Literature review: Impact of Chilean needle grass ... - Weeds Australia

Fossorial vertebrates are or were once a feature of the indigenous fauna of temperate grasslands worldwide. Darwin (1845 p. 51)
reported that “considerable tracts” of grassland of the Maldonada region in Uruguay were undermined by the extensive shallow
burrowing of the root-feeding Tucotuco Ctenomys brasiliensis Blainville (Rodentia: Ctenomyidae), while the commonest
mammal in grasslands between the Rio Negro and Bahía Blanca in Argentina was the burrowing Agouti or Mara (Dolichotis
patagonum Zimmerman) (as Cavia patagonica) (Caviidae). Another burrowing rodent, the Viscacha (or Plains Vizcacha)
Lagostomus maximus (Desmarest) (Chinchillidae), larger than the Agouti, lives in large groups in the pampas between the
Uruguay and Rio Rivers, makes deep, multi-chambered burrows with large soil mounds, known as viscacheras, and forages at
night on grasses and herbs. It is considered a”key ecosystem engineer” whose grazing and burrowing activities change the
structure and composition of the vegetation over extensive areas (Villarreal et al. 2008 p. 701). This speices remained abundant
at least until the early 1970s (Soriano et al. 1992). Rheas were abundant in the grasslands of Bahía Blanca, and live on “roots and
grass” (Darwin 1845 p. 89). Burrowing mammals have been implicated in significant changes in microtopography (soil mounds)
in Argentina (Noble 1993). The effects of L. maximus activities cascade through the ecosystem, and include altered plant
biomass distribution, nutrient cycling (primarily by deposition of faeces and urine in the burrow), nutrient content of plants and
fire regimes (Villarreal et al. 2008).
Other small mammals in the regions where N. neesiana is found include a group of Necromys mice (Rodentia: Cricetidae) of
open areas (D’Elía et al. 2008). N. lactens (Thomas) is found in high altitude grasslands (over 1500 m) in north-western
Argentina and southern Bolivia including Catamarca, south Jujuy and Tucuman; N. obscurus onthe Atlantic coast of Uruguay
and in areas around the La Plata River and N. lasiurus is very widely distributed including southern Buenos Aires Province
(D’Elía et al. 2008). The oldest Necromys fossils are 3.5-4 million years old from southern Buenos Aires Province and the group
probably radiated in the Pampean region during the late Pliocene (D’Elía et al. 2008).
The biopedturbation activities of mammals now extinct or rare in temperate Australian grasslands probably played a critical role
in the maintenance of forb diversity (Reynolds 2006). The mechanisms include alteration to the spatial distribution and cycling
of soil nutrients and water infiltration (Garkaklis et al. 2003). Bettongs, potoroos, bandicoots, bilbies and rodents are amongst the
most important digging and burrowing groups (Garkaklis et al. 2003). Bilbies are powerful burrowers, prefering soft soils such
as sand dunes (Noble 1993). Reptiles, including goannas, may also be important, and the feral animal diggings, including those
of rabbits, may function in a similar fashion to those of native vertabrates (James et al. 2009).
Bettongia species probably mostly feed on underground fungi and may be opportunistically insectivorous and omnivorous
(Seebeck and Rose 1989). They sometimes bury and store seed, “which are eaten later, often after germination” (Seebeck and
Rose 1989 p. 721). The Rufous Bettong Aepyprymnus rufescens (Gray) is primarily rhizophagous buts eats fungi throughout the
year (Seebeck and Rose 1989). Foraging activities of Bettongia penicllata Gray for hypogeous fungi commonly cover the ground
with small diggings of a range of different sizes and ages. In plan they are elliptial with a spoil heap at one end and a steep wall
to a depth of 10-15 cm at the other. These excavations accumulate litter, leading to concentrations of buried fungal hyphae which
become water repellent lenses in the soil after gradual infill of the excavations. The increased water infiltration in the
excavations is the probable cause of decreased available nitrate and sulfur found in the soil of old, simulated diggings, while
decreased ammonium may be due to rapid nitrification (Garkaklis et al. 2003).
The Burrowing Bettong Bettongia lesueur is considered to be the most fossorial of the potoroids (Strahan) and constructed
warrens up to 30 m in diameter that could contain over 100 entrances or were simple structures with only one or two entrances,
the former sometimes associated with rock caps and the latter sometimes on plains (Noble 1993, Noble et al. 2007). It is “a
powerful burrower ... capable of penetrating the underlying rock” (Noble 1993 p. 60) and its activities probably significantly
promoted landscape heterogeneity and plant diversity (Noble et al. 2007). B. lesueur “may have helped maitain vast areas as
grassland by eliminating shrubs” (Noble et al. 2007 p. 335).
Among the native mammals still present in some temperate Australian native grasslands, the biopedturbation activites of the
Short-beaked Echidna may be the most significant. Much of the foraging activity of the Echidna requires digging to obtain
invertebrates, and the animals shelter in temporary digs and prepared tunnels (Menkhorst 1995c). Nursery burrows are shallow
and 1-1.5 m long (Menkhorst 1995c) while foraging disturbances range from nose-poke holes, through shallow scrapes to deep
digs and extensive bulldozing (Eldridge and Mensinga 2007). In semi-arid woodlands with a grassy understorey this soil
disturbance has been found to make a large contribution to landscape patchiness (Eldridge and Mensinga 2007). The foraging
pits accumulated greater quantities of plant litter than undug areas, have moister and more porous soil, are cooler and have a
different suite and greater abundance of soil micro-arthropods than the surface soil. Contrary to expectations, increased litter in
pits did not result in increases in total or active C, total N and available P, although the N was probably largely immobilised in
the litter. Ultimately, echidna pits probably influence plant germination and establishment (Eldridge and Mensinga 2007).
The hip hole diggings of Macropus spp. are constructed so as to assist the animals to cool, and are generally located in the shade
of trees or shrubs (Eldridge and Rath 2002), so may be of little significance in grasslands.
Biopedturbation by invertebrates may be more important than that of vertebrates. Ants and earthworms are probably the most
important groups. Ants are a prominent feature of temperate south-eastern Australian grasslands. Many species construct surface
mounds of excavated material around their nest entrances, associated with tunnels that may descend well under the surface.
When the effects of their activity is quantified over the long term they can be viewed as ecological engineers whose activities
restructure the landscape, generate heterogeneity, and affect soil structure and porosity, the distribution of soil nutrients and
regeneration of the flora (Richards 2009). The vertical tunnels of Underground Grass Caterpillars Oncopera fasciculatus
(Walker) (Hepialidae) reach a depth of up to 23 cm at maturity, depending on the ease with which the soil can be dug, and the
excavated soil is deposited around the tunnel entrance and on the larval feeding runways (Madge 1954). Many other insects have
larvae which live beneath the soil surface and contribute to biopedturbation. Earthworm activity in temperate Australian
grasslands can also be substantial. However there appear to be no published studies of the effects of bioturbation by invertebrates
in temperate native grasslands.
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