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101 Cards in this Set
- Front
- Back
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Advantages of having wood
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1) competitive advantage for light (ability to grow taller)
2) above allows for increased PS = increased reproduction 3) wood provides structure and strength 4) water transport 5) protection from insects/pathogens/weather 6) accumulation of multi-year growth allows plants to maintain (and add to) height from year to year |
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What properties make wood a useful material
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useful w/o modification
biodegradable "breathable" long cells - good for pulp/paper insulating - air pockets/cell structure high strength to weight ratio easy to work flexible aesthetically pleasing somewhat to very impermeable (bordered pits/tyloses) very rot resistant when dry floats combustable |
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Downsides of wood
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decays (biodegradable)
burns limits to workability not uniform expands & contracts - differently in different directions wood is anisitropic not isotropic |
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anisitropic
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different strengths, swelling and shrinkage in different directions
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Conifer cell types - Longitudinal
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TRACHEIDS
>90% of wood volume ~ same dimensions as an eyelash dead at maturity -earlywood tracheids: large lumens, thinner cell walls, bordered pits -latewood tracheids: small lumens, thicker cell walls, few to no bordered pits Function: water transport, structure EPITHELIAL CELLS -in resin ducts -secrete resin |
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resin ducts
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-are not cells, they are "pipes" w/in wood that are lined with epithelial cells
-are the defence mechanism of (some) conifers against attack by insects etc -produce traumatic resin canals |
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Conifer cell types - transverse (axial)
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RAY PARENCHYMA
-alive at maturity -storage, transport and secretion functions RAY TRACHEIDS -water transport EPITHELIAL CELLS -in transverse resin ducts |
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Bordered Pits (Gymnosperms)
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-have pit pairs on either side
margo = sieve like membrane torus = intact piece of cell wall -water flows freely unless air enters either side (either tracheid) then the torus is pushed to one side, blocking one of the pit pairs -prevents runaway cavitation -how conifers contain drought damage or injury -in heartwood tend to be aspirated (why heartwood is less permeable than sapwood) |
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Angiosperm cell types - longitudinal
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VESSEL ELEMENTS
-large diameter, dead at maturity -stack up into vessels -water conduction via perforation plates (ends dissolve at maturity in a specific way to allow water transport) -many species have distinct early/late wood vessels FIBERS -long; thick cell walls; small diameter LONGITUDINAL PARENCHYMA -storage and secretion -often clustered around vessel elements (for formation of tyloses) |
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Ring porous species
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ie/ oak, ash, elm
have two distinct classes of vessel element: -very large, relatively uniform in early wood -much smaller ones in late wood |
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Semi-ring porous species
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have large vessel elements in the early wood, which gradually decrease in size to the late wood
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Diffuse porous species
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ie/ alder, poplar, tulip tree
have moderately large vessel elements scattered more-or-less evenly throughout the annual ring |
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perforation plate types
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simple - a hole surrounded by a rim (i.e./ oaks and poplars)
scalariform - the hole has 'bars' across it (i.e./ birch) reticulate - net like perforations on the plate |
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Tyloses
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-balloon-like protrusions of parenchyma wall which grow through pits into the lumens of adjacent vessel elements, sealing the vessels off
-play a role in sealing vessels during leaf abscission -usually form during conversion of sapwood to heartwood -also form when water column is disrupted by entry of air bubbles into sapwood or cavitation |
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paratracheal parenchyma
apotracheal parenchyma banded parenchyma |
-clustered around vessel elements
-not oriented around vessel elements, hardwoods that have this type of parenchyma won't have tyloses (ie/ white oak) -occurs in a band at the start or end of a growth ring |
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Angiosperm cell types - tranverse (axial)
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rays usually contain only parenchyma which may be:
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parenchyma orientation
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-elongated radially (procumbent) (most conifers, and some angiosperms)
-vertically (upright) (angiosperms) if only one orientation present they are homocellular, if both they are heterocellular (usually two layers of upright with a layer of procumbent in between) can be uniseriate (most conifers) or multiseriate with several or many files of cells -large mulitseriate rays can be seen with the naked eye on transverse sections, uniseriate rays require magnification to see |
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Wood Properties
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-made of cellulose, hemicellulose and lignin
