The South East Corner
Bioregion (SEC) extends from north of Ulladulla to near Lakes Entrance covering
just over 2.5 million hectares. There is no structural difference between
geologies on the tablelands and the coastal escarpment. Rather the latter has
been formed as a result of differential erosion rates[1]
due to proximity to the ocean and the associated atmospheric accession of sodium[2].
The western boundary
of the SEC is in line with the 700 metre contour and the lands within it can be
divided into three European land use categories. These are land largely cleared
for agriculture, land that supports commercial forestry operations and
non-commercial forests in largely inaccessible areas like the Wadbilliga-Deua
Wilderness.
Soil science tells us
that prior to the European invasion, Aboriginal management maintained soil
fertility by maintaining populations of the macro-organisms required for their
own survival. These species like pademelons, bettongs, potoroos and bandicoots,
are now either greatly depleted in number or regionally extinct.
In the pre-European environment populations of these species would have either increased or decreased depending on rainfall or the lack of it. In better times the major natural predator of these species, the Lace Monitor (Varanus varius) would also do well. Unlike other predators the Lace Monitor has the capacity to digest bones reducing them to a white faecal deposit, essentially pure calcium that readily dissolves and enters the soil with rain and counter the effects of sodium.
Reduced numbers of prey means reduced numbers of predators and over time the influence of sodium on soils has outweighed biological inputs. The outcome is that soils in all profiles, particularly the water holding clays become increasingly unstable and they disperse.
Hence forests on ridges and slopes have become susceptible to dry weather and drought, first observed in 1998. The breakdown of clay aggregates produces materials like soluble aluminium that are toxic to trees. These materials move with water through the soil profile to lower topographies were trees are then stressed and subject to Bell-Miner Associate Dieback (BMAD), recently listed as a Key Threatening Process in NSW.
“ In both forested and
agricultural lands, principles for sustainable land management will recognise
soil as a fundamental and integral part of an ecosystem, identify requirements
of the system and deal with them. In so doing, the precautionary principle
should be observed – “if there are threats of serious or irreversible
environmental damage, lack of full scientific certainty should not be used as a
reason for postponing measures to prevent environmental degradation (PROTEA
1991).” Tulau, M. 1997.