Yes, trees are defined by having tall, thick, and woody stems called trunks. This is what distinguishes them from other plants like shrubs, which have multiple stems that are closer to the ground, or herbaceous plants, which have soft, non-woody stems.

Here's why trees have these characteristics:

* Tall: Trees need to reach sunlight, which is essential for photosynthesis. This is why they grow tall and often compete with other trees for space.

* Thick: The thick trunk provides structural support to hold up the heavy branches and leaves, and helps to transport water and nutrients throughout the tree.

* Woody: The woody stem is made of hard, rigid material called lignin, which provides strength and durability to the tree. This allows trees to live for many years and withstand harsh weather conditions.

So, yes, tall, thick, and woody stems are the defining features of trees.