intro and tree form

silviculture

the theory and practice of controlling forest establishment, composition, structure, quality and growth (how it establishes, develops, and regenerates) to achieve the objectives of management

art and science of manipulating forest stands to achieve our objectives - such as the production of goods and services

history of silviculture

german origins, other origins in Asia more similar to agroforestry

until the 70s they focused on timber extraction, 80s-90s focused on multi-use forestry, now we are concerned with sustainable forest management - the future of trees is just as important as the harvest, future and replanting esp with concerns of climate change and unpredictability

why silviculture matters

connects ecology to action, regenerates forests after harvest or disturbance, tends stands for resilience, improve value and ecosystem services, adapts forests to climate / fire / pests / changing social expectations

challenges with herbicides

used to control competing vegetation such as grasses and understory, goal to increase tree growth

alternatives are also needed

considerations include biological and physical environment, operational constraints, policy, social, economic, and management objectives of course

what do we need to take into account with silviculture? (3)

economy - harvest, timber, firewood

ecology - environmental protection

social benefit - local population, recreation, etc

what do we do for silviculture?

site prep, seedlings, brushing, herbicides, etc

prescription plans depend on objectives / management goals - ex promoting biodiversity, maximizing timber yield, reduce fire risk, reduce erosion, etc

adaptive management in silviculture

use best available knowledge to make decisions

monitor results

adapt or modify practices based on observations

silviculture trends in AB

harvest is 22.5M m2 (2/3 of this conifer)

harvest area is increasing, doubling in past 30 years

most harvested area is planted, increase in herbicide use, but recent decrease

decrese in site prep

mostly spruce, but pine has also been increasing

how does tree growth begin?

leaf area capture light → photosynthesis fixes carbon → carbon allocation to leaves, stem, roots → growth in height, diameter, and crown

growth is controlled by leaf area - leaves grow trees

tree growth vs yield

the change in attribute of a tree or stand over a fixed time interval, biological production rate concept

vs the quantity of the attribute of a tree or stand at a given point in time, can be known as cumulative growth, is a accumulation or removal concept

sigmoidal growth curve pattern / logistic growth curve (S) holds true for many tree and stand level parameters (height, DBH, BA, volume, leaf area)

tree growth form

competition for light and space affects crown, branches and roots

forest grown vs open grown

forest grown

more competition, more trees in the same space, condenses

open grown

less competition, individual / few trees with more space

have larger leaf area

live crown ratio

proportion of the total stem length covered by living branching, as a percentage of total height

% = live crown length / total tree height *100

higher ratio indicates there is a longer crown length in proportion to height

influenced by stem density, shade tolerance, and type of trees

live crown length

from the base of the crown to the top of the crown / tree

crown width

take N-S and W-E widths of crown, perpendicular widths, and then take the average

friction is the abrasion between branches caused by wind, shyness is the empty space between crowns cause by wind probs

site index

common measure of productivity

top height at a given age, height is closely related to stand volume (but independent of density)

developed for single species, even-aged stands

so if you know the height and age of a tree you can find the volume

use the variables you do know to obtain what you don’t, useful for growth modelling

slenderness coefficient

height / DBH

preferred to be higher

excurrent branching

strong central leader (grows faster than lateral branches), common in conifers - grow as high as possible to reach light

strong apical dominance, control by gravity

crown architecture

decurrent branching

several major branches, less apical control / weak apical dominance, leader grows no faster than the lateral branches

rounded crowns and flat tops, common of broadleaf / hardwood trees

more likely to respond to light - bend towards canopy gaps

crown architecture

shade intolerant trees

put most of their growth in leaders in deep shade

race for sunlight or they will die

ex lodgepole pine and aspen

shade tolerant trees

leader is shorter than the lateral branches, sit and wait approach, respond to canopy gaps, seedling bank

ex balsam fir, sugar maple, beech

less competition / lower density

more lateral growing space, large and deep crowns, more persistent branches

more competition / higher density

restricted crown width, lower light beneath canopy, branch mortality and crown recession

competition in silviculture

generally prefer a lower density in forestry, but then need to pay the cost of thinning (balance)

in dense stands, height is maintained by DBH is constrained

we prefer taller trees, but exposing very slender trees means risk of the elements

indeterminate shoot growth

some shoot extensions are developed in the previous season and some are developed through the current season, promotes very rapid growth in good growing conditions

ex poplar, birch, ash, larch, elm

determinate shoot growth

all of the seasons shoot extension is preformed in the winter bud the previous year, allows for quick development of leaves in the spring

common in areas with a distinct dormant period

ex spruce, fir, ash, oak, pine

branching problems

ramicorn branch - upturned and competes with the main stem, occurs when terminal leader is killed and so other branches compete

water sprouts - release of buds on the main stem, common when bole exposed after thinning or pruning

lammas shoots - late season flush of terminal bud = susceptible to frost, could be fertilization issue

why do crowns differ?

1) genetics: species traits, branching patterns, shade tolerance

2) environment: light, moisture, wind, frost, space

3) competition: stand density, crown overlap, neighbours

4) management: thinning, pruning, damage - role of silviculture

tree form is the interaction between these, not just one or two causes

branch mortality / natural pruning

shading can cause low branch carbon balance → causing mortality → branch shedding, and clearer bole (main stem)

density and light environment influence branchiness, knot development, stem form and wood quality (as knots have lower quality got timber)

knots

records where a branch was incorporated into bole wood

live / tight: the branch is alive when stem wood grows around it, tissue intergrown

dead / loose: branch dies before it is enclosed, is less integrated so may fall out during processing

good vs bad pruning

retains natural architecture, avoid unnecessary large wounds, clear objectives

vs large cuts / topping, stress responses, weakly attached new shoots

artifical pruning

investing in more clear wood, remove selected branches early so knotty core gets covered up

good candidates include selected crop trees, vigorous trees, small branches, enough future diameter growth to add clear wood

remember trade off as leaves grow trees, can’t remove too much growth, and also is costly

how can we change the health of a tree?

pruning, provide nutrients, thinninga

allocation of photosynthates

respiration, height growth (foliage and buds), new roots, carbohydrate storage, diameter growth, protective secondary chemicals

• height growth is generally maintained preferentially for species

juvenile wood

10-20 years of first growth, wood has lower specific gravity, short fibers, low strength, low cellulose, and low yield of pulp

important to distinguish as yield volume, future actions, etc change

mature wood

develops further from the apical meristems and is characterized by more stable physical properties and greater strength than juvenile wood

important to distinguish as yield volume, future actions, etc change

reaction wood

wood with distinct anatomical characteristics produced in boles (trunk) or leaning trees or in wood with unusual center of gravity, can be caused by high winds

more warping in lumber, wood contributes to distortion and warping during processing

compression and tension wood

compression wood

more wood on the lower surfaces (acute angle) of the leaning bole

in conifers

a type of reaction wood

tension wood

more wood on the upper surfaces (obtuse angle) of the leaning bole, in hardwoods like aspen

type of reaction wood