-anisotropic -hygroscopic -biodegradable -combustable -relatively inert -durable (when used in dry environments, or others not amenable to organisms causing decomp.) -insulating due to structure and trapped air -~50% C, and is a major global sink for C |
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cellulose
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-crystalline structure of glucose
-straight chain -polysaccharide -> made of all glucose units -up to 10,000 glucose units in 1 cellulose molecule in cotton -in wood: ~300-1700 -long molecules H-bonded to each other in parallel creates crystalline structure -> CELLULOSE MICROFIBRIL -most common structure (~50% of wood) |
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lignin
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-amorphous and highly variable
-3D -class (or group) of chemicals -second most common (~30% of conifer wood and ~20% of angiosperm wood) -made up of phenylpropanoids -surrounds cellulose structures, hard to break down -slow to decomp., brown in colour -removed from wood during sulfite pulping as lignosulfonates (used in xylitol sugar, vanillin & DMSO) |
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hemicellulose
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-polysaccharide
-semi-crystalline, branched chain -20% of plant matter/biomass/wood -can link across cellulose molecules b/c it is branched and can H-bond (cross link w/ cellulose) |
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extractives
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-compounds that can be extracted with solvents
-most common: polyphenols -usually only a small % of wood dry mass, but some species have a very high content (i.e./ incense cedar) -not part of cell wall matrix, does not contribute support -determine colour and odour of wood (esp. heartwood) -produced by parenchyma cells during programmed cell death in sapwood to heartwood conversion (thus highest in newly formed heartwood, lowest in sapwood, decline towards middle of heartwood) |
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ash
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-0.1-0.5% of dry weight
-major components: Ca, K, Mg, Si -species high in Si (silica) dull tools rapidly, can be used as a defence mechanism |
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Secondary cell wall structure
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named in order that they are laid down
-middle lamella -primary cell wall layer -secondary cell wall layers: S1, S2, S3 |
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Primary cell wall layer (P)
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-10% cellulose, lots of pectin and hemicellulose
-very thin -cellulose microfibrils are oriented randomly -flexible, expands as cell grows |
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S1 cell wall layer
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-high microfibril angle (50-70 degrees off of vertical), more horizontal than vertical
-thin layer, 4-6 layers of microfibrils |
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S2 cell wall layer
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-main layer of secondary wall
-determines many properties of wood -low microfibril angle (10 - 30 degrees off of vertical) -up to 150 layers (called lamellae) -resist dimensional changes in cell length, but water can get between them and cause an increase in cell circumference (this is why normal wood doesn't swell or shrink much across the grain, but will do so against it) |
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S3 cell wall layer
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-thin
-high microfibril angle -sometimes absent |
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early wood
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-formed early in growing season
-thin cell walls -large lumens -main function: water transport -many bordered pits -high conductivity & flexibility |
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late wood
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-formed at end of growing season
-thick cell walls -small lumens -v.few or no bordered pits -main function: strength/support (comes from cell wall; thicker cell wall = stronger) |
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Auxin and early/late wood
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-vegetative activity in the crown of the tree in spring leads to enhanced auxin production
-auxin slowly travels down stem and promotes cambial activity in the stem -"wave" of cambial activation travels from crown down -auxin production falls again after bud set -this is what brings on the transition from early to late wood, creating annual rings |
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false rings
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-typically caused when the growing season is interrupted by drought, frost or defoliation
-ring of apparent late wood with thick cell walls and small lumens |
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discontinuous rings
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-growth rings that fail to form all the way around the whole circumference of the tree
-occurs with: trees with small, one-sided crowns (producing little auxin); trees with damaged vascular cambium (due to fire, cold, pathogens); heavily suppressed, defoliated, or overmature trees. |
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wood grain
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longitudinal alignment or orientation of wood cells
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straight grain
curly grain quilted grain birdseye grain |
when wood is split longitudinally
-flat surface -wavy in one dimension -wavy in two dimensions -small, conical deviations from straight grain (thought to be from epicormic buds growing radially slightly more then the surrounding xylem) |
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spalted wood
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-fungal infection resulting in alternating light and dark bands of wood rather than grain deviation from vertical
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spiral grain
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-longitudinal cells consistently oriented at an angle from vertical, with columns of of cells spiralling around tree
-generally longitudinal weaker and more prone to warping and twisting -results from oblique anitclinal divisions always occurring in same orientation |
