Reserve Design and Systematic Conservation Planning

The principles and quantitative methods used to decide where reserves should go and how they should be shaped to conserve biodiversity efficiently.

Definition

Reserve design is the choice of size, shape, number, and placement of protected areas to conserve target biodiversity. Systematic conservation planning is a structured, repeatable procedure for selecting reserve networks that represent biodiversity features comprehensively and efficiently, given limited resources.

Scope

Covers the design of individual reserves and the systematic assembly of reserve networks. Includes classic geometric design guidelines, the SLOSS debate, and the modern framework of systematic conservation planning built on representation, complementarity, irreplaceability, and cost. Excludes connectivity between reserves (sibling topic) and the assessment of whether existing reserves perform (treated under effectiveness).

Core questions

• How should reserves be sized and shaped to retain species?
• Is it better to have one large reserve or several small ones?
• How does complementarity make reserve selection efficient?
• How are cost and feasibility incorporated into planning?

Key concepts

• Representation and complementarity
• Irreplaceability
• Reserve size and shape
• SLOSS debate
• Conservation targets
• Gap analysis

Key theories

Complementarity and representation

Rather than repeatedly protecting the same common species, efficient networks add sites that contribute features not yet represented, achieving conservation targets with the least area or cost.

Irreplaceability and the planning framework

Systematic planning proceeds through explicit stages — setting targets, assessing existing reserves, selecting and implementing new areas — and ranks sites by how irreplaceable they are for meeting goals.

Clinical relevance

Systematic conservation planning is the standard method for designing reserve systems worldwide and underpins decision-support tools used by governments and NGOs. Applying complementarity and cost can dramatically reduce the area needed to meet conservation targets, making planning central to delivering protection efficiently.

History

Early reserve-design guidelines in the 1970s drew on island biogeography and sparked the SLOSS debate. The complementarity principle emerged in the 1980s, and Margules and Pressey's 2000 synthesis codified systematic conservation planning as a discipline, later operationalized in widely used software for reserve selection.

Debates

Single large or several small reserves (SLOSS)?

Geometric design rules suggested large, connected reserves are best, but several smaller reserves may capture more species turnover; the answer depends on the system, and the debate ultimately motivated the shift to complementarity-based selection.

Key figures

• Chris Margules
• Robert Pressey
• Jared Diamond
• Hugh Possingham

Seminal works

• margules2000
• primack2014
• groom2006

Frequently asked questions

What is complementarity in reserve selection?

The principle of choosing each new reserve to add species or features not already protected, rather than duplicating what existing reserves contain. It lets a network represent more biodiversity using less land or money.

What was the SLOSS debate?

A long-running argument over whether a Single Large Or Several Small reserves conserve more species for a given total area. There is no universal winner; the best choice depends on how much species composition varies among sites and on local threats.