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Successful conservation relies on choosing the right tools for each goal and context. As the world aims to protect 30% of Earth's land and seas under the Kunming鈥揗ontreal Global Biodiversity Framework, conservation planners face the challenge of selecting areas that deliver the highest benefit for biodiversity while minimizing costs and meeting other competing land use needs.

A new study, led by researchers at the University of Helsinki reveals that the way we select areas for protection, using either strict targets or more flexible rankings, can result in very different levels of protection for species. The research is in the journal Biological Conservation.

Finding areas that effectively protect biodiversity while also considering other goals, such as minimizing costs and supporting sustainable food production, is a complex task. To help with this, conservation planners rely on systematic conservation planning tools鈥攎ethods designed to identify the most important areas for conservation. However, different tools can produce markedly different results, even when using the same data and the same amount of area for protection.

This study compared two commonly used approaches: first, a method that sets clear protection goals for each species, such as ensuring that at least 30% of a species' habitat is protected at the minimum possible cost, and second, a method that aims to cover as much of all species' habitats as possible while minimizing costs.

The researchers tested these approaches in five study cases, including tree species, mammals, corals, butterflies and birds, to address a wide range of conservation challenges. For example, when using the same amount of area for protection, the European tree species case study showed higher habitat protection under the flexible approach, and the difference was even more pronounced for the global dataset of all extant terrestrial mammals.

However, this higher average protection came with a consequence: some species received much less protection than others, and minimum protection levels were not guaranteed. In contrast, the target-based approach ensured that all species reached their protection goals, but the overall average protection across species was lower. These findings highlight the trade-off between ensuring that every species meets its minimum protection target and trying to maximize protection across all species.

"Our results show that choosing between these approaches is not just a technical detail鈥攊t's a strategic decision with real consequences for biodiversity outcomes," says the lead author Thiago Cavalcante, a postdoctoral researcher at the University of Helsinki, Finnish Museum of Natural History. "We need to be transparent about these trade-offs to support better-informed conservation decisions."

By comparing different ways of protecting species across several case studies, this study offers practical advice for planners and policymakers on how to make conservation efforts more effective and transparent. The authors stress that it's important to share clear results showing how well all species are protected, not just how many species reached their targets, so that conservation decisions can lead to better outcomes.

The study was carried out using open data and provides reproducible code to promote transparency and support future research.