APES Notes 2.7 - Ecological Succession

Summary

In this educational video, Mr. Smeeds explores ecological succession, a process of change in forest ecosystems. He distinguishes between primary and secondary succession, detailing how pioneer species like moss and lichen initiate growth on bare rock in primary succession, while grasses and wildflowers take the lead in secondary succession where soil already exists. The video progresses through the stages of succession, from early to late, explaining how soil depth and nutrient richness develop over time, allowing for larger, slower-growing trees like maples and oaks to eventually dominate. The video concludes with a data analysis exercise, challenging viewers to determine the successional stage of spruce trees based on a graph showing their population changes post-glacial retreat.

Takeaways

• 🌿 Ecological succession is a series of predictable changes that occur in a forest ecosystem, involving the gradual replacement of one community of plants and animals by another over time.
• 📌 There are two types of succession: primary and secondary. Primary succession starts on bare rock with no soil, while secondary succession begins in areas where soil is already present but the existing plant community has been removed by a disturbance.
• 🌱 In primary succession, pioneer species like moss and lichen colonize the area, breaking down rocks and initiating soil formation through the secretion of acids.
• 🌼 Secondary succession starts with pioneer species like grasses, sedges, and wildflowers, which are quick to grow and tolerant of full sunlight, colonizing areas where the previous plant community has been disturbed.
• 🌲 The process of succession is marked by different stages, each dominated by species adapted to the conditions of that stage, progressing from early to mid to late successional species.
• 🌳 Pioneer species are characterized by wind or animal dispersal, rapid growth, and the ability to grow in nutrient-poor conditions, such as bare rock or recently disturbed soil.
• 🌳 Mid-successional species, like shrubs and fast-growing trees, require deeper, more nutrient-rich soil and can tolerate full sunlight but take longer to grow and establish.
• 🌳 Late successional or climax community species are large, slow-growing trees that are tolerant of shade and require deep, nutrient-rich soil to anchor their roots, often taking hundreds of years to reach maturity.
• 🔍 The video emphasizes the importance of understanding the characteristics of different successional stages and species to predict and manage ecological changes.
• 📊 The practice task involves analyzing data, such as a graph showing the number of spruce trees over time, to determine whether a species is early, middle, or late successional based on its population trends.

Q & A

What is ecological succession?

Ecological succession is a series of predictable changes that occur in an ecosystem over time, involving the gradual replacement of one community of plants and animals by another.

What are the two types of ecological succession?

The two types of ecological succession are primary succession and secondary succession.

How does primary succession begin?

Primary succession begins on bare exposed rock where no soil exists. It starts with pioneer species like moss and lichen that can grow directly on rocks and break them down to form soil.

What role do moss and lichen play in primary succession?

Moss and lichen play a crucial role in primary succession by secreting acids that break down rocks, releasing nutrients needed for their growth and eventually leading to soil formation.

What is secondary succession and how does it differ from primary succession?

Secondary succession occurs in an area that already has established soil but has lost its plant community due to a disturbance. It differs from primary succession in that it starts with grasses, sedges, and wildflowers rather than moss and lichen.

What are pioneer species and why are they important in succession?

Pioneer species are the first species to colonize an area during succession. They are important because they can grow in harsh conditions, help break down rocks or enrich soil, and create conditions for other species to grow.

What are mid-successional species and what characteristics do they have?

Mid-successional species appear after pioneer species have built up the soil. They are typically faster-growing, larger plants like shrubs and small trees that can tolerate full sunlight and require deeper, more nutrient-rich soil.

How do late successional or climax community species differ from pioneer and mid-successional species?

Late successional or climax community species are the last to colonize an area. They are large, slow-growing trees that can tolerate shade and require deep, nutrient-rich soil. They indicate the end of the succession process.

Why does secondary succession occur faster than primary succession?

Secondary succession occurs faster than primary succession because it starts with established soil, which already contains nutrients and organic matter, speeding up the process of plant colonization and growth.

