Chapter 1 Tree Biology
Wednesday, February 21, 2024 3:37 PM
Introduction
• Tree: woody perennial plant with single or multiple trunks
• Must learn how trees grow to manage them
• Anatomy/morphology - structure/form of a tree
• Physiology – biological, physical, chemical processes within the structure
Tree Anatomy
Basic structure: cells and tissues
• Meristems: tissue where the division of cells occurs, these cells undergo differentiation where
they develop into other tissues/organs that perform different functions – leaves, stems, roots,
flowers, cone, fruit
• Tree growth occurs in two ways
o Primary growth: from the root and shoot tips (height/length) - the apical
meristems
o Secondary growth: in the thickness of stems, branches, roots – the lateral
meristems
• Apical meristems are found inside buds
o Buds have overlapping scales/leaves that protect it and the developing shoot
(some species/tropical trees have naked buds however)
o It's protected by a root cap in the root tips
• Lateral meristems (2 kinds)
o Vascular cambium layer – thin sheath of dividing cells under the bark becoming
the vascular system of the tree and produces 2 kinds of tissues on each side of it
▪ Xylem: on the inside
▪ Phloem: on the outside
o Cork cambium layer – produces outer tissues (periderm), ultimately the bark
(palms lack secondary growth/bark)
• Cellulose – main substance of cell wall
• Lignin – more rigid substance in the cell walls (matrix of long chains of cellulose) that provides
strength for trees to grow tall
Xylem and Phloem
• Xylem - sapwood
• Secondary xylem: xylem produced during secondary growth aka wood with 4 primary
functions
o Conducts water and minerals (collectively sap)
o Mechanical support
o Storage of carbohydrates
o Defence against spread of dysfunction, disease, decay
• Comprised of both dead and living cells
• Cell walls of dead cells comprised of cellulose, lignin and hemicellulose – together they provide
strength that characterizes wood
• Gymnosperms (pines, spruces, etc.) composed of tracheids (conduct water) and parenchyma
cells (store carbs, defend decay – more abundant in angiosperms)
• Xylem vessels are the primary conducting elements in angiosperms – stacks of dead, open-
ended, hollow cells (like straws) and more efficient than tracheids
• The size and distribution of cell types in the xylem determine a lot of the physical and
biological properties of different trees
Ring porous – trees that form wide vessels early in growing season and narrower
ISA Study Guide Notes Page 1
, o Ring porous – trees that form wide vessels early in growing season and narrower
ones later (elm, oak, ash, etc.)
o Diffuse porous – trees that form vessels of uniform size throughout the season
(maple, planetree, linden, etc.)
• Growth rings of a cut tree show the seasonal xylem production, cells smaller as season
progresses
o Earlywood – cells produced early in the season
o Latewood – cells produced later in the season
o Contrast shows the diameter increase in a year
• Exceptions: conifers don't have vessels and palms constantly grow
• Sapwood – xylem that conducts water, and as they age the deeper layers turn into heartwood
• Heartwood – nonconducting, no living cells/biological function, contributes to mechanical
support of tree, resists microorganism invasion, stores carbon (no longer a physiological role
for the tree)
• Pith - central core of tree
• Phloem - inner bark
• Moves photosynthates such as carbohydrates (sugars) produced in the leaves throughout the
tree for storage or consumption
• Phloem transport requires energy while xylem does not (passive)
• Downward movement
• Rays – parenchyma cells that grow radially, extend across the xylem and phloem, transporting
carbs in and out of the sapwood, storing carbs, and restricting wood decay
• Bark – protective layer of the tree, covers branches, stems, sometimes roots, moderates
temperature, defends against injury, reduces water loss
o Lenticels – small openings in the bark, permitting gas exchange of oxygen and
carbon dioxide
Stems
• Apical/terminal buds – buds at the end of a shoot (most active typically)
• Axillary buds – buds along the stem (often dormant, the apical dominance of the terminal bud
prohibits growth sometimes) - they become more active when the shoot lengthens and ages
leading to new shoot development
• Adventitious buds – along the tree (ex: roots) where meristem tissue does not exist, could be
stimulated by loss of apical buds
o Some species (ex: trembling aspen) grow from these buds on the roots – many
trees with a common root system
• Latent buds – dormant under bark until growth is triggered by light or injury
o Epicormic shoots – the growth that occurs from latent buds
• Node – enlarged portion of the twig where leaves and buds develop
