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

Tree Form & Crown Shape

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

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?

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

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.

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.

Conifer Branch Angle Controlled by: Hormones Light

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

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. 1994. http://plantphys.info/index.html ( 9-1-2005).

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

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.

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.

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.

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.

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

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

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

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

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

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

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