Plant discussion exam

primary growth

(height/lengthening of shoots and roots)

secondary growth

(thickening of stems/trunks).

Where do you see signs of primary growth?

At shoot tips and root tips: buds, young leaves, or elongating twigs at branch

ends. Example: New green, flexible shoots at the tip of a redwood or maple

branch

Where do you see evidence of secondary growth?

Thickening of stems and trunks: annual rings, bark, and wood expansion.

Example: The thick trunk of an oak or redwood shows secondary xylem (wood)

added each year.

Why are both types of growth important for tree survival?

Primary growth allows the tree to reach new light and resources by increasing

height and root length. Secondary growth provides support, stability, and

water/nutrient transport capacity for a tall, long-lived organism.

Both together ensure trees can grow tall and strong over time

Can you find an example of proleptic branching (branches arise from buds that

rested before elongating)?

oak (Quercus spp.) — lateral buds form one year and then grow the next spring.

Branches have distinct bud scars

Can you find an example of sylleptic branching (lateral branches can grow out

during current season’s growth phase)?

poplar or willow (Populus, Salix spp.) — side shoots emerge during the same

season’s growth. Young stems show actively elongating side branches with no

resting buds between flushes.

excurrent tree

(single trunk, conical; e.g.pine)

Example: Pine or redwood

Outline: narrow, triangular shape — strong central leader

Better light capture in dense forests (leaves spread vertically).

Greater wind and snow resistance due to streamlined shape.

decurrent tree

(spreading; e.g., oak)

Example: Valley oak (Quercus lobata) or maple (Acer spp.)

Outline: broad, dome-like crown.

Advantages:

1)Wider canopy for light capture in open environments.

2)Strong lateral branches provide stability and more space for reproduction

(acorns, flowers)

What environmental factors might have influenced this shape—broad (e.g., light, wind, snow load, competition, human pruning)

Example observation:

Tree: Coast live oak (Quercus agrifolia)

Crown shape: Broad and spreading.

Environmental influences:

1)Open sunlight promotes wide lateral branching.

2)Low wind pressure in sheltered areas allows a broad crown.

3)Human pruning near paths may modify shape.

Leaves in the shade

Shade leaves are larger, thinner, with a thinner cuticle, darker green (more chlorophyll per

unit mass), less lobed, with half to a quarter the density of stomata. This allows them to work

efficiently and maximize light capture at lower light intensities.

Shade leaves tend to be more horizontal to maximize light capture, while sun leaves tend to

be more vertical to reduce midday light exposure and prevent overheating.

Leaves in the sun

Sun leaves are more deeply lobed, which reduces the boundary layer, allowing for more

cooling to prevent overheating in the sun. Thicker leaves contain more mesophyll per unit

area to maximize light utilization in the sun

Sun branches often grow more densely, with shorter internodes. They often grow more

horizontally to reduce self-shading. Shade branches tend to be longer and thinner with fewer

but larger leaves, growing more upright or outward to reach available light.

embolism

The formation of air bubbles in the xylem's water transport system

Water transport can be disrupted when air enters the xylem, forming embolisms that block

flow and reduce conductivity.

xylem conductivity

The ability of a plant's xylem tissue to transport water, often measured as the rate of water flow per unit cross-sectional area of xylem for a given pressure gradient

Which species had the longest vessels? How might vessel length influence water

transport efficiency?

Oaks and Chinese tallow tree generally have longer vessels than redwood, maple, or

redbud.

Redwoods is conifers, actually have tracheids instead of vessels, which are much

shorter.

Short vessels: many end walls → more resistance → slower overall water movement

Long vessels: fewer end walls → less resistance → higher transport efficiency

Long vessels are more prone to cavitation (air bubbles) and embolism spread:

• If an air bubble forms in a long vessel, it can spread through the entire length.

• In short vessels, embolisms tend to stay isolated.

• So plants in arid, drought-stressed environments often evolve shorter vessels for safety, even though they’re less efficient. (As soil dries, plants must pull harder on water columns.
  The longer the water column inside a vessel, the more tension it experiences.)

