By Céline Caron
Recently I listened to “Dr. Mercola and Courtney White Discuss Carbon Sequestration” (YouTube, Aug. 27, 2014; https://www.youtube.com/watch?v=LSgroKuuJFA). Both talked about incorporating wood chips into soil (with or without composting) and using them as mulch. Neither distinguished between wood chips and ramial wood chips. They obviously have not read my many articles about ramial wood chips published in The Maine Organic Farmer & Gardener nor the research that has been done in Quebec over the last 35 years.
The broad term “wood chips” can refer to chips coming from any or all parts of a tree, either trunk wood or ramial (smaller branch) wood, and to chips coming from either coniferous or hardwood trees. Ramial wood chips, on the other hand, come only from deciduous hardwood tree branches that are under 7 cm (2.8 inches) in diameter. A tremendous difference exists between wood chips from larger tree parts of mixed species and ramial wood chips, especially in the carbon-to-nitrogen (C:N) ratio.
The C:N ratio for ramial wood ranges from 30:1 to 170:1; for stem wood, 400:1 to 750:1. Deciduous tree branches under 7 cm in diameter, without their leaves, are the best choice for chipping. In North American tree species, concentrations of essential mineral nutrients (N, P, K, Ca, Mg, etc.) increase as branch diameter decreases. These concentrations reach a minimum in branches more than 7 cm in diameter, while branches less than 7 cm in diameter contain 75 percent fertilizing nutrients, based on dry weight. The smaller, the better; while the bigger branches are, the less digestible they become.
If sawdust made from tree trunks is mixed with soil, nitrogen deficiency will occur unless the sawdust is first composted with farm manure or some other nitrogenous material. The trunk of the tree supports the branches, which are the real biological center for wood production. The trunk has less nutrient value than the branches, and the enzymes of microflora and fauna cannot integrate lignin from tree trunks into the soil. For the forest, the trunk has no life and is attacked from the outside and transformed into CO2 with little benefit to the soil.
For a first agricultural treatment, ramial wood should not have green leaves, because green leaves contain chemical elements that are easily accessible to bacteria. These bacteria can prevail over Basidiomycetes (a class of aerobic fungi). When leaves are dead, these chemical elements are tied to brown pigments and will be released through soil mesofauna activity in perfect harmony with the activity of Basidiomycetes. Basidiomycetes produce humic substances – long-lasting soil carbon compounds – that are composed partly of humic acid and fulvic acid.
In the past, ramial wood from deciduous trees was considered a waste product to be disposed of, but it is actually the most important and richest part of the trees and the forest. It can introduce the soil-building mechanisms inherent in deciduous forest soils to agricultural soils – without the dominating trees. In other words, deciduous trees make fertile soil, in temperate and tropical climates.
Céline Caron is an evolutionary ecologist and Earth doctor. She has written extensively about ramial chipped wood for The MOF&G and other publications.