Lilian Karlsson

BIO600 Biology: Degree project 15 hec

Spring 2015

Examiner: Ulf Molau

Supervisor: Prof. Frank Götmark

Department of Biological and Environmental Sciences

University of Gothenburg

Predictions of long-term management

effects on epiphytic lichens in a woodland

pasture in southeast Sweden

2

Abstract

Many rare and red listed species occur in woodland pastures in southern Sweden, but the

management of this habitat is a challenge for nature conservation. The pastures are small and

fragmented, and the management of some conservation values might easily come into conflict with

others. Single large trees are important for epiphytic lichen populations and the species can persist

for as long as their host tree stand in unchanged habitat. However, the availability of new host trees

nearby is important for the populations to persist in the long term. This might come into conflict with

the prioritized management strategy of cutting around large trees, especially Quercus robur. Here I

test the hypothesis that a management strategy which strongly focus on large trees poses a threat to

epiphytic lichens of conservation values, in the long term.

The study was done in Yxnevik nature reserve, a woodland pasture with many old and large

deciduous trees. I asked three questions; 1) what epiphytic lichens of conservation values are found

in the reserve and how are they distributed on Fraxinus excelsior, Acer platanoides and Q. robur? 2)

Are there any other factors which could explain their occurrence, e.g. stem width (DBH), tree age,

bark crevice depth or stand history? 3) What are the possible long-term effects of different

management strategies for epiphytic lichens in the area?

Lichens were surveyed during June 2013 and occurred mainly on large, old trees with deep bark

crevices. The trees were located at the edge of the stand and some of the lichens occurred both on F.

excelsior and A. platanoides. No lichens were however common for Q. robur and the other two tree

species. There were some age gaps in the tree populations in the stand, and lichens occurred mainly

on trees originating from before the 1930’s. Based on the data I discuss possible effects of three

management alternatives; (i) clearing around large trees and cutting to create a more open

woodland suitable for grazing animals, but no grazing regulations; (ii) clearing around large trees, no

general cutting and no grazing regulations; and (iii) clearing around large trees, no general cutting,

grazing regulations. The lichen occurrence on old large trees could motivate clearing around them,

but a too extensive clearing might disfavor lichens over time if regrowth of new host trees is thereby

eliminated. As long as there are no grazing regulations, there will likely be increasing age gaps in the

tree populations, decreasing the possibility of future colonization of host trees.

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Sammanfattning

Många sällsynta och rödlistade arter är knutna till trädklädda betesmarker och förvaltningen av

dessa är en stor utmaning för naturvården. Områdena är ofta små och fragmenterade, vilket leder till

att en skötsel som utförs i syfte att främja vissa naturvärden lätt kan komma i konflikt med andra.

Enskilda grova träd är viktiga för epifytiska lavar och populationer kan fortleva så länge som

värdträdet lever, förutsatt att habitatet inte försämras. För en långsiktig fortlevnad är det däremot

viktigt att lämpliga ersättningsträd finns i närheten, något som kan motverkas av den frihuggning

som genomförs i syfte att gynna gamla/grova träd, i synnerhet ek. I detta arbete testar jag hypotesen

att en förvaltningsinriktning som stark förfördelar grova träd kan missgynna andra hotade och

naturvårdsintressanta arter över en längre tidsperiod.

Studien är utförd i naturreservatet Yxnevik, Kalmar län; en naturlig betesmark med hög andel grova

ädellövträd av olika trädslag. Jag har ställt följande frågor; 1) vilka naturvårdsintressanta epifytiska

lavar återfinns i reservatet och hur är de fördelade på de olika trädslagen; Quercus robur, Fraxinus

excelsior och Acer platanoides? 2) kan andra faktorer, som träddiameter, ålder, sprickdjup eller

beståndshistorik, förklara förekomsten av lavar? 3) vilka långsiktiga konsekvenser kan olika

skötselalternativ få för lavarna i området?

Naturvårdsintressanta epifytiska lavar inventerades under juni 2013 och återfanns främst på gamla,

grova träd med större sprickdjup i utkanten av beståndet. Vissa arter återfanns på både F. excelsior

och A. platanoides, men inga arter var gemensamma för dessa två trädslag och Q. robur. Jag

upptäckte ett flertal generationsglapp vid åldersbestämningen av träden och lavarna återfanns

övervägande på träd som fanns inom området innan det började växa igen på 1930-talet.

