Arthropod biodiversity after forest fires: winners and losers in the

winter fire regime of the southern Alps

Marco Moretti, Martin K. Obrist and Peter Duelli

Moretti, M., Obrist, M. K. and Duelli, P. 2004. Arthropod biodiversity after forestfires: winners and losers in the winter fire regime of the southern Alps. �/ Ecography27: 173�/186.

Since prehistoric times, natural and man made fires have been important factors ofnatural disturbance in many forest ecosystems, like those on the southern slopes of theAlps. Their effect on scarce, endangered or stenotopic species and on the diversity ofinvertebrate species assemblages which depend on a mosaic of successional habitatstages, is controversially discussed. In southern Switzerland, in a region affected byregular winter fires, we investigated the effect of the fire frequency on a large spectrumof taxonomic groups. We focussed on total biodiversity, taxonomic groups specific tocertain habitat types, and on scarce and endangered species. Overall species richnesswas significantly higher in plots with repeated fires than in the unburnt control sites.Plots with only one fire in the last 30 yr harboured intermediate species numbers. Firefrequency had a significantly positive effect on species richness of the guilds of interiorforest species and forest edge specialists. Species of open landscape, open forests andinterior forests were not influenced by fire frequency. A positive effect of fire on speciesrichness was observed for ground beetles (Carabidae), hoverflies (Syrphidae), beesand wasps (Hymenoptera aculeata, without Formicidae), and spiders (Araneae).True bugs (Heteroptera), lacewings (Neuroptera) and the saproxylic beetle fami-lies Cerambycidae, Buprestidae and Lucanidae showed positive trends, but nostatistically significant effects of fire on species numbers or/and abundances.Negative effects of fire on species numbers or/and abundances were found only forisopods and weevils (Curculionidae). A compromise for forest management issuggested, which considers the risk of damage by fire to people and goods, whileavoiding the risk of damage to biodiversity by imitating the effects of sporadic fires andproviding a mosaic forest with open gaps of different successional stages.

M. Moretti (marco.moretti@wsl.ch), WSL Swiss Federal Research Inst., SottostazioneSud delle Alpi, P.O. Box 57, CH-6504 Bellinzona, Switzerland. �/ M. K. Obrist and P.Duelli, WSL Swiss Federal Research Inst., CH-8903 Birmensdorf/ZH, Switzerland.

In many forest ecosystems of the world, wildfires

represent one of the most important factors of natural

disturbance (Pyne et al. 1996). This is also the case on

the southern slope of the Alps (from south-east France

to north-east Italy), where fires have contributed to

changes in species composition of the forest vegetation

since prehistoric times (Delarze et al. 1992, Hofmann et

al. 1998, Tinner et al. 1999). Some authors underline

that optimal habitat for fire intolerant species, or mid-

and late successional species, would never develop under

a regime of frequent fires (e.g. Yanovsky and Kiselev

1996, Økland et al. 1996, York 2000), while other

authors point out the importance of fire for invertebrates

in creating a habitat mosaic of different successional

stages (Buddle et al. 2000, Gandhi et al. 2001). Con-

cerning biodiversity, some studies emphasise the positive

role of fire as an important evolutionary force main-

taining species richness according to the intermediate

disturbance hypothesis, reducing exclusive competition

and even favouring threatened species of invertebrates

Accepted 30 September 2003

Copyright # ECOGRAPHY 2004ISSN 0906-7590

ECOGRAPHY 27: 173�/186, 2004

ECOGRAPHY 27:2 (2004) 173

(Bengtsson et al. 2000, Simila et al. 2002, Sippola et al.

2002), while others consider fire as a negative factor

which can endanger endemic and stenotopic species, and

those with low dispersal capacity (e.g. Yanovsky and

Kiselev 1996, Økland et al. 1996, Dajoz 2000).

Reasons for the apparently contradictory effects of fire

on invertebrates include the varying fire regimes, differ-

ing ecological pre- and post-fire conditions in the study

regions, as well as the difference in the taxonomic groups

in focus. More taxa should be concurrently included in

future analyses, promising a better understanding of the

complex ecological interactions, and minimising the risk

of generalising statements, based on studies of only a

limited number of taxonomic groups (Prodon et al.

1987).

Moreover, the current knowledge on the effects of fire

on invertebrates emanates from studies carried out in

Mediterranean regions, or in fire-climax ecosystems such

as savanna, chapparal, and boreal forests where fires

occur in summer time (see Castri et al. 1981, Viegas and

Andersen 1996, Andersen et al. 1998, DeBano et al.

1998, Trabaud 2000 for a review). Much less is known

about the role of fire in temperate forests where winter

fires predominate.

The aim of this study is to investigate the response of a

large spectrum of taxonomic groups to fire frequency in

a temperate deciduous forest with a winter fire regime.

The main questions are: 1) How is overall biodiversity

affected by the fire frequency? 2) Which groups suffer

and which profit from fire? 3) Does the abundance of

‘‘species of the forest interior’’ decrease after single or

repeated fires? 4) Are scarce and endangered species

threatened or furthered by fire?

This research is part of a multi-disciplinary study on

the effects of sporadic and regular wildfires on European

chestnut forests (Castanea sativa Mill. ) in southern

Switzerland (e.g. Delarze et al. 1992, Conedera et al.

1996, 2002, Tinner et al. 1999, Marxer 2002, Moretti et

al. 2002a,b).

Materials and methods

Study area and study sites

The study area is situated in the hilly and mountainous

belt of the southern Swiss Alps. The study sites were

chosen on a south-facing slope (450�/850 m a.s.l.) of

11�/15 km near Locarno (08844?E, 46809?N). The area

was selected based on the presence of a sufficient number

of burnt and unburnt surfaces to allow replication of

sites.

The study area has a moist, warm temperate climate,

which differs from the more southern regions with a

Mediterranean climate. Rainfall is higher in summer

(June-September: ca 800 mm) than in winter (Novem-

ber-February: ca 400 mm). Thus the area is prone to

fast-spreading surface fires during the period of vegeta-

tion dormancy (December�/April). More details about

the study area are given in (Moretti et al. 2002a).The

forest cover at all sites is represented by former coppice

stands of sweet chestnut Castanea sativa Miller. Chest-

nut was introduced in the region during Roman times

and does not therefore represent the climax vegetation.

