We employed a live trapping grid to analyse the effect of heterogeneity habitat on dispersion of Akodon azarae, Oxymycterus rutilans and Oryzomys delticola. The reproduction and survival of three species are associated with their residency in the grassland, avoided the use of woodland. A. azarae reproductive and non-reproductive individuals preferentially use the sites dominated by Ambrosia scabra (microhabitat 1). Their residency at those sites would present nutritional advantages due to higher availability of seeds. This species begins to use other microhabitats more frequently only after the population peak. O. delticola preferentially uses the sites dominated by Lonicera japonicaBaccharis spicata (microhabitat 3). As both species present similarities in their diets, the differential use of the grassland microhabitat would contributate to diminish competitive interactions between them. O. rutilans reproductive individuals do not show preference for either microhabitat. During autumn-winter, non-reproductive individuals are more frequently captured in microhabitat 1. The important diminution herbaceous cover among Cortaderia selloana bushes (microhabitat 2) and under the dominant shrubs of microhabitat 3, led as to think that predation could be an important factor regarding the habitat use pattern of A. azarae and O. rutilans during autumn and winter. The climbing ability of O. delticola would contribute to diminish the impact of predation it could suffer at microhabitat 3.Resume. -Les auteurs ont etudie ä Paide d'une grille de piegeage 1'effet d'un habitat heterogene sur la dispersion a'Akodon azarae, Oxymycterus rutilans et Oryzomys delticola. Les trois especes vivent dans la prairie et evitent la foret, ce qui assure leur reproduction et leur survie. A. azarae, qu'il soit ou non en reproduction, utilise de preference des sites ou domine Ambrosia scabra (microhabitat 1) oil il doit trouver des graines tres nourrissantes. Cette espece ne commence ä utiliser d'autres sites qu'apres le pic de population. O. delticola frequente de preference les sites ou dominent Lonicera japonica et Baccharis spicata (microhabitat 3). Les deux especes ayant des regimes alimentaires compa- Mammalia, t. 55, n° 3, 199L Brought to you by | University of Arizona Authenticated Download Date | 6/3/15 4:49 PM 340 MAMMALIA rabies, la frequentation par chacune de microhabitats differents dans la prairie peut contribuer ä diminuer la competition entre elles. O. rutilans en periode de reproduction ne montre pas de preference pour Tun ou Pautre microhabitat. En automne et hiver, les individus non reproducteurs sont plus frequemment captures dans le microhabitat 1. Une importante reduction du couvert herbace entre les buissons de Cortaderia selloana (microhabitat 2) et sous les plantes dominantes du microhabitat 3, conduit ä penser que la predation peut etre un facteur important d'utilisation de Phabitat a 1 A. azarae et de . rutilans en automne et en hiver. L'aptitude au grimper que presente O. delticola doit contribuer ä diminuer Pimpact...

The objective of this work consists of the identification of the ambient and management components which determine different productivities in a 12 years old Populus deltoides cv Catfish 2 plantation. The plantation occupies a surface of 2 hectares in an area protected by a perimetrical dike of the low Delta of the Paraná River in the Province of Buenos Aires (Argentina). The Salicaceae average yield increment for this region was estimated in 20-25 m3/ha/year. A plantation inventory was done and, later on, the whole set was subdivided into 199 plots of 96 m2 each. In each plot, the heights of the dominant and the average trees were measured, and also the land contour elevation readings, as well as, the number of broken plants by the wind because of the action of Platypus mutatus were registered. In each of three areas defined by the land elevation, 27 soil samples were analysed and studied. Those ambients defined as high lands or ridge of fertile land («albardón») and intermediate high lands or ridge of median fertile land (semi-albardón), protected by a perimetrical dike, moderate well drained and deep, pertaining to the franco-coarse textural family, presented wood yield average increments greater than 30 m3/ha/year, and also greater loss of commercial volume because of the Platypus mutatus attack , while those located in the low lands (bañado), protected by dike, with alkaline-sodium layers under surface and a slightly alkaline pH at a depth of 28 cm, showed an average increment of 28.5 m3/ha/year. In this commercial plantation, Carex riparia, Hydrocotyle bonariensis and Duchesnea indica are associated to good sites, but Rubus spp., Iris pseudacorus, Phalaris angusta and Bromus unioloides are associated to those sites of low quality.

In this work we studied the quality of forest site in a 12 years olds commercial plantation of Populus deltoides cv catfish 2, located in Paraná delta’s lowlands surrounded and protected by dams, using direct and indirect methods. In direct method we considered the mean dominant height through the development of height - age curves in which the site index was calculated as the dominant height to an age of 9 years old considered as base age. The Logistic model presented the best fit. The selected function sowed the following values: Dominant height = SI*(1+exp(2.78–0.504*9))/(1+exp(2.78–0.504*age). We studied the vegetation in relation to the height of dominant trees and the soil as indirect method. The greatest productivity (519 m3/ha), basal area (44 m2/ha), and height of dominant tree (30,10 m) were detected in high lands with high phosphorus contest in superficial stratum. The lowest productivity (79,2 m3/ha), basal area (9 m2/ha) and height of dominant trees (23,45 m) were detected in low relief lands, characterised by low assimilable phosphorus contest in superficial stratum. We registered a great number of fallen down trees by the wind during the vegetative period in low lands where it was carried out a bad water management. According to the results obtained from multivariate analysis (DCA) of vegetation we could identify vegetation species as indicators of site quality.

We studied the quality of forest site in a 6 years old commercial plantation of Salix nigra, located in the Paraná delta (Argentina), which shows a lower productivity than the average in the region. The objective of this study is to identify site components that determine this lower productivity. The environmental factors evaluated were the floristic community, the relief and the edafic factors and their relationship with the height of dominant trees and the site productivity. The lowest height growths were detected in high altitude sites or in plots with the former stratum of soil very wide (with clay-slimy texture), while the best height growths of trees were registered in low altitude sites with a very thin first soil horizon.