Draft banksia Woodlands of the Swan Coastal Plain – Draft description and threats



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1.5 Key diagnostic characteristics and condition thresholds


The key diagnostic characteristics presented here summarise the main features of the Banksia Woodlands. These are intended to aid the identification of the ecological community, noting that a broader description is given in earlier sections.

National listing focuses legal protection on remaining patches of the ecological community that are most functional, relatively natural (as defined by the ‘Description’) and in relatively good condition. Key diagnostic characteristics and condition thresholds assist in:



  • identifying a patch of the threatened ecological community;

  • determining whether the referral, environment assessment and compliance provisions of the EPBC Act are likely to apply to the ecological community; and,

  • distinguishing between patches of different quality.

Condition thresholds provide guidance for when a patch of a threatened ecological community retains sufficient conservation values to be considered as a Matter of National Environmental Significance, as defined under the EPBC Act. Patches that do not meet the minimum condition thresholds are excluded from full national protection. This means that the referral, assessment and compliance provisions of the EPBC Act are focussed on the most valuable elements of the ecological community, which may include restored communities.

The Banksia Woodlands ecological community encompasses a number of ‘sub-communities’, and may also exhibit various degrees of disturbance and degradation. Natural variation and degree of degradation has been taken into account in developing the key diagnostic characteristics and condition thresholds.


1.5.1 Key diagnostic characteristics


These key diagnostic characteristics are the first step in identifying the Banksia Woodlands ecological community, acknowledging that the ecological community encompasses a number of sub-communities (e.g. Floristic Community Types). Some of these sub-communities have a higher threatened status where listed individually under Western Australian legislation.

Location and physical environment:

  • Occurs predominantly within the Swan Coastal Plain IBRA bioregion, which is comprised of the Dandaragan Plateau (SWA1) and Perth (SWA2) subregions. The ecological community also includes some occurrences of Banksia Woodlands outside and adjacent to the mapped Swan Coastal Plain IBRA boundary, for example the lower parts of the Darling and Whicher escarpments to the east and south of the Swan Coastal Plain (Northern Jarrah Forest JAF01; Southern Jarrah Forest JAF02 IBRA subregions).

  • Typically occurs on well drained, low nutrient soils on sandplain landforms. In particular, on deep Bassendean and Spearwood sands, or rarely on Quindalup sands.


Structure:

  • The principal structural features of the ecological community are:

  • A distinctive upper sclerophyllous layer of large shrubs or small trees1 (see footnote 1 on page 3), typically more than 2 m tall.

  • An emergent tree layer of medium or tall (>10 m) height Eucalyptus or Allocasuarina species may be present above the Banksia canopy.

  • A lower shrub and/or ground layer of lower sclerophyllous shrubs, cord rushes, sedges and perennial and ephemeral forbs.

Composition:

  • A patch of the ecological community may contain a range of Banksia species but must include at least one of the following species:

  • Banksia attenuata (candlestick banksia)

  • Banksia menziesii (firewood banksia)

  • Banksia prionotes (acorn banksia)

  • Banksia ilicifolia (holly-leaved banksia)

  • The mid and ground layers contain a wide diversity of shrub and herb species that often vary from patch to patch. Some of the more widespread and potentially characteristic species present in the ecological community are outlined above in the Description section.

1.5.2 Condition thresholds


Condition thresholds are yet to be finalised for the Banksia Woodlands ecological community. They often include parameters such as a minimum patch size, minimum cover of native species and a minimum plant species diversity. For vegetation communities endemic to WA, they could also cross-refer to available and widely used condition scales such as that developed by Keighery (1994) for vegetation around Perth.

1.5.3 Further information to assist in determining the presence of the ecological community and significant impacts


The following information should also be taken into consideration when applying the key diagnostic characteristics and condition thresholds (to assess a site to determine if the EPBC-protected ecological community is present and determine the potential impacts on the ecological community).

Land use history will influence the state in which a patch of the ecological community is expressed. The surrounding vegetation may also influence how important a patch of the ecological community is in the broader landscape.

A patch is defined as a discrete and mostly continuous area of the ecological community that may encompass smaller subpatches of other vegetation communities. Patches can be spatially variable and are often characterised by one or more areas within a patch that meet the condition threshold criteria amongst areas of lower condition. Therefore a patch may include small-scale disturbances, such as tracks or breaks (including exposed soil, leaf and other plant litter, cryptogams) or small-scale variations in vegetation that do not significantly alter its overall functionality. Where there is a break in cover from the edge of the upper sclerophyllous layer of less than 30 m, then the gap is part of a single patch.

This ecological community is highly diverse and variable. Composition often changes across a patch, but structure and presence of a significant Banksia component are unifying features.

A buffer zone is a contiguous area immediately adjacent to a patch of the ecological community that is important for protecting its integrity. The purpose of the buffer zone is to help protect and manage the national threatened ecological community. The edges of a patch are considered particularly susceptible to disturbance and the presence of a buffer zone is intended to act as a barrier to further direct disturbance.

