Urban Trees and Landscapes
Trees are vital to cities and towns. Neighborhoods with healthy trees have less crime, more employment and business activity, cleaner air, and their human inhabitants are happier and more productive. However, maintaining a healthy population of trees in a city is easier said than done.
The first problem is that they are often planted in compacted debris left over from construction. Perhaps a small planting hole is dug for the sapling and filled with topsoil, but as the tree tries to grow, its roots cannot grow and/or have no access to the minerals it needs. It is common for heavy construction machinery to drive over the potential root zones of urban trees.
A further problem is that tree roots are often situated under sidewalks, streets and parking lots, with only a relatively small opening around the trunk to allow rainwater to penetrate to the roots. Hence urban trees are typically starved of both nutrients and water, with little space for their root systems.
The City of Stockholm has developed an innovative project whereby large planting / drainage pits are created around their trees. These pits are filled with layers of stone and biochar. Each pit has its own stormwater drain. The creation of these biochar pits is expensive, but the cost is more than paid for by the money the city saves from being able to signficantly reduce its stormwater processing capacity. The trees planted in biochar are vibrantly healthy.
All open parks with grass are being re-landscaped with a mix of biochar, small pebbles and some compost. The grass remains healthy because the biochar-pebble "soil" can't be compressed. Well trodden paths remain green. And heavy vehicles do not leave a destructive imprint, even if the biochar-pebble substrate is soaked with rainwater.