1. Ch. 6 Structure and Growth
Tree form
Shoots
Primary growth
Stems
Primary and secondary growth
Roots
Leaves
Primary growth = shoots of crown and the roots
Secondary growth = expansion of stem and root diameter

2. Tree Form & Crown Shape

3. Size, shape, and composition (# of branches, twigs, etc.)
Tree Form
Size, shape, and composition
(# of branches, twigs, etc.)
of the crown.
Greatly affects the amount & quality of wood produced as well as
stem taper
Fruit trees – want small, compact crowns with high
fruit yield

4. Open Growth Open-grown tree with strong epinastic control
(epinastic = growth that greater on the upper than lower side)
Where are the leaves found in a crown? Why?

5. Restricted Growth (even walls)
This trees have the same potential shape as on the previous page.
There is a constantly rising wall constraining tree growth
Lower branches abrade against wall and are shaded
slow their growth and die.
Dead branches may fall off or may persist depending on species
In this case, so much PSN is lost, even height growth slows.
Removal of wall allows tree to recover somewhat
-increase of foliage area
-retention of lower crown
-buildup of nonfunctional crown
-production of water sprouts
-densification of foliage
w/ weak epinastic control, limbs spread faster, creating a more
flat topped crown

6. Restricted Growth (uneven walls)
This trees also has the same potential shape as the first one.
The wall is at irregular distances from the tree
asymmetric crown
Wall stops rising – what happens to the crown as the tree grows
above it?
Crown size increases with tree height since the base no longer
recedes.

7. Excurrent Crown Shape Douglas fir juniper loblolly pine red spruce
defined central bole
narrow, columnar crowns
associated with high latitudes or xeric sites
more examples in Fig. 6.1
Selection pressures: snow, ice, wind
Strong apical control -
Terminal shoot grows faster than lateral branches
Not all conifers
pines of Southeast have strong central stem, but
have a more rounded shape
conifers of Southwest (pinyon pines, junipers) have
short, compact, round, bushy crown with
extensive root development
because of high temperatures, soil water stress
tall excurrent growth would expose them to strong, dry winds.

8. Conifer Branch Angle
Controlled by:
Hormones
Light

9. Decurrent Crown Shape black willow white elm
also called ‘deliquescent’
spreading crown
often has multiple stems
most common form is ovate to elongate
more examples in Fig. 6.1
black willow
white elm
Broadleaves are often excurrent for a few years, and then decurrent.
They shift sooner on some poor sites
deliquescent - tree trunk dividing into many large lateral branches; umbrella-shaped silhouett

10. Control of Crown Shape Hormonal control (or lack thereof)
Control of apical buds over lateral buds
Environment
Stand density
apical bud
lateral
bud
Apical – at the tip
Lateral – from the sides
Environment –
northern & alpine, mostly excurrent
“less harsh”, mostly decurrent
Stand density has the most effect
Image from:
Koning, Ross E. "Home Page for Ross Koning". Plant Physiology Information
Website ( ).

11. Competition & Crown Shape
A = early successional species (pioneer species)
“Stand Initiation”
A dominates, C developing
“Stem Exclusion”
A disappears, B dominates,
C/D compete for resources/light
“Understory Re-initiation”
B still dominates, but shape has changed – more room
(taller, narrower)
C/D have thinned, leaving more sunlight to get to forest floor
This leads to understory regeneration
“Old Growth”
B/C/D co-dominate
younger C/D developing (no younger B developing)
understory has thinned to sustainable levels

12. Fig. 8.5 – Competition & Crown Shape
Different stands have different light characteristics.
Some stands allow almost half the light to the sub-canopy,
while others allow none.

13. Competition & Crown Shape
Conifer stand
Almost all leaves are found in a singe layer.
Dramatic loss of light in that layer.
Low level (15%) at floor.

14. Competition & Crown Shape
Temperate Mixed Hardwood Stand
2 distinct canopies –
dominant canopy & an understory canopy
Through first canopy, light drops to 60% of full sunlight.
Through the second canopy, light drops another 10%
There is still 50% of the light reaching the forest floor.
This allows for a lot of understory should other conditions
be right.

15. Competition & Crown Shape
Tropical Forest
Complex multi-height canopy.
More gradual loss of light to about 40%
The light drops more quickly through the second canopy
layer, leaving practically no light at the forest floor.

16. Ch. 6 Structure and Growth
Tree form
Primary growth
Stems
Primary and secondary growth
Roots
Leaves
Primary growth = shoots of crown and the roots
Secondary growth = expansion of stem and root diameter

17. Seasonal Growth Patterns - Temperate Regions -
Dependent upon:
Fixed vs. Free growth
Fixed growth = buds form one year,
grow the next
Free growth = concurrent initiation
& growth
Environmental conditions
Daylength
Temperature
In Montana
Drought
Cold
Environmental Conditions occur mostly during summer
when maximum growth occurs

18. Seasonal Growth Patterns - Tropical Regions -
Dependent upon:
Leaf senescence
Leaf/root imbalance due to
water stress

19. Why prune a tree? Important for Fruit trees Christmas trees
Ornamentals
(shaping, e.g. bonsai trees)

20. Fig. 6.5 – Tree Growth Georgia Piedmont
After Zimmermann & Brown, 1971

21. Fig. 6.4 – Tree Growth seasonally dependent
Northern pines – preformed shoots & one annual growth flush
Southern pines – grow in recurrent flushes
Three southern pines = loblolly, shortleaf, slash

22. Tree Growth (live fast, die young)
Height 25 50
100
Age (years)
Douglas fir (Montana)
Southern Pines
Cottonwood
Southeastern trees grow faster initially and mature earlier
foresters take advantage of this for commercial logging
Montana trees end up growing bigger