Trees are pleasant to have around us. They offer protection from harsh sunlight and shelter from the rain. They provide homes for whole ecosystems and nesting places for birds. But there’s no escaping that they can be a nuisance. Roots spread and cause disruption to roads, pavements, and buildings. Branches have to be chopped if they pose a risk to falling onto vehicles or people. All this comes at a cost. But what is the true value of a tree?
I am currently in Sheffield. This is a city which houses 2 million trees and boasts of being the greenest city in Europe. But in the last 5 years over five thousand trees have been felled, and thousands more are scheduled to be chopped down. The Woodland Trust have dubbed this the Tree Massacre.
Trees and land plants provide around half the oxygen in our atmosphere (along with phytoplankton and other ocean organisms) and also absorb much of the carbon dioxide. Trees allow us to save energy in cities by diverting winds and providing shade. Trees act as great natural sound insulators. How can we place a value on a tree? Should we just take the value of the wood as a material?
The Millenium Ecosystem Assessment of 2005 (MEA) explored the benefits and future impacts of everything from trees to rock to rivers. In its wake, some studies found that rich countries owed more than $1.8 trillion for the damage they have caused from felling trees.
You may say that trying to value, in monetary terms, machines that benefit the ecosystem so much is futile. However, financial incentives can work. Costa Rica’s forest was declining to make way for more profitable crops. However, in 1997 a scheme was introduced that rewarded farmers to preserve forests. In the years that followed, forests grew by 2%.
Many people have tried to create formulae to calculate the value of a tree. Some, such as Rodney Helliwell’s method, focus mainly on aesthetic values. Others, such as Capital Asset Value for Amenity Trees (CAVAT), focus on the amenity of trees. There are many apps and online calculators that focus on different aspects of a tree’s benefits.
House values, too, can be impacted by trees. Trees can increase property prices by up to 18% and can help save energy by shading building in the summer and diverting cold winds in the winter.
David Nowak, an American ecologist, developed an algorithm to value trees based on both tree metrics, such as trunk size and canopy size, and local metrics, such as sunlight and local weather. Its valuation is based on environmental services (a term popularised by the MEA) and considers variables from shade to pollutant absorption to cancer prevention. Nowak has recently found that trees in the US save people $18.3 billion every year. The next step, he says, is to use the valuations to help us plan the urban forests of the future.