Oh, How the Phragmites Have Fallen

In our Watershed Stewards Academy class visit to Elms Environmental Education Center, our host, +Kurt Reitz showed us a freshwater pond that was walled in halfway around with deep stands of phragmites australis (the common reed), an invasive shoreline plant so tenacious that it requires herculean efforts to eradicate it. Typically, eradication requires cutting, spraying with glyphosate, burning the stubble, and repeat treatments a few years later. The toil and trouble associated with this regimen deters most attempts at restoration, so owners and environmentalists have essentially acceded to allowing phragmites to rob our ecosystems of their natural biodiversity.

These tenacious phragmites will weather this storm, no problem (Photo by Kurt Reitz)

The way phragmites dries up in the fall makes it a tempting target for conversion to biochar. Controlled open burns of phragmites risk turning into conflagrations that could touch off fires in surrounding areas. I wonder, though, if it may be feasible to avoid much of the cutting and spraying and make very hot fires out of phragmites stands by applying traditional charcoal-farming techniques.

Biochar could be made with phragmites similar to the Ankara system. One of the problems we have in the Chesapeake Bay area is that phragmites grows out of dredging deposits, but by using dredging spoils as the covering material for the Ankara-style burn, we would be able to kill the in situ phragmites and the seeds and rhizomes in the dredging material, as well. Open burning has been an ineffective way to eliminate phragmites since the deep rhizomes often survive and come back with a vengeance. With the Ankara approach, heat is concentrated and conducted down deeper into the soil, so there is a better chance that the rhizomes would be killed.

For phragmites, the way to apply this approach might involve cutting three-foot strips about every 12 feet, flattening the reeds in the 12 foot rows and adding the cut pieces, digging out the rhizome-filled soil from the cut areas and spreading it on the flattened reeds, adding dredging spoils (from nearby projects) to create a casing over the whole biomass, making vent holes at the ends and in the top of the ridge as necessary to maintain some air flow, lighting the biomass at both ends and keeping it going by opening or closing air vents while it cooks for several days. After it cools, it can be tilled and planted with winter hardy native plants.

Potential advantages of this approach are its economy, rapidity, sequestering of carbon, creation of a biochar nutrient filter along the shoreline, and improved soil properties for replanting.

Breakthrough!

Fragipan is one thing, but what about soils that are highly compacted from the top down? This is a problem common in urban landscaping, and not uncommon in parts of suburbia as well. Compaction makes it hard to start and grow plants, including trees, which serve many important functions, especially in cities. The solution is excavation and replacement of the compacted soil with a suitable growing medium.

Photo of urban landscaping by thanh.ha.dang (CC BY-NC-SA 2.0)

In Stockholm, Sweden, one enlightened leader grasped the choice of replacement growing medium as an opportunity to introduce biochar into the mix whenever trees are being planted in civic landscaping projects. Biochar brings many advantages over commonly used peat moss, including its resistance to compaction. The biochar techniques used by Bjorn Embrén, head of landscaping for the city, were developed over decades and have shown stupendous results in the growth rate and survival of trees. The mixes they use include relatively little soil, but massive amounts of various grades of gravel and biochar. Tree roots find the open structure very accommodating.

Embrén's advice to cities who are interested in these techniques is "Dare to try it and you will be convinced!"  What we, in Maryland, must do first is make a few changes to the specifications for growing media in the Stormwater Design Manual, which dictates a loam/sand mix for infiltration devices. Adopting these techniques would make it possible to select from a wider range of vegetation in bioretention and filter devices, as biochar-based filters drain more quickly than those that rely primarily on soil.

At any rate, we shouldn't have to take the full development and test approach to begin adopting these designs - that part has already been done. All we need is a few delegations visiting Stockholm to see how to make them successfully. They can start by reading this manual. It is a bit old and doesn't use the term "biochar." The term they use instead, "structural soil," could have been key to adoption of the changes since it sounds so common sense and familiar.