FOREST BOTANY

BOTANY INTRODUCTION

Botany is the science of studying plants. also called plant science (s) or plant biology, is the science of plant life and a branch of biology.

A forest is composed of many plants, so a forest is a good place for a botanist.

BASIC TREE BOTANY

The basic components of a trees are: Roots Trunk Branches Twigs Buds Leaves/needles Cones/flowers seeds

ROOTS

The roots act as an anchor, holding the tree firmly in place. They grow and spread out underground from the root tips, forming a huge network that draws nutrients to the tree and protects the soil from erosion.

If you grind up a human body, bones and all, and make a chemical analysis of what the body is made of, you'll find that in terms of weight we're mostly water -- sixty to eighty percent of every human body is nothing but water. The same is true of plants. About seventy-five percent of a typical land plant is water.

The topic of roots is an important one, for roots are the means by which most land plants acquire their water. Roots grow through the soil, soak up what water they can, and transport that water to the plant's other parts.

ROOTS AREN'T STRAWS

Here's something interesting to think about: Have you ever noticed that when you dig into soil, unless there's been a recent rain, precious little water appears to be present? Obviously, plant roots, in order to find so much water in a place where there doesn't seem to be much of it, must be doing something special.

Water movement in plants : http://www.youtube.com/watch?v=tRNe_UHw7F4

When a typical plant sends down roots, it's not at all like digging a well down to the water table. Typical roots don't grow downward through the soil until they hit water so they can suck up the water as if the roots were straws. Roots work in a whole different way, a way based on the principle of osmotic pressure, a way that enables plants to acquire water from soil that may look and feel fairly dry.  

When a seed germinates it sends up a sprout, and it sends down its first root, a special root referred to as the radicle. Soon the radicle sprouts many, perhaps thousands, of very slender, thinner-than-a-hair root hairs, which give the radicle a fuzzy-white appearance.

ROOT HAIRS

The fuzzy stuff on the two much-magnified roots at the right are root hairs on a grass root. Each root hair in this picture is less than 0.04-inch long (1 mm). Root hairs also form at the tips of much larger roots as they grow through the soil.

When you pull up a plant and look at its long, beard-like cluster of blackish roots,  very little of what you're seeing actually absorbs water for the plant's use! The big roots you're seeing help anchor the plant in the ground, and they do transport water, but nearly all the plant's water is absorbed not by them, but by the root hairs.

In a classic study by H.J. Dittmer, a single rye plant -- a kind of grass -- growing about 50cm high and consisting of a clump of about 80 shoots, was found to have 600 km of roots, and this included 14 billion root hairs! If all these root hairs had been split open and spread flat on a floor, their combined surface area would have covered more than 370 square metres-- about the floor space occupied by two or three good-sized houses. All this root-hair surface-area was absorbing water for that single clump of grass... No wonder rye can grow in fairly dry soil!

TRUNK [STEM]

Definition of a plant stem: A stem is the part of a plant

from which shoots and buds arise. The "classical stem" is a tree trunk, which in a

no-nonsense manner simply rises from the ground and supports the tree's leafy branches

An important variation on this simple theme is that of having multiple stems -- two or more stems arising from the roots.

Clumps of grass and certain bushes use this strategy. Clumped stems tend to protect one another from cold wind and hot sun, plus, if one stem breaks, it's less loss to the plant because other stems are available.

On the other hand, if a plant invests its energy in many stems, then it's unable to grow as high as it could with only one stem, and therefore may receive less sunlight than its taller neighbors.

Another important stem variation is the climbing stem. In our vegetable gardens, climbing beans have such stems, as do grapevines and morning-glory vines. At the left you can see Poison Ivy vines climbing up a tree trunk.

Notice how the vine twists around the tree . Having a climbing stem is a kind of sneaky adaptation. Essentially it enables the climbing plant to reach toward the sun without having to invest its own energy in building stiff, strong trunks or stems capable of holding themselves erect.

The trunk is the main stem of the tree. It supports the crown of branches, leaves/needles and transports food and water throughout the tree.

