântica do Nordeste do Brasil

The lowland tapir (Tapirus terrestris Linnaeus, 1758) is the largest mammalian herbivore in Brazil. Only small numbers remain in Atlantic Forest fragments in north-east Brazil. The population downfall of the lowland tapir is linked to hunting, and to the destruction and fragmentation of its habitat. Changes in the environment may impact the diet of this potentially at-risk mammal. We focused on tapirs living in the Mata dos Pintos, a 3 000 ha forest fragment on the Usina Serra Grande land (state of Alagoas, Brazil). We determined diet by following the paths of tapirs to collect plant species they foraged on. Foraging occurrence was assessed by visual identification of markings (teeth marks on stems and leaves) and seeds identification in the feces. Fifty-five plant species were identified as consumed by tapirs of Mata dos Pintos including 42 browsed species. The mostcommon plant families consumed were Rubiaceae, Melastomataceae and Arecaceae, which are all specific to secondary forest types or forest edge. Seeds of 19 plant species were found in the feces of tapirs. Of these species, fifteen were found with intact seeds and six of these possessed large seeds (>1,5 cm). The size of the intact seeds found in tapir feces and the long gastrointestinal passage time of this species implies that tapirs may act as long-distance seed dispersers for large-seeded plant species, which may have few alternative dispersal mechanisms in highly fragmented forests.A anta (Tapirus terrestris Linnaeus, 1758) é o maior mamífero herbívoro do Brasil. A população de anta está restrita somente a poucos indivíduos, nos fragmentos de mata Atlântica do nordeste brasileiro. Esta população reduzida está ligada à caça, à destruição e à fragmentação de seu habitat, uma vez que as mudanças ocorridas em seu ambiente podem impactar sua rotina diária e sua dieta. Duas antas que vivem no fragmento ”Mata dos Pintos”, Usina Serra Grande (Alagoas) foram o foco principal deste trabalho. A dieta das antas foi determinada seguindo suas trilhas. As plantas que apresentavam marcas de dentes nos caules e folhas foram coletadas, bem como as sementes encontradas nos excrementos. Quarenta e duas espécies vegetais foram consumidas pelas antas da mata dos Pintos, das quais as mais frequentes foram Rubiaceae, Melastomataceae e Arecaceae, típicas de florestas secundárias. Sementes de dezenove espécies foram encontradas nos excrementos das antas, destas 15 estavam intactas, sendo seis sementes grandes (> 1,5cm). O porte grande e o tempo de passagem digestivo da anta implica na dispersão a longas distâncias de sementes grandes, com poucos mecanismos alternativos de dispersão na floresta Atlântica altamente fragmentada

Species indicators of ecosystem recovery after reducing large herbivore density: Comparing taxa and testing species combinations

Indicator species have been used successfully for estimating ecosystem integrity, but comparative studies for defining optimal taxonomic group remain scarce. Furthermore, species combinations may constitute more integrative tools than single species indicators, but case studies are needed to test their efficiency. We used Indicator Species Analysis, which statistically determines the association of species to one or several groups of sites, to obtain indicators of ecosystem recovery after various deer density reductions. We used five taxonomic groups: plants, carabid beetles, bees, moths and songbirds. To test whether species combinations could complement single indicator species, we used plants as a model taxon and examined the indicator value of joint occurrence of two or three plant species. Our study relies on experimental controlled browsing enclosures established for six years on Anticosti Island (Quebec). Four levels of deer density (0, 7.5 and 15 deer km−2 and natural densities between 27 and 56 deer km−2) were studied in two vegetation cover types (uncut forests and cut-over areas), in a full factorial design for a total of eight experimental treatments. For all taxa but bees, we tested 54 treatment groups consisting in one specific density or in a sequence of two or more consecutive deer densities in one or both cover types (ten groups for bees, sampled only in cut-over areas). We found 12 plants, 11 moths and one songbird to be single species indicators of ecosystem conditions obtained under 12 different treatment groups. Six treatment groups were indicated by plants and six different ones by moths, of which one group was also identified by a songbird species. Moths were thus worth the extra sampling effort, especially since the groups they indicated were more treatment-specific (mainly one or two deer density treatments). We tested the same 54 treatment groups for plant species combinations represented by two or three co-occurring species. Plant combinations efficiently complemented plant singletons for detecting ecosystem conditions obtained under various deer densities. In fact, although singletons were highly predictive, 17 additional treatment groups were identified exclusively with two- and three-species combinations, some being more treatment-specific. Our findings show that plants and moths provide complementary indicators of ecosystem conditions under various deer densities, and that computing species combinations increases our capacity to monitor ecosystem recovery after reducing herbivore densities.Funding was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC)-Produits forestiers Anticosti Industrial Chair to SDC, the Ministère des Ressources Naturelles et de la Faune du Québec, the Canadian Forest Service of Natural Resources Canada and an NSERC scholarship to MB and NSERC DG to MP and SP. We are grateful to the Centre de la Science de la Biodiversité du Québec and Centre d’études nordiques for scholarships

