Interacting stressors drive landscape variation in demographic response of the endangered plant, Pectis imberbis (A. Gray)

Abstract

Anthropogenic change has increased extinction events to an estimated 100 times background rates, amplifying the need for conservation interventions to protect biodiversity. Rare plant research not only provides roadmaps for species protection, but also foundational understanding of how interacting stressors drive decline and the mechanisms by which extinctions occur. Pectis imberbis (Gray) is a recently listed endangered forb found in the biodiverse Sky Island Archipelago in the southwestern U.S. We investigated both intrinsic and extrinsic drivers of decline for this species by relating multiple stressors to vital rates calculated for the nine known P. imberbis populations of sufficient size to allow for demographic analysis. We observed an extraordinary recruitment event in 2022 and concomitantly high population growth across most populations. Despite this, long-term analysis reveals that only two populations have growth rates at or above replacement levels and indicates the importance of stochastic recruitment events in maintaining viability. Climate change is implicated in decline of P. imberbis, though evidence also suggests that browse by ungulates and competition with co-occurring plants depress vital rates. Conservation recommendations vary by population, due to positionality and jurisdictional management, but include reduction of co-occurring stressors, like installing fencing to prevent herbivory, and re-establishment of P. imberbis in climatically suitable areas. Long-term demographic monitoring of this species is warranted to quantify the contribution of stochastic events to viability, examine impacts of interacting stressors, and to project how populations will respond to climate change in this arid, biodiverse region.