The impact of Humulus scandens on native plant communities
Humulus scandens (Cannabaceae: EPPO A2 List) is native to Asia and in the EPPO region the species is present in Austria, Belgium, the Czech Republic, France, Germany, Italy, Hungary, Romania, Serbia, Slovakia, Slovenia, Switzerland and the Ukraine. The species thrives along riversides, particularly on the loose, bare surfaces of alluvial bars formed by river and streamsides by temporary floods. The plant can also invade ruderal areas under climates with no dry seasons. In Hungary and France, H. scandens has been shown to have a negative impact on native plant communities by reducing species richness and modifying species composition. To evaluate the impact of H. scandens on plant communities, a study was established that measured impact by comparing invaded plots, non-invaded plots and plots where H. scandens seedlings were removed along the river Gardon in Southern France. Plots were sampled 7 times over a two-year period. Sampling consisted of measuring seven plant traits such as, life form (e.g. annual, perennial), time of flower onset, flowering duration, plant height, seed mass, specific leaf area and leaf dry weight. In addition, species richness, functional richness (the amount of niche space occupied by a species), abundance and cover were measured at each site. Results showed that H. scandens had a strong negative impact on species and functional richness. Plant species that flowered before H. scandens reached a high cover, and species that had a short flowering duration were less affected than those that did not. Plant species that had a high seed production rate and species that grew taller were more likely to be successful in invaded stands. These results showed that invasion by H. scandens can change the structure of a plant community where some native plant species with certain traits can coexist more successfully than others.
Sources
Fried G, Carboni M, Mahaut L, Violle C (2019) Functional traits modulate plant community responses to alien plant invasion. Perspectives in Plant Ecology, Evolution and Systematics 37, 53-63.