Growing trees in the urban jungle By Alistair Johnston T here are many challenges a tree must face to reach maturity. Whether attacked by insects or disease, animal grazing or environmental stressors, no challenge is more significant for trees than human impact. In the naturally vegetated regions of Canada, trees tend to grow to maturity in large communities where soil, nutrients, and moisture are readily available. These tree communities follow a cycle of growth, failure, and regeneration, which maintains a relatively consistent canopy area. Introduce trees into the ‘urban jungle’ and a whole new world of challenges is born. Before taking a closer look at the challenges faced by trees in the urban environment, there are some interesting facts 1,2 to share. 14 May 2014 1. A single tree produces approximately 118 kg (260 lb) of oxygen (O) per year. That means two mature trees can supply enough oxygen annually to support a family of four. 2. A tree can absorb as much carbon (C) in a year as a car produces driving 40,000 km (24,855 miles). 3. Over the course of its life, a single tree can absorb one tonne (2,205 lb) of carbon dioxide (CO 2 ). 4. The average Canadian uses roughly 340 kg (750 lb) of paper every year, and 95 per cent of homes are built using wood. That means each person uses the equivalent of one 30-m (98-ft) tall, 0.4-m (1.3-ft) diameter tree every year for their paper and wood products. 5. A tree on a downtown city site has an average life expectancy of only 15 years.