Regional Ecological Linkages
Regional Ecological Linkages have been identified across the SWCC Region, initially through the South West Regional Ecological Linkages (SWREL) project (2009) which were then extended to the remainder of the SWCC Region in 2013. Both reports can be accessed in the links below.
SWCC Strategic Priority
Regional Ecological Linkages are identified within SWCC’s NRM Strategy as a high (first order) priority asset under the Terrestrial Biodiversity.
What is an Ecological Linkage?
A series of (both contiguous and non-contiguous) patches which, by virtue of their proximity to each other, act as stepping stones of habitat which facilitate the maintenance of ecological processes and the movement of organisms within, and across, the landscape.
Ecological linkages are not to be confused with biodiversity, or wildlife, corridors. Biodiversity corridors are generally considered to be linear strips of remnant vegetation or revegetation which directly connect patches. Instead, ecological linkages, as determined by the SWREL project (and extended in 2013) use axis lines which have been specifically designed to be used as a basis for recognising the ecological value of spatial relationships between patches of remnant vegetation when planning and managing biodiversity at both patch and landscape scales.
What is the purpose of Ecological Linkages?
The purpose of an Ecological Linkage is the recognition of a patch’s additional value to biodiversity conservation that results from its close proximity to other patches. This recognition of the value of connectivity allows biodiversity managers and planners to achieve more (ecologically) effective planning outcomes in regard to both strategic and management planning objectives. For this reason the identification and management of Ecological Linkages should not be regarded in isolation of other biodiversity values, but rather in consideration of other regional and local biodiversity conservation values and initiatives.
Having recognised Ecological Linkages, patches of remnant vegetation with a high landscape connectivity value can be identified and assigned (in consideration of other conservation planning initiatives and values) an appropriate level of consideration in regard to management and retention options (Molloy et al, 2007). It is also intended that less viable patches with a high landscape connectivity value will be considered for appropriate management actions. It is intended that such activities will be undertaken to improve their condition, increase their size, and to buffer them from threatening processes. This will enable these (previously) less viable patches to better function as stepping stones linking larger patches and/or regionally significant biodiversity conservation assets.
It should be noted that revegetation projects undertaken to physically connect patches within the Ecological Linkages (creating corridors) are generally considered to be of a lower priority than protecting and conducting landscape rehabilitation in existing patches (Del Marco et al., 2004, Dunlop and Brown 2008, Macklay et al. 2008, Molloy et al. 2007).
Regional Ecological Linkages
Designated Regional Ecological Linkages serve to link protected patches of regional significance (as defined in Molloy et al., 2007) by identifying the best condition patches available as stepping stones for flora and fauna between regionally significant areas. This increases the long-term viability of all the constituent areas. Regional linkages also need to connect regionally significant patches and biodiversity conservation assets which are situated outside of the study area (Del Marco et al. 2004, Molloy et al, 2007).
Local Ecological Linkages
The methodology used in identifying regional ecological linkages can be used to define a network of Local Ecological linkages which aim to link protected locally-significant patches to; each other, regionally significant patches and Regional Ecological Linkages. Local Ecological Linkages are an important part of improving the viability of patches that may be; too small, of an unsuitable shape, or in a condition which would significantly lessen their ability to otherwise persist. The viability of patches will be improved by including as many viable patches within each link as possible and by maximising the number of connections to each area.
Methodology for identifying Regional Ecological Linkages (Extended across the SWCC Region, 2013)
The following steps were taken in the generation of the ecological linkage axis lines:
- Linkage axis lines as defined and identified through the SWREL project (Molloy et al., 2009) were adapted as a starting point from which additional linkage lines were added to encompass the SWCC mandated region. Minor amendments were made to the existing SWREL lines through the Jarrah Forest IBRA regions to facilitate connectivity at the regional scale.
- In areas beyond the boundaries of the SWREL project area, appropriate major watercourses for the Eastern Jarrah Forest, Avon Wheatbelt and Mallee Interim Biogeographic Regions of Australia (IBRA) regions (within the extent of the SWCC mandated region) and the Serpentine-Jarrahdale Shire were selected and added to the SWREL axis lines.
- Within the areas covered by the Eastern Jarrah Forest, Avon Wheatbelt and Mallee IBRA regions and the Serpentine-Jarrahdale Shire two data sets were developed to inform the planning process. These were percentage of remnant vegetation per subcatchment and average fragmentation statistic (McGarigal et al., 2009) per sub catchment.
- The SWCC NRM Strategy Biolandscapes (Ecosystem Solutions Pty Ltd, 2009) were identified as priorities.
- Draft ecological linkage axis lines were identified using these data sets.
- The draft ecological linkages were then evaluated using a Proximity Analysis to assess their effectiveness.
- Ecological linkages were reviewed, edited and finalised.
As per the SWREL methodology, the following guiding principles were used to create the ecological linkage axis lines. However it is recognised that across much of the project area there may be insufficient patches with these properties available and in such cases patches not meeting these criteria were used.
- Where available, patches should be at least 10 ha in size and of good or better condition;
- Continuous stands of native vegetation with a preferred width of >500 m should be chosen where available;
- Thin remnants (<100m wide) should be avoided where it is practical to do so;
- Heterogeneity in patch structure should be sought;
- The widest possible diversity of habitat types should be sought within a linkage with similar habitats (preferably) less than 1000m apart;
- Open canopies over a highly disturbed understorey may be of little value except for highly mobile species;
- Where continuous stands of native vegetation are not available, linkages made up of patches which form stepping stones between larger intact patches should be selected;
- The target maximum between patches is <1000 m (although closer proximities between patches are preferred distances >1000m will be considered in highly fragmented landscapes);
- The greater a patch’s area the greater its capacity to maintain a larger and more viable suite of species;
- The number of linkages connecting to any given patch should be maximised as this improves overall connectivity across the landscape and long-term viability of individual patches;
- Patches should be chosen whose shapes minimise edge effects;
- The potential effects of stochastic and deterministic abiotic processes (such as the impacts of wind and water movements and their potential for secondary effects such as dryland salinity, erosion and acidification) within a landscape should be considered.
