Relatively little is known about the palatability of seedlings of different species to slugs and snails. As a general rule, as seedlings age they become increasingly less palatable, due to increases in the concentrations of various chemical substances and, in some cases, morphological features, such as surface hairs (Table 6.13). Trollius europaeus, for example, is rarely grazed by slugs as an adult, but is highly palatable as young seedlings (Hitchmough 2003). The same also appears to be true for many Primula species. Some forbs are attractive to molluscs even as adults and are correspondingly ephemeral in landscape projects. In sites with high densities of slugs and snails, control of these
Table 6.14. Examples of particularly robust but non-invasive forb species
herbivores during the emergence period will normally greatly increase the diversity and density of sown and weed species (Figure 6.10).