Ecological Role of Buddleia (Buddleja davidii) in Streambeds in Te Urewera National-Park

Replacement patterns under buddleia (Buddleja davidii) groves aged between 2 and 17 years were studied in streambeds in the western Ikawhenua Range and in the upper Waioeka catchment, Te Urewera National Park. Height and basal diameter growth followed an exponential pattern, with rapid early growth (0.5 m/year and 1 cm/year respectively), levelling off after 15 years or more. Intense self-thinning occurred in younger stands. Typical forest floor vegetation was developing within 15 years of colonisation by buddleia. Seedlings of ten indigenous trees and shrubs were widespread under buddleia, with primary colonising species (e.g. Hebe stricta, Kunzea ericoides) more common under young stands, and other seral species (e.g. Pseudopanax arboreus, Melicytus ramiflorus, Aristotelia serrata) more common under older stands. Buddleia quickly displaces primary native colonisers, herbaceous and woody, where it occurs en masse, accelerating successions to forest on fresh alluvium by replacing longer-lived species such as K. ericoides. It is a very effective coloniser of new surfaces, and is likely to continue spreading in the Park and persist indefinitely in lowland catchments subject to frequent flooding and alluviation.