Agriculture Reference
In-Depth Information
THE POTENTIAL FOR INTRODUCING NEW EARTHWORM
SPECIES INTO AUSTRALIA
The possibility also exists to introduce other earthworm species into southern Australia from
climatically matched regions overseas. No deliberate attempts to do this have yet been attempted,
although such a strategy was suggested by Barley (1959c) and Lee (1985). Broad-scale surveys
and intensive, seasonal monitoring of field populations suggest that the current earthworm fauna
in agricultural fields is represented poorly by deep-burrowing species. Virtually all earthworm
activity is confined to the top 10 cm or less of soil during winter and spring. The further spread
of
A. longa
within Australia will possibly help redress this limitation of the earthworm fauna, but
it is unlikely that
A. longa
will successfully colonize the strictly mediterranean climatic regions.
For instance, the natural distribution of
A. longa
does not extend into mediterranean regions of
countries such as France. Instead, other anecic species such as
Scherotheca
spp. are commonly
found there. These last species might also be considered for importation to Australia (Baker 1998a).
The native European distributions of several of the lumbricid earthworm species, now found in
Australia, are broad, ranging from the Mediterranean to Scandinavia (e.g.,
A. caliginosa
and
A. chlo-
rotica
). The majority of early European migrants to Australia, who presumably brought these lumbricid
earthworms with them accidentally (e.g., in potted plants), were mainly from countries with cool,
temperate climates, such as the U.K., Ireland, and Germany. It is sensible to question the likely suitability
of strains of earthworms from such countries when faced with the warmer and drier habitats in much
of southern Australia and whether Mediterranean strains of the same or other species might be more
appropriate (Baker 1998a,b). Dyer et al. (1998) used techniques based on polymerase chain reaction
to at least show that different geographic races of
A. trapezoides
can be recognized within Australia.
Perhaps such techniques could also be used to trace the origins of Australian earthworm populations
to Europe, check their ecological suitability, and select better ones. We actively select climatically
sensible strains or varieties of agricultural plants and biocontrol agents, so why not also earthworms?
There are risks attached to introducing taxa to new areas, whether these taxa come from overseas
or from elsewhere within Australia. Issues that must be faced include the possibility that the new
invaders might compete with the local earthworm fauna, disrupt ecosystem processes in nontarget
areas (e.g., native forests and pastures, compared with improved pastures and croplands), and carry
with them undesired diseases. These diseases can be controlled through rigorous quarantine pro-
cedures. Some preliminary studies have been completed that suggest
A. longa
is unlikely to invade
native woodlands in southern Australia and to compete with native earthworms there (Dalby et al.
1998b). There is little doubt that
A. longa
will have some impact on the abundance of resident
earthworms when introduced into pastures (Dalby et al. 1998a; Baker et al. 1999c; Baker et al.
2002a), but studies suggest that this potential impact is probably small, and that the overall
abundance and, most importantly, the functional diversity are increased.
EARTHWORMS IN PASTURES IN NORTHERN AUSTRALIA
The comments in preceding sections all refer to knowledge of the distribution, biology, and agricultural
value of earthworms in southern temperate or mediterranean climatic zones in Australia. Very little is
known of such topics for pastures in northern Australia. Baker et al. (1997a) documented the presence
of some earthworm species in tropical grasslands, noting they differed from those in the south (e.g.,
the exotic
P. corethrurus
) and indicated that some of the more southern species (e.g.,
Aporrectodea
spp.) can be found as far north as southern Queensland. Blakemore (1997) reported that the introductions
of exotic and native earthworm species increased pasture production on brigalow soils by 64% within
a year in southeastern Queensland. In other studies, Friend and Chan (1995) and Chan et al. (1997)
showed that native earthworms (e.g.,
Heteroporodrilus mediterreus
) can improve the structure (hydrau-
lic properties) of native pasture soils in northwestern N.S.W.
