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Gorse

Braided River Status

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Description

Gorse (Ulex europaeus), is probably the most widely recognise weed in New Zealand. It covers an estimated 5% of New Zealand’s agricultural and developed areas. A perennial densely branched thorny shrub native to western Europe, it was introduced to New Zealand in the early nineteenth century to grow hedges as a form of fencing.

Gorse typically grows to 2m tall, with main stems erect or spreading, densely branched and spiny in younger parts but eventually bare at the base. Terminal and lateral spines are rigid and deeply furrowed, 15~30mm long; secondary spines subtending lateral up to 12mm long. The yellow flowers solitary 1.5~3mm wide can be seen for around 9 months of the year, even in winter. Gorse reproduces vegetatively (sprouting off the main plant) and through seeds that germinate in spring, autumn, or spring to mid-summer. 

While gorse is useful as a nursery for many species for native bush regeneration, it is unsuitable for braided river environments that are by nature highly dynamic and not suited for native bush.

Illustration of gorse from Otto Wilhelm Thomé's book: Flora von Deutschland, Österreich und der Schweiz: 1885

Illustration of gorse from Otto Wilhelm Thomé’s book: Flora von Deutschland, Österreich und der Schweiz: 1885

Why is it a problem?

  • Prolific seeder that spreads rapidly, matures quickly, and colonises large areas, forming pure stands that dominate habitats, causing native plants to be excluded, disturbing the ecology of an area and encouraging further weed invasion.
  • Holds the gravel together, changing the hydrology of the stream so that fast-flowing channels, unsuitable for wading birds to feed in are formed.
  • Takes over the open spaces braided river birds need for nesting
  • Hides introduced predators like cats and stoats
  • Seeds can remain viable for up to 100 years (although most don’t last past 30 years)
  • Tolerant to frost and drought and slightly tolerant of poor drainage, so it can readily take hold in areas of braided riverbeds already infested by other species such as Russell lupin and broom

    Gorse infestation along riverbed, destroying the river's natural characteristics

    Gorse infestation along riverbed, destroying the river’s natural characteristics

How is it spread?

  • Seeds are dispersed by an explosive mechanism up to 6m from the parent plant, which means gorse located anywhere near braided rivers is a potential source of infestation
  • Machinery assists seed dispersal, during cultivation, roadside mowing, etc
  • Some seed is carried by water and shingle
  • Dispersed by some birds

Conservation activities

Environment Canterbury list gorse as a ‘containment control pest plant’

  1. (a)  Land occupiers shall eliminate gorse infestations that cover up to 50 square metres in area and are greater than five metres from other gorse infestations exceeding 50 square metres in area on the land that they occupy.
    For the purpose of this rule eliminate means the permanent preclusion of the gorse plant’s ability to set viable seed.
  2. (b) Land occupiers shall eliminate gorse infestations on the land that they occupy within 10 metres of any adjoining property occupied by another land occupier where that adjoining property is clear of, or being cleared of, gorse infestations within 10 metres of the boundary between the properties.
    For the purpose of this rule eliminate means the permanent preclusion of the gorse plant’s ability to set viable seed.
  3. (c) Land occupiers and other persons shall not sell, propagate or distribute any gorse plant or part thereof. A breach of any of these rules creates an offence under Section 154(r) of the Biosecurity Act 1993 and may initiate the regulatory procedures set out in Chapter 12.

Land occupiers are exempted from the provisions of this rule for the following:

  • the requirement to eliminate gorse when present as a hedge within a property; and
  • the requirement to eliminate gorse when present as a hedge on a boundary provided that the top and sides of the hedge are trimmed each year after flowering but before seed set to minimise seeding.

Land occupiers may apply for an exemption from any of the above rules in accordance with the procedures set out in Chapter 12.

More information

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