Does the burrowing activity of the fossorial rodent Ctenomys haigi (Ctenomyidae) have a great impact on the soil in
northwestern Patagonian grasslands?
Laboratorio Ecotono, Universidad Nacional del Comahue-Instituto Nacional de Investigaciones en Biodiversidad y Medio Ambiente, Conicet Bariloche-Argentina E-mail: firstname.lastname@example.org
Acebal Ghiorzi, Y., Ghermandi, L; Gonzalez, S.
Northwestern Patagonia grasslands dominated by tussock grasses and shrubs are used for livestock production. Fossorial rodents are ecosystem engineers that change the
physical environment in which they inhabit influencing vegetation dynamics especially plant recruitment (Borghi et al. 2020). Ctenomys haigi (Patagonian tuco-tuco,
Ctenomyidae) is a fossorial rodent very frequent in the northwestern Patagonian grasslands which burrows construction involves a large volume of soil displacement (Fig. 1 and
2). Ctenomys haigi mounds can have different physical and chemical properties compared to surrounding undisturbed soil impacting grassland biodiversity and productivity .
Our objective was to evaluate the physical and chemical changes produced in soil by the burrowing activity of C. haigi in a northwestern Patagonia grassland.
Fig. 1. Ctenomys haigi (Patagonian tuco-tuco) Fig. 2. Mound created by C. haigi.
Materials and Methods
In April 2021, we established three 625 m2plots in a grassland 30 km to the east of the Bariloche city, Northwestern
Patagonia, Argentina (41°03’19’’S, 71°01’50’’O) (Fig.3).
In each plot, we recorded all the fresh mounds, easily detectable because of the brown dark color, low soil consistency,
and no presence of vegetation to calculate the mound density and area occupied by mounds per ha.
We randomly selected 30 fresh mounds and measured their two perpendicular diameters and high to calculate the volume
of excavated soil per ha (Fig. 4).
We studied the soil physicochemical properties (soil compaction, rock fragments, pH, electric conductivity, P available, C
and N content) in mounds and adjacent gaps between dominant vegetation. In 15 mounds and 15 gaps, we measured the
soil compaction with a penetrometer in the first 10 cm (Fig.5) and gathered soil samples. In the laboratory, we sieved the
samples (2 mm mesh) to separate the rock fragments from the sandy soil, and we analyzed the chemical properties.
We compared between fresh mounds and gaps the soil compaction, percentage of rock fragments, and pH with the t-test;
the P available, electrical conductivity, and Cand N percentage with the Mann-Whitney test.
Fig. 3 Plot in the grassland Fig. 4 . Measurement of mound dimensions Fig. 5 Measuring the
soil compaction whith
We found 1024 ±241.6 mounds/ha. The area occupied by mounds was 1837.±237.4 m2/ha (a total percentage of 18.4%) whereas the volume of excavated soil was 120.4 ±28.3 m3/ha).
We found that the soil compaction and rock fragments were lower in the mounds than in the gaps (U =225,P= 0.001;and t29= 3.696,P= 0.001, respectively); the available P was higher in the gaps than in the
mounds (U =30 test, P= 0.001); the Ph and EC values were similar in the mounds and gaps (t29= -1.930;P= 0.064;and U = 74,P= 0.186, respectively) and the C and N percentage were higher in the mounds
than in the gaps (U =194,P< 0.001;and U = 196,P< 0.001, respectively).
properties Gaps Mounds
fragments (%) 25.1±
available (µg/g) 7.9±
lectric conductivity (µS/cm) 32.2±
content (%) 0.08±
content (%) 1.1±
Table 1. Mean and standard deviation of physical and chemical
soil properties in gaps and mounds. The different letters indicate
Discussion and Conclusions
The volume of soil removed by C. haigi in NW Patagonia was ten times more than the highest value recorded in USA prairies (Table 2).
Soil compaction in the mounds was lower than in the gaps between tussocks like was found in other studies of fossorial rodents of America (e.g.: Sherrod & Seastedt 2001; Whitesides & Butler 2016). In
Patagonian grasslands livestock trampling increases soil compaction and C. haigi burrowing counteracts this negative effect favoring plant establishment in grassland.
The rock fragments were lower in the mounds than in the gaps.In sandy soils, like Patagonia soils, the rock fragments are an important component for the cation exchange (Ugolini et al.2001).
The pH and EC were similar in mounds and in gaps.It may be due because the Haploxerolls have a similar pH superficially and to the C. haigi burrow depth (Gaitán et al.2004). In both microsites, the pH has
an optimum solubility value required for plant nutrition.
In contrast to other studies, our results showed that the P available was lower in the mounds than in the gaps (e.g.: Sherrod & Seastedt 2001; Galiano et al.2014). The N and C % was higher in the mounds than
in the gaps according to other studies of C. mendocinus in Argentina and Thomomys talpoides in USA (Lara et al.2007; Yurkewycz et al.2014). Fine roots are an important source of soil C and N, particularly in
arid regions where nutrient availability is limited and we found more fine roots in mounds than in gaps (unpublished data).
These findings demonstrate the high impact of C. haigi on the soil, which shows that it is a typical ecosystem engineer. This soil modification changes the vegetation dynamics and productivity of northwestern
Patagonian grasslands. We believe that this work opens the possibility of future comparative studies between North American and South American fossorial rodents impact on vegetation.
Argentina (this study)
Roig et al.1988)
Malizia et a
Gedeon et al.2012)
Litaor et al. 1996)
Winchel et al. 2016)
Table 2. Comparison of volume excavated of soil per ha of fossorial
rodents of America