THELOBARION, AN EPIPHYTIC COMMUNITY OF ANCIENT FORESTS THREATENED BY ACID RAIN

Lichenologist 27(1): 59–76 (1995)

THE LOBARION, AN EPIPHYTIC COMMUNITY OF ANCIENT FORESTS THREATENED BY ACID RAIN Y. GAUSLAA*

Abstract: Lobaria pulmonaria and other members of the Lobarion were found to inhabit drainage channels below old and large wounds on the trunks of various deciduous trees in stands of long ecological continuity in a forest reserve dominated by Picea abies in southeastern Norway. Such channels were richer in minerals and had a higher pH than normal bark, which was covered with more acidophytic epiphytic communities, mainly the Pseudevernion. Chemical microhabitat differentiation was most clear in edaphically poor sites. The restriction of a previously ubiquitous Lobarion to mineral-rich microsites on stems is probably an effect of acid rain. Since acidification seems to make the Lobarion more dependent upon old and damaged stems, modern forestry probably aggravates the damage caused by acid rain.

Introduction The Lobarion is a lichen-dominated, species-rich epiphytic plant community, declining in most parts of Europe (Degelius 1935; Mattick 1937; Wilmanns 1962; Hawksworth et al., 1973; Lerond 1977; Löfgren & Moberg 1984; Hallingbäck 1986, 1989; Hallingbäck & Martinsson 1987; Vänskä 1987; Wirth 1987; Rose 1988; Hallingbäck & Thor 1988; Liska & Pisˇu´t 1990). One of the most common characteristic species in Norway is Lobaria pulmonaria. This species with a previously wide European distribution is considered to be an indicator of ancient forests with a long ecological continuity (Rose 1974, 1976, 1988, 1992), since modern forestry using clear felling reduces the frequency of the species (Lettau 1911–1912; Hilitzer 1925; Erichsen 1928; Sernander 1936; Wilmanns 1962; Wirth 1968, 1976; Lesica et al., 1991). Air pollution, however, also threatens L. pulmonaria (Hallingbäck & Olsson 1987; Ekman 1989), which is sensitive to SO2 (Hawksworth & Rose 1970; Hawksworth et al., 1973). Since the Lobarion is restricted to bark that is not strongly buffered with a relatively high pH (5·0–6·0, Gauslaa 1985; Rose 1988), acid rain also has a negative effect (Gilbert 1986; Looney & James 1988; Farmer et al., 1991a, b, 1992). The chemical environment of bark exposed to acid rain is a product of airborne, mainly acidic depositions, and minerals taken up through the roots of the tree. Airborne depositions operate mainly on a scale measured in kilometres or more, with less variation within an intact forest. Minerals in bedrock and soil deposits operate on a scale measured in metres or more, causing a mosaic of ground vegetation types. It has previously been indicated that the Lobarion is often restricted to sites with a calcium-rich soil in areas *Department of Biology and Nature Conservation, Agricultural University of Norway, P.O. Box 5014, N-1432 Ås, Norway. 0024–2829/95/010059+18 $08.00/0

? 1995 The British Lichen Society

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F. 1. A, Location of the study site (/) in southeastern Norway. The two measuring stations for pollution data are included: P, Prestebakke; N, Nordmoen. The dashed line represents the border between Norway and Sweden. B, Distribution of Lobaria pulmonaria within Östmarka Forest Reserve. Dashed lines represent the boundary of the reserve. Shaded areas represent lakes.

influenced by acid rain (Gauslaa 1985; Farmer et al., 1991b; Bates 1992). Patches of bark are modified chemically by a spatial variation in bark topography and decomposition rate that operates on a scale measured in centimetres or less. Many lichens and mosses survive best around nutrient streaks that have a higher pH than the rest of the stem (Gilbert 1970). This study deals with the Lobarion in stands dominated by Picea abies within a boreal forest reserve with a long ecological continuity. However, most soils are leached and the reserve is influenced by acid rain. The Lobarion is therefore likely to be adversely affected. The present paper focuses on the small-scale spatial distribution of the Lobarion in this type of environment. The hypothesis is that the Lobarion is restricted to rich vegetation types and/or to microsites on the trunk enriched in minerals, resulting in a locally higher pH that is able to counteract the influence of acid rain. Materials and Methods Study site Östmarka Forest Reserve (size: 12·5 km2, Fig. 1) was selected as a study area since it is one of the few larger boreal forest areas in the southeastern lowlands of Norway that are still relatively little influenced by modern forestry. The reserve contains indicators of long ecological continuity that are otherwise rare in this region of Norway. The topography is varied with altitudes between 200 and 345 m. It is located at 59)50*N, 11)03*E, about 20 km south-east of Oslo (Fig. 1). This is well outside the area that is directly affected by SO2, according to a detailed study of distribution of epiphytic lichens by Øiseth & Aarvik (1980). The two nearest measuring stations for acid depositions are shown in Fig. 1. They have almost identical annual means of sulphur (S), nitrogen (N), and acidity depositions for the period 1987–91 (Table 1). These figures are therefore probably representative for the study area. The

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T 1. Air pollution data and rainfall as annual means within the period 1987–1991 for the two nearest measuring stations, indicated in Fig 1 Measuring stations Parameters

Prestebakke

Annual rainfall (mm) Sulphur (S): Wet deposited sulphate (mg S m "2) Dry deposited S (mg S m "2) Nitrogen (N): Wet deposited nitrate (mg N m "2) Wet deposited ammonium (mg N m "2) Dry deposited N (mg N m "2) Aciditry (H + ): Mean H + conc. expressed as pH of rainfall Wet deposited acidity (mekv H + m "2) SO2 (ìg S m "3): Mean value 1991 Maximum concentration 1991

