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Guide to Trees

Nature Guide Trees app

Nature Guide: Trees App

Search, discover, and learn all about trees! The easy-to-use guide, available on iOS devices, features 708 types of trees found in North America — with nearly 4,000 photographs, text descriptions to help identify tree species, and robust search functions to aid in species identification.



What Is a Tree?

Trees, similar to all living things grow, reproduce, and respond to their environment. Trees, like all plants, manufacture their food through photosynthesis. Trees are in the family of woody plants which have cambium, a special layer of cells that allow the tree to increase in girth and are self supporting with a single stem. Like some plants, trees are perennials and can live for many years.

The food for tree is produced through complex system starting with the leaves. Leaves produce sugar as a result of photosynthesis which combines carbon dioxide and sunlight. As a result of the process to create sugar the by-product that the trees produce is oxygen—a vital resource for other living organisms, including humans. That sugar that is produced runs down through the tree, under the bark down the trunk and to the roots of the tree. The sugar combines at the roots with minerals and water in the ground to move back up the tree trunk and under the bark back to the leaves to which starts the cycle of photosynthesis again. Along the way the minerals, water and sugar stimulate the growth and development of the tree or assist in its reproduction.

The roots gather minerals and water which are needed in the process of photosynthesis and for feeding the tree’s growth and development. The tree has one tap root and many lateral roots which help to keep it stable in wind and snow.

Parts of a Tree

The crown of the tree is made up of the leaves and branches.

The trunk of the tree supports the crown and serves as a highway for food made in the leaves to travel to the roots and for water and nutrients from the roots to travel to the leaves.

The heartwood of the tree develops as the tree gets older. It is old sapwood that no longer carries sap, and gives the trunk support and stiffness. In many kinds of trees, the heartwood is a darker color than the sapwood, since its water carrying tubes get clogged up.

The cambium is a layer or zone of cells, one cell thick, inside the inner bark. The cambium produces both the xylem and phloem cells. This is where diameter growth occurs, and where rings and inner bark are formed. In the xylem (sapwood) layer, tree sap (water plus nitrogen and mineral nutrients) is carried back up from the roots to the leaves. In the phloem (inner bark) layer, sugar that is made in the leaves or needles, is carried down to the branches, trunks, and roots, where it is converted into the food (starch) the tree needs for growth. The bark layer protects the tree from insects and disease, excessive heat and cold, and other injuries.

The roots of the tree support the trunk and crown, and also anchor the tree in the soil. They serve as a storage facility during the winter for the food produced by the leaves during the growing season. The roots also absorb water and nutrients from the soil for use by the tree.

Tree Types

Trees can divided into two categories: deciduous and coniferous.

Deciduous trees are also known as broadleaf trees because the leaves are generally larger and wider than those of conifers. The larger leaf size means a greater surface area for photosynthesis, but it also mean the leaf is too fragile to withstand winter conditions. Therefore, most deciduous trees drop their leaves in autumn.

Coniferous trees keep their leaves throughout the year, shedding only the oldest leaves. Usually these leaves are lower down on the tree and do not receive as much sunlight as newly developed leaves higher up. Some of the best-known members of the conifer family are pines, spruces, firs, and hemlocks. The cones of the conifers are its flowers.

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