Recent observations on oak decline in southern Belgium: nutritional aspects

In the Walloon region (southern Belgium), the forests of indigenous oaks (Quercus robur and Quercus petraea) cover about 80 000 ha (17% of the total forest surface ). They represent more than 39% of the standing hardwoods, with 14 million m3. As in neighbouring countries, they showed serious decline symptoms in the early 80s. The investigations conducted since that time didn't point out any single cause to the phenomenon. Far from observing a stabilization of the phenomenon, a recent outbreak occurred in 1998 and 1999. Locally, the number of dead trees reached values such as 20 to 25 individuals per hectare in mature forests. On the basis of sampling (82 plots, more than 2000 trees) covering all natural areas which are supposed to be favourable to both oak species, the study noted similar distribution of the trees in defoliation classes for Quercus petraea as well as Quercus robur .