Efectes dels impactes agroforestals d’aclarida forestal i d’estassada sobre poblacions de papallones de l’àrea de mostreig del cbms

Abstract

Agroforestry impacts have been highly prevalent in the Mediterranean Basin for

centuries, shaping ecosystems and influencing both animal and plant communities. This

study assesses the effects of agroforestry interventions, specifically forest thinning and

shrub clearing, on butterfly populations monitored by the CBMS (Catalan Butterfly

Monitoring Scheme), which is supported by a database with over 30 years of monitoring.

The scheme includes 254 transects across Catalonia, the Principality of Andorra, and the

Balearic Islands, with records of interventions carried out at various sites. The data

originate from citizen science, thanks to volunteers who walk their transects weekly

throughout the monitoring season. This study focuses on the CBMS transects that have

recorded agroforestry interventions. A new classification of these interventions has been

introduced in the CBMS database for use in future sampling campaigns. Transects with

either forest thinning or shrub clearing have been grouped for analysis. Using paired ttests, mean values of ecological indices for species richness and abundance were

compared between years before and after the interventions, distinguishing three climatic

regions in the sampling area: alpine, humid Mediterranean, and arid Mediterranean. The

results show that each ecosystem responds differently to the pressures generated. One-off

interventions were found to have more significant effects on butterfly populations than

continuous ones. Across all three climatic zones, particularly with isolated shrub

clearings, species richness and abundance values were higher in the years before the

intervention. In the years following, in alpine areas, shrub clearings showed greater

recovery in butterfly populations in terms of the ecological abundance index compared to

forest thinning. Conversely, in humid Mediterranean areas, both thinning and clearing led

to quicker recovery in butterfly populations, especially in abundance and also in richness.

In arid Mediterranean regions, butterfly population recovery was observed after isolated

shrub clearings, with an increase in species richness. These results highlight the need for

adaptive forest management, as each zone (forest, meadow, or terrace) responds

differently. It is also essential to understand the specific activities being undertaken and

their objectives. This study suggests that new analyses could be carried out using the

newly reclassified dataset to explore other agroforestry impacts present in the CBMS

territory and to study butterfly populations using additional recognised ecological indices

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