Tradescantia - Kaipatiki Roadside
Kaipatiki Roadside
Immediate and complete removal of the roadside canopy's Tradescantia in the Trial Site would have been quick, easy and probably permanent if done at the start of this Project in March when, after a week of light rain, the roadside Tradescantia was assessed for first intervention.
Exploration quickly revealed the scantiness of its rooted stems, despite their height and glossiness. The roadside edge includes some quite damp areas channelling runoff after rain, and some areas where the soil surface, whether covered by Tradescantia or leaf litter, remains dry even after heavy rain. Under some trees even the leaf litter’s surface remains dry after rain.
Within the 1999 planted canopy of this area the tradescantia is deep, and the only groundcover. There are no shrubs or wild revegetation either native or exotic, and few juveniles (mahoe, kawakawa and karamu).
At the edge of the mown roadside grass a narrow band of unmown exotic grasses and herbs holds a few wild ti kouka, aruhe, mapou and shrubby toatoa (Haloragis erecta). This area was in June 2018 invaded by Japanese honeysuckle, moth plant and Tree privet, many of which were suppressed during that and subsequent surveys, (releasing native trees both live and already dead) ) and the remainder further suppressed or removed in March/April 2019 at the start of this Trial.
Tradescantia limits the invasion of the grasses and herbs under the canopy.
Dry roadside at top of uncanopied bank
At the downstream end of the Tradescantia Trial site, (Zones Db-Eb) the lower half of the roadside bank holds about 10m x 10m of Elaeagnus, honeysuckle and blackberry, preventing revegetation now as it did in 1997, where this occurrence of Elaeagnus survived a prolonged and intensive weed control operation along the Kaipatiki Roadside streambanks by North Shore City Council Parks Dept. Stream weeding was obstructed at what was known as "Elaeagnus Block".
The stream at Zone Db is still, as in 1997, canopied by “Mama ti kouka” with its over 100 heads, but above Mama ti kouka there is little vegetation but Tradescantia, with a few mahoe and kanuka and karo and pittosporum at the roadside only.
The bank downstream of Mama ti kouka is also almost treeless, only the Elaeagnus, honeysuckle and blackberry forming an island in the sea of Tradescantia, with only a few separate mahoe, and a couple of wattles which are falling over.
At the roadside here the ground is very dry. Sun-exposed Tradescantia here turned purple during the drought, and even in the adjacent kanuka/mahoe/tanekaha canopy on the downstream side,
the ground remained dry and dusty to a depth of at least 1cm beneath dense Tradescantia and light tree canopy.
In this dry extent of roadside, Ehrharta erecta occurs wherever Tradescantia is less than extremely deep and dense, scattered in such patches for about 10 metres down the bank towards the stream,. Ehrharta erecta’s bamboo-like rhizomes are far-reaching and effectively suppress native regeneration, and its abundant seeds germinate within 5 days. This occurrence is poised to dominate should the Tradescantia cover weaken.
For these reasons, Tradescantia removal has not yet been undertaken, except to compacti it over large areas by piling additional Tradescantia on top of it, the idea being to retain moisture and create humus to assist hydration next summer.
While test-removals have continued throughout autumn and winter, and many tiny seedlings of kawaka, and a few karamu, have been observed under Tradescantia on these occasions, we have not yet found the conditions allowing safe removal of the ground cover, even in small areas, as fine white mahoe root fibres are visible on the surface beneath.
We continue to assess, hoping to create at least small pockets of clearance to see what species of seedlings occur here, and whether they survive in varying degrees of Tradescantia removal.
At the edge of the mown grass, a few isolated small groups of mapou, kawakawa and a dozen or so kowhai (possibly from planted S. microphylla) seedlings were found.
Beyond this grass/herb canopy margin, few seedlings of any kind were found during exploratory weeding and/or survey of the upper bank under the tradescantia among planted trees.
Notable were
- a 30cmH totara in a run-off channel just below the roadside, its top just hidden in the Tradescantia.
On release in October 2018 it was glossy and vigorous. In March 2019 it had dry slightly-shrunken leaves, a few browned, and was lightly mulched with Tradescantia but has not yet grown further.
- dozens of Lastreopsis microsorum to c.50cmH, only visible when Tradescantia was parted carefully by hand. These were all on the almost-vertical lower banks at the 1997-99 outer margin of wild revegetation.
https://inaturalist.nz/observations/24775860
Many of the Lastreopsis' fine brittle stems were were broken during exploration and weeding despite care, as they were effectively invisible under the Tradescantia. Tradescantia piles were applied as mulch to protect as many as possible of them from the ensuing drought, and many have survived and grown.
Lastreopsis uncovered so far have been on the Kaipatiki Roadside bank (KRS) in Zones Cb and Cc, in an area about c.10m x 3m. In addition, a sporeling of what appears to be Lastreopsis has emerged in a run-off channel further up the same bank, under one of the few kawakawa and mahoe juveniles between the 1999 tree planting and 1999 wild regeneration margin.
Comentarios
Añade un comentario