Study sites were selected after consultation of the

Wildfire Database of southern Switzerland, which con-

tains data from 1968 to 1997 (Conedera et al. 1996). The

sites were classified in three categories according to the

number of fires (fire frequency) occurring in the last 30

yr, verified by dendrochronological methods. A total of

22 study sites were selected: 8 sites had burnt only once

(single fire sites), 8 sites had burnt 3�/4 times (repeated

fires sites) and 6 sites had never suffered from fire in the

last 35 yr (control sites) (Table 1). The distribution of the

time elapsed since the last fire amongst the two

categories of fire frequency were equal, ranging from 0

yr (freshly burnt) to 24 yr (old fires) (Moretti et al.

2002a).

Burnt and unburnt (defined as no fires during at least

the last 35 yr) sites contrast strongly with respect to tree

and grass cover, as well as to forest structure. Forest

canopies were more open and the grass more luxuriant at

burnt sites (especially at recently burnt sites) than at

unburnt sites. Because of the resprouting of stools and

the high shoot mortality following each fire, repeatedly

burnt sites appeared more densely forested (average of 25

shoots per stool; 55% of shoots were dead) than unburnt

and single fire sites (average of 9 shoot per stool; 22% of

them dead). The dominant trees at repeatedly burnt sites

were smaller (diameter at breast height, DBH 10 cm)

than those of unburnt and single fire (DBH 30 cm).

Table 2 summarises the most evident site characteristics.

Table 1. Study sites grouped in three classes of fire frequency (C�/unburnt as control, i.e. sites which did not burn in the last 30 yr;S�/single fire, i.e. 1 fire in the last 30 yr; R�/repeated fires, i.e. 3�/4 fires in the last 30 yr) and 4 classes of time since last fire (B/ 1,1�/3, 6�/14, 17�/24 yr).

Fire frequency Unburnt Time since last fire Total

B/ 1 yr 1�/3 yr 6�/14 yr 17�/24 yr

Unburnt (control) [C] 6 6Single fire [S] 1 2 2 3 8Repeated fires [R] 1 2 4 1 8

Total trap sites 6 2 4 6 4 22

174 ECOGRAPHY 27:2 (2004)

Sampling methods

In order to obtain reproducible data, we used standar-

dised collecting methods (Duelli et al. 1999). Litter

dwelling species (e.g. isopods, spiders, carabids, other

epigaeic beetles) were sampled using pitfall traps and

surface eclectors. Pitfall traps consisted of plastic funnels

recessed into the soil (opening diameter of 15 cm) and

mounted on top of a plastic bottle containing 2%

formaldehyde solution. A transparent roof 10 cm above

the traps provided protection from the rain. For details

and limitation of the method, see Obrist and Duelli

(1996), Duelli et al. (1999) and Moretti et al. (2002a).

Surface eclectors (emergence traps), developed by

Brunhes (1981), consisted of a pyramid-like construction

(50�/50 cm at the base) fixed on the ground and covered

with a fine net (mesh widthB/0.5 mm) in order to

preserve the microclimatic conditions. Emerging insects

were trapped in collection vials on top of the dark

pyramid, when they tried to escape to the light.

Flying and flower visiting species were sampled using

window traps in combination with a yellow water pan

(Duelli et al. 1999) placed at a height of 1.5 m above

ground. Window interception traps are widely used to

study Coleoptera in forest ecosystems (e.g. Kaila et al.

1997, Schiegg 2001). According to Økland (1996) and

Martikainen et al. (2000) they are suitable for comparing

different forest environments and their ecological con-

ditions over wide areas.

The probability of an animal being caught by pitfall

and window traps is a function both of the number of

individuals present and their activity. This is not the case

for surface eclectors, where the probability is not

influenced by the animal’s activity. Thus the expression

‘‘number of individuals’’, includes both abundance and

activity.

Three sets of three traps (1 pitfall trap, 1 window trap,

1 eclector) were installed at each of the 22 study sites,

making a total of 66 trap sites. The minimum distance

between trap sites within each study site was at least 10

m, while the distance between the sample sites was ca

0.25 km. The traps were emptied weekly from the

beginning of March to the end of September 1997,

resulting in a total of 28 sampling periods, which covered

the main activity season for the different taxa.

Grouping the species

Most of the invertebrates caught were identified to

species level and grouped based on different criteria.

Taxonomic groups �/ species were pooled in eleven

systematic groups represented by one or more families of

seven different orders (Table 3): Isopoda, Araneae,

Coleoptera, Hymenoptera, Diptera, Neuroptera and

Hemiptera.

Habitat guilds �/ species were placed in four main

groups depending on their habitat requirements: interior

forest species (closed forest stands) (IF); open forest

species (clearings, light forests, clear cuts) (OF); forest

edge species (FE); open land species (fields, prairies)

(OL). Ubiquist species, or species for which ecological

knowledge is vague, were not classified. This grouping

was mainly based on information obtained from pub-

lished data (e.g. Stichel 1962, Kutter 1977, Hellrigl 1978,

Aspok et al. 1980, Koch 1989, Roder 1990, Marggi 1992,

Bense 1995, Hanggi et al. 1995, Seifert 1996, Westrich

1989, Blosch 2000, Duelli et al. 2002a) and from oral

communications of those experts, who had identified the

specimens (Table 4).

Exclusive species �/ species that were sampled exclu-

sively in one of the three categories of fire frequency

(unburnt, single fire, repeated fires).

Scarce species �/ due to the lack of published data on

the relative abundance and rarity of the different species

in Southern Switzerland, scarce species were defined for

the study areas as those species sampled with less than

five individuals.

Threatened species �/ IUCN Red lists (Hilton-Taylor

2000) and analogous lists for Switzerland, Germany and

Austria were used to define the prime species of

conservation concern (Collins and Wells 1987, Speight

1989, Duelli 1994, Gepp 1994, Binot et al. 1998).

Pyrophilous species �/ species that are known to be

fostered by fire events. We considered the list reported by

Wikars (1997).

