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

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Fig. 4. Distribution of 12 lichen communities on acid rock of a Sardinian “nuraghe”. A: upper part of the nuraghe; B: lower part of the nuraghe. Phaeophyscia orbicularis, Xanthoria c<strong>and</strong>elaria <strong>and</strong> Caloplaca citrina showed that nutrient enrichment of the stone substrate had caused lichen growth. The nitrates were attributed to fertilizers dusted on crops in the surrounding elds. On the tower of the Cathedral of Seville, la Giralda, calcicolous species (almost all crust-like <strong>and</strong> epilithic) have been identi ed. Their growthis associated withbird excrement. These species usually live on deteriorated calcareous substrates (Saiz-Jimenez, 1981). On the pavement mosaics of the Romanesque town of Italica (Seville), the tesserae <strong>and</strong> mortar were attacked by Aspicilia radiosa, Aspicilia ho mannii <strong>and</strong> several species of the genus Caloplaca (Garcia Rowe <strong>and</strong> Saiz-Jimenez, 1988). 2.5. Methods of prevention <strong>and</strong> control The opportunity of removing lichens from stone substrates must be evaluated case by case, since the damage caused by eachspecies is di erent. The rst step is to identify <strong>and</strong> perform an ecological characterization of the species so as to be able to choose a speci c agent to eliminate the lichen <strong>and</strong> the cause of its growth. Foliose <strong>and</strong> fruticose lichens have very di erent sensitivities to chemical agents (Giacobini et al., 1979). If the factors favoring lichen growth are known, preventive measures can be suggested to halt or slow down processes of colonization. Before removing nitrophilic species, which are relatively fast-growing <strong>and</strong> cause substantial damage, it is advisable to nd a way of avoiding nitrate enrichment of the stone surfaces. This can be achieved by controlling the bird populations of towns, the use of fertilizers in nearby elds, <strong>and</strong> water ow over the surfaces. Water run-o is generally avoided by sheltering or re-directing the water (Nimis <strong>and</strong> Monte, 1988). For surfaces colonized by endolithic lichens, Nimis <strong>and</strong> Zappa (1988) advise against elimination, as degeneration of the thallus leaves the surface porous <strong>and</strong> more vulnerable to environmental acids, whereas the damage caused by the lichens is limited due to their extremely slow growth. In the past, normal restoration practice involved the mechanical removal of the lichen thalli. Today this is done only for foliose <strong>and</strong> fruticose lichens since they do not adhere strongly to the substrate. Mechanical removal of crust-like lichens, the thallus of which penetrates deeply into the stone, requires the use of hard brushes <strong>and</strong> much washing with water <strong>and</strong> detergents. This process disperses the spores <strong>and</strong> causes much stone to be lost. To avoid these problems, Clarke (1976) advised applying an ammonium hydroxide solution to kill the thalli <strong>and</strong> loosen them, before mechanical removal. Nimis et al. (1987) advised against mechanical removal of thalli with soredia in order to avoid dispersal of these asexual reproductive structures <strong>and</strong> spread of the lichens. <strong>Lichens</strong> are generally removed by application of chemical products (see Appendix A) which may be combined with mechanical methods. A large variety of biocides that damage either the phycobiont (algicides) or the mycobiont (fungicides) are available (Lloyd, 1971). The most important parameters to consider in the choice of products to use for restoration are e cacy, nonreactivity with the substrate <strong>and</strong> toxicological characteristics. E cacy against the lichen should be a maximum at the minimum dose. The biocides should be of broad spectrum <strong>and</strong> have a long-lasting e ect. Chemical solutions should have a neutral pH to avoid corroding the stone <strong>and</strong> interfering with any soluble salts (Richardson, 1976). They should not cause changes in color, loss of translucence, whitening or increased re ectance. Richardson (1976, 1987) advises against the use of copper compounds <strong>and</strong> phenols because they color the substrate, <strong>and</strong> of borates that favor the formation of soluble salts. For vast areas it is preferable to use low toxicity products (Class III or IV, expressed as LD50 or LC50) so as to avoid contamination of the environment <strong>and</strong> poisoning of the operators. Biocides may be applied by spraying, brushing or pasting. Spraying should
