Long-term monitoring of Azorean forest arthropods: the BALA Project (1997-2022)

Study Extent

The foundational dataset comprises 4,929 sampling events conducted along 30 transects, distributed across 15 fragments within native Azorean humid forests spanning seven islands. Sampling activities unfolded over the period from 1997 to 2022, segmented into three comprehensive, multi-year campaigns: BALA1 (1997-2004), BALA2 (2010-2011), and BALA3 (2019-2022). The core dataset specifically includes transects situated in pristine native vegetation, consistently sampled throughout this timeframe. However, the ultimate dataset has been enriched by incorporating data from various projects that adhered to the same methodology for invertebrate sampling across the archipelago. Consequently, the final dataset encompasses information from 124 transects within 27 fragments across eight islands. While the majority of fragments represent primary native forests, the extended dataset also includes data from the early succession of lava flows and secondary forests, particularly on Graciosa island where no native vegetation remains

Sampling

Each site was sampled along a 150 m transect, in which, in order to map soil-dwelling fauna, 30 pitfall traps, each with a 5cm opening diameter, were placed at 5-meter intervals. In 15 traps the sampling/preservative liquid was ethylene-glycol and, in an alternating pattern, the remaining 15 traps employed Turquin’s solution. Additionally, for the purpose of capturing arthropods residing in the canopy, the study also involved the sampling of the three most prevalent native tree species using a beating technique. For a detailed description, readers should consult the works using the BALA protocol (Borges et al., 2005; Ribeiro et al. 2005).

Quality Control

Each sample was meticulously labeled and stored, with archive samples remaining accessible for additional data verification and analysis. While the majority of species identifications were performed by one of the authors (PAV Borges), challenging specimens were referred to expert taxonomists specializing in the respective taxa. Rigorous checks were undertaken to prevent transcription errors, and various tests were executed to detect and address outliers in the data. Furthermore, segments of the dataset have already been utilized in numerous analyses. To ensure accuracy, all names underwent automatic verification against the GBIF Taxonomy Backbone

Method steps

1. Several taxonomists identified morphospecies from BALA 1, which were fundamental for the success of the project, namely, Artur R.M. Serrano, Arturo Baz, Fernando Ilharco, Henrik Enghoff, Jordi Ribes, Jörg Wunderlich, Luís Carlos Crespo, Margarida T. Pitta, Ole Karsholt, Richard zur Strassen, Virgílio Vieira, Volker Assing, Volker Mahnert and Wolfgang Rücker

All arthropod taxa, with the exclusion of mites (Acari) and Collembola, were collected. Specimens were categorized to morphospecies and, when possible, identified to their respective species or higher taxonomic levels. Due to the difficulty of their identification, Diptera and Hymenoptera (excluding Formicidae) were not separated to morphospecies but kept in the samples

1. Arthropoda
   common name: Arthropods rank: phylum

In our study, eight islands of the Azorean archipelago, from west to east were sampled: Flores, Faial, Pico, São Jorge, Graciosa, Terceira, São Miguel, and Santa Maria