o Internode – part of stem between nodes, shows leaf scars and terminal bud scale
scars (scars from when they fall off) - used to measure twig growth
• Lenticels – pores for gas exchange along stem
• Branches – produce and store carbohydrates (sustain themselves, but long distance transport
from trunk/roots occurs too)
o Branch collar – the "shoulder"/swollen area of tissue between the branch and
trunk at the base – this branch union allows for the growth of specialized wood –
dense
o Branch bark ridge – raised area of bark where the branch attaches to the trunk
o Included bark – a defect that develops when the branch and trunk (or two
branches) grow closely together and the bark embeds itself weakening the
junction
Leaves
ISA Study Guide Notes Page 2
,Leaves
• produce food for the tree
o Chlorophyll – green leaf pigment that absorbs sunlight in the chloroplasts (cells)
o Photosynthesis – converts this energy into carbohydrates
o Transpiration – loss of water vapour through leaves (leaf cools)
o Cuticle – protective waxy outer surface of the leaf
o Stomata – small pores on underside of leaf that control loss of water and
exchange of gases
o Guard cells – regulate the opening and closing of the stomata for water/carbon
dioxide movement (respond to light, temperature, humidity)
o Veins – contain phloem and xylem tissues, transport water, elements, and
carbohydrates
o Deciduous – trees that shed their leaves periodically/yearly - due to environmental
changes
o Abscission zone – cell layer formed at the base of the petiole that allows for leaf
drop and then protects the area
o Evergreen – trees that hold their leaves for more than one year
o Fall colours – weather enhances sugars (stored for spring) and triggers breakdown
of chlorophyll allowing other pigments to show – these colours protect from
ultraviolet radiation
▪ Anthocyanins (reds/purples)
▪ Carotenoids (yellows/oranges/reds)
Roots
• Serve 4 primary functions – anchorage, storage, absorption, conduction
o Absorbing roots – small, fibrous tissues at ends of woody roots, hairs that aid in
uptake of water and minerals (like shoot tips they have meristematic zone at the
tip for growth), upper 30cm/12 in of soil
o Lateral roots – near soil surface
o Sinker roots – grow vertically down off lateral roots to anchor and access deeper
water
o Taproot – large, central dominant root in young trees, gets outgrown by other
roots or stopped due to compaction in mature trees
o Root crown/trunk flare – area where roots join the main stem
o Extent and direction of root growth dependent on the soil environment
o Mycorrhizae – the symbiotic relationship between roots and fungi, tree and fungi
benefit one another in nourishment, water/mineral absorption
Tree Physiology
Photosynthesis
• Process by which plants use light energy to build carbon molecules that make carbohydrates
• Takes place in cells that contain chloroplasts
• Chloroplasts contain molecules of chlorophyll - the light-absorbing pigment giving plants green
colour
• Two components involved: carbon dioxide and oxygen
○ Carbon dioxide absorbed from atmosphere through stomata
○ Light energy contained in the chloroplasts are converted to chemical energy
(carbohydrates) and used for growth or stored as starch for later use
○ Oxygen is a by-product released through the stomata
• Photosynthates
○ sugar products resulting from photosynthesis that combined with other elements
produce important compounds
○ Stored as starch for later use if not needed immediately
Respiration
ISA Study Guide Notes Page 3
, Respiration
• Process where carbohydrates are converted into energy
• Independent of light, continues at night
• Important that photosynthesis (energy production) exceeds respiration (energy use)
• It's why it is important that trees must have stored carbohydrates
• Ex: tree defoliated by pests, no foliage, photosynthesis stops/reduced, can used stored starch
to survive
Transpiration
• Loss of water from leaf surfaces in the form of water vapour
• Cools leaves, helps moves water up through the xylem
• Waxy surface of leaves helps prevent uncontrolled water loss
• Gas exchange in stomata - water vapour and oxygen released, carbon dioxide absorbed
○ Each stomatal pore has two guard cells that regulate opening and is influenced by light
(open when light), temperature, cell turgor (the pressure of water inside guard cells),
humidity
○ Transpiration also affected by cuticle thickness, hairs on leaf surface, and
number/location of stomata (ex: thick cuticle, small/hairy leaves - adapted to hot/dry
conditions)
Absorption, Translocation and the Vascular System
• Water is essential to all living cells - used in photosynthesis, maintains cell firmness/fullness,
transports essential elements, roots absorb it and it is used for growth/metabolism, but most
lost through transpiration