After introducing embolisms, how did the flow of water change? Why?

When embolisms (air bubbles) form, they block water flow in the affected vessels.

The flow rate decreases because water must detour through fewer, narrower, or less

efficient pathways

What natural conditions (e.g., drought, freezing, strong heat) could cause

embolisms to form in plants?

Drought: Low soil moisture increases tension in water columns, pulling air into xylem.

Freezing temperature: Ice formation excludes air; when it thaws, bubbles remain and

block vessels

Examine the coast redwood trees and read the informational signs. Describe a few of the

characteristics of the redwood trees and explain how they help the redwoods survive in their

environment.

Redwoods are from a very different environment from Davis - moist, cool, and foggy with

occasional fire

Many characteristics that help them survive them in this environment (just a few highlighted

here):

• Fire-resistant bark allows mature trees to survive intermittent fires

• Leaves can absorb moisture from fog

• Trees can resprout from their bases after fire (generally quite rare in conifers)

Think about how new redwoods would get established here. Do you see redwoods of

different ages? Can you see examples of both vegetative and sexual reproduction?

Redwoods have tiny seeds – what soil surface conditions do you think they need to get

started, and what might create those conditions

Vegetative - sprouting at bases of mature trees

Sexual - scattered smaller trees independent of a larger individual

Most of the youngest shoots are vegetative sprouting at the base of mature leaves. We see

evidence of some seedling recruitment as there are some younger trees scattered through

the grove but this is generally quite rare.

Redwood seeds need the litter on the forest floor to be cleared in order to effectively

germinate (the litter here is quite thick). In the wild this would be the result of fire or flooding.

Redwood leaves from the top of the tree and the

bottom of the tree. How are they different? Why do you think this is?

Similar to sun leaves vs. shade leaves exercise. “Leaves” (scale-like needles) closer to the

top of the tree in direct sun are smaller, spikier, and denser while “leaves” towards the

bottom of the tree are flatter, wider, and more planar

Describe the climate within the redwood grove (how do you think it might differ from the

outside climate in the summer). How do the Redwoods modify the environment?

The redwoods form a cooler, more moist microclimate in the shade of their branches.

Additionally, the dense branches provide protection to the understory against strong wind.

Look at the trees at the edge of the redwood grove (along the road). Describe any

difference you notice between those trees and those in the center of the grove. What

natural features and processes might create similar conditions to the grove edges you

observed?

The edges of the grove are exposed to direct sun and are in conditions that can get quite

harsh in the summer. The trees at the edges produce sun “leaves” throughout their height

while those sheltered in the middle of the grove produce mostly shade “leaves” except on

their highest branches. The trees at the edge are also generally less healthy, being battered

by the more extreme conditions while those in the middle are more lush.

Examine a tree growing in the understory of the redwood Grove. What characteristics

help it to survive in this environment? How is it different from the redwoods?

As opposed to the redwoods that grow really tall to access light, many trees growing in the

understory are shade adapted and have large, thin leaves to maximize sunlight capture in

the lower light conditions.

What is the overall goal of cultural burning?

To manage the land for production of cultural resources (food, medicine, basketry materials, etc.

Briefly explain the importance of the Mariposa gray leaf manzanita (Arctostaphylos

mariposa). How does fire use affect this plant

Many parts of the plants are useful - the bark can be used as a remedy for poison oak, the berries are edible and can be fermented for medicine. Smoke exposure encourages new growth and increases berry production

How does fire use impact water supply and quality?

Fire use encourages new growth that increases the capacity for roots to hold water, increasing

water levels in the soil.

What is the top priority objective for a prescribed burn?

To clear out potential fuel for larger wildfires

What is the history of fire suppression and how did it oppress Indigenous communities?

Settlers saw fire as dangerous and did not understand the importance of it to Indigenous

stewardship of the land. Fire suppression was implemented to maximize trees, which they

thought was beneficial to the landscape, which simultaneously acted as cultural suppression of

Indigenous communities

What are the outcomes of fire suppression?

