Kānuka and Gorse as Ecosytem Engineers: A Study on Motutapu

Kānuka (Kunzea ericoides) is the primary successional plant used on Motutapu island for regeneration of original native species assemblages. This study investigates contrasts floral and invertebrate diversity between kānuka and gorse (Ulex europaeus), a plant which has been used elsewhere as an efficient primary successional shelter, and as an equivalent harbour for invert diversity. Six stands, three of gorse, three of kanuka, were sampled using transects totalling five samples per stand. The stands measured were too immature to support understory, but kānuka was significantly more diverse in invert fauna than gorse. This may have been due to unavoidable influences on the experiment posed by the flora of Motutapu. The results do give a clear enough picture for some recommendations on further study on Motutapu.

Introduction

Motutapu is an island in the Hauraki Gulf, Auckland region, and is half of the Rangitoto-Motutapu complex of ecosystems. It is the site of an ongoing restoration effort, the largest in New Zealand, which aims to reforest a large portion of the island by 2050. The main method employed thus far is planting of Kunzea ericoides (kānuka) and Leptospermum scoparium (mānuka) pioneer cover, followed by further planting of broadleafed understories of common New Zealand coastal forest species. Mammalian pests have recently been almost eradicated from both Rangitoto and Motutapu, a development which will likely have an impact on the reforestation efforts. However, the current reforestation is moving slowly at great effort, and expense and may not meet its targets by 2050 (Motutapu Trust 2009a, Motutapu Trust pers. comm).

Ulex europaeus (gorse), a notorious weed in New Zealand, was noted to be part of the introduce...

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