Nordmoen

827

904

687 175

700 143

441 339 279

407 338 335

4·30 42

4·32 44

0·50 4·2

0·30 3·4

Data are from Statens Forurensningstilsyn (1992). mean concentration of sulphate has decreased by about 30% in southern Norway since 1979 (Statens Forurensningstilsyn 1992). Methods All trees with L. pulmonaria that were found during 19 one-day visits within the periods May 15th to October 19th in 1990 and 1991 were selected as localities for further study. The following data were recorded at each locality: altitude above sea level (to the nearest 10 m according to maps), altitude above the nearest valley, altitude below the nearest peak, exposure (compass direction), slope, and girth of the trunk supporting growth of L. pulmonaria. Traces of old disturbances such as old stumps and fire-scars in surrounding trees were searched for. The basal area of the trees (m2 ha "1), measured by a relascope (Bitterlich 1984), and height of trees carrying L. pulmonaria were only measured in 65% of the localities, since the relascope and height meter were available only during parts of the field work. Cover abundance of epiphytic lichens and bryophytes were recorded on the lower 2 m of selected trunks by means of Domin’s scale (Krajina 1933, revised by Dahl 1956). One bark sample, consisting of several pieces less than 3 mm thick was collected beneath thalli of L. pulmonaria from all selected trees (n=43). Epiphytic vegetation was found to be more or less homogeneous all around the stem in 14 of the selected trees. Only one bark sample was collected from these 14 stems. The remaining 29 stems supported a mosaic of Lobarion and other vegetation types, mainly Pseudevernion (in the sense of James et al., 1977). From these trunks one additional bark sample was taken underneath the normally dominating Pseudevernion. Pseudevernion bark was sampled in the same way as Lobarion bark, and consisted also of several subsamples. Bark samples were carefully freed from epiphytes and detritus, air dried at room temperature and finely ground in a ball mill with grinding vessels and balls made of sintered alumina. The pH was measured in two samples each of 0·5 g air-dried bark mixed with 5 ml deionized water, corked to prevent CO2 contamination and left overnight before measuring the pH. A third sample was analysed with respect to the total content of C, Kjeldahl-N, S, B, P, K, Mg, Ca, Na, Fe, Cu, Mn, Zn, Mo, Al and Cd by the Norwegian Agricultural Service Laboratory. Measurements of intact bark pH were made in the field as described by Looney & James (1988) and Farmer et al. (1990) on one Populus tremula with a distinct gradient from well-developed Lobarion to Pseudevernion. The bark was moistened by a droplet of 25 m KCl before measurements, using an Orion pH meter, model 230A, with a surface Ross electrode, model 81–35.

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Soil fertility was estimated through an indirect approach, using vascular plants on the ground as indicator species by means of the reaction number of Ellenberg (1986). This approach was selected for many reasons. Chemical analyses of soil minerals do not necessarily give a meaningful measure of the availability of nutrients, as the cycling speed of nutrients through withering and/or decomposition may be more important than actual levels of soluble minerals in nutrient-poor soils with plants dependent upon mycorrhiza. It has been shown in numerous studies that species composition at ground level in a range of boreal forest types is influenced mainly by soil chemistry (Dahl et al., 1967; Økland 1990). Secondly, since a tree extracts nutrients from a large volume of soil, representative sampling for the root zone(s) of a whole tree is difficult, especially since few sites have a homogeneous soil around the roots due to rough topography and shallow soils. Thirdly, soil analyses are costly and time-consuming. The procedure was as follows: a circular relevé, with a radius of 3 m centred around the selected trunk was analysed with respect to the occurrence of vascular plants. The mean reaction numbers of Ellenberg (1986) were calculated for each relevé by adding the reaction number for all species for which numbers were given, and then dividing by the number of species having a reaction number. Statistics A Pearson correlation matrix was computed for all environmental variables in the Lobarion and Pseudevernion samples, such as chemical factors, mean reaction number of Ellenberg (1986), number of eutrophic, oligotrophic, and moisture-demanding vascular species around the stems (defined in Gauslaa 1994), basal area of the stand, altitude above sea level, altitude above the nearest valley, altitude below the nearest peak, exposure, slope, tree height, girth of trunk and some epiphyte variables such as number of epiphytes, lichens, lichens with cyanobacteria, mosses, vitality, cover and number of colonies of L. pulmonaria. The matrix was computed pairwise as a few variables such as basal area were not measured for all sites. The correlation matrix was computed separately for the whole set of data, for Populus tremula and for Salix caprea, which were the two most common hosts. Other trees were sampled in too low a number. Matrices were scanned to search for significant correlations. A step-down method was applied in a multiple regression analysis for explaining bark pH by means of measured element concentrations in bark samples. The model started with all elements. The variable giving the least significant contribution was removed step by step until all remaining variables contributed significantly (P<0·05). A Minimum Spanning Tree (MST) analysis (Gower & Ross 1969) was used for grouping relevés with respect to chemical content of the bark. The results from chemical analyses were standardized by subtracting the mean value of the respective element and dividing by the standard deviation. Euclidean distances were used as distance measures. Sorting was done by starting with one random unit. The next step was a search through the distance matrix for the unit with the shortest distance to the first. The third step was a search for the next unit that was most close to one of the two first units, and so on.

Results Host trees L. pulmonaria A total of 43 trees was analysed, covering most of the forest reserve. About ten additional trees with L. pulmonaria shown in the distribution map (Fig. 1) were not included in the following analyses, since they were found later. As L. pulmonaria was not a common species in the forest reserve, most of the population was probably recorded during the field work. Lobaria pulmonaria was found on Populus tremula (n=19), Salix caprea (n=14), Acer platanoides (n=5), Sorbus aucuparia (n=3) and Betula pubescens (n=2), but it was never seen on Picea abies or Pinus sylvestris, which were the most common trees in the reserve. The trees were ranked according to their association with eutrophic vascular species on the ground, based on the mean reaction number (Table 2). Betula pubescens, Populus tremula and S. aucuparia

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T 2. Summary statistics of tree and stand characteristics of trees carrying Lobaria pulmonaria* Tree species

Parameters Number of observations Characteristics of analysed trees or stands Girth at breast height (cm) Tree height (m) Basal area (relascopesum, m2 ha "1) Vitality of phorophytes Altitude (m above sea level) Height below nearest top (m) Height above nearest valley (m) Epiphytic vegetation Mean number of lichens hepatics and mosses lichens with cyanobacterial photobiont Total number of lichens Hepatics and mosses Index of uniformity (s1/á) Index of diversity (á) Ground vegetation (vascular plants) Mean number of eutrophic species oligotrophic species moisture-demanding species ubiquists, or special ecology R-number of Ellenberg (1986) Total number of vascular species Index of uniformity (S1/á) Index of diversity (á)

