Baden-Württemberg - Lichens of Wales

1.3.1 Decline of Lichens
Many lichen species are becoming rare, while
their living area due to the activities of man is
destroyed or all to frequently is subjected to
change. Their slow growth, often also in
association with the late onset of reproduction,
brings about an always stronger and more
frequent meshing with the onset of an ominous
environment. The dwindling of the occurrence
of lichens has reached a dismaying degree. In
Baden-Württemberg alone, that by its richly
variable landscape offers much better conditions
for the existence and the survival of lichens than
many other regions of Germany, clearly over
10% of the species are missing or extinct.
Dozens of lichens here are immediately
threatened with extinction. Many have only a
few refugia where especially favorable climatic
and pure air conditions as well as little
disturbance make survival possible up to this
time. By stopping stronger decimation of the
incidence and populations is to reckon with the
complete disappearance of these lichens within
the next year or next two decades.
Evidence for the decline is produced by old
publications about the lichen flora, from others
still maintaining access to collections of lichens
from an earlier time. In old herbaria species are
represented, which no longer exist today; many
lichens extremely rare today are present from
places, where they in the meantime have
certainly disappeared.
The reasons for the decline of lichens are
many fold. The intensive land and economic
utilization in the widest sense, e.g. “destoning”
and fertilization of poor turf (especially in the
Black Forest) and the shifting of vineyards with
the destruction of the typical vineyard wall on
sloping sites. The massive clearing of farm land
in the severe style of the years of the sixties and
seventies have led to a scarcely assessable
decimation of the lichen populations. A greater
loss to the occurrence of the typical bark lichen
flora came about through cutting down the street
trees. From topographic maps we can determine
that within the past forty years at least four fifths
of the rows of trees along avenues and streets
were exterminated. Methods of forestry
utilization have lead to considerable
impoverishment and to a change in the lichen
vegetation of the forest, which had the effect of
habitat alteration on large areas, especially clearcutting
and afforestation with exotic tree species,
above all conifers. The scarcity of old trees in
today’s managed forests produces a very
negative effect upon the species diversity. It
demonstrates that near natural richly structured
forests with a correspondingly high portion of
older trees and dead trees are especially rich in
lichen species.
The most important causes of lichen decline
includes the air pollution by power stations,
industry, domestic combustion, and traffic.
Lichens react to the emissions in many ways
essentially as susceptible as other organisms; the
modest resistance depends likely upon their
(already referred to) special constitution,
particularly their symbiotic nature, the lack of an
effective protective tissue and their longevity.
According to our knowledge, acid producing
emissions are especially devastating, on the one
hand directly as toxic substances, on the other
hand indirectly by acidifying rain water, that as a
rule is directly taken up by the lichen thallus.
Sulfur dioxide is especially injurious to lichens,
as it leads to injury of fundamental metabolic
processes, which arise by acidifying the water
and the substrates, resulting in many lichen
species being no longer supported.
The impoverishment of the lichen flora is
further advanced, as the increase in the burden of
acid emissions. Many species are especially
sensitive and therefore only still occur in regions
with nearly pure air. Other species disappear in
the case of moderate or at first stronger
concentration of harmful materials. One can
correlate the reading of the lichen flora, as an
approximation of the degree of the burden of
lichen damaging air pollution; that apparently the
sulfur dioxide and the acid content of the rain
water are most significant in the decimation of
lichens, leading to indexing the region with more
or less higher burden with respect to these factors
with the help of certain lichen species (Wirth
1987). Numerous widespread species of barkdwelling
lichen species in this book allow – by
the knowledge of the ecology of these groups –
the use of bio-indication of that kind of burden.
Lately – as a result of decreasing sulfur
dioxide emissions – a recovery has been
identified in many species. The acid emissions,
especially sulfur dioxide, are an especially
important factor in emission caused lichen
decline, but by no means the only one. Even dust
and heavy metals play a role. In earlier times
eutrification (fertilizing) increased air pollution
and led then to extensive alteration of the lichen
vegetation.
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