An assessment of the invasive alien tree, Robinia pseudoacacia canopy traits and its effect on grassland microclimates and subsequent arthropod assemblages

Invasive alien trees transform landscapes and subsequent ecosystem function. For grassland ecosystems, fragmentation following invasion by alien woody species is of concern. In this study, we examined how an invasive alien tree, Robinia pseudoacacia L. (Fabaceae) impacts grassland microclimates and the subsequent assemblages of endemic arthropods. The phenological trajectory of R. pseudoacacia, temperature and light intensity, as well as arthropod abundances in both invaded and uninvaded habitats, were monitored. Results showed that R. pseudoacacia significantly lowers average understory temperatures and light penetration in grassland ecosystems. Average temperatures were at least 2 °C lower in understory habitats than open grasslands while light intensity was lower by more than 1200 lumens/ft2. In addition, arthropod communities differed between invaded and uninvaded habitats. The most affected taxa were Acridids from the order Orthoptera as they were excluded from understory habitats while Coleopterans were more abundant under R. pseudoacacia. Apart from absence of main host plants, invasion mediated differences in microenvironments appeared to be the main driver of this shift in affected arthropod taxa. These results highlight the need to sustainably manage R. pseudoacacia invasions especially in grassland ecosystems. In addition to their conservation value due to their role in nutrient cycling, grassland arthropods also serve as important indicators of ecosystem health. Hence, they can be used to monitor ecosystem recovery post invasive alien tree management.