Investigating Stratification
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2.6 Ecological Pattern of Stratification
Fundamentals of Ecology
Concept 3: Stratification
Success Criteria & Vocabulary
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I can describe the podocarp-broadleaf forest community.
I can explain the physical conditions in each of the five strata.
I can discuss why stratification happens, and why it is important.
Click this drop-down menu to see the list of Vocabulary.
Biodiversity: Variety of plant and animal life in an ecosystem.
Canopy layer: Upper strata in a stratified forest, comprising of tall trees that make up most of the forest canopy.
Common name: Names given to species in the native language, used in day-to-day conversation. Each species has many of these names.
Emergent layer: Uppermost strata in a stratified forest, comprising of the tallest trees that ‘stick out’ of the forest canopy.
Epiphyte: Type of plant that grows on another plant (host) in the canopy or emergent stata to access more light. Has a commensalism relationship with its host.
Foliage: Leaves of a plant.
Germination: Process by which an organism grows from a seed.
Ground layer: Lowermost strata in a stratified forest, comprising of ground ferns and seedlings.
Host: Plant used by epiphyte to access more light. Has a commensalism relationship with the epiphyte.
Scientific name: Names given to species that are internationally accepted and used in formal literature. Each species has only one of this name.
Seedling: Young plant that developed from a seed.
Shrub layer: Lower strata in a stratified forest, comprising of bush species.
Strata: One of a number of layers in a stratified forest.
Stratification: Pattern of vertical layering in a forest community.
Subcanopy layer: Middle strata in a stratified forest, comprising mostly of tree ferns.
Tasks
Learn the 15 keywords using Quizlet
Concept 3: Support Notes
What is a Podocarp-Broadleaf Forest?
New Zealand has two types of native forests: Podocarp-Broadleaf forests and Beech forests. For the purposes of this Achievement Standard, we will be focusing on Podocarp-Broadleaf forests because that’s the type of forest we will be visiting on our field trip.
Podocarp-broadleaf forests are very dense forests that contain podocarp trees and broadleaf trees, as well as other trees and plants.
There are 2 million hectares of podocarp-broadleaf forest in New Zealand.
What are some examples of podocarp trees?
Podocarp trees like rimu and kahikatea have narrow, scale-like leaves.
They don’t have flowers or fruit. Instead they produce brightly coloured seed cones that attract birds. If birds eat these seed cones, they will distribute the seeds throughout the forest through their poop.
Pictured: rimu (Dacrycarpus cupressinum)
What are some examples of broadleaf trees?
Broadleaf trees like kohekohe, rata, nikau and karaka are flowering trees. They produce bright-coloured fruit that birds are attracted to, so this is how their seeds are distributed.
Like their name describes, their leaves are broad.
Pictured: northern rātā (Metrosideros robusta)
What is a Stratification?
Forests throughout the world show STRATIFICATION: a pattern of vertical layering in a forest community.
New Zealand’s podocarp-broadleaf forests have 5 distinct vertical layers: EMERGENT, CANOPY, SUBCANOPY, SHRUB, and GROUND.
For each STRATA, you MUST be able to write about:
Rough height range
ABIOTIC FACTORS in that layer (e.g. light intensity, wind strength, humidity, temperature).
BIOTIC FACTORS in that layer (e.g. an example of a plant species inhabiting that strata, explanation of a species interaction in that strata).
What are some Abiotic and Biotic Factors in each Strata?
Emergent layer
The emergent layer is the layer furthest from the ground. Trees in this layer of the forest are exposed to full sun. This means they get full light intensity and very high temperatures. Trees are also exposed to full wind strength, as there’s nothing to cover them. Because this layer is exposed to full sun and full wind, the humidity levels are very low.
Examples of trees found in this layer are rimu and kahikatea. These trees are called emergents because they grow through and above the trees in the canopy layer.
Canopy layer
The canopy layer is the next layer below from the emergent layer, and the second furthest from the ground. This layer is usually sheltered by trees in the emergent layer, so they are not as exposed to full sun and full wind strength. So trees in this layer experience high light intensity, high temperatures, and high wind strength, but low humidity.