Flapping rates of migrating and foraging Turkey Vultures Cathartes aura in Costa Rica

Local and migrating populations of Turkey Vultures Cathartes aura co-exist in Costa Rica in autumn and spring (Stiles & Skutch 1989). We studied the flapping rates of individuals from these two populations to compare flight modes and the amount of energy invested in active flight. Migrants tended to fly higher in more stable air than local birds, which often fly low over the forest canopy while searching for carrion. Overall, migrants flapped at lower rates than did local, non-migratory birds. Migrants, but not local birds, flapped more on cloudy days than on sunny days, and more at the start and end of the day than at mid-day. RésuméDes populations résidentes et migratrices d'Urubus à tête rouge coexiste au Costa Rica en automne et au printemps. La recherche avait pour but de mesurer le taux de battements d'ailes des individus des deux populations et de comparer le type de vol et la quantité d'énergie investie dans le vol actif. Les individus migrateurs volent généralement à plus haute altitude dans une atmosphère plus stable que les individus résidents, qui volent à plus basse altitude à la recherche de nourriture. En moyenne, les oiseaux migrateurs battaient des ailes moins souvent que les oiseaux locaux. Finalement, les individus migrateurs, et non les individus résidents, battaient plus souvent des ailes les journées nuageuses que les journées ensoleillées, et aussi au début et à la fin de la journée comparer au milieu de la journée. Vulture News Vol. 53 2005: 4-

Dieta de Tapirus terrestris Linnaeus em um fragmento de Mata Atlântica do Nordeste do Brasil

The lowland tapir (Tapirus terrestris Linnaeus, 1758) is the largest mammalian herbivore in Brazil. Only small numbers remain in Atlantic Forest fragments in north-east Brazil. The population downfall of the lowland tapir is linked to hunting, and to the destruction and fragmentation of its habitat. Changes in the environment may impact the diet of this potentially at-risk mammal. We focused on tapirs living in the Mata dos Pintos, a 3 000 ha forest fragment on the Usina Serra Grande land (state of Alagoas, Brazil). We determined diet by following the paths of tapirs to collect plant species they foraged on. Foraging occurrence was assessed by visual identification of markings (teeth marks on stems and leaves) and seeds identification in the feces. Fifty-five plant species were identified as consumed by tapirs of Mata dos Pintos including 42 browsed species. The mostcommon plant families consumed were Rubiaceae, Melastomataceae and Arecaceae, which are all specific to secondary forest types or forest edge. Seeds of 19 plant species were found in the feces of tapirs. Of these species, fifteen were found with intact seeds and six of these possessed large seeds (>1,5 cm). The size of the intact seeds found in tapir feces and the long gastrointestinal passage time of this species implies that tapirs may act as long-distance seed dispersers for large-seeded plant species, which may have few alternative dispersal mechanisms in highly fragmented forests.A anta (Tapirus terrestris Linnaeus, 1758) é o maior mamífero herbívoro do Brasil. A população de anta está restrita somente a poucos indivíduos, nos fragmentos de mata Atlântica do nordeste brasileiro. Esta população reduzida está ligada à caça, à destruição e à fragmentação de seu habitat, uma vez que as mudanças ocorridas em seu ambiente podem impactar sua rotina diária e sua dieta. Duas antas que vivem no fragmento ”Mata dos Pintos”, Usina Serra Grande (Alagoas) foram o foco principal deste trabalho. A dieta das antas foi determinada seguindo suas trilhas. As plantas que apresentavam marcas de dentes nos caules e folhas foram coletadas, bem como as sementes encontradas nos excrementos. Quarenta e duas espécies vegetais foram consumidas pelas antas da mata dos Pintos, das quais as mais frequentes foram Rubiaceae, Melastomataceae e Arecaceae, típicas de florestas secundárias. Sementes de dezenove espécies foram encontradas nos excrementos das antas, destas 15 estavam intactas, sendo seis sementes grandes (> 1,5cm). O porte grande e o tempo de passagem digestivo da anta implica na dispersão a longas distâncias de sementes grandes, com poucos mecanismos alternativos de dispersão na floresta Atlântica altamente fragmentada

