Gorse and goats : considerations for biological control of gorse

Recent proposals have been made to introduce biological agents to naturally regulate gorse (Ulex europaeus) in New Zealand (Hillcost-benefit analysis, 1986). Gorse is a serious scrub weed to both farmers and foresters, but does provide some economic benefits. A comparison of the costs and benefits (Sandrey, 1985) led to the recommendation that, provided all reasonable steps were taken to ensure that agents are host specific, the introduction of these agents is economically efficient. However, several limitations of the study were noted, including the issue of goat enterprises on land containing gorse. Research into using goats to control gorse has been conducted over the last 6 years at Ballantrae, Palmerston North and Loburn, Canterbury. This research has clearly demonstrated that goats can effectively control gorse (Lambert et al., 1981 and Radcliffe, 1983, 1985). The economics of using goats for this purpose has been documented using data from trials at Ballantrae (Krause et al., 1984). With the expansion of the New Zealand goat industry interest in a low input system growing gorse to sustain goats has been expressed (Radcliffe, 1986). This is an extension of using goats to control gorse, and may present an alternative to conventional sheep and cattle production on marginal hill country in the future. The problem is that control of gorse by biological agents may preclude the development of a gorse for goats farming system. If the agents establish successfully and have a major impact on the gorse plant, the cost of controlling these same agents may make such a system uneconomical. Thus, an irreversible situation. The objective of this paper is to examine the concept of irreversibility and the consequences of making an irreversible or irrevocable decision using natural regulation of gorse and the goat industry as an example