alluviation

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.

During the last 1800 years there have been eight periods of increased erosion and alluvial sedimentation in New Zealand, which have generally decreased in magnitude towards the present. Throughout New Zealand, alluvium of all erosion periods contains abundant remains of plants as evidence of widespread destruction of vegetation during erosion periods. Indices of the relative magnitude of alluviation, and estimates of the damage to vegetation in the current Waipawa Period (since 1950), are applied to estimate the impact of earlier erosion periods.