Mot bakgrund av detta diskuterar jag möjliga långsiktiga konsekvenser av tre olika

skötselstrategier; (i) frihuggning runt grövre träd, generell avverkning för att skapa ett mer öppet

landskap som lämpar sig för betesdjur men utan att reglera betet (ii) frihuggning runt grövre träd,

ingen generell avverkning, ingen reglering av betet (iii) frihuggning runt grövre träd, ingen generell

avverkning, reglering av betet. Lavar förekom i synnerhet på äldre/grövre träd, något som skulle

kunna motivera en frihuggning av dessa, men en alltför omfattande frihuggning skulle kunna

missgynna lavarna på långt sikt genom att minska tillgången på framtida ersättningsträd. Om inte

betet regleras kommer troligen även åldersglappet bland yngre träd att fortsätta öka, något som

ytterligare skulle kunna försvåra en framtida kolonisation.

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Table of contents

Abstract ................................................................................................................................................... 2

Sammanfattning ...................................................................................................................................... 3

Introduction ............................................................................................................................................. 5

Materials and methods ........................................................................................................................... 6

Study site ............................................................................................................................................. 6

Lichen species ...................................................................................................................................... 7

Field methods ...................................................................................................................................... 7

Statistical analysis ................................................................................................................................ 9

Results ................................................................................................................................................... 10

Lichen species and host tree preferences ......................................................................................... 10

Other explanatory factors ................................................................................................................. 11

DBH and bark crevice depth .......................................................................................................... 11

DBH, bark crevice depth and minimum tree age .......................................................................... 12

Stand history .................................................................................................................................. 12

Discussion .............................................................................................................................................. 17

Occurrence patterns of lichens in Yxnevik ........................................................................................ 17

Long-term management effects ........................................................................................................ 19

Conclusions ........................................................................................................................................ 20

Acknowledgements ............................................................................................................................... 21

References ............................................................................................................................................. 22

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Introduction

Woodland pastures are included in the category Agricultural landscapes in the Swedish red list, a

landscape type which hosts half of the red-listed species in Sweden. Many of these are related to

isolated trees or woodland pastures with sparse trees and these environments are considered

especially important for many epiphytic and epixylic lichens (Gärdenfors 2010, Hallingbäck 1995).

The areas of woodland pastures have decreased during the last century due to agricultural changes,

which have resulted in a denser forest with the loss of many species related to more open

conditions. Traditional methods like mowing, grazing and coppicing are therefore now reintroduced

with conservational purposes (Gärdenfors 2010; Paltto et al. 2011; Naturvårdsverket 2013).

However, since the remaining areas are small and fragmented, conservation actions to favor certain

organism groups might easily come into conflict with others, due to contrasting ecological demands

(Karlsson 2013).

Many lichens of conservation concern are assumed to have poor dispersal abilities, and therefore

slow colonization rates. However, the extinction rate of subpopulations is also slow and lichens can

persist as long as their host trees stand in unchanged habitat. Species with low turnover rates needs

a long time to reach a new equilibrium when the habitat change (Ranius et al. 2008b; Johansson et

al. 2012; Johansson et al. 2013 a, b) and old trees might therefore act as “life-boats” for lichens

during periods of less favorable conditions, offering an opportunity for re-colonization of other trees

when conditions improve (provided that suitable new host trees are available). Stand history may

therefore be a strong predictor of lichen occurrence (Johansson et al. 2013 a, b; Ranius et al. 2008b;

Jönsson et al. 2011). Epiphytes depending on just one or a few trees are however more vulnerable to

local extinction, which might occur both by tree fall and management cessation in woodland

pastures (Snäll et al. 2005; Johansson et al. 2012; Paltto et al. 2010). Today, many of the woodland

pasture sites are dominated by large trees and the regeneration is scarce (Sundell Eklund 2013;

Naturvårdsverket 2012). This creates an age gap which might over time lead to the extinction of

epiphytes, especially species with poor dispersal abilities or those related to old and large trees

(Johansson et al. 2013 a).

Clearing around large trees is a highly prioritized management strategy in the national guidelines,

and the high diversity and large amount of threatened epiphytes on Quercus robur motivates

conservation efforts to favor this particular tree (Naturvårdsverket 2012; Naturvårdsverket 2013).