As the area of the buffer lies to the outside, around a patch, it is not part of the ecological community and is not formally protected as a matter of national environmental significance. Where the buffer on a particular property is subject to existing land uses, such as cropping, ploughing, grazing, spraying, etc., they can continue due to ‘continuing use’ exemptions in the EPBC Act. However, practical application of a buffer zone is strongly recommended. For instance, it is recommended that care be exercised in the buffer zone to minimise the risk of any significant adverse impacts extending into those patches (significant impacts from activity within the buffer zone would require EPBC Act approval).



The recommended minimum buffer zone for the ecological community is 30 metres from the outer edge of a patch. A larger buffer zone should be applied, where practical, to protect patches that are of particularly high conservation value, or if patches are down slope of drainage lines or a source of nutrient enrichment, or to protect groundwater sources.

Restored (revegetated or replanted) sites are considered part of the listed ecological community where such a patch meets the description, key diagnostic characteristics and condition thresholds above, and there is evidence of post-regeneration recruitment or patch longevity. It is recognised that revegetation or restoration requires appropriate techniques as well as long-term management and considerable time for a degraded patch to repair functionality and reach higher quality condition (Stevens et al., 2016).

Sampling protocols. Thorough and representative on-ground surveys are essential to accurately assess the extent and condition of the ecological community. A minimal sampling protocol involves developing a quick/simple map of the vegetation, landscape qualities and management history (where possible) of the site. The site should then be thoroughly sampled to represent the range of variation in vegetation cover and species diversity, starting with the area of maximum apparent native plant species diversity. At least one hour per plot in early to mid spring and a second survey in late spring may be required to detect the majority of species. Sampling should be based upon plot sizes of least 100 m² (= 0.01 ha, 10m x 10m, or an appropriate shape of equivalent size). However, larger and more variable areas of vegetation will need more samples or plots to assess a site accurately. Recording the search effort (identifying the number of person hours per plot and across the entire patch; along with the surveyor’s level of expertise) can be useful for future reference.

Timing of surveys. Whilst identifying the ecological community and its general condition is possible at most times of the year, consideration must be given to the role that season and disturbance history may play in an assessment. For example, flowering may be necessary to identify some shrub species and active growth will indicate population sizes of annual weeds. Immediately after a fire one or more vegetation layers, or groups of species (e.g. obligate seeders), may not be evident for a time. The cover of native plants also varies between seasons and between years in response to variability in environmental conditions, and also with respect to cycles of recurring disturbance such as fire. Timing of surveys should therefore allow for a reasonable interval after a disturbance (natural or human-induced) to allow for regeneration, and be timed to enable component species to be detected and identified. For instance, surveys one year post fire may be required to assess a site against the key diagnostic characteristics and minimum condition thresholds.

Surrounding environment, landscape context and other significance considerations –The ecological community is dynamic and exists as a complex mosaic of species determined partly by water availability, substrate and landscape position. On top of this natural variation, a variety of anthropogenic disturbances have been imposed upon the ecological community since European settlement of the region.

Patches that are more species rich and less disturbed are likely to provide greater biodiversity value. Additionally, patches that provide corridors or linkages within a largely modified landscape are particularly important as wildlife habitat and to the viability of biota within those patches of the ecological community into the future, provided that threats are adequately managed.

Therefore, in the context of actions that may have ‘significant impacts’ and require approval under the EPBC Act, it is important to consider the environment surrounding patches that meet the condition thresholds. Some patches that meet the condition thresholds occur in isolation and require protection, as well as priority actions, to link them with other patches. Other patches that are interconnected with other ecological communities have additional conservation values, such as contributing to landscape complementarity, or providing movement opportunities for biota. In these instances, the following indicators should be considered when assessing the impacts of actions or proposed actions under the EPBC Act, or when considering recovery, management and funding priorities for a particular patch:


  • Large size and/or a large area to boundary ratio – larger area/boundary ratios are less exposed and more resilient to edge effect disturbances such as weed invasion and human impacts;

  • Evidence of recruitment of key native plant species following disturbance (including through successful assisted regeneration);

  • Faunal habitat as indicated by patches that meet a diversity of habitat requirements, and that contribute to movement corridors;

  • High species richness, most evident from the variety of native plant species but may also be shown by a high number of native fauna species;

  • Presence of listed threatened species or key functional species such as key pollinator and dispersal animals;

  • Scarcity of weeds and feral animals or opportunities to manage them efficiently;

  • Absence or limited symptoms of dieback;

  • Connectivity to other native vegetation remnants or restoration works (e.g. native plantings). In particular, a patch in an important position between (or linking) other patches in the landscape (taking into account that connectivity should aim to not exacerbate the incidence or spread of threats e.g. weeds); and,

  • Occurrence of the patch is:

    • in an area where the ecological community has been most heavily cleared and degraded, or is of a ‘sub-community’ (e.g. WA listed threatened or priority ecological community) that has been heavily cleared and degraded; or

    • at the edge of the range of the ecological community.


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