The tough, outer bark protects the tree from heat, cold, moisture loss and injury.

The soft inner bark carries food from the leaves and needles to all living parts of the tree.

Beneath the inner bark is a thin layer called the cambium that each year develops new cells of inner bark on its outer wall and new sapwood cells on its inner wall. The sapwood carries water from the roots up to the leaves/needles.

As the tree grows, old inner layers of sapwood die and become heartwood, a rigid fiber that gives the tree its strength.

BRANCHES & TWIGS

Branches and twigs support the leaves, holding them up to receive the sun's light and warmth. They also produce buds that form new twigs, leaves and flowers.

TWIGS At the right you see a cross section of

a tree stem. In real life the stem was a little thicker than a pencil.

You already know that bark is what you see when you look at a living tree trunk or branch. It's composed of several kinds of tissue.

Much of it is tough cork which, among other things, protects the tree from physical damage.

Inside the bark, next to the cambium layer, is phloem tissue -- the part of the tree's plumbing system that transports the tree's photosynthesized food downward from the leaves or upward to growing buds or fruits.

The cambium layer is the only living part of the stem -- even though it's such a thin zone that in the picture probably it doesn't show up at all. We just know that it exists between the darker bark and the lighter wood. Cambium cells, which form a kind of cylinder inside the twig, divide and produce bark tissue on one side, and wood tissue on the other.

Wood is familiar to everyone, but the thing to know about it

here is that it is composed of dead cells (even in living trees) and that these cells, unlike the phloem, conduct water and dissolved salts upward from the roots. When we think in terms of the wood's cell structure and its job of conducting water and salts, we refer to the tissue as xylem.

The pith is a food-storage area in the center of the stem.

At the left you see the cross-section of a three-year-old stem of a Black Oak tree. You can see the three growth rings, also called annual rings. On this twig the inner part of each ring is pale, consisting of wood deposited in the spring when the tree was growing fast, and the outer part is darker, consisting of wood deposited later in the year when the tree was growing slower.

You can also see the pale pith in the stem's center. The pith of oak tree twigs is often star-shaped, which you can more or less see in this image.

Another feature of cross-sections of oak tree twigs and trunks is the light-colored streaks seen spreading outward from the pith. These streaks are vascular rays, which are important to the tree for food storage and the lateral, or sideways, conduction of food and water. Vascular rays occur in other trees, but they're seldom as conspicuous as among the oaks.

Below is a knothole in a rough sheet of plywood. See the knothole's growth rings? To understand what a knothole is you must visualize a tree trunk with a branch growing from it. The inside of the branch is solid wood attached to the solid wood inside the tree trunk. Therefore, as the tree trunk enlarges with age, its outside parts must grow around the branch's base, burying the base inside the trunk's growing wood. Well, that's what a knothole is -- it's a cross section of a branch or twig around which the tree trunk grew, burying it inside the trunk's wood.

In the below picture, in the area to the right of the knothole, notice the ray-like lines. These lines are also growth rings, except that the tree trunk, instead of being cut in cross-section so we can see concentric rings as in the knothole , has been cut length-wise.

BUDS

Every spring the tree grows taller as a new set of branches develops at its top, and wider as buds develop along the older branches, twigs and tips. Soft tissue inside the buds is protected from damage by a tough covering of moisture-saving bud scales.

LEAVES/NEEDLES

Leaves and needles are the food factories in the tree's crown. Food-making, or photosynthesis, begins when the sun's warmth

and light is trapped by green chlorophyll in the leaves. This energy is used to combine carbon dioxide from the

atmosphere with water drawn from the roots to create sugar and starch. The inner bark then carries this food to all living parts of the tree. In turn, oxygen and water are released into the atmosphere as by-products of photosynthesis.

CONES/FLOWERS/SEEDS

Trees produce flowers or cones that hold fertilized seeds. In late summer or fall, the seeds come loose and are scattered by wind, water and wildlife. Within each seed is the soft tissue that is the basis a new tree. Seeds have a tough coating that protects them during dispersal to their new home.