Audrey Alignier

Weed dispersal by farming at various spatial scales. A review

Reducing pesticide use in agriculture is necessary to preserve natural resources. However, pest control without pesticides is a challenging issue. In particular, weed infestation may cause severe losses of crop yield. Weeds have been traditionally managed solely at the field level. However, larger scales must be considered because invasive and herbicide-tolerant weeds are spreading over larger scales. This review discusses three spatial scales at which agricultural management might affect the dispersal of weeds and, in turn, their distribution and abundance in agricultural fields. The main points are: (1) at the field level, crop and margin management impact mass effect, i.e., local exchanges between the field margin and the cultivated field; (2) at the farm level crop allocation, the management of field boundaries and agricultural circulation in the farm strongly impact the intensity and direction of weed dispersal; and (3) at the landscape level, the spatial farms distribution controls the distribution of weed habitat and, in turn, landscape species pool and long-distance weed dispersal. We conclude that weed dispersal is driven by agricultural management at multiple scales. Weed scientists should thus extend their view on weed dispersal from within-field scales to among-field and landscape scales.

Patterns of forest vegetation responses to edge effect as revealed by a continuous approach

ContextUnderstanding the variability of vegetation distribution and its determinants is a central issue for addressing the effects of edges on ecological processes. Recent studies have revealed inconsistencies in the patterns of responses to edge effects that raise important questions about their determinants. We investigated the edge effect response patterns by adapting a recently proposed continuous approach to the case of small forest fragments in southwestern France.MethodsWe surveyed forest understory vegetation (composition, species richness, and percent cover) and abiotic variables (soil temperature, moisture, pH, and canopy openness) along 28 transects across hard forest edges. We tested five statistical models to describe the response pattern of each variable (1) over all transects and (2) per transect. We then compared the response patterns as a function of the attributes of the edge (orientation, topography, and adjacent land cover) and forest patch size.ResultsOver all transects, a general decreasing trend was observed for all variables as the distance from the edge increased. In the individual transects, we evidenced a large variability in the response patterns that was not related to edge attributes or to patch size.ConclusionIt is difficult to assess the depth of edge influence in highly fragmented forests and to identify the determinants of edge effects. We recommend that care should be taken with studies using pool of transects, and that further studies should be carried out including situations with neutral patterns, in order to gain a broader understanding of edge effects on vegetation.

Can contrast between forest and adjacent open habitat explain the edge effects on plant diversity

Abstract Forest edges are key features in human-dominated landscape. Located between forest and non-forest habitats, edges induce biotic and abiotic changes, which may have profound consequences on vegetation diversity. Recent studies suggest the importance of different edge types in the modulation of edge-related responses. However, edge effect on the spatial dynamic of vegetation, from forest to non-forest habitats, remains unclear. Our aim was to compare the species richness and diversity of vegetation communities between forest and open habitats with their respective edges, in high-contrast versus low-contrast situations. The degree of contrast was defined according to the disturbance regimen of non-forest habitats. We surveyed vascular vegetation along transects in forest and open habitats and in their respective edges, in three regions of France. We showed that edge effects occur on plant diversity, whatever the region, but asymmetrically. Edge effect tends to be greater on the open side than on the forest side of the border. Species richness and diversity were generally higher in open edge than in open habitat, whereas no significant difference was observed between forest edge and forest habitat, whatever the contrast situation encountered. This study shows that the edge effects detected along a forest–edge–exterior habitat gradient may depend in large part on the disturbance regimen in open habitats as well as the vegetation pool size. We highlighted the need to carefully consider the edge types, e.g. their contrast with adjoining non-forest habitat, in further studies to identify the relevant factors and mechanisms behind edge-related response patterns of biodiversity in human-dominated landscapes.

