Intérêt des saules et des peupliers pour le boisement des marais desséchés de l'Ouest

Coastal areas of W. France include drained, intensively cultivated land (animal husbandry and cereals), which are typically on clay-rich soils with salinity at depth, in exposed situations. In order to assess the potential for afforestation, a trial was carried out at Triaize, N. of La Rochelle, in which 23 clones of Salix alba, 8 of Populus alba, 22 of P. tremula XP. alba, 3 of P. tremuloides XP alba and 3 of P. canescens (all 2 yr old) were planted on a former pasture (in autumn 1981) which had had one of four drainage treatments : (1) control (no site preparation), trees planted at 3X7 m spacing (476 plants/ha) ; (2) soil ridges 7 m apart, formed by bulldozer, tress planted on ridge summits at 3-m spacing (476 plants/ha) ; (3) ditches 9 m apart (2 m wide, 1 m deep) formed by mechanical digger, trees planted at 3-m intervals on ditch material (370 plants/ha) ; and (4) ditches 7 m apart (476 plants/ha). At age 9 yr, P. alba plants had greatest percentage survival (mean 87%) and best growth rate ; Populus hybrids also survived well on better drained plots (60-70%) but had the slowest growth ; Salix clones had the lowest survival rates (mean 43%) although growth, on well-drained sites, was good. Les marais littoraux de l'Ouest couvrent 250.000 hectares et sont caractérisés par un taux élevé d'argile, et une salinité importante. Parmi les salicacées, Populus alba est l'espèce qui tolère le mieux ces conditions difficiles. Sa croissance reste cependant limitée en l'absence d'un modelage du sol et d'un drainage intensif par fossé. La réussite économique de reboisements en plant destinée à la production de bois n'est donc pas possible. Par contre, Populus alba et Salix alba peuvent être utilisés pour la réalisation de boisements linéaires en bordure des artères hydrauliques.