Effects Of Wild Ungulates Research Articles

Wild ungulates compound herbicide-mediated simplification of early successional plant communities in forest plantations

Understanding the degree to which management interacts with ecological processes to drive the structuring of biodiversity remains a central challenge in ecology. For instance, the effects of herbivores on post-disturbance vegetation development may depend on the degree to which anthropogenic interventions have altered plant communities.We hypothesized that by simplifying plant species composition at local scales, intensive forest management practices should amplify herbivore-mediated changes in early-successional vegetation development and diversity at multiple levels of biological observation (i.e., alpha, beta, and gamma diversity). To test this hypothesis, we implemented a six-year experiment that manipulated post-timber harvest vegetation establishment via a gradient in vegetation management intensity (i.e., herbicides), and quantified compositional changes with and without wild-ungulate herbivores.Increasingly intensive herbicide treatments suppressed broadleaf vegetation and reduced plant diversity at alpha and gamma levels, while the effects of wild-ungulates were most evident in measures of community change and beta diversity for a commonly applied treatment type. Following the broad-spectrum and follow-up herbaceous treatment combination, herbivory contributed to the suppression of vegetation cover, slowing plant community development by 21%, and resulting in 27% less among-plot heterogeneity (i.e., lower beta diversity). We found no effects of herbivory alpha diversity, but the divergence in communities subjected to herbivory resulted in disparate community composition and lower gamma diversity.Herbicide and herbivore-mediated alterations in community composition was due the suppression of broadleaf species and subsequent release of common herbivory-tolerant herbaceous species. Although herbivory also slowed vegetation development without herbicides, the high diversity and abundance of broadleaf forages likely buffered untreated sites from the herbivore-mediated alterations of plant composition at alpha, beta, and gamma levels.The variation in effects of herbicide and herbivory in this experiment highlight the importance of testing for interactions between natural and anthropogenic agents on vegetation development and quantifying diversity responses beyond local scales. These results also suggest that large herbivores may contribute to management-induced simplification of young forests, with potential implications for successional processes and regional biodiversity conservation.

Livestock Riparian Guidelines May Not Promote Woody Species Recovery Where Wild Ungulate Populations Are High

Stubble height, streambank alteration, and woody species use are indicators used to monitor livestock impacts on riparian areas in the western United States. Effects of wild ungulates on riparian conditions are often not monitored and assumed to be represented by indicators developed for livestock. We tested this assumption by evaluating effects of elk (Cervus canadensis) and mule deer (Odocoileus hemionus) on grazing indicators along Meadow Creek, a salmonid-bearing stream in northeastern Oregon. Wild ungulates reduced stubble height by 20% to 30%. Mean streambank alteration was 1.1% (ranged from 0.3–8%). Woody species use was negatively related to stubble height and positively related to streambank alteration (P < 0.05). Despite maintenance of stubble height and streambank alteration within regulatory guidelines, wild ungulate use of preferred woody species was moderate to high (>50%). Adherence to guidelines developed for livestock may not result in desired riparian conditions where wild ungulate populations are high.

Mesure et suivi de l’empreinte écologique des ongulés sauvages sur la végétation forestière

Les populations d’ongulés sauvages ont progressé depuis les années 80 au point aujourd'hui de poser des problèmes économiques, sociaux et environnementaux. Une gestion durable des forêts suppose de trouver un compromis entre les effets nuisibles (économiques, sanitaires et écologiques) et les services rendus (économiques, patrimoniaux et écologiques) à l’homme et à l’écosystème. Une composante essentielle de la gestion durable est d’évaluer et de suivre ces effets afin d’éviter des dégâts excessifs ou des dommages irréversibles. Elle repose donc sur des indicateurs, que nous détaillons ici pour les aspects principalement écologiques en lien avec la végétation forestière. Basés sur les principes de la gestion adaptative, les Indicateurs de Changement Écologique (ICE) mettent à disposition aux décideurs/gestionnaires des indicateurs qui renseignent sur l’évolution du couple population animale-milieu. Néanmoins, parmi eux, manquent des indicateurs pour évaluer et suivre les dégâts sur la régénération forestière et les effets sur le fonctionnement et la biodiversité de l’écosystème. Nous proposons ici d’utiliser les réponses des plantes à l’échelle des populations ou des communautés végétales afin d’évaluer et suivre l’empreinte écologique des ongulés sauvages en milieu forestier. La notion de l’empreinte écologique prend en compte le fait que les effets d’ongulés sauvages ont, selon le contexte, des effets bénéfiques ou délétères sur le fonctionnement de l’écosystème. A terme, ces indicateurs pourraient être intégrés dans la démarche des indicateurs de la gestion durable des forêts françaises.