APPLES AND OAKS

Did we intend to use the popular idiom “Apples and Oranges”?¹

No. Our intention is not to compare apples and oranges, which are very different indeed. But they are after all both fruit trees. And fruit trees, as we shall see, can be pruned mercilessly and bear fruit on new growth the following year.

The art and science of pruning apple trees has developed over millennia.² And as the science of pruning agricultural food crops has developed, the trees themselves have adapted to accommodate the pruning.

In the image below it is difficult to recognize the form as an apple tree. The plants have become smaller and smaller and more productive. Is it correct to call this form a tree?

The apple tree below is pruned back to the main branches each year, yet continues to bear fruit on new shoots each year.

These apple trees may be deformed, even ugly to some of us. But the purpose of an apple tree (or any other agricultural food crop) is to economically produce a crop.

What is the purpose of a street tree?

The purpose of a street tree, on the other hand, is historically to provide beauty, or as it is called in our sources, amenity. Increasingly street trees, and indeed the entire urban forest, are also called upon to provide a purely practical function: to protect our cities and the humans who live in them from an increasingly harsh urban climate. The urban forest does this admirably while at the same time providing amenity.

The International Society of Arboriculture (ISA), as far as we know, does not offer a special certification in the pruning of fruit trees. The fruit trees are left to the scientists, agronomists, and professional orchardists themselves, for the most part. As it should be.

Unfortunately the practice of pruning of fruit trees has crossed over into the practice of pruning our urban forest. Too many of our home owners, tree service personnel, and even some arborists prune our canopy trees as if they are fruit trees.

In some cases owners prune the entire canopy off their amenity trees; this is misguided. We’ve heard of arborists who recommend removing up to 60% of the canopy of shade trees annually; this too is misguided. Typically, pruning advice on the internet (some of it from the ISA) claims it is acceptable to remove 25-30% of a tree annually. Even this amount of pruning on a mature broadleaf tree is an unnecessary and damaging carry-over from the inherited practice of pruning fruit trees.

The former rule of thumb for pruning is now widely ignored: every cut³ is a wound which requires resources to compartmentalize, and which provides an opening for pathogens.

Tree People recommends the advice published elsewhere on this forum: on mature canopy trees, remove only The Four D’s.