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Hieracium in short tussock grasslands
Hawkweed (Hieracium spp) has become a major weed in many short tussock grasslands. Many studies have been conducted to investigate the relationship between grazing management and rate of Hieracium spread, and associated trends in vegetation composition. The majority of studies have focussed on induced fescue tussock grassland communities. In summary workers highlight the following:
A summary of findings - Hawkweed studies
- Hieracium occurs in grasslands which continue to be grazed as well as grasslands which have been retired from grazing (Rose et al., 1995; Rose, 1996).
- Many induced fescue tussock grasslands are being invaded by exotic grasses and herbs (e.g. browntop, hawkweed), with an accompanying decline in tussock cover (Scott et al., 1988; Hunter, 1994; Rose et al., 1995)
- There is not much optimism that grazing management can prevent Hieracium spread. The following are suggestions derived from scientific information combined with farmer observations (see O'Connor and Duncan, 1996):
- The maintenance of tall dense vegetation with a deep litter layer may help to prevent Hieracium spread via seed rain.
- This will be hard to achieve in a short tussock grassland because tussock cover is already so fragmented, and low growing.
- It will only be effective for those species of Hieracium that depend on establishment by seed rain (e.g. H. lepidulum). H. pilosella can spread by vegetative means also, so it's rate of spread may only possibly be reduced.
- Summer grazing may help to prevent some species (i.e. H. lepidulum, H. praealtum, and possibly H. caespitosum) from seeding and spreading, by eating the flower heads off.
- This approach might possibly work for H. pilosella (which can also spread by vegetation means) where the grassland has no Hieracium present, or it is in early stages of invasion. Once established, grazing of H. pilosella will encourage it to spread by vegetative means instead.
- Hieracium species tolerate different environmental conditions. It is inevitable that, irrespective of management, at least one species will invade short tussocks grasslands
- Given that short tussock grassland are highly predisposed to invasion by weeds, if Hieracium is successfully controlled, it is likely that another weed species would take it's place
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