The Legacy o Logging—Es ima ing A bo eal Lichen
Occu ence in a Bo eal Mul iple-Use Landscape on a Two
Cen u y Scale
Tim Ho s ko e
1
*, Jon Moen
1
, Tomas La
¨ma
˚s
2
, Timo Helle
3
1Depa men o Ecology and En i onmen al Science, Umea
˚Uni e si y, Umea
˚, Sweden, 2Depa men o Fo es Resou ce Managemen , Swedish Uni e si y o Ag icul u al
Sciences, Umea
˚, Sweden, 3Finnish Fo es Resea ch Ins i u e, Ro aniemi, Finland
Abs ac
In no he n Sweden, he a ailabili y o a bo eal lichens (B yo ia uscescens, Alec o ia sa men osa) as win e g azing esou ces
is an impo an elemen in eindee husband y. Wi h he indus ializa ion o o es y, o es s ich in a bo eal lichens ha e
diminished conside ably. He e, we analyze how o es y has impac ed lichen a ailabili y om he 1920’s o he p esen day
and model i s u u e de elopmen assuming di e en o es managemen scena ios. We eco ded he cu en occu ence
o B. uscescens in 144 sampling plo s, s a i ied by o es age class and dominan ee species in a 26,600 ha bo eal o es
landscape ha is used o bo h eindee he ding and o es y. Lichen abundance was isually es ima ed in ou classes:
none, spa se, mode a e and abundan . A bina y logis ic model using o es age as he independen a iable was de eloped
o p edic he p obabili y o lichens being p esen . Using his model, we ound ha lichens we e p esen in s ands ha a e
a leas 63 yea s old. Because o he ela i e pauci y o s ands ich in a bo eal lichens, i was no possible o eliably
de e mine how age a ec s he a ia ion in abundance o olde o es s ands. The his o ical de elopmen o o es s whe e
a bo eal lichens could po en ially occu was s udied using his o ic o es y eco ds da ing back 80 yea s. Be ween 1926 and
he p esen day, o es y has educed he co e o o es s olde han 60 yea s om 84% o 34%. The likely u u e spa ial
co e age o hese s ands o e he nex 120 yea s was es ima ed o wo di e en managemen scena ios and an
unmanaged e e ence scena io, using he Heu eka s a egic planning p og am. Unde bo h he ‘‘business as usual’’ scena io
and ha in ol ing mo e in ensi e o es y, con inued dec eases in lichen a ailabili y a e p ojec ed. Ou esul s emphasize
he impo ance o al e na i e o es y p ac ices, such as p olonged o a ion pe iods, o inc ease he a ailabili y o a bo eal
lichens as a g azing esou ce o eindee .
Ci a ion: Ho s ko e T, Moen J, La
¨ma
˚s T, Helle T (2011) The Legacy o Logging—Es ima ing A bo eal Lichen Occu ence in a Bo eal Mul iple-Use Landscape on a
Two Cen u y Scale. PLoS ONE 6(12): e28779. doi:10.1371/jou nal.pone.0028779
Edi o : Da en Ma k E ans, Uni e si y o Hull, Uni ed Kingdom
Recei ed July 7, 2011; Accep ed No embe 15, 2011; Published Decembe 16, 2011
Copy igh : ß2011 Ho s ko e e al. This is an open-access a icle dis ibu ed unde he e ms o he C ea i e Commons A ibu ion License, which pe mi s
un es ic ed use, dis ibu ion, and ep oduc ion in any medium, p o ided he o iginal au ho and sou ce a e c edi ed.
Funding: This wo k was suppo ed by g an s om he Swedish Resea ch Council o En i onmen , Ag icul u al Sciences and Spa ial Planning FORMAS
(510057203) (h p://www. o mas.se) o JM and he ‘‘Gunna and Ru h Bjo
¨ kmans und o no he n bo anical esea ch’’ (Dn 223-1 129-09) o T. Ho s ko e. The
unde s had no ole in s udy design, da a collec ion and analysis, decision o publish, o p epa a ion o he manusc ip .
Compe ing In e es s: The au ho s ha e decla ed ha no compe ing in e es s exis .
* E-mail: im.ho s ko [email protected]
In oduc ion
Many na u al esou ces a e simul aneously exploi ed by se e al
ac o s, including indigenous peoples and indus y, some imes wi h
ensuing con lic s. Such mul iple-use si ua ions equi e collabo a-
i e managemen s a egies in ol ing all o he a ec ed s akehold-
e s i he ocal esou ces a e o be sha ed sus ainably and in a way
ha minimizes ad e se en i onmen al impac [1], known as co-
managemen . Whe e indigenous peoples a e in ol ed, hei
poli ical au onomy is seen as equi ed o hei cul u al iden i y
and e ec i e con ibu ion esou ce managemen [2]. While
indigenous peoples o en accoun o a mino i y o he o al
popula ion, Lane [3] a gues ha in wes e n pos -se le s a es, in
which he descendan s o o me colonize s now o m he
‘‘na ion’’, he p ima y challenge o esou ce sha ing is less a
p oblem o app o ing indigenous igh s and sel -de e mina ion. I
is a he he easonable and ealis ic way o alloca ing esou ces
be ween di e en claiman s in planning and adminis a i e
p ocesses. The con as ing demands placed upon na u al esou c-
es, as pe cei ed by indigenous peoples and o he ex ac o s
necessi a e a ade-o be ween comme cial uses o a landscape and
o he alues, such as social, cul u al and biological alues [4].
This is he si ua ion in he bo eal o es s o No he n Sweden,
whe e eindee husband y (Rangi e . a andus L.) is p ac iced by he
indigenous Sami people. Th oughou no he n Fennoscandia,
eindee husband y is o high cul u al ele ance o he Sami. In
Sweden, his o m o pas o alism, mig a ing be ween summe
g azing g ounds in he wes e n Scandic moun ains and win e
g azing in bo eal o es s nea he Bal ic coas , became es ablished
in he 17
h
cen u y, albei in a di e en o m han p ac iced oday
[5]. E e since, eindee husband y has unde gone nume ous
changes and adap a ions [6-8]. Du ing he las cen u y in
pa icula , i s demands ha e inc easingly come in o con lic wi h
hose o o he o ms o land use. Fo example, he cons uc ions o
hyd oelec ic powe plan s and dams subme ged aluable pas u e
lands, cal ing g ounds and adi ional mig a ion ou es be ween
summe and win e pas u es [9]. Mo eo e , clea -cu ing o o es s
was in oduced on a la ge scale in no he n Sweden du ing he
1950’s and was subsequen ly made manda o y by he Fo es y Ac
o 1979 [8] o eplace na u al i e-d i en dis u bance dynamics.
