New Zealand Plant Protection Journal - Abstracts
Assessing risk of wilding spread
Nick Ledgard, Scientist, Scion, Christchurch
Contact email: nick.ledgard@scionresearch.co.nz
Abstract
The natural regeneration or spread of introduced conifers (wilding spread) is causing concern in parts of New Zealand. Two decision support systems (DSS) have been developed to assess a) the threat of spread from new plantings and b) the risk of wildings establishing at any particular site. Questions in the DSSs relate to the species involved, their spreading vigour (combines seedling growth rate, age of coning, seed production and seed weight), palatability, siting of the parent seed trees, and vegetation cover land use, particularly downwind of the seed source. The two DSSs can be used by land managers to quickly undertake a desktop assessment of likely risk of wilding spread. Depending on the resulting score, they can test how they might lower the risk by changing input factors. In this way, spread risk can be mitigated or avoided by good decision making prior to unwanted wilding spread occurring.
Vegetation successions during 30 years of high country grassland invasion by contorta pine
Nick Ledgard1 and Thomas Paul2
Contact email: nick.ledgard@scionresearch.com
Abstract
The invasion of a high country grassland site (850 m asl) by contorta pine (Pinus contorta) wildings was monitored over 32 years in the Craigieburn Range, Canterbury. The first wildings appeared in 1975. By 1985, density had reached 34,550 stems/ha., with a mean height of 1.85 m and a basal area of 17 m2/ha. By 2007, stocking had dropped to 11,400 stems/ha, with a mean top height of 14.3 m and a basal area of 104 m2/ha. Thirty-eight plant species were present 10 years after wilding invasion started. Twenty-six species (68%) were indigenous. By 2007, the number of species present had dropped to seven, none of which were indigenous. The introduced tussock hawkweed (Hieracium lepidulum) featured in both assessments. We conclude that more species are likely to invade as the canopy opens up, but if native species are wanted they may have to be introduced by artificial seeding.
Scientists, Scion, 1Christchurch and 2Rotorua