Sorbus aucuparia+ Betula pubescens

Populus tremula

Salix caprea

Acer platanoides

5

19

14

5

73·8&10·1 18

133·2&7·5 20·8&1·3

126·2&7·8 11·5&1·2

63·0&9·3 15·3&0·9

21 2·4&0·4 274&10 28&6 39&9

20·8&2·0 2·3&0·3 295&5 26&3 65&5

15·8&2·0 2·4&0·1 264&7 61&8 19&4

23·0&3·0 1·0&0·0 260&10 78&10 15&9

16·2&2·4 8·2&0·6

18·2&1·5 6·4&0·9

17·1&2·3 9·9&1·3

17·4&0·8 9·6&1·0

2·0&0·5 34 13 1·5 16

3·5&0·3 74 21 0·8 31

5·3&0·6 71 37 0·7 40

5·2&0·9 36 18 1·4 19

1·0&0·0 4·8&0·7 0·6&0·4 2·2&0·2 2·53&0·06 16 1·7 5

3·4&1·1 6·8&0·5 0·4&0·2 3·3&0·2 2·88&0·15 44 1·2 12

11·1&1·6 5·9&0·5 1·4&0·5 3·2&0·3 4·26&0·18 45 2·4 9

14·6&2·5 3·8&0·5 2·4&0·8 2·6&0·2 4·61&0·39 66 0·5 45

*Epiphytic vegetation was recorded on the lower 2 m of the trunk of sampled trees, and vascular plants on the ground in a circular relevé of 3 m radius, centred around each tree. Means&standard error of means are given. For tree height and relascopesum the numbers of observations were: Sorbus aucuparia and Betula pubescens, n=1; Populus tremula, n=13; Salix caprea, n=10; Acer platanoides, n=4. Vitality of trees was estimated according to the following scale: 1, healthy with no wounds; 2, healthy, but with a dead top or one or more big and dead branches, or wounds on the trunk; 3, not healthy, more than 50% of the canopy is dead; 4, dead. The index of diversity and index of uniformity are according to Dahl (1960).

were growing together with oligotrophic species; Salix caprea and A. platanoides with clearly eutrophic series (Table 2). A subjective ranking of the deciduous trees after their frequency in the reserve could be: B. pubescens, P. tremula>Sorbus aucuparia, Salix caprea> A. platanoides. Lobaria pulmonaria was

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therefore over-represented on trees surrounded by a more demanding ground vegetation, discriminating trees in an oligotrophic environment. The average phorophyte height ranged from 20·8 m in P. tremula to 11·5 m in S. caprea (Table 2); the tallest stem was a P. tremula of 34 m. Trees were frequently of low vitality (Table 2); the top of the tree and/or big branches were normally broken or dead. Stems were often infected by fungi of the Polyporaceae. The five investigated A. platanoides trunks were all healthy, with no visible signs of damage. They were, unlike most others, situated in somewhat moister valleys (Table 2) with a denser and more shady surrounding stand. All A. platanoides stems had uniform Lobarion vegetation on the two lower metres of stems. Some S. caprea stems also had relatively uniform Lobarion vegetation, but the epiphytic vegetation was normally more patchy with the best developed Lobarion below large wounds. On P. tremula and B. pubescens, however, there was a striking difference in epiphytic vegetation between the Lobarion, localized to drainage channels below large and old wounds, and the Pseudevernion, inhabiting the dominant part of the stem. Influence of forestry and fire Lobaria pulmonaria was often found in or near steep slopes, and often in convex parts of the landscape. The stands were relatively open with a low basal area (19·4&1·3 m2 ha "1) and much diffuse light, the patches covered with Lobarion being normally shaded from direct radiation during parts of the day when the sun is high. Lobaria pulmonaria was exclusively found in old forests that formed islands in a mosaic of more even-aged, younger and/or denser stands. Old stumps could be seen in most localities, an indication of old selective fellings, probably as far back as the end of the 1800s or beginning of the 1900s. The scarcity of big and dead trunks at different degradation levels indicated that the stands were not virgin forests. Only a few Lobarion localities were found near the larger lakes and waterways that were previously used for floating timber. Most of the forests along such lakes were influenced by old clearings, probably around 60 years ago. Such areas were poor in lichen species. Old fire scars on dead pine wood were found in only a few L. pulmonaria localities, and were restricted to places where there were healthy nearby populations of Lobarion species in moister areas that had probably escaped the fire. Epiphytic vegetation Altogether 105 lichens and 45 bryophytes were found on the 43 trunks analysed (Table 3). Cladonia species were common, but were not recorded since they were often poorly developed. The species composition of Lobarion communities was not analysed separately, since they often had a patchy distribution on the trunk. Epiphytes were ranked in Table 3 according to their occurrence on investigated tree species, which were ranked according to the oligotrophic–eutrophic gradient, as in Table 2. The first species in Table 3 (Platismatia glauca to Pertusaria amara) are mainly Pseudevernion lichens, with a preference for more oligotrophic bark. All of them contain green algae. The

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central part of Table 3 contains ubiquitous species such as Phlyctis argena, Lepraria incana and the leafy liverwort Frullania dilatata, but also the most common Lobarion species such as Lobaria pulmonaria, Nephroma parile, Parmeliella triptophylla and associated bryophytes such as Dicranum scoparium, Drepanocladus uncinatus and Radula complanata. The remaining species that were closely associated with L. pulmonaria are found in the lower part of Table 3, such as Collema flaccidum, C. subnigrescens, Heterodermia speciosa, Leptogium teretiusculum, Lobaria scrobiculata, Nephroma spp., Peltigera spp., Sticta fuliginosa, the liverwort Metzgeria furcata, some crustose lichens, and some other bryophytes. The lower part of Table 3 contains a mixture of species with different sociological affinities, but many have their optimum in old forests with a high and relatively constant humidity. Few belong to the Pseudevernion, and the majority have a stronger preference for less acidic bark than the uppermost species. Most Lobarion species were rare. Species such as Sticta sylvatica and Heterodermia speciosa were found on one single tree only. Dead portions of lobes of L. pulmonaria were observed on as much as 23% of investigated trees; in two cases as much as 25% of the total thalli were dead. Such observations indicate an impoverished epiphytic flora. Bark chemistry Different tree species had bark with different chemistry (Table 4). An MST analysis showed that A. platanoides was the most distinct tree chemically (Fig. 2), as the five trunks exclusively formed one section. Bark of A. platanoides was especially high in Ca, N, P, Mn, Cd, had a high pH, and was most similar to bark of S. caprea. S. caprea had, however, the lowest content of Mn, Al, K, Na. Betula pubescens, S. aucuparia and P. tremula were highest in C and lowest in Ca, and P. tremula had very high C/N ratio. Spatial variations in bark chemistry within a single stem were prominent, especially on stems with a distinct pattern in epiphytic vegetation. Lobarion bark differed from Pseudevernion bark in having a higher pH and a higher T 3. Epiphytes found on at least three of the investigated trunks* Tree species Species recorded