Table 2. Environmental variables (mean9/SD) sampled at sites with different fire frequency: [C] unburnt, control: sites which didnot burn in the last 30 yr; [S] single fire: sites where fire occurred once in 30 yr; [R] repeated fires: sites where fire occurred 3�/4 timesin the last 30 yr (n�/number of study sites); DBH�/diameter at breast height.

Environmental variables Classes of fire frequency

Unburnt [C] n�/6 Single fire [S] n�/8 Repeated fires [R] n�/8

Tree cover (%) 909/5.5 859/29.7 809/33.5Bush cover (%) 59/6.1 109/5.9 209/7.9Grass cover (%) 89/13.6 149/22.7 339/20.2DBH of dominant trees (cm) 309/0.3 259/0.9 109/0.5Number of shoots per stool per 99/2.6 179/23.2 259/19.8Dead stools per shoot 29/1.2 99/5.4 159/5.7

ECOGRAPHY 27:2 (2004) 175

Data analysis

At a distance of 15�/40 m between traps, we do not

expect any depletion of insects due to the traps. There-

fore the number of specimens caught in the various trap

sites were assumed to be independent of each other

(Obrist and Duelli 1996) and were used as the sample

units in the analysis. Using these data, the mean value

(9/SD) of species richness and number of individuals

were calculated for each class of fire frequency. Analyses

were performed on the overall data set and separately on

the 12 different taxonomic groups representing different

ecological niches and trophic levels.

We analysed the mean number of species and of

individuals (9/SD) per trap site with regard to the three

classes of fire frequency (control, single and repeated

fires) using ANOVA with subsequent Scheffe post-hoc

tests. When the homogeneity of variances was not

Table 4. Total number of species (spp) and individuals (ind) of the 11 taxonomic groups analysed (Table 3), grouped into the fourhabitat guilds. Only the species with specific and well known environmental requirements were classified (IF�/interior forest species,OF�/open forest species, FE�/forest edge species, OL�/open land species).

Taxonomic group Total Habitat guild Total IF-OF-FE-OL

IF OF FE OL

Isopoda spp 12 0 1 4 0 5ind 1.113 0 310 86 0 396

Araneae spp 131 8 50 56 3 117ind 8.061 670 5.453 24 459 6.606

Carabidae spp 37 12 5 10 4 31ind 8.256 5.592 1.482 104 18 7.196

Curculionidae spp 77 12 34 12 15 73ind 8.834 725 4.891 174 57 5.847

Cerambycidae, Buprestidae, Lucanidae spp 53 3 39 10 1 53ind 810 35 508 267 0 810

remaining coleopteran families spp 199 21 106 48 8 183ind 10.912 274 4.280 1.758 209 6.521

Formicidae spp 42 1 10 12 16 39ind 19.614 5.066 2.258 3.007 6.388 16.719

Aculeata without Formicidae spp 284 2 20 154 12 188ind 44.553 14 4.342 27.370 103 31.829

Syrphidae spp 80 3 33 19 4 59ind 2.754 3 988 765 11 1.767

Neuroptera spp 46 0 31 9 0 40ind 2.406 0 843 679 0 1.522

Heteroptera spp 124 4 0 2 8 14ind 3.179 11 0 6 70 87

Total species 1085 66 329 336 71 802Total individuals 110 482 12 390 25 355 34 240 7 315 79 300

Table 3. List of the taxonomic orders and groups considered. For each group a short description of the ecological niche andsampling methods is given.

Order Taxonomic group Ecological niche Sampling methods*

PF WT SE

Isopoda Isopoda (isopods) Saprophagous, epigaeic x xAraneae Araneae (spiders) Zoophagous, epigaeic xColeoptera Carabidae (ground beetles) Mainly zoophagous, epigaeic x x x

Cerambycidae, Buprestidae, Lucanidae(long horn-, jewel- and stag beetles)

Xylophagous at larval stage x x x

Curculionidae (weevils) Phytophagous, flying insects, epigaeic oron vegetation

x x

remaining coleopteran families** Flying or epigaeic insects, polyphagous x xHymenoptera Formicidae (ants) Polyphagous, epigaeic x x

Aculeata without Formicidae (bees, wasps) Flying insects, predators and pollinophagous x xDiptera Syrphidae (hoverflies) Flying insects, pollinophagous x xNeuroptera Neuroptera (lacewings) Flying insects, aphidophagous xHemiptera Heteroptera (bugs) Flying insects and epigaeic, polyphagous x x x

*PF�/pitfall trap, WT�/window trap, SE�/surface eclector**Aderidae, Alleculidae, Anobiidae, Anthicidae, Anthribidae, Attelabidae, Bostrychidae, Byrrhidae, Byturidae, Cantharidae,Choleridae, Chrysomelidae, Ciidae, Cisidae, Cleridae, Coccinellidae, Colonidae, Colydiidae, Cryptophagidae, Cucujidae, Dasytidae,Dermestidae, Derodontidae, Drilidae, Elateridae, Endomychidae, Erotylidae, Eucnemidae, Lagriidae, Lampyridae, Lathridiidae,Leiodidae, Lymexylonidae, Melandryidae, Meloidae, Mordellidae, Mycetophagidae, Nitidulidae, Oedemeridae, Orthoperidae,Pselaphidae, Ptiliidae, Ptinidae, Rhipiphoridae, Rhizophagidae, Salpingidae, Scaphidiidae, Scarabaeidae, Scydmaenidae, Silphidae,Sphindidae, Tenebrionidae, Throscidae, Trogositidae.

176 ECOGRAPHY 27:2 (2004)

achieved even after log-transformation of the data

(Lilliefors test, Systat SPSS) non-parametric Kruskal-

Wallis ANOVA by ranks and Mann-Whitney U-test with

Bonferroni correction between two groups was applied

(Zar 1984). All analyses were performed using Systat 6.0

(Systat, SPSS). The influence of the fire frequency

on species composition was tested by canonical corre-

spondence analysis (ter Braak 1986) using the

program CANOCO 4.0 (ter Braak and Smilauer 1998).

‘‘Geographical coordinates’’ were allocated as co-vari-

ables, in order to control for the geographical location of

the sites (Legendre and Legendre 1998). Most variables

related to forest structures shown in Table 2 were highly

correlated with the fire frequency and were therefore

excluded from the analysis to avoid redundancy. For this

analysis, we considered only those species for which at

least five individuals were sampled. The number of

individuals was log(x�/1)-transformed, in order to

reduce the weight of very abundant species.

