First thing first

The first thing to know about trees is, what is a tree? Sounds like a simple question but go ahead, if you haven't thought about this before - what makes a tree a tree? This is one of the very first questions asked at Maine Trees, Top to Bottom.

Trees live for many, many years - decades and sometimes centuries. From its seedling start to its sapling stage and then as a young tree, it keeps reaching for sunshine at its top, stretching its roots through the soil at its bottom, and adding growth rings to its trunk. Shrubs also live for many years, but the above-ground parts of herbaceous plants (grasses, ferns, wildflowers) die back at the end of each season.

A tree has a single stem, unlike shrubs which have multiple stems at their bases. There are a few considerations to make here. For example, in a post-harvest forest you might find several stump-sprout trees coming out of one base, like the photo to the right. This happens after the original tree is cut down and a few dormant buds emerge and send up new main stems (trunks). Another scenario is where Gray Birch (Betula populifolia) or poplar/aspen may propagate vegetatively, that is, underground so you get a small grove of the same species. In both cases, think about the tree species and whether you'd usually, or ever, see it growing as a single-trunk tree. It is not uncommon to see a single Gray Birch or a lone Trembling Aspen (Populus tremuloides). Shrubs ALWAYS have multiple stems no matter where or when you see them - think of staghorn sumac, lilacs, or highbush blueberry.

A tree has a woody stem, unlike fibrous herbaceous plants. A woody stem persists year after year, adding more growth to the tips of the branches and roots, and more growth to the girth of its trunk. An example of a fibrous non-woody plant is blackberry whose dried canes persist through the winter, but new growth comes up every spring.

Size is another consideration when distinguishing trees from other plants. Mature trees are generally taller than 15 feet and have a diameter of more than 3 inches. Of course, tree seedlings and saplings won't meet these criteria but they will have single woody stems, and it's likely there are mature representatives in the same area. So that's it - a tree has a single woody stem and at maturity is taller than 15 feet with a diameter greater than 3 inches.