Omnipresence of leaf herbivory by invertebrates and leaf infections by fungal pathogens in agriculturally used grassland of the Swiss Alps, but low plant damage

Agriculturally used grasslands in the Alps are characterised by a trade-off between high fodder production in some and high plant species richness in others. In contrast to plant species richness and production, however, little is known on the relevance of biological interactions between plants, invertebrate herbivores, and fungal pathogens for grasslands in the Alps. At the time when the vegetation was fully developed, but prior to agricultural use, we examined whether leaf damage by herbivory and fungal pathogen infection, and their diversity, are affected by plant functional group, land use, and altitude. Moreover, we studied whether extent and diversity of leaf damage are related to each other, to plant species richness, and to standing crop. We recorded the leaf area damaged by ten types of herbivory and five types of fungal pathogen infection on 12,054 plant leaves of legumes, other forbs, and graminoids collected in 215 grassland parcels in 12 valleys in the Swiss Alps. With 83 % of all leaves infested, herbivory and fungal pathogen infection were omnipresent. However, only 2.7 % leaf area was damaged by herbivory and 1.2 % by fungal pathogens. Damage by herbivory was highest on legumes, and damage by fungal pathogens was highest on graminoids. More leaf damage by herbivory occurred in traditionally mown sites and at lower altitudes, while damage by fungal pathogen infection was independent of land use and altitude. Most types of herbivory were found on legumes and on leaves from fertilised sites, whereas the number of fungal pathogen types was highest on graminoids and in unfertilised sites. Larger standing crop was associated with higher leaf damage and diversity of herbivory types per leaf. Neither damage by herbivory nor by fungal pathogens was correlated with plant species diversity. In more plant species rich parcels, the number of herbivory types was lower at the leaf level, but tended to be higher at the parcel level. Our results highlight the omnipresence of plant–herbivore and plant–pathogen interactions. They suggest that current land use changes from mowing to grazing or to abandonment decrease the diversity of herbivory, and that fertilisation decreases pathogen diversity. As our results did not reveal conservation conflicts between diversities of plants, herbivores, and fungal pathogens, and as the damage from herbivory and pathogens is generally low, we conclude that for protecting the high diversity of plant–herbivore and plant–pathogen interactions a diverse low-intensity land use should be maintained

Adaptation of Poa alpina to altitude and land use in the Swiss Alps

Current land use and climate change are prompting questions about the ability of plants to adapt to such environmental change. Therefore, we experimentally addressed plant performance and quantitative-genetic diversity of the common Alpine Meadow Grass Poa alpina. We asked how land use and altitude affect the occurrence of P. alpina in the field and whether its common-garden performance suggests adaptation to conditions at plant origin and differences in quantitative genetic diversity among plant origins. Among 216 candidate grassland sites of different land use and altitude from 12 villages in the Swiss Alps, P. alpina occurred preferentially in fertilized and grazed sites and at higher elevations. In a common garden at 1,500 m asl, we grew two plants of >600 genotypes representing 78 grassland sites. After 2 years, nearly 90% of all plants had reproduced. In agreement with adaptive advantages of vegetative reproduction at higher altitudes, only 23% of reproductive plants from lower altitudes reproduced via vegetative bulbils, but 55% of plants from higher altitudes. In agreement with adaptive advantages of reproduction in grazed sites, allocation to reproductive biomass was higher in plants from grazed grasslands than from mown ones. For 53 grasslands, we also investigated broad-sense heritability H2, which was significant for all studied traits and twice as high for grazed as for mown grasslands. Moreover, possibly associated with their higher landscape diversity, H2 was higher for sites of villages of Romanic cultural tradition than for those of Germanic and Walser traditions. We suggest promoting diverse land use regimes to conserve not only landscape and plant species diversity, but also adaptive genetic differentiation and heritable genetic variation

Participatory modelling of social and ecological dynamics in mountain landscapes subjected to spontaneous ash reforestation

International audienceThe future of the agriculture in mountain areas constitutes an important stake for sustainable development in relation to landscape functions and their role in local economies. This future depends highly on its ability to develop innovative and multifunctional agricultural systems and to preserve its attractiveness for future generations. Encroachment and reforestation of landscapes, which comes from land abandonment and extensification of land use, raise important topical issues. In Pyrenean valleys, where the land is colonised by the ash tree (Fraxinus excelsior), local land managers and policy-makers want to understand better the relationships between the ecological and social processes in order to assist in the design of policies supporting constructive change. Here we present the “companion modelling” approach in which we are all together constructing a simulation model for carrying out a prospective study of land use and landscape changes in the region. According to the principles of this participatory approach, we started developing a spatialised multi-agent model, whose main conceptual aspects are presented here below. The model simulates the evolution of land cover of the agricultural landscape in relation to both the natural and anthropogenic dynamics. Ecological field studies having stressed the role of mowing and grazing practices at the parcel level on colonisation of the local landscape by the ash tree, we focus on the account of prospective change in farmers’ land management practices (viewed as a set of decision rules) and their impact. This ongoing study underlines the interest of spatially explicit modelling of the inter-relationships between social and ecological dynamics at the agricultural landscape scale based on an interdisciplinary approach for dealing with rural development topical issues. Both the advantages gained and the difficulties raised are discussed.L’avenir de l’agriculture en zone de montagne spécialisée sur l’élevage constitue un enjeu de développement important, fortement conditionné par sa capacité à développer des systèmes innovants pour assurer les différents services nécessaires au développement durable de ces territoires. En particulier, les conséquences du boisement spontané des paysages par le frêne (Fraxinus excelsior) suite à l'abandon ou la réduction de leur exploitation par les agriculteurs interpellent les acteurs du développement des territoires de montagne, qui souhaitent mieux comprendre les relations entre processus écologiques et sociaux pour définir les politiques les mieux adaptées aux enjeux du maintien de la qualité visuelle et culturelle des paysages, de la préservation de la biodiversité et des ressources naturelles. Dans ce contexte, nous présentons la démarche de« modélisation d'accompagnement » qui a été mise en oeuvre dans une commune des Pyrénées françaises pour co-construire entre chercheurs et acteurs du développement un modèle d'analyse prospective des changements de l’utilisation des terres et des paysages. Cette méthode participative a conduit à entreprendre le développement d'un modèle multi agent spatialisé dont nous présentons les aspects conceptuels les plus importants. Ce modèle permet de simuler l'évolution de l'occupation du sol de l’ensemble des exploitations agricoles sous l'effet de dynamiques naturelles et anthropiques conjointes prenant en compte les stratégies et pratiques de gestion des éleveurs, du niveau de l’exploitation à celui de la parcelle et leur effet sur l'installation potentielle du frêne (à travers les opérations de fauche et de pâturage des parcelles). Cette étude dont le développement se poursuit illustre l'intérêt d’une modélisation intégrée et spatialement explicite des relations entre dynamiques sociales et dynamiques écologiques à l’échelle d'un paysage agricole dans un cadre interdisciplinaire pour l’appui au développement. L'originalité de la méthode mise en oeuvre et les difficultés soulevées sont discutées