Effects of Rhododendron ponticum on the forest understory
Rhododendron ponticum (Ericaceae: EPPO Observation List of invasive alien plants) is frequently grown as an ornamental species in parks and gardens in the EPPO region. However, in some areas it can be a highly invasive species with detrimental impacts on native plants. It has the potential to transform habitats changing the structure and species composition. As a woody shrub, it can invade forest understories and change the characteristics of the habitat including decomposition rates on the forest floor and other soil parameters. A study was undertaken in a woodland in northern France to assess the impact of R. ponticum on the understory microclimate including soil carbon transformation. In 30 plots, 15 invaded and 15 uninvaded, measurements were made on structural plant parameters and abiotic microhabitat measurements. The results showed that R. ponticum can alter microclimatic conditions in invaded sites by reducing light availability, the daily temperature range and soil moisture. However, even though the microclimate under R. ponticum was drier and more isolated compared to uninvaded sites, these parameters did not have an effect on carbon transformation. The study showed that the leaf litter from R. ponticum has more influence on carbon cycling as the leaves take longer to break down compared to native litter decomposition.
Sources
Le Jeune E, Guiller A, Spincher F, Horen H (2026) How does the invasion of forests by Rhododendron ponticum disrupt the transformation of carbon in soils? Biological Invasions 28, 43. https://doi.org/10.1007/s10530-025-03745-8