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interlocked grain
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grain that reverses in direction in successive layers
-very hard to split |
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sapwood
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-outer area of the wood that contains living rays
-active in water transport -rays contain proteins, carbs, lipids and other compounds that support fungal and bacterial growth, therefore is attacked vigorously by these things (blue stain fungus from pine beetle only affects sapwood) |
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heartwood
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-inner area of the wood that is completely dead
-bordered pits are aspirated, vessel elements are blocked by tyloses -more fragrant and darker because of extractives deposited by ray cells in programmed cell death -makes heartwood less permeable and more resistant to rot -lower water content than sapwood |
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ray volume & composition
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angiosperms:
-~17% of wood volume -completely composed of parenchyma conifers: -~8% of wood volume (living parenchyma cells make up only 1-5% of sapwood volume) -contain parenchyma, ray tracheids and resin ducts |
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"pipe theory"
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-cross-sectional area of sapwood is determined by the biomass or area of foliage being supplied with water
-cross-sectional sapwood area should be constant up the trunk until the base of the live crown, but decrease from base of live crown to the top of the tree |
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heartwood/sapwood
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-boundary between sapwood & heartwood does not necessarily coincide with any annual ring, the age at which it changes varies with species, site, health etc
-in absence of decay have same strength, dry mater/cm^3, density |
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juvenile (crown-formed) wood
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-produced under high auxin conc.
-v.young trees produce only juvenile wood, mature trees produce both -high microfibril angle, more lignin, shorter tracheids, lower density b/c of thinner cell walls, ~30% weaker |
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mature (stem-formed) wood
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-stronger (higher density, thicker cell walls)
-less prone to longitudinal shrinkage (lower microfibril angle) -better pulp and paper yield per unit volume (higher cellulose to lignin ratio) and quality (longer tracheids) *a board with juvenile wood on one side and mature wood on the other will warp upon drying due to unequal shrinkage properties |
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annual diameter growth crown to base
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-is less at base then at the crown (although accumulated growth is greater at the bottom) due to delay in growth initiation from the top to the bottom of the crown, and due to decreased auxin levels and available photosynthate lower in the crown.
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wood distribution within tree
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-more late wood below live crown
-trees with high live crowns have proportionately moreclear, mature wood: large, older trees; trees in relatively dense stands; shade tolerant species (crown recedes more rapidly) |
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intermediate species
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ie western red cedar
-less prominent tree rings b/c active canopy growth (& auxin production) is more steady and takes place over a longer period of time -there is more early wood, therefore wood overall is less dense |
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reaction wood
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produced in response to stress
-tree is displaced by wind or some other factor -helps branches resist increased downwards stress has several commercially undesirable properties |
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compression wood
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-reaction wood in conifers
-on underside of branches/stems that are bent or leaning, pushes them upright -higher in lignin, tree rings produced are thicker and denser (over time can straighten stem) -very brittle, cannot be used in anything that relies on strength heavily -shrinks similarly in juvenile wood -shorter, rounder tracheids with thick walls, more lignin, less cellulose, and large intercellular spaces -S3 layer often absent, S2 layer has high microfibril angle and is loose packed, resulting in crack like striations in S2 -occurs in rx to gravity, not compression, auxin and/or ethylene involved |
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tension wood
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-angiosperms
-forms on upper side, contracts to pull the limb/stem upwards, produces wider growth rings to straighten tree. -v. high in cellulose -has new cell wall layer: S4 or G (for gelatinous), almost pure cellulose and very low microfibril angle, shrinks very little longitudinally, sticks out when wood is cut making it fuzzy and difficult to work. Common in poplars |
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reaction wood in roots
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forms in lateral roots to contribute to the development of resistance to blow down
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wood density
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major determinant of wood strength
-g/cm^3 -determined by cell wall thickness and lumen size -aka wood specific gravity -latewood > earlywood -stem-formed > crown-formed *species vary widely; variation within a species from the EW:LW ratio |
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types of stress related to strength
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-compressive stress (tends to reduce the size or volume)
-tensile stress (tends to increase size or volume) -shear stress (causes part of an object to move in the opposite direction to another part) *bending stress combines all three of these *strength is defined as the ability to resist these stresses |
