Nystrom's Nursery
Gardeners Page

hollow trees

By Neil Peterson

Last Updated Aug 14, 2010 11:26:22 AM

                When one performs landscape services, it is inevitable that questions about hollow trees will come up. This is about clarifying why it happens and what it means.

        First, one must understand a little of tree anatomy. The wood of a tree is divided into two categories: heartwood and sapwood. Heartwood is the inner tissue that we use for lumber. In cross-section, this tissue is usually about 1 to 2 inches in from the bark (of course, that’s a highly subjective to tree type and health). This wood is dead. Sapwood is the living tissue that makes up this and the last few seasons growth. Every year, the tree grows two sets of new “rings”-spring and summer. The rings to the interior become less and less productive and are eventually turned into heartwood.

Trees, which are a lot more complicated than generally given credit for, plan for this conversion. Some trees-like Oaks-will fill the cells with tannins and waxes to preserve the tissue. Trees also develop a series of walls between the living and dead tissue to keep healthy. Over time, as trees age, the heartwood can decay. This is the important part- it’s an entirely normal, healthy process.

The truth goes something like this-60 to 80% of mature trees-whether in a landscape or a forest, are hollow. Even more interesting is trees which are hollow, are more likely to fare better in thunder and ice storms. Imagine a skyscraper; they are nearly hollow. This allows an ability to flex in wind. Same principle applies to trees-a 100’ tree filled with multiple tons of dead wood is going to be too top heavy to deal with 60 mile-per-hour winds. Furthermore, hollow trees provide huge quantities of living space to bugs, birds, mammals, and microorganisms.

Trees have been going through this process…well, since forever. 900-year-old Beech trees in Britain certainly attest to the ability for hollow trees to live very long lives. One of the worst things a person can do to a beloved tree with a cavity-is try to fill it. These plants are highly adapted and capable. So remember, the next time hollow trees come up, it’s a positive.