ORIGINAL PAPER

Conflict between insect conservation and public safety: the casestudy of a saproxylic beetle (Osmoderma eremita) in urban parks

Giuseppe Maria Carpaneto • Adriano Mazziotta •

Giorgia Coletti • Luca Luiselli • Paolo Audisio

Received: 21 July 2009 / Accepted: 17 February 2010 / Published online: 4 March 2010

� Springer Science+Business Media B.V. 2010

Abstract Urban parks can harbour small populations of

saproxylic insects of high conservation concern, such as

Osmoderma eremita and other rare beetles. These areas

often host old trees which have become very uncommon in

rural areas where they are threatened by commercial for-

estry management procedures based on frequent tree cut-

ting. Nevertheless, old trees of urban parks may represent a

hazard for public safety and are sometimes cut by man-

agement authorities. The aim of this work was to assess the

loss of reproductive sites for saproxylic beetles of the

Scarabaeidae, Lucanidae and Cerambycidae, when felling

plans are adopted according to a Visual Tree Assessment

Procedure (VTA), in a Mediterranean urban park. On July–

August 2004, 1,247 holm oaks were surveyed within the

border of an urban park of Rome (Villa Borghese). The

occurrence of saproxylic beetles (i.e. the presence of frass,

living insects or their remains) was verified in 66 old holm

oaks, 41% of which were doomed to cutting by VTA.

Eleven of these trees (41% of the trees doomed to be cut)

held fragments of adults and sometimes living larvae of

Osmoderma eremita, and four of them (36%) were inclu-

ded in the felling plan. The presence of Osmoderma ere-

mita in tree holes was more frequent in deep cavities. The

presence of frass in the cavities was positively associated

with tree height and a high degree of damage at the root

collar and negatively with the presence of hole-nesting

birds.

Keywords Dead wood � Habitat directive �Saproxylic beetles � Site of community importance �Urban ecosystems � Visual tree assessment

Introduction

Saproxylic beetles are fundamental links in the trophic

chains of forest ecosystems (Grove 2002; Jonsson et al. 2005;

Hanula et al. 2006; Johansson 2006). They supply at least

two different services to temperate forest ecosystems: (1)

they are an important food resource for forest birds (e.g.

woodpeckers, owls, crows) and mammals (e.g. bats, rodents,

carnivores) (Beckwith and Bull 1985; Radu 2007); (2)

together with fungi, they contribute to fragmentation and

breakdown of dead wood (Ausmus 1977; Edmonds and

Eglitis 1989). The latter, however, is of great concern to

managers of urban parks, because the increase in the

decaying rate of trees may represent a danger to the public.

For this reason, nature conservation and public safety often

conflict in human settlements. Old trees in urban parks rep-

resent reservoirs for saproxylic insects of high conservation

priority listed on Appendix II of the European Habitat

Directive (Anonymous 1992; Luce 1996). Among these

Osmoderma eremita (Scopoli 1763) (Family: Scarabaeidae),

is also considered Vulnerable by the IUCN Red List of

Threatened Species, i.e. it is facing a high risk of extinction in

the wild in the medium-term future, because its population is

declining in their area of occupancy, extent of occurrence

and quality of habitat (World Conservation Monitoring

G. M. Carpaneto (&) � A. Mazziotta

Department of Biology, University ‘‘Roma Tre’’, Viale G.

Marconi 446, 00146 Rome, Italy

e-mail: carpanet@uniroma3.it

G. Coletti � P. Audisio

Department of Animal and Human Biology, ‘‘Sapienza’’

University, Rome, Italy

L. Luiselli

Centre of Environmental Studies Demetra S.r.l., via Olona 7,

00198 Rome, Italy

123

J Insect Conserv (2010) 14:555–565

DOI 10.1007/s10841-010-9283-5

Centre 1996). The status of this species should be updated in

the light of the recent researches conducted in different

European countries (for a review, Ranius et al. 2005). The

larvae of these beetles develop in wood mould of decaying

trunks. In a recent review, Ranius et al. (2005) mentioned

several study cases, e.g. Austria, France, Germany, Latvia,

Lithuania, Poland, Russia, Slovakia, and Switzerland where

Osmoderma eremita occurs in urban parklands. These

authors also pointed out the potential conflict of interests

between the needs of preserving saproxylic insect and the

necessity of assuring public safety.

The status of these insects is often critical in forested

areas because of forestry management procedures consist-

ing of premature cutting and removal of trees (Ranius et al.

