Un SIG pour analyser les stratégies de mise en valeur du milieu par des éleveurs de moutons

Une base de données géographique «Milieu naturel - pratiques d’élevage» a été mise en place sur un secteur de l’arrière-pays méditerranéen, le Lodévois (Hérault)

A spatial stochastic algorithm to reconstruct artificial drainage networks from incomplete network delineations

Contact: [email protected], [email protected], [email protected] spatial stochastic algorithm that aims to reconstruct an entire artificial drainage network of a cultivated landscape from disconnected reaches of the network is proposed here. This algorithm uses random network initialisation and a simulated annealing algorithm, both of which are based on random pruning or branching processes, to converge the multi-objective properties of the networks; the reconstructed networks are directed tree graphs, conform to a given cumulative length and maximise the proportion of reconnected reaches. This algorithm runs within a directed plot boundaries lattice, with the direction governed by elevation. The proposed algorithm was applied to a 2.6-km2 catchment of a Languedocian vineyard in the south of France. The 24-km-long reconstructed networks maximised the reconnection of the reaches obtained either from a hydrographic database or remote sensing data processing. The distribution of the reconstructed networks compared to the actual networks was determined using specific topographical and topological metrics on the networks. The results show that adding data on disconnected reaches to constrain reconstruction, while increasing the accuracy of the reconstructed network topology, also adds biases to the geometry and topography of the reconstructed network. This network reconstruction method allows the mapping of uncertainties in the representation while integrating most of the available knowledge about the networks, including local data and global characteristics. It also permits the assessment of the benefits of the remote sensing partial detection process in drainage network mapping

Simulating the effects of spatial configurations of agricultural ditch drainage networks on surface runoff from agricultural catchments

The study of runoff is a crucial issue because it is closely related to flooding, water quality and erosion. In cultivated catchments, agricultural ditch drainage networks are known to influence runoff. As anthropogenic elements, agricultural ditch drainage networks can therefore be altered to better manage surface runoff in cultivated catchments. However, the relationship between the spatial configuration, i.e., the density and the topology, of agricultural ditch drainage networks and surface runoff in cultivated catchments is not understood. We studied this relationship by using a random network simulator that was coupled to a distributed hydrological model. The simulations explored a large variety of spatial configurations corresponding to a thousand stochastic agricultural ditch drainage networks on a 6.4 km2 Mediterranean cultivated catchment. Next, several distributed hydrological functions were used to compute water flow-paths and runoff for each simulation. The results showed that (i) denser networks increased the drained volume and the peak discharge and decreased hillslopes runoff, (ii) greater network density did not affect the surface runoff any further above a given network density, (iii) the correlation between network density and runoff was weaker for small subcatchments (< 2 km2) where the variability in the drained area that resulted from changes in agricultural ditch drainage networks increased the variability of runoff and (iv) the actual agricultural ditch drainage network appeared to be well optimized for managing runoff as compared with the simulated networks. Finally, our results highlighted the role of agricultural ditch drainage networks in intercepting and decreasing overland flow on hillslopes and increasing runoff in drainage networks

La forêt fleurit aussi... Quelques arbres à caractère mellifère et paysager : les sorbiers et les alisiers

Ce texte fait suite à plusieurs articles parus dans de précédents numéros de notre revue, dans lesquels les auteurs nous présentaient le programme Sylvapi et les plantations mellifères. Après y avoir abordé l'intérêt mellifère des arbres et arbustes et les différentes formes d'aménagement et de sylviculture favorables, ils s'attachent ici, à décrire quelques arbres mellifères et plus particulièrement les sorbiers et les alisiers

La forêt fleurit aussi... Le programme Sylvapi et les plantations mellifères

Dans le cadre du programme "Sylvapi", les auteurs de cet article s'attachent plus particulièrement à nous présenter l'intérêt mellifère de certaines plantations, ainsi que les bases et les différentes formes d'aménagement api-sylvicole et les principes de sylviculture favorable

Développement en Languedoc Roussillon de plantations à caractère paysager, mellifère, cynégétique.

Les partenariats engagés sur le terrain entre propriétaires, des groupes de producteurs et des collectivités témoignent de l'intérêt porté à ces plantations pour conforter, par exemple, une économie touristique ou l'image de marque d'un produiT