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Why Are Cities Planting Fast Growing Trees?

Most attention on recycling tends to go to materials produced by man – plastics, paper and electronics are probably the big three issues. That’s not the end of the story though. Trees and other plants make up a large percentage of what we throw away. According to EPA figures yard trimmings account for 13.5 percent of municipal solid waste – 110 pounds of grass clippings, old pot plants and dead Christmas trees for every American per year. Then figure in lopped branches from forestry, unharvested parts of crops and the huge amount of plant matter disposed of by the food industry and we’re talking about millions of tons of plant matter to be disposed of every year. If left to decompose it will release huge amounts of carbon into the atmosphere, so sending it to landfill counts as a very bad idea. What gets done to it instead?

Fast Growing Tree Trunk

Large public works projects such as roads and commercialized areas require the clearing of land. This is usually in the form of vacant forests of varying sizes. All of the trees and plants that are cleared get filtered to their respective industries; large trees get sourced for timber while the remaining shrubs and smaller plant material is filtered down the recycling line. Environmental advocates have pushed hard for reforestation bills that ensure whatever trees are cut down are replaced so that there is almost no negative environmental impact. Many municipalities have enacted laws such as these and are considered 1 for 1: however many acres of forest are cut down, they replace that same amount of land with new saplings to regrow the forest. Because the goal is to reforest cheaply and quickly, municipalities choose from a list of fast growing trees for their area so that the saplings mature quickly to continue pulling harmful greenhouse gasses such as CO2 from the air. Although these bills are not nationwide, they are quickly taking hold as more and more cities adopt these laws. So what happens with the actual trees and plants that are cut down and discarded?

Tree Farm

Probably the most valuable resource in plant waste is wood. What goes for recycling isn’t usually good enough quality to be used for timber or furniture, otherwise it would be used in those industries, but it’s still wood and it can be processed into several useful products. The basic way of processing it is by chipping. Foliage is stripped away and the wood is mechanically reduced to small chips of varying sizes. Where it goes from there depends on the type and quality of the wood. Softwood can be fully pulped and turned into paper, although most of the demand for that is met by recycling existing paper or wood from managed forests. Chips can also be formed into wood-based construction materials like particle board, which is cheaper than solid timber and performs better in many applications. It also reduces the need to cut forests for raw materials. Lower grades of particle board can be made from much of the wood sent to recycling.

Wood chips, waste and pulp

Another option that’s becoming more popular is biomass power. This is a fuel source, usually used for electricity generation, which exploits organic waste. Wood and a wide variety of other materials, including spent sugarcane, can be chipped and burned as a fuel in suitable boilers. This then generates steam, which turns a turbine to create electrical power. With carbon sequestration equipment fitted this is a low-pollution and sustainable method of generation that doesn’t use up scarce fossil fuels.

As well as wood there are huge quantities of soft plant matter to consider. The most efficient way to use this is through composting. By managing the decomposition of plant material a rich natural fertilizer can be produced. This has been done for thousands of years by simply piling waste in a heap and keeping it damp, but industrial processes have now been developed. Stricter control of the process improves the quality of the compost and also minimizes the emission of greenhouse gases like methane. The largest stainless steel building on the continent is a composting plant in Alberta, Canada; it’s the size of 14 NHL rinks and every year it turns 250,000 tons of waste into 80,000 tons of compost.

Tree and plant waste is produced in huge quantities and can be bulky, but because it’s all natural material it can be recycled using low-tech and usually economical methods. However it is carbon rich, which is potentially a serious environmental hazard. Properly managed, though, it’s a valuable resource and one that’s being exploited with increasing efficiency.