BIODIVERSITY
RESEARCH
Anthropogenic fires increase alien and
native annual species in the Chilean
coastal matorral
Susana Go´mez-Gonza´lez1*, Cristian Torres-Dı´az2, Graciela Valencia1,3,
Patricio Torres-Morales1, Lohengrin A. Cavieres1,3 and Juli G. Pausas4
INTRODUCTION
Fire is a common driver of alien plant invasion in ecosystems
around the world (D’Antonio, 2000). However, general rules
on the relationship between fire and non-native species remain
elusive. This is because the invasibility of a given ecosystem
after fire depends on the interaction of a complex set of factors
including historic fire regime, biological characteristics of alien
and native species, and propagule supply (Zouhar et al., 2008).
Understanding the relative role of such factors in explaining
invasion patterns after fire is a major challenge in ecology
(D’Antonio et al., 2001) and crucial for effective management
1Departamento de Bota´nica, Facultad de
Ciencias Naturales y Oceanogra´ficas,
Universidad de Concepcio´n, Casilla 160-C,
Concepcio´n, Chile, 2Laboratorio de Geno´mica
y Biodiversidad, Departamento de Ciencias
Ba´sicas, Facultad de Ciencias, Universidad del
Bı´o-Bı´o, Chilla´n, Chile, 3Instituto de Ecologı´a
y Biodiversidad (IEB), Casilla 653, Santiago,
Chile, 4Centro de Investigaciones sobre
Desertificacio´n (CIDE, CSIC-UV), Camı´ de la
Marjal s/n, Apartado Oficial 46470, Albal,
Valencia, Spain
*Correspondence: Susana Go´mez-Gonza´lez,
Departamento de Bota´nica, Facultad de
Ciencias Naturales y Oceanogra´ficas,
Universidad de Concepcio´n, Casilla 160-C,
Concepcio´n, Chile.
E-mail: sgomez@udec.cl
ABSTRACT
Aim We tested the hypothesis that anthropogenic fires favour the successful
establishment of alien annual species to the detriment of natives in the Chilean
coastal matorral.
Location Valparaı´so Region, central Chile.
Methods We sampled seed rain, seedbank emergence and establishment of
species in four paired burned and unburned areas and compared (using GLMM)
fire resistance and propagule arrival of alien and native species. To assess the
relative importance of seed dispersal and seedbank survival in explaining plant
establishment after fire, we compared seed rain and seedbank structure with post-
fire vegetation using ordination analyses.
Results Fire did not change the proportion of alien species in the coastal
matorral. However, fire increased the number of annual species (natives and
aliens) of which 87% were aliens. Fire reduced the alien seedbank and not the
native seedbank, but alien species remained dominant in burned soil samples
(66% of the total species richness). Seed rain was higher for alien annuals than for
native annuals or perennials, thus contributing to their establishment after fire.
Nevertheless, seed rain was less important than seedbank survival in explaining
plant establishment in burned areas.
Main conclusions Anthropogenic fires favoured alien and native annuals. Thus,
fire did not increase the alien/native ratio but increased the richness of alien
species. The successful establishment of alien annuals was attributable to their
ability to maintain rich seedbanks in burned areas and to the greater propagule
arrival compared to native species. The native seedbank also survived fire,
indicating that the herbaceous community has become highly resilient after
centuries of human disturbances. Our results demonstrate that fire is a relevant
factor for the maintenance of alien-dominated grasslands in the matorral and
highlight the importance of considering the interactive effect of seed rain and
seedbank survival to understand plant invasion patterns in fire-prone ecosystems.
Keywords
Biological invasions, central Chile, disturbance ecology, mediterranean-type
ecosystems, plant invasions, propagule pressure, seedling emergence.
Diversity and Distributions, (Diversity Distrib.) (2011) 17, 58–67
DOI:10.1111/j.1472-4642.2010.00728.x
58 http://wileyonlinelibrary.com/journal/ddi ª 2010 Blackwell Publishing Ltd
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and conservation of natural communities. This is particularly
relevant in biodiversity hot spots such as mediterranean-type
ecosystems, where mild climatic conditions attract people from
everywhere (source of aliens) and fire frequency is increasing
owing to global climate change (Pausas, 2004; Running, 2006).
It has been suggested that plant communities under novel
fire regimes are more susceptible to invasion than those under
a natural (historical) fire regime (Trabaud, 1991; D’Antonio,
2000). For example, in most mediterranean-type ecosystems,
fire has been an important selective force shaping adaptive
traits in native plant species (e.g. Pausas et al., 2006). Under
conditions of natural fire frequency, the ability of native species
to cope with fire leads to a relatively high resilience to invasion,
because alien species that colonize open areas are rapidly
excluded from the system (Trabaud, 1991; Keeley, 2006).