Examples of trees found in this layer are nikau, kohekohe, and pigeonwood.
Emergent/Canopy layers - Epiphytes
EPIPHYTES are a type of plant found in the canopy or emergent strata. An epiphyte is a plant that grows on another plant - the plant it grows on is called the HOST.
Epiphyte seeds get pooped onto tree trunks and branches by birds, and that is where the seeds GERMINATE. Epiphytes need high light intensity to establish and grow, that’s why those seeds that land in the canopy or emergent strata do best.
An example of an epiphyte that you’ll see throughout Arataki is the perching lily (Collospermum hastatum), that’s likely to be on a rimu tree (Dacrycarpus cupressinum).
Emergent/Canopy layers - Tree Epiphytes that Strangle
A different type of epiphyte is a tree epiphyte like the Northern rātā. Like the perching lily, Northern rata seeds get pooped onto tree trunks and branches by birds, and the seeds germinate.
Interestingly, eventually the Northern rata’s roots grow down the trunk of the host tree, and develops a massive root system. After many many years, the host tree succumbs to the strangulation and dies, and at this point, the Northern rata is able to stand on its own.
Of note, it’s possible for Northern rata seeds to germinate on the ground, but it’s more common for it to start life as an epiphyte.
Pictured: Northern rātā (Metrosideros robusta) circling a rimu tree (Dacrycarpus cupressinum).
Emergent/Canopy layers - Vines
In contrast to epiphytes, climbing vines like the climbing rātā germinate on the ground and grow up large trees like rimu, using it like a ladder. When the stems reach full light, they form a bush growth of branches that extend away from the host.
Climbing rātā are quite different to Northern rātā in that they don’t kill the host tree.
Pictured: climbing rātā (Metrosideros fulgens) climbing a rimu tree (Dacrycarpus cupressinum).
Subcanopy layer
The subcanopy layer is the layer below the canopy, and the third layer from furthest from the ground.
Trees in the canopy layer have dense foliage that shelter the subcanopy layer from the sun and wind. Therefore trees in this layer experience medium light intensity, medium temperatures, medium wind strength and medium humidity.
Examples of trees found in this layer are mahoe, karaka, brown tree fern, and the silver fern (as well as young canopy and emergent trees).
Shrub layer
The shrub layer is the layer second closest to the ground.
FOLIAGE of trees from the layers above greatly shelter the shrub layer from sun and wind. Therefore trees in this layer experience low light intensity, low temperatures, low wind strength, and high humidity.
Examples of plants found in this layer are karamu, kanono, and hangehange (as well as seedlings and young trees and tree ferns).
Ground layer
The ground layer is the layer closest to the ground. It’s very sheltered from the elements, so plants in this layer experience very low light intensity, very low temperature, very low wind strength, and very high humidity.
In this layer you’ll mostly see moss and ground ferns. You will also see plenty of seedlings because this strata provides the low light intensity and a damp, cool, humd habitat that’s suitable for the GERMINATION of seeds.
In this picture you can see a high density of SEEDLINGS, like nikau seedlings that look like grass, as well as seedlings of emergent trees like kahikatea and rimu.
The seeds that these seedlings have grown from were dispersed by birds like the kereru and tui.
Summarising the 5 Strata
This is a table that summarises the physical conditions and examples of plant species inhabiting each STRATA. As you can see each strata has a different set of physical conditions or ABIOTIC FACTORS. And therefore each layer is a different HABITAT for different species of plants to occupy.
The main physical condition controlling the distribution of plants in the different strata is light.
Plants in the emergent and canopy layers receive high light intensity, and the plants in the lower strata receive less and less light intensity.
Why does Stratification occur? Why is it Important?
STRATIFICATION occurs because plants in the tall plants in the CANOPY and EMERGENT layers filter the sun and shelter from the wind, causing a drop in temperature and increase in humidity for the layers below.
This forms different microclimates, different physical conditions at each strata, creating many NICHES that different species of plants can occupy.
Trees in the emergent layer have adaptations to thrive in that very high light intensity niche, and plants in the shrub layer have adaptations to thrive in that low-light intensity niche.