2005; Fontaine et al. 2007). This hampers the natural

ageing of trees and precludes the formation of natural

cavities needed by insects and other animals such as

rodents, birds and lizards (Lindenmayer et al. 2006; Ranius

et al. 2009). By contrast, old trees are often left alive in

some urban parks because they (1) have an aesthetical and

symbolic value in recreational areas; (2) provide people

with shadow and coolness; (3) are not prioritized for timber

exploitation. For this reason, urban parks can harbour

populations of saproxylic insects and have the role of small

biodiversity reservoirs for this insect community. However,

old trees in urban parks may become a public danger,

because diseased branches can fall and jeopardize life.

Therefore, cut and removal procedures are carried out in

the management of urban green areas to reduce human risk.

The occurrence of beetles protected by the Habitat Direc-

tive (not only Osmoderma eremita, but also Lucanus cervus

and Cerambyx cerdo) requires management authorities of

the urban green areas to carry out a study of Environmental

Impact Assessment, before any intervention.

We surveyed all the species belonging to Scarabaeidae,

Lucanidae and Cerambycidae (hereafter named ‘‘target

species’’) at an historical green area in the centre of Rome

(Villa Borghese). These families include species of con-

servation concern, including Osmoderma eremita. More-

over, anecdotic information gathered from Italian

entomologists suggests a marked decline of most of the

saproxylic species belonging to these three families. The

aim of this work was to assess the loss of reproductive sites

for saproxylic beetles of these families when felling plans

are adopted, according to a Visual Tree Assessment Pro-

cedure (VTA), in a Mediterranean urban park. We mea-

sured different characteristics of the trees and analysed

which of them were the best predictors of presence/absence

of the surveyed species (verified through the occurrence of

live specimens, larval frass, exoskeletal fragments) and

species richness. Finally, suggestions are given for pre-

serving both hollow trees and public safety, without

affecting insect diversity.

Materials and methods

Study area

This research was conducted in Villa Borghese, one of the

green areas of Rome (159 ha including also the Pincio

Garden, mean altitude: 60 m a.s.l.), located in the centre of

the city (coordinates for the core area of the study site:

projection WGS84 UTM Zone 33 N; 41�5404500N,

12�2901200E). The habitat is a continuous parkland, com-

prising an open woodland formed by scattered trees and

several clearings. Dominant trees are either native or

introduced species of oaks and other hardwood trees,

interspersed with conifers (cedars, pines, cypresses). The

most common landmark trees are old holm oaks (Quercus

ilex), an evergreen component that is the dominant tree

species of Mediterranean sclerophyllous scrub forest.

Villa Borghese was included in the list of the proposed

Sites of Community Importance (pSCIs) (IT6030052) of

the European Commission, together with another urban

park of Rome (Villa Pamphili), because of the presence of

Osmoderma eremita (Ranius et al. 2005). The management

authorities of Villa Borghese (Servizio Giardini di Roma)

divided the park into eight sectors, and four of these sectors

were subject to a Visual Tree Assessment procedure (see

below for details), in order to assess their status and the risk

for public safety due to falling trunks or branches. We

inspected all the 1,247 holm oaks included in those sectors,

focusing on those potentially harbouring saproxylic beetles

associated with tree hollows.

The visual tree assessment procedure (VTA)

The visual tree assessment (VTA) procedure was devel-

oped by Mattheck and Breloer (1994) to assess the risk for

public safety by falling trees. It was applied in urban areas

by Matheny and Clark (1993) and was used in the study

area to minimise the risk of tree failure by planning

interventions. These precautionary measures ranged from

cutting the decaying branches of a given tree to the

removal of the whole tree. A Falling Risk Category (FRC)

was assigned to each tree, ranging from A (healthy tree) to

D (seriously damaged), as an increasing scale of risk cat-

egory. Both C and D categories were divided into seven

subcategories (C1-3, CD, D1-3). These categories and

subcategories were assigned by evaluating the status of the

collar, trunk, and canopy. This information was obtained

using a resistograph, an instrument measuring the resis-

tance to a needle inserted into the wood under constant

drive, and a fractometer, an instrument measuring the

strength loss of the tree due to decay. This method is an

alternative to the method developed by Pacyniak (1992) to

assess tree health, and also used by Oleksa et al. (2006,

556 J Insect Conserv (2010) 14:555–565

123

2007) to verify the presence of the target saproxylic beetles

by means of tree features. This was based on a five steps

scale: (1) trunk and crown healthy; (2) hollows present, up

to 25% of crown damaged (loss); (3) 25–50% damaged

(loss); (4) 50–75% damaged (loss); (5) above 75% dam-

aged (loss) or a dead tree).

