Clematis vitalba: an invader of disturbed ecosystems
'Otherwise (apart from primary colonisation sites), the disturbance in the natural system that almost always seems to be necessary for plant invaders to be successful is caused by human activities' (Baker, 1986).
Clematis vitalba L. (old man's beard) was introduced into New Zealand as a garden plant, by homesick immigrants. This deciduous vine was first apparent as a naturalised plant in the late 1920-5. It occupied urban 'wasteland', hedges, and reverting cleared land around urban centres. It established along rivers from water-bourne seed while wind-dispersed seed allowed colonisation further from urban centres and homesteads. People cut back vines in their gardens and carried vegetative material to rural roadsides where they dumped it. Today C. vitalba is a serious problem in many reserves, along many rivers, and impinges on five National Parks in the central part of the country. This vine is capable of destroying fragmented forest and riparian vegetation.
C. vitalba has many attributes of a colonising plant: high reproductive capacity; small, easily dispersed seeds; short-term persistence in the seedbank; high light demand; and fast growth rates. Unlike many colonising plants, it has well-developed vegetative reproduction and can occupy a site indefinitely. Features of the biology of C. vitalba that lead to its success as an exploiter of disturbed ecosystems will be discussed.