Different microclimates = more niches = more different species can coexist in the same forest = increased biodiversity = more robust forest ecosystem.
The stratification pattern increases the number of species in a forest community, and therefore increases BIODIVERSITY. Biodiversity is the variety of plant and animal life. It does this by increasing the number of NICHES available, and therefore reducing COMPETITION between different species, which relates back to GAUSE'S PRINCIPLE that states that two different species with similar ecological niches cannot stably coexist in the same HABITAT.
For example, rimu trees in the emergent layer do not have to compete with kanono plants in the shrub layer because they occupy different niches.
A forest with many vertical layers is more complex and has greater biodiversity because it can have more plant and animal species in it, more complex ECOSYSTEM. If one of the layers were lost, it will make other layers vulnerable. For example, if pests like possums BROWSED on too much FOLIAGE of canopy trees, too much light, heat, and wind will reach the forest floor, decreasing the humidity. Plants on the forest floor like mosses, ferns, and seedlings are not adapted to these conditions and they’re likely to shrivel up and die if exposed to full sun and wind.
So in summary, stratification:
- Increases the number of niches available, which reduces interspecific competition (link this back to Gause's competitive exclusion principle).
- Increases the number of species in a forest community, which increases biodiversity, and makes the forest ecosystem more robust.
Concept 4: Collecting & Processing Data
Success Criteria & Vocabulary
Click this drop-down menu to see the Success Criteria.
I can collect transect data and record it on a table.
I can accurately draw a profile diagram.
I can describe how to collect abiotic data, and interpret it.
Click this drop-down menu to see the list of Vocabulary.
%: Unit of relative humidity.
degrees Celsius: Unit of temperature.
Lux: Unit of light intensity.
Lux meter: Instrument that can measure light intensity, as well as temperature and relative humidity.
Profile diagram: Visual representation of forest structure along a transect.
Transect: Line across a habitat.
Tasks
Video: Collecting & Processing Data
Learn the 6 keywords using Quizlet:
Concept 4: Support Notes
How to collect Biotic Data in a Stratified forest
It’s important to collect data on our stratified forests so we can get an idea of how the forest community changes over time.
We do this through plotting a profile diagram. A profile diagram is a visual representation of forest structure along a transect.
A transect is a line across a habitat.
To create a profile diagram, you will need to collect the following data:
Distance along transect in metres, using a piece of string marked at 1 metre intervals. Each plant located on or near the transect will be recorded.
Estimated height of plant in metres, using a meter ruler.
You should record the data collected on a table, like so:
How to Plot Data on a Profile Diagram
How to collect Abiotic Data in a Stratified forest
You will also be collecting the following abiotic data at Arataki, using a lux meter.
The table below shows what your abiotic data could look like.
Note that if you want to estimate the conditions in the emergent layer, you can’t climb up a 30 metre high tree, or you can’t go up a very tall building. But you can place your measuring device out in the open, on the ground that’s not shaded by anything, to mimic emergent layer conditions.
To estimate the conditions in the shrub layer, you could stand in the forest and hold your measuring device to about 2 metres above ground.
And to estimate the conditions on the ground layer, you could just place our measuring device in the forest, on the ground.
Concept 5: Adaptations to Abiotic Factors
Success Criteria & Vocabulary
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I can describe the adaptations plants have to get enough light for photosynthesis.
I can describe the adaptations plants have to minimise water loss (transpiration).
I can describe the adaptations plants have to withstand the wind.
Click this drop-down menu to see the list of Vocabulary.
Abiotic factor: Physical conditions in an ecosystem.
Adaptation: Any inherited trait that helps an organism survive in its habitat.
Buttress roots: Large, wide roots that prevent the tree from falling over.
Chlorophyll: Green molecule that absorbs light energy from the sun.
Chloroplast: Organelles found in plant cells that are the site for photosynthesis.
Desiccation: Drying out.
Diffusion: Movement of molecules, such as oxygen and carbon dioxide, from an area of high concentration to an area of low concentration.
Ecological niche: Functional position of an organism in its environment; way in which organisms survive in their environment.
