Vegetation management for fire safety during restoration of forest margin

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Interesting the article said invasive aliens draw water, diminishing water resoures.

I have often wondered about the net water gain or loss from arid-tolerant plants, from the Verbena incomta and linearis which proliferated on about 60 sq metres of ground released from other invasive weeds in my forest margin restoration plot (providing low shade for an area that would have been otherwise comletely exposed to hot sun and wind throughout last summer), to the Brush and black wattle trees that are common in the neighbourhood.

This summer the ground is dry even in the forest itself, and sun reaches it in places through thin canopy.

20 years ago someone told me that wattles suck all the water away from the native trees. Is there evidence of that? If so, it might help persuade local land managers to remove them. The cost of arborism is the deterrent to removal in most cases, but as things become more serious that might change.

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Hard evidence of invasive aliens guzzling water?
@tony.rebeloi ?

If interested in a discussion on the effects of increasing western juniper densities on water in the western US, pp 5-6:

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I just visited a friend who grew up in Muisenberg (spelling?; = “Mouse mountain”) in Cape Town in the 1940s. She showed me pictures of the area in several books and talked about some of the changes she had seen. She knew an invasive tree species (Banksia i think) was removed at some time and resulted in a wetland :) and she told me fynbos is a flora unique in the world.

Kind of like the dry kauri ridge plant community I am working with, i suppose. Though this has trees - big ones.

With a z Muizenberg our plummy GPS lady battles with that name.

That Banksia invading was a first for me.

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…also @kiwifergus. I don’t know if it’s very relevant but Elsdon Best wrote about the rarauhe (bracken fern) and mentions that every few years communities would burn the plants. This would destroy all the ‘weeds’ and the ferns would quickly recover. Younger roots would sprout (presumably due to the newly available space around them) and so the next fern root harvest would be of the nicer finer roots (which were a valued food). The burning was done while the hinau was flowering but before the rata flowered. He also mentions that leaving the ferns alone leads to scrub taking over and forest following that.


maybe not specifically relevant to fire safety or restoration - except that, unsurprisingly, leaving it alone resullts in successional species development - but interesting as an example of habitat modification by humans. i guess it was an early form of agriculture in NZ.
And interesting for @kiwifergus as he may be looking at some burnt areas in upcoming bioblitz not far from the recent Napier forestry fire???

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Very relevant! Not so much in terms of “early indigenous foods for the first arrivals”, but certainly in terms of cultivated foods derived from local fauna, and DEFINITELY in terms of vegetation management for fire safety… .the looking to nature/environment for the timings of fires is critical.


Thanks Mark, could you expand on the bit about vegetation management for fire safety?

oh, and i think you meant “flora” not “fauna”? :)

I don’t think we will be undertaking the bioblitz in that burnt area specifically, but I am sure the proximity will be a catalyst for some sort of involvement.


Do you mean the Banksia invasion my friend referred to was a first experience of invasive plants for you, or you made the first observation of it, or your banksia obs were the first you’d seen?

btw when i visited that friend yesterday I went over the (invisible:) boundary between Auckland and Northland. The dryness of the grass looked pretty much the same as here on the North Shore of Auckland at present, the pasture was dry but there was some, and the cornfields(maize) seemed to be doing alright (unlikely to be irrigated, but I may be out of touch). But they had had some good rainfalls a few weeks ago that missed North Shore Auckland.

I noticed huge (invasive) Bamboo stands both beside a railway line and along roadside margins of Conservation land “Dome Valley” (wonderful forest, by the looks of it). Since it produces a lot of dry leaf around the stand, i would think that is quite flammable. But I don’t know about the flammability of the canes.

The Banksia was a first only for me. It gets depressing to keep finding new to me invasive aliens. But we have a project on iNat which will follow up the invasives, if I report them.

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to clarify my comments about my own back yard, I don’t have any garden waste to dump as we have almost no garden and I use a worm bin for composting most of it.

But i have been retaining fallen Cordyline australis (cabbage tree) leaves under their trees, as habitat for the native (endemic?) cabbage tree moth larvae, and as moisture retention. In wet seasons gone by these long woody/fibrous leaves made it possible to walk on the ground without sinking into wet clay.

I have started gathering up some of the surface layer of these leaves and placing them in barrels of water, leaving tips exposed along with some sticks so insects that fall in (eg weta) can climb out, and hopefully some of the potentially drowned invertebrates can escape.

Under the big trees at the bottom of the slope, at the top of the quasi-forest ( a mix of exotic and native trees allowed to grow wild over the last 50 years on a 3/4 acre section around a neighbouring house), the trees and treeferns drop branches and leaves. I have been here 20 years and have not removed any, with much of it rotting over that time.

So its underlayers are less dry, and the bottom layer moist in places, perhaps only after my occasional watering of it. When I remove the top layers the lower ones dry out, presumably drought-stressing the trees and possibly creating greater flammability of the trees.