Results

Overall biodiversity after the fire

A total of 1085 species were identified, reaching a total

of 110 482 individuals (Table 4); 510 species (47%) were

sampled with 4 or less individuals, while 284 species

(26%) were observed exclusively at one sample site.

The mean number of species per trap site was higher at

repeatedly burnt sites, insignificantly lower at single

burnt sites and significantly smaller at unburnt sites

(Fig. 1). The overall number of individuals tended to

decrease with the increase of the fire frequency, but the

difference was not significant.

Most of the species identified (802 of the 1085) could

be attributed to four habitat types: the pooled samples

included 66 (8.2%) interior forest species, 329 (41.0%)

open forest species, 336 (41.9%) forest edge species, and

71 (8.9%) open land species. ‘‘Interior forest species’’

were affected negatively only at sites burnt once

(Kruskal-Wallis test, n�/66, p�/ 0.039), but did not

differ significantly from the control (no fire) after

repeated fires. ‘‘Open forest species’’ and ‘‘open land

species’’ did not show any significant effects after single

or repeated fires. On the other hand, ‘‘forest edge

species’’ increased with increasing fire frequency

(Kruskal-Wallis test, n�/66, pB/ 0.001) (Table 5). The

same was true for ‘‘forest edge species’’ with regard to

abundance: relative to the control, their numbers of

individuals was increased due to the influence of fires

(Kruskal-Wallis test, n�/66, p�/ 0.002) (Table 5). How-

ever, the overall number of individuals of both ‘‘interior

forest species’’ and ‘‘open forest species’’ decreased

significantly after the fire (Kruskal-Wallis test, n�/66,

pB/ 0.001 and p�/0.008 respectively).

This change in species composition was confirmed

also by canonical correspondence analysis, which in-

dicated that the overall change in species assemblage was

highly correlated with the fire frequency (cor. coef. 0.941)

which explained 11.5% of the overall species variance

(p�/0.005, Monte Carlo test) (Table 6).

Effects of fire on different taxonomic groupsSpecies richness and number of individuals

Figures 2a�/d show that fire frequency affected distinct

taxonomic groups differently. The species richness of 4

groups of the 11 investigated in this study increased at

sites burnt repeatedly, similarly to the results of the

overall biodiversity (Carabidae, Araneae, Syrphidae and

Aculeata without Formicidae). On the other hand,

species richness decreases in Curculionidae, Isopoda

and Formicidae, the latter only at sites which had

experienced a single fire. No significant differences

were observed in several coleopteran families, Neurop-

tera, Heteroptera, and the complex of Cerambycidae-

Buprestidae-Lucanidae.

With regard to the number of individuals, three

taxonomic groups were negatively affected by fire

(Formicidae, Isopoda, diverse coleopteran families),

Fig. 1. Overall biodiversity (speciesrichness [N spp] and number ofindividuals [N ind]; mean per trapsite [t.s.]9/SE) of the 11 differenttaxonomic groups pooled withregard to fire frequency (C�/

unburnt, control; S�/single firesites; R�/repeated fires sites). Barswith different letters aresignificantly different (pB/0.05;ANOVA with subsequent Scheffepost-hoc test).

ECOGRAPHY 27:2 (2004) 177

while higher numbers of individuals were observed in

Araneae at sites repeatedly burnt and in Syrphidae at

sites burnt once. Numbers of individuals did not change

significantly in any of the other groups.

Species composition

Canonical correspondence analysis showed that species

composition of a majority of taxonomic groups (9 of 11)

changed significantly after the fire (Table 6): Carabidae,

Araneae, Aculeata, Formicidae, Isopoda, Cerambyci-

dae-Buprestidae-Lucanidae, Neuroptera, Heteroptera

and other Coleoptera families; only Curculionidae and

Syrphidae did not change significantly. The correlation

coefficients between ‘‘species assemblage’’ and ‘‘fire

frequency’’ varied from 0.660 (Isopoda) to 0.953 (other

Coleoptera), while the variance of the species assemblage

explained by the fire frequency varied from 7.9%

(Curculionidae; not significant) to 15.1% (Formicidae)

(Table 6).

The number of individuals of 29 species of which at

least 50 individuals were sampled varied by at least a

factor of 10 after the fire (Table 7). Three species were

negatively affected by fire, while 26 species were

favoured, 6 of which were sampled only at burnt sites.

The effect of fire frequency on the species richness and

on the number of individuals of different taxa grouped

into the four habitat guilds was mostly similar to that of

the overall biodiversity, except for ‘‘open forest species’’

of some groups (Table 8): the number of the ‘‘open forest

species’’ of Araneae and Aculeata without Formicidae

increased with the increase of fire frequency (Kruskal-

Wallis test, n�/66, p�/ 0.002 and p�/ 0.005 respec-

tively), while those of Formicidae decreased (Kruskal-

Wallis test, n�/66, p�/ 0.003); the number of individuals

of the ‘‘open forest species’’ of ‘‘diverse Coleoptera

families’’ decreased significantly after the fire (Kruskall-

Wallis test, n�/66, pB/ 0.001 respectively).

Effects of fire on scarce, exclusive and/or threatened

(red-listed) species

The number of threatened species was higher at repeat-

edly burnt sites than in unburnt sites (Kruskal-Wallis

test; n�/66; 3.09/1.7 vs 5.09/4.4 species, p�/ 0.041); the

number of exclusive species was also higher at repeatedly

burnt sites than at unburnt sites (Kruskal-Wallis test;

n�/66; 20.09/5.0 vs 25.09/5.8 species, p�/ 0.043). The

overall numbers of individuals did not change in these

groups. The difference in numbers of scarce species after

single and repeated fires was not significant.

Concerning the group of species considered to be

threatened in central Europe, 12.3 and 21.4% were

sampled exclusively at singly and repeatedly burnt sites,

respectively, while 10.8% were collected only at unburnt

sites. We sampled 30 threatened species with �/10

individuals, with a variation of at least a factor of 2

between unburnt and burnt sites (Table 9): 3 species were

negatively affected by fire, 3 other species only by

repeated fires, while the abundance of 24 species

increased after fire (of these, 33% were open forest

species; 42% forest edge species; 25% open land species).