Emergent layer: Uppermost strata in a stratified forest, comprising of the tallest trees that ‘stick out’ of the forest canopy.
Guard cells: Pair of cells responsible for opening and closing the stomata.
Koru: Structure that unfurls to reveal pinnate fronds. Allows tree ferns to grow upwards.
Lignin: Molecule that greatly strengthens cell walls of plants, especially those in trunks of tree ferns.
Osmosis: Movement of water molecules from an area of high concentration to an area of low concentration.
Photosynthesis: Process by which plants use light, water, and carbon dioxide to produce glucose and oxygen.
Physiological adaptation: Internal processes in an organism that help it survive in its habitat (type of adaptation).
Pinnate: Compound leaf that maximises surface area. Leaflets arranged on either side of the stem, such as in ferns.
Shrub layer: Lower strata in a stratified forest, comprising of bush species.
Stomata: Tiny holes on the underside of a leaf where carbon dioxide and water vapour can enter and exit the leaf.
Strata: One of a number of layers in a stratified forest.
Structural adaptation: Physical traits that help an organism survive in its habitat (type of adaptation).
Sub-canopy layer: Middle strata in a stratified forest, comprising mostly of tree ferns.
Transpiration: Process by which water vapour evaporates from plant leaves.
Waxy cuticle: Outer layer covering the leaves and stems of all plants. Has a protective role as well as reduces transpiration.
Tasks
Learn the 23 keywords using Quizlet:
Concept 5: Support Notes
Plants have Different Adaptations to occupy Different Niches
Remember this from Concept 3?
Stratification:
- Increases the number of niches available, which reduces interspecific competition (link this back to Gause's competitive exclusion principle).
- Increases the number of species in a forest community, which increases biodiversity, and makes the forest ecosystem more robust.
Having many STRATA creates many NICHES to be occupied. Plants occupying different niches need to have different ADAPTATIONS. For example, trees in the EMERGENT layer and plants in the SHRUB layer must have different adaptations to occupy their different niches.
Because remember, Gause’s Competitive Exclusion Principle states that no two species can occupy the same exact niche and stably coexist - so plants must have different adaptations to occupy different niches.
Plant Adaptations that Allow for Photosynthesis
Plants need light, carbon dioxide, and water in order to PHOTOSYNTHESISE.
Photosynthesis is the process in which plants use light, water, and carbon dioxide to produce glucose and oxygen.
This glucose produced will go on to produce the energy plants need to grow and produce flowers and seeds for reproduction.
How does the plant obtain sunlight?
Plants have CHLOROPHYLL, which is the green molecule that absorbs light energy from the sun.
Chlorophyll is a PHYSIOLOGICAL ADAPTATION because it’s an internal trait, it comes from inside the cells.
Chlorophyll molecules are found in the CHLOROPLASTS. Chloroplasts are organelles found in plant cells, and are the location for PHOTOSYNTHESIS.
In the picture to the right, you can see individual plant cells, and inside the plant cells are many chloroplasts (these circle blobs). And they’re green because they contain many chlorophyll molecules.
How does the plant obtain water?
Water is absorbed by the roots of the plant through a process called OSMOSIS, the movement of water molecules from an area of high concentration to an area of low concentration. Plant roots are a STRUCTURAL ADAPTATION.
How does the plant obtain carbon dioxide?
Carbon dioxide from the air enters through tiny holes on the underside of a leaf called STOMATA through a process called DIFFUSION, the movement of molecules from an area of high concentration to an area of low concentration.
Stomata are a structural adaptation. They can actually open and close, depending on the physical conditions outside. When stomata open, CO2 enters the plant and water vapour exits; when the stomata close there’s no movement in CO2 and water vapour.
Plant Adaptations that Reduce the Rate of Transpiration
TRANSPIRATION is the process by which water vapour evaporates from plant leaves. It helps the plant draw water up from its roots. But too much transpiration is not a good thing. So, all plants need to have ADAPTATIONS to reduce the rate of transpiration, to slow down water loss from leaves.
