Assessing arthropod species/groups as bioindicators of ecosystem health in the native forests of Terceira Island

Abstract

Global changes are profoundly affecting biodiversity worldwide, with human activities like

resource exploitation, pollution, and habitat fragmentation playing significant roles. These

impacts are especially dramatic on islands due to their unique ecological characteristics and

the higher vulnerability of insular species to extinction. Understanding the status of vulnerable

habitats is crucial for all species’ well-being and effective conservation strategies. This study

aims to evaluate the Index of Biotic Integrity (IBI) across various sites on Terceira Island (Azores)

and reliably identify key arthropod species that indicate ecological conditions. We used data

from two comprehensive projects—the SLAM (entitled “SLAM project - Long Term Ecological

Study of the Impacts of Climate Change in the Natural Forests of the Azores”) project and the

BALA (Biodiversity of Arthropods from Laurisilva of the Azores) project—to analyse arthropod

biodiversity and its implications for forest conservation. Different sampling methods, including

SLAM traps and canopy beating, provided a multifaceted understanding of the arthropod

communities.

Using a generalised linear mixed model (GLMM) for both databases, we identified specific

arthropod species, such as Pinalitus oromii and Ommatoiulus moreleti, as key bioindicators of

forest health. Pinalitus oromii, an endemic species, showed a positive correlation with higher

IBI values, suggesting its potential as a reliable indicator of pristine forest conditions. In

contrast, Ommatoiulus moreleti, an invasive species, exhibited a negative relationship with IBI

values. These findings highlight the importance of integrating multiple ecological indicators and

biogeographic categorizations in monitoring forest health, providing valuable insights for

conservation strategies in the Azorean native forests.

The study further emphasises the need to select and analyse various environmental

variables such as altitude, distance to roads, and forest structure, which significantly influence

habitat quality and biodiversity. By employing a comprehensive dataset from long-term

monitoring projects, this research offers a robust analysis of arthropod community dynamics

over time. The application of the IBI tailored for the Azorean forest ecosystem incorporates

diverse taxonomic and ecological parameters, facilitating a multimetric evaluation of biological

integrity. Comparative analyses using both the IBI-SLAM and IBI-Canopy indices across different

forest strata ensure a thorough assessment of forest biodiversity and ecosystem health.

Our study underscores the importance of selecting appropriate bioindicator species for

effective biodiversity monitoring and conservation efforts. It suggests that certain arthropod

species can be used as indicators of native forest conditions with high ease of sampling and

1

identification. These results have significant implications for conservation strategies on Terceira

Island, laying the groundwork for future research and the development of effective

management plans to preserve the Azores' unique biodiversity