Greater accumulation of fuel (dead leaves, branches) and higher density of trees that allows for

fires to rapidly get large

What are a few issues with the catastrophic large, high severity “super fires” we are seeing

today?

Many - they are strong enough to remove the entire seedbank, slowing down recovery

The super fires are also strong enough that they are extremely challenging to control once they

start, leading to major damage to the landscape and potentially to human infrastructure

Describe the complicated relationship between USFS and tribes in the context of fire

management.

The USFS was involved in fire suppression but there is greater acceptance for use of regular

prescribed burns to reduce fuel loads. The USFS now has strong interests in reducing massive

forest fires and has been working with tribes to conduct prescribed burns / cultural burns to

achieve the goals of both. Communication and collaboration between the two will be important

moving forward.

Epiphytes

Are plants that grow on other plants but are not parasitic. They obtain

nutrients and water from the air, rain, and debris that accumulates around them.

Epiphytes grow on larger plants, such as trees, but they do not harm their host plants.

Many orchids are epiphytic and have succulent growth forms to conserve water between rain as

their exposed positions in the canopies dry out between precipitation events

Additionally, they often have thickened roots that absorb moisture from the air and can

photosynthesize as they are exposed to light

Lianas

Are woody vines that grow in tropical rainforests. They begin as seedlings

on the forest floor but grow upward, using other trees or plants as support to reach the

sunlight in the canopy. Lianas are not parasitic, but they can be competitive and

sometimes affect the growth of their host trees.

Lianas have stems that are both strong and flexible, as they need to provide strong support from

the forest floor to the canopy but also have the flexibility to twist around their tree supports, ex: wisteria

Mutualism

Is a type of symbiotic relationship between two different species in

which both species benefit from the interaction. In the tropical plant conservatory, you

can observe various examples of mutualism between plants, animals, and other

organisms. These interactions are essential for maintaining the health and balance of

tropical ecosystems.

Acacia-Ant: The acacia tree benefits because the ants protect it from herbivores and

other pests. Ants will aggressively defend the tree by attacking and driving away

herbivores, such as grazing insects, and other threats. This helps the acacia maintain its

leaves and overall health.

Plant - lichen: provides a protective structure and retains moisture. Plant perform

photosynthesis, providing the lichen with organic nutrients.

Not all tropical plants grow in warm environments. Go to the cloud forest room and

write down some observations of plants there compared to in the warm tropical room.

The cloud forest room is cool and wet. Many of the plants grow in constantly damp conditions so

lack adaptations for water storage. Additionally, many grow in low light conditions so there are

lots of ferns, mosses, and clubmosses.

Go to the dry room. What do you notice about differences in leaf biomass and

morphology of plants in this room vs. in the wet forest rooms?

As opposed to the cloud forest and warm tropical rooms, much less allocation to leaf biomass is

present here - most of the leaves in this room are small to reduce evapotranspiration. Stems are

often huge an modified for water / nutrient storage as those are limiting in these environments.

Additionally, many plants are well-protected with spines / thorns as they invested a lot of

resources into growing the water storage organs

Think about how the facilities and equipment across the different rooms provide the

ideal environments for different types of plants to grow. Write down some of the ways in

which we imitate the conditions for different tropical plants to thrive (think about light

availability, water, temperature, humidity, etc)

Supplemental lighting - this turns on to mimic the longer photoperiod of tropical days in

the short day length of our winters

Humidifiers are present in the cloud forest and tropical forest rooms to increase

moisture content in the air, while dehumidifiers are used in the dry room.

Heaters are present to make sure the rooms stay warmer in our winters. There are also

fans and swamp coolers to cool down the rooms in our hot summers (especially

important in the cloud forest room).

Compound leaf

leaves which are divided into leaflets

Vessel summary

● Shorter cells with large perforations (holes) on their end walls, allowing for direct water flow between stacked cells.

● Connect end-to-end, forming long, continuous tubes for efficient water transport.

● The primary water conducting cells in flowering plants, enabling faster water transport compared to tracheids.