B+So

P

S

A

Platismatia glauca Ochrolechia androgyna Micarea prasina Usnea filipendula Hypogymnia tubulosa Lopadium disciforme Vulpicida pinastri Parmelia saxatilis Parmeliopsis ambigua Pseudevernia furfuracea

41263 33332 . 313. . 1. 14 1. . 33 . 2. 32 . . . 22 . . . 31 ....1 ....3

. . 4. 3. 6. 4423. 2142. 2 4. 4. . 3. . 2. . 2. . 53125 . . . 1. . . . . 32. . 3. 33. 4 . . 1. 2. 2. 11. 2. 1. . 1. 1 . . 2. 2. . . 21. 4. 2. . . . 2 2. . . . . . . . 12. . . . . . . . . . 2. 1. 2. 3. 22. 32. 111 3. 33. . 5. 23. . . . 424. 4 . . 2. 2. 3. 4. 32. 1222. 1 . . 2. . . 2. . . . 1. . . 1. . 1

2. . 2. 4. . 325. 53 2. . . . 4. . . . 2232 . . . . 2. . . . . 23. . 5. . . . 3. . . . 4. 31 2. . . . 3. . 3. 2. 21 . . . . 322. 2. . 133 2. . . . 2. . . . 2. 1. 2. . . . 5. . . 2. . . . . 2. . . . 1. . . . 1. . 1 . . . 1. 1. . . . 3. . .

..... ..... ..... ..... ..... ..... ..... ..... .....

Table continued overleaf

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T 3. Continued Tree species Species recorded

B+So

P

S

A

Mycoblastus sanguinarius Ochrolechia pallescens Lecidea albofuscescens Loxospora elatina Bryoria capillaris B. fuscescens Ramalina farinacea Buellia griseovirens Cetraria chlorophylla Parmeliopsis hyperopta Dimerella pineti Pertusaria coccodes Ulota crispa Dicranum montanum Plagiothecium sp. Lophozia longidens Hypnum cupressiforme Parmelia sulcata Hypogymnia physodes Pertusaria amara Phlyctis argena Lepraria incana Ptilidium pulcherrimum Dicranum scoparium Drepanocladus uncinatus Lobaria pulmonaria Nephroma parile Parmeliella triptophylla Frullania dilatata Radula complanata Orthotrichum sp. Hylocomium splendens Arthonia didyma Bacidia beckhausii B. subincompta Nephroma bellum Pachyphiale fagicola Blepharostoma trichophyllum Bacidia absistens Collema subnigrescens Lobaria scrobiculata Nephroma laevigatum Peltigera horizontalis Rhytidiadelphus triquetrus Pylaisia polyantha Plagiochila porelloides Isothecium myurum Nyholmiella obtusifolia

. . . 22 ..... 11. . 2 ....2 ....1 . . . 2. ..... . . . 3. ..... ..... 3. . . . ....2 12. 2. . 2. 3. . . 3. . . 222. . 3233 2. 34. 35254 34223 24314 34533 33542 15332 332. 3 24434 . . 232 . 2. 2. 2. 235 23333 . . 1. 3 . 2. 2. ....2 ....2 . . . 2. . . 3. . ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... .....

. . 3. . . 3. . . . . . . . . 2. . 2. . . . . 2. . . . 3. . 1. 3. . ..................2 . . . . . . . . 1. . . . . . . . . . ................... . . . . 1. . . 1. . 2. . . . . . . . . . . . . 1. . . . . . . . 13. . . . . . . . . . . . . . . 23. . . 2 . . . 11. . . . . . . . . . . . . . . . 3. . . 2. 2. . . . . 1. 2. . . 1. . . . . 1. . . . . . . . . . . . . . . . . . . . . . . . . 32. . . . 1. . . . . . . . . 1. 32. . 2. . . . . . . . . . . 3. . . . 1. . . ................... . . . . . 1. . . . . . . . . . . 22 . . . . . . . . 33. . . . . 2. . . . . 3. 2. 3. 3142. 313521 5. 42514. 4335. 534414 7. 4. . 24. 2. 233242334 3533223734453453374 3348432245435334425 3234. 24. 33443433334 . 221. 2. . 4. 332332123 3322. 3. 6322. 443. . 53 4144142125125564343 . 111. . 2. 32. . 3. 33. 2. 24. 3. 3. 33. 33. 443342 342311. 422453345542 . 5. 31. . 43132343424. 1. . . . . . . 2. . . 321. 4. . . . . . . . . . . . . . . . 2. . . . . . . . . . . . . . . . . . . . . 2. . . . . . 1. . . . . . 3. 3. 222 . . . . . . . 33. . . 2. 244. 2 2. 2. . . . . . . . . . . . 1. . 1 . . . . . . . . . 1. . . . . . . . . . . . . . . . . . . . . . . . 2. . . . . . . . . . . . . . . . . . . 2. 2 . . . . . . . . . . . 3. . . 22. . . . . . . . . . . . . . . . 3. . . 1 . . . . . . . . . . . . 3. . . 11. . 1. . . . . . . . . . . . . . . . . . . 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. . . . . . . . . . . . . . . . . 1. . . . 3. . . . . . . . . . . . . . 1. . . . . . . . . 22. . . . 3. . . . .