In addition to the above mentioned species, two

pyrophilous species (Wikars 1997) were sampled exclu-

sively at freshly burnt sites: 6 individuals of Aradus

lugubris Fallen 1807 (Heteroptera) and 2 individuals of

Sericoda quadripunctata (De Geer 1774) (Coleoptera:

Carabidae).

Table 5. Effects of fire frequency on species richness (spp) and number of individuals (ind) (mean value per trap site�/SD) of 4habitat guilds of 11 taxonomic groups pooled for a total of 1085 species and 110 482 individuals. Differences among the threecategories of fire frequency (horizontally) were tested using Kruskal-Wallis test. Pairwise comparisons were performed using Mann-Whitney U test by applying Bonferroni correction; values with different letters are significantly different in this test.

Habitat guilds Kruskal-Wallis test p Categories of fire frequency

Unburnt [C] Single fire [S] Repeated fires [R]

Interior forest species spp 0.039 159/0.9 a 139/0.5 b 149/0.6 abind B/0.001 2799/45.3 a 1229/25.7 b 1109/18.5 b

Open forest species spp n.s. 579/1.7 a 609/1.8 a 629/2.0 aind 0.008 6519/58.1 a 4369/30.3 b 5259/51.9 b

Forest edge species spp B/0.001 519/1.9 a 619/2.1 b 649/3.8 cind 0.002 4499/35.4 a 5549/58.5 b 5449/108.8 b

Open land species spp n.s. 69/0.5 a 79/0.8 a 79/0.9 aind n.s. 809/29.8 a 559/47.9 a 659/18.5 a

Fig. 2. (a�/d). Species richness and number (N spp) of individuals (N ind) (mean per trap site [t.s.]9/SE) of the 11 differenttaxonomic groups pooled with regard to fire frequency (C�/unburnt, control; S�/single fire sites; R�/repeated fires sites). ANOVAwith subsequent Scheffe post-hoc test). ANOVA with post-hoc Scheffe test was used when the homogeneity of variances achievedeven log-transformation; in the other cases non-parametric Kruskal-Wallis ANOVA by ranks and Mann-Whitney U-test betweentwo groups was applied. Bars with different letters are significantly different.

178 ECOGRAPHY 27:2 (2004)

ECOGRAPHY 27:2 (2004) 179

Discussion

Overall biodiversity after the fire

Many studies from boreal and tropical forests suggest

that species richness, species composition and number of

individuals of invertebrates change after fire (e.g. Sgar-

delis and Margaris 1993, Yanovsky and Kiselev 1996,

Orgeas and Andersen 2001, Simila et al. 2002), and that

the direct impact of fire depends principally on the fire

intensity (e.g. York 2000, Wikars 2001).

According to several authors (e.g. Muona and Ruta-

nen 1994, Buddle et al. 2000) most of the faunistic

groups recover within a short time in fire-adapted

ecosystems, where the number of species and individuals

tends to be higher during the first few years after the fire

compared to unburnt areas. This was confirmed by our

studies of fast-spreading surface fires in winter time on

the southern slope of the Swiss Alps, where repeated

fires in particular seem to favour the overall species

richness without significant influence on the number of

individuals. Nevertheless, after repeated fires the shift of

dominant numbers of individuals of ‘‘interior forest

species’’ (�/53.7%) to ‘‘forest edge species’’ (�/29.5%)

suggests that the current distribution and abundance of

species, such as those of the forest interior, could have

been historically limited first by fire, and later, up to the

middle of the last century, by intensive forest manage-

ment (Focarile 1987). The present species composition of

invertebrates in the forests of the southern Alps seems to

be the result of adaptation to disturbance.

Effects of fire on different taxonomic groups

Fire affects the different layers (litter, herbs, shrubs and

canopy) and taxonomic groups of the forest differen-

tially (Prodon et al. 1987, Nunes et al. 2000 for a review).

Our data show that fast spreading winter fires on the

southern slope of the Alps affect litter-dwelling groups

(Isopoda, Curculionidae, Formicidae, some families of

the Coleoptera) negatively. This was also observed by

other authors in different forest ecosystems, such as

boreal forests in Scandinavian or dry Eucalyptus forests

in Australia (e.g. Sgardelis and Margaris 1993, York

1999, Nunes et al. 2000), and is probably due to the loss

of litter and the lethal surface temperatures during the

fire (up to 7008C; Marxer 2002). Ananthakrishnan

(1996) suggested that structure, composition and the

chemical and physical properties of the litter are

important for the species assemblage of litter dwelling

communities, which agrees with the low resilience of

these communities observed by other authors (e.g.

Huhta 1979, Prodon et al. 1987, York 1999, Nunes et

al. 2000 for a review). Therefore, in the case of short

intervals between fires (7�/10 yr in our study at sites

repeatedly burnt), the litter hardly recovers, and condi-

tions remain unstable.

On the other hand, we observed a positive effect on

epigaeic and mobile groups, in particular with Araneae

and Carabidae. Many authors suggest that these groups,

after having been reduced during the fire, increase

quickly by profiting from abundant food in the post-

fire mosaic of ground habitats (Reed 1997, Dajoz 1998,

Buddle et al. 2000, Moretti et al. 2002a).

The post-fire conditions of herbs, shrubs and trees

seem to favour heliophilous and floricol insects (e.g.

Aculeata and Syrphidae). They profit from the reduced

tree cover and the higher number of flowering plants,

which resprout vigorously after the fire season (Moretti

et al. 2002b). This is in contrast to Ne’eman et al. (2000)

and Potts et al. (2001), who observed a negative effect of

fire on flower-visiting insects in Israel, where fires occur

in summer time when vegetation and insects are already

active.

Our results show that repeated fires influence the

species composition of flying insects (e.g. Neuroptera,

Heteroptera, Cerambycidae, Lucanidae and Bupresti-

dae) favouring the mobile heliophilous and thermophi-

lous species, but without affecting the number of species

and individuals. This is partially in accordance with

studies on similar phytophagous and wood-eating

Table 6. Variance of the species composition explained by the ‘‘fire frequency’’ as environmental variable and by ‘‘geographicalcoordinates’’ as covariables. (‘‘Spp-Fire frequency’’ correlation�/correlation between species assemblage and fire frequency; %var�/percent of the variance of the species assemblage explained by the number of fires; p�/probability of the Monte Carlo testimplemented in the canonical correspondence analysis; *�/see Table 2).

