Tree BiologyAshley PeeblesDelaware Forest Service

AngiospermsPhylum Magnoliophyta

• taxonomic class of plants in which the mature seed is surrounded by the ovule

• trees are often referred to as hardwoods• Angiosperms are trees have broad leaves

that usually change color and die every autumn

Examples: oaks, maples, dogwoods are examples of deciduous trees.

Some angiosperms that hold their leaves include rhododendron, live oak, and sweetbay magnolia

• taxonomic class of plants whose seeds are not enclosed in an ovule

• trees are often referred to as softwoods• Gymnosperms usually have needles that

stay green throughout the year

Examples: pines, cedars, spruces and firs

Some gymnosperms do drop their leaves - ginkgo, dawn redwood, and baldcypress, to name a few.

GymnospermsPhylum Pinophyta

• is a woody perennial plant - usually more than 10 feet tall

• has one main , well defined stem that is at least 3 inches in diameter

• a recognizable, formed crown

A TREE

drip line • absorb water and nutrients from the soil

• store sugar • anchor the tree upright in the

ground

tap root

lateral roots

surface roots

ROOTS

root hairs

TRUNK

• Comprised mostly of dead , woody tissue and supports the crown

• gives the tree its support and shape

• anchor the tree upright in the ground

• consists of four layers of tissue

HEARTWOOD• Comprised of dead xylem cells• Gives tree its support

SAPWOOD / XYLEM• Network of thick-walled cells

that transport water and nutrients from the roots to the rest of tree

CAMBIUM• Very thin layer of cells that is always dividing• Each growing season, the cambium produces new xylem/annual rings

PHLOEM / INNER BARK• A layer of living tissue found between the cambium and the outer bark• Acts as a food supply line by carrying sap produced by the leaves to

the rest of the tree

BARK• Formed of old phloem cells that have died and been shed outward• Acts as a coat of armor protecting the delicate inner bark and

cambium

VASCULAR SYSTEMA peek inside

sapwood/xylem(transports water from the roots to the leaves)

phloem/ inner bark(carries food from leaves to rest of tree)

heartwood(dead xylem, provides strength)

cambium layer(new cells)

Annual rings

outer bark(dead phloem, provides protection)

CROWN

• comprised of leaves born on twigs• contains the reproductive parts of the

tree• helps to cool the air around it by

shade• reduces the impact of rainfall on the

soil below

branches and twigs

flowers and seeds

LEAVES

• manufacture food through photosynthesis

• aid in gas (air) exchange – cellular respiration

• protect vegetative and floral buds

• water transport – transpiration • store food during germination

Trees are producers

Photosynthesis is a process unique to green plants in which sugars (tree food) are produced

Sugars produced are a chemical way to store energy for future use (metabolism)

Energy is stored in the bonds of the sugar molecules such as glucose and fructose

These sugars are later broken apart and the released energy drives a variety of metabolic actions

CO2 + H2O + ENERGY C6H12O6 + O2

Respiration

Trees both produce AND use oxygen

The process of breaking down sugars = respiration

C6H12O6 + O2 CO2 + H2O + ENERGY

PHOTOSYNTHESIS: CO2 + H20 >>>>> C6H12O6 + O2

Energy Allocation within trees

Energy is not a limitless resource for trees

A tree will typically move energy according to the priorities below. As energy in the form of glucose becomes limited, a tree will begin to reduce resources spent beginning with the lowest priority.

1. Maintain respiration of all parts

2. Produce fine roots and leaves

3. Produce flowers and seed

4. Extend branches and roots

5. Store energy rich chemicals

6. Add wood to stem, roots, and branches,

7. Create anti-pest chemicals for defense

Tree Growth

The most common material made by a tree is called cellulose, a complex sugar that is the main component of woods and many other plant tissue

Cellulose is an extremely useful material for human uses (food products, paper, strengthener in plastic and concrete, clothing and other things

A tree grows in three places 1. at the twig meristem

2. at the root meristem

3. around the outside of the truck, branches, roots (cambium)

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TREE GROWTH ZONES

Buds, elongation, height growthLeaf expansion

Cambium growthDiameter increase

Root hairsRoot growth

Tolerance of Shade

Difference species of trees have differing abilities to tolerate extended periods under a closed canopy

Trees that require high amounts of sunlight are sensitive to shade.

Species are generally divided into tolerant and intolerant (there is an intermediate category)

Shade tolerance is a key component of forest management systems

Intolerant Species

Intolerant species are generally the “first in” after an event such as a clear-cut or major fire that substantially opens the canopy

These trees are often called pioneer species and tend to:

be fast growing be short lived have light seeds

Examples:

Sweetgum, maples, tulip poplar, red cedar, loblolly

Tolerant Species

These trees normally are not the first to colonize open areas but instead grow up into an existing canopy.

These trees are usually found in a “climax community”

These trees tend to: Live a long time Grow slowly Have heavier seeds

Examples:

American beech, some oaks, hemlocks, spruces

Succession

The change in species composition that occurs in a stand over time. Can be natural or man-made

An area is colonized by intolerant, fast-growing species. Eventually, tolerant trees become established in the understory and start growing into the canopy

One of two things then happens….. The intolerants die naturally and are replaced by the

tolerants that have been present in the understory for some time OR

The tolerant trees finally overtop the intolerants and shade them out, causing them to die

Environmental Factors

Rainfall or precipitation As you move north and west, rainfall declines and so do number

of tree species

Soil variability This is largely related to the amount of available nutrients in the

soil, the nutrient demand of a species, and the tree’s ability to extract those nutrients

Moisture This is related to both rainfall and soils. The amount of available

moisture varies during the year.

Biotic factors These are the living parts of an ecosystem that trees interact

with.

Range and Distribution

Each species on our planet occupies a unique geological range where members of its various populations live, feed, and reproduce

Some species have extensive geographical ranges that stretch over several continents

Geographical ranges of organisms continually shift, expand, and contract with the passage of time.

Most species appear to be limited in at least part of their geographical range by abiotic factors.

All species have specific limits of tolerance to physical factors that directly effect their survival or reproductive success.

Species Habitat

The place where a population of a species normally lives and its surroundings, both living and nonliving.

Habitat is generally characterized by dominant plant form (e.g. broadleaf deciduous forest) and/or physical characteristics (e.g. fast-moving stream with rocky substrate)

RANGE AND DISTRIBUTION Nova Scotia to Florida and westward to Lake Superior, North Dakota, southward to western Texas. Common throughout Delaware

HABITATPrefers rich deep soils but will thrive on poorer soils. Is generally tap-rooted and seems to prefer sunlight