2. . . . 2. . . . 3. 2. .............. .............2 . . . . . . . . . . . 2. . 2. . . . 2. . . . 3. . . 4. . . . . . . . . 3.2. . . . . . . . . 1. 2. . . . . . . . . . . . . . . 3. 1. . . . . . . . . 3. . . . . . . . 2. . . . . . . . 1. 1. . . . . . . 22. . . . . . . 4. . . . . . . 2 2. . . . 1. . . . . 23. 3. . . . . . . . 12. . 2 . 1. . . . . . . . . . 22 3. 33. . . 2. . . . 33 23. 28. . 1634. 4. 4. . . . 1. . 322. 21 6. . 414113. 6332 4. . . . 2. . 3. 2. 21 3324. 21. . . 34. 4 33763345424456 51233244333344 23342221. 44353 2834. 26546. 546 53344342425644 3322123. 2. 2. 34 . 32. 1. 32. 2. 333 23. . 3. 3. . . 232. 23322. 543. 3444 . . . . . . 2. . . . . . . . 44. . . 3. . 4. . 3. .............. 11. . . . . . . . . 2. . . . 12. 13. . . . . . . . 3. . . 3. . . 2. 134 . . . . . . . . . . 12. . . 33. . . . . . . . . . . . . . . . . . . . . 23. . .............. 2. . . . 1. . . . . . . . .............1 . . . . . . . . 2. . 2. . . 4. . . . 24. . . . . . 1. . . . . . . . . . 33. . 24. . . . . . . . . . 1 . 3. 4. . 2. . . . 2. . ..............

..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ....1 ..... ..... ..... ..... ..... 1. . . . 1. . . 1 1. . 24 24535 23454 . . 2. 2 . . 222 . 3533 32245 2. 41. 8. 333 35534 55645 11211 . . 2. . . 1. . . ....1 . 533. 2. 3. . . 1. . . ..... ..... ..... ..... ..... ..... ..... ..... ..... . 4. . . . . . 3.

Table continued

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T 3. Continued Tree species Species recorded

B+So

P

S

A

Biatora carneoalbida Catinaria atropurpurea Megalaria grossa Collema flaccidum Melanelia fuliginosa Lecanora subfusca group Lecidea erythrophaea Leptogium teretiusculum Metzgeria furcata Peltigera collina P. polydactyla P. praetextata Biatora epixanthoides Nephroma resupinatum Bacidia laurocerasi Lecidella euphorea Homalothecium sericeum Eurhynchium angustirete Bryum capillare Amblystegiella subtilis Pertusaria leucostoma Biatora helvola Graphis scripta

..... ..... ..... ..... ..... ..... ..... ..... ....3 ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... ..... .....

. . . . . . . 4. . . . . . . 3. 3. . 1. . 2. . 1. . . . . . . 1233 . . . . . 1. 2. 3. . . 4. . . 5. . . . . . 2. 4. . . . . 3. 2. 3. . . . . 2. 2. . . . . . 3. . . . 1 2. . . . 12. . . . 4. . . . 433 . 1. . . . . 4. 2. . . 3. 3. 3. . . . . . . . 3. . . . . 3. . . . . . 4. 3. . . . . 3. . . . . . . . . ................... . . . . . . . . . . . . . . . 2. . . . 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32. . . . ................... ................... . . . . . . . . . . . . . . . . . 2. ................... ................... ................... ................... ................... ................... ...................

. 2. . . . . . . . . . . . . . . . . . . . . . . 2. 3 .............. . 3. . . . . . . . . . . . . . . 1. . . . . . . . . . . . . . 11. . . . 2. . . .............. . 3. . . . . . . . . 3. 3 . 3. 33. 3. 3335. 2 . 1. 2. . . . 32. . . . . 22. . . . . . . . . . . . 4. 23. 24532343 .............. . 3. . 2. . 3. 1. 3. . . . . . . . . . . . . 2. 1 .............. .............. . 3. . . . . . . . . . . . . . . . . . . . . . 2. . . .............. .............. .............. ..............

22. . . 3. . 22 2. 3. 3 . . . 1. 1. 2. . 143. 2 . . 3. 3 . 332. 34446 . . 33. . 2. . . 3. 352 2. . . 3 1. . . . . 1. . 2 353. 3 32. 3. . 322. 3. . 3. . 557. 132. . . 222. . 2. 13

*Trees were ranked according to their mean R-number of Ellenberg (1986) as given in Table 2. Epiphytes were tentatively ranked according to their occurrence along this R-number gradient. B, Betula pubescens; So, Sorbus aucuparia; P, Populus tremula; S, Salix caprea; and A, Acer platanoides. Numbers refer to cover abundance classes according to Domin’s scale (Krajina 1933, revised by Dahl 1956). Nomenclature follows Santesson (1993) for lichens, Smith (1978) for mosses and Smith (1990) for liverworts. The following species were found in less than three relevès: Lichens: Acrocordia gemmata (A), Alectoria sarmentosa (S), Arthonia cf. muscigena (P), Arthopyrenia lapponina (A), Bacidia circumspecta (P,S), Bacidia rubella (S), Biatora gyrophorica (So,S), B. vernalis (B,So), Bryoria bicolor (S), Calicium glaucellum (S), C. lichenoides (S), Caloplaca flavorubescens (P), Chaenotheca chrysocephala (S), C. gracillima (S), C. xyloxena (S), Cystocoleus ebeneus (P), Evernia prunastri (S), Heterodermia speciosa (P), Hypogymnia bitteriana (P), Imshaugia aleurites (P), Lecidea betulicola (P), Leproloma membranaceum (P), Mycoblimiba hypnorum (S), Pannaria pezizoides (S,P), Peltigera canina (S), P. leucophlebia (S), Pertusaria albescens (P), P. hemisphaerica (P,A), P. ophthalmiza (B), Physcia caesia (P), Polyblastia/Agonimia sp. (S), Rinodina archaea (S), R. sheardii (P), Sticta fuliginosa (S), Thelotrema lepadinum (A), Xanthoria parietina (P). Bryophytes: Antitrichia curtipendula (S), Barbilophozia barbata (P,S), B. lycopodioides (S), Brachythecium populeum (S), B. reflexum (A), Eurhynchium schleicheri (S), Frullania fragilifolia (S), Heterocladium dimorphum (S), Homalia trichomanioides (A), Hylocomium umbratum (S), Lejeunia cavifolia (P,S), Lophocolea heterophylla (S), L. minor (S), Mnium stellare (S), Neckera crispa (A), Pleurozium schreberi (S), Pseudoleskeella nervosa (P), Ptilium cristacastrensis (S), Rhodobryum roseum (A), Rhytidiadelphus loreus (S), Tetraphis pellucida (S), Timmia austriaca (S). The following lichens were found but overlooked during the field-work period, either because of small size or because chemical tests were required: Fuscidea arboricola, F. pusilla, Hypocenomyce leucococca, Biatora efflorescens, Lecidea nylanderi, Mycoblastus fucatus, Ochrolechia microstictoides, Ochrolechia turneri, Placynthiella dasaea, Rinodina degeliana, Japewia subaurifera.

