What is a TREE?
• Woody plant (stems, branches, roots)
• Long lived (typically 100’s of yrs.—
sometimes 10’s or 1000’s)
• Single main axis (stem, trunk, bole)
• Typically 20-30’ tall at maturity (note
variability)
• Annual height AND diameter growth
(woody plants have 3 meristems)
• Ability to compartmentalize problems
• Not everything called a tree meets
this definition
• How many species?
– Perhaps 8-10,000
– Depends on definition and
interpretation
But what about these?
Systems and Organs
• 3 systems:
– Dermal: skin
– Vascular: circulatory
system
– Fundamental:
structural (skeletal)
• 6 organs:
– Vegetative: leaves,
shoots, roots
– Reproductive: flowers,
fruits, seeds
Structure of Leaves
3 parts of a leaf: blade,
petiole, stipules
Blade
• Simple
• Compound/multiple
compound
Petiole
• Petiolate
• Sessile
Stipules
• Often absent
• Common in tropical plants
STRUCTURE OF A BROADLEAF LEAF
Dermal System: cuticle, epidermis, stomata, guard cells
Vascular System: xylem, phloem, bundle sheath
Structural System: mesophyll, pith (includes the various –enchyma cells)
Leaf stoma, guard cells,
stomatal bloom
Cross Section of Pine Needle
Leaf Variation
Sun/shade leaves in western
hemlock
Snowberry and canyon live oak
Structure of woody stems
Function
• Support
• Conduction
• Storage
Form
• Tapering columns of
annual sheaths
• Similar to stacking
cones—except for
connectivity between
rings and around branches
• Annual growth rings (on
trunk and branches)
Internal structure of a tree
Outer bark
Inner bark
Vascular cambium
Sapwood
Heartwood
(can’t see pith)
How Do Trees Work?
Wood (xylem)
• Sapwood (conductive)
– Young xylem
• Heartwood (non-conductive,
structural)
– Older xylem
Vascular Cambium
– Thin layer of cells
– Produces xylem (to the inside)
and phloem (to the outside)
Bark
– Inner bark (conductive)
• Includes phloem and cortex
– Outer bark (protective)
Cork cambium
– Produces cortex (to the inside)
and cork (to the outside)
Earlywood—Latewood
(Springwood—Summerwood)
Occurs within a single annual ring
Occurs because earlywood cells are
thin walled (light in color) and
latewood cells are thick walled
(darker in color)
Very distinct in some trees, not in
others
Wood properties are affected by
rate of diameter growth
• Slow growth results in tight rings
and high wood quality
• Fast growth results in wider rings
and sometimes problems
Not all cross sections look the same
Burls and Lignotubers
Bark:
complex structure with many layers
cork oak
Quercus suber
Variations in Bark
Special properties of bark
• Inert (non-reactive)
• Insulating
• Non-porous to liquids
and gasses
• Example: corkbark oak
from Spain and
Portugal
Roots
Many depictions of roots—mostly
wrong
Function
• Anchorage
• Absorption
• Storage (food and extractives)
Primary roots
• Trace origin to radicle
• Taproots (many misconceptions)
Adventitious roots
• Arise from phloem parenchyma
(unpredictable pattern)
• Help trees adapt to changing
conditions (e.g. redwoods)
Root Structure
Typical root tip
Mycorrhizal infected root tip
Some special adaptations of roots
Prop roots: adventitious
roots that help support
the plant
Pneumataphores: aerial
roots that help plants
breath in poorly
aerated soils
Some special adaptations of roots
Buttressed roots: help
stabilize the tree
Aerial roots:
Some special adaptations of roots
Nodulated roots: fix
atmospheric nitrogen
and convert it to a form
plants can use.
Mycorrhizal roots:
fungus-root association.
Tree feeds fungus but
benefits by increased
uptake of water and
nutrients.
Some special adaptations of roots
Strangler figs: germinate in tree top
and send roots down to ground—
may kill host
Special Adaptations of Roots
Root Trivia
• Spread laterally well beyond crown width
• Most roots lie within 12-18” of soil surface, even when soils
are deep
– This is why compaction is such a problem
• Western soils are shallow, so roots are shallow
• Plants in dry climates have/need more roots than plants in
moist climates
• Root systems require large inputs of energy to maintain
themselves—and are importnat in nutrient cycling
– Fine roots don’t live long (weeks to months)
• Root grafts allow trees to share resources, but also
diseases (argues against same species urban plantings)
• In PNW, fall is prime root growing time (before winter
cold and summer drought)
• Living roots are white; dead roots are brown
• Mature oak trees may have 500 million living root tips
Vegetative Growth
Growth occurs in cycles—
seasonal, annual, over life
span
Growth is centered in
meristems—lateral and
apical.
Growth occurs in spurts—
it’s not continuous even
within a season.
Shoot Elongation
Results in taller trees and longer
branches (wider crowns)
Originates from buds
• Terminal
• Lateral
• Adventitious
– Develop in unpredictable pattern
Buds result in:
• Vegetative growth
• Reproductive growth
• Mixed
States of activity:
• Active
• Dormant
– common at root collar
– Activated when environment changes
Adventitious and Dormant Buds
Leaf Growth
Individual leaves
• Broadleaves may take 2-40
days to develop
• Conifer leaves take longer
– Some add weight
throughout their lives
Whole plants
• Some develop all leaves
early in season
• Some add leaves
throughout season
Deciduous leaves
• Last one growing season
(ended by cold or drought)
• Sometimes multiple
growing seasons w/in
single year
• Leaf fall is programmed—
nutrients are reculceld
• Abscission layer forms
Evergreen leaves
• Don’t last forever
• Highly variable by species
Shoot growth
Characterized by:
Characterized by:
Location
• terminal, lateral, basal, water
shoots
Determinate:
• Occurs from true terminal buds
• Typically only 1 flush/yr., but some
are recurrent
• Most pines, spruces, oaks,
hickories
Type of bud
• Coppice (from root collar)
• Epicormic (from advnetitious
buds on stem
Indeterminate
• No terminal bud is set—winter die
back occurs to hardened bud
• Birches, sycamores, locusts,
basswood, hawthrons
Shoot Growth
Fixed vs. Free Growth
Abnormal Shoot Growth
Fixed:
• Predetermined growth based on
previous growing season
• Examples: Dougals-fir,
hemlocks, spruces, firs
Free growth
• No predetrmination
• Growth continues based on
growing season
• Examples: poplars, apples,
larches, tropical pines
Recurrent flushing
• Multiple flushes w/in 1 season
• Common in sub-tropical and
tropical species
• Difficult to count rings, affects
wood quality, may result in
winter damage if planted too far
north
Abnormal late season flushes
• Lammas growth if terminal
• Prolecptic growth if lateral
• Often results in winter damage
Shoot Growth w/in a single tree
Apical dominance
• Pattern is determined
within a single growing
season
• Pattern is controlled by
auxin, a growth hormone
Strong dominance:
• terminal shoot elongates
more than laterals
• Examples: Douglas-fir, true
firs, spruces
Weak dominance:
• laterals may elongate as
much as or more than
terminals
• Examples: western
hemlock, knobcone pine,
many broadleaved trees.
Maximum height
All trees have a maximum
height (more or less)
• Regardless of light, water,
and nutrients they receive
• Determined by genetics
• Not much influence by
growth rate or longevity
• Some trees that grow
rapidly are short lived
• Some that grow very
slowly are very long-lived
• Some do both