Wednesday, January 18, 2012

Short Trees Won’t Power High-Performance Green Infrastructure

Communities such as my adopted hometown of Durham are making a costly mistake when they replace towering street trees as they age out or are destroyed by sidewalk construction or power lines with varieties too short when mature to be anything more than aesthetics, especially in downtown areas or other areas of “extreme pavement” and hardscape.

The issue isn't just about aesthetics, although the aesthetic value of trees and especially tree canopy is held dearly by residents, especially newcomers who have not yet begun to take them for granted as a remarkable part of Durham’s unique sense of place.

Researchers have found that “large canopy trees (greater than 50 feet in height and canopy spread) outperform small trees (less than 25 feet) by a factor of 15, and they do not start adding significant environmental performance until they reach 30 feet.”

These researchers go on to add that “in the quest to make the urban forest into a high-performance green infrastructure, lots of big trees are required, especially in the most environmentally compromised zones: streets, plazas, parking lots, and commercial strips.”

Fussing developers who grudgingly and sparsely populate parking lots with only small trees along with utility and cable companies who refuse to bury power lines and even public works and planning officials who neglect or refuse to include or require technologies such as DeepRoot are in reality saddling the unsuspecting public with hidden spillover costs or externalities.

If these entities truly grasped and incorporated the long-term value of large trees for not only aesthetics, but also for reduction in heating and cooling costs, net atmospheric reduction of CO2, air pollution reduction, water purification, crime reduction, storm water reduction and increased property and rental values -- all of which have now been quantified by scientists -- they would gladly make accommodation.

Many developers have done as the company that originally developed The Streets at Southpoint and Main Street did when they planted large specimen trees that cost as much as $10,000 each or as the Research Triangle Foundation did when they carved the world famous research Park out of southeast Durham pinelands and restricted development to only a portion of the area allotted each tenant or owner,  thereby leaving the remainder of the site in its natural wooded state.

Until the free market begins to universally incorporate the true cost benefit of large trees, as these two developers did, it is vital that local governments protect the public from hidden spillover costs through much more effective tree ordinances for development and internal public works projects by requiring the use of technologies such as DeepRoot which research conducted over a 50 year period has quantified at a more than $28,000 cost benefit per tree.

It is time to take trees seriously!


Alex Johnson said...

I couldn't agree more, small trees don't equate with large ones in terms of benefits given or return on investment. In pursuing my street tree replacement I have often upset potential partners by refusing to plant their desired crepe myrtle when the space is appropriate for a large maturing tree. The tree selected for each site is the largest one deemed appropriate weighing all potential infrastructure conflicts. These include narrow planting strips and overhead utilities. I am aiming for a "zero loss" policy for tree planting (and have Public Works on board for partial funding), at minimum that would mean a 1 to 1 replacement for each tree removed within the city (by the city). If looked at as a "zero canopy loss" policy, it would be more like 15 to 1 rate of replacement. Not a goal I could realistically approach without some serious increases in scope and funding.

Unknown said...

Thanks for highlighting some of the work DeepRoot is trying to do! Trees are somewhat unique in being at the intersection of engineering, architecture, and community health. We need everyone's support and buy-in in order to really move the needle on tree health in our cities!