Marxan

Marxan is a reserve planning tool.

Description

Marxan is software that delivers decision support for reserve system design. Marxan finds reasonably efficient solutions to the problem of selecting a system of spatially cohesive sites that meet a suite of biodiversity targets. Given reasonably uniform data on species, habitats and/or other relevant biodiversity features and surrogates for a number of planning units (recently increased to more than 20,000) Marxan minimizes the cost (a weighted sum of area and boundary length) while meeting user-defined biodiversity targets.

The optimisation algorithm that attempts to find good systems of sites is 'simulated annealing'. The number of possible solutions is vast (for 200 planning units there are over 1.6 x 10^60 solutions) and because the problem is NP-complete there is no possible method for extracting an optimal solution in reasonable time for large problems. Because of this there is no real hope (or indeed incentive) to find an optimal solution: Marxan will find good solutions using simulated annealing. The user can also invoke a variety of less sophisticated, but often faster, heuristic algorithms. We have found that one of the most useful outputs from the decision support software is the 'summed irreplaceability' output (see figure below)  This output shows how often each planning unit is in one of the good systems. Planning units that are chosen more than 50% of the time can be thought of as being essential for efficiently meeting biodiversity goals. Sites that are rarely selected can be ignored.

Figure. An example of SPEXAN's 'summed irreplaceability' capacity. The shading represents the number of times a 10 km x 10 km block of the Florida Keys was chosen from 100 relatively efficient solutions where the goal was representing 20% of each habitat type.1

Developed by Ian Ball and Hugh Possingham at University of Queensland.

Function

• Analysis tools
  • Complex

Why use this tool?

To provide planning information about sites that should be reserved, and those sites that may not be needed.

The basic idea is that the reserve designer has a large number of potential sites or planning units from which to select a reserve system. They wish to devise a reserve system which is made up of a selection of these planning units which will satisfy a number of ecological, social and economic criteria.2

Who will use this tool?

• Data users
  • Expert
  • Skilled

 How will the tool be used?

• Desktop application
• Requires Windows/DOS
• Standard output is text format suitable for ArcGIS
• Standard input is a set of five text format data files
• User input is required to initially set up the data, and then running different options.

 Where in the data chain could this tool be used?

• User’s machine
• Post data preparation

 When could this tool be used?

• As a post process, after data is with the user

Availability

• Marxan: http://www.ecology.uq.edu.au/marxan.htm
• Download: http://www.ecology.uq.edu.au/marxan.htm
• Thorough manual available
• Current version 2.0.2     April 2007
• Freely available with attribution.3 The right to use Marxan comes with it a responsibility to inform, share and discuss.

Contact:

Professor Hugh Possingham

Director of The Ecology Centre

Departments of Zoology and Mathematics

The University of Queensland

St Lucia, QLD 4072

AUSTRALIA

Tel: 61 7 3365 9766

Fax: 61 7 3365 4828

Email: h.possingham@uq.edu.au

Comments

• What ALA architecture is required to support the tool?

The increasing complexity of spatial planning problems has lead to the development of MarZone, a new software program that extends on the capabilities of Marxan. MarZone incorporates new functionalities to support spatial planning with multiple zones, multiple costs and multiple objectives. Using MarZone, practitioners in natural resource management can identify configurations of sites that contribute to management objectives, whilst minimising cost. 4