This study of the saproxylic beetles and the dead wood in 4 alpine forests shows that the
        saproxylic communities are individualized according to the geographical area. The type of dead wood is a
        key parameter of this distribution. Softwood gathers mostly xylophagous species while hardwood is occupied
        by mycophagous and zoophagous taxa. Our data underline the theoretical relationship between quantity
        of habitat and biological diversity because the number of woody fragments is explaining the taxonomical
        diversity better than the total volume doesCette étude des coléoptères saproxyliques et du bois mort dans 4 forêts alpines montre que les communautés saproxyliques présentent de fortes
        individualités correspondant au secteur géographique mais également aux types d'essences en présence. La distinction se fait entre taxons vivant à partir des bois de feuillus (principalement des mycophages et des saproxylophages) et de résineux (principalement des xylophages). Nos données
        confortent la relation théorique entre la quantité d'habitat et la diversité biologique puisque le nombre de fragments ligneux explique mieux la richesse taxinomique que le volume total

DODELIN, Benoit

I-Revues

Rev. Écol. (Terre Vie), suppt. 10, 2008.
 – 55  –
ASPECTS OF THE REPARTITION OF THE SAPROXYLIC BEETLES IN FORESTS 
(FRENCH ALPS)
Benoît DODELIN1
RÉSUMÉ. — Aspects de la répartition des coléoptères saproxyliques en forêt (Alpes françaises). — Cette 
étude des coléoptères saproxyliques et du bois mort dans 4 forêts alpines montre que les communautés 
saproxyliques présentent de fortes individualités correspondant au secteur géographique mais également 
aux types d’essences en présence. La distinction se fait entre taxons vivant à partir des bois de feuillus 
(principalement des mycophages et des saproxylophages) et de résineux (principalement des xylophages). 
Nos données confortent la relation théorique entre la quantité d’habitat et la diversité biologique puisque le 
nombre de fragments ligneux explique mieux la richesse taxinomique que le volume total.
Mots-clés: Quantité d’habitat, bois mort, coléoptères saproxyliques
SUMMARY. — This study of the saproxylic beetles and the dead wood in 4 alpine forests shows that the 
saproxylic communities are individualized according to the geographical area. The type of dead wood is a 
key parameter of this distribution. Softwood gathers mostly xylophagous species while hardwood is occu-
pied by mycophagous and zoophagous taxa. Our data underline the theoretical relationship between quantity 
of habitat and biological diversity because the number of woody fragments is explaining the taxonomical 
diversity better than the total volume does.
Keywords: Habitat quantity, dead wood, saproxylic coleoptera
Dead wood is a key habitat largely threatened by forest activities (Ehnström, 2001). 
Indeed, trunk export is short-circuiting the cyclic development of the forest by excluding three 
essential phases from the forested stand: over-maturity, senescence and death (Odum, 1989; 
Christensen & Emborg, 1996; André, 1997). The reduction of dead wood availability is one 
of the main threats pressing on the saproxylic beetles, a particularly abundant and diversifi ed 
group of insects. In Sweden for example, the beetle red list includes nearly 50% of forest spe-
cies among which 85% are saproxylic (Jonsell et al., 1998).
An effective management of dead wood and its biodiversity in commercial forests needs 
the development of new procedures and a good knowledge of these two elements. Many 
authors have already proposed some adapted modes of management but frequently these ones 
are related to a local context or to particular types of dead wood (Davies et al., 2006). For 
example, Lindhe et al. (2005) have focused on the interest of high-stumps creation for the 
saproxylic beetles. Thus, these investigations are far from being completed. It is necessary to 
increase our knowledge on both dead wood and saproxylic insects if one wishes to manage 
these two elements as well as possible.
1 40 avenue Jean Jaurès. F-69007 Lyon. E-mail: benoit.dodelin@laposte.net
 – 56  –
This study aims to know better the ecology of the saproxylic beetles, i.e. the relations they 
establish with dead wood stocks. The following questions were approached:
(1) Are abundance and species richness related to dead wood amount? We investigated 
this aspect for the total volume of dead wood and for the number of dead woody elements.
(2) How are saproxylic beetles distributed among forests differing in fuel composition and 
in management history? Are some species restricted to special forest types?
STUDY AREA
The study sites are located in the north of the French Alps. In this area, slope, economic context and geography 
are currently unfavourable to the wood sale. In the least accessible sectors, the accumulation of living or dead wood is 
substantial (Ministère de l’agriculture et de la pêche, 2000; Vallauri & Poncet, 2002; Dodelin et al., 2004).
Ten stations were selected in four forests. These sites have important dead wood stocks and forest continuities 
(canopy cover) are more than 200 years old (Tab. I). The stations were preferably chosen in the old phases of the forest 
cycle, which are interesting for their high content of dead wood (Siitonen et al., 2000; Carmona et al., 2002). Three 
forests belong to the beech complex and one to the spruce forests group (Ozenda, 1985).
TABLE I
Study sites (stations) with a short description of the works carried out
