There was interest from restoration volunteers in a post in which I highlighted the regenerative power and value of wild Gahnia xanthocarpa along the ridgetop part of the Eskdale Forest loop track constructed in 2020. Some were encouraged to try planting it, and I didnt think this would be effective, for several reasons.
One is that Gahnia is notoriously difficult to propagate, so nursery supplies are likely to be lacking.
Another is that I see herbicide is used on many planting sites, and, being a kauri-forest specialist, Gahnia xanthocarpa might depend on the famously unique mycorrhizal fungal network in kauri forest soil, which can survive after deforestation among pines, manuka or kanuka, but cannot survive agrichemicals (according to a technical report on the MPI website regarding manuka honey production).
I could not articulate my intuition-based response to the email enquiry at the time, so I did not pass on my doubts, but today I was pondering whether in fact my beliefs about this issue were correct, so I asked the google AI about it.
The response was pretty much what I had thought, and a lot easier to copy here than write out myself, so I am posting it here. As we all know by now, AI can make mistakes…. lots of them… but there should be enough info here to launch your own investigations, perhaps pooling experiences of conservationists and reserve volunteers, if it hasnt been done already:
1. The Impact of Humus Loss on Gahnia xanthocarpa
Gahnia xanthocarpa naturally acts as a foundational ground cover in kauri forest communities. While it is incredibly resilient once established—and can even colonise bare clay banks on ridge tracks exposed by heavy disturbance—it thrives best in permanently damp, humus-rich soil. [1, 2, 3, 4, 5]
- The Moisture Problem: Stripping all vegetation on an exposed ridge eliminates the sponge-like capacity of humus. Without organic matter to retain water, the soil bakes, hardens, and suffers from rapid moisture loss. Young Gahnia, which are already highly prone to shock during transplanting, will struggle immensely to establish roots in dry, nutrient-stripped clay. [1, 2, 3, 4]
- Glyphosate Mobility: In low-organic-matter soils (where there is no humus to bind it), glyphosate becomes more mobile. If high rainfall occurs shortly after spraying, remaining chemical traces can drift into the root zone of newly planted natives, causing hidden stress. [1]
2. Destruction of Soil Flora (The Underground Network)
Kauri ridges feature uniquely acidic, highly leached podzolised (“gumland”) soils. The native plants here rely completely on an intricate web of soil flora, specifically mycorrhizal fungi and beneficial bacteria, to mine nutrients from this low-fertility ground. [1]
- Microbial Crash: Completely clearing vegetation with Roundup starves the soil biology. Without live root exudates or decaying organic mulch to feed on, beneficial fungal networks collapse. [1]
- Pathogen Vulnerability: Sterilising the native microbial workforce leaves a biological vacuum. In a kauri ecosystem, this is dangerous. It leaves the site wide open to devastating soil-borne pathogens like Phytophthora agathidicida (kauri dieback), which attacks root systems and thrives in disturbed, compromised soils. [1, 2]
3. Disruption of Natural Soil “EMF” (Bioelectricity)
From a bio-ecological perspective, a living forest floor functions as a dynamic electrical circuit.
- Live plants, humic compounds, and wet mycelial networks act as natural conductors that maintain a subtle electrochemical gradient (redox potential and bioelectric fields) between the atmosphere and the earth.
- Applying a synthetic, chelating chemical like glyphosate across a bare landscape acts as an insulator or disruptive agent. It alters soil chemistry, breaks the living fungal “wires,” and desiccates the upper soil layers. This shuts down the subterranean bioelectric flow that plants use for signaling, nutrient uptake, and root orientation.
How to Pivot for Successful Regeneration
If the area has already been sprayed and stripped, planting Gahnia straight into the bare dirt will likely result in high failure rates. To fix this:
- Rebuild the Humus Layer: Do not leave the soil naked. Layer the site with aged, untreated sawdust (which Gahnia seeds and roots uniquely love) or native leaf mulch to re-introduce organic carbon. [1, 2]
- Utilise a Nursery Crop: Instead of fighting weeds exclusively with chemicals, consider allowing non-invasive or temporary “nursery” plants (like mānuka or even controlled gorse, which adds nitrogen and humus) to establish first. They provide the shade, windbreaks, and root networks needed to bring the soil flora back to life before you introduce sensitive climax species like Gahnia and kauri. [1, 2, 3]