9.1 Land Clearing and Fragmentation
The ultimate cause of declines of many woodland birds and other species is straightforward - "the loss of habitat in areas has been so extensive that populations cannot be maintained. In extreme examples in some districts there is simply no habitat left to maintain even single family groups of species. The declines have been exacerbated by the disproportionate loss of habitat on fertile soils, which was likely to have supported higher densities of many [taxa], and which possibly also act as drought refuges" (Trail & Duncan 2000).

"Often extinctions in regions occur in some districts 10-20 years after habitat loss effectively ceased" (Traill 1999). This phenomenon is referred to as 'extinction debt' because it is a case of impacts from past degradation, fragmentation and simplification taking many years to manifest. "The most likely scenario is that the habitat remaining is simply not extensive enough to maintain viable populations in the long term" (Traill 1999).

In addition to simple habitat removal, many woodland birds are now "disappearing from smaller remnants of remaining woodland, even in areas where the woodlands remain in structurally good condition. The loss of some woodland birds populations from remnants may in many cases reflect the loss of populations that are simply too small to survive in the longer term due to normal population fluctuations and natural perturbations such as droughts" (Trail & Duncan 2000).

Vegetation in the BBSB has been subject to high levels of fragmentation. An assessment of available data indicates that approximately 16% of the remaining vegetation of the region (which is only a fraction of original vegetation) occurs in fragments less than 1000ha in size.

However, the BBSB region is unique amongst all remaining temperate woodlands in Australia because it does contain six patches of contiguous woodland which are greater than 50,000ha in size. These include Pilliga West, Pilliga East, Goonoo, Coolah Tops, Mt Kaputar and the Bebo-Severn River area. These areas represent a core refuge for woodland species west of the Great Dividing Range and their adequate protection is critical to the survival of a large number of woodland species.

The role of these larger fragments, and particularly Pilliga and Goonoo, to the conservation of woodland species has been recognised by Date & Paull (2000) as follows "agricultural lands are barriers to the dispersal and population viability of all but a few forest and woodland fauna. Fauna in small State Forests are at a higher risk of extinction than in large State Forests as a result of current patterns of vegetation clearance and fragmentation".

However, on a landscape scale it is both large fragments and smaller 'stepping stones' and their collective distribution across the landscape that ultimately determines overall connectivity and affects movement between patches and maintenance of biological diversity throughout the region.

In order to identify linkages and reveal smaller patches of vegetation that were significant for connectivity across the region, an analysis of vegetation patch size and distribution was conducted for this report. This contributed to the assessment of the conservation value of State Forest areas and indicated an increased importance for protection of areas that represent cores or critical stepping stones for vegetation continuity in the region.

In the context of this on-going habitat loss and fragmentation in the BBSB region, the adequate protection of larger remnants and vegetated areas of connectivity is considered critical to the on-going survival of a large number of species.

Mining exploration and forestry activities within vegetated areas cause habitat fragmentation through the construction of access roads and seismic lines. Mining is particularly responsible for increased fragmentation due to the use of an intensive grid of roads and cleared pads for wellheads of approximately 1ha per well.

9.2 Hollow-bearing Tree Decline
Gibbons and Lindenmeyer (2002) estimate that at least 303 vertebrate fauna species in Australia use hollows "as diurnal or nocturnal shelter sites, for rearing young, for feeding, for thermoregulation, and to facilitate ranging behaviour and dispersal. For many of these species the use of hollows is obligate - no other habitat resource represents a feasible substitute".

According to Gibbons & Lindenmeyer 2002, the distribution of hollow-using species across Australia varies with major vegetation formations. They estimate that 70% of the total number of hollow-using vertebrate species in Australia occur in woodlands, compared with only 47% occurring in forests and 32% in closed forests. This indicates that the adequate protection of woodland ecosystems will be critical to the survival of large segments of the Australian vertebrate fauna which use hollows.

Gibbons and Lindenmeyer note that "native forest silviculture, firewood collection, rural dieback, grazing and clearing are causing ongoing depletion of the hollow resource" (Gibbons & Lindenmeyer 2002). This has been recognised as a major issue in the BBSB by Date and Paull 2000 who note that "levels of hollow availability and recruitment have been reduced in many areas of commercial forest in the study area."

As foreshadowed by the Gibbons and Lindenmeyer work, there are a total of 43 bird species, 13 mammals and 17 bats in the BBSB region which are known to utilise hollows (Date & Paull 2000). These include a large number of threatened and significant species such as the Brushtail Possum, Yellow-bellied Sheathtail Bat, Eastern Pygmy Possum, Feathertail Glider, Masked Owl, Glossy Black Cockatoo and Turquoise Parrot. Many other species are also dependent on mature trees for other critical habitat characteristics such as abundant nectar sources, large trees for nesting and mistletoe loads.

Studies such as those by Date & Paull 2000 have shown that "the largest eucalypts and range of eucalypt sizes…were associated with the transects of highest richness of arboreal and terrestrial mammal species across the study area". And "species rich fauna communities were found in areas with low and moderate frequencies of logging and thinning" (Date & Paull 2000).