PLoS ONE | www.plosone.o g 1 Decembe 2011 | Volume 6 | Issue 12 | e28779
Howe e , mode n clea -cu ing is a mo e ex ensi e han any
na u al dis u bance pa e n [10]. Selec i e logging o o es s,
which used o be ela i ely common, esul s in slowe ee
egene a ion han does clea -cu ing wi h subsequen soil p epa-
a ion, o ins ance by soil sca i ica ion. As a consequence,
managed o es s ha e become much dense , while he mean age
o he ees wi hin hem has dec eased conside ably [11]. Al hough
hese changes inc ease he p o i abili y o imbe p oduc ion, his
indus ialized o es y has had ce ain ad e se ecological conse-
quences and has elimina ed ce ain niches [12]. Impo an ly o
eindee husband y, his sil icul u al in ensi ica ion has dec eased
he abundance o he mos impo an win e o age o eindee ,
i.e. e es ial and a bo eal lichens [13,14], and deg aded he
ca ying capaci y o win e g azing g ounds [15].
In win e , snow co e a ec s he a ailabili y o o age [13,16]
and he ene gy expended by he dee while digging o lichens
benea h he snow [17]. Unde ce ain ci cums ances, pas u es can
become inaccessibly o eindee due o he o ma ion o hick ice
c us s. This is pa icula ly common du ing la e win e and ea ly
sp ing, a e p olonged ma u a ion o he snow co e o a e
wea he e en s such as eeze- haw-cycles [18] o ain-on-snow
[19]. The a ailabili y o a bo eal lichens such as B yo ia uscescens
and Alec o ia sa men osa is essen ial o he mi iga ion o such c i ical
si ua ions, du ing which he wind h ow o lichen-bea ing ees
and he li e all o a bo eal lichen agmen s becomes an
impo an sou ce o eindee o age [20,21]. A bo eal lichens a e
mo e abundan in old-g ow h o es s [22,23], which ha e become
signi ican ly less widesp ead in No he n Sweden as a esul o
speci ic o es managemen p ac ices [24,22].
Dec eases in he abundance o a bo eal lichens can inc ease he
need o supplemen a y eeding and/o necessi a e a educ ion in
he d size [25], especially du ing win e s wi h ad e se snow
condi ions. As epo ed by Helle & Jaakkola [7], abundan
a bo eal lichens ha e his o ically sus ained eindee he ds
h oughou he win e , e en unde highly ad e se snow condi ions.
Swi ching o a bo eal lichens he e o e was an adap i e s a egy
ha allowed eindee o o e come sho ages o g ound lichens.
Consequen ly, he capaci y o eindee husband y o adap o
ad e se snow condi ions inc eases wi h he ecological a ie y o he
a ailable pas u es [26]. The ansi ion o a highly agmen ed and,
on he s and le el, less di e se landscape has nega i ely a ec ed
he abundance o a bo eal lichens, p ima ily due o hei slow
g ow h, low dispe sal a es, and s ong dependence on he
a ailabili y o sui able g owing subs a es [27].
Today, he educed a ailabili y o his esou ce has s ong
implica ions o he sus ainabili y o eindee husband y [28,7], i.e.
he abili y o main ain i s p oduc i i y in he ace o dis u bance
e en s [29]. He e, we in es iga e how he ans o ma ion o he
bo eal landscape o e he las cen u y (1926–2006) by comme cial
o es y has a ec ed a bo eal lichens in a eindee he ding a ea,
and simula e possible u u e condi ions. We do his by analyzing
how he po en ial habi a o a bo eal lichens has changed o e
ime by (i) iden i ying ela ionship be ween o es age and a bo eal
lichen abundance, and by (ii) analyzing he change in hese habi a
ac o s due o o es managemen o e he las 80 yea s. Finally
(iii), we simula e he u u e de elopmen o he po en ial a bo eal
lichen habi a o e he nex 120 yea s unde a ious di e en
scena ios wi h di e ing in ensi ies o o es y.
Ma e ials and Me hods
S udy si e
Loca ed a la i ude 66u209N, mid-bo eal ege a ion cha ac e -
izes he s udy a ea o ca. 26,600 ha (Fig. 1). I s o es s a e
domina ed by Sco s pine (Pinus syl es is), wi h a ew s ands
domina ed by No way sp uce (Picea abies). Deciduous ees, such as
bi ch (Be ula pendula), goa willow (Salix cap ea), and aspen (Populus
emula), a e p esen bu no common. The g ound laye consis s
o dwa sh ubs (Junipe us communis, Vaccinum my illus, Vaccinum
uliginosum, Empe um nig um), mosses, and g ound lichens (Cladonia
spp., Ce a ia spp.) g owing on d y glacio- lu ial soils. Se e al small
lakes and mi es a e sca e ed ac oss he landscape, co e ing ca.
Figu e 1. Loca ion o he s udy a ea. The g ay a ea in he o e iew map illus a es he Swedish eindee he ding a ea.
doi:10.1371/jou nal.pone.0028779.g001
E ec s o Logging on A bo eal Lichen Occu ence
PLoS ONE | www.plosone.o g 2 Decembe 2011 | Volume 6 | Issue 12 | e28779
24% o he a ea. The i e Pi e A
¨l en uns h ough he a ea, and
was o me ly an impo an means o anspo ing imbe . The
si e’s ele a ion a ies om 277 m abo e sea le el along he i e
alleys o 550 m a mo aine hill ops. The s udy a ea, which
consis s o o me Na ional Fo es s Akkajau and Ab au (he ea e
e e ed o collec i ely as Akkajau ), is used o yea - ound
eindee g azing by he Sami he ding dis ic s O
¨s a Kikkejau
and S a˚kke, and as a mig a ion co ido and win e g azing a ea
by he Luok a-Ma as he ding dis ic . In 1936, Akkajau was
ex ended no hwa ds, inc easing i s a ea by ca. 17% (4,620 ha) o
i s cu en size.
Da a collec ion
A au´jo & Williams [30] iden i ied local-in insic ac o s, such as
sui able habi a , and egional-in insic ac o s, such as coloniza ion
om o he a eas based on he connec i i y o simila habi a s
wi hin he landscape, as essen ial o he pe sis ence o a species. In
his s udy, we ocus on local-in insic aspec s, by which we mean
he cha ac e is ics o he o es a he s and le el.