But epiphytic lichen communities may differ depending on tree species and other trees like Fraxinus

excelsior, Ulmus glabra and Acer platanoides also host many threatened species (Gärdenfors 2010;

Thor et al. 2010). The tree species preferences among epiphytic lichens can be classified by bark

characteristics, like pH and porosity, where lichens found on trees with low bark pH (Q. robur) form a

6

poor-bark community and those found on trees with high pH (F. excelsior, U. glabra and A.

platanoides) form a rich-bark community (DuRietz 1945, Barkman 1958). Due to this classification,

there may be some species overlaps among the rich-bark trees while the same lichen species are less

likely to occur on both rich- and poor-bark trees.

Altogether, this leads to the hypothesis that present management in woodland pastures might

threaten rare epiphytes over time by not creating enough substrate to replace the older trees. This

risk might also be more urgent for epiphytes related to other deciduous trees than Q. robur, since

management tends to favor this tree. Two of the other trees (F. excelsior, U. glabra) are also

threatened by disease, further increasing the extinction risk for associated lichens (Jönsson & Thor

2012).

Here I attempt to test this hypothesis by investigating and predicting the possible long term effects

of different management strategies on epiphytic lichens that occur on three different tree species;

Quercus robur, Fraxinus excelsior and Acer platanoides, in a nature reserve in southeast Sweden. To

do this I ask the following specific questions; 1) what epiphytic lichens of conservation values are

found in the reserve and how are they distributed on F. excelsior, Q. robur and A. platanoides? 2) Are

there any other factors which could explain the occurrence, e.g. stem width, tree age, bark crevice

depth or stand history? 3) What are the possible long-term effects of different management

strategies for epiphytic lichens in the area?

Materials and methods

Study site

This study was performed during June 2013 in the nature reserve Yxnevik on the southeastern

coast of Sweden. The land area consists of a varied terrain with a woodland pasture shifting into a

Pinus sylvestris dominated heathland. Although relatively stony, the ground is mostly covered by

grass and herbs. Quercus robur is the dominant large tree in the wooded pasture, which covers an

area of 13,3 ha, but other large deciduous trees like Fraxinus excelsior, Ulmus glabra, Acer

platanoides and Tilia cordata are also present.

The area has a long history of grazing and the traditional land use is still visible by coppiced and

large wide trees. Grazing declined in the 1930’s which by time lead to invasion by especially Picea

abies. This lasted until 1985 when the landowner started to restore the area by removing coniferous

trees. Some grazing may have occurred during the period between the 1930’s and late 1970’s, but as

the forest grew denser, the animals might have preferred the more open landscape nearby (Alf

Hornborg, pers. comm.). Since 1979, the area has primarily been grazed by sheep in the summer

7

months, with the exception of the years 1999-2012 when Hereford livestock grazed the area. Today,

older trees dominate the pasture, and regeneration is scarce (Sundell Eklund 2013).

Lichen species

Ten epiphytic lichens were selected for this study (Table 1). The selection was based on expert

opinions (L. Arvidsson; B. Nordén) of which lichens could be expected in the area. Species currently

used as indicators of conservation values were chosen, some of which are also included in the

Swedish Red list (Nitare 2000; Gärdefors 2010).

Table 1: The selection of lichen species was based on both expert opinions and the use of indicator species

Arthonia spadicea

Arthonia vinosa

Buellia alboatra

Calicium adspersum

Gyalecta ulmi (NT)

Lobaria pulmonaria (NT)

Megalaria grossa (VU)

Opegrapha illecebrosa (VU)

Schismatomma decolorans (NT)

Sclerophora spp

Field methods

Three tree species were selected for this study; Quercus robur, Acer platanoides and Fraxinus

excelsior. As previously noted, Q. robur was the dominant tree while the populations of

A. platanoides and F. excelsior were mainly concentrated to certain areas, with scattered trees over

the rest of the reserve. Therefore, the selection of Q. robur was made by using north-south aligning

transects covering the reserve with 100 m intervals (for further information, see Sundell Eklund

2013). For F. excelsior and A. platanoides, trees which occurred in the same area as the selected Q.

robur were marked by numbers and DBH (diameter at breast height, 1.3 m) was measured on all

three tree species. For trees located in a slope, we measured DBH at the highest ground level (near

the stem) and if the tree split into two stems below 1.3 meters height, DBH was measured on the

thickest stem.

For all tree species, ten trees were randomly selected in each of three different size classes;

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DBH: 7-15.5 cm, DBH: 16-29.5 cm and DBH: >30 cm. The total number of trees, before and after the

selection, is given in Table 2. Since there was a lack of Q. robur in the smallest size class when only

using transects, the same selection method as for F. excelsior and A. platanoides was used to

increase the number of trees in this specific size class.

Table 2: Total number of trees in three size classes, before and after the randomized selection.