Adaptation 1: Waxy cuticle around stems and leaves
All plants have a WAXY CUTICLE around stems and leaves. The waxy cuticle helps seal in water. It also protects plants from heat, so some plants have a thicker waxy cuticle than others, kind of like layers of clothing.
For example succulent plants are adapted to withstand drought conditions, so they have very thick, very obvious waxy cuticles. You can clearly see them when you snap a succulent leaf and pull one part of the leaf against the other, peeling away the cuticle. It covers the leaf like Glad-wrap, and holds all of that glistening moisture of the plant in, so the plant doesn’t dry out or DESICCATE in drought conditions.
The waxy cuticle is also a thick transparent layer. It needs to be transparent so that it doesn’t block the sunlight from reaching the CHLOROPLASTS and being captured by green CHLOROPHYLL.
Adaptation 2: Guard cells of stomata open and close, depending on the conditions.
All plants have STOMATA - the holes and only passageway for CO2 and water vapour to leave the plant leaf. The stomata just describes the hole. It’s the GUARD CELLS that actually do the opening and closing of stomata to control the rate of TRANSPIRATION. Guard cells close the stomata when the sun is out to prevent transpiration, and guard cells open the stomata at night to allow CO2 to enter the leaf.
Adaptation 3: Reduced number of stomata
Some plants may even reduce the number of stomata, especially if they’re in hot environments, like desert cacti.
In these pictures, you can see the single layer of plant cells that are directly inside the waxy cuticle layer. You can see tiles of normal plant cells, and spaced between those are guard cells that open and close the stomata. Guard cells are doing the opening and closing, whereas the stomata is the actual hole where CO2 and water vapour move across.
Adaptations of Plants in the Emergent, Sub-canopy, and Shrub Layers
In your report, focus on writing about adaptations to abiotic factors in these 3 strata: EMERGENT, SUB-CANOPY, and SHRUB layers.
Describe what adaptations plants in these STRATA have, to help them withstand the ABIOTIC FACTORS in that strata.
To the right:
Adaptations in the Emergent Layer
Adaptations in the Sub-canopy Layer
Adaptations in the Shrub Layer
Concept 6: Adaptations to Biotic Factors
Success Criteria & Vocabulary
Click this drop-down menu to see the Success Criteria.
I can explain mutualism using examples from Arataki.
I can explain commensalism using examples from Arataki.
I can explain exploitation using examples from Arataki.
I can explain competition using examples from Arataki.
Click this drop-down menu to see the list of Vocabulary.
Adaptation: Any inherited trait that helps an organism survive in its habitat.
Browsing: Type of exploitation where an animal eats high-growing plants.
Canopy layer: Upper strata in a stratified forest, comprising of tall trees that make up most of the forest canopy.
Commensalism: Interrelationship where one species benefits from the relationship, while the host species is unaffected.
Epiphyte: Type of plant that grows on another plant (host) in the canopy or emergent stata to access more light. Has a commensalism relationship with its host.
Exploitation: Interrelationship where one species benefits at the expense of the other.
Foliage: Leaves of a plant.
Germination: Process by which an organism grows from a seed.
Host: Plant used by epiphyte to access more light. Has a commensalism relationship with the epiphyte.
Interspecific competition: Type of competition between individuals from different species.
Intraspecific competition: Type of competition between individuals from the same species.
Mutualism: Interrelationship where both species benefit from the relationship.
Physiological adaptation: Internal processes in an organism that help it survive in its habitat (type of adaptation).
Seedling: Young plant that developed from a seed.
Structural adaptation: Physical traits that help an organism survive in its habitat (type of adaptation).
Tasks
Learn the 15 keywords using Quizlet:
Concept 6: Support Notes
In your assessment report, I would like you to include an explanation of at least 3 different species interrelationships. Make sure you explain each interrelationship well, by covering the following points:
What is the relationship?
Who benefits/is harmed? Why?
What ADAPTATIONS enable this?
Examples of Mutualism
Rimu/Kahikatea and the Kererū
Rimu and Kahikatea produce fleshy seed cones that are brightly coloured (STRUCTURAL ADAPTATION) to attract birds like Kererū. Kererū have good eyesight (PHYSIOLOGICAL ADAPTATION).
