Cover ofStipa neesianaTrin. & Rupr. (Chilean needle grass) on agricultural and pastoral land near Lake Grassmere, Marlborough

Abstract

Abstract A census of 7 269 ha of farmland in the vicinity of Lake Grassmere in Marlborough, was carried out during the 1986/87 and 87/88 summers to determine the distribution and ground cover of the alien tufted grass Stipa neesiana. A modified version of the Braun-Blanquet cover-abundance method was used Of 897 paddocks on 30 farms, 161 (1 558 ha) con-tained S. neesiana and a total of 129 ha was occupied solely by S. neesiana. The dominant agricultural activity on infested paddocks was sheep grazing “improved” pasture (133 paddocks). Of 18 farms supporting populations of S. neesiana, 16 formed a contiguous group. The distribution of the infested paddocks among cover classes was; 131 paddocks (1 271 ha) with <5% cover of the species, 16paddocks (123 ha) with 5-25% cover, 7 paddocks (117 ha) with 25-50% cover, 3 paddocks (16 ha) with 50-75% cover and 4 paddocks (32 ha) with >75% cover. The distribution of infested paddocks among dispersion modes was; 41 (298 ha) as solitary plants, 104 (1 066 ha) as clumps or dense groups and 16 (194 ha) as large almost pure stands. The pattern of cover suggests that S. neesiana is radiating outward from a central point of introduction. The occurrence of extensive areas of apparently suitable yet uninfested habitat, and anecdotal information suggesting introduction occurred about 60 years ago, indicates the invasion may be in a lag phase