F. excelsior A. platanoides Q. robur

DBH (cm) before (n) after (n) before (n) after (n) before (n) after (n)

7-15,5 46 10 39 10 16 10

16-29,5 16 10 34 10 17 10

>30 23 10 14 10 29 10

Total 85 30 87 30 62 30

We did not quantify bryophyte cover on the stems since it was rare on the surveyed height, but if

the tree had a more abundant bryophyte cover (Figure 1) this was noted.

Occurrence/no occurrence of the selected lichen species was noted for every surveyed tree, but no

further abundance measurements were made. The trees were surveyed by placing a metal grid

(610x195 mm) on the south side of the stems with its upper side at 1.6 meter (Figure 1). Each square

was surveyed for lichens by using a hand lens with LED-light (magnification x 10). For the smallest

trees (DBH 7-15.5 cm) the whole southern half of the stem was surveyed on the height 0.99-1.6

meters (Figure 2). The field work was performed by two persons (the author, and J. Sundell Eklund)

working close to each other, but surveying separate trees. To ensure that the trees were surveyed in

a similar and consistent manner, we trained on trees in the area before the study began and then

continuously consulted each other during the field work. All lichens of interest were collected and

later identified in a lab by microscopic spore analysis and chemical analysis, supervised and verified

by an expert (Lars Arvidsson, Dept of Biological and Environmental Sciences, University of

Gothenburg).

I determined tree age by taking increment cores, three in every size class for each tree species.

These trees were randomly selected and two of the Q. robur in the smallest size class were located at

the same spot; a rocky slope on the edge of the forest, close to heathland. Both of these trees were

included in the study, but another tree in this size class was added to increase the variation.

When it was possible, I took increment cores at 0.5 m height, but if the trees were rotten or located

in a difficult terrain they were taken higher up (1.3-2.5 m). The cores were sanded, annual rings

9

counted in a stereomicroscope (Wild M5), and the minimum tree age noted. No conclusions could be

drawn about actual age, since the innermost core of the stems often was missing. Indistinct rings and

structures which raised doubts, like possible false rings or stem damages, were not counted.

Figure 1 (left): On trees with a DBH >16 cm lichens were surveyed by placing a metal grid on 1.6 m

height on the southern side of the stem. Bryophyte cover was not quantified since it was generally

rare on this height. On some trees however, bryophytes were noted when abundant.

Figure 2 (right): For trees with a DBH <16 cm the whole southern side was surveyed at the same

height as the larger trees.

Statistical analysis

The statistical analyses were performed in Excel 2013 and IBM SPSS statistics 21. At first, the

distribution and frequency of lichens on the different tree species were visualized by a diagram

(Figure 3). The same was done for lichen occurrence and DBH (Figure 4).

A Fisher’s exact test was used to test if the lichen occurrence was related to tree size. Because of

small samples (each tree species: n=30, but low lichen occurrences) the three size classes were

10

merged into two. This was done by splitting the intermediate size class by the median, resulting in

two DBH-intervals for every tree species; F. excelsior: 7-18.5 cm and >19.5 cm; Q. robur: 7-23 cm and

>24.5 cm; A. platanoides: 7-21 cm and >21 cm. The same test was then performed to test if lichen

occurrence was related to bark crevice depth. Similar to the previous procedure, all trees were

divided into two groups depending on bark crevice depth, resulting in the following intervals;

F. excelsior: 0-4 mm and 5-13 mm; Q. robur: 3-8 mm and 9-28 mm; A. platanoides: 0-6 mm and 7-27

mm. Since increment cores were taken only from a smaller amount of trees, of which few had a

lichen occurrence, the relation between minimum tree age and lichen occurrence could not be

tested directly. Instead, a Spearman’s rank correlation (Rho) was performed to test for correlations

between minimum tree age, DBH and bark crevice depth, for each tree species separately.

Results

Lichen species and host tree preferences

Three different lichen species from the list were found in the survey; Arthonia vinosa, Calicium

adspersum and Sclerophora nivea. Gyalecta fagicola was not originally on the list, but was found in

the following lab analyses and included in the study since we found it unlikely overlooking this

species (Figure 3). The only lichen that occurred on more than one tree species was S. nivea, which

was found on both F. excelsior and A. platanoides. The two lichens A. vinosa and C. adspersum were

found exclusively on Q. robur, while G. fagicola was recorded only on F. excelsior.

