1 Introduction
During the past 40 years, large areas of primary forests in China have
been rapidly logged and converted to secondary and plantation forests
due to economic development (Jian et al., 2011). Forest conversion could
directly or indirectly affect species distributions and the composition
of biological communities (Meiners & Pickett, 1999; Suchomel et al.,
2014; Tinya et al., 2021), resulting in significant changes in the
structure of forestry biotic communities and associated
ecosystem services (Hughes, 2017;
Zhang et al., 2020). Primary forests can be climax or subclimax forests,
where dominant trees are close to or older than their age at
physiological maturity (Hilbert & Wiensczyk, 2007; Morales-Hidalgo et
al., 2015). Secondary forests can be understood as a degradation of the
primary forests and differ from primary forests in many respects, such
as vegetation structure, primary productivity and ecological function
(Grau et al., 1997). Plantation forests usually consist of one or
several indigenous or exotic tree species that grow rapidly, with a
simple vegetation structure and high tree abundance (Felton et al.,
2008). Numerous studies have demonstrated that primary forests play an
indispensable role in the conservation of birds (Lindenmayer et al.,
2015; Manuwal & Huff, 1987), plants (Kosulic et al., 2020), carabids
(Elek et al., 2001; Magura et al., 2015), moths (Luque et al., 2007) and
small mammals (Umetsu et al., 2007; Bogdziewicz et al., 2014; Rebelo et
al, 2019) especially those that are forest-dependent or/and endemic.
However, some studies have shown that the diversity of plants (Graham et
al., 2019), small mammals (Suchomel et al 2012; Suchomel et al., 2014;
Heer et al., 2015), and birds (Zhang et al., 2020) in secondary and
plantation forests were equal to or even higher than that in primary
forests, especially in heterogeneous landscape regions where secondary
and plantation forests are distributed adjacent to primary forests
(Bernard et al., 2009; Yang et al., 2015; Zhang et al., 2020).
Small mammals play an important role
in food web dynamics (Ernest & Brown, 2001; Wu et al., 2019).
Insectivores that prey on invertebrates (e.g., insects) can
significantly affect the functioning of forest ecosystems, and
herbivorous species (e.g., Tamiops swinhoei ) (including
granivores and frugivores) serve as seed dispersers (Urgoiti et al.,
2018). On the other hand, they are prey for birds, reptiles and large
mammals (Chubbs & Trimper, 1998; Dawson & Bortolotti, 2000; Zhao et
al., 2020). In addition, small mammals are easy to investigate and
characterized by low dispersal ability and strong ecological
adaptability. Consequently, small mammals are usually treated as
ecological indicators of environmental change (Carey & Johnson, 1995;
Ernest & Brown, 2001), making them ideal models for examining the
effects of forest compositional change on biodiversity and community
structures (Carey & Johnson, 1995).
Although taxonomic diversity (TD) is the most commonly used metric for
assessing the conservation values of different regions,
limitations
exist in its ability to locate the conservation priority area because it
implicitly treats all species equally (Davis et al. 2018). In nature,
species perform different ecological functions in an ecosystem and have
different degrees of phylogenetic relatedness. Therefore, functional
diversity (FD) and phylogenetic diversity (PD), which take into account
the functional traits and species-specific evolutionary history
respectively, have been suggested as important diversity metrics in
conservation biology (Diaz & Cabido, 2001; Diaz et al., 2013). In
addition, understanding the processes of
community
assembly and the underlying mechanisms community assembly are important
for
the development of conservation rules. With the development of
statistical methodology, it has become possible to quantify the relative
importance of habitat filtering, interspecific competition and neutral
assembly in community assembly based on the phylogenetic and functional
information of species (Montano-Centellas et al., 2020; Webb et al.,
2002; Zhang et al., 2020).
For small mammals, most previous studies comparing diversity and
community structures between different forest types (e.g., primary,
secondary, and plantation forests) did not consider the effect of
seasonality (Rebelo et al., 2019; Wu et al., 2019). Because resource
availability (e.g., leaves, fruits
and seeds) and habitat structures (e.g., crown density, herb coverage
and shrub coverage; Williams et al., 2010) in a forest vary among
seasons, seasonality should be taken as an important covariate in
elucidating species diversity pattern and community assembly (Hurlbert
& Haskell, 2003). Therefore, integrated studies comparing
the
TD, FD, PD and community structures of small mammals among seasons are
valuable to replenish our understanding how forest conversion affects
small mammal diversity and community structures. Unfortunately, such
studies are extremely rare (but see Pedersen et al., 2010).
Mt. Liangshan, located in the southwestern part of Sichuan Province,
have large areas of primary forests. However, primary forests in Mt.
Liangshan were logged heavily and converted to secondary and plantation
forests due to the increasing demand for timber during the 1960 s-1970
s. With the establishment of nature reserves and the implementation of
policy of prohibiting logging (e.g. the Natural Forest Protection
Program), all forests in the nature reserves, protected by law then and
therefore, were exposed to little human disturbance. Zhang et al. (2020)
assessed the differences in three dimensions of avian diversity (TD, FD
and PD) and community structures among the primary, secondary and
plantation forests in the Meigu Dafengding Nature Reserve in Mt.
Liangshan. They found that TD, FD and PD in the secondary forests were
significantly greater than those in the primary forests. In addition,
habitat filtering was the dominant process in the primary forests.
However, these results cannot be simply extrapolated to other taxa
because the taxa in an ecosystem generally differ in their evolutionary
histories and ecological service functions.
In this study, using a robust dataset obtained from
four-years field survey, we studied
small mammal diversity (TD, FD and PD) and community structures in the
primary, secondary and plantation forests in Mt. Liangshan. We aimed to
answer the following two questions:
Are small mammal taxonomic, functional and phylogenetic diversity
affected by forest conversion?
Do the ecological processes structuring small mammal communities
differ among the three types of forests?