Scope and extent of wood biology

Over the last two decades, major advances have been made in the field of wood biology. This chapter reviews these advances in the major thematic areas within the field. First, the diversity of wood structure of tropical trees is presented, starting with growth rings and climate-growth relationships, which are important for climate reconstructions. In addition, by describing the cellular wood structure of characteristic tree species from various tropical growth zones, multiple anatomical structures correlating with environmental conditions become obvious. The large diversity in wood structure could have developed over millions of years because no ice ages occurred in equatorial zones. Second, an overview is given of the three main functions of wood in the living tree. Of special interest is the long-distance transport of water, since very efficient transport systems with large vessels have evolved in the tropics (e.g., as in lianas). Besides water transport, mechanical stability also plays a key role in tropical trees, which often reach heights of 60 m and have to be stable against mechanical loads such as wind. As a consequence, buttresses providing mechanical support have been developed only in tropical tree species, and their characteristics and functions are described here. Finally, emphasis is given to the third physiological function of wood: the storage of reserve materials such as carbohydrates, fats, and proteins, and the current state of knowledge on this topic is summarized.