Freshwater eDNA reveals dramatic biological shifts linked to deforestation of New Zealand

Deforestation is considered a major threat to biodiversity across many parts of the globe, but the biological impacts of this dramatic ecosystem disturbance often remain incompletely understood. In New Zealand - the world's last major landmass to be colonised by humans - widespread deforestation over recent centuries has left a highly fragmented suite of relict forest stands, ideal for assessing anthropogenic biological change. We hypothesise that this widespread environmental disturbance has underpinned repeated and predictable ecological shifts across distinct rivers and regions. Here we use freshwater environmental DNA (eDNA) data (113 samples across 38 locations; 89 insect taxa) to test for concordant biological shifts linked to this deforestation. eDNA analyses highlight consistent compositional and functional differentiation between forested versus deforested assemblages, including turnover of 'cryptic' congeneric taxa that are morphologically similar yet ecologically and genetically distinct. These dramatic biological shifts are evident even over fine spatial scales within streams, emphasising the widespread emergence of a novel 'deforested' assemblage. Our results illustrate that environmental change can drive predictable biological shifts across broad geographic regions, and highlight the power of eDNA for assessing anthropogenic ecosystem change over large geographic scales.

Automated summary

Deforestation is a major threat to biodiversity, but the biological impacts of this disturbance are not fully understood. In New Zealand, deforestation has led to fragmented forest stands, providing an opportunity to study anthropogenic biological change. This study used freshwater environmental DNA (eDNA) data to test for biological shifts related to deforestation. The results showed consistent differences in species composition and function between forested and deforested areas, indicating the emergence of a new 'deforested' assemblage. These findings demonstrate that environmental change can drive predictable biological shifts over large geographic regions, and highlight the power of eDNA analysis in assessing anthropogenic ecosystem change.