Li, C., Huang, P., Chen, B., Chen, H., Li, Z., Wang, F., Jiang, M., 2025.

Effects of designed species diversity on community resilience to weed invasion

Urbanisation has resulted in significant habitat loss, leading to a global decline in species diversity. Landscape design and management play a crucial role in enhancing biodiversity within urban greenspaces. Species-rich herbaceous communities are considered effective alternatives to conventional lawns, which are typically characterised by low species diversity and limited visual interest. These communities can address such limitations while also reducing maintenance costs. Among the various maintenance tasks, weed management constitutes a major component, largely influenced by the community's susceptibility to invasion. A better understanding of the relationship between species diversity and community resistance to invasion can help landscape practitioners establish more sustainable herbaceous plantings. This study investigated species-rich herbaceous communities in the Guanzhong region of China. Bermudagrass (Cynodon dactylon) was used as a base lawn species, with forb richness manipulated across five treatments: 1, 4, 8, 12, and 16 forb species (including a control group consisted of Bermudagrass alone, without any forb species). Within 1, 4, 8, and 12 species treatment, three combinations for each treatment were designed. In total, 14 treatment combinations and 42 plots were established. Data on species diversity indices and weed biomass were collected over a six-month period. The results showed that cultivated forb richness declined by an average of 3.03 species in the 4-, 8-, 12-, and 16-species treatments after six months - approximately a 50 % reduction. All treatments experienced varying degrees of weed invasion, with weed richness ranging from 4.4 to 9.2 species per plot (average: 6.2). A total of 54 weed species were identified over the study period, and mean monthly weed biomass per plot ranged from 22.1 to 181.0 g (average: 58.2 g). Weed emergence followed a clear seasonal pattern, with biomass peaking in June and August, forming a bimodal distribution. Both weed biomass and weed richness initially increased and then decreased with rising forb richness. The highest weed biomass was observed in the 8-species treatment, while peak weed richness occurred in the 4-species treatment. These findings suggest a trade-off between interspecific competition and complementary effects in shaping the relationship between forb diversity and community invasibility. The results also imply the existence of a species saturation point for invasibility--possibly around 16 forb species--contradicting the predictions of the plant richness hypothesis. Based on these findings, we recommend maintaining forb richness at either 1-4 or 12-16 species per planting to minimise management costs. Additionally, weed control strategies should be adapted to local seasonal weed growth patterns.