Diario del proyecto Gahnia Grove - Site summary and discussion

Thanks to @chrise (a co-author) for the link to this 1985 Forest Research Institute publication about pampas and toetoe:
https://cdm20044.contentdm.oclc.org/digital/collection/p20044coll6/id/155

It will be confusing for some newer naturalists to see toetoe referred to as Cortaderia though! I only discovered the new name, or classification, a year ago on joining iNat, and already I was momentarilly perturbed to see the name "Cortaderia" applied to a native!

Having no formal education in ecology, I was most interested to see pampas described as a forest weed, as I have been removing small plants from this margin of dry kauri ridge regen forest underpines, tanekaha and other podocarps and understorey.

Not surprisingly, the clumps were larger and more numerous in the outer margin of solely manuka. I had been wondering, for a year, if this is an infestation on the way out as shade increases, or a growing invasion. I assumed it would get suppressed if dense shade increases fast enough, and removing or suppressing the pampas gives the forest time to develop the necessary dense shade. I have little experience of forest except urban Auckland.

Anyway, I am glad to confirm it has been easy to trample and later uproot all plants found under canopy whether inlight or heavy shade, and to suppress the large ones in the sunny margin by breaking down the culms and tall shoots and throwing the foliage over the clump, with a single summer follow-up intervention resulting of rotting of the whole plant gradually. I was told this is 1997 by a contractor. I can't remember if he used herbicide as well, but it doesn't seem to be necessary. Our single 6mH-3mW clump in full sun is now c.50cmH and mostly dead. It has live shoots remaining over about 1m x .5m, because we chose to allow growth to resume on one side, beside a public walkway, during the months of the summer drought.

I learnt from the pamphlet linked above that some native species have erect flowerheads, which is important as I had recently been told that erect flowerheads indicated pampas as a blanket rule.

[UPDATE April 2021:
Both species were reduced and suppressed, but regrowth of both was subsequently retained in some places where alternate ground cover was not yet established and the need for shade was high.]

V. incompta has proved an excellent shade to 2-3mH, remaining green longer through summer drought on this dry ridge-top than any other shrubby herb species including totatoa and Senecio eslierii.]

Both these species germinated with great abundance and density thorughout the bared clay banks, and grew to provide essential shade and shelter for these bared areas during Summer and Autumn. We expected to see them develop as tall single stemmed annuals, allowing other plants to grow beneath them as we recalled having in 1999 seen "Purple top", believed to be Verbena bonariensis, along Kaipatiki Roadside, where it was easy to knock down once mature.

Whether the incompta we have had identified here is the same species or not, in the conditions of a dry poor-soil ridge from which competing kikuyu and shrub weeds had been eradicated and native plants were not yet present, neither of these species showed any sign of yielding to old age by mid-August, and between the two of them they had achieved dominance over most of the area, with wild carrot and ox-tongue becoming scarce.

Both these Verbena species are known to be extremely tolerant of arid soils, and both developed many spreading stems from thick long woody roots at ground level.

So we decided it was time to remove them while they can still be composted usefully before Spring germination of both native plants and less-aggressive exotic herbs.

Few could be uprooted, and cutting stems low often leaves a large root mass on the surface, so we have broken most plants down over themselves, cutting the thickest (ie 8-10mm) stems as low as possible, and covered all roots and stem bases with their softer upper stems and foliage.

Hopefully most will weaken and be able to be uprooted. If not, this task will be ongoing for the coming year at least, unless enough mulch to suppress them can be produced from Spring growth of ox-tongue, wild carrot, Black nightshade and anything else leafy.

In either case, we expect to have to mulch a lot of Verbena seedlings this year.

These plants were difficult to uproot even as small seedlings. So though their welcome growth provided quick low shade, moisture retention and, when rains came at last, erosion control, in the conditions this year at Gahnia Grove we might have better advanced benign plant cover and the transition to native vegetation by mulching over most of them as seedlings.

But it is impossible to be sure, as without their hardiness through summer, the drought might have had even more impact on the existing native vegetation and the growth of benign exotics.