17·8&0·9 80·57&8·28 10·09&0·74 219·7&31·7 186·5&13·5 0·206&0·027 112·4&9·8 35·7&6·1

B (mg kg "1) Fe (mg kg "1) Cu (mg kg "1) Mn (mg kg "1) Zn (mg kg "1) Mo (mg kg "1) Al (mg kg "1) Cd (ìg kg "1) 4·36&0·15*** 216&10***

15·5&0·8 n.s. 50·08&3·74** 7·97&0·69*** 104·3&11·0** 130·8&6·5** 0·192&0·031 n.s. 65·0&4·1** 25·9&4·4 n.s.

1·62&0·38 n.s. 0·19&0·01* 6·48&0·50 n.s. 0·70&0·08**

2·49&0·11*** 523·6&1·7*** 0·147&0·011*** 0·47&0·03*

Pseud. n=14

5·06&0·11 93&8

17·5&0·7 72·91&8·72 7·49&0·50 70·6&7·9 163·0&13·5 0·154&0·029 75·8&6·9 75·4&24·9

0·48&0·09 0·10&0·01 15·84&1·03 0·65&0·09

5·58&0·29 487·0&2·5 0·302&0·016 0·62&0·03

Lob. n=14

Pseud. n=11

4·47&0·07*** 151&10***

16·6&0·8 n.s. 53·05&6·13* 7·18&0·64 n.s. 28·5&7·4*** 136·2&15·6 n.s. 0·119&0·030 n.s. 61·2&6·9* 57·4& 13·5 n.s.

0·46&0·07 n.s. 0·10&0·01 n.s. 13·95&1·81 n.s. 0·48&0·07 n.s.

3·53&0·23*** 507·8&4·1*** 0·241&0·028 n.s. 0·55&0·06 n.s.

Salix

5·38 67

14·3 225·2 9·52 1732 107·6 0·279 206·8 37·0

1·01 0·11 7·15 0·62

9·63 536 0·483 0·90

Lob. n=3

0·74 0·09 5·57 0·40

5·80 616 0·310 0·71

Pseud. n=2

4·82 124

12·5 116·3 9·70 373 48·8 0·167 90·4 20·0

Sorbus

Tree species

6·25 75

14·0 159·6 10·95 1181 245·6 0·251 202·0 78·5

3·73 0·32 8·62 1·97

7·40 549 0·435 0·83

Lob. n=2

0·42 0·11 2·98 0·43

4·80 598 0·260 0·54

Pseud. n=2

4·62 129

6·0 99·1 7·71 226 97·6 0·098 65·7 9·0

Betula

Level of significance of differences between Lobarion (Lob.) and Pseudevernion (Pseud.) bark (paired t-test): *P<0·05; **P<0·01; ***P<0·001.

5·40&0·16 122&9

2·30&0·31 0·27&0·02 8·08&0·65 1·08&0·08

K (g kg "1) Na (g kg "1) Ca (g kg "1) Mg (g kg "1)

pH C/N

4·49&0·24 513·1&1·8 0·306&0·020 0·63&0·03

Lob. n=19

N (g kg "1) C (g kg "1) P (g kg "1) S (g kg "1)

Elements

Populus

6·77&0·12 53&2

17·4&0·4 80·70&13·26 12·02&0·79 2073&392 155·7&22·4 0·191&0·043 102·2&14·1 119·0&30·1

1·72&0·20 0·21&0·03 32·37&2·29 1·18&0·12

9·26&0·57 484·0&23·2 0·510&0·022 0·94&0·12

Lob. n=5

Acer

5·49&0·12 98&6

17·2&0·5 91·86&8·08 9·47&0·44 537&125 172·5&8·7 0·195&0·019 110·1&8·5 60·4&10·0

1·62&0·21 0·20&0·02 13·39&1·30 0·96&0·07

5·89&0·36 504·4&4·8 0·347&0·016 0·70&0·03

Lob. n=43

4·45&0·08*** 179&10***

15·0&0·7* 59·1&5·1*** 7·77&0·43*** 103&19** 124·9&7·8*** 0·156&0·020 n.s. 65·4&3·7*** 36·2&6·3 n.s.

1·04&0·21* 0·14&0·01* 9·01&1·04 n.s. 0·58&0·05***

3·27&0·24*** 529&6·4*** 0·202&0·016*** 0·51&0·03**

Pseud. n=29

All trees combined

T 4. Mineral content (mean&standard error of mean per unit dry weight) and pH of Lobarion and Pseudevernion bark samples from the trees investigated

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12a 5a 43b

28a 25b

34a 11a

<4

33a 35a

25a 30b 21a 37a 31b 10a 17a 36b 6a 12b 5b 7a 14a 16a 20a 17b 18a 38b 16b 29b 2b 43a 10b 36a 14b 23a 18b 9a 32a 3a 24a 20b 19b 24b 41a 26b 44a 15a 4a 40a 44b 13a 1b 2a 40b 26a 7b 22b 37b 21b 42b 6b 42a

<4·25 <4·5 <4·75

<5

<5·25 <5·5 <5·75

27a

1a

19a

<6

29a 31a 22a

8a

38a 30a

9b

<6·25 <6·5

≥6·5

F. 2. Minimum spanning tree based upon chemical content (total content of N, P, C, K, Mg, Ca, Na, Fe, Cu, Mn, Zn, Mo, Al, Cd; B and S were excluded due to missing values) of bark samples from the trees analysed. Original values were transformed by: (1) subtracting the mean value; (2) dividing by the standard deviation. Euclidean distances were used as distance measures. ,, Populus tremula; ., Salix caprea; 0, Betula pubescens; 1, Sorbus aucuparia; , Acer platanoides, Open symbols and a represent Lobarion bark, filled symbols and b represent Pseudevernion bark. Size of symbols represents the pH of bark samples (see key). Numbers refer to tree number. Numbers with a only refers to trees with a uniform Lobarion around the 2 lower metres of the stem.

