Delairea odorata Lemaire

Alvarez reported pyrrolizidine alkaloids and xanthones in Cape ivy, making it toxic to mammals, spiders, and fish (1). Cape ivy is toxic to Paramecium and arthropods. Thus, toxicity to aquatic microorganisms could be due to these alkaloids and xanthones. (Kozsiz, 2013)

We have observed Delairea vines covering individual trees for over 10 years without killing them; however, vigor and production of flowers and pods seem reduced, probably because of reduced light levels. (Banko et al. 2002)

In a comparative study, we found that Cape-ivy invasion was associated with reductions in the species richness and diversity (H9) of both native and nonnative species, and this pattern existed during both spring and summer sampling periods. In addition, the abundance of native and nonnative seedlings were each significantly lower in plots invaded by Cape ivy compared to uninvaded plots. Results from our field experiment strongly support these findings and demonstrate that they are due to the negative effects of Cape ivy, rather than differences between invaded and uninvaded areas. (...) Presumably, this invader reduces plant species richness, diversity, and seedling abundance by monopolizing limiting resources, such as light, water, and soil nutrients. (Alvarez & Cushman, 2002)

Cape-ivy forms impenetrable mats in both shade and sun, and climbs native shrubs and trees forming a dark canopy layer up to nine meters in height. Grasses and annual species are consistently missing from Cape-ivy infested plant communities. In addition, the abundance and richness of seedling plants is significantly reduced indicating that as plants age and die, there may be little establishment of native plants in Cape-ivy infested sites. (Alvarez, 1997) Alvarez and Cushman (2002) showed that Cape-ivy reduced species diversity by 31%, abundance of native seedlings by 88%, and abundance of non native seedlings by 92% in riparian communities.

There is also evidence that Cape-ivy is associated with a significant reduction in the abundance of two insect orders (Coleoptera and Diptera) for two riparian plant communities which could affect other species dependent on these insects (Fisher 1997). (Alvarez, 1997) In coastal California, it covers the understory of riparian forests in a solid mat (Elliott, 1994). Forms a solid cover that blocks light and smothers vegetation (Bossard et al., 2000). The weight of the ivy sometimes causes trees to fall (Bossard et al., 2000). Affects some plant life forms (e.g., grasses and forbs) more than others (Alvarez and Cushman, 2002). Affects community structure (Alvarez, 1998). Displaces native forests in state parks in California (Elliott, 1994). (Department of Agriculture, 2013)