• Xylem - series of continuous, tiny conduits for water from roots to tips of shoots, where
evaporation of water from leaves pulls water up through the trees from the roots
• Osmosis - process of water entering young/mycorrhizal roots from region of high water
potential to regional of low water potential
○ Pure water has highest potential (minerals/sugars lowers it)
○ Water moves into roots where the water potential is lower than the soil - but water will
move from roots to soil if opposite (ex: salt concentrations high in soil)
• Food products/carbohydrates/photosynthates are moved through the phloem (requires
energy)
○ "source and sink" - source being the leaves (high carbohydrate concentration) and
moved to the sinks being parts that use more energy than they produce (ex: young
leaves)
○ Does not move all to roots as most think - either utilized or stored in proximity to where
it was produced
• Longitudinal/axial transport: movement of water in the xylem, and photosynthates in the
phloem
• Radial transport: movement of water/nutrients within the tree between cells of different
ages - primarily through ray cells (move things laterally)
Control of Growth and Development
• A tree grows based on its genetic potential and its environmental conditions
○ Ex: a species can have a huge growth potential but is limited by the urban environment
• Light, temperature, gravity are all important to survival
○ Ex: long period of cold exposure may be necessary for budbreak, flowering, seed
germination
• Plant growth regulators/hormones
○ Chemical messengers that control part of the coordination of these processes
○ Processes include cell division, cell elongation, flowering, fruit ripening, leaf drop,
dormancy, root development
○ Major hormone groups include auxins, gibberelins, cytokinins, ethylene, abscisic acid
o Auxins: regulates every aspect of plant growth and development, primarily is in
shoot tips but also important to root development (ex: shoots tips get cut, root
growth inhibited and lateral shoots triggered - do not heavy crown prune to
ISA Study Guide Notes Page 4
Wednesday, February 21, 2024 3:37 PM
Introduction
• Tree: woody perennial plant with single or multiple trunks
• Must learn how trees grow to manage them
• Anatomy/morphology - structure/form of a tree
• Physiology – biological, physical, chemical processes within the structure
Tree Anatomy
Basic structure: cells and tissues
• Meristems: tissue where the division of cells occurs, these cells undergo differentiation where
they develop into other tissues/organs that perform different functions – leaves, stems, roots,
flowers, cone, fruit
• Tree growth occurs in two ways
o Primary growth: from the root and shoot tips (height/length) - the apical
meristems
o Secondary growth: in the thickness of stems, branches, roots – the lateral
meristems
• Apical meristems are found inside buds
o Buds have overlapping scales/leaves that protect it and the developing shoot
(some species/tropical trees have naked buds however)
o It's protected by a root cap in the root tips
• Lateral meristems (2 kinds)
o Vascular cambium layer – thin sheath of dividing cells under the bark becoming
the vascular system of the tree and produces 2 kinds of tissues on each side of it
▪ Xylem: on the inside
▪ Phloem: on the outside
o Cork cambium layer – produces outer tissues (periderm), ultimately the bark
(palms lack secondary growth/bark)
• Cellulose – main substance of cell wall
• Lignin – more rigid substance in the cell walls (matrix of long chains of cellulose) that provides
strength for trees to grow tall
Xylem and Phloem
• Xylem - sapwood
• Secondary xylem: xylem produced during secondary growth aka wood with 4 primary
functions
o Conducts water and minerals (collectively sap)
o Mechanical support
o Storage of carbohydrates
o Defence against spread of dysfunction, disease, decay
• Comprised of both dead and living cells
• Cell walls of dead cells comprised of cellulose, lignin and hemicellulose – together they provide
strength that characterizes wood
• Gymnosperms (pines, spruces, etc.) composed of tracheids (conduct water) and parenchyma
cells (store carbs, defend decay – more abundant in angiosperms)
• Xylem vessels are the primary conducting elements in angiosperms – stacks of dead, open-
ended, hollow cells (like straws) and more efficient than tracheids
• The size and distribution of cell types in the xylem determine a lot of the physical and
biological properties of different trees
Ring porous – trees that form wide vessels early in growing season and narrower
ISA Study Guide Notes Page 1
, o Ring porous – trees that form wide vessels early in growing season and narrower
ones later (elm, oak, ash, etc.)
o Diffuse porous – trees that form vessels of uniform size throughout the season
(maple, planetree, linden, etc.)