Forest Coordinates
CORINE
and (Bear)
classifi cations
Dominant trees
(ordered 
according
to dominance)
Station
Maturity and 
brief history
Number 
of
window 
traps
Transects 
for the
dead wood
inventory
La Charmette
N: 45,324
E: 05,737
Z: 1300
42.1 & 42.2
(13-F5b)
Picea abies
Abies alba
Fagus sylvatica
C1
Selective logging. Last 
management in 2002 
(1 year before this study)
4
Parallels 
(0,599 ha)
C2
Selective logging. Last 
management in 1997 
(6 years before this study)
3
Parallels 
(0,104 ha)
Les Écouges
N: 45,185
E: 05,510
Z: 
1050-1300
41.1, 41.4
& 42.2
(13-F5b)
Picea abies
(plantation)
E1 Old growth forest 2
Crossed 
(0,081 ha)
E2 Mature plantation 2
Crossed 
(0,080 ha)
Fagus sylvatica
Picea abies
E3
Intensively logged approx. 
5 years before this study
2
Crossed 
(0,072 ha)
E4
Old growth forest. Last 
management approx 
20 years before this study
2
Crossed 
(0,086 ha)
Fagus sylvatica
Picea abies
Abies alba
Quercus sp.
E5 Young stand 2
Crossed 
(0,080 ha)
Méolans-Revel
N: 44,388
E: 06,485
Z: 
1200-1650
42.2
(1-D9)
Picea abies
Abies alba
Pinus sylvestris
Larix decidua
Quercus sp.
Salix sp.
M1
Old growth forest. Last 
management >50 years
5
Parallels 
(0,264 ha)
M2
Old growth forest. Last 
management >50 years
4
Parallels 
(0,260 ha)
Rhonne
N: 45,659
E: 06,407
Z: 650-1000
42.1 & 42.2
(13-F5b)
Picea abies
Abies alba
Fagus sylvatica
R1
Selective logging. Old 
growth forest. Last 
management in 1988 
(25 years before this study)
6
Parallels 
(0,300 ha)
 – 57  –
METHODS
Our working principle was an inventory of the dead wood and a sampling of the saproxylic beetles in the same 
stations.
DEAD WOOD STOCK INVENTORY AND FOREST DESCRIPTION
Dead wood inventory was realized with the strip surveying method (Ståhl et al., 2001). Transects were 100 to 
250 m long and 2 m wide. In forests which are heterogeneous at a large scale they were installed along orthogonal 
crosses; this in order to inventory approximately 1-ha homogeneous sectors (homogeneity in terms of dead wood, forest 
structure and type). In the relatively homogeneous forests, transects were placed on parallel lines separated by 100 m.
The pieces of dead wood were measured if at least one diameter equalized or exceeded 7.5 cm for the standing dead 
trees and 10 cm for the other fragments. The number of elements and the total volume of dead wood per hectare were 
noted (see Dodelin et al. (2004) and Dodelin (2006) for more details).
Forest description variables used were the forest type, the history of the management and the stand structure.
DATA CONCERNING SAPROXYLIC BEETLES
Saproxylic beetles sampling was realized with 32 window traps, a systematic system with no favoured direction. 
These very effective traps are described at length in the entomological literature (Økland, 1996; Brustel, 2001, 2003). 
The traps were emptied every fi fteen days from the end of spring to autumn in each of the 10 stations. 
Specimen identifi cation was detailed at least to the family for the beetles and to the species for saproxylic beetles. 
Some families with delicate taxonomy were identifi ed by E. De Laclot (Scolytidae) and L. Micas (Buprestidae, 
Cerambycidae). Four taxonomical groups were used to gather the species which are diffi cult to separate: Cis (Ciidae) 
differing from C. boleti (Scopoli), Enicmus (Corticariidae) differing from E. testaceus (Stephens), Cartodere differing 
from C. nodifer (Westwood) and the others Corticariidae. 
The ecology of each species is taken from the Nordic Database, a database coordinated by J. Stokland, that is 
synthesizing most of the entomological works published for Finland, Norway and Sweden (see: http://www.saproxylic.
org/). A broad French entomological bibliography and our personal data were used to complement the Nordic 
Database.
STATISTICAL METHODS
The univariate relations were explored by means of linear regressions to account for the effect of the volume of 
dead wood and the number of dead wood pieces on individual abundance and taxonomic richness.
To explore the link between species and forest types and management history, we used the IndVal software 
provided by Dufrêne & Legendre (1997). For each species i in each site group j, the IndVal program computes the mean 
abundance of species i in the sites of group j (Aij) compared to all groups in the study, by Bij, the relative frequency of 
occurrence of species i in the sites of group j, as follows: 
Aij = N individuals ij / N individuals i
Bij = N sites ij/ N sites j
IndValij = Aij * Bij * 100
Where IndVal is the Indicator Value of species i in site cluster j.
RESULTS
More than 445 beetles species (8137 individuals) were counted, among which 198 taxa 
belonged to the saproxylic group (almost the same number of species) with 3483 individuals.
The relation between abundance of individuals and quantities of dead wood (volume or 
number of fragments) is positive but the regression coeffi cients are low (R2 = 0.097 for the 
number of fragments and R2 = 0.127 for the volume, see Fig. 1).
On the other hand, the relation is clearer between the taxonomic richness and the number 
of elements (R2 = 0.335) while the volume seems to have a minor effect on the taxonomic rich-
ness (R2 = 0.175). 
In this fi rst analysis, dead wood stocks characteristics of all forest types have been melted. 
One can expect that saproxylic species are occurring only in forests where suitable dead wood 
is present. That means for example forests with dead wood of the right host tree.