Field wo k was conduc ed in Augus 2009 and 2010. Using
digi ized maps o he s udy a ea in a geog aphical in o ma ion
sys em (GIS), we s a i ied o es s ands in o 9 classes acco ding
o hei age (young = 1–39 y s, ma u e = 40-120 y s, and
old = .120 y s) and species composi ion (pine, sp uce, mixed) on
he basis o in en o ies conduc ed by he o es ’s owne , S easkog
(Table 1, see also 11). A s and was deno ed as a pine o sp uce
s and i he species in ques ion accoun ed o 80% o mo e o he
s ems.
The sampling uni s we e posi ioned be ween 500 m and 20 m
away om he nea es o es oad so as o a oid oad e ec s.
Wi hin his bu e zone, o es s ands we e selec ed by andom
sampling. Ci cula sampling plo s, co e ing ca 0.1 ha, we e semi-
andomly dis ibu ed in he selec ed o es s ands o he 9 s a a
(Table 1). Plo s we e loca ed in he ield wi h a GPS ecei e . A
ha poin , he basal a ea o he espec i e o es s and was
measu ed using a elascope, and he heigh o a ep esen a i e ee
in he s and was eco ded.
The canopy closu e a each sampling plo was calcula ed om a
single digi al hemisphe ic pho og aph aken a each plo wi h a ish
eye lens, a e con e sion o bina y images using he p og am Gap
Ligh Analyze [31]. As B yo ia uscescens is p e e ed o age by
eindee [20], we ocused on his species. Alec o ia sa men osa, which
was also p esen in he a ea in low abundance, p e e s la e
successional sp uce and mois e habi a s ands han he d y pine
o es s o Akkajau [32,33]. The biomass o B yo ia uscescens in he
s and was es ima ed isually and classi ied in o one o 4 abundance
ca ego ies, ep esen ing mean alues o a bo eal lichen biomass:
none (0), spa se (1; #35 kg ha
21
), mode a e (2; 35–120 kg ha
21
),
and abundan (3; $120 kg ha
21
). This classi ica ion sys em was
based on he indings o Helle e al. [34], who used an o en-d ied
lichen clump o known mass o classi y lichen biomass using hese
ou ca ego ies. As he clump me hod unde es ima es biomass o
a bo eal lichens in ees, he bias in oduced by isual es ima ion
has o be co ec ed. In he me hod o Helle e al. [35], his was
done by using eg ession equa ions, ha compa e he es ima ed
biomass on a b anch o he o en-d ied biomass emo ed om he
same b anch.
S ands con aining no lichens we e assigned o ca ego y 0.
Ca ego y 1 was assigned o s ands in which indi idual lichen halli
we e de ec ed on a small numbe o ees and in low quan i ies.
S ands in which lichen clumps we e eadily appa en on each ee
we e assigned o ca ego y 2; none o he s udied s ands con ained
enough lichens o be assigned o ca ego y 3. Lichen abundance
was hus a e aged o e he ees wi hin he sampling plo , and his
a e age was aken as he s and le el. Using he same me hod,
Jaakkola e al. [35], ound a maximum lichen biomass on whole
ees o 474 kg ha
21
a esh si es in ma u e sp uce o es s.
In o de o o ally elimina e edge e ec s, e.g. om neighbo ing
open a eas, i would ha e been necessa y o ocus exclusi ely on
sampling plo s wi h a dis ance o 50 m in e e y di ec ion o
neighbo ing s ands [33], which would equi e a minimum a ea o
0.79 ha assuming a ci cula o es s and. Howe e , he o es
pa ches in he s udy a ea we e no always shaped in a way ha
would make his possible, especially in he olde o es s ands.
Howe e , sampling plo s in close p oximi y o open places such as
la ge lakes o mi es we e no common in ou da ase .
In o al, we sampled 144 o es s ands. One hi d o he sample
plo s we e in ma u e pine o es s, 19% we e in old pine o es s, and
17% we e in young pine s ands. The emaining plo s we e loca ed
in less abundan o es ypes (Table 1). S ands domina ed by
sp uce we e especially a e.
I has p e iously been epo ed ha he e is a s ong ela ion
be ween o es age and a bo eal lichen biomass [33], al hough
o he au ho s ha e sugges ed ha he co ela ion wi h olume is
s onge [35]. S and age was s ongly co ela ed wi h many o he
o es cha ac e is ics speci ied in he o es owne ’s s and egis y
(Table 2) and wi h he canopy closu e calcula ed om ou ish –
eye pho o analysis. We chose o use age as a p edic o a iable in
ou models, since i can easily be compa ed ac oss di e en s udies
and is eco ded in mos o es da abases.
Pe mission o conduc ing he s udy was gi en by he o es
owne S easkog. No endange ed o p o ec ed species we e
in ol ed in he s udy.
S a is ical analysis
We used bina y logis ic eg ession analysis o model he
abundance o lichens in ela ion o o es s and age. This was
done by con e ing he a bo eal lichen abundance classes in o
dicho omous da a. Two di e en app oaches we e adop ed:
compa ing plo s in which no lichens we e p esen (i.e. hose in
ca ego y 0) o hose wi h a a lichen class o a leas 1, and
Table 1. Numbe o sampled o es s ands in s a a, sepa a ed by dominan ee species and age ( o al o es s ands N = 852,
sampled o es s ands n = 144).
Pine Sp uce Mixed
S a um o al sampled % o sampled S a um o al sampled % o sampled S a um o al sampled % o sampled
Young 177 24 17 2 1 1 35 10 7
Ma u e 352 48 33 1 1 1 44 12 8
Old 177 28 19 13 7 5 51 13 9
doi:10.1371/jou nal.pone.0028779. 001
E ec s o Logging on A bo eal Lichen Occu ence
PLoS ONE | www.plosone.o g 3 Decembe 2011 | Volume 6 | Issue 12 | e28779
compa isons be ween plo s wi h a lichen class o 1 and hose wi h a
lichen class o 2.
In a logis ic eg ession analysis, he dependen dicho omous
a iable x(i.e. he p esence [1] o absence [0] o lichens) is no
modeled di ec ly. Ins ead, he eg ession es ima es he p obabili y
p(x) ha he ou come will be ‘‘posi i e’’, i.e. ha lichens will be
p esen in a pa icula plo o a gi en alue o he independen
a iable. A logis ic eg ession akes he o m:
p(x)~
eazbx
1zeazbx
Bo h he cons an aand he p edic o coe icien ba e i ed by he
logis ic model; he coe icien bgi es he slope o he eg ession.