Detection of adult beetles

The search for adult saproxylic beetles of the families

Scarabaeidae, Lucanidae and Cerambycidae (hereafter

quoted as ‘‘target beetles’’) was conducted during the after-

noons (from 2 to 7 p.m.), from 19 July 2004 to 28 August

2004. Each sector (see ‘‘Study area’’) was visited once every

4 days, for five periods throughout the duration of the study.

A torch, ladder and climbing equipment were used to explore

each hollow located up to 5 m above the ground. Target

beetles were initially searched for over all the trees, subse-

quently searching was confined to trees belonging to C and D

categories, i.e. to the trees showing hollows or a decaying

status. These were the trees both potentially harbouring

saproxylic beetles and affected by a higher falling risk,

included in ‘‘cut and removal’’ procedures.

The following procedure was applied each day:

• accurate visual checking of all the trees, to verify the

presence of hollows suitable for the development of

Scarabaeidae and Lucanidae, and the occurrence

of adult target beetles on the bark and on the surface

of wood mould in the cavities;

• olfactory searching of Osmoderma eremita following

the strong scent track left by male pheromones (Larsson

et al. 2003; Svensson et al. 2003); no other saproxylic

beetle have this scent which can be smelt by humans at

a distance of some meters;

• searching of specimens and/or fragments of adult body

parts, examining the inner surface of the cavity and

gently extracting by hand the wood mould from the

hole, then scattering it over a white oilcloth to detect

body fragments and frass (larval excrement of lamelli-

corn beetles), and finally replacing the wood mould into

the hollow;

• placing of 10 empty pitfall traps in each sector and

checking them every 3 days, in order to capture adult

beetles. Pitfall traps were buried in the wood mould to

the brim, inside the tree hollows.

Detection of larvae and frass

The search for larvae of saproxylic scarab beetles and their

excrement (frass), together with the description of tree

features, was conducted from 1 to 30 September 2004

(from 9 a.m. to 6 p.m.). Each sector was visited 3 times.

The wood mould inside hollows was accurately examined

with the same procedure adopted for the search of adult

body fragments, i.e. scattering it over a white oilcloth, in

order to detect larvae and frass of saproxylic scarab beetles

(Stegner 2002), and immediately relocated in the same tree.

Larvae of darkling beetles (Tenebrionidae) and click bee-

tles (Elateridae) were found but not identified.

Regarding the environmental variables that may affect

the occurrence of the target beetles in tree hollows, we

chose the physical characteristics of individual hollow trees

that previous authors considered to be associated with

microclimate, nutrient supply and successional stages of

the trees in northern Europe (Ranius and Nilsson 1997), in

order to test the same correlations in Mediterranean habi-

tats (Table 1). We added the distance between a hollow

tree and the nearest hollow tree as a surrogate of connec-

tivity. The continuous tree cover did not permit identifi-

cation of individual stand level features. We also added a

variable adapted to the specific objective of this work, the

Falling Risk Category (FRC).

Statistical analyses

For the analyses, the tree features (Table 1) were consid-

ered as predictor variables. The response variables were:

(a) presence/absence of excrement of saproxylic scarab

beetles in tree hollows (frass); (b) presence/absence of

fragments of Osmoderma eremita in tree hollows (frag-

ments); (c) the species richness of target beetles (species).

Some continuous variables were transformed into ordinal

variables by assigning categorical scores for each of them

(see Table 1 for the list of all covariates and their codes). In

order to satisfy homogeneity of variances, all data were

log-transformed, and in this case parametric statistics were

used. When data were not normalizable, nonparametric

tests were used. Spearman rank correlation coefficient (for

non-normal variables) were used to explore pairwise

association among variables, with alpha set at 5%.

Sixty-one cavities (a single cavity randomly selected for

each tree) were analysed twice by a logistic regression (by

alternatively using the Forward and Backward entry Step-

wise design models) to predict the way in which the asso-

ciation of environmental predictor variables may influence

significantly the presence/absence of both larval frass (frass)

and adult fragments (fragments) of Osmoderma eremita in

hollow trees (Hosmer and Lemeshow 2000). For this anal-

ysis, categorical covariates were treated with the Polynomial

contrast method because their values were equally spaced.

