Why Are These 40 Year Old Trees Such Different Sizes?

This picture here is just one example of what we’re all about at DeepRoot.

(Apologies for the car right in the middle of the photo — I swear, we are not all about minivans).

This picture was taken in February 2010 in Milton Keynes, UK. Both trees, which we believe are chestnuts, were planted at the same time about 40 years ago. The tree on the left is a pretty sad specimen; it doesn’t look more than 5-7 years old. The tree on the right looks pretty good, however. Both have the same size tree opening and have had the same standard of care over the course of their lifetimes. They are situated in nearly identical spots on the same street. How can their dramatic size difference be explained?

There is one important detail in the placement of the trees that may not be immediately obvious. The tree on the left is directly next to a road on one side and to a parking area on the other, while the tree on the right in next to a pedestrian walkway and, we can see, within “reach” (root reach, that is) of some small lawns and open soil volumes in front on the adjacent apartments. Although those soil volumes are maybe 6 feet away from the root ball, they are close enough to have sustained this tree and allowed it to reach a decent trunk size and canopy diameter. The tree on the left is simply hanging on for dear life.

If you have any doubt that this is the explanation for the stark difference between these two trees, look at another photo from the same street.

Even adjusting for the fact that the biggest tree also appears in the foreground of the photo, it’s easy to see that all the trees planted closer to the road are visibly smaller than those trees that were planted closer to the walkway and adjacent lawns and gardens. In this instance, the roadway is essentially serving as a tunnel for the tree roots to access the “break-out” zone of the lawn containing the additional soil they require.

It is well understood that available soil volume is directly related to tree growth and health, and that the shade provided by trees is tremendously valuable both to the streets themselves and to the surrounding community. Milton Keynes was originally designed as a “forest city” and is home to the rather unusual tree cathedral. Still, trees like the ones shown here can be found throughout cities and towns all across the globe. While the urban enviornment is not a naturally hospitable place for tree growth, examples like this demonstrate that there are many simple design choices available to promote healthy, large tree growth without impeding street design or urban infrastructure.

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