What is a Tree?

A tree is a perennial plant with woody supportive tissue and a single main stem or trunk. The above ground part of a tree (trunk, branches and leaves) captures light and transports sugars from leaves to fruits and roots. The below ground portion of a tree (roots) takes up water and nutrients and transports them to the leaves and fruit. All plants must acquire resources (nutrients, water, and light) to survive and reproduce.

A few simple principles govern the processes of tree resource capture and reproduction, and give rise to the wide variety of trees that we see on a daily basis. In this section, we will explore the factors governing how trees optimize light capture and fruit production. Root function and water and nutrient acquisition will be covered in the Rootstock section of the website.

Plant species with “tree” growth forms have evolved in many different groups of plants. Some of the more distinct tree species on earth grow in California, including:

• the world’s tallest tree, the coastal redwood (Sequoia sepervirens, Fig 1a)
• the world’s oldest tree, the bristle cone pine (Pinus longaeva, Fig 1b)
• many flowering trees, including the western redbud (Cercis occidentalis, Fig 1c).

The dramatic differences among the species shown in Figure 1, and among the tree fruit and nut crop species grown in California, provide excellent examples of how plants have evolved different ways of capturing resources and reproducing in different environments (from the coast of California to the arid Eastern Sierra). An understanding of the components of a tree that are needed to acquire resources and reproduce will enable a grower to make informed decisions to modify tree fruit and nut growth form and environment with the goal of optimizing crop production.