Lichens and higher plants on stone: a review - AseanBiodiversity.info

monuments in towns. Chemicals should not be used indiscriminately
in towns as problems of elimination could arise
withalready polluted air.
4. Current trends <strong>and</strong> research
Until a few years ago, researchon this topic consisted of
classi cation of the vegetation growing in these anthropized
environments. As far as lichens were concerned, even this
type of study was rare up until the sixties. Recently, however,
there has been much interest in lichens <strong>and</strong> they have
been studied not only from the taxonomic point of view, but
also as environmental bioindicators or sensors of pollution,
<strong>and</strong> as agents degrading building materials <strong>and</strong> monuments.
As bioindicators, lichens supply useful information on atmospheric
pollution <strong>and</strong> other parameters that a ect the
conservation of monuments. Lichen damage to buildings
varies in severity according to species <strong>and</strong> substrate, <strong>and</strong> is
usually much slower than that caused by vascular <strong>plants</strong>.
The decision to eliminate lichens with chemical substances
should be evaluated on a case by case basis, considering in
addition the e ects that atmospheric pollutants could cause
to a surface devoid of lichens. As new products are tested
for the elimination of lichens, it is necessary to st<strong>and</strong>ardize
the methods to ascertain quickly whether the death of the
lichen has occurred, rather than wait for the slower appearance
of morphological changes. If environmental conditions
do not change after treatment with chemical products,
new forms of biological colonization will sooner or later
occur. A new attack of lichens <strong>and</strong>=or microorganisms
is facilitated by the porosity of the substrate left by the
previous colony. It is therefore advisable to protect surfaces
with substances that render them compact <strong>and</strong> resistant to
biological agents.
As far as <strong>higher</strong> <strong>plants</strong> are concerned, papers on the applied
ecology of wall <strong>plants</strong> have recently appeared. The
microsites in which these <strong>plants</strong> grow have been identi ed
(Lisci <strong>and</strong> Pacini, 1993a, b) <strong>and</strong> germination trials are underway
on the seeds of the most common <strong>and</strong> most harmful
among them (Lisci <strong>and</strong> Pacini, 1994). The purpose of this is
to nd weak points in the development of these <strong>plants</strong> with
a view to prevention <strong>and</strong> control. In parallel, zoologists have
been studying ways to limit bird fauna from roosting on Italian
centers of art. The bird excrement causes four-fold damage:
Corrosion; aesthetic damage; dispersal of seeds of wall
vegetation (e.g. g seeds); <strong>and</strong> contributes to the formation
of substrates for plant growth. Another line of research is
concerned with what species to plant on archaeological sites.
Such <strong>plants</strong> should have the following characteristics: (a)
they should not invade the ruins; (b) they should be green
for most of the year to grace the ruins; (c) they should be
native to the surrounding environment; <strong>and</strong> (d) they should
not cause allergies.
<strong>Lichens</strong> form a patina that testi es to the aging of a monument,
whereas <strong>plants</strong> contribute a picturesque appearance.
These two aspects, however, need to be controlled if we are
to enjoy the monument for as long as possible.
Appendix A. List of some commonly used herbicides in
Italian archaeological <strong>and</strong> monumental areas as shown in
Table 2
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