Besides the species found in the study, three additional species were recorded; Lobaria pulmonaria

(red-listed NT, near threat) occurred on one of the A. platanoides which hosted S. nivea, but also on

other trees nearby and on a single T. cordata further away. The two species Gyalecta ulmi (red-listed

NT) and Arthonia spadicea (indicator species) were recorded on F. excelsior. Altogether, we found

seven lichen species, of which two were red-listed (Table 3).

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Figure 3: The distribution and frequency of lichens on the three tree species. Only S. nivea was

recorded on more than one tree species

Table 3. Tree preferences for all lichens found in Yxnevik. Lichens included in the study are marked*.

Acer platanoides Fraxinus excelsior Tilia cordata Quercus robur

Arthonia spadicea X

Arthonia vinosa* X

Calicium adspersum * X

Gyalecta fagicola* X

Gyalecta ulmi (NT) X

Lobaria pulmonaria (NT) x x

Sclerophora nivea* x X

Other explanatory factors

DBH and bark crevice depth

The occurrence of lichens increased with tree DBH (Figure 4) and two species; A. vinosa and G.

fagicola were found on medium-sized trees, with the DBH = 16-29.5 cm. However, when merging the

three size classes into two, all lichens were found in the larger size class with the deepest bark

crevice depth. The difference in occurrence depending on both tree size and bark crevice depth was

significant in Fisher’s exact test (p=0.00607; N=90).

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

Fraxinus excelsior N=30 Acer platanoides N=30 Quercus robur N=30

Freq

uen

cy

Lichen distribution and frequency - tree species

No occurrence

Arthonia vinosa

Calicium adspersum

Sclerophora nivea

Gyalecta fagicola

12

Figure 4: Lichen occurrence increased with tree size and no lichens were found on trees in the smallest

size class.

DBH, bark crevice depth and minimum tree age

Spearman’s rho confirmed positive correlations between minimum tree age, DBH and bark crevice

depth for all tree species (Table 4). The correlations were generally significant at the 0.01 level, with

exception for the correlations between minimum tree age/DBH and minimum tree age/bark crevice

depth for F. excelsior which was significant at the 0.05 level.

Table 4: Spearman correlations between minimum tree age, DBH and bark crevice depth for each tree

species.

F. excelsior (N=9) Q. robur (N=10) A. platanoides (N=9)

Min. tree age/DBH rs=0,69; p=0,04 rs =0,93; p=<0,001 rs =0,83; p=0,005

Min. tree age/crevice depth rs=0,74; p=0,022 rs =0,84; p=0,002 rs =0,88; p=0,002

DBH/crevice depth rs=0,84; p=0,004 rs =0,95; p=<0,001 rs =0,92; p=<0,001

Stand history

Age gaps were discovered for all three tree species by taking increment cores and determining

minimum tree age. The periods with and without tree recruitment are presented in Table 5, together

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

7-15,5 16-29,5 >30

Freq

uen

cy

Tree DBH (cm)

Lichen distribution and frequency - DBH

No occurrence

Sclerophora nivea

Gyalecta fagicola

Calicium adspersum

Arthonia vinosa

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with years for resumed grazing and restoration of the area. Five out of seven lichens occurred on

trees recruited before 1897 (F. excelsior), 1887 (A. platanoides) or 1908 (Q. robur).

Table 5. Periods with and without tree recruitment for the three tree species studied in Yxnevik,

together with years for resumed grazing and restoration of the area.

No recruitment Recruitment Grazing Restoration

Fraxinus excelsior 1897-1953 1954-1966 1979- 1985

Acer platanoides 1887-1944 1945-1974 1979- 1985

Quercus robur 1908-1947 1948-1989 1979- 1985

Figure 5 shows the relation between minimum tree age and DBH for F. excelsior and the age gap

with no trees 60-116 years. This is also indicated in the population DBH-distribution (Figure 6, red

arrow) where the gap occurred at 24.5-29.5 cm.

On F. excelsior, G. fagicola was found on a tree with DBH 23 cm and S. nivea occurred on a tree

with DBH 32.5 cm. These trees are marked yellow in Figure 6. No trees with DBH>51 cm were

surveyed for lichens and no increment cores were taken on trees with DBH > 38.5 cm. The possible

age gaps in Figure 6 (green arrows) can therefore not be confirmed by age data.

Figure 5: Relationship between minimum tree age and DBH. No trees were found in the age of 60-116

years which indicates an age gap.

