Japanese honeysuckle release assisted through root-rotting
A new technique has been learned from the results of ongoing release of these trees and ground from an invasion of Japanese honeysuckle.
The invasion appears to have been in progress for many years, with stems up to 6cm diameter, in addition to hundreds of smaller ones, forming a dense network throughout about 20m2 of clay soil with Montbretia, Watsonia, kikuyu and little other vegetation. The vine was rooted at hundreds of nodes, crisscrossing throughout the "open" area (where it is presumed that previously planted trees died some years ago), and rooted on all sides of the most affected trees, pinning them down.
Along the c40m length of the adjacent mature manuka/kanuka, hundredsof slender young runners entered the canopy both by climbing the trunks and branches of trees, and by creeeping, largely hidden, along the forest floor, reaching up to 7m before forming nodes. Many of these canopied nodes were already rooted but most could still be pulled out by hand.
However, their removal by hand required observation and care, in some cases cutting the runners between nodes to avoid uplifitng the roots of adjacent native trees and shrubs and entirely uprooting native seedlings.
Initial strategy:
In the area of dead and dying honeysuckle-covered trees, vines were cut wherever they were accessible, ie generally the outermost foliage.
As the rooted nodes became accessible, vines were cut near the base, leaving at least one length of vine by which to pull on the rooted node. There were usually 2-4? sturdy roots at each node.
Pulling on the vines often pulled out or broke off one or more of the roots of a large woody node, leaving the node attached by only one or two of its origninal roots. The rooted length of vine was then bent over on itself so that the root was stressed, and any attached stems and foliage remaining were piled more or less in place, ie over the root until later removal.
On returning several days--3 weeks later, it was found thatin cases where a large mount of vine and foliage has been left attached, piled back on the root, and the mass compacted by its own weight and/or additional cut vine and other herbaceous material, the nodes' roots had weakened and loosened.
Whereas vigorous early regrowth was observed from nodes from which all vine had been cut, and the root left uncovered.
Vigorous early regrowth was also observed on short lengths of stem cut at both ends and left in the trees they had grown in; ie exposed to light and air. (The potential duration and extent of regrowth of such unrooted material has not yet been observed, as we were pretty keen to curtail it at this point).
There was no visible regrowth, and roots were found to be weakened and easily pulled out, where partially pruned nodes were left with a large amount of attached foliage left piled on top.
Further trial needed:
- Armed with this knowledge, it would be interesting to approach an area of invasion (where affected trees were not facing imminent death), by staging removal over a longer term, using the foliage as mulch to invoke the rotting factor and avoiding much of the energy-consuming root-pulling.
Regrowth from cut vines might be a factor over a longer-term removal, particularly during a season of strong growth (Spring?)
- Every rooted node discovered during this trial had had at least one stem cut at or within .5m of the base, as this was assumed to be essential to weakening the roots.
We have no data for self-mulching of vines from a higher point. It would be interesting to trial this also, in an invasion where the trees were not facing imminent serious decline.
- The recent wet cold weather on this clay soil was felt to have been helpful. It would be interesting to see how much rotting of self-mulched nodes occurs in dry weather.
Similarly infested areas of bush margin nearby may provide the opportunity to trial these aspects in due course.
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