For these analyses, we considered only those variables that

were not significantly associated with each other in pairwise

comparison (i.e. bird_nest, fungus, aspect, canopy_cover,

wood_mould, root_status, trunk_status, dist_hollow_tree,

height, DBH, width, dist_hollow_surface).

J Insect Conserv (2010) 14:555–565 557

123

In order to analyse the influence of the joint contribution

of the other covariates in predicting species richness of the

target beetles (species), we also performed independent

regressions, and then assessed their significance using the

Bonferroni correction for multiple simultaneous tests.

As for the logistic regression, the way in which inde-

pendent predictors were introduced into the analysis was

chosen according to the lowest alpha value of the full

models. All statistical elaborations were carried out using

two software packages: SPSS 8.0 (SPSS Inc.) and STAT-

ISTICA 7.0 (Statsoft).

Results

Saproxylic beetles and hazardous trees

Ten species of target beetles (Cerambycidae, Lucanidae

and Scarabaeidae) were found (Table 2), including

Cerambyx cerdo and Osmoderma eremita which are

included in Appendix 2 of the Habitat Directive.

Among the 1,247 trees occurring in the four sectors

examined, 76 trees belonged to the D3 FRC category (i.e.

6.1% of the total), representing a hazard for humans and

therefore requiring a urgent cut and removal procedure.

Sixty-six trees (5.3% of the total) belonging to different

Falling Risk Categories had signs of target beetles (i.e.

fragments, frass, living adult insects or larvae). Of these

trees, 27 (41%) belonged to D3 category and contained

fragments, living adult insects or larvae; only 39 trees

contained frass (51.3% D3, 23.1% C–D, 10.3% C3, 10.3%

D1, 5.1% D2) (Fig. 1C). Only the occurrence of larvae

and/or frass gave us the evidence that a tree was a breeding

site for at least one species. Larvae of the tribe Cetoniinae

(Osmoderma, Cetonia, Potosia, Eupotosia, Netocia) were

only found in five trees. Larvae of Osmoderma eremita

were found only in two trees and some remains of dead

adults of Osmoderma eremita were found in eleven trees.

Only one live adult was found. The eleven trees where we

found Osmoderma eremita (larvae or adults and their

remains) belonged to different categories: four trees

belonged to D3, one tree to D1 and six trees to C–D

(Fig. 1).

Features of the hollow trees

All the 66 hollow trees examined (i.e. the trees which

showed at least one cavity and signs of presence of target

beetles) were alive (living) (Fig. 2). The median value of

the distances among two hollow trees (dist_hollow_tree)

Table 1 Code, classes, typology and description of the variables used in the regression analysis

Code Class Type Description of variables

FRC CT TC Falling Risk Category (C3 = 1; C-D = 2; D1 = 3; D2 = 4, D3 = 5)

Living CT TC Living tree (No = 0, Yes = 1)

Cracks CT TC Cracks (absent = 0; present = 1)

Dist_hollow_tree CN TC Distance from the nearest hollow tree (m)

Height CN TC Tree height (m)

DBH CN TC Trunk diameter at breast height (DBH), i.e. 1.30 m above ground (cm)

Dist_ground_hollow CN TC Distance between the ground and the hollow entrance (m)

Width CN TC Maximum width of the hollow (cm)

Dist_hollow_surface CN TC Vertical distance between the entrance hollow and the surface of the wood mould (cm)

Bird_nest CT TC Bird nest remnants (absence = 0; presence = 1)

Fungus CT TC Fungus infestation (less than 10% of the interior cavity surface = 0; more than 10% = 1)

Direction CT TC Direction of the entrance hole respect to the ground (horizontal = 0; angulated or vertical = 1)

Aspect CT TC Aspect of entrance hole (NE = 1; N o E = 2; NW o SE = 3, W o S = 4; SW = 5)

Canopy_cover CT TC Canopy cover, i.e. % of the sky covered by canopy over the hollow (coverage B 50% = 0;

coverage [ 50% = 1)

Wood_mould CT TC Would mould quantity in the cavity (volume B 2 litres = 0; volume [ 2 litres = 1)

Frass CT SD Excrement of lamellicorn beetles (absence = 0; presence = 1)

Fragments CT SD Fragments of Osmoderma eremita (absence = 0, presence = 1)

