全 文 ：Thinning an Old-growth Forest Increased Diversity
and Productivity of Mushrooms
Egli Simon? , Ayer Fran?ois
( Swiss Federal Research Institute WSL , Birmensdorf, Switzerland)
Abstract : A current long-termstudyon fungal reserve inwestern Switzerland started in1977 aims at determiningtheeffects
of various factors onthediversity and productivity of wildforest mushrooms . Here theeffect of an increment thinningof an
old-growth forest is described . Fruit bodies of all the epigeous macro-fungal specieswere identified and counted at weekly
intervals between 1997 and 2006 in5 experimental plots . In oneof the plots an increment thinning was performed inearly
spring1987 in order to lighten the dense old-growthforest and to favour the understory . The thinning induced a significant
increaseof fungal species richness, aswell as of fruit body numbers, especially of theectomycorrhizal species . Comparing
the period before ( 1977 - 1986) with the period after the thinning (1987 - 2006) , seven times more species and 23 times
more fruit bodieswerecountedonaverageper year . Themycorrhizal species producedmuchmore, up to9 times morespe-
cies and 32 times more fruit bodies on average after the thinning . Obligatory beech-specific mycorrhizal fungi clearly in-
creased their dominance after the thinning, their species number increasing from36% to 54 % and the fruit body number
from 19% to70% . Thesechangesarediscussed inrelation to thepossiblegrowth reactions of theremaininghost trees after
the artificial intervention .
Key words: Biodiversity; Forest management; Wild forest mushrooms; Non-wood forest product
CLC number : Q 16 Document Code : A Article ID: 0253 - 2700 (2009 ) Suppl.ⅩⅥ - 062 - 07
Introduction
Most of the edible forest mushrooms, such as the
boletes, the chanterelles and truffles, belong to the
category of mycorrhizal fungi . These fungi areobligato-
ry biotrophic and only grow and fruit together with a
living host tree . Their cultivation is not feasible on ar-
tificial substrates, as it is for saprotrophic species like
the Button mushroom ( Agaricusbisporus) or the Oyster
Mushroom ( Pleurotus ostreatus) or Shiitake ( Lentinus
edodes) . Although there have been some promising re-
sults with cultivating the golden chanterelle ( Danell
and Comacho, 1997 ) , these attempts arefar fromcom-
mercial use . With regard to this situation it makes
sense to research the mechanisms of fruit body produc-
tion and to find measures for maintaining or even im-
proving the natural yields of mycorrhizal forest mushro-
oms as thevaluable non-wood forest products .
It is common knowledge that good or poor mush-
roomyears aredetermined by climatic factors, but this
does not explain mushroom occurrence exhaustively
(Straatsma et al. , 2001; Agerer, 1985) . Other factors
must be involved . There is abundant evidence from
current knowledge that the carbohydrate supply from
thehost tree to the mycorrhizal fungal mycelium plays
an important role in this context . Mycorrhizal fungi de-
pend on photosynthetically fixed carbon produced by
the associated host trees to extend their vegetative my-
celium in the soil and toformfruit bodies for sexual re-
production . A reduction or an interruptionof the carbo-
hydrate flow fromthehost tree to the roots affect mycor-
rhizal colonization and fruit body production: the elimi-
nation of the photosynthetic active green part of the
tree, e . g . by clear cutting, leads to an immediate
disruption of ectomycorrhizal fruit body formation
( Kropp and Albee, 1996; Visser and Parkinson,
1999; Ohenoja, 1988) . Accordingly, treegirdling re-
duces fruit body productionof ectomycorrhizal fungi vir-
tually to zero (H?gberg et al. , 2008 ) , and in shading
experiments fruit body production of Telephora terrestris
(Hacskaylo, 1965) and Laccaria bicolor ( Lamhamedi
云 南 植 物 研 究 2009 , Suppl . ⅩⅥ : 62～68
Acta Botanica Yunnanica
? ?Author for correspondence; E-mail : simon. egli@wsl. ch; Tel . + 4144 7392271 ; Fax: + 4144 7392215
et al. , 1994 ) was reduced . Herbivores reduce mycor-
rhizal colonization and alter mycorrhizal fungal commu-
nity composition as well ( Gehring and Whitham,
2002) , and in defoliation experiments fruitbody num-
bersof ectomycorrhizal fungi decreased to one third on
defoliated trees compared with control trees (Kuikka et
al. , 2003) .