We were delighted to meet onsite with the Community Ranger and review our management of the existing Gahnia Grove site, our ad hoc release of a few of the nearest trees from the Japanese honeysuckle invasion of neighbouring canopy margin to the North, and our proposed extension downhill to the Top Forest path, encompassing an area of almost weed-free (other than radiata and Black pines) Tanekaha and other podocarp/broadleaf regeneration, with extensive moss beds and many species of kauri dry ridge community in a dense understorey.

To provide meaningful data on plant communities and their restoration, it is necessary to differentiate this site, which we are referring to here as Tanekaha Ridge, with its species list, habitats and management, from the Gahnia Grove roadside grass margin site where benign exotic herbs are currently occupying a large area of previous dense exotic vine, shrub and grass invasions.

Some observations of our Tanekaha Ridge surveys to date, and ad hoc weed control during those surveys, have already been uploaded. Tanekaha Ridge will eventually have named subsites to follow particular communities of interest within it, particularly in relation to its margins and neighbouring weed invasions.

A Project for Tanekaha Ridge
https://inaturalist.nz/projects/tanekaha-ridge-eskdale-forest-auckland

is now part of the Gahnia Grove Umbrella Project,
https://inaturalist.nz/projects/gahnia-grove-umbrella-project

while the observations for Gahnia Grove should be unaffected, here at https://inaturalist.nz/projects/gahnia-grove-site-summary-and-discussion

For useful data on the time requirements of manual restoration by this method, expected to continue to diminish at the Gahnia Grove site, we are recording the hours of site work separately. Other time spent, eg liaison, monitoring, data collection and presentation, are combined for both sites. All data will continue to be presented in the Gahnia Grove reports.

There is still the occasional regrowth of small roots in the clay bank near the top of CHF Bank, with more and thicker vines on FTZ Bank. This is expected, as weed control did not reach these areas till Oct-Dec 2018, and was not done as extensively on FTZ Bank as it had only been accessed once, by the contractor assigened to assist us for a few hours in this heavy work on a steep bank, and because arborism was expected for the Flame Trees.

The dense deep Tradescantia has made ongoing extension of control relatively easy, with semi-rotted roots being uplifted successively as the Trad mulch piles are moved around.

This process is likely to be successful in eradicating the remainder of the honeysuckle from FTZ Bank, but thereafter there is a vast honeysuckle invasion covering many mature and juvenile native trees, from the kikuyu margin to an unknown point down the steep bank of what appears in satellite view to be a gully head, with two separate run off channels meeting near the top forest Path ("Kauri Path") below.

Mature trees affected include puriri, titoko, karo, ti kouka, tarata, Pseudopanax and manuka, with juveniles of the same species, as well as kanono and kauri, either already dead or hidden, or facing total light exclusion by the end of this summer (based on the progress of this invasion observed over the last year).

Moth plant and Madeira are also present in the honeysuckle, and a large area of Palmgrass is hidden behind it.

Aiming to save as much as possible of this valuable habitat and the birds and other life they support, we have been releasing the nearest trees progressively, so far having released three ti kouka (possibly trunks of the same tree), a horizontal tarata and almost horizontal puahou, two puriri, a mature manuka and karamu which may not survive, several manuka, ti kouka and karamu which are unlikely to survive, and a number of dead trunks and branches of unidentified species.

Since the honeysuckle and moth plant are now reaching older trees on the bank below through the canopy alone, there is no way to control the vine from the ground beneath these trees, so the invasion will proceed through the canopy until cut off at all points where it is rooted.

We have spent a few hours cutting as much as possible to help disclose the remaining live vines, but have only scratched the surface. It remains to be seen whether we will find time to extend this release of trees.

Here are some observations, as seen from the top of the bank, of the honeysuckle zone.

Caught with a berry in its beak, the lone bird perched on an Elaeagnus branch amidst impenetrable honeysuckle was unperturbed by our proximity, and continued to quietly select berries.