Abstract
Major disturbance events can profoundly impact biodiversity patterns. Deforestation and exotic plantations are widely regarded as significant anthropogenic activities that pose serious threats to biodiversity in many regions around the world. However, the biological impacts of these two types of severe forest disturbances are often poorly understood, and the predictability of the changes they cause is also not well established.
A systematic review of global papers on the impact of deforestation on biodiversity patterns reveals a consistent response of alpha diversity to deforestation worldwide, along with a highly variable trend in beta diversity following disturbance. This reflects that deforestation’s influence on biodiversity is mainly unaffected by geographical factors or the presence of endemic species pools, threatening overall diversity and altering species composition in most areas.
As one of the last major landmasses to be colonised by humans, New Zealand, with its highly fragmented remnants of ancient forests due to widespread deforestation over recent centuries, provides an ideal setting for assessing anthropogenic biodiversity changes. I used environmental DNA (eDNA) to compare insect communities in forested streams across different islands with those in recently deforested streams, aiming to test whether large-scale disturbances result in parallel changes. Despite the eDNA analysis revealing significant differences in species pools across regions, it identified consistent functional biodiversity changes linked to recent deforestation, including parallel declines in grazing taxa diversity. Even taxonomically distinct freshwater communities experienced similar functional shifts following deforestation, indicating that disturbances can drive deterministic ecological changes. In contrast, some closely related species within functional groups responded differently to deforestation, suggesting that ecological divergence among cryptic species may result in specific changes. These findings highlight the potential of eDNA to detect subtle species-level differences within anthropogenically impacted ecological assemblages.
Since forestry is New Zealand’s third-largest export sector and the area of monocultural radiata pine plantations is expanding, it is essential to assess the impact of exotic plantations on the country’s unique freshwater ecosystems. I hypothesised that this widespread environmental disturbance would similarly drive predictable ecological changes across rivers and regions. I collected eDNA samples from the Dunedin and Queenstown regions to test for consistent biological changes associated with exotic plantations. eDNA analysis highlighted the reduced diversity in exotic plantations still affected by the legacy of past clear-cutting and the consistent compositional and functional differentiation between restored exotic plantations and native forest assemblages. This emphasises that the presence of vegetation cover, rather than forest type, is the decisive factor in shaping community composition patterns. It suggests that human-planted forests can drive predictable biological changes across broad geographical areas, confirms that exotic plantations also play a positive role in maintaining stream ecosystems, and highlights the potential of eDNA in assessing ecosystem changes caused by different types of human disturbances across large geographical areas.