There are many undeveloped urban spaces that have the potential to be used as a resource. The space between highway clovers, for example, is a space that is unoccupied, but not adequate for housing or commercial use. In addition, as the shared economy grows and the public becomes more environmentally conscious, less parking spaces will be needed in urban areas, creating vacant and unused parking lots and parking structures. All of these spaces can be adapted for use to offset other environmental impacts.
One of the potential uses for these spaces is growing timber. In Providence, Rhode Island, if all of these potential spaces were converted into timber fields, up to 25% of the timber used annually could be grown locally, rotating which spaces are harvested on a five year cycle.
Poplar is a very common wood used in timber construction. A Poplar tree grows up to 8 feet per year, and mature at 40 feet tall, or 5 years of growth. At this height, the Poplar will be about 2 feet in diameter at the time of harvesting. This will yield up to 125 cubic feet of wood, conservatively 100 cubic feet after being cut and sized. Lastly, Poplar trees need to be planted 5 feet apart from each other.
Every year, about 43 cubic feet of timber is used for each American. Providence, Rhode Island has a population of around 180,000. Using these numbers, it can be estimated that the city of Providence uses around 77,400 Poplar trees worth of timber. Each American used about 43 cubic feet of wood a year
Mapping the city of Providence, I found that the total space available in highway voids is 475,000 square feet in the downtown area. Each tree must be planted 5 feet on center, allowing for about 17,500 trees. Divided into five plots for the five year growing cycle of Poplar, this allows for 3,500 to be harvested annually. That means 3,500 less trees harvested through deforestation, and 17,500 more trees helping to offset carbon emissions in downtown Providence, Rhode Island. This replaces 2.5% of the timber used within Providence, Rhode Island by utilizing space that is already vacant.
If the parking lots and parking garages are used as well as the highway voids, this number grows from 3,500 trees annually harvested to 23,500 trees harvest annually, 25% of the timber used within Providence, Rhode Island. These timber fields can also replace the noise barriers often constructed along side highways.