Our Research
Carbon Sequestration Through Wood Burial
The Problem
Natural forests are typically littered with dead trees. In addition, forest thinning operations to reduce the size and extent of wildfires produce large quantities of timber. Ning Zeng has proposed burial of these trees in trenches under a layer of soil. This would prevent their carbon from returning to the atmosphere, as it would if the trees were to decompose or be burned in slash piles. The resulting anaerobic conditions under the soil will slow the decomposition of the buried wood. The question that remains largely unanswered is “How long will the carbon remain sequestered?”
Aerial view of forest
Cottonwood Heights, Utah.
Dead trees in a natural North American deciduous forest, Belwood, Maryland.
Our Solution
In cooperation with Yale’s Carbon Containment Lab, Terraffirm has two ongoing experiments to determine the rate of decomposition of wood as a function of depth of burial, type and shape of wood, composition of soil, ambient temperature, water content of the soi, rainfall, etc.
Experiment 1 - Wooden Disks
In the first experiment we used 10cm diameter by 5cm long disks of Monterey Pine and Blue Gum Eucalyptus. At each of eighteen sites we buried disks at 1m and at 2m depths and placed a third disk on the surface. The weight of each disk after drying was recorded, along with its volume. In addition, five samples of each species were analyzed to determine their carbon content. At intervals of one year, three years and five years, disks at six of the burial locations will be recovered and analyzed to determine the rate of decomposition.
Eucalyptus Wood “cookies” after labeling.
Trench used for burial. Note hole on left side.
Monterey Pine cookies during drying.
Trench after back-filling. Reference cookies on the surface.
Experiment 2 - Pine Logs
For the second experiment we used twelve Monterey Pine logs, 1.2m long and 20cm in diameter. We place nine of the logs at the bottom of a trench 65cm wide and 3m deep. The logs were arranged in three layers of three logs each, with 3cm of soil between each layer. After burial, the trench was backfilled with soil and the three remaining logs were placed on the surface. Two-centimeter-long samples were taken from each log and analyzed to determine their carbon content. After one year we will remove the logs from the top layer and measure their carbon content. Similarly, after three years and five years, we’ll remove and analyze the second and third layers of logs.
Monterey Pine logs before burial.
Second layer of buried logs.
First layer of buried logs.
Trench after back-filling, outline marked by stakes.
The Impact
Zeng estimates that a sustainable long-term carbon sequestration potential for wood burial is from 5 to 10 gigatons of carbon per year, or 18 to 36 gigatons of carbon dioxide per year. The Global Carbon Project estimates that the net carbon dioxide increase in the atmosphere is 19 gigatons. If these experiments show that a substantial percentage of the carbon in the buried wood is sequestered for long periods, this method could provide a very meaningful way of addressing climate change.
Perturbation of the global carbon cycle caused by anthropogenic activities, averaged globally for the decade 2010–2019 (GtCO2/yr)