The ou pu o he model anges om 0 o 1 o each s and, wi h an
inc ease in he p obabili y, p, co esponding o a posi i e ou come.
The model’s coe icien s a e mos easily in e p e ed in e ms o
odds a ios (OR). An OR measu es how likely an e en (such as
he p esence o lichens) is ela i e o i s opposi e (in his case, he
absence o lichens) o any gi en alue o he independen a iable.
The OR hus indica es he a e o change in p(x) o a one uni
change in he independen a iable x[36,37]. An OR la ge han
1 indica es a posi i e ela ionship be ween he dependen and
independen a iables; alues below 1 indica e he opposi e. The
odds a io is ob ained as ollows:
OR~ebx
Model i , cu -o selec ion and model alida ion
We in es iga ed he models’ goodness-o - i , i.e. he accu acy o
hei classi ica ion o occupied and unoccupied si es, using a
Recei e Ope a ing Cha ac e is ic cu e (ROC). This cu e is
cons uc ed using he ac ion o co ec ly classi ied e en s, i.e. he
ue posi i e ac ion (sensi i i y) and ue nega i e ac ion
(speci ici y) o e e y h eshold alue ha could po en ially be
used o disc imina e be ween occupied and unoccupied si es.
Plo ing he sensi i i y agains (1 – speci ici y) o all possible
alues calcula ed by he model, a ROC cu e is de i ed [38,39].
This cu e illus a es he model’s abili y o disc imina e be ween
occupied and unoccupied si es o e he whole ange o possible
h eshold alues ha could be used o seg ega e he da a se . I
he model is unable o disc imina e be ween he si e ypes, he
ROC - cu e will be a s aigh line wi h a g adien o 45uand he
model ou comes a e no mo e eliable han chance. The close he
cu e is o he le and op axes, he be e i s disc imina i e
abili y and he be e he model i [40]. Pea ce & Fe ie [38]
sugges ha he a ea unde he ROC cu e (AUC) is an indica o
o he model’s disc imina i e abili y; an AUC be ween 0.5 and
0.7 indica es weak disc imina i e abili y, while a alue be ween
0.7 and 0.9 indica es easonable disc imina ion and alues
exceeding 0.9 indica e a e y good abili y o disc imina e be-
ween occupied and unoccupied pa ches using he bina y
classi ica ion scheme.
The model alues calcula ed using bina y logis ic eg ession,
ep esen con inuous p obabili ies o occu ence. To classi y a
o es ype as being occupied o unoccupied by lichens, he model
alues ha e o be spli a a ce ain h eshold alue. The ROC
cu e illus a es he comp omises ha a e made be ween he ue
and alse posi i es as he decision h eshold is changed, making i
possible o iden i y an op imal h eshold using he sensi i i y and
speci ici y [38]. Ou s a egy o inding he mos obus cu -o
poin was o spli he da a se a he poin whe e he sum o he
sensi i i y ( ue posi i es) and he speci ici y ( ue nega i es) is a i s
maximum, i.e. he alue ha gi es he highes a es o co ec
classi ica ion o occupied and unoccupied si es.
The model’s pe o mance was es ed using c oss- alida ion
[39,41]. The da a se was andomly di ided in o wo pa s - a
aining se consis ing o 80% o he da a and a es se consis ing
o he emaining 20%. To assess he consis ency be ween he
p edic ions o he aining model and he es model ega ding he
p esence o lichens, he co esponding model ou comes we e
binned in o 10 equal-sized classes (0-0.1; 0.1-0.2;…; 0.9-1). A
s able model would be expec ed o ha e a simila p opo ion o i s
o al ou comes in each bin o bo h he aining and he es se .
Signi ican Spea man’s Rank co ela ions (
s
) be ween he
equencies o he wo se s indica e ha he model is applicable
o bo h he aining and he es se [39]. We epea ed he
p ocedu e o andom da a-pa i ioning and co ela ion o bin-
equencies ou imes, and calcula ed he a e age co ela ion
coe icien and signi icance o he i e esul ing co ela ions.
Table 2. Two- ailed Spea man’s ank co ela ions (
s
) be ween sample s and cha ac e is ics, n = numbe o sampled s ands.
Fo es Age (y s) Volume (m
3
/ha) Basal A ea (m
2
) Diame e (cm) Heigh (m) Canopy Closu e (%)
Fo es Age 1- - ---
n144
Volume 0,776
**
1- ---
n144 144
Basal A ea 0,512
**
0,898
**
1---
n134 134 134
Diame e 0,898
**
0,712
**
0,435
**
1--
n125 125 125 125
Heigh 0,856
**
0,904
**
0,654
**
0,878
**
1-
n144 144 134 125
Canopy Closu e 0,561
**
0,611
**
0,526
**
0,304
**
0,556
**
1
n144 144 134 125 144 144
**Co ela ions a e signi ican a he 0.01 le el.
doi:10.1371/jou nal.pone.0028779. 002
E ec s o Logging on A bo eal Lichen Occu ence
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Compila ion o his o ical o es age da a
His o ical o es s in en o ies o he yea s 1926, 1936, 1960
we e ob ained om a chi al sou ces [11], and he mos ecen
in en o y, o 2006, was ob ained om he o es company
S easkog. These in en o ies di e in bo h he quali y and quan i y
o he epo ed o es cha ac e is ics. Fo ins ance, he way in
which o es age is calcula ed di e s, as he scope o o es y shi ed
om selec i e cu ing o clea -cu ing in he 1950s [11]. While he
mean age o o es s ands is a ailable o he mos ecen su ey
yea (2006), olde da a om 1926, 1936 and 1960 had o be
in e p e ed in di e en ways. The 1926 and 1936 in en o ies
eco ded he age o each o es s and as a composi e o 5 age
classes, each co e ing a 40-yea in e al (1-40 yea s, 41-80 yea s,
…, 120-160, .161 yea s). These sou ces did no p o ide any
g anula i y wi h espec o he ages o s ands olde han 161 yea s
because o es s o ha age we e le unmanaged. The olde sou ces
p o ide da a on he pe cen age o he a ea o each s and co e ed
by ees in each age b acke . This lexible classi ica ion scheme
e lec s he a iable age s uc u e ypical o o es pa ches a ha
ime. Using hese pe cen ages and he mean o each 40 yea - age
class, an a ea-weigh ed a e age age was calcula ed o each o es
s and. The hypo he ical maximum age o a s and ha could be
calcula ed using his scheme would be 161 yea s, o a s and ha
was en i ely co e ed by ees wi hin he highes age b acke .