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silviculture
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practice of cultivating trees for forest products
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wood quality
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dependent on the final product or use of the wood
-single best measure is density |
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wood uniformity
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-important for wood uses including workability in manufacturing and ability to retain paint
-important w/in growth rings and between growth rings in successive years |
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fiber length
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length of tracheids in softwoods & fibres in hardwoods
-shortest when vascular cambium is young (crown-formed wood) and continues to lengthen in age in stem-formed wood -long fibres have higher quality for most aspects of pulp and paper |
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knots
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-size, frequency and type is critical for lumber and veneer quality and value
-decrease value b/c of impact on wood strength and appearance -all trees have knotty core, but highest value of wood is produced when this area is small and there is a high proportion of clear, stem-formed wood outside of this core |
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clear wood
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knot-free wood
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live knots
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aka tight knots
-produced while branches were living, thus the annual rings of the branch are continuous with those of the tree -stronger and well-integrated into the wood |
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dead knots
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-aka loose knots
-formed when secondary growth encompasses dead branches -not well-connected to the wood in the stem and tend to fall out of boards leaving knot holes |
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chemical compostion desirable for pulp
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-high cellulose
-low lignin, hemicellulose, and extractive content -want silvicultural practices that that reduce the proportion of crown-formed and compression wood |
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tree spacing
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-relatively little impact on tree height, except in very dense or very sparse stands
-strongly affects tree diameter |
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trees grown at low density
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<500 trees per hectare
-have long live crowns and large branches -results in high proportion of crown-formed wood and many large knots -individual tree diameter will be larger than those grown at a higher density |
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trees grown at high density
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~2,000 trees per hectare
-maximizes biomass production -live crown recedes quickly |
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thinning
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-done to stands initially planted at high density, once the live crown recedes
-removal of some trees to allow more room for the remaining trees to grow, growth per tree increases and trees produce stem-formed wood |
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pruning
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-removal of branches to induce production of stem-formed wood
-expensive, only used in high value stands -branches pruned when live as close as possible to stem to allow vascular cambium to grow over branch stubs and minimize dead knots -decreases growth rate somewhat as it reduces the amount of foliage available for PS |
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tree growth can be increased by
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-tree breeding
-fertilization -irrigation |
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effect of tree growth on wood quality
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-varies with treatment, depends on if additional growth is latewood (increasing quality) earlywood (decreasing quality) or both (no effect on quality)
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tree breeding
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-if fast growing trees are selected, wood quality will decrease
-usually low-density, fast growing trees are avoided |
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fertilization
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-increase wood production, but may increase, decrease or have no effect on quality
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irrigation
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-increases quality if it increases latewood production, but decreases it if delays transition form early to late wood
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cross dating
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matching tree ring patterns from tree to tree to determine tree age, and account for false and missing rings
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complacent rings
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don't vary much from year to year
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sensitive rings
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highly variable (b/c of snow pack, drought etc)
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cloning
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-vegetative or asexual reproduction
-propagation of plants using vegetative tissues -cell division by mitosis -genetic duplication, making multiple individuals from one individual that have the same genetic sequence |
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ortet
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original "mother" plant (donor)
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ramet
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cloned "offspring" from the ortet
(genetically identical to ortet ) |
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why clone?