To investigate the infl uence of forest types on saproxylic beetles distribution, we used the 
IndVal program and selected all maximal individual values equal or superior to 50% and statis-
tically signifi cant at 5%. These indicator species ranged as fi gured in Fig. 2.
 – 58  –
Figure 1. — Linear regressions between the dead wood volume/ha (VTOT), the number of pieces of dead wood/ha 
(NTOT), the abundance (ABOND) and the taxonomic richness (RICHTAX).
Figure 2. — Distribution of indicator species between forests types after the IndVal routine. Only species with 
IndVal ≥ 50% and statistically signifi cant at 5% level are shown.
 – 59  –
Species composition of forest types is strongly different between mixed forests with beech 
and spruce dominated forests without beech. Beech mixed forest are represented by species 
like Ampedus erythrogonus, Cerylon ferrugineum, Ptilinus pectinicornis, etc. while coniferous 
forests are dominated by Ampedus praeustus, Melanotus castanipes, Mycetochara thoracica, 
fi ve Scolytidae and associated species, two Cerambycidae. In this second forest type, some spe-
cies have a preference for the boreal climatic conditions while no species can be related to the 
more temperate part of the forest located at the slope base. Some of these species, like Xylita 
livida, are known to be boreal species.
Because of the lack of sampling replication in this study, mainly due to the weak quantity 
of traps, it is diffi cult to get detailed information with the IndVal method. Species belonging to 
the genus Enicmus are largely distributed among plantations and stands cut ten or twenty years 
before. Coxelus pictus and Hylis olexai seem to prefer recently cut stands with a strong man-
agement pressure. In these places, most of the woody debris is sun exposed because the canopy 
is largely open (this is not true for the stand managed with selective logging). Like these two 
species, the Eucnemid Xylophilus corticalis is indicating managed stands (i.e. regularly man-
aged). This may surprise because this species is regularly found in stands with large amount of 
dead wood (Dodelin et al., 2003). It must be noticed that these managed stands contain quanti-
ties of dead wood largely superior to what is usually observed in low altitude forests. It is a case 
of an artifi cial large supply of dead wood consecutively to wood exploitation.
DISCUSSION
The total volume of dead wood is used by many authors as a measurement of the diversity 
of the resources available for the saproxylic beetles. A traditional interpretation states that the 
habitats are multiplied when the total volume of dead wood increases at the forest scale or also 
at the dead wood fragment scale (Hilt & Ammer, 1994). This may enhance the possibilities of 
coexistence for the species. Thus, in the presence of greater quantities of dead wood one can 
expect to observe a greater diversity of saproxylic beetles (Sprecher-Uebersax, 1989; Økland 
et al., 1996; Welti, 1998; Endrestøl, 2003). In our study, it seems that this relation is verifi ed 
once again, since the number of dead wood elements, expressing the diversity of the dead wood 
habitats more precisely than the volume, is positively correlated with the taxonomic richness.
We showed that the forests had a strong individuality corresponding to the fuel composi-
tion and, in this particular study design, geographical area (because spruce forests are located 
in the centre of the Alps while mixed beech forests are on the Alps border). We have shown 
that it exists indicator species for each of these two forest types. Few taxa are related to banal 
forest stands like plantations. Some species belong expressly to the managed forests, indicating 
that the special features of mountain forests management, namely leaving on the fl oor stumps, 
branches and trunks parts with no commercial value, can have a positive impact on specifi c 
saproxylic beetles.
In the saproxylic beetles, the specifi city for a host plant is more frequent in the groups 
initiating the disorganization of wood, which are mainly the xylophagous organisms. It is for 
example the case of the Scolytidae (Chararas, 1986). This specifi city seems to decrease when 
the decomposition advances. In the Swedish red list of saproxylic beetles, the most recent 
decomposition class includes signifi cantly more monophagous species than the second (43% 
against 31%) which includes some more than the third class (23%), the latter similar to the 
fourth class (Jonsell et al., 1998). According to these reports, our observation of preferences 
for forest types raises new questions. For example, do mixed coniferous forests host more 
monophagous species than forests composed by broadleaved and coniferous trees? Are species 
hosted by hardwood mainly dependent on lignicolous fungi or on the fuel type of their woody 
hosts? Solving these questions will indubitably require more researches.
 – 60  –
ACKNOWLEDGEMENTS
This work was partly funded by the Conseil Général de l’Isère (Écouges forest), the National forest offi ce, the 
European Union, the Provence-Alpes-Côte-d’Azur region and the Alpes-de-Haute-Provence departement (Objective 2 
UE program in the Méolans forest).
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Aspects de la répartition des coléoptères saproxyliques en forêt (Alpes françaises)

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Aspects de la répartition des coléoptères saproxyliques en forêt (Alpes françaises)

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