Introduction
Burrowing mammals play an important role in their ecosystem (Beca et
al., 2021; Davidson et al., 2012; Root-Bernstein & Ebensperger, 2013),
and have been described as keystone species (Whitford & Steinberger,
2010) and ecosystem engineers (Wesche et al., 2007). Burrows form
microhabitats that are used as shelter by other vertebrates (Ewacha et
al., 2016; Murdoch et al., 2009) and invertebrates (Sorokina & Pont,
2011; Yoshihara et al., 2010). Burrowing mammals can occur in high
densities, therefore they also impact their environment through
non-engineering effects (Prugh & Brashares, 2012) and can be important
prey for predators (Davidson et al., 2012). But probably the most
affected group of organisms are plants. The forming of mounds of burrow
material and exposing soils through trampling and herbivory alters the
competition between plants, promoting pioneer species. Additionally,
mounds mainly consist of soil from beyond the surface, which has
different chemical properties. Thus, it promotes different plant species
than in the surrounding area. Hence, an increase in plant biodiversity
and species richness can occur (Ballová et al., 2019; La et al., 2003;
Lindtner et al., 2018; Niu et al., 2020; Valkó et al., 2020). Colonies
and single burrows offer varied microhabitats and each can support a
different plant community (Ballová et al., 2019; Sasaki et al., 2013).
Faeces, urine and animal carcasses (in the case of burrows of predators)
increase soil nutrient content around the burrow. The vegetation around
the burrow profits from this, increasing its nutritional status. In the
proximity of burrows, the content of nitrogen and phosphorus in plant
biomass is usually 20-30% higher than in the surrounding area
(Villarreal et al., 2008; Whicker & Detling, 1988), but some studies
show an increase of up to 100% in N and 200% in P (Van Staalduinen &
Werger, 2007). On the other hand, the positive effect on plant growth
fades above some level of burrow density (Guo et al., 2012), as the high
level of disturbance (grazing, digging and trampling) results in the
creation of bare soil patches with no vegetation, which are more prone
to water evaporation and N loss (Pang et al., 2020). Therefore, the
relationship between burrowing animal activity and vegetation cover can
be manifold. In habitats where undisturbed areas are completely covered
with vegetation, the presence of burrows and mounds obviously decreases
total vegetation cover (Louw et al., 2019). However, burrowing animals
can also cause an increase in vegetation cover, but it is limited to a
certain magnitude of disturbance, above which cover drops (Tang et al.,
2019). This type of unimodal relationship is also found for the impact
of burrowing animals on species richness or aboveground biomass (English
& Bowers, 1994; Guo et al., 2012; Pang & Guo, 2017; Whicker &
Detling, 1988) and is considered a classical example to support the
intermediate disturbance hypothesis (Connell, 1978; Grime, 1973).
Because of the reasons mentioned above, burrowing animals (mainly
mammals) were often considered and treated as pests: an approach which
has been criticized by scientists due to the need for biodiversity
preservation and the role of burrowing species in the environment
(Delibes-Mateos et al., 2011; Smith & Foggin, 1999), but also because
their negative impact on plant yield and pasture productivity is
doubtful (Bagchi et al., 2006; Guričeva, 1985).
Studies on the impact of burrowing animals on vegetation are numerous,
but the majority of them were conducted on steppes, arid and semi-arid
plains, including pastures or alpine meadows, as well as hot deserts
(Beca et al., 2021; Davidson et al., 2012; Mallen-Cooper et al., 2019;
Platt et al., 2016; Root-Bernstein & Ebensperger, 2013). Almost no
studies show the ecological roles of burrowing mammals in extremely arid
high-altitude habitats in an early stage of soil formation and plant
succession, where plant productivity is limited by water shortage and
low temperatures, rather than nutrient availability and competition for
space. High-altitude habitats are among the regions where climate change
is the most rapid (Kohler et al., 2010). Melting glaciers are exposing
mineral soils, which are slowly being colonised by microorganisms and
plants (Egli et al., 2012). Whether this process can be facilitated by
burrowing ecosystem engineers is unknown. The first step to answering
this question should be a study of the impact of burrowing mammals on
plant communities already established in glacier forelands.
We studied the response of vegetation to the activity of long-tailed
marmots (Marmota caudata, hereafter referred to as marmots, as
they are the only species from this genus in the study area) inhabiting
the valley of the Koksoy river, which flows from the Ujsu glacier in the
Eastern Pamir mountains – an extremely dry habitat with hampered soil
development and plant succession (Kabala et al., 2021). We used an
unmanned aerial vehicle to take images of the area and map vegetation.
Given the initial character of our study, this method would allow us to
preliminarily assess the relationship between the presence of marmot
burrows and vegetation cover in a high number of replicates (burrows),
without indicating the precise cause of this relationship. We also
measured N and P content in aboveground green plant biomass in a
distance gradient from burrow entrances, to check whether plants are
utilizing the nutrient input from marmot faeces. We also used stable
isotope composition as a marker of animal-derived N. Preliminary field
observations of vegetation in the study area suggested, that the impact
of marmots on plants is not pronounced, as there was no visible increase
in vegetation properties around burrows (Suska-Malawska et al. unpubl.),
unlike in many other studies (Ballová et al., 2019; Fafard et al.,
2019). Also, faeces were seen mainly on mounds, close to the burrow
entrance. Therefore, we planned our study on a small scale, in 20-meter
buffers around burrow entrances.