Effect of cattle activities on gap colonization in mountain pastures

Cattle influences gap dynamics in pastures in two ways: (1) by creating gaps and (2) by affecting the colonization process. This effect of cattle activity on gap revegetation can be subdivided in three main factors: herbage removal, trampling and dung and urine deposition. The objective of this study was to assess how these three effects moderate the plant succession following gap creation. In an exclosure, four controlled treatments simulating cattle activity (repeated mowing, trampling, manuring and untreated control) were applied on plots of 2 × 2 m. In the centre of each plot, one artificial gap of 60 × 60 cm was created. During three years, vegetation changes were monitored in spring and in autumn, with a square grid of 100 cells of 0.01 m2 centred on the gap. Our experiment confirmed that fine-scale gap creation may have a high impact on relative abundances of species in the community. The gap environment acts on species as a filter and this filtering was described in terms of regenerative attributes. Colonizers were species with small seeds, unspecialized seed dispersal, persistent seed bank and high vegetation spread. However, the role of dung deposition, herbage removal or trampling by cattle did not seem to be of primary importance in the revegetation process, but could moderate vegetation response. Therefore, the different cattle effects act as secondary filters that selectively favoured or disadvantaged different species from the gap-regenerating community. These complex interactions are probably keys to understand plant coexistence in perennial grassland

Templeuve – Rue Grande Campagne

Suite à un projet immobilier déposé par la société Bouygues, une intervention d’archéologie préventive a été prescrite par le service régional de l’archéologie du Nord-Pas-de-Calais à Templeuve-en-Pévèle, rue Grande Campagne. Le site avait fait l’objet d’un diagnostic préalable en 2014, lequel révéla la présence d’un axe routier gallo-romain associé à une tombe à caractère privilégié (Neaud 2014). Durant le mois de mai 2015, une campagne de fouille a été menée sur une emprise de 6 123 m2. À l..

Spatial and Seasonal Patterns of Cattle Habitat use in a Mountain Wooded Pasture

Management-oriented models of cattle habitat use often treat grazing pressure as a single variable summarizing all cattle activities. This paper addresses the following questions: How does the spatial pattern of cattle effects vary between cattle activities in a highly heterogeneous landscape? Do these patterns change over the grazing season as forage availability decreases? What are the respective roles of natural and management-introduced structures? We estimated the intensity of herbage removal, dung deposition and trampling after each of three grazing periods on a grid of 25m×25m cells covering an entire paddock in the Swiss Jura Mountains. We found no significant positive correlations between cattle effects. Spatial patterns weakened through the season for grazing and trampling, whereas dunging patterns changed little between grazing periods. Redundancy analysis showed that different cattle effects were correlated with different environmental variables and that the importance of management-introduced variables was highest for herbage removal. Autocorrelograms and partial redundancy analyses using principal coordinates of neighbour matrices suggested that dunging patterns were more coarse-grained than the others. Systematic differences in the spatial and seasonal patterns of cattle effects may result in complex interactions with vegetation involving feedback effects through nutrient shift, with strong implications for ecosystem management. In heterogeneous environments, such as pasture-woodland landscapes, spatially explicit models of vegetation dynamics need to model cattle effects separatel

Spatial and Seasonal Patterns of Cattle Habitat use in a Mountain Wooded Pasture

Management-oriented models of cattle habitat use often treat grazing pressure as a single variable summarizing all cattle activities. This paper addresses the following questions: How does the spatial pattern of cattle effects vary between cattle activities in a highly heterogeneous landscape? Do these patterns change over the grazing season as forage availability decreases? What are the respective roles of natural and management-introduced structures? We estimated the intensity of herbage removal, dung deposition and trampling after each of three grazing periods on a grid of 25 m × 25 m cells covering an entire paddock in the Swiss Jura Mountains. We found no significant positive correlations between cattle effects. Spatial patterns weakened through the season for grazing and trampling, whereas dunging patterns changed little between grazing periods. Redundancy analysis showed that different cattle effects were correlated with different environmental variables and that the importance of management-introduced variables was highest for herbage removal. Autocorrelograms and partial redundancy analyses using principal coordinates of neighbour matrices suggested that dunging patterns were more coarse-grained than the others. Systematic differences in the spatial and seasonal patterns of cattle effects may result in complex interactions with vegetation involving feedback effects through nutrient shift, with strong implications for ecosystem management. In heterogeneous environments, such as pasture-woodland landscapes, spatially explicit models of vegetation dynamics need to model cattle effects separately

Survival of Heterogeneous Stress Distributions Created by Precursory Slip at Frictional Interfaces

We study the dynamics of successive slip events at a frictional interface with finite-element simulations. Because of the viscous properties of the material, the stress concentrations created by the arrest of precursory slip are not erased by the propagation of the following rupture but reappear with the relaxation of the material. We show that the amplitude of the stress concentrations follows an exponential decay, which is controlled by the bulk material properties. These results highlight the importance of viscosity in the heterogeneous stress state of a frictional interface and reveal the “memory effect” that affects successive ruptures

Tree growth and mortality of 42 timber species in central Africa

peer reviewedTree growth and mortality are two central processes in the functioning of mixed and structurally complex moist tropical forests. The outcome of these processes is usually predicted using estimates of tree growth and mortality rates. Nevertheless, the accurate estimates of these parameters are still scarce which impedes our ability to predict forest evolution and build reliable management plans. To partly fill this gap, we carried out the permanent monitoring of 21,180 trees belonging to 42 species that are exploited for timber production in central Africa. Besides reporting new species-specific estimates of diameter increments and mortality rates, we aimed to evaluate how tree growth varies with tree size and logging history. Additionally, we discussed our results in regards to the reference values of diameter increments, mortality rates and minimum cutting diameters that are used to build forest management plans. Diameter increment was found to significantly depend on tree size for the majority of the studied species. The significant relationships between diameter increment and tree size were mostly hump-back shaped. The trees with a diameter close to or lower than the reference minimum cutting diameter were growing faster than the average. Moreover, we found that tree growth was reduced during 1-2 years after timber exploitation and then spurred during at least 5 years. Such tree growth response to logging was nevertheless species-specific. This study provided new estimates of tree growth and mortality rates that could help performing more accurate forest projections and establish sustainable management plans