Systematic Reserve Design

Introduction to Systematic Reserve Design

In recent years it has become recognized that selecting areas in an ad-hoc manner to be biodiversity reserves is likely to be an inefficient use of resources. Rather, a systematic approach to identifying possible reserves will lead to better recognition of needs and tradeoffs and improved decision-making. In 2000 Margules and Pressey listed six stages to follow in conservation planning: 1) measure and map biodiversity 2) identify conservation goals for the planning region 3) review existing reserves 4) select additional reserves 5) implement conservation actions on the ground and 6) manage and monitor the reserves.

The tasks of reviewing existing reserves and selecting new ones lends itself to an optimization approach. Since resources to create new reserves are always limited, selecting locations that provide the "most bang for the buck" according to one's metrics of value and cost is an important goal, and can be treated as an optimization problem. There are a number of key concepts in this treatment:

  • Comprehensiveness - does the reserve system sample the full range of biodiversity, both typical and atypical?
  • Representativeness - does the reserve system capture biodiversity that is representative of its surroundings?
  • Efficiency - to what degree is is the cost of the reserve network minimized while meeting all the biodiversity goals?
  • Spatial compactness and connectedness - are the reserves compact in shape (have a low edge-to-area ratio) and well-connected to one another? Or are they elongated and fragmented?
  • Flexibility - does one have options to achieve conservation goals in a number of ways?
  • Complementarity - to what extent does an added reserve element advance the goal of representing biodiversity in a network by contributing unique elements?
  • Irreplaceability - to what extent is a particular site essential to achieving a conservation target?
  • Adequacy - does the reserve system ensure the persistence of all elements given the population viability, ecological processes, and interaction between species, ecosystems, and landscape dynamics?

Algorithms for Systematic Reserve Design

As suits an optimization problem, systematic reserve design can be described mathematically. One such formulation might run as follows. Sum the cost of the proposed reserve network, and sum a set of penalty factors for biodiversity elements that are not represented. Optionally sum over terms representing the total boundary length of reserves in the network. The optimization problem is then to choose a set of reserve elements so as to minimize the total sum over all the above terms.

As the number of possible elements in the reserve increases, finding an exact solution to this minimization problem quickly becomes computationally intractable. Instead, conservation practitioners usually adopt heuristic approaches to solve the problem: algorithms that are not guaranteed to provide the mathematically optimally solution, but usually return a solution that is close to the optimum one. Two popular platforms for implementing these heuristic algorithms for reserve design are Zonation, initially developed by Atte Mollinen, and Marxan, initially created by Hugh Possingham.

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