Radial growth of mature pedunculate and sessile oaks in response to drainage, fertilization and weeding on acid pseudogley soils

Abstract

In NE France, forest soils on an old alluvial terraces are generally unfavourable, strongly acid and often characterized by superficial temporary water tables. In this case, the ground vegetation is dominated by a dense cover of Carex brizoides on the moderately hydromorphic soils (Carex site) or Molinia caerulea on the strongly hydromorphic soils (Molinia site). Both pedunculate Quercus robor and sessile oaks Quercus petraea are present in the Molinia site, and practically only pedunculate oak in the Carex site. The effect of drainage depended on the site type, the oak species and the age of the trees. Drainage had practically no effect in the Carex site. In the Molinia site, the effect was positive (+20%) for the young (≤110 years old) sessile oaks only. It became even depressive (-15%) for the old (>110 years old) pedunculate oaks. The effect of weeding differed according to the site type, the age of the trees and the drainage modality. Whatever the drainage modality, the effect was depressive (-13%) for the young trees and nonsignificant for the old ones in the Carex site. There was a positive interaction between weeding and drainage in the Molinia site, in the old trees (+22%) as well as in the young ones (+17%), whereas weeding alone had a negative effect (-5%). The effect of fertilization was strongly beneficial (about +20%) in all cases.