This situation more or less replicates the situation i have in my volunteer plot, though that has the addition of large areas of exotic herbs that have replaced the weed vines, shrubs and grasses removed in 2018.

Since weed removal, many of the native trees have recovered and are growing well, and now provide a little more shade - a plus for moisture retention and the development of green ground cover.

The hydration of the recovering small trees and also of the older forestmargin trees is, i believe, currently supported by the retention of as many of the exotic herbs as i feel is fire-safe. Leaving the herbs keeps the ground shaded and cool, despite being dry and cracked, whereas removing the herbs exposes the ground to more sun and wind - but removes flammable material from the forest margin.

Removing the herbs also creates even more dry material to dispose of with almost no shaded and damp places left, even in the forest itself. My plan was to remove them while still green, so they could be used as mulch around trees and would compost or rot rather than dry. However, due to the prolonged drought, even culling them while in their prime resulted in no rotting, and they became just more dry brittle herbs to dispose of.

So i have reverted to my practice so far, ie to remove the exotic herbs as they become dry, and place them as far from the publicly-accessible exposed roadside and walkway, in as shaded and sheltered a spot i can find, then trample and crush them on the ground as they dry further.

As the native herbs increase in the ratio with the exotic ones, i will have to assess THEIR flammability. I know of no guidlines for fire-safety management of native herbs. I expect i will have to treat them the same as the exotics, ie cut and remove when they become dry, unless we get significant rain.

The surrounding area, ie the forest margin on either side of my plot, has the same exotic plants drying in dense stands with no intervention or plan at all, it seems. Some parts have dense long grass that has been sprayed and is completely dry. I consider that a fire hazard but it seems the landowners/managers (City/Regional council) do not assess for fire safety, leaving it to the Fire Service “if a complaint is made”. Nonetheless I attempt to mitigate the hazards on my own plot within the Reserve, as best I can.


There’s an old news article from 1937 about tree planting on a hill in Wellington, New Zealand where “provision is made for protection from fire”. Apparently the plan was “to put in at suitable places three rows of karaka trees and three rows of lucerne.” They also had five men “engaged in the planting and care of the tress” with “grass and undergrowth being kept away from their roots”.
I think the main fire risk would have been gorse and dry grass.
Presumably planting 3 rows of karaka and lucerne(?) isn’t an option for you @kaipatiki_naturewatc but the idea of planting something might be worth considering? Even though not native, a border of something like agapanthus could maybe add some protection.

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Planting karaka is an option, though the poor-soil dry ridge with roading metal mixed in the surface soil, and kauri podsol beneath, might not allow them to grow for a while. Worth considering as part of a long term plan.
However at present the dead leaves under them would be the sort of thing I am trying to assess and manage if possible. The comments of a well known politician about “sweeping the forest”, though misleading as well as garbled, nonetheless sounded like he was misquoting some sort of actual useful advice by some forest management or fire prevention agency, which I have been reflecting on ever since.
I have a 4mH karaka in my garden and have been spraying it with water in the evening about once a week to perhaps help at least a bottom layer of leaf litter break down. There’s no irrigation in the Reserve though of course.
There is a published list of flammability of NZ trees and shrubs that I occasionally consult, sorry I don’t have the link. The less flammable species naturally occurring here that are likely to grow include Coprosma robusta, (karamu, already common and I am taking great care of existing adults, juveniles and seedlings), harakeke (already planted all along the margin, a pain to keep kikuyu out of and producing a lot of dry leaves that take years to rot even in wet ground) and others I forget at present.
So my aim has been to support the existing emergence and increasing dominance of karamu in the manuka/kanuka margin’s outer edge. Thanks for the reminder about planting and species…if we ever have a planting season I may ask for planting, though my aim was to demonstrate the natural development of appropriate plant communities through weeding, as in normal conditions at least it is more successful.

There are hundeeds of planted natives along the ridge either side of my plot, and they are nearly all dead or dying under weeds. At a cost of at least $10 a plant.

As for Agapanthus, yes I can’t imagine a less flammable plant! Also v. Difficult to control or eradicate, and I have almost eradicated it from my part of the inner forest and margin. Around here it forms a monoculture along many driveways and roadsides and any untended patch of garden or Reserve, and competes effectively with the other weeds in disturbed forest margins, preventing any chance of trees growing, ever, so the situation would have to be dire before allowing Agapanthus back in😊



A global perspective from a NZ fire / forest specialist

Sorry Diana this was not meant as a reply to you, just a general reply


Here is a news article about a rural community creating a firebreak by …well, read it.

EDIT sorry, forgot to paste the link, here it is:

My thoughts and questions are echoed in the reader comments that follow.

There have been a couple of press releases by NZ Fire and Emergency Service recently encouraging awareness etc, no specific answers though, and from reading the opposing viewpoints of Australian forest fire experts about their particular vegetation and fire behaviours, withover 40 national reviews and changes in policy direction to match, it seems unlikely anyone has a convincing and comprehensive solution.

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Planting manuka for honey money?