Characteristics of tree seedlings and neighbouring vegetation have an additive influence on browsing by generalist herbivores

Browsing of commercial tree seedlings by mammalian herbivores can reduce long-term plantation productivity, and is an economic problem worldwide. Characteristics of both tree seedlings and their neighbours can influence browsing on the former, particularly by generalist herbivores. The nature of the combined effects of seedlings and their neighbours is, however, unknown. If effects are additive, it should be possible to exploit the capacity of herbivores to make foraging decisions at multiple scales in order to manage browsing of tree seedlings in forestry plantations. We conducted a field trial that focussed on browsing of Eucalyptus globulus seedlings by native marsupial herbivores. Our aim was to determine the absolute and relative importance of characteristics of both seedlings and neighbouring vegetation on browsing of seedlings. Seedlings with and without a chemical repellent were planted in vegetation patches that varied in the abundance and height of thistles. Browsing of seedlings was assessed over 16 weeks. Characteristics of both seedlings and neighbouring vegetation were shown to influence the degree to which seedlings were browsed, and the effects were additive. Repellent-treated seedlings received less browsing than those without repellent; and browsing decreased with increasing thistle cover. The presence of thistles also increased the time it took for browsers to find seedlings. Results are consistent with the associational plant refuge hypothesis, and vegetation effects may be manifested via an alteration in plant apparency. These results have applications in the forestry industry. They demonstrate the principle that the use of less palatable seedlings combined with tall, unpalatable vegetation can reduce browsing on plantation seedlings in the short-term, and that the effects are additive.