Ecosystem engineering by digging mammals: effects on soil fertility and condition in Tasmanian temperate woodland

Abstract

Many small- and medium-sized mammals dig for their food. This activity potentially affects soil condition and fertility. Digging is well developed especially in Australian mammals, many of which have recently become rare or extinct. We measured the effects of digging by mammals on soil in a Tasmanian temperate dry sclerophyll forest with an intact mammal community. The density of diggings was 5812 ha−1, affecting 11% of the forest floor. Diggings were created at a rate of around 3113 diggings ha−1 yr−1, disturbing 6.5% of the forest floor and displacing 7.1 m3 ha−1 of soil annually. Most diggings were made by eastern bettongs (Bettongia gaimardi) and short-beaked echidnas (Tachyglossus aculeatus). Many (approx. 30%) fresh diggings consisted of re-excavations of old diggings. Novel diggings displaced 5 m3 ha yr−1 of soil. Diggings acted as traps for organic matter and sites for the formation of new soil, which had higher fertility and moisture content and lower hardness than undisturbed topsoil. These effects on soil fertility and structure were strongest in habitats with dry and poor soil. Creation of fine-scaled heterogeneity by mammals, and amelioration of dry and infertile soil, is a valuable ecosystem service that could be restored by reintroduction of digging mammals to habitats from which they have declined or gone extinct.

Experimental evidence for ecological cascades following threatened mammal reintroduction

“…The importance of digging mammals as ecosystem engineers is well known (Davidson et al 2012). Excluding digging mammals tended to decrease bare ground cover, consistent with previous studies showing that they increase soil turnover, and bury ground cover vegetation and litter (Davidson et al 1999, 2012, Davies et al 2019, Decker et al 2019). Herbivorous digging mammals also consume ground cover vegetation, further increasing bare ground (Davidson et al 2012, Verdon et al 2016).…”

Effects of digging by a native and introduced ecosystem engineer on soil physical and chemical properties in temperate grassy woodland

“…The eastern bettong pits measured at Mulligan’s Flat are also considerably smaller and shallower than the pits of other species such as the bilby or the burrowing bettong (Newell, 2008) or those of the same species recorded in Tasmanian dry sclerophyll forest (Davies et al, 2019), so they may not be as effective at incorporating organic matter into the deeper layers of soil. The reason for this difference in pit size is unclear, but could be due to differences in soil type, depth, moisture or compaction making it harder to dig, the availability of food at different depths, or the fact that bettongs and other digging animals have long been absent from the site.…”

A Review of the Engineering Role of Burrowing Animals: Implication of Chinese Pangolin as an Ecosystem Engineer

“…Davies et al (2019) distinguished three plant types in Tasmanian temperate woodlands, and they detected soil fertility and structure to explore the different effects of burrowing engineers on soil. These effects on soil fertility and structure were strongest in habitats with dry and poor soil [25] . Burbidge et al (2007) detected the difference in soil physicochemical properties between the burrow mounds and the undisturbed areas at the landscape scale, and they found the soil penetrability typically at mounds far greater than surrounding soil that often has a hard pan [29] .…”

“…At the habitat and landscape scales, bioturbation is affected by different environmental factors, including plant type, precipitation (different degrees of drying), altitude, etc., they are selected as concomitant variables to quantify the interaction between environment and burrowing engineers [21,25,26,27,28] . Davies et al (2019) distinguished three plant types in Tasmanian temperate woodlands, and they detected soil fertility and structure to explore the different effects of burrowing engineers on soil.…”

“…Considerable studies about the engineering effect on soil property caused by burrowing engineers have concentrated on arid and semiarid environments (Figure 3) [4,39,40,41,42,43,44] . More evidence has demonstrated that engineering effect is stronger in arid and semiarid regions than in mesic and semi-mesic regions [25,38] . This may be due to increased water infiltration (moist soil excavated by engineers) in xeric environments which may make a substantial difference in plant survival and growth, as soil nutrients are more easily absorbed when in solution [45] .…”