Can bad be good?

Today I visited my favourite stub. Yes, A stub, not a pruning cut but a stub. I also got to try out my new rope wrench; its purple, so it doesn’t go as fast as the red ones and it’s not as cool as the black ones – the wrench worked well, the climber… not so well.

Anyway, my favourite stub sits about 12 meters up a grand old Atlas cedar. The stub is about 1.4 meters long and about 900mm in diameter; it is all that is left of a substantial limb that blew out of the tree about six or seven years ago.

When the tree crew came to clean up the mess I intervened and asked them to leave the stub. As good young arborists they were not too keen on leaving a stub; ‘stubs are bad, rot will set in and the tree will surely die.’ I didn’t see it that way and some convincing was required to retain the stub.

My problem was that I was asking good arborists to do bad tree work – bad tree work that would actually be good for the tree. The contradiction in my ask was more than apparent.

To be clear, I don’t believe in fracture-pruning, coronet-cuts or other dark-art voodoo pruning techniques. I’m not suggesting that leaving stubs is good practice, or should become the new norm’, I just think that every now and then, good arboricultural practice can be bad for trees. This was one such instance.

You can look at pruning cuts, old and new, and see the rate that response growth (callous tissue and woundwood) is being produced. My tree is about 150 years old, and she isn’t doing anything fast (if she were a climber, I’m sure she’d use a purple rope wrench).

A correct pruning cut creates a wound with the smallest surface area, located in a position where the tree can grow over and around the wound in the shortest possible time-frame; Natural Target Pruning (NTP). The surface area of a broken branch end will be many times greater than the surface area of a correct pruning cut. With a tree so old and slow, NTP would ensure the fastest wound closure – which is correct, but… my argument was not about the size of the wound, it was about the location of the wound. I successfully argued that a very large wound I.4 meters from the trunk were better than a large wound on the trunk. In this instance, I felt that NTP would create a structural weakness in the trunk and potentially compromised the tree.

If the tree was growing faster, things may have been different, but it wasn’t. Woundwood can actually be stronger than wood that is normally formed, a trunk that has an open wound with sufficient woundwood around it may be just as strong as a trunk with no wound at all.

Conifers also have antifungal and antibacterial properties (tannins in the bark and biocides in the heartwood), these properties can act as wood preservatives and conifers can often resist decay for considerable periods of time. Knowing that rot would set in at some stage, I felt that having it set in further away from the trunk would give the tree more time. In this instance, leaving the stub would delay the onset of decay into structurally important parts of the tree.

What I found harder to defend, was the look. The look of an ugly stub, sat there giving the finger to conventional pruning and accepted practice. What if the public saw it and thought stubs were good? There isn’t really a strong argument for that, except that the public doesn’t look up. I said that if anyone complained, I’d go up there and remove it – no one complained.

So, I visited my favourite stub today, and after six or seven years everything is looking good. Sometimes, every now and then, best practice may not actually be what is best, sometimes dong something different can be good.