The e o e, all age es ima ions we e cons ained by his uppe limi ,
e en hose de i ed om mo e ecen in en o ies in which olde
mean ages we e epo ed. The o es age da a o he 1960
in en o y a e epo ed using a classi ica ion scheme consis ing o
en age classes a he s and le el, each o which spans 20 yea s.
This e lec s a change in o es managemen p ac ices ha a o ed
mo e e enly-aged s ands [24]. Due o hese es ic ions, o es ages
de i ed om he his o ical in en o ies should be ega ded as
app oxima ions o he eal si ua ion in hose imes.
Simula ion o u u e managemen scena ios
We chose h ee possible scena ios o u u e o es managemen ,
all di e ing in hei impac on o es age s uc u e and hus on
po en ial a bo eal lichen abundance. The i s was a ‘‘business as
usual’’ scena io (BAU), in which i is assumed ha he o es s will
be managed as hey cu en ly a e by hei owne s, wi h he in en
o sa is ying con empo a y imbe managemen and na u e
conse a ion objec i es. The second in ol es mo e in ensi e
o es y (INT), while he hi d in ol es a o al absence o
managemen , i.e. no o es y wha soe e (NO). All h ee scena ios
we e de eloped using he S andWise so wa e package, which is
pa o he Heu eka sys em. This sys em was de eloped by he
Swedish Uni e si y o Ag icul u al Sciences (SLU) o o es
managemen planning and analysis on se e al scales [42,43]. Fo
BAU and INT he economic ou come o o es y was maximized
in e ms o he Ne P esen Value (NPV), i.e. he sum o all
discoun ed u u e ne cos s and incomes ( o a eal in e es a e o
2,5%). An e en low o imbe ha es s was ensu ed by penalizing
luc ua ions in ha es s in he op imiza ion p oblem goal unc ion.
The bes managemen al e na i e among he se o po en ial
managemen al e na i es o each s and was ound by sol ing he
op imiza ion model using linea p og amming. The beha io
displayed unde he h ee di e en scena ios was subjec ed o he
age dis ibu ion o o es s ands gi en in 2006. The ollowing
assump ions we e made o he di e en scena ios:
NIn BAU, a eas cu en ly unde p o ec ion we e le unman-
aged, as we e o es s olde han 160 y s ( o al co e ed a ea:
2268 ha). Fo s ands olde han 120 yea s, o a ion pe iods
we e p olonged and hey we e no allowed o be inal elled
un il a e he nex en yea pe iod ( o al co e ed a ea:
1848 ha); comple e inal elling h oughou his second a ea
immedia ely a e he end o hese en yea s was p e en ed by
he e en imbe low c i e ion in he goal unc ion. O he
s ands we e assumed o be managed acco ding o hei cu en
managemen egimes in e ms o hinning p og ams and inal
elling, including 1-2 hinning e en s and a inal elling age o
a ound 100 yea s. The minimum inal elling age was ha
s ipula ed by he Fo es y Ac , i.e. ypically 90 yea s.
NINT assumes ha all s ands can be cu , including hose in
p o ec ed a eas o ha a e mo e han 160 yea s old. S ands
olde han 120 yea s we e allowed o be cu immedia ely,
which esul ed in sho e ini ial o a ions compa ed o he
BAU scena io.
NNO is a simple ex apola ion o o es aging in o he u u e,
wi hou conside ing any dis u bances o pa ch dynamics,
whe he human o na u al in o igin. In eali y, unmanaged
o es s a e subjec o na u al dis up ing e en s such as o es
i es o insec b eakou s, which mean he o es s a e
main ained in a dynamic s a e wi h di e se succession phases.
Assessmen o landscape agmen a ion
To analyze he deg ee o agmen a ion, we imposed a bu e o
200 m a ound o es s ands iden i ied as h eshold pa ches by he
model (see abo e). This bu e was based on he po en ial o
dispe sal o a bo eal lichens as epo ed by De ki & Esseen [44].
In o he sou ces, he dispe sal dis ance has been epo ed o ange
om 100 m, wi h he numbe o dispe sed halli dec easing by
50% om old g ow h o es s [45], o 350 m om o es s ands
wi h high lichen abundance [46]. We also calcula ed he la ges
pa ch size index (LPI) in F ags a s [47] o quan i y he change in
he a ea co e age o connec ed h eshold s ands iden i ied by he
eg ession model.
The gene al agmen a ion o all o es s ands p esen in
Akkajau due o o es y was calcula ed as he a ea-weigh ed
a e age s and size (S
a
). This is an app op ia e me hod o a e aging
when he equency dis ibu ion o la ge and small s ands is skewed
[48]. Using A
i
o e e o he size o he i- h s and, i is calcula ed as
Sa~
S(Ai2)
S(Ai)
Because we compa ed changes in he age dis ibu ion wi hin he
o es o e se e al decades, i was necessa y o ensu e ha he da a
o di e en yea s was compa able. Adminis a i e decisions and
he e ec s o o es y ha e caused he numbe o o es s ands,
hei spa ial con igu a ion, and he size o he s udy a ea o change
o e he s udied pe iod o ime. The e o e, changes in he size and
quan i y o o es s ands o a gi en age ha e o be conside ed o
p ope ly unde s and he o es y-d i en landscape dynamics o he
a ea and hei in luence on he beha io o he logis ic eg ession
model. Fo ins ance, la ge s ands o young ees con ibu e mo e o
he landscape con igu a ion han many small s ands o much olde
ees, bu he la e would ha e a mo e p onounced in luence on
he eg ession model because o hei age. To accoun o hese
empo al changes in he spa ial con igu a ion o Akkajau in e ms
o he p opo ion o s ands o di e en ages and hei in luence on
he model, we calcula ed an ‘‘a ea-weigh ed model’’. In his
model, he aw modeled alue o a gi en s and, being only
depended on s and age, is mul iplied by i s ela i e size as a
pe cen age o he o al s udy a ea. This scales he pu ely age-
dependen model alue o a gi en o es s and acco ding o he
E ec s o Logging on A bo eal Lichen Occu ence
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magni ude o i s spa ial con ibu ion o he landscape pa e n.