The number and types of hollows vary with different tree species. The large number of animal species and their varied requirements means that a wide range of tree species must be reserved. The fact that a large number of hollow-bearing trees have been removed from many forests, the long periods of time needed for hollow formation, and the fact that many species change hollows regularly demands that special protection should be afforded to hollow-bearing trees. It is also necessary to maintain younger age classes of trees in sufficient numbers to ensure adequate future recruits for hollows.

The protection of the oldest remaining components of commercial vegetation types such as Narrow-leaved Ironbark is a key component of this proposal. Adequate reservation of samples of older, commercial woodland ecosystems and the implementation of rigorous off-reserve retention measures is urgently required to redress the decline of mature ironbark trees and associated dependent species decline.

9.3 Habitat Degradation
As noted by Reid 1999 in his work on woodland birds of the wheat/sheep belt "Land clearance, with its cascading effects of direct habitat loss and fragmentation, is viewed here as the ultimate driver of decline and extinction of birds…..However, the ongoing decline in habitat quality at the patch level is equally as serious, and can be viewed as the proximate driver, especially with regard to patch extinctions". Therefore, it is essential that management of remaining woodland patches in the bioregion is aimed at protecting biological values and minimising threats which degrade habitats in order to enhance the survival of woodland birds and other fauna species.

The degradation caused by logging, firewood collection, grazing and inappropriate burning regimes on vegetation structure of woodland ecosystems is well documented (Reid 1999, Reid 2000, Traill 1999). Logging has resulted in the conversion of mixed ironbark and cypress woodlands to dense 'monocultures' of regrowth cypress, weed invasion, and modification of understorey structure and habitat availability. Similarly, the ingress of feral animals and native predators into degraded areas is also recognised as a threat to natural ecosystems function (Robinson & Traill 1996).

Seddon, Briggs & Doyle (2001) found that diversities of all bird species and of woodland birds were related to shrub cover, independently of effects of remnant area on species diversity. This confirms previous studies which have shown that number of shrub species, shrub cover, pine cover, number of logs and fallen branches and isolation have been related to diversity of woodland birds (various, quoted in Seddon, Briggs & Doyle 2001).

Traill & Duncan (2000) continue:

"Key resources used by many declining woodland birds are tree hollows, nectar, and an intact ground cover and understorey vegetation in which to forage. These resources have been greatly reduced in many remnants. Remaining woodlands on public land and some private lands have had histories of intensive use for wood production. This has reduced average tree size and led to the disproportionate loss of large, mature trees".

"A large proportion of the declining woodland birds are ground feeders and may be especially susceptible to changes to ground cover caused by stock, rabbit and kangaroo over-grazing and weed invasion".

The threats posed by habitat fragmentation of all types require the protection of highest conservation value areas and the mitigation of impacts through ecologically sustainable management practices where the threatening uses continue.

9.4 Salinity
Much of the remaining vegetation in the BBSB occurs in places that are major intake areas for the Great Artesian Basin, as well as source areas for important aquifers in several major river valleys such as the Macquarie and Namoi.

Most of the BBSB does not rate as a high-risk salinity region, though a few high risk areas do occur and most evidence seems to indicate worsening trends (National Land and Water Resources Audit 2000). From a hydrological point of view, the highly permeable sandstone substrata of the BBSB acts more as a recharge zone for groundwater. The Pilliga for example is known to be a significant recharge zone for the Great Artesian Basin and is part of a regional groundwater flow system. As groundwater entry points, the wooded sandstone communities are critical for the maintenance of clean water and a healthy hydrology.

However, the National Action Plan for Salinity (2000) identified a number of rivers, such as the Talbregar on the southern edge of Goonoo State Forest, with some of the highest salinity levels in the state.

Other evidence indicates the high risk of salinity inherent in the local groundwater. Recent drilling for gas production on the eastern side of The Pilliga has caused groundwater saline levels at four times the level present at similar operations in the Camden area. The better conservation management of recharge areas can alleviate the risk of worsening salinity problems in the groundwater and river systems.

The importance of wooded areas to attract rainfall and in so doing maintain necessary water cycles has been known for some time.

9.5 Soil Erosion
Sandstone based soils and country are among the most susceptible to soil degradation due to their highly permeable nature. Cleared areas on sandy soils are very prone to wind erosion and this type of ecosystem is very prone to gully erosion if natural water flows are disrupted. Widespread disturbance can also cause movement of top sand into lower parts of the catchment.

There is evidence of these processes in the Pilliga and Goonoo including examples of badly eroded gullies, and sediment build-up in creeks. This is most likely due to modification of the surrounding vegetation and hydrology by human activities. It is imperative that these issues are addressed in any assessment of the health of the landscape.

Most of the better soils in the bioregion have been developed for stock or cropping but some of the most important vegetation remnants remain in these sandy areas. In terms of soil retention, native grasses and vegetation does this job best because of the symbiotic relationship they have with the soils and being adapted to seasonal and rainfall variability.