0

20

40

60

80

100

120

140

160

180

0 5 10 15 20 25 30 35 40 45

Min

imu

m t

ree

age

DBH (cm)

Minimum tree age relationship to DBH - Fraxinus excelsior

14

Figure 6: Stem diameters (DBH) for 79 trees of Fraxinus excelsior. The age gap noted by taking incre-

ment cores is marked by a red arrow. Other possible age gaps outside of the sample range (DBH: 7-

38.5 cm) are also visible as thresholds (green arrows). Trees with lichen occurrence are marked

yellow.

A similar age gap was detected among Q. robur with no trees in the ages 65-104 years (Figure 7).

Again, this was also indicated in the DBH population distribution (Figure 8, red arrow). As for F.

excelsior there might be another age gap among the older/larger trees (Figure 8, green arrow). But I

found no age gap among smaller Q. robur (Figure 7) even if the DBH-distribution might give that

impression (Figure 8, blue arrow).

C. adspersum was found on a Q. robur with the DBH 47.5 cm while A. vinosa was found on two

nearby trees (< 15 m apart) with DBH 28 cm and 94 cm.

0

10

20

30

40

50

60

70

80

90

100

1 3 5 7 9 1113151719212325272931333537394143454749515355575961636567697173757779

DB

H (

cm)

Individual trees #

DBH for total individual trees - Fraxinus excelsior

15

Figure 7: Minimum tree age related to DBH for Q. robur. As for F. excelsior, an age gap is visible with

no trees in the ages of 65-104 years.

Figure 8: Stem diameters (DBH) for 47 tree individuals of Q. robur. The age gap noted by taking

increment cores is marked by a red arrow while another possible age gap outside of the age-sampling

range (DBH: 7-65 cm) is marked by a green arrow. A third arrow (blue) marks a large threshold

0

50

100

150

200

250

0 10 20 30 40 50 60 70

Min

imu

m t

ree

age

DBH (cm)

Minimum tree age relationship to DBH - Quercus robur

0

10

20

30

40

50

60

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90

100

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47

DB

H (

cm)

Individual trees #

DBH for total individual trees - Quercus robur

16

among the younger trees. According to the data in Figure 5, this threshold is however not related to

minimum tree age. Trees with lichen occurrence are marked yellow.

A similar pattern is found for A. platanoides. No trees are noted in the ages of 65-126 years (Figure

9) and there is a corresponding gap in the DBH population distribution (Figure 10, red arrow). Some

of the other thresholds in DBH might also be age gaps (Figure 10, green arrows) and are quite similar

to the thresholds among F. excelsior (Figure 6, green arrows).

S. nivea was found on two trees with the DBH 33 cm and 62.5 cm (marked yellow in Figure 10).

Figure 9: Minimum tree age related to DBH for A. platanoides, with no trees in the ages of 69-126

years.

0

20

40

60

80

100

120

140

160

180

0 10 20 30 40 50 60

Min

imu

m t

ree

age

DBH (cm)

Minimum tree age relationship to DBH - Acer platanoides

17

Figure 10: Stem width (DBH) for 86 tree individuals of A. platanoides. A corresponding age gap as for

F. excelsior and Q. robur is noted by the red arrow. The green arrows show potential age gaps outside

the age-sampling range (DBH 7-53 cm). Trees with lichen occurrence are marked yellow.

Discussion

Occurrence patterns of lichens in Yxnevik

The lichens found in this study showed tree species preferences, where the lichens found on Q.

robur were not found on any of the other rich-bark trees (Figure 3). These however, seemed to have

some species overlaps, since S. nivea was found on both F. excelsior and A. platanoides. This was

expected due to the rich-bark-hypothesis of DuRietz (1945) and suggests that a mixed tree stand with

both rich- and poor-bark trees would gain more lichen diversity than a tree stand consisting only of

one of these groups.

If supported also by other studies, this could lead to the conclusion that it is of minor importance

which rich-bark trees are represented in a stand. However, some lichens (e.g. G. fagicola, G. ulmi)

were only found on one tree species and might therefore have stronger tree species preferences. It is

also important to preserve (and maybe create) an overall mixed tree stand since the populations of

different deciduous tree species are mostly concentrated to certain areas in the reserve and

therefore more vulnerable to stochastic effects, like diseases. Dutch elm disease or ash dieback could

for example reduce the number of trees considerably.

The occurrence of lichens were related to stem width (DBH), bark crevice depth and thereby

indirectly to tree age. These three factors are often hard to separate (Snäll et al. 2003; Ranius et al.

