Perhaps it is because they appear to be so still and silent that we take the tree for granted, but as we learn in Dorling Kindersley's Eyewitness Video: Trees, they are anything but still they are alive with constant motion. Although thankfully they still cover half of the planet's land mass, trees used to cover four fifths. Trees are a constant oxygen factory. The very thing we need to survive is merely a byproduct of trees as they take in the carbon dioxide we produce and convert it to oxygen which we inhale. This fascinating video defines what makes a tree a tree (a single stem, the ability to make wood and, usually, height) and differentiates them from other plant life. If trees could speak our language they would have incredible stories to tell, the oldest living thing on Earth today is a tree, but they can speak silently in death as their rings reveal periods of growth and harsher times. At any given time a single tree is crawling with life, often acting like a hotel for animals, birds and insects. Plenty of unwanted guests can harm trees such as woodpeckers, termites and the mistletoe plant. Many questions are answered in this thirty minute video: what causes leaves to change color; do trees hibernate; what is the biggest tree and what is the smallest; what is tree farming; and, sadly, what are the effects of deforestation. Ancient mythology often centers around a 'tree of life' and in the Garden of Eden, a tree is where man sought knowledge. As we learn over the running time of this video, not only do we use trees as a natural resource for lumber for homes and ships, they provide us with some of the ingredients for art and culture: paper, pencils (and erasers), and musical instruments. Trees also provide medicine, the treatment for world's greatest killer, malaria, comes from the bark of a tree. This insightful addition to the Eyewitness series will give viewers a whole new respect for trees, not only for the resources they provide, but for their greatest gift we take for granted: beauty. We need to be responsible in how we use trees, because if we callously threaten their very existence, they will eventually threaten our own.