Bosvitaliteitsinventaris 2007: resultaten van de kroonbeoordelingen in het bosvitaliteitsmeetnet

The crown condition survey was conducted on 72 plots in a 4x4 km grid. Ten of these plots are part of the international 16x16 km grid. In 2007 1732 trees were assessed.
The mean defoliation was 21.1% and 17.3% of the trees were in defoliation classes 2-4. 0.2% of the sample trees died. The share of damaged trees was 18.8% in broadleaves and 14.1% in conifers. There was a smaller difference in mean defoliation: 21.5% in coniferous trees and 20.8% in broadleaved species.
Compared to last year mean defoliation decreased by 0.2% points while the share of damaged trees decreased by 1.2% points. Most of the tree species showed an improvement of the crown condition.
Pinus sylvestris is the species with the best crown condition. Moderate to severe needle loss was observed on 11.3% of the sample trees. Corsican pine (Pinus nigra subsp. Laricio) revealed on average a higher defoliation level than P. sylvestris, with 24.8% trees being damaged. Pinus nigra suffered from fungal infection and one sample tree died because of Sphaeropsis sapinea infection. In some pine stands infection by Scirrhia pini (Red band needle blight) was recorded.
The least affected broadleaved species was Quercus rubra with 12.3% of the trees in defoliation classes 2-4. Fagus sylvatica is the only species with a higher defoliation score in comparison to 2006. 13.3% of the trees showed moderate to severe defoliation. Populus sp. remained the species with the worst crown condition, with a high proportion of damaged trees (33.3%). Although population densities of Oak Processionary Moth (Thaumetopoea processionea) in 2007 were high, especially in the eastern part of the Flemish Region, the share of moderately to severely defoliated Quercus robur trees remained stable (19.2%).
The warm and dry weather circumstances during the month of April did not have a negative influence on the crown condition. Because of wind damage 1,7% of the sample trees had to be replaced. In several conifer stands discolouration due to hailstorms was observed.