Ectomycorrhizal communities arealso influencedby
forest management . Durall and Jones ( 2005 ) gave a
complete reviewon current knowledge . Inmanaged fore-
sts thinning is a common silvicultural practice aimed at
increasing the dimensions and quality of trees, as well
as at inducing regeneration . The available results on the
effects of thinningon the fungal community are inconsis-
tent . Buée et al . (2005) and Kropp and Albee (1996)
found that somefungi were adversely affectedwhileoth-
ers were positively affected by thinning . A thinningof a
12 year old Scots pine plantation had little effect on the
ectomycorrhizal fruitbody production: out of 19 species
tested, only threespecies ( Suillusbovinus, Gomphidius
roseus and Cortinarius semisanguineus) responded sig-
nificantly to the thinning, with increased fruit body pro-
duction (Shaw et al. , 2003) . Pilz et al . (2006) found
that the chanterelle ( Cantharellus formosus) number
and weight were significantly decreased by thinning in
thefirstyear after logging, but all evidenceof differenc-
es disappeared within the following six years . Ayer et
al . ( 2006 ) observed highest species richness and fruit
body abundance in medium dense stands compared to
stands with high and stands with low densities . Ohenoja
(1988 ) mentions two unpublished studies in Southern
Finland and in Eastern Karelia, both showing higher
fruit body yields in thinned forests compared to denser
stands . In contrast, another study ( Luoma et al. ,
2004) shows that green-tree retention causes fruitbody
production decline, but these effects vary strongly ac-
cording to the season, and retention type and level .
The present study describes the effects of an in-
crement thinning on the diversity patterns and the pro-
ductivity of associated forest mushrooms in the fungus
reserve La Chanéaz, Switzerland . The thinning took
placewithin thenormal silvicultural management plani-
fication of the local forest service ten years after the
start of the mycological inventory . The inventory was
continued for another 20 years . Four other study plots
with the same size and inventoried in the same way as
the thinned plot served as‘non-thinned’control plots .
We hypothesize that thinning and the resulting
growth reactions of trees influence diversity and growth
reaction of the associated mycorrhizal fungi .
Materials and Methods
Study site
The studywas carriedout in the 75 hectarefungus
reserve“ La Chanéaz”established in 1975 in south-
western Switzerland . It is located in a dominant forest
typeof theSwissCentral Plateau at575 mabovesea le-
ver, in a mixed old-growth forest with deciduous and
coniferous tree speciesof different age ( Fagussilvatica
L ., Quercus robur L ., Picea abies ( L .) Karst .,
Abies alba Mill ., Pinus silvestris L ., Pinus strobus
L ., and Larix decidua Mill .) . The forest type repre-
sents an important and highly frequented habitat for
mushroomharvesting in Switzerland . The annual mean
temperature is9 .4℃ and the annual mean precipitation
is 1 000 mm .
Five observation plots of 300 m2 (30 m×10 m)
were installed in 1977 . In one of the plots an increment
thinning was performed in early spring 1987 in order to
lighten the dense old-growth forest and to favor the un-
derstory . 14 of the total 24 dominating trees livingin the
upper crown level were cleared . The other four plots
represent unthinned controls . The plots were enclosed
by2 m high fences to exclude all inconvenient impacts
caused by mushroompickers and large forest animals .
Data collection
In the five plots all fruit bodies of the epigeous
macro-fungal species were identified and counted at
weekly intervals from May to December ( weeks 21 -
52) . When first recorded, the fruitbodies were marked
withmethylene blue on the cap to avoid double count-
ing . The survey was started in 1977 and continued un-
til 2005 ( unthinned plots) and 2006 ( thinned plot) .
Between 1980 and 1983 only the edible fungi were
recorded . These four incomplete years were excluded
from the analyses .
36增刊ⅩⅥ Egli and Ayer: Thinning an Old-growth Forest Increased Diversity and Productivity of Mushrooms
Data analysis
To examine differences in species and fruit body
numbers before and after thinning we compared the an-
nual means of the two periods using a two-sample t-
test . The analyses were performed with the statistical
software R ( R Development Core Team, 2007) .
To compensate a possible shift between the peri-
ods before thinning ( 1977 - 1986 ) and after thinning
(1987 - 2006) , thedataof the thinned plot were trans-
formed by multiplying themby themean factor between
the two periods of the four non-thinned plots .