Species CN SD Number of saproxylic target species in the cavity

Root_status CT TC Status of the root collar (good = 1, discrete = 2, sufficient = 3, mediocre = 4, scarce = 5)

Trunk_status CT TC Status of the trunk (good = 1, discrete = 2, sufficient = 3, mediocre = 4, scarce = 5)

Canopy_status CT TC Status of the canopy (good = 1, discrete = 2, sufficient = 3, mediocre = 4, scarce = 5)

Class: categorical (CT) or continuous (CN). Type: species data = SD, tree characteristics = TC

558 J Insect Conserv (2010) 14:555–565

123

was 13.3 m (Fig. 1A). The median value of tree height

(height) was 16 m (Fig. 1A), the median diameter of the

trunk (DBH) was 71.5 cm (Fig. 1B). In the majority of the

cavities (42) only a small quantity of wood mould

(wood_mould) was found (about 2 l), while in 24 holes the

quantity was higher (up to 10 l) (Fig. 2). The median of the

maximum width values for all the cavities (width) was

18 cm; only two holes were more than 50 cm (Fig. 1B).

Table 2 Species and taxonomic ranks of the target beetles (live or

dead adults, or their body fragments), total number of trees and

number of D3 trees (i.e., requiring an urgent cut and removal

procedure) where species were harvested, percent values of D3 trees

respect to the total number of trees where each species was collected;

record typology

Species Taxonomic ranks N. trees N. D3 trees % Record type

Cerambyx welensii Kuster, 1846 Cerambycidae 7 4 57.1 A,F

Cerambyx cerdo Linne, 1758 Cerambycidae 2 1 50.0 F

Dorcus parallelipipedus (Linne, 1758) Lucanidae 7 3 42.9 A,F

Oryctes nasicornis (Linne, 1758) Scarabaeidae Dynastinae 11 8 72.7 F,A,L

Amadotrogus quercanus (Burmeister, 1855) Scarabaeidae Melolonthinae 2 1 50.0 A

Osmoderma eremita (Scopoli, 1763) Scarabaeidae Cetoniinae 11 4 40.0 F,A,L

Cetonia aurata (Linne, 1758) Scarabaeidae Cetoniinae 2 2 100.0 F,A

Eupotosia affinis (Andersch, 1797) Scarabaeidae Cetoniinae 3 1 33.3 F

Potosia cuprea (Fabricius, 1775) Scarabaeidae Cetoniinae 5 3 60.0 F

Netocia morio (Fabricius, 1781) Scarabaeidae Cetoniinae 1 1 100.0 A

Total species = 10 Target beetles 28 9 33.7 All record types

A living adult, L living larva, F fragment of adult body

dist_hollow_tree height0

20

40

60

80

100

met

res

A

DBH dist_ground_hollow width dist_hollow_surface0

100

200

300

400

500

cent

imet

res

B

FRCaspect

root_statustrunk_status

canopy_status0

1

2

3

4

5C

ateg

ory

C

Fig. 1 Trend of the predictor and response variables for the 66 trees

(where a single cavity was randomly selected) (see Table 1 for coding

and measure units). The variables measured by the same unit were

grouped together in separate graphs (A, B, C) to render more

immediate the cross references to figures in the text (square= median, rectangular box = interquartile range, whiskers (lines)

= non-outlier range; circle = outliers, asterisk = extreme values)

J Insect Conserv (2010) 14:555–565 559

123

A large number of holes had a northward (or NE) or

eastward (SE) sun exposure (aspect) (Fig. 1C).

The Spearman correlation coefficients were calculated

for all the predictor variables of 66 full-data cavities

occurring in the 66 trees selected from all the sectors

(Table 3). The following significant results (at least

P \ 0.05) were obtained:

(1) the hazard degree (FRC categories score) increased

with the degradation of the root collar (root) and with

the degradation of the status of the canopy

(canopy_status);

(2) cracks in the trees (cracks) took place preferentially

in short trees (height), with a good canopy cover

(canopy_cover);

(3) tall trees (height) frequently had a poor status of the

canopy (canopy_status);

(4) the status of the canopy (canopy_status) got worse in

trees with fungus infestations in the cavity (fungus);

(5) the quantity of wood mould (wood_mould) existing in

the trunks was higher in trees with larger holes

(width).

Environmental features and beetle occurrence

The presence of fragments of Osmoderma eremita (frag-

ments) was associated with hollows characterized by a

higher vertical distance between the surface of wood mould

and the entrance hole (dist_hollow_surface) (see Table 3).

