Why Keep Big Old (Healthy) Trees?

Most of our big trees are healthy survivors
New trees are unlikely to be as successful

In the winter of 2015/16 Sheffield City Council published several lists of trees to be felled in preparation for the 2016 highway renewal works

553 trees were condemned, for 521 of them Sheffield City Council published an indication of health*, of these 183 were listed as ‘diseased’, dead, dying or structurally dangerous. The other 338 were to be removed because they were causing damage or disruption to footways or making it difficult to renew the road surface in the preferred way. A very small number were causing ‘obstructions’ although these were not necessarily serious, for example some trees intruded a few inches into the roadway on quiet streets.

So by Sheffield City Council’s standards** 65% of these trees were healthy.

But if you look at the different kinds of trees the picture changes quite a lot. Street trees in Sheffield are either smaller decorative trees, like Cherries or Crabapples, planted in the past 50 years, or they are very big trees like Limes or London Planes. The bigger ones are usually over 100 years old, planted at the time the houses were built.

Dividing the condemned trees into these two groups by size reveals a big difference between the two.

84% of big condemned trees are healthy (207/247)
48% of small condemned trees are healthy (131/274)

So nearly all of the big Edwardian trees are in good shape. I asked an arboriculturist about this and his explanation was that these trees had a relatively easy start in life because the road surfaces of the day were more permeable – a photograph of Ladysmith Avenue back in those days shows paving stones (with gaps) on the footway and what looks like an unmade road surface. So the trees did not have to scavenge for water under the tarmac as they do today.

Also the trees we have today are the ones that had a good start and were able to resist any disease or pollution, the ones that were less resilient died off a long time ago. So our big trees today are the tough survivors from that planting, having had easy conditions to get them started, new young trees today might have a much lower chance of surviving.

It’s not surprising that a lot more of the small trees are unhealthy or dying, they have a shorter life so have to be replaced more often. There is no reason to replace any healthy tree just to fit in with a particular idea about how to maintain roads, but felling those big ones will be a very big loss indeed.

And of course the time taken for a new big tree to grow to a comparable size is measured in decades. Removing so many in one swoop ensures that the street environment is degraded for decades to come. A measured approach to sustaining our trees with a planned scheme for gradual replacement should take decades, not weeks. Renewing trees is not like buying a new fridge.

*35 condemned trees on Rivelin Valley Rd could not be included in this analysis as the data provided by Sheffield City Council does not allow their descriptions to be included in the map.

**In using Sheffield City Council’s data I am not endorsing the decisions in it about tree health. Even if they are not completely reliable those numbers probably give a good sense of the pattern of things.