Contributing to an evidence-based discourse regarding invasibility, stage of invasion and impacts of Robinia pseudoacacia L. in European forests

Abstract

Robinia pseudoacacia L. (black locust) is a deciduous tree native to North America, widely introduced and naturalized in Europe. Despite being one of the world's most invasive woody angiosperms, its role in European forest policy remains contentious, with debates about its invasion potential, ecological impacts, and control measures and it is not formally classified as invasive in European regulation. This study uses data from three cycles of the Spanish National Forest Inventory (SFI) to examine the distribution, abundance, and dominance of black locust in Spanish forests over the past three decades. The study also assesses the invasibility and invasion stage across various forest types, identifying the biotic and abiotic factors influencing its distribution. Additionally, the impacts of black locust on forest ecosystem services, such as native tree species diversity and abundance, are evaluated. Black locust now occupies over 75,000 hectares of Spanish woodlands, with an average invasion degree of 1.55% at the forest type level. Its population has steadily increased, reaching an established invasion stage in most invaded native forests. The invasion affects forest attributes, including native species abundance and dominance, and overall plot richness. The impact varies with the degree of invasibility and invasion stage, being particularly significant in priority conservation habitats like depleted temperate and alluvial forests. These findings highlight the need for further research on black locust impacts in forest ecosystems to contribute to an evidence-based discourse regarding the reconsideration as an invasive species in European and national regulations.