HAKEA-SALICIFOLIA - BIOLOGY AND ROLE IN SUCCESSION IN ABEL TASMAN NATIONAL-PARK, NEW-ZEALAND

Aspects of the biology and role in vegetation succession of Hakea salicifolia are examined in relation to its status as a weed in Abel Tasman National Park. The vegetation composition was assessed within plots, and many H. salicifolia bushes were felled and their follicles were counted and classified according to their maturity. Bushes accumulate follicles rapidly with age and they have about 1000 follicles at 5-10 cm stem diameter and 13,000 at 15-20 cm diameter at an estimated age of c. 30 years. Dense stands with up to 0.8 stems m-2 support 500-600 closed follicles m-2. The viability of seeds within closed follicles of different ages on the same trees was tested. Seed viability declines negligibly with time while the follicles remain closed. Seeds were buried in mesh bags on sunny (north) and shady (south) faces. All seed germinated rapidly on the shady face, and seed on the sunny face had either germinated or disappeared after 22 weeks. H. salicifolia does not produce annual rings and the proportion of closed to open follicles was used as an indicator of the relative age-state (e.g. whether reproductive) of the bushes. H. salicifolia forms both pure stands and mixed scrub and forest with Kunzea ericoides and Leptospermum scoparium. Age estimates derived from associated K. ericoides suggest H. salicifolia reaches a maximum height of 8 m in about 30-40 years, whereas K. ericoides continues to grow and eventually overtops the H. salicifolia. Once the production of new follicles ceases the trees become senile and fall, often aided by wind on exposed sites. On relatively thick soils, H. salicifolia appears to be giving way to native vegetation, perhaps 50-60 years after establishment On the thinnest soils, which naturally support open K. ericoides - L. scoparium shrublands, H. salicifolia is still invading. Several pathways and mechanisms are suggested for these successional changes. It may be worthwhile to control H. salicifolia in the shrublands to prevent further spread in the event of accidental fire.