Forestry 303 Long answer questions.


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1. What adaptations do gymnosperms have to withstand dry conditions?
1) Needles have a low surface area to volume ration, helping them retain moisture
2) The needles often have a thick waxy cuticle covering the epidermis.
3) beneath the epidermis are other layers of compactly packed thick walled cells, the hypodermal layer
4) stomata are sunken beneath the surface layer in pits, giving them a mini boundary layer
5) stomata can be filled with a waxy plug to further reduce water loss
How do sun leaves and shade leaves differ in their size, shape and color and why do these differences exist?
Sun Leaves
- situated near the top of the tree, growing in high light
- have less chlorophyll
- are smaller and thicker
- makes them able to tolerate bright light without wilting

Shade Leaves
- growing near bottom of tree in lower light
- have more chlorophyll, making them darker in color: helps them absorb what little light is available to them
- can die from bright light

These differences exist because of the different locations and functions associated with these leaves. Sun leaves are the first point of contact with light, and get an abundance. They need to be tough and require less repair. Shade leaves need to be frugal and generate as much energy as possible with as little light as possible.
What part of the plant senses changes in photoperiod?
The part of the plant that sense the change in photoperiod is the leaf.
What problem can occur if a pine ecotype adapted to southern latitudes is planted at a more northerly latitude? Why?
A pine from a southern ecotype might associate length of day with certain temps (ex 14 hours daylight = 15 degrees). Photoperiods further north can be just as long, but temperatures tend to be colder. Therefor, 14 hours daylight could mean 6. The ecotype would mistakenly think that it does not have to set bud and get damaged by a frost.
. Why are roots generally less frost tolerant than shoots?
roots develop the least frost hardiness because they are accustomed to being buried and insulated by snow and soil, and as such they do not usually freeze. Shoots do not have this luxury and must therefor develop frost hardiness. Nevertheless, frost hardiness in roots varies between species.
What is the difference between the chilling requirement and heat sums in trees?
Chilling requirement is a threshold that must be met in order for dormancy to be broken. The purpose of this is for the tree to know that winter has occured, and that once good weather comes around it will be able to grow again.

Heat sum is a cumulative amount of heat, measured in degree days, that is "counted" by trees and acts as a signal to tell them when to germinate. Only once the heat sum has been met will buds flush.

In recap: Chilling requirement signals to break the dormancy, heat sum signals to start germination
How can the environment during the year of growth affect growth of a determinate tree species?
Determinate trees have their leaf primordia set in their buds at the end of the previous growing season. As such, the factor that can be affected is the internodal length, the length between each leaf, which depends on current year conditions.
8. How do angiosperm trees and gymnosperm trees differ in the development of frost hardiness?
Gymnosperms will diminish the amount of water contained in their needle cells, and put it in the space between cells. Their cell membranes then become larger and more permeable. They then increase their solute concentration with sugars and other dissolved materials in their cells.

Angiosperms will usually ship the chlorophyll out of the leaves and into their stem, as it is rich in nitrogen. The Angiosperms then abscise their leaves, greatly reducing evaporative surface area.

