When it comes to value creation ‘climate’ trees (klimaatboom in Dutch) are playing on an olympic level. Financially houses are worth 8-15% more with adjacent green and trees according to brokers. Socially, people are happier in a green environment with trees. Old trees do even better: they evaporate more moisture and absorb more water (up to 500 times) than a young tree. So, how is it possible that trees often die young, whereas an old tree is much more valuable?
In cities, lack of expertise on how to lay out and dig for underground cables and pipes is a frequent reason for ermanent damage. Digging within 6 meters of a tree of 1 meter diameter or within 2 meters of a tree up to 30 cm diameter impacts the tree’s roots.Today, trees are sometimes placed on top of a cable and pipe or the cable is laid underneath. When the cable is replaced (once every 25 years) tree roots are severely damaged, and with fungal ingrowth, the tree dies a few years later. Ideally cables and pipes are at least 2 meters from trees if we want to get trees big and old. So, we can do better, can’t we?
In the past small trees were also planted on two sides in the sidewalk of narrow streets. With reduced fitness and less space for roots, growing old is a major achievement for a tree then! Today, often more space is reserved for trees, both above and underground, in order to have trees that age sustainably. A tree squeezed in between the pavement does not have a long life. 9 m3 of rootable space above the groundwater level is required for a small tree up to 6 meters in height. Want a large tree of more than 24 meters in height? You’ll need at least 65 m3 of rootable space. It’s no wonder that tree roots push up pavement when there is no space and moisture, while they are searching for nutrients.
So, keep the distance and give city trees the space they deserve, and let us humans enjoy the values created and the full range of ecosystem services to adapt to climate change.
This post is based on a memo by Frans Lubbers, maintenance specialist water and green @Zaanstad Municipality accompanied by an article by Bart Mullink in Boomzorg 3/2021.