Vegetation fragmentation

Vegetation fragmentation is caused by clearing which separates vegetation into smaller patches of vegetation.  These patches are therefore no longer continuous and are disconnected by barriers such as roads, urban development, agriculture and mining, plantations. This can isolate species and restrict the movement of flora, fauna and genetics across the landscape, making species more susceptible to pressures.

Smaller more isolated patches of vegetation [and the species that rely on these patches for habitat] are less resilient to threats such as invasive weeds, pest animals, drought and high-intensity fire, disease, and/or climate change. As patch size decreases, so too does the resilience of flora, fauna and habitat continuity.

The remaining native vegetation in the SWCC Region is contained within a large number (77,411)1(Ecotones, 2018) of fragmented patches (patches of vegetation that are no longer continuous and are separated by barriers such as roads, urban development, agriculture, mining, plantations, etc). Very few patches (314) in the SWCC remain in patch sizes greater than 1000ha compared to the number of patches (47,243) remaining in patch sizes less than 2ha1 (Ecotones, 2018).  This indicates a highly fragmented landscape.  Smaller more isolated patches of vegetation are less resilient to threats such as invasive weeds, pest animals, drought and high-intensity fire.  As patch size decreases, so too does the resilience of flora, fauna and habitat continuity.

Approximately 53% of the SWCC region has been cleared with more severe losses of 80% in the Wheatbelt and Swan Coastal Plain (see also Loss of Vegetation) 1 (Ecotones, 2018).  Consequently, fragmentation is also greater in these sub-regions and this coincides with the landuse of these areas ie: housing, industry and agriculture.  While there are only 314 patches in areas of greater than 1000ha, these areas account for a large proportion (65.8%) of all remaining vegetation in the SWCC region and mostly occur in the Warren and Jarrah Forest IBRA Regions; again coinciding with the landuse of these areas1 (Ecotones, 2018).

While high levels of fragmentation impact flora and fauna, a small patch size does not necessarily denote low ecologically value.  Even individual trees can be important food sources and habitat for threatened and other species.  Also, some small vegetation patches could contain threatened flora species or a threatened ecological community (TEC) and could represent a large proportion of what is remaining of that threatened flora or TEC.

Pressure on the environment from historical and future clearing poses significant challenges for land managers as addressing and mitigating the impacts is costly and difficult.

Data Source

1 Department of Primary Industries and Regional Development Native Vegetation Extent data (updated August 2017). [link] [accessed March 2018]. 

Disclaimer

The Department of Department of Primary Industries and Regional Development maintains remnant vegetation data, which is used by a number of agencies for conservation policy and planning; and was also used for this analysis. However, there are significant differences between areas of the State in terms of the age and resolution of the mapping.

References

1 Ecotones. 2018. Environmental Snapshot GIS & Data Analysis. Report for South West Catchments Council.