A cover crop for reducing mammal browsing damage

Eucalypt plantations on ex-pasture sites sown with a cover crop of bitter lupins have reduced browsing damage to seedlings from mammalian herbivores. Bitter lupins also enhanced short-term height growth of eucalypt seedlings, whether they were exposed to browsing or not.

In a collaborative project between the Resource Protection Program, Sustainable Management Program and Gunns Limited, Clare McArthur, Philip Smethurst, Elizabeth Pietrzykowski and Chris Barnes found that bitter lupin established successfully in five of six regions of an ex-pasture plantation in southern Tasmania. Sweet lupins were browsed severely on germination and never established. Bitter lupins successfully reduced browsing of E. nitens seedlings by mammals compared with both sweet lupin and control (herbicided) plots.

Although overall browsing damage was relatively low in these regions, the reduced damage in bitter lupin plots was still sufficient to improve growth of seedlings over the 12-week period. The mean increase in seedling height from planting to the end of the study 12 weeks later was 12.3cm (42%), 15.4cm (53%) and 18.6cm (64%) for control, sweet lupin and bitter lupin treatments respectively.

In the absence of mammal browsing, height growth was enhanced when seedlings were surrounded by up to 90% bitter lupin cover. This was probably the result of lateral shading of seedlings by lupin. Long-term effects of the cover crop on eucalypt growth will be monitored.
These results demonstrate the potential for using plantation vegetation to manage mammal browsing. If used in combination with other methods, such as reducing seedling palatability in the nursery (reported as a major development in CRC-SPF Annual Report 1999/2000), these techniques may reduce browsing to an acceptable level.