Tree Biology
Ashley Peebles
Delaware Forest Service
Angiosperms
Phylum 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
Gymnosperms
Phylum Pinophyta
• 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.
A TREE
• 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
ROOTS
drip line
• absorb water and nutrients from the
soil
• store sugar
• anchor the tree upright in the ground
surface roots
root hairs
lateral roots
tap root
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
VASCULAR SYSTEM
A peek inside
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
Annual rings
heartwood
(dead xylem, provides
strength)
sapwood/xylem
(transports water from
the roots to the leaves)
cambium layer
(new cells)
phloem/ inner bark
(carries food from leaves to
rest of tree)
outer bark
(dead phloem, provides
protection)
CROWN
branches and twigs
flowers and seeds
•
•
•
•
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
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)
CROWN
TRUNK
Buds, elongation,
height growth
Leaf expansion
Cambium growth
Diameter increase
ROOTS
TREE GROWTH ZONES
Root hairs
Root 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
HABITAT
Prefers rich deep soils but will
thrive on poorer soils. Is generally
tap-rooted and seems to prefer
sunlight