9. Which of the phytohormones are considered to be "growth promoting"?
Auxins, cytokines and gibberellins are considered to be the growth promoting hormones.
What changes occur in deciduous leaves that turn red in the fall?
As the production of chlorophyll diminishes, the production of red anthocyanins increases. The chlorophyll then gets stored in the stem, making the leaves less green and even redder.
11. What are reactive oxygen species (ROS)?
ROS are molecules of O2 that become super energized into one of several super damaging derivatives. The most common one is an O2 with an extra electron, called a superoxide anion, it can give rise to another ROS.
How does phytochrome affect stem growth and form in a crowded stand of trees?
In a crowded stand of trees, there is more far red light than red light reaching the bottom leaves. As such, the phytocrome signals the tree to increase apical meristem growth and decrease lateral growth, making it grow taller not larger, to try and get above its competition (literally)
Trees and plants need water. How do trees and plants use water?
They use it as:
- a medium for biochemical reactions
- a participant in many chemical reactions (eg: photosynthesis)
- solvent for the movement of materials
- maintenance of turgidity, function and form
- temperature regulation (usually for cooling)
What key characteristic does a plant community have to have to be a climax community?
In a climax community, the conditions continue to be suitable so that climax species (eg western hemlock) continue to reproduce, regenerate and grow under their parents
What is the main determining factor in the development of global forest regions?
Water availability. That's it! ;)
List and briefly define the various types of seed dormancy.
Embryo Dormancy
- Dormancy that is broken when the ratio of growth promoting to growth inhibiting sways towards more growth promoting. An example would be seeds with a chilling requirement, a form of embryo dormancy.
Embryo immaturity
- dormancy that requires time to be broken, need a period of ripening
Seed coat impermeability
- the seed coat must be scarified or damaged a little bit in order to break dormancy
Seed coat Dormancy
- the seed coat will break dormancy after certain chemicals have been leeched out of, ex seeds in the desert with rain
light requiring seed
- light is required in order to break dormancy (some species of spruce and pine)
- not a true form of dormancy, some serotinous cones only release their seeds after a certain temperature melts the resin (ex fire and lodgepole pine)
No dormancy
Heat Requirement (boiling water over buckbrush)
18. How does the root of a germinating seed "know" which way is down?
the leucoplasts are heavy and sink to the bottom of the statocyte cell, which causes the redistribution of the phytohormone auxin in the cells surrounding this lower part of the root, promoting downward growth.
19. What is the difference between mitosis and meiosis? In your answer include the main function of each of these two processes.
Mitosis is the form of cell division that produces regular diploid cells, and it's primary function is to form new regular cell, primary function is growth. 2n cell makes 2 2n cells.

Meiosis is the form of cell division that produce haploid daughter cells (called gametes, or sex cells) from one single mother cell, and these cells are used for sexual reproduction. 1 2n mother cell makes 2 N daughter cells that are then used to make a 2n embryo.
What type of benefits can plants theoretically derive from being infected with mycorrhizal fungi.
- increased absorption of nutrients, especially soil phosphorus and nitrogen (and enhanced access of N from organic sources from decomposing)
- protection from plant pathogens
- tolerance to soil toxins (like heavy metals)
- lengthening of root life (eg. 45% in pine)
- improved soil structure so more air and water can enter and leave
Describe the main differences between ectomycorrhizae and endomycorrhizae?
1. Sheath (also called mantle) - proliferation of the fungus on the root surface and into the surrounding soil
2. Hartig Net - inner extension of mantle ramifying intercellular (between cells) spaces of the root
(a) between the epidermis and endodermis in gymnosperms e.g., Doulgas-fir, hemlock, pines
(b) only the epidermis in angiosperms e.g., oak, birch
3. Rhizomorphs - aggregation of fungus hyphal strands into cord-like structures that function as extensions of the root system

Endomycorrhizae, meaning inside
- No sheath or hartig net
- Fungal strands (called hyphae) infect discrete
areas of the root cortex - not every root cell is
- Infection is intercellular and intracellular (within
cells but surrounded by an extension of the plant
cell membrane)
- Form arbuscules within plant cells - coils of
hyphae inside plant cells to facilitate nutrient
- Some (VAM) form storage vesicles, usually for
lipids, within other plant host cells
22. What's the difference between primary and secondary tree growth?
Primary growth is the process by which plants get taller and roots grow longer. It includes the 3 processes of
1) cell division
2) cell expansion
3) cell Differentiation