• Growth rings of a cut tree show the seasonal xylem production, cells smaller as season
progresses
o Earlywood – cells produced early in the season
o Latewood – cells produced later in the season
o Contrast shows the diameter increase in a year
• Exceptions: conifers don't have vessels and palms constantly grow
• Sapwood – xylem that conducts water, and as they age the deeper layers turn into heartwood
• Heartwood – nonconducting, no living cells/biological function, contributes to mechanical
support of tree, resists microorganism invasion, stores carbon (no longer a physiological role
for the tree)
• Pith - central core of tree
• Phloem - inner bark
• Moves photosynthates such as carbohydrates (sugars) produced in the leaves throughout the
tree for storage or consumption
• Phloem transport requires energy while xylem does not (passive)
• Downward movement
• Rays – parenchyma cells that grow radially, extend across the xylem and phloem, transporting
carbs in and out of the sapwood, storing carbs, and restricting wood decay
• Bark – protective layer of the tree, covers branches, stems, sometimes roots, moderates
temperature, defends against injury, reduces water loss
o Lenticels – small openings in the bark, permitting gas exchange of oxygen and
carbon dioxide
Stems
• Apical/terminal buds – buds at the end of a shoot (most active typically)
• Axillary buds – buds along the stem (often dormant, the apical dominance of the terminal bud
prohibits growth sometimes) - they become more active when the shoot lengthens and ages
leading to new shoot development
• Adventitious buds – along the tree (ex: roots) where meristem tissue does not exist, could be
stimulated by loss of apical buds
o Some species (ex: trembling aspen) grow from these buds on the roots – many
trees with a common root system
• Latent buds – dormant under bark until growth is triggered by light or injury
o Epicormic shoots – the growth that occurs from latent buds
• Node – enlarged portion of the twig where leaves and buds develop
o Internode – part of stem between nodes, shows leaf scars and terminal bud scale
scars (scars from when they fall off) - used to measure twig growth
• Lenticels – pores for gas exchange along stem
• Branches – produce and store carbohydrates (sustain themselves, but long distance transport
from trunk/roots occurs too)
o Branch collar – the "shoulder"/swollen area of tissue between the branch and
trunk at the base – this branch union allows for the growth of specialized wood –
dense
o Branch bark ridge – raised area of bark where the branch attaches to the trunk
o Included bark – a defect that develops when the branch and trunk (or two
branches) grow closely together and the bark embeds itself weakening the
junction
Leaves
ISA Study Guide Notes Page 2
,Leaves
• produce food for the tree
o Chlorophyll – green leaf pigment that absorbs sunlight in the chloroplasts (cells)
o Photosynthesis – converts this energy into carbohydrates
o Transpiration – loss of water vapour through leaves (leaf cools)
o Cuticle – protective waxy outer surface of the leaf
o Stomata – small pores on underside of leaf that control loss of water and
exchange of gases
o Guard cells – regulate the opening and closing of the stomata for water/carbon
dioxide movement (respond to light, temperature, humidity)
o Veins – contain phloem and xylem tissues, transport water, elements, and
carbohydrates
o Deciduous – trees that shed their leaves periodically/yearly - due to environmental
changes
o Abscission zone – cell layer formed at the base of the petiole that allows for leaf
drop and then protects the area
o Evergreen – trees that hold their leaves for more than one year
o Fall colours – weather enhances sugars (stored for spring) and triggers breakdown
of chlorophyll allowing other pigments to show – these colours protect from
ultraviolet radiation
▪ Anthocyanins (reds/purples)
▪ Carotenoids (yellows/oranges/reds)
Roots
• Serve 4 primary functions – anchorage, storage, absorption, conduction
o Absorbing roots – small, fibrous tissues at ends of woody roots, hairs that aid in
uptake of water and minerals (like shoot tips they have meristematic zone at the
tip for growth), upper 30cm/12 in of soil
o Lateral roots – near soil surface
o Sinker roots – grow vertically down off lateral roots to anchor and access deeper
water
o Taproot – large, central dominant root in young trees, gets outgrown by other
roots or stopped due to compaction in mature trees
