Which tree substance is often tapped for its commercial value?

The substance commonly tapped for its commercial value is pitch, which is derived from the resin of certain trees, particularly conifers like pine. When trees are tapped, the resin can be collected for various uses, ranging from the production of turpentine and rosin to being utilized in wood preservation and as an ingredient in various industrial products. The tapping process does not harm the tree significantly and allows for continued growth, making it a sustainable practice in forestry.

In contrast, while wood is a valuable resource harvested from trees, it is not tapped but rather cut down and processed. Bark can also be harvested, but it typically serves purposes like mulching or making certain products rather than being tapped and collected for its natural resins. Leaf extract can be valuable in other contexts, particularly for medicinal or nutritional uses, but it is not a substance typically tapped from trees in a commercial sense. Thus, pitch is recognized for its unique properties and economic importance, setting it apart from the other substances listed.