Secondary growth on the other hand occurs laterally and is the job of the vascular cambium.
What products does the vascular cambium produce?
The vascular cambium produces vascular rays, earlywood (composed of xylem), latewood (also composed of xylem) and phloem (for sugary sap and other metabolites)
What tissue is responsible for producing the outer layer of bark we see on trees?
The cork cambium.
If there are 5 needles in a pine fascicle, draw the shape each needle would have in cross section.
What is the difference between tree species with determinate growth and trees with indeterminate growth?
In determinate species, the number of primordia present are determined by the previous growing season(internodal length can still change depending on current season however), whereas as in indeterminate species, primordia can be added as the season progresses.
How is phytochrome thought to measure daylength?
It actually measure the absence of daylight. The structure of phytochrome is modified by light, and it reverts to its original form in the dark. When the lenght of night reaches a certain threshold, the amount of Pr:Pfr signals to start setting buds. It's more complex than this though LOOOK THIS UP
What problem can occur if a pine ecotype adapted to northern latitudes is planted at a more southerly latitude? Why?
The tree can be confused and suffer frost damage. Basically, it might associate daylength with certain temperatures. While 14 hours daylight might correlate to 15 degrees in the south, up north, the same daylength might correlate to much lower temperatures. Therefor, the tree reads 14 hours and thinks that it can still keep growing, unaware of potential frosts! Therefore, if a plantation of southern ecotypes is planted further north, they could all die from frost damage.
Briefly list the main stages that occur in the development of frost hardiness in Douglas-fir.
The main step that needs to take place is for the plants to diminish the water content in their cells!
Induction: exposure to near freezing temperatures
- cell membrane makes it easier to move water out of the cell
- cell membrane becomes more permeable to water
- cell surface area is increase
- sugars and other dissolved substances increase solute concentration of remaining water and act as antifreeze
For each pair or structures, which is more frost hardy:
Terminal buds or lateral buds:
Vegetative buds or reproductive buds:
Roots or shoots:
terminal buds
vegetative buds
31. How can the environment during the previous year affect growth of a determinate species?
32. What changes occur at the cellular level when gymnosperms develop frost hardiness?
1) They make it easier for water to exit the cells from osmosis and move the water to spaces between cells
2) the cell membrane becomes more permeable
3) the surface area of the cell is increased
4) the solute concentration of the water left inside the cells is increase
5) the ability to tolerate desiccation is vital, as they only have 10% left
Which of the phytohormones are considered to "growth inhibiting"?
The phytohormones ABA and ethelyene promote leaf fall, these are considered to be growth inhibiting
What changes occur in deciduous leaves that turn yellow or orange in the fall?
The chlorophyll is removed and stored in the stem for its nitrogen content, and in doing so, reveals yellow xanthophyll and orange carotene (it was masking them, and now they are not masked anymore). anthocyanins would be red and show over this, so plants that turn orange and yellow generally lack anthocyanins
List and briefly describe the 3 types of root systems trees may possess.
tap root system
- in some species, the primary root system is well developed and dominates in size compared to the other roots, reaching far into the ground

shallow root system
- growth of the primary root slows early in seedling development, resulting in the lateral roots growing as vigorously as the primary root

heart root system
-intermediate to shallow and tap root systems, the primary and lateral roots grow to moderately deep levels
How does water get to the top of a tree?
Water evaporates from the stomata during evapotranspiration, pulling up on the next molecule of water (with the strength of hydrogen bonds), through a very thin tube of xylem. So the tree does not pump the water up, the water is actually pulled!
Why does ecological succession occur, i.e., what is the driving force?
Organisms growing in a certain area can change the conditions and make them more suitable for another species than itself. Some pioneer species might not be able to reproduce under their own shade.
Compare and contrast primary and secondary succession?
Primary succesion occurs on areas devoid of substrate, such as landslide beds, rock faces or even urban parking lots etc. This is a slow process that can take 100's of years to form a soil layer.

Seccondary succession on the other hand, can only be classified as such when the soil substrate is already present, and as a result, it is usually 5 to 10X faster!
How are latitude and elevation related regarding the type of plant ecosystem one might expect to find as one goes from south to north or low elevation to high elevation?
The main point to understand here is that a low latitude + high altitude = high latitude + low altitude.

Starting at the equator, one would see similar progressions of vegetation going towards the poles or going up a mountainside:
tropical rainforest -> deciduous forest -> boreal forest -> tundra -> barren rock or snow
What's the difference between early wood and late wood and how do they relate to tree rings?
Early wood is the first wood produced during a growing season, and characteristically has large lumens and thin cell walls.

As the season draws on, the characteristics of the wood produced are such that the lumens become smaller and the cell walls become thicker, this is called latewood!

A ring of earlywood with its surrounding latewood combine to make a growth ring.
What environmental conditions contribute to the development of frost hardiness?
Some frost hardiness is initiated by shorter day length, but in order for full development to take place, exposure to near freezing temperatures must take place.
How does a tree "know" that it's safe to start growing in the spring?
Even after dormancy has been broken, buds will not flush until a cumulative amount of heat threshold has been passed. This is measured in degree days, and the tree starts counting after a certain temperature has been attained.