0

10

20

30

40

50

60

70

80

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85

DB

H (

cm)

Individual trees #

DBH for total individual trees - Acer platanoides

18

2008a; Johansson et al. 2007). Many of the lichens were found on single large trees, often at the

edge of the tree stand. Interestingly, when plotting tree age to DBH (Figure 5, 7 and 9) there was an

age gap for about the same ages for all tree species and the lichens were mainly found on the

larger/older trees. The age gaps can be explained by the stand history (Table 5) where periods of

intense grazing might have inhibited the tree recruitment in the same way as today (Sundell Eklund

2013).

Since many lichens of conservation concern are assumed to have poor dispersal abilities, this would

indicate that the lichens occurring in the area are mainly rest-populations, remnants of populations

from before the 1930’s when grazing declined and the forest grew denser. Lichens might then have

persisted on single trees at the edge of the stand where light conditions were better for

photosynthesis. Lichen occurrence on smaller/younger trees in the reserve might not necessarily be a

matter of a recent colonization. For A. platanoides, the smaller tree with lichen occurrence (S. nivea)

was located in a north facing slope and might therefore be older than expected. This is supported by

the rich abundance of L. pulmonaria on the same tree and the large variation in growth rate among

A. platanoides in that size (Figure 9). Since the smaller trees with lichen occurrence among F.

excelsior and Q. robur grew in more favorable conditions there is no reason to believe that they

might be older than expected. These two trees are therefore probably colonized after the 1930’s and

the small distance between the two findings of A. vinosa on Q. robur (<15 m) indicates a successful

dispersal from the larger/older tree. This supports the observations in the experimental study by

Nordén et al. (2012) in the Swedish Oak Project, where A. vinosa responded rapidly to habitat

improvement (partial cutting).

The finding of G. fagicola on medium sized F. excelsior also reflects the different ecological

demands of this species, since it often prefers smooth-bark trees (Foucard 2001).

There were few other trees that could be considered recently colonized by lichens, and many large

trees with seemingly suitable bark characteristics that had no lichen occurrence. This may be

interpreted as follows; 1) Lichen response after a restoration might be very slow and a long term

management perspective is therefore important 2) Lichens are more likely to spread to trees nearby

and distance from host tree might therefore be a strong or at least additional predictor of lichen

occurrence 3) Lichen populations in Yxnevik may to some extent be considered rest-populations,

depending on some single host trees for their immediate survival. However, it is also possible that

(some) colonization occurred during the last 50-70 years as the trees aged and came to provide

microhabitat suitable for the lichens. In the study of Nordén et al. (2012), lichen colonization

occurred over less than six years and the turnover among (common) lichens on the stems was

considerable.

19

Long-term management effects

Based on the lichen occurrences in Yxnevik I now consider some possible long-term effects of three

management strategies. These are (i) clearing around large trees and cutting to create a more open

woodland suitable for grazing animals, but no grazing regulations; (ii) clearing around large trees, no

general cutting and no grazing regulations; and (iii) clearing around large trees, no general cutting,

grazing regulations.

(i) Clearing around large trees and cutting to create a more open woodland suitable for grazing

animals, but no grazing regulations.

This option includes grazing, clearing around large trees and general cutting to create a more open

woodland. This may be considered as the most common option in Sweden. Both grazing and general

cutting might affect lichens negatively in a (very) long term. Grazing has reduced the recruitment of

the three tree species in the reserve strongly and even if there is a large amount of seedlings, few

grow above grazing level. This is the cause of a current age gap (Sundell Eklund 2013) which could be

further enhanced by cutting medium sized trees in order to favor larger trees, or by cutting trees to

create a more open woodland. The dispersal of lichens to future replacement trees might therefore

be inhibited, both by the decreasing number of suitable trees, and by the increasing distance.

On the other hand, if clearing creates more optimal conditions for lichens of conservation values on

single trees, the chance of dispersal to other trees nearby could be enhanced. However, the lichens

found in the reserve seem to be adapted to semi-open woodland (Nordic Lichen Flora 1999,

Gärdenfors 2010) and might not be favored by a too extensive clearing.

