Drought Hardening with Biochar

The Oregon forest is exhibiting widespread drought stress, and biochar can help.

This year saw the highest fir mortality in Oregon since the 1950’s, after several years of drought. Firs have been accustomed to ample rainfall in the Pacific Northwest, but that regime has been altered by climate change.

Of the four principal benefits of biochar to soil, its water-retention property is the most beneficial when it comes to stabilizing drought-stressed forests. The other benefits (nutrient retention, microbe habitat, and carbon sequestration) also have roles in countering drought, but without adequate retention in the soil, water becomes the limiting factor. Abundant rainfall can mask a soil’s low water retention, but in a drought, the mask is removed and trees start to die. Biochar’s “sponge” effect can be enough to pull a forest through a drought.

The Oregon forest is vast, climate change is accelerating, and it is impossible to prevent wildfire from completing the devastation. There is not enough time and people to stop the conversion of the forest to one with fewer firs, in most cases. But locally, human resources can mitigate the effect with biochar.

Broadcasting biochar in the forest as a top dressing is an effective way to add it to the soil. Leaves and other litter cover it, so that it gradually is incorporated in the humus layer, where it soon begins providing its ecological functions—holding water and nutrients, providing habitat for microbes, and sequestering carbon. The usual steps of grinding and inoculation can be omitted, because nature accomplishes them by itself over time; those steps only matter when you’re burying the biochar. You’re also omitting the work of transporting and burying it. By top dressing, more of your time can be devoted to production.

Biochar quality varies. Its durability and purity matter when it’s designated for agriculture, sale, or carbon credits. In that context, quality control is important. Not so for broadcast! As long as it’s applied as a top dressing, biochar can be made by pile-burning, raked out while extinguishing the fire with water, and left in place. All biochar retains water. How many hundreds of years it does so, and how completely the biomass is converted to biochar, are relatively unimportant for forest application.

If you use a kiln, such as the Ring of Fire or the one shown on this website, the volume of biochar that you make might overwhelm the spot where you make it. There’s no established maximum, but more than a couple of inches of biochar probably ought to be distributed better, to spread the benefits. Thicker layers will temporarily function as a sheet mulch, which has its place in suppressing weeds but not in suppressing small forest plants.

We still need to phase out the cause of climate change: burning fossil fuel. But however that happens—and it will, one way or another—biochar can soften the transition, for ourselves and for our forest relatives.