Results
In first three years following the thinning mush-
room production was very low, and then the species
numbers as well as thefruit body numbers started to in-
crease sharply ( Fig. 1 ) . Comparing the period before
thinning ( 1977 - 1986 ) with the period after thinning
(1987 - 2006) , seven times morespecies and 23 times
more fruit bodies were counted on average per year .
This increase was especially pronounced for themycor-
rhizal species: they produced 9 times more species and
32 times more fruit bodies on average after the thinning
(Table 1 ) .
However, also in the 4 non-thinned plots thenum-
ber of species and the number of fruit bodies was two to
three times higher in the1987 - 2006 period compared to
the 1975 - 1986 period . We compensated this shift by
Fig . 1 Fungal species and fruit body numbers from 1977 to 2006 in the thinned plot
46 云 南 植 物 研 究 增刊ⅩⅥ
Table 1 Mean number of fungal species and fruit bodies in the period before (1977 - 1986) and after
(1987 - 2006 ) the thinning treatment ( plot 59 ) and the 4 control plots ( 47 , 51 , 54 , 58 ) ,
with indication of the significance levels between the two periods
mean numbers
59 ?
77-86 87-06
59 (corr .)
77-86 87-06
58
77-86 87-06
54
77-86 87-06
all species 6 ?40 ( *** ) 6 G24 y( *** ) 17 33 ( ** ) 43 f59 ( * )
mycorrhizal species 3 ?26 ( *** ) 3 G16 y( *** ) 11 21 ( * ) 32 f39 ns
saprotrophic-terricol species 3 ?9 ( *** ) 3 G5 fns 4 9 ( ** ) 8 S14 ( ** )
saprotrophic-lignicolous species 0 ?5 ( *** ) 0 G3 f( *** ) 2 3 ns 3 S6 r( ** )
parasitic?pathogenic
all fruit bodies 32 ?740 ?( *** ) 32 Z328 ( *** ) 276 718 ( * ) 739 x134 ns
mycorrhizal fruit bodies 15 ?483 ?( *** ) 15 Z250 ( *** ) 225 490 510 x695 ns
saprotrophic-terricol fruit bodies 16 ?119 ?( *** ) 16 Z45 y( ** ) 44 111 ( * ) 175 x315 ( * )
saprotrophic-lignicolous fruit bodies 1 ?138 ?( *** ) 1 G38 y( *** ) 7 118 ( *** ) 55 f124 ( * )
parasitic?patogenic
mean numbers
51 ?
77-86 87-06
47 y
77-86 87-06
corr . factor
77 g-86?87-06
all species 18 ?52 ( ** ) 17 Z23 yns 0 .59
mycorrhizal species 14 ?35 ( ** ) 8 G10 yns 0 .64
saprotrophic-terricol species 3 ?15 ( *** ) 7 G9 fns 0 .50
saprotrophic-lignicolous species 1 ?3 ns 2 G3 fns 0 .52
parasitic?pathogenic
all fruit bodies 303 ?833 ?( ** ) 241 l646 ( ** ) 0 .44
mycorrhizal fruit bodies 216 ?554 ?( ** ) 156 l321 ( * ) 0 .52
saprotrophic-terricol fruit bodies 82 ?253 ?( ** ) 60 Z261 ( ** ) 0 .38
saprotrophic-lignicolous fruit bodies 5 ?25 ns 25 Z65 yns 0 .28
parasitic?patogenic
( ns: not significant; ( * ) : P < 0 .05 , ( ** ) : P < 0 .01 , ( *** ) : P < 0 .001 )
Table 2 Relative proportion of the 4 ecological fungal groups before
( 1977 - 1986 ) and after ( 1987 - 2006) the thinning treatment
1977 ?- 1986
species
fruit
bodies
1987 - 2006
species
fruit
bodies
all species 100 ?100 100 100
mycorrhizal 48 ?44 55 w63
obligatory beech-specific ( 36 ?) (19) (54 w) ( 70)
facultatively beech-specific ( 46 ?) (70) (24 w) ( 15)
non beech-specific ( 18 ?) (11) (22 w) ( 15)
saprotrophic-terricol 48 ?53 31 w15
saprotrophic- lignicolous 4 ?3 12 w18
parasitic, pathogenic 0 ?0 2 d4
multiplying the data of the thinned plot by the increase
factor of the non-thinned plots to eliminate possible ef-
fectsother than the experimental thinning effect . These
corrected values still show highly significant differences
between“before thinning” and“ after thinning”: 4
times more species and 10 times more fruit bodies .
