I first learned about "chipped branch wood" or "ramial wood chip" about a decade ago. But it takes training and care to separate out the ramial branches to get this particular form of chipped wood.
Anyone here with experience of setting up a reliable source of ramial chipped branch wood?
Background & evidence:
My understanding is, any deciduous tree branch below about 7 cm / 3 in in diameter, will have a significantly lower carbon content than the trunk wood or general older mixed trunk & branch deciduous chip.
"The C:N ratio for ramial woodchips ranges from 30:1 to 170:1; and for stem wood, 400:1 to 750:1."
Ramial woodchips
https://zerodig.earth/ramial-woodchips/
The late farmer-philosopher Dave of Darlington did important work on ramial chipped branch wood in the late C20th:
Growing Sustainably, collected essays of Dave of Darlington,
https://veganorganic.net/book-review-growing-sustainability/
"Nutritionally these are the richest parts of trees, with young tree branches containing as much as 75% of the minerals, amino acids, proteins, phytohormones and enzymes found in the tree."
Ramial woodchip production and use on farm, 2020, Organic Research Centre
https://www.organicresearchcentre.com/news-events/ramial-woodchip-production-and-use-on-farm/
Pioneering agroecologist Iain Tolhurst has great success with ramial chipped branch wood, particularly for nourishing the soil ecology or biome on their 20 acre farm:
"It brings the forest to the farm with increased fungal activity in the soil and additional nutritional benefits. In the last five years, their yields have doubled."
Propagation substrates: Is woodchip a viable alternative to peat? Q&A with Iain Tolhurst,
https://www.innovativefarmers.org/knowledge-hub/propagation-substrates-is-woodchip-a-viable-alternative-to-peat-qa-with-iain-tolhurst/
Lots more detail:
Ramial chipped wood amendment drives shifts in soil microbial carbon and phosphorus cycling networks across a depth gradient, 2026, González-Coria et al.
https://www.sciencedirect.com/science/article/pii/S0167198726000929