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-stressful cold or dry conditions
-propagate plants that have desirable traits A) hard to find a mate B) sexual reproduction requires a lot of energy C) cloning has a shorter time frame D) a genotype that is well developed to a particular environment can spread E) Ramet connected to ortet, can provide some support & protection in harsh environments |
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layering
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-drooping lower branch contacts the soil (pushed dow by snow or vegetation)
-adventitious roots form at point of contact with soil -branch tip starts to turn upwards -if branch is then broken, a new individual is formed -many high-elevation tree species -short growing season not sufficient to complete sexual reproduction cycle |
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stump sprouts
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epicormic shoots (from dormant buds), cause new shoots to emerge from stump
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stool sprouts
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-adventitious buds, don't usually grow much
-useful in poplars to provide stem cuttings or whips for rooting -produced when auxin:CK ratio drops following removal of most of the stem |
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coppicing
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-regeneration via stump sprouting after harvest
-used for coast redwood regeneration |
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suckering
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-from roots, via adventitious shoots
-in shallow-rooted species following disturbance -promoted by low auxin:CK ratio -as auxin is produced by growing shoot tips and transported down, CK is produced by roots and transported up, cutting down the stem of a tree results in low akin:CK ratio |
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rooted cuttings
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-relatively rare in nature
-can be important for riparian species -ie/ branches of black cottonwood (& willows) can break off, be borne downstream, lodge in substrate and form adventitious roots -much more commonly used by humans |
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rhizomes
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horizontal, underground stems form new adventitious shoots and roots
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corms, bulbs, tubers
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-below-ground vegetative propagules of herbaceous plants
-corms: thickened, vertical underground stems from which plants can regenerate -bulbs: specialized buds with thickened, fleshy scales -tubers: thickened rhizomes for storage from which plants can regenerate |
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runners
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aka stolons
-above-ground horizontal shoots -first node will produce only leaves, second node produces adventitious roots at which point the shoot will turn upwards and produce a new plant |
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apomixis
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-method of reproduction via seeds
-embryos are clone of mother plant, produced without fertilization -propagules have advantage of being animal dispersed in fruit, so single plant can easily colonize new location |
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types of vegetative reproduction in nature
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layering
sprouting & suckering rooted cuttings rhizomes, stolons, bulbs, corms & tubers apomixis |
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artificial methods of vegetative reproduction
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rooted cuttings (aka stecklings)
air layering grafting tissue culture, including somatic embryogenisis |
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rooted cuttings (aka stecklings)
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-most common method used in forestry worldwide
-cut stem segments containing at least one bud are placed in a rooting medium -auxins accumulate and adventitious roots develop at the cut end -application of auxin improves rooting success -rooting success varies with species, age (younger is better), positon of donor tree the cutting is from (lower = more juvenile, therefore better), and time of year (early spring rooting of hard cuttings is good) -in forestry: cuttings taken from juvenile seedlings or trees where juvenility is maintained through regular hedging -physiologically moe mature than juvenile seedlings, can produce trees that are less vulnerable to juvenile disease or have better stem form with less taper |
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air layering
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-wounding a shoot and wrapping the wound in moist medium (ie sphagnum) surrounded by waterproof covering
-adventitious roots arise near the wound site -not used much for many species -effective with mature ramets where other methods fail |
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grafting
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-attaching a shoot (or a bud) from individual being cloned to the root system and lower stem (root stock) of another tree
-produces genetic mosaic, with the stem and crown being one genotype, and the root stock being another -useful for cloning older trees of many species -dominant scion is harvested from upper crown of tree to be cloned in mid to late winter -attached to top of cut stem of a seedling with approx same diameter -important that xylem, phloem and cambium of root stock and scion are in contact -wound callus is formed by both -then they grow together and develop continuous vascular tissue -need to be genetically compatible -used for seed orchards, unique trees for horticultural purposes |
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scion
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shoot cutting with terminal bud
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explant
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piece of leaf, cotyledon or embryo
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tissue culture - method 1
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-place explant onto a growth medium containing hormones, sugars, amino acids and micronutrients
-initially callus tissue and adventitious buds produced -adventitious shoots are then detached and transferred to growth medium promoting root formation (high auxin level) |
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tissue culture - method 2
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-take individual cells from callus and grow them in liquid culture
-then regenerate whole plants from individual protoplasts -most desirable form of propagation following genetic engineering -impossible with conifers, difficult to do with most important forestry species (either type of tissue culture) |
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somatic embryogenesis
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-tissue culture that is successful with conifers
-embryo from seed is placed in on a growing medium -first callus culture grows -then culture becomes embryogenic and tissues for "somatic embryos" differentiate -these can then be germinated and grown into "somatic emblings", packaged in artificial seeds or cryopreserved -used to cone the offspring of desirable parents , not the mature trees themselves |
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cryopreserved
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stored at very low temps while individual clones are tested for desirable traits
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