Obligatory beech-specific mycorrhizal fungi clearly
increased their dominance after the thinning, their spe-
cies number increasing from36% to 54% and the fruit
body number from19% to70% . The percentageof sa-
protrophic species decreased slightly after the thinning,
with a shift fromterricolous to lignicolous species ( Ta-
ble 2) .
On the thinned plot a total of 23 species was
counted in the 1977 - 1986 period, compared to 173 in
the 1987 - 2006 period . Over the whole period 176
species weredetected . Three species ( Agaricussilvico-
la, Entoloma conferendum, Otidea onotica) only ap-
peared in the first period and in very low numbers .
96 of the 176 species aremycorrhizal , 52 of them
areobligatory beech-specific, the other 23 are faculta-
tive beech-specific, and 21 arenot beech-specific . The
definition‘obligatory beech-specific’ is not generally
valid but related to the special tree assemblage of the
plot, i . e . a fungal species is called obligatory beech-
specific if there is no other potential tree species than
beechon the plot which could act as symbiont .
Many edible mushrooms occured exclusively after
the thinning: Boletus edulis, Xerocomus badius, and
some Russula species, Craterellus cornucopioides,
Amanita rubescens, Hypholoma capnoides .
56增刊ⅩⅥ Egli and Ayer: Thinning an Old-growth Forest Increased Diversity and Productivity of Mushrooms
Discussion
The results show a clear temporal coincidence be-
tween thinning and thereaction of the associated fungal
flora . What are the reasons for this very distinct reac-
tion? Changes in soil temperature andmoisture regimes
on the forest floor caused by the thinning might be an
influencing factor for the fungal reaction . However, it
is not an evidencehow important these changes are . In
a study of the forest floor temperature and the relative
humidity over a 12-year chronosequence of timber har-
vests these effects are estimated as minimal and short-
term (Brooks and Snowman, 2008 ) . In our study the
microclimatic changes seem to be short-term too . Just
after the intervention the disturbance was important in
terms of soil disturbanceby logging and by a drying ef-
fect caused by the exposure of the soil to the sun . In
fact, in the first threeyears nearly no fruit bodies were
found . But the canopy began to close again and themi-
croclimatic conditions must have returned very quickly
to those before thinning . The fungal diversity and fruit
body production, however, remained unchanged on a
very high level . This indicates that factors other than
microclimate must be primarily responsible for the shift
in fungal diversity and fruit body numbers .
Sincemainly themycorrhizal species increased af-
ter the thinning we hypothesize that the reaction must
have something to dowith thehost tree and its possible
reactions in the carbohydrate balance . Saprotrophic
species increased too, but not to the same extent . It
has repeatedly been demonstrated that an interruption
or a reduction of the carbohydrate supply fromthe host
tree to the fungal mycelium reduces fruit body produc-
tion: after clear cutting (Kropp andAlbee, 1996; Viss-
er and Parkinson, 1999) , after defoliation (Last et al. ,
1979) , after forest girdling ( H?gberg et al. , 2008 ) or
after herbivory (Gehring and Whitham, 2002) . In our
study we generated the opposite process by a thinning
treatment: an increased tree growth and a positive ef-
fect on the carbohydrate balance . Before thinning, the
old trees forming the upper crown level had nearly
stopped growing . Their photosynthetic activity must
have been near zero due to their age . Also the sup-
pressed beech trees standing in the shadow of the old
trees had reducedgrowth .Theoverall growth activityof
the forest before the thinning can be assumed to have
been very low . This would explain thevery low produc-
tivity of fruit bodies in this period .The thinning altered
this situation considerably: the formerly suppressed
beech trees increased their growth dramatically . With
thegrowth increase, theoverall photosynthesis potential
increased andwas proportioned to less tree individuals .