Excrement (frass) was found in the majority of the trees

where bird nests or feathers were not found in their cavities

(bird_nest) or the root collar was damaged (root_status)

(see Table 3). The higher richness of target species

(species) was found in trees with a high Falling Risk

Category (FRC) whose cavities did not contain bird nests

or feathers (bird_nest), the root collar was damaged

(root_status), and the presence of frass was verified (frass)

(see Table 3). The presence of frass (frass) and the degree

of damage for root collar (root_status) were also jointly

related with the richness of target species, accounting for

the Bonferroni correction (P \ 0.0167).

Logistic regression

The logistic regressions performed for the 66 trees pointed

out a positive significant predictive power of the tree height

(height) and of the fungus infestation (fungus) on the pres-

ence of frass in the cavities (frass) (best model selection

method: Backward; v2 = 37.6; df = 11; P \ 0.001; logit

link function: log (frass ? 1) = (9.144 ± 3.975) 9 log

(height ? 1) ? (2.229 ± 0.905) 9 log (fungus ? 1). The

observed presence of frass in the cavities matched the

expected presence in 82.5% (33/40) of the cavities, while

the observed absence corresponded to the expected absence

in 76.9% (20/26) of the cavities. On the whole, 80.3% of the

observed cavities matched the expected values.

Osmoderma eremita remains (fragments) were predicted

to occur more frequently in cavities with a high dis-

tance between the entrance hollow and the surface of

wood mould (dist_hollow_surface) (best model selection

method: Forward; v2 = 8.127; df = 1; P = 0.004; logit

link function: log (fragments ? 1) = (-2.578 ± 0.542) ?

(1.320 ± 0.481) 9 log (dist_hollow_surface ? 1). The

observed presence of fragments in the cavities matched the

expected presence in 100.0% (3/3) of the cavities, while

the observed absence corresponded to the expected absence

0%

10%

20%

30%

40%

50%

60%

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ks

bird_

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Fig. 2 Percent values of two-states categorical variables for the 66 trees (see Table 1 for the code)

560 J Insect Conserv (2010) 14:555–565

123

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J Insect Conserv (2010) 14:555–565 561

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562 J Insect Conserv (2010) 14:555–565

123

in 88.9% (56/63) of the cavities. On the whole, 89.4% of

the observed cavities matched the expected values.

Discussion

Saproxylic diversity in the urban park

Eight species of saproxylic scarab beetles (Scarabaeidae

and Lucanidae) were found in Villa Borghese (urban area,

159 ha) (Table 2). This richness corresponded to 47% of

the number of species (17) observed in the Presidential

Estate of Castelporziano, the nearest forest, at about 25 km

of distance, 5,892 ha), during a previous intensive research

for a faunistic inventory (Carpaneto et al., unpublished

data). Moreover, Villa Borghese is one of just nine local-

ities of Osmoderma eremita known for Latium (Ruffo and

Stoch 2004), the administrative region of Rome. Latium

has an area of approximately 17,227 km2, of which 13.6%

is included in protected areas (reserves and parks). In this

region, woodlands cover 35% of the whole surface (IFNC

2005, and official data from: www.regione.lazio.it), but old

living hollow trees are poorly represented across the

landscape. Therefore, urban parklands like Villa Borghese,

whose purpose is not wood production, harbour a consid-

erable number of veteran trees and may therefore have a

role of source areas for saproxylic beetles.

In the study area, 41% of the trees inhabited by target

beetles were labelled as dangerous for citizens, represent-

ing a clash of interests between biodiversity conservation

and public safety. Moreover, a considerable amount of the

trees inhabited by Osmoderma eremita were included in a

felling project.

Suitability of hollow trees for saproxylic beetles

The field detection of Osmoderma eremita in central and

southern Europe is very difficult because of the secluded

life of the species inside hollow trees, its limited dispersal

activity, and its low population density (Bubler and Muller

2009; Carpaneto et al., unpublished data). Therefore, the

definition and use of predictor variables could be an

important tool to make provision for the occurrence of the

species and for monitoring protected areas.

