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SHORT COMMUNICATION
Does understory clutter reduce bat activity in forestry
pine plantations?
Annia Rodríguez-San Pedro &Javier A. Simonetti
Received: 9 May 2014 /Revised: 25 September 2014 /Accepted: 6 October 2014
#Springer-Verlag Berlin Heidelberg 2014
Abstract Forestry plantations supporting native species
exhibit a dense understory, which might reduce bat
activity within plantations. We compared bat activity in
Monterrey pine plantations with and without an under-
story in central Chile. Total activity did not differ be-
tween plantations with a developed understory and those
without it, being higher on-track than off-tracks sites.
Trails provide commuting areas for bats within planta-
tions allowing its use regardless of their degree of
structural clutter. Promoting understory in plantations
provides habitats for bats and might enhance their con-
servation in human-modified landscapes.
Keywords Chile .Pinus radiata .Structural complexity
Introduction
Forestry plantations are often regarded as “biological
deserts”and a threat to biodiversity (Hartley 2002).
Consequently, environmentally friendly practices are
demanded to mitigate their negative effects (Rousseau
et al. 2005). Enhancing the occurrence of a developed
understory vegetation is one such practice. Plantations
with developed understories provide cover, and food for
wildlife, which might mitigate their impact upon habitat
quality. In such cases, species richness and abundance
are higher in forestry plantations with a developed un-
dergrowth than in those without it, enhancing diversity
of invertebrates, birds and mammals (Brockerhoff et al.
2008,Simonettietal.2013).
A developed understory leads to increased structural
clutter within forestry plantations, however, which may
adversely affect bats. This structural complexity may in-
fluence bats’choice of foraging habitat, as they may
avoid navigating in cluttered habitats (Kusch et al.
2004). Undergrowth in forestry plantations might then
reduce flight efficiency or hamper the detection of poten-
tial prey for some bat species (Broders et al. 2004; Rainho
et al. 2010). Therefore, while the presence of understory
might generally enhance forestry plantations as habitat for
a wide array of fauna, it might specifically conflict with
foraging conditions desirable for aerial insectivorous bats.
Clutter, however, might increase the activity of bat species
with high maneuverability and FM broadband echoloca-
tion calls, while cluttering might reduce activity of low
maneuverability and CF narrowband calls (Tibbels and
Kurta 2003; Patriquin and Barclay 2003).
Bats may overcome the physical constraints of clutter
by using trails in forested areas (Law and Chidel 2002).
If bats also use roads and trails in plantations, this may
facilitate use of habitats otherwise inhospitable (Law
and Chidel 2002; Monadjem et al. 2010), as well as
mitigate potential conflict regarding the value of under-
story between bats and other fauna. Following this
framework, we assessed the effect of undergrowth on
the occurrence of bats in Monterrey pine (Pinus
radiata) plantations in central Chile. If well-developed
undergrowth reduces the use of forestry plantations by
bats, we expected that activity should be lower in plan-
tations with a developed understory than in a stand with
no or little understory. Similarly, we expected that bat
activity would be higher along plantation trails than
away from tracks in both complex and simple planta-
tions, due to reduced vegetation clutter.
Communicated by P. Acevedo
A. Rodríguez-San Pedro (*):J. A. Simonetti
Departamento de Ciencias Ecológicas, Facultad de Ciencias,
Universidad de Chile, Casilla 653, Santiago, Chile
e-mail: sanpedro@ug.uchile.cl
Eur J Wildl Res
DOI 10.1007/s10344-014-0871-7
Materials and methods
Acoustic surveys were conducted in Monterrey pine planta-
tions located at Tregualemu, central Chile. The area comprises
pine plantations, large tracts, and scattered fragments of native
forest and surrounding agricultural lands. According to struc-
tural complexity, plantations were classified as simple when
woody plant density 1 m above ground was less than 0.5 indi-
viduals/m
2
and complex when understory density was above
0.5 individuals/m
2
. Structurally complex plantations have 2.2
more woody species, an understory density four times higher
and vegetation volume 12 times higher (see Poch and
Simonetti 2013 for details).
Bat activity was sampled at 10 locations within structurally
simple and 10 locations within structurally complex sites.
Survey sites were located at different stands and at least
300 m away from each other. Tracks within plantations
consisted of linear flyways ranging from 1 to 5 m wide,
included trails and dirt roads. At each sampling location, bat
activity was recorded for 10 min on-track and 10 min off-track
sites per night, moving randomly between sampling locations.
Bat activity was recorded using an ultrasound bat detector
model D240X (Pettersson Elektronic AB) coupled to a digital
recorder MicroTrack II (M-Audio) operated in manual mode.