Taxonomic group ‘‘Spp-Fire frequency’’ correlation % var p

All taxonomic groups 0.941 11.5 0.005Carabidae 0.801 9.1 0.045Araneae 0.909 10.8 0.005Syrphidae 0.867 8.0 n.s.Aculeata whithout Formicidae 0.928 12.2 0.005Curculionidae 0.864 7.9 n.s.Isopoda 0.660 11.6 0.015Formicidae 0.751 15.1 0.005Cerambycidae, Buprestidae, Lucanidae 0.850 13.9 0.005Neuroptera 0.807 13.8 0.005Heteroptera 0.893 12.5 0.005remaining coleopteran families* 0.953 10.8 0.005

180 ECOGRAPHY 27:2 (2004)

Tab

le7

.S

pec

ies

mo

reth

an

10

tim

esa

sab

un

dan

ta

)in

un

bu

rnt

site

s(C

)a

sin

sin

gle

bu

rnt

site

s(S

)o

rin

rep

eate

db

urn

tsi

tes

(R);

b)

inS

or

inR

as

inC

.T

he

tab

leco

nsi

der

so

nly

the

spec

ies

for

wh

ich

atle

ast

50

ind

ivid

ua

lsw

ere

sam

ple

d.

Hab

itat

gu

ild

s:IF

�/in

teri

or

fore

stsp

ecie

s,O

F�

/op

enfo

rest

spec

ies,

FE�

/fore

sted

ge

spec

ies,

OL�

/op

enla

nd

spec

ies,

U�

/

ub

iqu

ist,

?�

/un

kn

ow

n.

Sp

ecie

sG

rou

pF

ire

freq

uen

cyH

abit

at

gu

ild

un

bu

rnt

site

sC

(n�

/6)

sin

gle

fire

S(n�

/8)

rep

eate

dfi

res

R(n�

/8)

a)

Sp

ecie

sn

egat

ivel

ya

ffec

ted

by

sin

gle

an

dre

pea

ted

fire

sL

epto

tho

rax

ny

lan

der

iF

orm

icid

ae

37

09

12

00

15

7IF

Kle

idoce

rys

rese

da

eH

eter

op

tera

56

56

84

6?

En

icm

us

min

utu

sC

ole

op

tera

div

.6

97

5U

b)

Sp

ecie

sfa

vou

red

by

fire

Excl

usi

ve

spec

ies

atb

urn

tsi

tes

Fo

rmic

ap

rate

nsi

sF

orm

icid

ae

68

OL

Sci

odre

po

ides

wa

tso

ni

Co

leo

pte

rad

iv.

56

UO

riu

sh

orv

ath

iH

eter

op

tera

70

10

9?

Fo

rmic

asa

ng

uin

eaF

orm

icid

ae

21

54

FE

Ch

loro

ph

oru

sfi

gu

ratu

sC

er-B

ub

-Lu

c5

75

FE

Ste

no

pte

rus

rufu

sC

er-B

ub

-Lu

c1

86

1F

ES

pec

ies

favo

ure

db

y:

�/re

pea

ted

fire

sM

yrm

ica

rugin

odis

Fo

rmic

ida

e4

76

11

39

OF

Oed

emer

afl

avi

pes

Co

leo

pte

rad

iv.

53

63

96

OL

La

siu

sp

sam

mo

phil

us

Fo

rmic

ida

e1

04

91

83

OL

Hy

laeu

sg

ibb

us

Acu

leata

45

21

27

FE

Lep

tura

ma

cula

taC

er-B

ub

-Lu

c5

35

10

2O

FM

yrm

ica

sabule

tiF

orm

icid

ae

31

71

04

FE

Try

pox

ylo

nm

inu

sA

cule

ata

31

69

8F

EM

ica

ria

fulg

ens

Ara

nea

e6

15

81

OF

Pem

ph

red

on

ino

rna

taA

cule

ata

11

65

8F

EH

op

lia

fari

nosa

Co

leo

pte

rad

iv.

14

52

FE

Zo

rasp

inim

an

aA

ran

eae

46

46

OF

Ara

chn

osp

ila

spis

saA

cule

ata

23

48

?A

gri

lus

an

gust

ulu

sC

er-B

ub

-Lu

c2

15

33

OF

� /si

ng

lefi

res

Dip

lost

yla

conco

lor

Ara

nea

e5

11

01

0F

EL

asi

ogl

oss

um

rufi

tars

eA

cule

ata

36

82

1O

FD

icy

ph

us

erra

ns

Het

ero

pte

ra1

59

10

?S

pec

ies

favo

ure

db

ysi

ng

lea

nd

rep

eate

dfi

res

Hy

laeu

sco

mm

un

isA

cule

ata

95

86

89

4F

E

Co

rtic

ari

afe

rrug

inea

Co

leo

pte

rad

iv.

13

27

42

92

OF

Xy

lota

seg

nis

Sy

rph

ida

e1

22

33

14

8O

FS

ph

aer

op

ho

ria

scri

pta

Sy

rph

ida

e4

51

48

FE

ECOGRAPHY 27:2 (2004) 181

groups after disturbance (Barbalat and Getaz 1999,

Golden and Crist 1999, Di Giulio Muller 2000).

Exclusive, scarce and threatened species

Many authors (e.g. Goldammer et al. 1997, Bengtsson et

al. 2000, Simila et al. 2002) suggested that fire favours

the biodiversity, not only by increasing the species

richness, but also by favouring scarce and threatened

species. Our data confirm that burnt and particularly

repeatedly burnt sites host more scarce and endangered

species than unburnt sites. Only Aphaenogaster subterra-

nea (Latreille 1798) (a red-listed species in Switzerland)

might be locally threatened by repeated fires, being a

species that avoids open land and xeric conditions. This

contrasts to the results of other authors (Springett 1976,

Økland 1994, Yanovsky and Kiselev 1996, York 1998),

which argue that fire can seriously threaten endangered,

endemic, and other scarce species. From the list of

threatened species found in our study it is clear that fire

tends to favour species of forest edge habitats and of

open land, which are nowadays endangered by forests

closing in, and the intensive management and urbanisa-

tion of the open land close to the forest (Collins and

Wells 1987, Speight 1989, Duelli 1994, Gepp 1994, Binot

et al. 1998).

