When a tree grows every year, it produces new leaves and branches. Where do they come from? The new growth comes from buds which are made up of "embryonic" tissue. Embryonic tissue has the potential to become flowers, leaves, or stems, depending on the circumstances.

What is an "apical bud?"

The "apical bud" is the bud at the top of the main stem. You can remember "apical," because it's like "apex," which means top or tip. This bud produces chemicals that keep all the other buds (below it) from growing as much. This way, the apical bud can grow more than the others, and the tree continues to grow straight upward.

How do trees grow more than one stem? Why does krummholz happen?

When the apical bud is killed, the other buds compete for apical dominance-- they all want to be the main bud. Blowing ice crystals often kill apical buds, but apical buds can be killed in other ways-- like by a hungry porcupine. When this happens, there is no dominant bud, and several leading stems begin to grow. None of the stems is big enough to take over, so they all grow for awhile until one eventually does.

If this happens several times, the tree tends to grow more outward instead of upward, and becomes a "krummholz" growth form like the tree in the picture.


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