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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.
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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
Forestry plantations are often regarded as biological
desertsand 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.
A developed understory leads to increased structural
clutter within forestry plantations, however, which may
adversely affect bats. This structural complexity may in-
fluence batschoice 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
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-
and complex when understory density was above
0.5 individuals/m
. 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 (Morans
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, P0.001)
(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, P0.05 and
U=25.0, P0.05, respectively; Fig. 2). Activity of
H. montanus and L.cinereus did not differ between plantation
types (U48.0, 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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Spectral and temporal features of echolocation calls emitted by 22 bat species from Italy (three rhinolophids, 18 vespertilionids and the molossid Tadarida teniotis) are described. Time-expanded recordings of calls from 950 bats of known identity were examined. Rhinolophus ferrumequinum, R. hipposideros, R. euryale and T. teniotis could be identified by measuring the call frequency of highest energy (FMAXE). Quadratic discriminant function analysis with cross-validation was applied to calls from the remaining 18 species. A function based on start frequency (SF), end frequency (EF), FMAXE and duration (D) provided a correct overall classification of approximately 82%. A classification model at genus level that also comprised middle frequency (MF) and inter-pulse interval (IPI) reached 94% correct classification. Two separate discriminant functions were devised for species emitting FM (frequency modulated) and FM/QCF calls (i.e. calls consisting of a frequency-modulated component followed by a terminal part whose frequency is almost constant) respectively. The former function included SF, EF, FMAXE and D and provided an overall classification rate of 71%; the latter comprised EF, MF, D and IPI, and reached 96%. The functions may be applied to bat habitat surveys in southern Italy since they cover most of the species occurring in the area.
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T op-down limitation of herbivores is an im-portant ecosystem service that facilitates agricultural production (1). Several experi-ments in natural and managed ecosystems demon-strate the importance of avian predators in arthropod control (2). Although insectivorous bats are ex-pected to have major impacts on arthropods (3), few studies have quantified the effects of bats on standing crops of arthropods. Because all previ-ous exclosure-based studies of avian insectivory have left exclosures up during the night, it is possible that a proportion of predation attributed to birds may represent predation by foliage-gleaning bats. Here, we report an exclosure experiment conducted in a Mexican coffee agroforest, in which we directly measured the impact of pre-dation by foliage-gleaning birds and bats on ar-thropods found on coffee plants. We used exclosures made of agricultural net-ting erected around individual coffee plants in Finca Irlanda, an organic shade coffee plantation harboring abundant populations of ≥120 bird species and ≥45 bat species. We established 22 blocks of four treatments: birds-only excluded (exclosure netting in place only during the day), bats-only excluded (netting in place only during the night), both excluded (netting in place day and night), and control (no netting). We visually censused noncolonial arthropods (primarily insects, but also spiders, harvestmen, and mites) on all plants at the beginning of the experiments, every 2 weeks thereafter, and at the end of the experiment. We conducted the experiment for a 7-week period beginning January 2007 (dry season) and for an 8-week period beginning June 2007 (wet season). Exclusion of birds and bats resulted in sig-nificant increases in total arthropods on experi-mental plants, although a significant amount of variation was also explained by foliage biomass and initial arthropod density (table S1). On average, total arthropod densities on plants from which both predators were excluded were 46% higher than those observed on control plants. There was a clear seasonal effect with regard to bats: Although bats did not have significant ef-fects on arthropod densities in the dry season, their impacts were highly significant in the wet season, with an 84% increase in arthropod den-sity in bat-only exclosures, exceeding the effects of birds (Fig. 1). In neither season was there a significant interaction between bats and birds, indicating an additive effect. Regardless of sea-son, arthropod densities increased the most on plants from which both birds and bats were ex-cluded (Fig. 1). These seasonal and additive pat-terns held for various arthropod taxa (table S2), although only birds significantly reduced spiders. Although predator exclusions resulted in increased arthropod density, no significant differences were seen between treatments in the prevalence or the intensity of leaf damage. At our site, bats were as important as birds in regulating insect populations across the course of the year. We suspect that increased impacts of birds in the dry season may result from an influx of insectivorous overwintering migrants from North America (4). We have no data on the ab-solute density of bats versus birds; however, at our site the capture rates (and presumably abundance) and reproductive activity of bats increased during the wet season. Bats' relatively higher surface area may result in greater heat loss and concom-itantly higher energy requirements (5), and reproduction increases females' energetic needs; thus, increased bat abundance and reproduction in the wet season may result in an increased impact of bat predation on understory arthropods. Our results are consistent with arguments that functional diversity is central to the main-tenance of ecosystem services (6). In this case, the presence of these two vertebrate taxa main-tains a functional difference that enhances the efficacy of arthropod reduction. Previous exclo-sure studies have not differentiated between diurnal and nocturnal predators, attributing ob-served changes to birds. We suggest that these studies of the impacts of "bird" predation may have underestimated the importance of bats in limiting insects. Bat pop-ulations are declining worldwide (7), but mon-itoring programs and conservation plans for bats lag far behind those for birds. Declin-ing bat populations may compromise critical eco-system services, making an improved understanding of their conservation status vital.
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Intraspecific variability in echolocation calls could be an important factor hampering the accurate acoustic identification species in the field. We studied variations in the echolocation behavior of Lasiurus varius in relation to habitat structure. Echolocation calls of L. varius reflected the degree of clutter present in their foraging areas. Bats foraging in an uncluttered habitat emitted longer and lower bandwidth calls, with the lowest frequency values, while bats foraging in a cluttered habitat broadcast shorter and broadband signals showing an increase in frequency content of its calls. Discriminant function analysis gave an overall classification of 76% of the calls emitted in the different flight situations. Our results highlight the need for independent recordings at each study area or habitat type to circumvent potential echolocation call variations, particularly in fragmented landscapes.