Chronic deer browsing leads to biotic homogenization of minerotrophic peatlands

Peatlands could become important foraging habitats, and their plant communities threatened, in areas with an overabundance of large herbivores. Peatland response to herbivore exclusion may vary widely according to abiotic conditions and associated species, due to a strong minerotrophic gradient. We assessed the impact of white-tailed deer (Odocoileus virginianus Zimm.) on peatland vegetation using an exclosure experiment. A total of 53 pairs of exclosures and unprotected plots were set up in bogs (13 pairs), sedge fens (20), shrub fens (7) and laggs (13), and surveyed prior to exclosure construction as well as three, five and eight years after. Vascular plant composition of exclosures diverged from that of unprotected plots through time only in shrub fens and laggs. Bryophytes remained constant in all habitats. On average, shrub cover was 30% higher in exclosures in all habitats after five years, while herb cover increased only in laggs, by 43%, after eight years. Reclassification of sites by pH showed deer exclusion promoted alpha diversity in low- and high-moderate rich fens (pH 5.3-6.8) and beta diversity in the latter as well as in rich fens (pH 6.3-7.5). Overall, our results suggest that conservation efforts in areas with overabundant large herbivores should target richer peatland habitats since they showed a higher resilience and fostered alpha and beta diversity.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

La flore des tourbières de l’île d’Anticosti lorsque soustraite au broutement par le cerf de Virginie

Depuis son introduction, il y a plus d’une centaine d’années, le cerf de Virginie (Odocoileus virginianus Zimm.) a fortement perturbé la flore de l’île d’Anticosti. Les communautés forestières sont sans contredit celles qui ont été les plus affectées. Toutefois, le cerf exploite et perturbe aussi d’autres écosystèmes, comme les tourbières. Dans ce contexte, nous voulions savoir quelle serait la diversité végétale des tourbières à la suite du retrait du cerf. Pour ce faire, 53 exclos ont été mis en place en 2007 et suivis pendant 8 ans. Au total, 125 espèces végétales ont été identifiées dans l’ensemble des exclos en 2007 et 151 espèces après 8 ans d’exclusion du cerf, ce qui représente une hausse de 21 %. Le nombre d’espèces indicatrices, c’est-à-dire celles caractéristiques d’un habitat donné, a également augmenté, passant de 33 à 48, la hausse étant particulièrement importante dans les laggs (écotones entre la forêt et la tourbière). Le recouvrement des espèces préférées par le cerf a grandement augmenté, notamment celui du bouleau nain (Betula pumila L.) et de la sanguisorbe du Canada (Sanguisorba canadensis L.) (respectivement 2 et 8 fois). Au final, les tourbières de l’île d’Anticosti possèdent un potentiel de diversité végétale plus élevé qui peut s’exprimer avec l’arrêt du broutement par le cerf de Virginie.White-tailed deer (Odocoileus virginianus Zimm.) were introduced to Anticosti Island (Québec, Canada) more than 100 years ago, where they are now considered overabundant and have greatly modified the flora. While forest communities have been the most heavily affected, deer also use and disturb other ecosystems, such as peatlands. This study sought to determine the potential plant diversity of peatlands on the island in the absence of deer. To achieve this, 53 exclosures were established in 2007 and the vegetation monitored over an 8 year period. At the start of the study, 125 plant species were recorded, and after 8 years of deer exclusion this had risen by 21% to 151 species. Over the same period, the number of indicator species (i.e., species associated with a specific habitat) grew from 33 to 48, with the increase being particularly marked in the laggs (ecotones between forest and peatland). After 8 years of exclusion, the vegetation cover of species preferentially grazed by deer had also risen greatly, with bog birch (Betula pumila L.) increasing twofold and Canadian burnet (Sanguisorba canadensis L.), eightfold. In conclusion, peatlands on Anticosti Island have a potential for greater plant richness, which can be expressed after white-tailed deer exclusion