The analysis of predictor variables confirms the impor-

tance for target beetles of hollow trees which are still alive, as

their cavities represent a suitable microhabitat and probably

will maintain this role until the death of the trees (cf. Ranius

and Nilsson 1997; Schaffrath 2003a, b). The analysis of the

66 trees with different signs of presence of target beetles also

indicates that good connectivity (i.e. short distance among

hollow trees) favours the target beetles. For example Os-

moderma eremita, has a dispersal range varying from 30 toTa

ble

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J Insect Conserv (2010) 14:555–565 563

123

200 m in Northern Europe (for Sweden: Ranius and Hedin

2001; Ranius 2006; Hedin et al. 2008) and reaches up to

700 m in Southern Europe (for France: Dubois and Vignon

2008). Almost all the trees which were hosts of the target

beetles were big trees; height and diameter had a positive

influence on the quantity of wood mould found in each

hollow. Most of the tree cavities with target beetles had a

small entrance hole, and were northward or eastward sun-

exposed, all factors that maintain a stable and humid

microclimate (Ranius and Nilsson 1997).

The pairwise comparison of predictor variables showed

that Falling Risk Categories for hollow trees were really

associated with different indications of decay and these

signs were related to each other. Substantially, the state of

the variables determining the frequency of occurrence of

the target beetles in Southern Europe were practically the

same detected by other authors in Northern Europe (Ranius

and Nilsson 1997).

According to the results of pairwise comparison and

logistic regression, the frass of saproxylic scarab beetles

and the species richness had a positive response to old trees

with signs of ageing (in particular a damaged root collar)

and without bird nesting activity, in agreement with

the results obtained by other authors in Northern Europe

(Ranius and Nilsson 1997). Osmoderma eremita fragments

were preferentially found in deep cavities. However, a

more extensive analysis of the relations between the

occurrence of Osmoderma eremita and environmental

variables should be carried out in different ecogeographical

contexts to assess the ecological requirements of this spe-

cies throughout its range. The importance of high trees in

preserving the target beetles was related with the high

probability that a tall tree harbours more hollows and

sheltered cavities in its high trunks.

Conclusions and management proposals

An urban park entrapped inside a big city can be a reservoir

for threatened saproxylic beetles and can host a diverse

community of these insects, owing to the occurrence of

monumental trees. On the contrary, out of cities, aged

veteran trees represent a rare and scattered resource either

in managed woodlands or in the forest remnants of a

fragmented landscape. Thus, the deadwood resource of

urban parks may be more suitable to host species of the

genus Osmoderma, than those of the countryside. Never-

theless, these species are at risk of removal from these

urban refuges because of the clash of interests between

biodiversity conservation and public safety. In the study

area, the presence of Osmoderma eremita together with a

guild of saproxylic beetles was confirmed in old trees and

predicted by some variables associated with a category of

high Falling Risk, as designated by the Visual Tree

Assessment Procedure (VTA).

The following reference list summarizes the main

requirements for the life cycle of saproxylic scarab beetles,

especially for Osmoderma eremita: (1) living trees with

abundant wood mould in the hollows; (2) cavities adequate

to maintain high humidity and cool temperatures in sum-

mer; (3) old hollow trees located at short distance each

other (maximum 100 m), to favour adult dispersion and

encounter between them; (4) cavities not affected by bird

nesting activity. The latter requirement may be explained

by the current increasing population of the starling (Sturnus

vulgaris), an invasive hole-nesting bird which usually feeds

on large insects, and could represent a direct threat for

Osmoderma eremita and other saproxylic scarab beetles.

The designation of Falling Risk Categories associated

with trees allows wildlife managers to identify conserva-

tion hotspots for threatened saproxylic beetles. The fol-

lowing recommendations are given to promote the

conservation of saproxylic insects in urban green areas, in

agreement with actions for public safety: (1) reducing cuts

of secondary tree branches to conserve a canopy cover and

optimal microclimate conditions within the holes; (2)

leaving the largest branches and trunks on the ground after

cutting, in order to increase development sites for sapr-

oxylic larvae; (3) using steel ropes and other shores to hold

collapsing trees; (4) applying Natural Fracture Techniques

such as pruning methods used to mimic fractured ends

which naturally occur on trunks and branches; (5) remov-

ing inadequate reinforcement materials used in the past to

strengthen old trees or to occlude hollows; (6) removing

trash and other objects left in hollows by people, in order to

recover habitat conditions.

Acknowledgments We are grateful to Bruno Cignini, executive

manager of the Rome Municipality (10th Department: Environment

and Agriculture Policies/Conservation and management of vast areas

and biodiversity) for providing facilities and funding. A special thank

is due for Fabio Nicolai (Zoological Museum, Rome) for field

assistance and help.

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