Pour une évaluation sensible à l’environnement des interventions : l’analyse de l’implantation

Dans cet article, les auteurs exposent une méthode pour faciliter l'analyse de l'implantation des interventions. Cette forme d'évaluation a son origine dans les limites reconnues du modèle de la « boîte noire », modèle prédominant dans l'analyse des effets des interventions. Elle vise à expliquer les conditions de mise en oeuvre et les processus de production des effets des interventions. Plus précisément, l'analyse de l'implantation comprend trois composantes, soit l'analyse de l'influence : 1) des déterminants contextuels sur le degré de mise en oeuvre des interventions, 2) de l'interaction entre le contexte d'implantation et l'intervention sur les effets observés, et 3) des variations dans l'implantation sur son efficacité. L'utilité de ce type d'évaluation est d'accroître la validité externe des recherches évaluatives

Spatial extent of neighboring plants influences the strength of associational effects on mammal herbivory

There is high variability in the level of herbivory between individual plants from the same species with potential effects on population dynamics, community composition, and ecosystem structure and function. This variability can be partly explained by associational effects (i.e., the impact of the presence of neighboring plants on the level of herbivory experienced by a focal plant) but it is still unclear how the spatial scale of plant neighborhood modulates foraging choice of herbivores, an inherently spatial process in itself. Using a meta-analysis, we investigated how spatial scale modifies associational effects on the susceptibility to browsing by herbivores with movement capacities similar to deer. From 2496 articles found in literature databases, we selected 46 studies providing a total of 168 differences of means in damage by herbivores or survival to woody plants (mostly) with and without neighboring plants. Spatial scales were reported as distance between plants or as plot size. We estimated the relationships between the effect sizes and spatial scale, type of associational effects, and nature of the experiment using meta-analysis mixed models. The strength of associational effects declined with increasing plot size, regardless of the type of associational effects. Associational defenses (i.e., decrease in herbivory for focal plants associated with unpalatable neighbors) had stronger magnitude than associational susceptibilities. The high remaining heterogeneity among studies suggests that untested factors modulate associational effects, such as nutritional quality of focal and neighboring plants, density of herbivores, timing of browsing, etc. Associational effects are already considered in multiple restoration contexts worldwide, but a better understanding of these relationships could improve their use in conservation, restoration, and forest exploitation when browsing is a concern. This study is the first to investigate spatial patterns of associational effects across species and ecosystems, an issue that is essential to determine differential herbivory damages among plants

Tolerance of an expanding subarctic shrub, Betula glandulosa, to simulated caribou browsing

Densification of the shrub layer has been reported in many subarctic regions, raising questions about the implication for large herbivores and their resources. Shrubs can tolerate browsing and their level of tolerance could be affected by browsing and soils productivity, eventually modifying resource availability for the caribou. Our objective was to assess the compensatory growth potential of a subarctic shrub, Betula glandulosa Michx., in relation with caribou browsing and nutriment availability for the plants. We used a simulated browsing (0, 25 and 75% of available shoots) and nitrogenfertilisation (0 and 10 g m22) experiment to test two main hypotheses linking tolerance to resource availability, the Compensatory Continuum Hypothesis and the Growth Rate Hypothesis as well as the predictions from the Limiting Resource Model. We seek to explicitly integrate the relative browsing pressure in our predictions since the amount of tissues removed could affect the capacity of long-lived plants to compensate. Birches fully compensated for moderate browsing with an overall leaf biomass similar to unbrowsed birches but undercompensated under heavy browsing pressure. The main mechanism explaining compensation appears to be the conversion of short shoots into long shoots. The leaf area increased under heavy browsing pressure but only led to undercompensation. Fertilisation for two consecutive years did not influence the response of birch, thus we conclude that our results support the LRM hypothesis of equal tolerance under both high and low nitrogen availability. Our results highlight that the potential for compensatory growth in dwarf birch is surpassed under heavy browsing pressure independently of the fertilisation regime. In the context of the worldwide decline in caribou herds, the reduction in browsing pressur