content of N, P, Al, Fe, Cu, Zn, Mg (P<0·001); Mn, S (P<0·01); and Na, K, B (P<0·05), and lower C and C/N (P<0·001, Table 4). Ca, Mo and Cd did not differ significantly between Lobarion and Pseudevernion bark. In general the same trend was found in a pairwise t-test of individual trees as in a pooled sample of all trees. Pseudevernion samples that were most acid are located near the centre of the MST (Fig. 2), and are spaced with relatively short distances, whereas Lobarion samples form the outer parts of MST branches, and are spaced with longer distances. Accordingly, different tree species as well as different trunks were more similar to each other with respect to bark chemistry beneath the dominating Pseudevernion community compared to Lobarion bark. A Pearson correlation matrix showed that the correlation between a certain mineral in Lobarion versus Pseudevernion bark was generally poor, which means that the two categories of bark were not closely linked. In the correlation matrix for Populus tremula only Cu showed a significant positive correlation (r=0·839, P<0·001). For S. caprea Cu gave also the only significant positive correlation (r=0·668, P<0·05), while P showed a negative correlation (r= "0·737, P<0·01). The complete matrix including all trees gave significant correlations for Mn (r=0·834, P<0·001), N (r=0·811, P<0·001), Fe (r=0·770, P<0·001), Cu (r=0·719, P<0·001), Ca (r=0·582, P<0·001), C (r=0·575, P<0·001), K (r=0·483, P<0·01), B (r=0·454, P<0·05), Na (r=0·444, P<0·05), Al (r=0·413, P<0·05) and Mo (r=0·376, P<0·05), but apart from Ca and Mo these correlations appeared mainly because of phorophyte-specific differences.

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F. 3. Percentage cover (., right axis) of Lobaria pulmonaria and pH (left axis) as a function of the distance from a drainage channel probably made by lightening many years ago in a Populus tremula; 0, pH measured on the surface of intact bark; -, pH measured in finely ground bark samples.

The results from a case study from one P. tremula stem (Fig. 3) showed a steep chemical gradient away from a distinct drainage channel. This stem had a long, vertical drainage channel of several metres, with dense and healthy colonies of L. pulmonaria, while the remaining parts had typical Pseudevernion vegetation. Within a distance of a few centimetres the cover of L. pulmonaria fell from 100 to 0%, with a corresponding decrease in pH from more than 5 to less than 4. There was a good correspondence between pH of the bark surface measured in situ and pH of macerated bark samples. The pH of Lobarion bark correlated strongly with many minerals in the Lobarion bark samples, namely Mg (r=0·698, P<0·001), P (r=0·648, P<0·001), Mn (r=0·617, P<0·001), K (r=0·583, P<0·001), Ca (r=0·551, P<0·001), Na (r=0·506, P<0·001), N (r=0·351, P<0·05) and S (r=0·350, P<0·05). A step-down multiple regression analysis starting with all measured elements in Lobarion bark resulted in the model: pH of Lobarion bark=3·82+0·43 Ca (P<0·001)+6·42 Mg (P<0·001)+18·08 Na (P=0·01)+0·00 Mn (P=0·003), explaining 81·7% of the variation in pH. Another model using predictors (Ca, Mg, K, P), that were thought to be important for pH, explained 82·8% of the variation in pH. The pH in Lobarion samples correlated negatively, although not significantly, with many minerals in corresponding Pseudevernion samples, and no significant positive correlations were found. The pH of Pseudevernion bark correlated only with Mg (r=0·564, P<0·001), P (r=426, P<0·05) and N (r=0·381, P<0·05), mentioned in decreasing order of the correlation coefficient. Only Mg remained significant in a step-down multiple regression analysis starting with all

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elements in Pseudevernion bark, explaining only 29·3% of the variation in pH. Similar results were found when the same analysis was done with a set of data containing Populus tremula only. The elemental composition of Lobarion bark was more closely linked to soil characteristics, as reflected in the mean reaction number of Ellenberg of the ground vegetation, than that of Pseudevernion bark samples. This was demonstrated by means of a linear regression analysis. There was a strong correlation (r=0·688, P<0·001) between Ca in Lobarion bark and mean reaction number, as well as negative correlations with elements generally showing elevated levels in the litter layer in oligotrophic environments such as C (r= "0·574, P<0·001), Na (r= "0·416, P<0·01), K (r= "0·425, P<0·01), Al (r= "0·426, P<0·01). For Pseudevernion samples there was only one significant correlation, namely a negative one between the mean reaction number of Ellenberg and Mn (r= "0·461, P<0·001). The relative altitude of the sites, compared to the altitude of the nearest topographic peak, seemed to be of importance. Based on the Pearson correlation matrix including all variables, the amount of Ca in Lobarion bark (r=0·662, P<0·001), number of epiphytic mosses (r=0·471, P<0·01), and number of lichens with cyanobacteria (r=0·447, P<0·01), reaction number based on ground vegetation (r=0·640, P<0·001), number of eutrophic vascular plants (r=0·612, P<0·001), and number of moisture-demanding vascular plants (r=0·526, P<0·001), increased with increasing altitudinal difference between the site and its nearest peak. The concentrations of C (r= "0·524, P<0·001), K (r= "0·300, P<0·05), Na (r= "0·308, P<0·05), Al (r= "0·343, P<0·05), all in Lobarion bark, and number of oligotrophic vascular plants (r= "0·315, P<0·05) decreased with increasing altitude below the nearest peak. None of the elements in Pseudevernion bark correlated with altitude below the nearest peak. Table 2 also shows that the two most demanding trees edaphically, A. platanoides and S. caprea, were situated further away from the top than the more oligotrophic P. tremula, S. aucuparia and B. pubescens. In general, the trees with the most clear-cut boundary between the Lobarion and Pseudevernion, such as the tree illustrated in Fig. 3, were situated closer to local peaks than trees without (A. platanoides), or with a more diffuse epiphytic vegetation pattern (some S. caprea) (Table 2). Discussion There are indications that the Lobarion was a previously ubiquitous epiphytic community in Europe (Rose 1988). The Lobarion is scattered in the forest reserve investigated (Fig. 1), like islands of stands with a long ecological continuity in a landscape of young and/or more even-aged stands. The patchy distribution, the low frequency of most Lobarion species, and the high frequency of damaged L. pulmonaria, suggest a relict status. The previous old selective fellings probably did not cause a dramatic break in the long ecological continuity with respect to canopy cover, since they mimicked natural gap formation. The microclimate in naturally formed gaps combines ample, good-quality light and a high air humidity (Stoutesdijk & Barkman 1992), which is often considered to be of importance to many epiphytes (Barkman