This is MUTUALISM because both species benefit. Kererū benefit from food, while Rimu and Kahikatea benefit from seed dispersal.
Nīkau and the Kererū
Nīkau produce berries that are brightly coloured (structural) to attract birds like Kererū.
This is MUTUALISM because both species benefits. Kererū benefit from food, while Nīkau benefit from seed dispersal.
Perching lily and the Kererū
Perching lilies produce berries that are brightly coloured (structural) to attract birds like Kererū.
This is MUTUALISM because both species benefit. Kererū benefit from food, while the perching lily benefits because their seeds get pooped high up in trees. This is important because perching lily seeds only germinate in areas of high light intensity.
Nīkau/Perching lily and the Tui
Nīkau and perching lilies produce pale yellow flowers (STRUCTURAL ADAPTATION) that attract pollinator birds like Tui.
Tui benefit from drinking nectar (PHYSIOLOGICAL ADAPTATION from plant).
Nīkau and perching lilies benefit as tui bring pollen from flowers from one plant to another plant (behavioural) → sexual reproduction. So it is MUTUALISM.
Example of Exploitation - Herbivory - Browsing
Northern rātā + Possum
Possums have a strong preference for browsing on Rātā leaves, flowers, and fruit. It constitute 30% of its diet.
Northern rātā cannot tolerate. A mature tree can be killed in three years with intensive browsing. This is EXPLOITATION because one species benefits at the expense of another.
Example of Commensalism
Rimu and Perching lily
Perching lilies benefit from ‘perching’ on the branches/trunks of rimu trees because they can obtain high light intensity. The host rimu is not affected.
The perching lily doesn’t spend energy sending roots to the ground so:
Root system at the centre of the plant. Makes its own soil.
Dead insects & leaves fall into the centre of the plant and decomposes. Adds to the soil created by the plant. Provides nutrients for the plant.
V-shaped leaves act like a funnel and direct water into central root system.
Perching lilies have very tough leaves that don’t wilt easily in hot, low humidity conditions, so the V-shaped leaves can act like a funnel in dry conditions.
This is COMMENSALISM because one species benefits while the other is unaffected.
Example of INTRAspecific Competition
Many Nīkau Seedlings
Kererū can poop out several nīkau seeds in the same area. Nīkau SEEDLINGS that GERMINATE in the same area are in direct competition for light, space, water, and nutrients.
From these seedlings, only one will reach the CANOPY (if any).
This INTRASPECIFIC COMPETITION is because multiple individuals from the same species are competing for the same resources.
Example of INTERspecific Competition
Various Species of Seedlings
Nīkau SEEDLINGS also compete for light, water, space, and nutrients with seedlings from other species that GERMINATE in the same area.
They cannot all survive to adulthood. Few individuals will outcompete all others.
This is INTERSPECIFIC COMPETITION because multiple individuals from different species are competing for the same resources.
Rimu and Northern rātā: Commensalism AND Interspecific Competition
Northern rātā seeds can GERMINATE on the ground, but most seeds germinate on tree branches and become EPIPHYTES.
It benefits by being exposed to more sunlight, while the HOST tree (E.g. rimu) is not harmed.
As an epiphyte, Northern rātā have tuber-like swellings on its roots to help with water storage.
Eventually, the Northern rātā epiphyte sends roots down to the ground. The roots encircle the trunk of the host plant (E.g. rimu) and develops into a massive trunk and root system. FOLIAGE overshade the host.
The Northern rātā is now directly competing with its HOST (E.g. rimu) for light, water, and nutrients from the soil.
Concept 7: Gause's Principle (EXCELLENCE)
Success Criteria & Vocabulary
Click this drop-down menu to see the Success Criteria.
I can discuss Gause’s Principle using the Rimu, Northern rātā, and Perching lily examples.
I can discuss Gause’s Principle in terms of forest stratification.
Click this drop-down menu to see the list of Vocabulary.
Adaptation: Any inherited trait that helps an organism survive in its habitat.
Competition: Interrelationship where species/individuals compete for the same resources.