Consequently, the carbohydrate production per tree in-
creased and the generated carbohydrate surplus was
available for the mycorrhizal fungi . Kranabetter &
Kroeger (2001) came to the same conclusion in a par-
tial cutting experiment . They hypothesize that increas-
ing growth of residual trees might enhance mushroom
fruiting through greater tree vigour and photosynthetic
capability . Our assumption is also supported by results
of Cranswick ( 1979 ) who showed that starch content
increased substantially in formerly shaded trees when
overstory trees were removed . And, as demonstrated by
Kuikka et al . (2003) , the biomass of ectomycorrhizal
fruit bodies per tree positively correlates with starch
concentration in fine roots . This allows for the assump-
tion that ectomycorrhizal fruit body productionmight be
coupled with the physiological status of the associated
tree: trees growing well produce more ectomycorrhizal
fruit bodies compared with poorly growing trees . This
was already postulated as a hypothesis by Pilz et al . in
1998 . The findings of Fellner and Pesková ( 1995 )
support this assumption too: fruit body production of
ectomycorrhizal fungi were drastically reduced in forest
stands with higher degrees of damage, whereas sapro-
trophic fungal species were less affected or even in-
creased their fruit body abundance .
If the hypothesis that tree growth influences fruit
body production is true, this should be expressed in the
fungal composition of the associated mycorrhizal fungi .
The thinning resulted in a change in tree species com-
position as beech became thedominant treespecies and
themain carbohydrate supplier after the thinning . This
means that we should find a shift in the fungal commu-
nity towards beech-specific fungi . In fact, this is clear-
ly confirmed by our results . The increase of obligatory
beech-specific species is distinctive; they reach 70%
66 云 南 植 物 研 究 增刊ⅩⅥ
of the mycorrhizal species in fruit body numbers com-
pared with 19% before the thinning .
Why was fruit body reaction delayed for 3 years
compared to the tree growth increase? 1987 and 1988
were poor mushroom years, probably due to the distur-
bance of the site by the intervention . 1989 was gener-
ally a very poor season with nearly no fruit body pro-
duction in the whole region due to exceptional meteoro-
logical conditions; it was a relatively dry and hot sea-
son . Again, 1991 was a dry season temporarily break-
ing the increase trend . In a thinning experiment de-
scribed by Pilz et al . ( 2006 ) Cantharellus formosus
decreased in theyear after thinning and then recreated
in the following years . The reason was probably also
the site disturbance caused by the thinning .
A delay in fruit body reaction after thinning could
also be due to the carbon consumption strategy of the
mycorrhizal fungi . An increase or a surplus of carbo-
hydratesmight first be invested in myceliumgrowth and
then in fruit body production . In this special situation
themycorrhizal fungi were undernourished for years and
probably needed a kind of recovery phase to fill up the
reserves in the vegetative mycelium before investing in
fruit body production .
An unexpected observation was that in the non-
thinned plots the number of species and the number of
fruit bodies was also higher in the 1987 - 2006 period
compared with ones in the 1975 - 1986 period . That
is, a general shift in fungal diversity and productivity
over the last 30 years can be observed . Especially
since the beginning of the nineties production has in-
creased . A possible explanation might be that this peri-
od could havebeenmore adequatefor mushroomgrowth
in terms of climatic conditions . Recently, Gange et al .
(2007) have shown a dramatic increase in the overall
fruiting period in Great Britain in the last decades:
mushroomseasons have begun earlier and have ended
later in the years since the mid′80s . They could also
demonstrate that many species have fruited twice per
year in recent years, presumably due to global warm-
ing . Consequently, higher total numbers of fruit bodies
have resulted . The authors ascribe this phenomenon to
global warming . This might be the explanation for the
increase of fruit body production in the non-thinned
plots inour study . But even if such an effect exists, it
is overruledby thethinning effect: after eliminatingthe
shift through a correction factor the difference between
the two periods still remains highly significant .
The results clearly indicate the relationship be-
tween a forest management intervention and the growth
of forest mushrooms . Even if the results do not allow to
exhaustively prove the causality between tree growth
and fungal reaction, there is sound evidencefor acaus-
al relationship, especially by the clear shift of the my-
corrhizal community to beech-specific fungi after the
thinning .
The current results teach us that the health of
trees and of our forests is important for the growth of
associated mycorrhizal fungi and that we must ensure
that forests are able to produce this important natural
resource in a sustainable way, especially in regions
where mushroom harvesting is of fundamentally social
and economic importance .
Acknowledgements : We would like to thank the Forest Service
of the Canton of Fribourgfor the support andfor the authorization
to use the site La Chanéaz for our study . We are alsograteful to
M . Fenaroli for critical reading of themanuscript .
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