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It has been assumed that habitat differences influence the ability to detect ultrasonic calls produced by bats. This could mask or inflate differences in levels of bat activity among different habitats, possibly resulting in false conclusions about the ecology of bats. We measured the ability to detect 25- and 40-kHz sounds in various forest types in northern Alberta, Canada. We found that sound transmission varied among forest types (deciduous, coniferous, and mixed). Increases in vegetation density among open, thinned, and intact forest patches did not significantly reduce the ability to detect 40-kHz sound. However, it was more difficult to detect 25-kHz sound in intact patches than in thinned patches. These results have important implications for the design and interpretation of studies on habitat use by bats.
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The Convention on Biological Diversity (CBD) expects forestry plantations to contribute to biodiversity conservation. A well-developed understory in forestry plantations might serve as a surrogate habitat for native species and mitigate the negative effect of plantations on species richness. We experimentally tested this hypothesis by removing the understory in Monterey pine (Pinus radiata) plantations in central Chile and assessing changes in species richness and abundance of medium-sized mammals. Frequency of occurrence of mammals, including kodkods (Leopardus guigna), culpeo foxes (Pseudalopex culpaeus), lesser grisons (Conepatus chinga), and Southern pudu deer (Pudu puda), was low in forest stands with little to no understory relative to stands with well-developed undergrowth vegetation. After removing the understory, their frequency of occurrence decreased significantly, whereas in control stands, where understory was not removed, their frequency did not change. This result strongly supports the idea that facilitating the development of undergrowth vegetation may turn forestry stands into secondary habitats as opposed to their containing no habitat for native mammals. This forestry practice could contribute to conservation of biological diversity as it pertains to CBD targets. Proporcionando Hábitat para Mamíferos Nativos Mediante el Mejoramiento del Sotobosque en Plantaciones Forestales.
The habitat choice of foraging bats depends on the local food supply as well as on vegetation structures that may enable the animals to orientate by echolocation. We examined the associations of bats with different types of landscape elements. Effects of the local insect occurrence, of the canopy structure and of linear vegetation elements on the presence of bats were compared. Bat activity increased with the insect abundance (p = 0.025). Furthermore, regression analysis revealed that bat activity was positively correlated (p = 0.004) with the relative area of open canopy type (clearances, still waters), and vise versa was negatively associated with the area of closed canopy (p = 0.0005). Bat species that predominantly forage in different vertical strata (above or below the canopy), differed in the activity at the various habitat types. Pipistrelle bats and Myotis species favoured open canopy areas (p = 0.007; p = 0.029), whereas Nyctalus species were not significantly more active at this patch type, compared to closed canopy areas (p = 0.0712). Linear characteristics of the vegetation (edges, paths) in general did not regulate the local preferences of bats (p = 0.154), but they corresponded to bat activity in complex structured areas (e.g. clearances with trees; p = 0.008).
Increasing evidence suggests that, depending on the structural complexity of a plantation, it can act as complementary habitat for insectivore birds and mammals. The magnitude of interactions such as insectivory, in turn, have been determined by species’ richness and abundance in an ecosystem. Therefore, insectivory can vary in function of the plantation’s complexity, and thereby, decrease chance of plantations damage due to herbivorous insects. Through an experimental procedure, the insect larvae mortality risk in pine plantations with different degree of structural complexity was measured, together with the herbivory levels on Aristotelia chilensis related to each plantation type.Attacks to artificial caterpillars were significantly greater and herbivory significantly less in structurally complex plantations, where we found higher woody species richness and abundance and a greater understory development, compared to simple plantations. These results suggest that insectivory does vary in function of the structural complexity within forestry plantations, and it is greater in those with higher species diversity, mediating a trophic cascade effect over vegetation, significantly diminishing herbivory. Therefore, forestry plantations should be managed into more structurally complex ones in order to allow a win–win scenario, where maintaining a greater biodiversity increases the provision of useful ecosystem services for these plantations.
Vertebrate insectivores such as bats are a pervasive top-down force on prey populations in forest ecosystems. Conservation focusing on forest-dwelling bats requires understanding of community-level interactions between these predators and their insect prey. Our study assessed bat activity and insect occurrence (abundance and diversity) across a gradient of forest disturbance and structure (silvicultural treatments) in the Central Appalachian region of North America. We conducted acoustic surveys of bat echolocation concurrent with insect surveys using blacklight and malaise traps over 2 years. Predator activity, prey occurrence and prey biomass varied seasonally and across the region. The number of bat echolocation pulses was positively related with forest disturbance, whereas prey demonstrated varied trends. Lepidopteran abundance was negatively related with disturbance, while dipteran abundance and diversity was positively related with disturbance. Coleoptera were unaffected. Neither bat nor insect response variables differed between plot interiors and edges. Correlations between bat activity and vegetative structure reflected differences in foraging behavior among ensembles. Activity of myotine bats was correlated with variables describing sub-canopy vegetation, whereas activity of lasiurine bats was more closely correlated with canopy-level vegetation. Lepidopteran abundance was correlated with variables describing canopy and sub-canopy vegetation, whereas coleopteran and dipteran occurrence were more closely correlated with canopy-level vegetative structure. Our study demonstrates regional variation in bat activity and prey occurrence across a forested disturbance gradient. Land management and conservation efforts should consider the importance of vegetation structure and plant species richness to sustain forest-dwelling bats and their insect prey.