Zonation - Waikato Biodiversity Ranking

This project, carried out by the Waikato Regional Council (WRC), aims to provide an updated set of rankings for natural ecosystems within the Waikato region.

The project builds on earlier works for biodiversity ranking of similar nature but differs in several respects, with the goal of a higher level view of understanding indigenous biodiversity within the region. This project did this through the more detailed consideration of lakes, rivers, updated descriptions of terrestrial systems and also a new approach to consider biological connectivity both across the landscape considering terrestrial systems and lakes as well as through river networks.

Zonation was utilised in this project for its ability to perform ranking analysis that could then be used to inform council staff and management of indigenous biodiversity priorities within the Waikato Region. This information could then be used to guide processes to meet council goals of protecting a representative range of indigenous ecosystems with links to both terrestrial and aquatic systems.

Methods

The zonation software calculates a continuous ranking of priority for all locations across a landscape of interest. The Information used for this ranking process consists of gridded data layers, with one layer describing the spatial distribution of each biodiversity feature of interest, in this case ecosystem types.

Additional layers can be used to describe:

  • The condition of biodiversity features
  • The difference that management would make and its cost
  • Define planning units.

During ranking, grid cells are removed in a backwards stepwise process where the grid cell(s) making the lowest contribution to the representation of biodiversity features are removed at each step.

 Findings

Outputs from the Zonation tool included maps, based on the input grid features, which displayed the biodiversity priority ranking of all study sites, as well as tabular data with descriptions of the protection provided to each biodiversity feature as a function of site priority . These outputs, including a ranked value from 0-1, can then be used in the development of management strategies. Priorities for budgeting and project development are then able to be assigned to those areas which have a highest priority output from the modelling, as such being deemed the more valuable or vulnerable areas of biodiversity.

Zonation Waikato Outputs

Estimated condition of terrestrial sites, as calculated by combining estimates of intrinsic condition and recent management gain.

 

Zonation Aquatic Condition

Estimated condition of aquatic ecosystems including lakes, and river/streams - shown here for the lower Waipa catchment.

 

Conclusions

Within this modelling of the Waikato Region it was noted that there can be some inherent difficulties with using a ranking system, such as is used in Zonation, in the comparison of diverse sections of land. An example was raised of a scenario where budgeting restrictions directed funds into what is deemed the top 30% of sites. Within that top 30% can one define a site in the top 10% as more valuable that a similar site ranked by modelling as in the top 20%? The conclusion is that in reality sometime the answer is yes and sometimes it is no and as such there are limits to the outcome of this modelling.

Other outcomes from this study include the importance of understanding why the model is creating the outputs it does. the key example listed is that Zonation considers the size of a site in its modelling giving a higher weighting to smaller sized sited in an effort to ensure that these features are fairly represented, this approach has the potential to designate a high weighting to a site which contains relatively common and wide spread features based more on the size of site rather than biodiversity value. The result of this is that once a budgeting decision is made to support only a proportion of sites care should be taken in choosing that 30% based on more than just modelled rankings. 

               

Zonation Example of 30 priority Zoning

Priority sites comprising 30% of Waikato Regiona's surviving native-dominated terrestrial cover.

Associated Models

Zonation

The ZONATION tool provides methods and software for ecologically based land use planning including decision support for spatial conservation resource allocation.

References

John Leathwick (2016): Integrated biodiversity ranking and prioritisation for the Waikato region. Waikato Regional Council Technical Report 2016/12.