NOTE Compositional and functional trajectories of herbaceous communities after deer density control in clear-cut boreal forests

Abstract: Overabundant populations of large herbivores have strong persistent effects on forest composition, structure, and function. However, the mechanism through which plant communities recover their original composition and function after herbivore management remains poorly understood. We assessed the temporal trajectories of the herbaceous communities in Abies balsamea (L.) Mill. and Picea glauca (Moench) Voss stands on Anticosti Island (Quebec, Canada) over 8 years following clear-cutting and deer management. The impact of deer exclusion or reduction to 7.5 and 15 deer·km -2 was compared with benchmark in situ deer densities (27 and 56 deer·km -2 ). Effects of deer management treatments on plant species and functional trait assemblages over time were assessed using principal response curves. Although complete deer exclusion seemed necessary to modify species composition from that occurring under intense browsing, a reduced density of 7.5 deer·km -2 was sufficient to induce significant changes in functional trait assemblages of regenerating stands. For instance, reduced deer densities favored plants with brightly colored flowers and compound inflorescences pollinated by animals and producing large seeds and fleshy fruits dispersed by animals. We conclude that the boreal forest's herbaceous communities are resilient to chronic browsing when deer population reduction and forest clearcutting are applied in synergy. Key words: resilience, species composition, functional traits, plant-herbivore interactions, deer. Résumé : Les populations surabondantes de grands herbivores ont des effets majeurs et persistants sur la composition, la structure et le fonctionnement de la forêt. Toutefois, le mécanisme par lequel les communautés végétales retrouvent leur composition et leur fonctionnement originels en réponse au contrôle des herbivores demeure mal compris. Nous avons évalué les trajectoires temporelles des communautés herbacées dans des peuplements d'Abies balsamea (L.) Mill. et de Picea glauca (Moench) Voss à l'île d'Anticosti (Québec, Canada) pendant 8 années après avoir effectué une coupe à blanc et contrôlé les populations de cerfs. L'impact de l'exclusion du cerf ou d'une réduction de la densité à 7,5 ou 15 cerfs·km -2 a été comparé à des densités témoins in situ (27 et 56 cerfs·km -2 ). Les effets des traitements de gestion du cerf sur les espèces végétales et les assemblages de traits fonctionnels ont été évalués en fonction du temps au moyen de la méthode des courbes de réponses principales. Bien que l'exclusion complète du cerf ait semblé nécessaire pour modifier la composition spécifique par rapport à celle observée en conditions de broutage intense, une densité réduite à 7,5 cerfs·km -2 était suffisante pour induire des changements significatifs dans les assemblages de traits fonctionnels des peuplements en régénération. À titre d'exemple, des densités réduites de cerfs ont favorisé les plantes à fleurs de couleur vive et les plantes à fleurs composées pollinisées par les animaux et produisant de grosses graines et des fruits charnus dispersés par les animaux. Nous concluons que les communautés herbacées de la forêt boréale sont résilientes au broutage chronique quand une réduction des populations de cerfs et une coupe forestière à blanc sont appliquées en synergie. [Traduit par la Rédaction