A very interesting report (500 pages) about Forest Resources
was published, by UNECE, at
http://www.unece.org/trade/timber/fra/tbfra-ad.htm
http://www.unece.org/trade/timber/fra/welcome.htm
DEFOLIATION
Information on defoliation as an indicator of the extent
of tree damage from one or a combination of causes,
including air pollution, is provided. The indicators used
are the percentages of trees of different defoliation
classes for each year between 1986 and 1997, divided
into equal to or less than 25 per cent and more than
25 per cent defoliation for all species, coniferous species
and broadleaved species. The use of defoliation as an
indicator of forest health has been the subject of intensive
debate. The definition of defoliation, as adopted by the
UN/ECE is needle or leaf loss in the assessable crown as
compared to a reference tree. There is evidence of some
trends in individual countries, these should be treated with
great caution. A comparison of the years 1992 and 1998
reveals that there are more plots in Europe (31.2 per cent)
where mean crown condition deteriorated than plots where
there was a significant improvement (15.4 per cent).
Deteriorating plots are spread all over Europe, with an
accumulation in the west (France) and south (mainly Italy).
Plots with a significant recuperation are clustered in the
so-called sub-Atlantic region, which mainly comprises Germany
and Poland. In-depth evaluations show that in all other regions
a slight deterioration took place during the last seven years.
Mean crown condition remained on the same level only in the
boreal region (mainly covering Scandinavia).
POLLUTION DAMAGES
The greatest levels of damage were reported in south-eastern
Europe, with 11,900 ha in Albania, 7,000 ha in Austria,
18,000 ha in the Czech Republic, 66,900 ha in Romania,
64,900 ha in Yugoslavia. A further 12,000 ha of damage was
reported from the USA. In relation to the forest area,
Liechtenstein had the highest proportion of forest damaged by
local pollution sources (4.05 per cent), followed by Yugoslavia
(1.86 per cent), Albania (1.15 per cent), Romania (1 per cent)
and the Czech Republic (0.68 per cent). In all other countries
reporting this form of damage, the area affected was less
than 0.5 per cent.
CONCLUSIONS
The reported figures indicate that defoliation is much more
widespread in Europe than in North America. In the USA
the proportions of trees with more than 25 per cent defoliation
is generally less than 1 per cent. In Canada, it is generally less
than 10 per cent, whereas in Europe in recent years, it has been
more than 20 per cent. This almost certainly reflects differences
in standards between Europe and North America. The european
figures reflect a trend for increasing defoliation. The proportion
of trees assessed every year between 1988 and 1997 with more
than 25 per cent defoliation has increased from 13.2 per cent in
1988 to 23.1 per cent in 1997. No information is available on the
cause of this reported increase in defoliation.
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