Al hough dimensionless, he a ea-weigh ing gi es a be e
unde s anding o how he landscape may be ‘‘pe cei ed’’ as an
a bo eal lichen habi a . All s a is ics we e compu ed using PASW
S a is ics ( e sion 18).
Resul s
Modeling a bo eal lichen abundance in o es s ands
Nea ly hal o he sampled s ands we e wi hou a bo eal lichens
(45%). Low a bo eal lichen abundance (abundance class 1) was
eco ded in 34% o all s ands, while a bo eal lichens we e
mode a ely abundan in he emaining 21% (abundance class 2;
Table 3).
Bina y logis ic eg ession analysis success ully disc imina ed
be ween s ands ha did and did no con ain lichens (i.e. be ween
hose in class 0 and hose in ei he class 1 o class 2), using o es
age as he independen a iable (Table 4). Exponen ia ing he
eg ession coe icien o o es age ga e an odds a io o 1.04. This
indica es ha he likelihood o he s and con aining lichens
inc eases by 4% pe yea o age. Fig. 2 illus a es he inc ease in
he p edic ed p obabili y o lichen occu ence (p) wi h o es age.
No model capable o achie ing s a is ically-signi ican disc imina-
ion on he basis o age be ween s ands in class 1 and class 2 could
be iden i ied; all o he models examined exhibi ed low AUC
alues (0.64), indica ing poo disc imina o y abili y (da a no
shown). None o he o he o es a iables (Table 2) p oduced
signi ican models ei he , p obably due o he low sample size o
o es s in which B yo ia was abundan (N = 30, Table 3). All o he
emaining analysis and discussion he e o e ocuses on he
p esence-absence model.
Model i , h eshold alue selec ion, and alida ion
The la ge a ea unde he ROC cu e (AUC: 0.92; p,0.001,
SE = 0.03) demons a es he model o be well- i ; i co ec ly
disc imina es be ween s ands wi h and wi hou lichens on he basis
o s and age in 92% o he cases examined. The sum o he
sensi i i y ( ue posi i es) and speci ici y ( ue nega i es) peaked a
a o es age o 63 yea s, which was used as he cu -o poin (Fig. 2).
The eplica ed c oss- alida ion o he logis ic model esul ed in a
highly signi ican Spea man-co ela ion (p,0.001; co ela ion
coe icien
s
= 0.945) be ween he es and aining se s, con i ming
he model’s obus ness. The abili y o he model o es ima e he
his o ical p obabili y o lichen abundance is limi ed by he ac ha
he his o ical sou ces used did no eco d he ages o ees olde
han 160 yea s, which in oduces some bias in o he model.
Howe e , he p obabili y ha a bo eal lichens will be p esen in
s ands o ha age is 0.97, and so he a i icial limi imposed by he
olde da a has only a small e ec on he es ima ed p obabili y ha
lichens we e p esen in his o ical s ands.
Age h eshold
Ou model iden i ied he s and age h eshold beyond which
lichens a e mo e likely o be p esen han absen as 63 yea s
(Fig. 2). This cu -o poin is also easonable o apply in ligh o he
his o ical da a, since all o he di e en age classi ica ion schemes
used in he his o ical in en o ies included an age class o ees
‘‘olde han 60’’. We he e o e used a cu o o 60 yea s in he
subsequen analyses, o e ain consis ency wi h he his o ical da a.
O e ime, he p opo ion o o es s olde han 60 yea s
dec eased, om 86% co e in 1926 o 34% in 2006 (Fig. 3).
Consequen ly, he e is li le connec i i y o hese o es pa ches,
which es ic ed he scope o lichen dispe sal, especially a e
1960. As hese olde o es s became less common and ceased o
occu in close p oximi y o one-ano he , he bu e zone o 200 m
a ound he o es pa ches inc eased ela i e o he a ea co e ed by
hese olde s ands om 1960 onwa ds (Fig. 3). The la ges
connec ed o es pa ch co e ed 50% o Akkajau in 1926, bu only
6% in 2006 (Table 5). The 74% dec ease in a ea-weigh ed mean
s and size S
a
unde lines he inc easing isola ion o hese abo e-
h eshold s ands om hei nea es simila ly-aged neighbo s
(Table 5).
Gene ally, a ia ion in s and numbe and size is a measu e o
agmen a ion, since he c ea ion o mo e disc e e s ands in he
same a ea spli s he a ea in o smalle pa s. A e he ex ension o
Akkajau in 1936, he o e all s and numbe ose by 12% in 1960,
and by ano he 28% in 2006 (Table 6). As a esul , he mean s and
a ea dec eased by 40% be ween 1936 and 2006. The a ea co e ed
by s ands olde han 140 yea s dec eased by 50% be ween 1926
and 2006.
Fu u e scena ios
We used he 60-yea h eshold o quan i y he consequences o
h ee di e en u u e app oaches o o es managemen , one
co esponding o in ensi e o es y, one o ‘‘business as usual’’, and
one in which no managemen was unde aken. Fig. 3 illus a es he
incidence o o es s ands olde han 60 yea s in he h ee
scena ios.
Unde he ‘‘business as usual’’ scena io, he a ea co e ed by
s ands ha p o ide a sui able habi a o lichens will inc ease by
abou 30% ela i e o he p esen day a e 40 yea s, as he many
young s ands ma u e. Howe e , u u e ha es ing will educe his
le el back o ha which cu en ly ob ains a e a pe iod o 120
yea s. Mo e in ensi e o es y is p ojec ed o educe he co e age
o lichen s ands, as logging would be ocused on he olde ,
p e iously-p o ec ed o es s ands. This would only educe he size
o he lichen habi a by 5% ela i e o he p esen day, bu would
gene ally esul in a smalle lichen habi a han he BAU scena io
o e ime. Con e sely, lea ing he a ea unmanaged would
inc ease he a ea o he lichen s ands o almos hei o me
ex en wi hin 40 yea s. Howe e , i should be no ed ha his
scena io does no accoun o na u al dynamics such as o es i es
and gap dynamics, which would also a ec lichen dispe sal,
es ablishmen and abundance.
Changes in age dis ibu ion and o es pa e ns
In 1926, Akkajau was domina ed by olde s ands (.140 y s),
which co e ed nea ly hal i s o al a ea (Fig. 4). This p opo ion
had dec eased o only 9% in 2006, when he landscape was
domina ed by s ands younge han 60 yea s (Fig. 4). Be ween 1926
and 1936, selec i e logging o olde ees educed mean s and age
(Fig. 4). Ex ensi e clea -cu ing be ween 1936 and 1960 educed
he a ea co e ed by all age classes, gi ing ise o a bimodal
dis ibu ion o clea cu s/young s ands oge he wi h old s ands
(Fig. 4).
