Forest Condition in Europe - ICP Forests

Forest Condition in Europe 2013 73
The proportion of moderately to severely defoliated ‘other broadleaves’ was 34.0%. There
was a considerable increase of damage in one Alnus glutinosa plot. Defoliation was caused by
Phytophthora alni infection, resulting in 21 dead trees and 74.2% of the trees being damaged.
Because of the large number of sample trees in this plot, the results influenced the whole survey.
The most affected other species were Quercus robur, Pinus nigra subsp. laricio and
Populus sp. The crown condition of Populus sp. was comparable to last year but the condition
of Q. robur and P. nigra deteriorated. The share of trees in defoliation classes 2-4 was 25.8%
for Populus sp., 34.7% for Q. robur and 39.9% for P. nigra.
The condition of Fagus sylvatica improved, with only 8.3% of the trees showing more than
25% defoliation. Other less affected species were Q. rubra and P. sylvestris, with 9.7% and
14.0% moderately to severely defoliated trees.
Damage by defoliators was observed in several oak plots. On 41.4% of the Q. robur trees,
more than 10% of defoliation was caused by insects. In one plot, consecutive years of severe
defoliation by Thaumatopoea processionea resulted in tree death.
Symptoms of fungi were recorded frequently on Populus sp. (Melampsora larici-populina,
rust infection), Q. robur (Microsphaera alphitoides, powdery mildew) and P. nigra (Scirrhia
pini, red needle blight). Severe discolouration by Scirrhia pini was recorded on 35.9% of the
P. nigra trees. There was a higher incidence of S. pini compared to previous years. Microsphaera
alphitoides infection resulted in 32.0% of Q. robur trees with discolouration on more
than 10% of the leaf area. The wet summer of 2012 stimulated the spread of fungal diseases
like M. alphitoides.
Belgium-Wallonia
The survey in 2012 concerned 816 trees on 36 plots, on a regional 8x8 km systematic grid.
The percentage of trees with a defoliation >=25% shows different long term trend for conifers
and broad-leaved:
The conifers, which were two time more defoliated in the beginning of the nineties, show this
year a rate of 21,6%, lower than last but higher than the last decade.
The broad-leaved showed an increase from 10% in 1990 to about 20% in 2005. These damages
were mainly due to the degradation of the beech (scolytidae in 2000-2002, drougth in 2003
followed by fruiting in 2004) and of the European oak (drougth in 2003). The rate decrease
from 2006 till 2008 with 15,2%, but severely increased in 2009 with 32% and in 2010 with
33,4%; this year the rate is increasing to 39,2 which is the upper level observed!
Concerning the mean defoliation observed for the four main species, after an improvement
since 2006 for beech and European oak, they increase to about 27,5% for beech and 27,9% for
European oak this year. Sessile oak is at a bad condition this year with 22,2%, 5% upper than
last year. Spruce shows a non significant increase, with 16,1% this year.
Climatic conditions in 2012 do not explain the bad condition of trees; rainfall was at a high
level from April to July, with just a dryer period in August and September, with normal temperatures.
But the trend is negative since 2008, and we suppose a cumulative effect of stresses
in the previous years.