(ii) Clearing around large trees, no general cutting and no grazing regulations

This management strategy might both favor large key trees and the colonization of lichens on

medium sized trees. The age gaps noticed among the trees in this study might therefore be bridged,

but the age gap among smaller trees noted by Sundell Eklund (2013) will be enhanced for as long as

there are no grazing regulations. This might not be a problem if grazing varies in an unpredictable

manner over time, which may happen due to political and economic changes. There is however

problems in relying on such changes for tree regeneration. Firstly, there is no guarantee that grazing

will cease in time to bridge the age gap. Secondly, if grazing ceases, saplings would appear all over

the reserve and there is a risk that large key trees will be disfavored. Thirdly, if grazing does not

resume in time, other competing trees might take over. This is well illustrated by the area itself

where the cessation of grazing in the 1930’s seems to have led to an increased regeneration among

deciduous trees at first. According to the minimum tree age, regeneration took place during the

following periods; A. platanoides 1945-1974; F. excelsior 1954-1966 and Q. robur 1949-1989. Other

20

trees (e.g. P. abies) invaded the area until it was restored in 1985 (Alf Hornborg, pers comm.). Among

the three trees in the study, Q. robur seems to have had the most successful regeneration (until the

late 1980’s), but mainly on poor heathland soil. However, as described in the method; smaller Q.

robur (DBH: 7-15.5 cm) was very rare.

(iii) Clearing around large trees, no general cutting, grazing regulations

This option might not only benefit lichens on key trees and increase their chances to spread to

younger trees - it may also prevent the age gap among smaller trees from increasing. As previously

stated, single key trees are crucial for epiphyte survival and clearing around these might be

motivated, but not all large trees had the expected lichen flora. Key trees must therefore be

identified, not by size but by epiphyte surveys, to be able to make adequate management priorities.

The extent of the clearing should be based on the overall picture and also consider other

conservation values associated with large trees, like coarse deadwood and hollow trees. If there is no

general cutting, the possibility of lichen colonization on some recruited trees could increase over

time. This could also maintain deadwood resources, which is important for the beetle fauna in the

area (Franc et al. 2007, Karlsson 2013).

Tree recruitment might be accomplished by fencing off the grazing animals from certain areas until

the saplings have reached a height of about 3 m. These exclosures should be placed where the

upcoming trees do not interfere with present conservational values. In order to create a multi-

layered stand structure, the exclosures ought to be distributed across the reserve and include several

different tree species.

Conclusions

The present management strategy has so far favored large trees and tree recruitment has been

considered to occur mainly outside of the reserve (Karlsson 2013), but as this study indicates, trees in

proximity to old key trees are important for lichens. This is supported by Johansson et al. (2013 a)

that stress the importance of regeneration to decrease the extinction risk, especially in areas with a

high density of old trees. To preserve lichens in Yxnevik in the long term it is therefore important not

only to preserve key trees, but to also safeguard tree recruitment and include the conservation of

medium sized trees in the management strategy.

Because of the size of the reserve and the abundance of large trees, it might not be possible, or

even desirable, to strive for a degree of openness which would optimize the conditions for individual

trees. Instead it is important to remember that many of the relevant epiphytes are adapted to semi-

open conditions and that other conservation values are created when trees are not in their optimal

21

condition. This might in turn favor other organisms (Franc et al. 2007, Karlsson 2013).

Since lichens, as well as many other organisms, have certain preferences (e.g. tree age, bark

characteristics and tree species) it is important to manage for a multi-layered tree structure, with

several different tree species. In my study, many lichens of conservation value were found on other

trees than Q. robur, so management should not solely focus on this tree. This is also supported by the

national guidelines which emphasize that present conservation values should not be lost in order to

create future conservation values (Naturvårdsverket 2013) and might be especially important for

trees like U. glabra and F. excelsior which themselves are red-listed (Gärdenfors 2010). Epiphyte

surveys are also valuable and should precede management actions like cutting medium sized trees.

This could identify both key trees and younger, newly colonized trees.

Acknowledgements

I would like to thank my supervisor, prof. Frank Götmark, for a dedicated and inspiring tutorship. I

would also like to thank the landowners; Alf and Anne-Christine Hornborg, for their hospitality and

help, Lars Arvidsson for supervising and helping me with the species determination and thereby

increasing my fascination for lichens, Björn Nordén, who together with Lars Arvidsson helped me

with the selection of lichen species, Magnus Grimheden, County Administrative Board Kalmar, for his

responsiveness and interest in the area, and Markus Fridell, Västervik county, for helping with

historical maps. Finally, a warm thank to my friend and fellow student Jonas Sundell Eklund for his

help and valuable perspective. Thank you!

22

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Verbal information

Arvidsson Lars, Dept of Biological and Environmental Sciences, University of Gothenburg

Hornborg Alf, Yxnevik

Nordén Björn, NINA - Norsk Institutt for Naturforskning, Oslo