Can saliva from moose, Alces alces, affect growth responses in the sallow, Salix caprea?

Herbivores have the potential to affect the morphological traits of the plants they feed on, such as the breaking of apical dominance that occurs when shoot tips are browsed, leading to increased lateral branching and decreased competition among growing points. Despite such effects, however, it remains unclear whether components in the saliva of the browsing animals are directly involved in amplifying and/or reducing the plant growth responses. To test this possibility, a controlled experiment was performed in which herbivory by moose (Alees alces) was simulated by tearing 60 sallow saplings (Salix caprea) with a moose jaw. Of these 60, half were also treated with moose saliva. Selected growth traits of the torn plants with and without saliva treatment were examined directly after treatment (week 0) and 1, 2, 4, 6, 8, 10, 12 and 15 weeks after the tearing. Also included in the study was an untreated (no tearing, no saliva) control group of another 30 sallow saplings. Traits monitored on the saplings were height and the number of branches, buds and leaves. Application of moose saliva on torn saplings led to significantly more branches than on saplings without saliva treatment. Moose saliva, however, had no significant effects on the other growth traits, although for most of these characteristics both groups of torn saplings showed increased values compared to the undamaged control. Overall, these results demonstrate that moose saliva has a consistent stimulatory effect on branching of sallow saplings but not on the other growth traits examined in this study.