Each sampling point was visited nine times between January
2010 and January 2012. Off-track recordings were set >50 m
from tracks and the detector was pointed toward small gaps to
minimize bat call attenuation from vegetation (Patriquin et al.
2003). Sampling began at dusk and extended for four hours to
coincide with the peak foraging periods of insectivorous bats
(Kuenzi and Morrison 2003). Bat activity was quantified by
pooling the number of bat passes across nights for each
sampling point (Walsh et al. 2004). There was no sig-
nificant spatial autocorrelation of bat activity (Moran’s
I=−0.106, P=0.48).
Bat passes were classified to species using Discriminant
Function Analysis (Russo and Jones 2002). Classification
functions were computed using a library of validated reference
calls from hand-released bats at the study area (Rodríguez-San
Pedro and Simonetti 2013). Parameters used in the classifica-
tion analysis were extracted from Batsound 2.1 software
(Pettersson Elektronic AB). A two-way ANOVA (Box-Cox
transformation for normality) followed by a post hoc Tukey
tests was used to test for differences between overall bat
activity according to understory development and track posi-
tion. Differences between simple and complex plantations in
bat activity were tested using a Mann-Whitney Utest (indi-
vidual species data could not be transformed to fit a normal
distribution; Zar 2010).
Results and discussion
A total of 193 echolocation passes were recorded. Of these, 84
could not be analyzed at the species level due to the low
Fig. 1 Total bat activity (mean±SE) in complex and simple pine planta-
tions, on-track and off-track. Different letters indicate significant differ-
ences at P<0.001
Fig. 2 Bat activity per species
(median±percentile) in complex
and simple pine plantations.
Different letters indicate
significant differences at P<0.05
Eur J Wildl Res
intensity of the recorded calls being classified as “unknown”
and were omitted from species-level analysis. The remaining
109 passes were assigned to four of the six species known for
the area: Histiotus montanus (32 passes), Lasiurus varius (32),
Myotis chiloensis (26), and Lasiurus cinereus (19).
Overall bat activity did not differ between complex and
simple plantations (F
(1, 36)
=0.001,P= 0.97); however, activity
was higher on-track than off-tracks (F
(1, 36)
=87.2, P≤0.001)
(Fig. 1). Activity of individual species was quantified by
pooling the number of passes recorded at both on-track and
off-track positions since most passes (84 %) were recorded
on-track. At the species level, M. chiloensis and L. varius were
more frequent in plantations with developed understory than
in plantations with scarce understory (U=20.5, P≤0.05 and
U=25.0, P≤0.05, respectively; Fig. 2). Activity of
H. montanus and L.cinereus did not differ between plantation
types (U≤48.0, P>0.07 in both cases).
Contrary to our predictions, overall bat activity was similar
across plantations regardless of understory condition; howev-
er, there were differences in bat activity at the species level
depicted by bats in other clutter environments (Patriquin and
Barclay 2003; Dodd et al. 2012). Wing morphology and
echolocation calls constrain bats flights to specific habitats
(Norberg and Rayner 1987; Broders et al. 2004). L. varius,
with high wing loading and aspect ratio, is a fast flying species
with low maneuverability, expected to be clutter-sensitive
(Schnitzler et al. 2003), but its use of tracks as flyways would
explain its use of clutter plantations. Furthermore, it adjusts
echolocation calls when flying in cluttered areas (Rodríguez-
San Pedro and Simonetti 2014). The short, round wings and
frequency modulated calls of M. chiloensis enhance its forag-
ing in cluttered habitats (Rodríguez-San Pedro and Simonetti
2013), accounting for its presence in these plantations.
Trails facilitated access and use of forestry plantations
regardless of the degree of structural clutter, consistent with
bat use of tracks in other forests (Law and Chidel 2002;
Monadjem et al. 2010), and provide internal corridors
allowing both clutter-sensitive and clutter-tolerant bats to use
the edges of densely vegetated plantations.
Our data suggest that plantations with a developed under-
story can provide suitable habitat for flying bats, in addition to
other taxa (Estades et al. 2012). Promoting undergrowth veg-
etation in Monterrey pine plantations may not only promote
biodiversity but may also benefit managers through the eco-
system services provided by insectivorous bats (Williams-
Guillén et al. 2008). To the extent that plantations provide
wildlife habitat, this production-oriented land use may simul-
taneously manage for biodiversity conservation.
Acknowledgments Forestal Masisa and CONAF VII Región granted
permits to work on their states. Thanks to Y. Cerda, R. Zúñiga, and F.
Campos for field assistance. The research supported by FONDECYT
1095046. ARSP is a PhD fellow from CONICYT, Chile.
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