Ecological niche: Functional position of an organism in its environment; way in which organisms survive in their environment.
Ecosystem: A community of organisms AND physical conditions interacting as a system.
Epiphyte: Type of plant that grows on another plant (host) in the canopy or emergent stata to access more light. Has a commensalism relationship with its host.
Gause's competitive exclusion principle: Two different species CANNOT occupy the same ecological niche in a habitat and coexist stably.
Habitat: Place in which an organism lives.
Host: Plant used by epiphyte to access more light. Has a commensalism relationship with the epiphyte.
Interspecific competition: Type of competition between individuals from different species.
Strata: One of a number of layers in a stratified forest.
Stratification: Pattern of vertical layering in a forest community.
Tasks
Learn the 11 keywords using Quizlet:
Concept 7: Support Notes
In previous concepts you learned about:
GAUSE'S PRINCIPLE which states that two different species cannot occupy the same ECOLOGICAL NICHE in a HABITAT and stably coexist. Two species with the same niche will directly COMPETE for the same resources, and one species will ultimately outcompete the other.
How the Northern rātā starts off as an EPIPHYTE, using the HOST tree rimu to get access to more sunlight at a higher layer in the forest.
But then it sends down roots to the ground and begins to compete with the host rimu tree for sunlight, water, and nutrients from the soil. We’ve got two different species occupying the same ecological niche, and according to Gause’s Principle, two species occupying the same ecological niche can’t stably coexist. According to Gause’s Principle one species will outcompete the other.
Northern Rātā Outcompetes Rimu
Usually the host rimu tree is old, and is definitely much older that the Northern rātā around it. The Northern rata ends up out-living the rimu tree. This is because the younger Northern rātā tree is more robust, and can outcompete the rimu. As the host tree dies and the Northern rātā takes over the space and replaces the Rimu in its role in the ecosystem.
How come the young epiphyte version of Northern rātā doesn't compete with the host rimu?
Rimu and the EPIPHYTE version of Northern rātā are able to coexist stably because they occupy different NICHES. Specifically, Northern rata have tuber-like swellings on its roots that help with water storage, and so it’s not in direct COMPETITION with its rimu tree HOST for water.
But once the Northern rata establishes a complex root system, the Northern rata and its rimu host now occupy the same ecological niche - they are now in fierce and direct competition. They cannot stably coexist. The Northern rata has ADAPTATIONS that give it an advantage, allowing it to outlive and outcompete its rimu host.
How come epiphytes like the perching lily don’t compete with their rimu host?
Perching lilies and rimu occupy different ecological NICHES. And because they occupy different niches, they are not in direct COMPETITION with one another, and they can stably co-exist.
They don’t occupy the same ecological niche because perching lilies and rimu trees don’t absorb water and nutrients from the same soil. Rimu trees absorb water and nutrients from the soil on the ground, whereas perching lilies absorb water and nutrients from soil that has accumulated up in tree trunks or branches where the perching lily is. Remember that the perching lily has a central root system, a structural adaptation, that water is directed into by the V-shaped leaves that act like a funnel.
Insects breed and die within this central root system, and leaves fall and decompose within this central root system to provide the perching lily with its nutrients. As a result of these root and leaf adaptations, the perching lily doesn’t have to send roots to the ground, and therefore it doesn’t have to compete with the HOST rimu for water and nutrients. Because they occupy different niches, the perching lily and rimu host can coexist stably.
Stratification is Important because it Increases Biodiversity
I’d like to conclude these series of lessons by going back to why STRATIFICATION is so important. Stratification is the vertical layering in a forest community where each layer or STRATA has a different microclimate. This increases the number of NICHES available to be occupied. Because there are more niches, there is relatively less INTERSPECIFIC COMPETITION. Because there is less interspecific competition, more species can coexist stably. This increases the number of species in a forest community and increases BIODIVERSITY.
High levels of biodiversity is an awesome thing to have because it makes an ecosystem more resilient to changes in the climate. Forests with high levels of biodiversity are more likely to survive and recover from a disastrous event than a forest with low levels of biodiversity.