Leveraging species richness and ecological condition indices to guide systematic conservation planning

The global crises of biodiversity loss and climate change are interconnected in root cause and solutions. Targeted land conservation has emerged as a leading strategy to protect vulnerable species and buffer climate impacts, however, consistent methods to assess biodiversity and prioritize areas for protection have not yet been estab-lished. Recent landscape-scale planning initiatives in California present an opportunity to conserve biodiversity, but to enhance their effectiveness, assessment approaches should move beyond commonly used measures of terrestrial species richness. In this study, we compile publicly available datasets and explore how distinct biodiversity conservation indices -including indicators of terrestrial and aquatic species richness and of biotic and physical ecosystem condition -are represented in watersheds of the northern Sierra Nevada mountain region of California (n = 253). We also evaluate the extent to which the existing protected area network covers wa-tersheds that support high species richness and intact ecosystems. Terrestrial and aquatic species richness showed unique spatial patterns (Spearman R = 0.27), with highest richness of aquatic species in the low-elevation watersheds of the study area and highest richness of terrestrial species in mid-and high-elevation watersheds. Watersheds with the highest ecosystem condition were concentrated in upper-elevations and were poorly correlated with those with the highest species richness (Spearman R = - 0.34). We found that 28% of watersheds in the study area are conserved by the existing protected area network. Protected watersheds had higher ecosystem condition (mean rank-normalized score = 0.71) than unprotected areas (0.42), but species richness was generally lower (0.33 in protected versus 0.57 in unprotected watersheds). We illustrate how the comple-mentary measures of species richness and ecosystem condition can be used to guide strategies for landscape-scale ecosystem management, including prioritization of watersheds for targeted protection, restoration, monitoring, and multi-benefit management. Though designed for California, application of these indices to guide conser-vation planning, design monitoring networks, and implement landscape-scale management interventions pro-vides a model for other regions of the world.

Automated summary

The global crises of biodiversity loss and climate change are connected in their root cause and solutions. Targeted land conservation is an effective strategy for protecting vulnerable species and mitigating climate impacts, but there is a lack of consistent methods for assessing biodiversity and prioritizing areas for protection. This study focuses on landscape-scale planning in the northern Sierra Nevada mountain region of California and evaluates the representation of biodiversity conservation indices in watersheds. The study finds that the existing protected area network covers only 28% of the watersheds that support high species richness and intact ecosystems, highlighting the need for comprehensive assessment approaches to guide conservation strategies.