Conversely, in those ecosystems where fire frequency is higher
than the historical fire regimes, it reduces the native vegetation
and seedbank, thus generating a more favourable environment
for colonization and establishment of alien species (Zouhar
et al., 2008). This idea fits to the ‘alteration of selection
regimes’ hypothesis (Byers, 2002), which proposes that
anthropogenic disturbances may suddenly put previously
well-adapted native species at a competitive disadvantage with
non-native species, thus promoting the invasion process.
Unlike other mediterranean-type ecosystems, recurrent fires
play a little role in the evolutionary history of the Chilean
matorral (Aravena et al., 2003; Villa-Martı´nez et al., 2003).
However, palaeoclimatic records based on fossil charcoal
suggest that anthropogenic fires appeared with the first
indigenous settlements (14000 yr bp), with several peaks of
fire activity between 2000 and 5000 yr bp, and then fire
frequency increased exponentially from the time of the Spanish
colonization (1536) to the present (Aravena et al., 2003; Villa-
Martı´nez et al., 2003). Although most of the native woody
species resprout after fire (Araya & A´vila, 1981), post-fire seed
germination of local populations is generally inhibited by the
heat shock and smoke produced by fires (Mun˜oz & Fuentes,
1989; Segura et al., 1998; Go´mez-Gonza´lez et al., 2008;
Go´mez-Gonza´lez & Cavieres, 2009). Some native herbs have
a certain resistance to moderate fires (Go´mez-Gonza´lez &
Cavieres, 2009; Figueroa et al., 2009), but there is no fire-
enhanced recruitment as reported in the other mediterranean-
type ecosystems (Keeley & Fotheringham, 2000; Moreira et al.,
2010).
The Chilean matorral has been strongly modified by human
activities (logging, burning, grazing, etc.) and currently
consists of clumps of shrubs and trees surrounded by a
seasonal herbaceous matrix dominated by alien plants (Keeley
& Johnson, 1977; Fuentes et al., 1984; Montenegro et al., 1991;
Holmgren et al., 2000). The percentage of alien species ranges
from 20 up to 50% in the coastal range (Figueroa et al., 2004),
and most of them are annual grasses and forbs coming from
the Mediterranean Basin (Montenegro et al., 1991). Annuals
from the Mediterranean Basin are successful invaders in
ecosystems with frequent, human-made fires (D’Antonio &
Vitousek, 1992; Norton et al., 2007), because they are very
competitive in the open spaces created after fire (high
irradiance, mortality of native species, high resource availabil-
ity, etc.). Probably, this is because the Mediterranean Basin had
long history of (natural and anthropogenic) disturbances such
as fire (Daniau et al., 2007; Pausas & Keeley, 2009) and
livestock grazing (Perevolotsky & Seligman, 1998). The con-
trast in the fire history between the Chilean matorral and the
original habitats of alien species suggests that fire could favour
the invasion process by producing more negative effects on
native species. For example, there is evidence that the seedbank
of native matorral species is more sensitive to high-intensity
fires than the seedbank of coexisting alien species (Go´mez-
Gonza´lez & Cavieres, 2009). Some field studies have reported
that alien species are favoured over natives in recently burned
sites (A´vila et al., 1981; Sax, 2002), while other studies found
no effects (Keeley & Johnson, 1977; Holmgren et al., 2000).
This discrepancy may be related to differences between sites in
terms of seedbank composition, level of grazing and propagule
availability; therefore, field studies where these confounding
factors are controlled are needed.
Invasion success after fire also depends on the availability
and mobility of propagules from adjacent unburned areas. In
ecosystems where fire is not a historical natural disturbance
(such as the Chilean matorral), the resistance to invasion
after fire should be relatively low and alien plant establish-
ment may be favoured even in conditions of low propagule
supply (D’Antonio et al., 2001). Despite the fact that
propagule availability is regarded as an important factor
affecting ecosystem invasibility (Lockwood et al., 2005; Von
Holle & Simberloff, 2005), it has rarely been considered in
studies of biological invasions (Colautti et al., 2006). Fur-
thermore, few studies have quantitatively evaluated the
relative influence of propagule supply and biotic resistance
in determining invasion patterns after fire (D’Antonio et al.,
2001; Zouhar et al., 2008).
We tested the hypothesis that fire increases the establish-
ment of alien annual plants (in relation to native species) and
that this process is attributable to a more resistant seedbank in
aliens than in native species. Alternatively, the increase in alien
annuals may be driven by a larger seed rain. To test this
hypothesis, we studied seed rain, emergence and establishment
of alien and native species in paired burned and unburned
areas in four coastal matorral communities of Chile.
METHODS
Study sites
This study was carried out during 2006 and 2007 on the
western foothills of the coastal range in the Region of
Valparaı´so (central Chile). The climate is mediterranean, with
a rainy cold season from May to September and a longer warm
dry season from October to April (DiCastri & Hajek, 1976).
During the study period, from January to November 2006 and
2007, the accumulated precipitation was 238 and 204 mm
(respectively), and the mean temperature was 14.5 and 13.9C
Fire and plant invasion in the matorral
Diversity and Distributions, 17, 58–67, ª 2010 Blackwell Publishing Ltd 59