Table 3. Lichen classes and hei subdi ision in abundance
classes as eco ded a sampling plo s in o es s ands,
Abundance Classes 1 and 2 bo h belong o Lichen class
‘‘P esen ’’.
Lichen Class Abundance Class Mean Biomass (kg/ha) N %
Absen 00 6545
P esen 135 4934
2 120 30 21
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A ea-weigh ed model: accoun ing o landscape changes
The model’s ou pu alues a e di ec ly dependen on s and age.
Howe e , calcula ions based on s and age alone canno p ope ly
ep esen he capaci y o he whole landscape o sus ain a bo eal
lichens, because hey do no accoun o he size o indi idual
s ands ela i e o he o al a ea. Consequen ly, he a ea-weigh ed
model was used o compa e he his o ical ends in he model
alues due o o es y in a way ha e lec s bo h s and age and
spa ial a ea. Fig. 4 shows he cumula i e dis ibu ion o esul s
calcula ed using he a ea-weigh ed model, i.e. he con ibu ion o
each o es age class o he sum o he a ea-weigh ed model alues
o each yea s udied.
In he yea s p io o 2006, o es s olde han 120 yea s
con ibu ed subs an ially o he a ea-weigh ed p obabili y o
lichen occu ence, p. Landscape agmen a ion, i.e. he dec eases
in he numbe and s and size o olde o es s and he dec easing
s and ages owa ds 2006 had a nega i e e ec on pa he
landscape scale. The cumula i e cu es become less s eep om
yea o yea , i.e. he in luence o olde age classes on lichen
occu ence (p) dec eases due o he educ ion in he a ea o land
hey co e . The cumula i e a ea-weigh ed model indica es ha
hei in luence dec eased by 51% be ween 1926 and 2006,
because o es s ands wi h a high p obabili y o lichen occu ence
became bo h smalle and less abundan (Fig. 4). In con as o he
si ua ion in 1960, he high abundance o o es s aged be ween 40
and 60 yea s in 2006 could no compensa e o he loss o e y
old o es s.
Discussion
The cu -o poin and i s p ac ical ele ance
The his o ical land usage pa e ns o he Sami people in
ex ac ing subsis ence esou ces ha e shaped he bo eal o es s o
Sapmi in o a ‘‘cul u al landscape’’ sensu Be kes & Da idson-Hun
[49]; such uses include he emo al o he inne ba k om pine
ees o ac as a plan ood esou ce [50,51] o cu ing lichen- ich
ees as eme gency ood o eindee in ha sh win e s o o o he
he ding p ac ices [52]. In con as , comme cial imbe ex ac ion
u ned he o es s in o an ‘‘economic landscape’’ ha in which he
a ailabili y o a bo eal lichens ha sus ain eindee he ding is
limi ed compa ed o he condi ions p io o he in ensi ica ion o
o es y. Ou analysis has quan i ied some o he impac s o es y
has had on a bo eal lichens in Akkajau .
Ra he han modeling B yo ia biomass in ela ion o s and age
[33,44], we modeled he p obabili y o lichen occu ence [53].
This iden i ied he alue and impo ance ha an a ea migh
possess, making ou app oach analogous o ha adop ed by
Juu inen e al. [54] in hei e alua ion o he conse a ion alue o
a gi en o es . A h eshold age o 63 yea s was iden i ied o ou
s udy a ea, wi h i s pa icula his o y o imbe ha es ing; unde
Figu e 2. P edic ed p obabili y o a bo eal lichen p esence and cu -o poin selec ion. Resul s om he logis ic eg ession in ci cles,
sensi i i y plus speci ici y as solid line and he chosen o es age cu -o o disc imina ing be ween s ands wi h and wi hou lichen as dashed line.
doi:10.1371/jou nal.pone.0028779.g002
Table 4. Reg ession coe icien s o p edic ing he p esence o lichens on he basis o o es age.
Coe icien s (b) S.E. d Sig. Nagelke ke R
2
Goodness o i x2 Sig. Exp(b)95% C.I. o Exp(b)
Lowe Uppe
Fo es Age 0,04 ,0,01 1 ,0,001 0,63 20,116 ,0,001 1,04 1,03 1,06
Cons an -3,11 0,53 1 ,0,001 0,045
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cu en condi ions, B yo ia is e y likely o be p esen in s ands
abo e his age (Fig. 2). This h eshold could concei ably be used as
an indica o o e alua e he po en ial o sus ainable eindee
husband y.
Simila h eshold ages we e epo ed by Gowa d & Campbell
[55] o an unmanaged s and o Abies lasioca pa,Picea engelmanni and
Pinus con o a in eas -cen al B i ish Columbia. In hese ees, i ook
60 yea s o B yo ia o g ow as a as he ou e ips o he ee
b anches, which is he poin when lichen accumula ion begins.
Likewise, S one e al. [56] ound a signi ican inc ease in lichen
biomass 70 yea s a e ha es ing in eas e n Canada. In a sp uce
and pine domina ed o es in sou h-cen al Sweden, Uliczka &
Angels am [57] eco ded ha B yo ia agmen s we e p esen on
5% o sampled ees aged be ween 61 and 80 in ci cula plo s o
10 m adius (N = 90).
This h eshold needs o be es ed in o he pa s o he
Fennoscandian eindee he ding a ea be o e i can be gene ally
applied. Fo ins ance, si es wi h highe p oduc i i y a e domina ed
by sp uce [22], leading o niche pa i ioning be ween Alec o ia
sa men osa, which p e e s he lowe canopy, and B yo ia uscescens in
he uppe canopy [58]; his changes he g owing condi ions. We
he e o e ecommend ha ou model should be es ed in a di e se
se o habi a ypes o iden i y addi ional habi a - ela ed a iables
ha in luence he occu ence o a bo eal lichens.
As ou esul s show, main aining bo h he spa ial and empo al
co e age o a key habi a , i.e. o es olde han 63 yea s, can
inc ease he likelihood ha lichens will be p esen as a g azing
esou ce o eindee . Because he p obabili y o lichen occu ence
inc eases wi h age, ex ending o a ion imes could g ea ly inc ease
he abundance o a bo eal lichens [27,44]. Fu he , he con inui y
o key o es habi a s is cen al o he main enance o high lichen
abundances: Esseen e al. [33] showed lichen biomass o be highe
in un-ha es ed old g ow h o es s han in selec i ely logged o es s
o he same age The e o e, empo al and spa ial con inui y is
especially impo an ; he a ailabili y o sui able o es s ands alone
does no gua an ee he p esence o B yo ia, especially when
oppo uni ies o coloniza ion ha e been limi ed du ing he o es ’s
his o y [59].