o Root crown/trunk flare – area where roots join the main stem
o Extent and direction of root growth dependent on the soil environment
o Mycorrhizae – the symbiotic relationship between roots and fungi, tree and fungi
benefit one another in nourishment, water/mineral absorption
Tree Physiology
Photosynthesis
• Process by which plants use light energy to build carbon molecules that make carbohydrates
• Takes place in cells that contain chloroplasts
• Chloroplasts contain molecules of chlorophyll - the light-absorbing pigment giving plants green
colour
• Two components involved: carbon dioxide and oxygen
○ Carbon dioxide absorbed from atmosphere through stomata
○ Light energy contained in the chloroplasts are converted to chemical energy
(carbohydrates) and used for growth or stored as starch for later use
○ Oxygen is a by-product released through the stomata
• Photosynthates
○ sugar products resulting from photosynthesis that combined with other elements
produce important compounds
○ Stored as starch for later use if not needed immediately
Respiration
ISA Study Guide Notes Page 3
, Respiration
• Process where carbohydrates are converted into energy
• Independent of light, continues at night
• Important that photosynthesis (energy production) exceeds respiration (energy use)
• It's why it is important that trees must have stored carbohydrates
• Ex: tree defoliated by pests, no foliage, photosynthesis stops/reduced, can used stored starch
to survive
Transpiration
• Loss of water from leaf surfaces in the form of water vapour
• Cools leaves, helps moves water up through the xylem
• Waxy surface of leaves helps prevent uncontrolled water loss
• Gas exchange in stomata - water vapour and oxygen released, carbon dioxide absorbed
○ Each stomatal pore has two guard cells that regulate opening and is influenced by light
(open when light), temperature, cell turgor (the pressure of water inside guard cells),
humidity
○ Transpiration also affected by cuticle thickness, hairs on leaf surface, and
number/location of stomata (ex: thick cuticle, small/hairy leaves - adapted to hot/dry
conditions)
Absorption, Translocation and the Vascular System
• Water is essential to all living cells - used in photosynthesis, maintains cell firmness/fullness,
transports essential elements, roots absorb it and it is used for growth/metabolism, but most
lost through transpiration
• Xylem - series of continuous, tiny conduits for water from roots to tips of shoots, where
evaporation of water from leaves pulls water up through the trees from the roots
• Osmosis - process of water entering young/mycorrhizal roots from region of high water
potential to regional of low water potential
○ Pure water has highest potential (minerals/sugars lowers it)
○ Water moves into roots where the water potential is lower than the soil - but water will
move from roots to soil if opposite (ex: salt concentrations high in soil)
• Food products/carbohydrates/photosynthates are moved through the phloem (requires
energy)
○ "source and sink" - source being the leaves (high carbohydrate concentration) and
moved to the sinks being parts that use more energy than they produce (ex: young
leaves)
○ Does not move all to roots as most think - either utilized or stored in proximity to where
it was produced
• Longitudinal/axial transport: movement of water in the xylem, and photosynthates in the
phloem
• Radial transport: movement of water/nutrients within the tree between cells of different
ages - primarily through ray cells (move things laterally)
Control of Growth and Development
• A tree grows based on its genetic potential and its environmental conditions
○ Ex: a species can have a huge growth potential but is limited by the urban environment
• Light, temperature, gravity are all important to survival
○ Ex: long period of cold exposure may be necessary for budbreak, flowering, seed
germination
• Plant growth regulators/hormones
○ Chemical messengers that control part of the coordination of these processes
○ Processes include cell division, cell elongation, flowering, fruit ripening, leaf drop,
dormancy, root development
○ Major hormone groups include auxins, gibberelins, cytokinins, ethylene, abscisic acid
o Auxins: regulates every aspect of plant growth and development, primarily is in
shoot tips but also important to root development (ex: shoots tips get cut, root
growth inhibited and lateral shoots triggered - do not heavy crown prune to
ISA Study Guide Notes Page 4