As per the SWREL methodology, the following areas have been given high priority for inclusion in the linkage:
- Patches forming the most direct links with regionally significant patches or other identified Ecological Linkage;
- Ecological Linkages should be selected whose directions facilitate normal migration, and aid in the adaptation of species and assemblages to climate change;
- Riparian vegetation along waterways including an appropriate buffer of non-riparian vegetation;
- Patches that enhance the viability of significant biodiversity conservation assets and initiatives through conserving both species and structural heterogeneity and therefore habitat values;
- Patches at high points in the landscape that are in the line of sight of other patches. Line of sight is important for species dispersal and home range utilisation.
In addition, the following areas have been given high priority for inclusion in the linkage:
- Sub-catchments with a high percentage of remnant vegetation;
- Sub-catchments with a high average fragstat statistic;
- SWCC NRM Strategy Biolandscapes (Ecosystem Solutions Pty Ltd, 2009).
Note: These principles are aspirational in nature and, given the extent of fragmentation across much of the SWCC region, may not be practical in all landscapes. For example; some landscapes may not have sufficient patches with an area of >10ha or a width of >100m available to form a linkage or suitable patches may be > 1000m apart.
Fragmentation statistics, or proximity indices, were calculated using the V-Late 2.0 beta extension for ArcGIS 10.1®. Statistics are computed as the sum, over all patches of the corresponding patch type whose edges are within the search radius of the focal patch, of each patch size divided by the square of its distance from the focal patch. Proximity is then averaged across all patches with a buffered distance for each patch, thereby quantifying the spatial context of a patch in relation to its neighbors of the same class; specifically, the index distinguishes sparse distributions of small patches from configurations where the class forms a complex cluster of larger patches. Thus, the proximity index measures both the degree of patch isolation and the degree of fragmentation of the corresponding patch type within the specified neighborhood for each patch (McGarigal et al., 2009). In this application, sub-catchments were categorised by IBRA region, reflecting the different levels of fragmentation within each region, with overlaps to compensate for variation between relevant boundaries. Fragmentation statistics were calculated for all patches of remnant vegetation within (both totally and partially) each sub-catchment and an average value calculated. Results were presented as quintiles defined by natural, Jenk’s breaks for
each IBRA region.
Remnant vegetation extent
As with the Fragstat analysis, sub-catchments were categorised by IBRA region, reflecting the different levels of fragmentation within each region, with overlaps to compensate for variation between relevant boundaries. Percentage of remnant vegetation for each subcatchment was calculated with ArcGIS 10.1®. Results were presented as quintiles defined by natural, Jenk’s, breaks for each IBRA region.
The proximity analysis methodology relies on assigning a connectivity value to a patch relative to a linkage axis line.
Values are defined as:
- 1a – The whole of a patch whose edge touches, or comes within a distance 100m from, a linkage axis line.
- 1b – The whole of a patch whose edge comes within a distance 100m from, a 1a patch.
- 1c – The whole of a patch whose edge comes within a distance 100m from a 1b patch.
- 2a – The whole of a patch whose edge comes within a distance 500m from a linkage axis line.
- 2b – The whole of a patch whose edge comes within a distance 500m from a 2a patch.
- 2c – The whole of a patch whose edge comes within a distance 500m from a 2b patch.
- 3a – The whole of a patch whose edge comes within a distance 1000m from a linkage axis line.
- 3b – The whole of a patch whose edge comes within a distance 1000m from a 3a patch.
- 3c – The whole of a patch whose edge comes within a distance 1000m from a 3b patch.
Where a patch is assigned multiple values, the first value assigned will be kept as the nominal value. Patches not assigned a value will not be considered part of the ecological linkage.
- The ecological linkages produced in this project have been designed to function at the regional scale and to meet regional planning objectives. They have not been designed to supplant local scale connectivity planning. Rather, it is the purpose of this project to help recognise the contributions made through localised conservation planning initiatives towards conservation outcomes throughout the whole SWCC region.
- As patches of remnant vegetation are removed from the matrix, or if they are diminished or enhanced in area, proximity values should be recalculated.
- This project is static in nature; potential future impacts resulting from changes in variables such as climate, land use or hydrology have not been considered. Consequently, project products should be used in recognition of the accuracy of the data used in, and the scope of, their development.
- As a preliminary planning exercise, the products of this project have been developed through a desktop GIS process without the benefit of ground truthing or community consultation. They have been designed for implementation at the regional scale to complement finer scale connectivity planning, not to replace it.
The regional ecological linkages axis lines and remnant vegetation by proximity value (using 2012 DAFWA remnant vegetation) can be viewed on the Regional Priorities – map here.
- Molloy, S.W. and Deeley, J (2013). Extending the South West Regional Ecological Linkages across the South West Catchments Council Region: Developing the Draft Linkages. Bunbury: South West Catchments Council.
- Molloy, S., Wood, J., Hall, S., Wallrodt, S. and Whisson, G. (2009) South West Regional Ecological Linkages Technical Report, Western Australian Local Government Association and Department of Environment and Conservation, Perth.
- Molloy, S., O’Connor, T., Wood, J. and Wallrodt, S. (2007) Addendum for the South West Biodiversity Project Area, Western Australian Local Government Association, West Perth.