Fo es his o y: Loss o impo an landscape elemen s
On he landscape scale, o es s ands in Akkajau we e
consecu i ely agmen ed in o e e -smalle s ands o e he 80
yea s examined in his s udy. This a ec ed old o es s ands in
pa icula (Fig. 4), and he mean s and age dec eased subs an ially
(Table 6). As a esul , he p obabili y o a bo eal lichens being
Figu e 3. Pas and po en ial u u e changes in he a ea co e ed by s ands olde han 60 yea s. The inc easing agmen a ion om 1920
o 2006 is illus a ed by inc easing a ea isola ing s ands olde han 60 yea s om each o he , exp essed as a ea co e ed by a 200 m-bu e .
doi:10.1371/jou nal.pone.0028779.g003
Table 5. La ges pa ch index (LPI) in % and a ea-weigh ed
mean s and a ea (ha) o abo e- h eshold s ands.
1926 1936 1960 2006
LPI (%) 50.2 39.8 24.3 5.9
S
a
(ha) 163 155 160 43
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Table 6. Changes o e ime in he s and numbe (N), mean
a ea (ha), s anda d de ia ion and o al a ea (ha).
1926 1936 1960 2006
N696 575 651 900
Mean a ea (ha) 32 49 44 30
Mean a ea S d. De 62 77 64 30
To al a ea (ha) 21,979 28,283 28,869 26,600
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p esen in a gi en egion dec eased due o losses o aluable
habi a and educed connec i i y be ween abo e- h eshold s ands
in space and ime. In Akkajau , he pos -1960 loss o he
emaining la ge con inuous old o es s, which had a high
p obabili y o lichen occu ence cons i u es a ‘‘bo leneck’’ in
habi a a ailabili y and educed he landscape’s abili y o p o ide
a bo eal lichens as o age o eindee . The con ibu ion o old
o es s ands o he p obabili y o a bo eal lichen being p esen a
he landscape le el in 2006 is he e o e low in e ms o a ea
(Fig. 4).
Since B yo ia is a species wi h limi ed dispe sal abili ies, he
spa ial s uc u e o i s habi a is essen ial o i s su i al and abili y
o colonize new pa ches [45,60]. Because s ochas ici y in i s
su i al and ep oduc ion may a ec popula ion sizes [61],
changes in i s spa ial and empo al habi a pa e ns a e especially
impo an o unde s anding he impac s o agmen a ion and
habi a loss. In pa icula , small and/o isola ed pa ches do no
eadily eco e om en i onmen al dis u bances, no do hey
acili a e immig a ion and es ablishmen . This is he si ua ion in
many bo eal o es s in bo h Scandina ia and Canada [62]. The
educed iabili y o he lichen popula ion may he e o e esul in
local ex inc ion due o s ochas ic e en s, e.g. when pa ches a e oo
isola ed o be colonized [61]. Fu he , a species’ esponse o a
speci ic dis u bance may be subjec o ime lag. This makes i
pa icula ly impo an o s udy his o ical landscape pa e ns, as
hey can explain mode n day species dis ibu ion pa e ns [63].
His o ical landscape ans o ma ions he e o e c ea e a pa h
dependence, i.e. u u e op ions and changes depend on decisions
aken bo h in he pas and a p esen [64]. Because o he slow
dynamics o o es s, managemen decisions will impac hei spa ial
and empo al de elopmen on long (mul i-decade) imescales, and
will limi o acili a e u u e op ions (Fig. 3). Ou u u e p ojec ions
illus a e he possible ou comes o some di e en managemen
app oaches.
Managemen scena ios
The p ojec ed e ec s o he h ee di e en o es y managemen
scena ios on he abundance o h eshold s ands p o ides insigh
in o he likely u u e de elopmen o he o es s in ques ion, which
a e pa icula ly impo an habi a s o a bo eal lichens (Fig. 3).
Unde bo h he business-as-usual and he in ensi e scena ios, he
co e age o h eshold s ands will ini ially inc ease ela i e o he
p esen day si ua ion, because o he cu en p edominance o
young and middle-aged s ands oday. The BAU app oach is
ocused on main aining a cons an imbe ha es . Howe e , i has
di e en consequences o a bo eal lichens. Unde BAU, o es s
olde han 160 yea s a e le unmanaged, as a e p o ec ed a eas.
These a eas will he e o e se e as ‘‘sou ce habi a s’’ o lichen
dispe sal. Due o he dynamic pa e n o eme ging and
disappea ing h eshold s ands, lichen es ablishmen and pe sis-
ence will be mainly es ic ed by he empo al and spa ial
a ailabili y o colonizing habi a s.
Unde he in ensi e scena io, all o he a eas ha a e le
unmanaged in he BAU scena io a e a ailable o ha es ing. This
esul s in a loss o lichen- ich s ands and is also likely o u he
dec ease he dispe sal abili y o he lichens due o mo e
p onounced agmen a ion. As such, al hough some o es s abo e
he h eshold age a e e ained unde his scena io, hey a e less
likely o be colonized o he same ex en as would be he case
unde BAU. One could easonably specula e ha he age
h eshold migh shi upwa ds, al hough such olde ees would
be mo e likely o be ha es ed. I should be no ed ha his
managemen s a egy is no allowed unde he cu en Swedish
Fo es y Ac .
The con inui y o o es co e inc eases unde he No
Managemen scena io. This s a egy would suppo he sp ead
o a bo eal lichen agmen s o dispe sal uni s and consequen ly
p omo e hei es ablishmen . A he same ime, lichen abundance
would inc ease in al eady-colonized habi a s. This, howe e , does
Figu e 4. Changes in age composi ion in Akkajau 1926–2006. A ea in % co e ed by age classes illus a ed by columns, hei cumula i e
con ibu ion o he a ea-weigh ed model by he dashed line.
doi:10.1371/jou nal.pone.0028779.g004
E ec s o Logging on A bo eal Lichen Occu ence
PLoS ONE | www.plosone.o g 9 Decembe 2011 | Volume 6 | Issue 12 | e28779