The old-growth species and those intolerant to

disturbance might already have disappeared from the

southern slopes of the Alps a long time ago, as observed

in many forests in Europe (e.g. Speight 1989, Økland

1994, Schiegg 2001, Grove 2002).

In our study sites, the presence of only 8 individuals of

two pyrophilous species, both red list species in Switzer-

land, has to be considered as poor if compared to post-

fire data published from boreal forests (Wikars 1997,

Dajoz 2000 for a review). Nevertheless, Wikars (1997)

suggests that knowledge about pyrophilous species of

southern Europe is very scarce. It is also likely that

pyrophilous species related to winter fires differ from

those of regions where fires occur in summer time. Better

knowledge of the Mediterranean pyrophilous species

and those related to winter fire regimes is therefore

needed.

Implications for management and conservation

Recently, the role of natural hazards such as windthrow,

fire, landslides, as well as that of management such as

clearing, logging, and thinning have been reinterpreted

from the viewpoint of disturbance ecology, biodiversity,

and species conservation (e.g. Wermelinger et al. 1995,

Granstrom 1996, Goldammer et al. 1997, Barbalat 1998,

Kirby and Watkins 1998, Duelli and Obrist 1999,

Trabaud 2000, Bengtsson et al. 2000, Floren and

Linsenmair 2001, White and Jentsch 2001, Wohlgemuth

et al. 2002). The authors highlight the conservation value

of the first stage of natural succession with large

amounts of dead wood, even old growth forests, because

this stage maintains a different species composition

Table 8. Effects of fire frequency on species richness (spp) and number of individuals (ind) of 11 faunistic groups and of alltaxonomic groups (Table 2) (Effect ‘‘�/’’: the number of species or individuals increases significantly by increasing of fire frequency;‘‘B/’’: the number decreases significantly; ‘‘�/’’: the variation is negligible). Significance of the effect of the fire frequency byKruskal�/Wallis test: * pB/0.05, ** pB/0.01, *** pB/0.001, n.s. not significant. Isopoda and Heteroptera do not appear, because thedata set was too small.

Taxonomic group Interior forestspecies

Open forestspecies

Forest edgespecies

Open landspecies

Effect p Effect p Effect p Effect p

All groups spp B/ * �/ n.s. �/ ** �/ n.s.ind B/ *** �/ ** �/ ** �/ n.s.

Carabidae spp B/ * �/ *** �/ n.s. �/ n.s.ind �/ n.s. �/ n.s. �/ * �/ n.s.

Araneae spp B/ * �/ ** �/ *** �/ n.s.ind B/ ** �/ ** �/ ** �/ n.s.

Syrphidae spp �/ n.s. �/ n.s. �/ ** �/ n.s.ind �/ n.s. �/ ** n.s. n.s. �/ n.s.

Aculeata without Formicidae spp �/ n.s. �/ * �/ ** �/ n.s.ind �/ n.s. �/ n.s. �/ ** �/ n.s.

Curculionidae spp B/ * �/ n.s. �/ n.s. �/ n.s.ind B/ *** �/ n.s. �/ n.s. �/ n.s.

Formicidae spp �/ n.s. B/ ** �/ n.s. �/ n.s.ind B/ *** �/ n.s. �/ n.s. �/ n.s.

Remaining coleopteran families spp �/ n.s. �/ n.s. �/ n.s. �/ n.s.ind �/ n.s. B/ *** �/ n.s. �/ n.s.

Neuroptera spp �/ n.s. �/ n.s. �/ n.s. �/ n.s.ind �/ n.s. �/ n.s. �/ n.s. �/ n.s.

Cerambycidae, Buprestidae, Lucanidae spp �/ n.s. �/ n.s. �/ * �/ n.s.ind �/ n.s. �/ n.s. �/ * �/ n.s.

182 ECOGRAPHY 27:2 (2004)

Tab

le9

.T

hre

aten

edsp

ecie

sin

cen

tral

Eu

rop

e(r

ed-l

iste

din

atle

ast

on

eo

fth

efo

llo

win

gco

un

trie

s:G

erm

an

y,A

ust

ria,

Sw

itze

rlan

d)

mo

reth

an

twic

ea

sab

un

da

nt

a)

inu

nb

urn

tsi

tes

(C)

as

insi

ngle

bu

rnt

site

s(S

)a

nd

inre

pea

ted

lyb

urn

tsi

tes

(R);

b)

inC

an

dS

as

inR

;c)

inS

an

d/o

rR

as

inC

.T

he

tab

leco

nsi

der

so

nly

the

spec

ies

for

wh

ich

at

least

10

ind

ivid

ua

lsw

ere

sam

ple

d.

Hab

itat

gu

ild

s:IF

�/in

teri

or

fore

stsp

ecie

s,O

F�

/op

enfo

rest

spec

ies,

FE�

/fore

sted

ge

spec

ies,

OL�

/op

enla

nd

spec

ies,

?�

/un

kn

ow

n;

*�

/py

rop

hil

ou

ssp

ecie

s(W

ika

rs1

99

7).

Sp

ecie

sG

rou

pF

ire

freq

uen

cyH

abit

at

gu

ild

un

bu

rnt

site

sC

(n�

/6)

sin

gle

fire

S(n�

/8)

rep

eate

dfi

res

R(n�

/8)

a)

Sp

ecie

sn

egat

ivel

ya

ffec

ted

by

sin

gle

an

dre

pea

ted

fire

sP

edia

cus

der

mes

toid

esC

ole

op

tera

div

.4

21

65

OF

Ca

eno

cara

aff

inis

Co

leo

pte

rad

iv.

