Background to this Trial of manual Tradescantia removal
In 1999 Tradescantia was deep and dense throughout most streambanks throughout this length. Hand removal from most points of the streambank revealed ferns and the seedlings of many native angiosperms and monocots, and resulted in their rapid growth and proliferation along the streambanks, in islets in the stream, and under streamside native tree canopy where it existed.
The 1997-99 restoration was by removal of exotic plants from within native canopy outwards to its dripline, using available leaf litter and other natural debris as replacement ground cover where available, without interference with canopied soil other than superficial disturbance in the uprooting of weeds.
Any weed material unsuitable or not required for ground cover was piled for decomposition by either rotting or drying, placed as mulch along the dripline, where it was easily monitored for regrowth, and the material withdrawn further outwards as needed for ongoing development of any native seedlings and sporelings in the dripline.
The community's view of the site in 997 was as a rubbish-filled, weed-covered stormwater drain, and this, combined with the common scepticism of the possibility of manual control of Tradescantia, led us to assuage doubts on both counts by removing Tradescantia completely from the entire length of dripline, revealing a diverse native habitat.
On low banks near the stream sporelings and seedlings developed rapidly, producing dense lush native vegetation. Further downstream and away from the water's edge, the total removal of Tradescantia over large areas resulted in bare clay which hardened in summer.
The complete Tradescantia control in these areas may thus have slowed or halted regeneration, and in one such area, zone Ua-Vb, the 1999 outer canopy margin was observed compacted and almost bare of seedlings in August-December 2018, despite being buffered since 1999 by several metres width of native tree planting.
This area was also observed to be notably free of Tradescantia, but it has not been possible to determine whether there has been any control, either manual or chemical, of Tradescantia during the intervening years, so permanent eradication of Tradescantia from those area by the 1997-99 manual removal and any subsequent Kaipatiki Project interventions cannot be confirmed in this study.
Further downstream on estuarine banks, from August-December 2018 we observed native seedlings of many species beside or amongst light to moderate coverage by Tradescantia both at saltmarsh edge and on the wide, level banks canopied by karaka, mahoe, kanuka and pin oaks, from zones Va to Za.
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