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1958). Some of the best localities were open shade habitats in the sense of Stoutesdijk (1974), sheltered from sunlight but with ample diffuse light resulting in low surface temperatures, minimal transpiration, and frequent condensation of water vapour. Transplantation experiments have shown that L. pulmonaria is readily transplanted by means of soredia if the bark pH is sufficiently high (Gilbert 1977, 1990; Hallingbäck 1990). Such experiments indicate that vacant habitats are available and that fragmentation of forests through clearing is a severe obstacle for dispersal of L. pulmonaria. However, Farmer et al. (1992) failed to reintroduce Lobarion species in a site where acid depositions probably had caused extinction, illustrating the importance of acidification. The Lobarion is often considered to be replaced by the Pseudevernion in areas affected by acid rain (Rose 1988). A more than 160-year-old observation of a ubiquitous occurrence of Lobarion species on Quercus, probably mainly Q. petraea, near the southern tip of Norway (Blytt 1829) suggests that the normal bark pH of Quercus before the industrial revolution was higher than 5·0, which is the preferred pH of Lobarion (Gauslaa 1985). After decades of imported acid rain, the normal pH range of Quercus is now well below 5·0 (Du Rietz 1945; Barkman 1958; Egerhei 1978; Pedersen 1980; Müller 1981), which is too low to support a healthy Lobarion. This could also apply to tree species investigated in the present study. The stem flow of Fagus sylvatica is so acidic in southern Sweden that even the soil around tree bases becomes acidified (Falkengren-Grerup 1989). Lobaria pulmonaria declines rapidly in an impoverished bark ionic environment (Farmer et al., 1991b). The Lobarion, at least in areas influenced by acid rain, is nowadays often restricted to sites with a soil rich in Ca (Gauslaa 1985; Farmer et al., 1991b; Bates 1992). A Ca-rich soil seems to be able to counteract bark acidification partially, maintaining a higher bark pH. This is probably the reason why the Lobarion was clearly over-represented in edaphically rich sites as well as on edaphically demanding tree species within the study area. The elemental composition of Lobarion bark seemed to reflect the nutrient status of the soil, as there were correlations between bark elements and the mean reaction number of Ellenberg (1986) based on ground vegetation. The mean reaction number for forest stands in Norway correlates well with the actual degree of base saturation and pH of the litter layer (Vevle & Aase 1980). Elements taken up through roots and incorporated in the biomass become released through decomposition of woody biomass in old, large wounds and enrich the stem flow below. Pseudevernion bark, on the other hand, was probably more leached and relatively more influenced by the elemental composition in airborne depositions, since there were few and weak correlations between bark elements and mean reaction number. The chemistry was also more uniform in Pseudevernion bark when different tree species were compared (Fig. 2), indicating that a factor other than the local soil dominates the chemical composition of Pseudevernion bark. Old wounds on the stem cause a considerable spatial variation in bark chemistry, which is reflected in the epiphytic vegetation (Gilbert 1970). Wounds seem to be sources of cations enriching the bark in drainage channels

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below. The bark was often porous under a Lobarion, possibly as a result of a more favourable elemental composition for decomposing micro-organisms; Pseudevernion bark was harder. A porous bark, with a better water-holding capacity, may be more favourable for hydrophytic species such as L. pulmonaria. However, drainage channels without old wounds did not support a Lobarion, thereby excluding the moisture factor alone as crucial for the spatial variation in epiphytic flora. The altitudinal gradient from oligotrophic sites at or near peaks to more eutrophic sites with decreasing altitude also influenced the epiphytic vegetation. The Lobarion became more and more restricted to clear-cut drainage channels below old and large wounds in the most oligotrophic sites near local peaks. The increased exposure to airborne acid depositions near ridges (Medwecka-Kornas et al., 1989) probably influences the Lobarion negatively (Bates 1992). Leaching through thousands of years, speeded up by the more recent acidification, has probably resulted in more oligotrophic ecosystems around local peaks. The preference for damaged trees indicates that modern forestry strengthens the negative influence of acid rain, since healthy trees apart from A. platanoides are no longer able to support the Lobarion in the field-work area. The rotational period in modern forestry is generally too short to allow trees to enter a degeneration phase. Secondly, an intact forest canopy protects against airborne pollution, as the lowest pollution has been demonstrated inside forests, and the highest near forest edges or near road (MedweckaKornas et al., 1989). Since forestry in the past mainly utilized the forests near lakes and waterways, the more eutrophic part of the gradient was more exploited than the nutrient-poor areas closer to local peaks. Forests situated in lower parts of the landscape normally lack the required long ecological continuity for Lobarion to develop. The Lobarion becomes more species rich and more viable with increasing distance from local peaks, in spite of the fact that few such localities were found. The richest Lobarion sites had probably been destroyed by forestry in the past. There are relatively more undisturbed forests near local peaks, but with a relatively poor epiphytic flora, probably because of acidification. The following persons are gratefully acknowledged for verifications/identifications of critical crustose species: Tor Tønsberg, Stefan Ekman, Håkon Holien, Lars-Erik Muhr, Roland Moberg, Alan Orange and Rikard Sundin. The Nansen Foundation and Directorate for Nature Management (Norway) are thanked for funding the chemical analyses. R Barkman, J. J. (1958) Phytosociology and Ecology of Cryptogamic Epiphytes. Assen: van Gorcum. Bates, J. W. (1992) Influence of chemical and physical factors on Quercus and Fraxinus epiphytes at Loch Sunart, western Scotland: a multivariate analysis. Journal of Ecology 80: 163–179. Bitterlich, W. (1984) The Relascope Idea. Relative Measurements in Forestry. Slough: Commonwealth Agricultural Bureaux. Blytt, M. N. (1829) Botaniske Optegnelser paa en Reise i Sommeren 1829. Magazin Naturvidenskaberne 9: 241–283. Dahl, E. (1956) Rondane mountain vegetation in south Norway and its relation to the environment. Skrifter Det Norske Videnskaps-Akademi i Oslo. I. Mat.-Naturv. Klasse 1956(3): 1–374.

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