22

11

2O

FS

ym

ph

ero

biu

sk

lap

ale

ki

Neu

rop

tera

15

72

OF

b)

Sp

ecie

sn

egat

ivel

ya

ffec

ted

by

rep

eate

dfi

res

Ap

ha

eno

gast

ersu

bte

rra

nea

Fo

rmic

ida

e7

44

72

43

FE

An

dre

na

com

bin

ata

Acu

leata

14

18

1F

ES

coti

na

cela

ns

Ara

nea

e1

18

1F

Ec)

Sp

ecie

sfa

vou

red

by

fire

Excl

usi

ve

spec

ies

at

bu

rnt

site

sF

orm

ica

pra

ten

sis

Fo

rmic

ida

e6

8O

LC

ala

thu

sru

bri

pes

Ca

rab

ida

e4

7O

FT

ap

ino

ma

am

big

uu

mF

orm

icid

ae

18

OL

Sil

ph

aca

rin

ata

Co

leo

pte

rad

iv.

15

FE

Fo

rmic

asa

ngu

inea

Fo

rmic

ida

e2

15

4F

EC

hlo

rop

horu

sfi

gu

ratu

sC

er-B

ub

-Lu

c5

75

FE

Ca

llim

us

an

gula

tus

Cer

-Bu

b-L

uc

41

5O

FZ

elo

tes

ereb

eus

Ara

nea

e1

14

FE

Xa

nto

chro

aca

rnio

lica

Co

leo

pte

rad

iv.

78

OF

Do

lich

od

eru

sq

ua

dri

pu

nct

atu

sF

orm

icid

ae

68

OF

Enic

mu

sa

tric

eps

Co

leo

pte

rad

iv.

64

OF

My

rmic

alo

na

eF

orm

icid

ae

46

FE

An

dre

na

curv

un

gula

Acu

leata

55

FE

Ara

du

slu

gu

bri

s*H

eter

op

tera

33

?P

on

era

coa

rcta

taF

orm

icid

ae

17

2O

FS

eric

od

aq

ua

dri

pun

cta

ta*

Ca

rab

ida

e2

?S

pec

ies

favo

ure

db

y:� /

rep

eate

dfi

res

Lasi

ogl

oss

um

pyg

ma

eum

Acu

leata

41

31

241

OL

Ha

lict

us

sub

au

ratu

sA

cule

ata

11

13

OL

Hy

laeu

sd

iffo

rmis

Acu

leata

16

12

FE

Ca

llil

epis

no

ctu

rna

Ara

nea

e1

51

2O

FC

on

op

alp

us

test

ace

us

Co

leo

pte

rad

iv.

36

19

OF

An

tha

xia

fun

eru

laC

er-B

ub

-Lu

c1

39

OL

Dio

des

ma

sub

terr

an

eaC

ole

op

tera

div

.1

36

OF

�/si

ng

lefi

res

Dei

lus

fug

ax

Cer

-Bu

b-L

uc

11

51

FE

Sp

ecie

sfa

vou

red

by

fire

Lasi

ogl

oss

um

min

utu

lum

Acu

leata

45

864

628

FE

Lasi

us

mer

idio

nali

sF

orm

icid

ae

19

9O

L

ECOGRAPHY 27:2 (2004) 183

compared to closed forests (Duelli et al. 2002b), includ-

ing many threatened species of both early and late

successional stages (Simila et al. 2002, Sippola et al.

2002).

The forests in fire-prone regions on the southern slope

of the Alps consist of a mosaic of small burnt sites in

different successional stages, alternating with large areas

of intact forest. In fact, in the past 30 yr, only 10% of the

gaps impacted by fires were �/1.8 ha in southern

Switzerland (Conedera et al. 1996). Similar conditions

seem to be ideal for both saproxylic and non-saproxylic

species, which profit from a large gradient of environ-

mental and trophic conditions (Moretti et al. 2002a,b).

Nowadays, fires in southern Switzerland are seen as a

major threat to the natural succession of the chestnut

forest towards mixed stands, to protection against

erosion and, very importantly from a psychological

and financial standpoint, to the life and property of

local residents and tourists. Therefore, intensive and

expensive measures are taken to prevent and fight fires

under all circumstances.

On the other hand, the long fire history of the

deciduous forests on the southern slope of the Alps

has led to an evolutionary process where natural and

human-induced disturbances interacted for a long per-

iod if time. The result today is an adapted fauna with a

varied spectrum of species which, to different extents, are

negatively or positively influenced by sporadic or regular

fires.

Any attempt to prevent all fires would require a form

of management in which dead wood is strictly removed,

as in earlier times when harvesting chestnut timber was

still profitable. Apart from creating enormous costs, such

a procedure would threaten many fire adapted species,

which depend on dead wood and favour open, sunny

habitats (Simila et al. 2002).

Similarly, logging or clear-cutting of large areas, where

all the wood is removed, has a negative impact on

biodiversity and should be avoided (Speight 1989,

Økland 1994, Grove 2002).

Prescribed burns a measure to prevent fire cannot be

proposed due to the high risk of erosion and landslide in

the densely inhabited areas of the hilly region south of

the Alps (Marxer et al. 1998, Providoli et al. 2002). After

all, what can be done to minimize both, the damage to

people created by fire and the damage to biodiversity

created by preventing fires?

We suggest a forest management which attempts to

mimic frequent disturbance of low intensity in fire-prone

locations, with short clear-cut rotations on small areas

where part of the cut and dead wood is left. At the same

time, old forest stands should be preserved, which

provide optimal habitat for the less mobile and steno-

topic species of the mid- and last successional stages

(Gandhi et al. 2001).

A mosaic forest with temporary, small gaps of

different successional stages can sustain a high biodi-

versity and at the same time allows for selective manage-

ment in areas of high risk of fire. This asks for a supra-

regional coordination of forest management plans in the

southern part of Switzerland.

Acknowledgements �/ We would like to thank M. Zanini forhelping in data analysis and M. Conedera for his comments onthe manuscript. Many thanks are due to the various personswho helped in the fieldwork (P. Hordegen, P. Wirz, F. Fibbioli,K. Sigrist) and who identified or checked the species (F. Amiet,S. Barbalat, R. Barfuss, C. Besuchet, C. Germann, I. Giacalone,A. Hanggi, X. Heer, P. Hordegen, O. Monga, P. Stucky, D.Wyniger, P. Zahradnik).

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