Landscape effects on the abundance and larval diet of the polyphagous pest Helicoverpa armigera in cotton fields in North Benin

BACKGROUND The noctuid Helicoverpa armigera is one of the key cotton pests in the Old World. One possible pest regulation method may be the management of host crop in the landscapes. For polyphagous pests such as H. armigera, crop diversity and rotations can offer sequential and alternate resources that may enhance abundance. We explore the impact of landscape composition and host crop diversity on the abundance and natal host plant use of H. armigera in northern Benin. RESULTS Host plant diversity at the largest scale examined (500 m diameter) was positively correlated with H. armigera abundance. Host plant diversity and the cover of tomato crops were the most important variables in relation to high abundance of H. armigera. Host plant (cotton, maize, tomato, sorghum) proportions and C3 versus C4 plants did not consistently correlate positively with H. armigera abundance. Moth proportion derived from cotton-fed larvae was low, 15% in 2011 and 11% in 2012, and not significantly related to H. armigera abundance. CONCLUSION Cotton crop cover was not significantly related to H. armigera abundance and may be considered as a sink crop. Landscape composition and sequential availability of host plants should be considered as keys factors for further studies on H. armigera regulation.

Ecology for Sustainable and Multifunctional Agriculture

The Green Revolution and the introduction of chemical fertilizers, synthetic pesticides and high yield crops had enabled to increase food production in the mid and late 20th. The benefits of this agricultural intensification have however reached their limits since yields are no longer increasing for many crops, negative externalities on the environment and human health are now recognized and economic inequality between farmers have increased. Agroecology has been proposed to secure food supply with fewer or lower negative environmental and social impacts than intensive agriculture. Agroecology principles are based on the recognition that biodiversity in agroecosystems can provide more than only food, fibre and timber. Hence, biodiversity and its associated functions, such as pollination, pest control, and mechanisms that maintain or improve soil fertility, may improve production efficiency and sustainability of agroecosystems. Although appealing, promoting ecological-based agricultural production is not straightforward since agroecosystems are socio-ecosystems with complex interactions between the ecological and social systems that act at different spatial and temporal scales. To be operational, agroecology thus requires understanding the relationships between biodiversity, functions and management, as well as to take into account the links between agriculture, ecology and the society. Here we review current knowledge on (i) the effect of landscape context on biodiversity and ecosystem functions and (ii) trophic and non-trophic interactions in ecological networks in agroecosystems. In particular, many insights have been made these two previous decades on (i) the interacting effects of management and landscape characteristics on biodiversity, (ii) the crucial role of plant diversity in delivering multiple services and (iii) the variety of ecological belowground mechanisms determining soil fertility in interaction with aboveground processes. However, we also pinpointed the absence of consensus on the effects of landscape heterogeneity on biodiversity and the need for a better mechanistic understanding of the effects of landscape and agricultural variables on farmland food webs and related services. We end by proposing new research avenues to fill knowledge gaps and implement agroecological principles within operational management strategies.

Effet de l’exposition sur la richesse et la composition floristique des lisières forestières dans le Gâtinais oriental (Loiret)

Les lisières forestières marquent la limite de la forêt, le terme de forêt désignant par convention une association d’arbres formés de troncs et de houppiers d’une hauteur d’au moins 5 m constituant une unité physionomique (Otto, 1998). Elles forment une zone de transition entre l’environnement relativement stable de la forêt et les larges fluctuations microclimatiques du milieu ouvert adjacent (Chen et al., 1995) qui, dans les paysages ruraux, est souvent anthropisé (cultures, prairies...). Ainsi, les conditions environnementales (température, humidité de l’air et du sol) mais aussi la structure et la composition de la végétation sont modifiées dans l’environnement proche des lisières. Ces modifications sont appelées « effet de lisière » (Murcia, 1995 ; Ries et al., 2004). Des études montrent que ces modifications s’observent en général jusqu’à 20 m de part et d’autre de la lisière (Cadenasso et al., 1997) mais peuvent atteindre parfois plusieurs centaines de mètres à l’intérieur de la forêt (Chen et al., 1995 ; Ries et al. 2004 ; Pellissier et al., 2013).