City plans to use LiDAR technology to help determine health of tree canopy

Edmonton is a city of suburbs and cement connected by ribbons of trees tied together by the river valley. And officials want to find out if the city’s already lush tree canopy is expanding, and by how much.

Over the next year, the city will develop a plan that sets a clear direction for the management, maintenance and growth of the city’s trees. By 2020, under Edmonton’s urban forest management plan, the city hopes to grow its tree canopy by one-fifth.

“Trees and natural areas, unlike other urban infrastructure, grow and appreciate with time, and so do the benefits that they provide,” said Crispin Wood, Edmonton’s urban forestry unit management supervisor. “If we invest wisely, that relationship only improves with age.”

Several studies have shown the benefits of trees. They help reduce the heat island effect (where an urban area is significantly warmer than surrounding rural areas because of human activities), improve air quality (in 2009, it was estimated trees removed 531 tonnes of pollutants in Edmonton alone) and increase property values by as much as 20 per cent — and even help reduce crime.

Catherine Shier, the city ’s principal ecological planner, said unlike man-made infrastructure such as buildings, air purifiers and water filtration units, which are in their best condition when first built and then decline over time, trees and natural areas increase their performance and naturally renew themselves.

City officials want to use a technology involving laser pulses — Light Detection and Ranging (LiDAR) — either this year or next to measure how much more area the tree canopy covers. LiDAR is already used by multiple departments in the city, and is a costeffective approach to accurately measure and monitor tree canopy, Shier said.

When the canopy was measured in 2009 using vegetation data from 300 random plots, it stood at 10.5 per cent of the land within the city. It was measured again in 2013 using aerial imagery and LiDAR, and was shown to be 13.8 per cent of total land.

“We used different methodologies in 2010 versus 2013, so we need to be cautious when making comparisons,” Shier said. “However, the upward trend is encouraging.”

The city plants between 5,000 and 7,000 trees a year along streets and in parks, and replaces trees lost due to natural causes and construction. It also plants 45,000 native saplings a year through its naturalization and Root4Trees programs.

Edmonton’s trees — encompassing an area of 3,715 hectares — are valued at $1.2 billion. The average value of a tree on an Edmonton street is between $2,400 and $8,000, although the older it is, the higher the value. For instance, an elm tree more than a metre in diameter can be valued as much as $65,000.