e avoided on windy days <strong>and</strong> brushing when the surface is friable. Paste is used when the agent must be kept in contact with the surface for a longer period. The materials usually used for pasting are paper pulp, rice paper, cotton wool <strong>and</strong> substances suchas carboxymethylcellulose (Mora <strong>and</strong> Mora, 1972). Richardson (1976) recommends the use of quaternary ammonia salts applied witha low pressure spray. The concentration should be chosen in relation to the porosity of the substrate. Samidi (1981) successfully used a solution of quaternary ammonia salts to eliminate lichens from the temple of Boradubur in Indonesia. He recommends performing the operation in a dry period as rain could cancel the inhibitory e ect of the products. Solutions of pentachlorophenol <strong>and</strong> PanaciderJ have been applied by brushto Aboriginal rock paintings in Australia (Clarke, 1976). Small silicon channels were mounted above these paintings to prevent water from owing over the painted surface. An interesting study by Lloyd (1971) reports the testing of pentachloro-phenyl-laurate, Cu-8-quinolate, <strong>and</strong> pentachloro- <strong>and</strong> trichloro-phenoxy-isopropanol on algae of the genus Trebouxia <strong>and</strong> fungi of the genus Cladosporium. Since it is di cult to determine the moment in which the lichen is no longer alive because its death does not imply loss of its chitin structure, deciding the appropriate dose can be problematical. Only a long time after treatment is it possible to observe morphological changes indicative of death. In fact this problem underlies the not always positive results obtained by Giacobini et al. (1979) when his group applied uometuron, chlorobromuron, terbutryn <strong>and</strong> vaneide 51 by spray <strong>and</strong> paste to a large variety of stone substrates. More than a year was necessary to be able to observed lichen death directly. Bettini <strong>and</strong> Villa (1981) proposed the following program of treatments: • repeated washing with water <strong>and</strong> the non-ionic detergent Lito 7, brushing <strong>and</strong> nal rinsing to remove dirt <strong>and</strong> dust trapped in the lichens; • application of the biocides, Lito 3, <strong>and</strong> further brushing to remove dry material. In central India, vigorous cleaning withagents suchas acetic acid, hydrogen peroxide <strong>and</strong> ammonia teepol was performed before applying agents to kill lichens (Santobrite, benzal, konium chloride) on Indian temples (Sharma et al., 1985). The use of these products is questionable as they have very acid or basic pH <strong>and</strong> could corrode the stone. 3. Higher <strong>plants</strong> 3.1. Invasion <strong>and</strong> colonization The growth of <strong>plants</strong> on a historical building depends on its state of conservation, the building material <strong>and</strong> climate (Fig. 1). Plants usually take more than 10 years to colonize a wall. In that period of time, Parietaria di usa, for instance, will grow to a diameter of 20–30 cm in the mortar between the bricks of a wall. In the colonization process, there are Fig. 5. The stages of one mode of colonization of a wall. Hardy pioneer <strong>plants</strong> grow in substrate created by break-down of the wall structure <strong>and</strong> are succeeded by less hardy <strong>plants</strong> on a more abundant substrate. always pioneer <strong>plants</strong> (herbaceous annuals <strong>and</strong> perennials) that cause little damage, <strong>and</strong> are replaced by more detrimental <strong>plants</strong> suchas small shrubs or trees (Plate 2a <strong>and</strong> 2b). On the basis of this sequence, two modes of colonization that di er in relation to position, water availability <strong>and</strong> the type of <strong>plants</strong> that succeed each other can be identi ed. Fig. 5 shows the various stages of one type of colonization that is independent of the positions illustrated in Fig. 7 <strong>and</strong> occurs even when little water is available. The rst assault on the wall is usually the result of abiotic factors (Fig. 5), that create conditions suitable for the growth of bacteria, fungi <strong>and</strong> lichens (Hyvarinen et al., 2002). These organisms accelerate the deterioration of the structure <strong>and</strong> lead to the formation of a substrate for the germination of seeds of hardy pioneer <strong>plants</strong> such as Sonchus tenerrimus (herbaceous annual) <strong>and</strong> Parietaria di usa (herbaceous perennial). Atmospheric dust, bird excrement <strong>and</strong> human wastes contribute to the layer of substrate so that other <strong>plants</strong> can develop. In some cases, the detritus of the pioneer <strong>plants</strong> forms a suitable substrate for the <strong>plants</strong> that follow. The second mode of colonization occurs mostly on horizontal surfaces witha better water supply (Fig. 6). In this case the pioneer <strong>plants</strong> are mosses that trap atmospheric dust, leading to the formation of su cient substrate for the germination of other <strong>plants</strong> (Plate 2c). Plants can grow in mortar between stones or bricks, in building material itself <strong>and</strong> on substrate formed as described above. The type of stone used determines the species that grow. Soft, porous stone that is not very compact, like travertine, crumbles readily, retains water <strong>and</strong> hosts mosses <strong>and</strong> <strong>higher</strong> <strong>plants</strong>. In either case, the roots of <strong>higher</strong> <strong>plants</strong> penetrate the wall, destroying the materials <strong>and</strong> increasing the quantity of substrate.
Page 1 and 2: Abstract Lichens <
Page 3 and 4: Plate 1. (a) Statue in archaeologic
Page 5: Fig. 3. Di erent structures of vege
Page 10 and 11: Fig. 6. The stages of a second mode
Page 12 and 13: 3.3. Damage Vegetation growing on h
Page 14 and 15: Table 1. Continued Families <strong
Page 16 and 17: Corball, R., Paz-Bermudez, G., Sanc

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