What is the role of disturbances in ecological succession?

Disturbances, such as wildfires, storms, or human activities, can initiate secondary succession by clearing away existing vegetation and creating space for pioneer species to colonize and start the succession process anew.

How can data analysis skills be applied to understand ecological succession?

Data analysis skills can be applied to ecological succession by examining trends in species populations over time, such as the graph showing the number of spruce trees per hectare after a glacial retreat, to determine the successional stage of a species.

Outlines

00:00

🌿 Ecological Succession Overview

Mr. Smeeds introduces the concept of ecological succession, focusing on its definition and impact on ecosystem structure. He explains the two types of succession: primary and secondary. Primary succession begins on bare rock with no soil, where moss and lichen pioneer the ecosystem by breaking down rocks and initiating soil formation. Secondary succession occurs in areas with established soil but where the plant community has been removed by a disturbance like wildfire or human activity. Here, pioneer species such as grasses, sedges, and wildflowers quickly colonize the area. The video aims to develop data analysis skills by examining trends in ecological data.

05:00

🌱 Successional Stages and Species Characteristics

The paragraph delves into the stages of ecological succession, detailing the characteristics of pioneer, mid-successional, and late successional species. Pioneer species, like moss and lichen in primary succession or grasses and wildflowers in secondary succession, are the first to colonize an area. They are wind or animal-dispersed and can grow in harsh conditions. Mid-successional species, such as shrubs and fast-growing trees like pines and cherries, arrive after the soil has been enriched by the pioneer species. Late successional or climax community species, including large, slow-growing, and shade-tolerant trees like maples and oaks, require deep, nutrient-rich soil and take the longest to establish. The paragraph emphasizes the importance of soil development over time, which is crucial for supporting the growth of these large trees.

10:01

🔍 Analyzing Data on Spruce Trees in Succession

In the final paragraph, the focus shifts to practicing data analysis skills. A graph is presented showing the number of spruce trees per hectare over time following a glacial retreat. The audience is prompted to determine whether spruce trees are early, middle, or late successional species based on the graph. The analysis should consider the typical characteristics of each successional stage to make an informed conclusion about the spruce trees' role in the ecosystem's development.

Keywords

💡Ecological Succession

Ecological succession refers to the process of change in the species structure that occurs in an ecosystem over time. It is the main theme of the video, as it discusses how different species dominate at various stages of an ecosystem's development. The video explains two types of succession: primary and secondary, each with distinct starting conditions and progressions.

💡Primary Succession

Primary succession is a type of ecological succession that occurs in an environment that has never been vegetated before or where the previous vegetation has been completely removed, leaving only bare exposed rock. The video describes how it starts with pioneer species like moss and lichen that can grow directly on rocks, breaking them down to form soil.

💡Secondary Succession

Secondary succession is the process that occurs in an area where the soil is already in place but the existing vegetation has been removed by some disturbance, such as wildfire or human activity. The video explains that this type of succession starts with grasses, sedges, and wildflowers, which are quick to colonize and help in rebuilding the ecosystem.

💡Pioneer Species

Pioneer species are the first organisms to colonize an area during ecological succession. They are typically hardy species that can grow in harsh conditions. In the video, moss and lichen are cited as pioneer species in primary succession, while grasses, sedges, and wildflowers are examples in secondary succession.

💡Soil Formation

Soil formation is a critical aspect of ecological succession, as it provides the medium for plant growth. The video describes how pioneer species contribute to soil formation by breaking down rocks and adding organic matter. This process is particularly emphasized in primary succession, where no soil initially exists.

💡Mid-Successional Species

Mid-successional species are those that appear after the pioneer species have established a basic soil structure. These species are typically faster-growing and can tolerate full sunlight. The video mentions shrubs and smaller trees like pine and cherry as examples of mid-successional species that can grow in the slightly enriched soil left by pioneers.

💡Late Successional Species

Late successional species, also known as climax community members, are the last to colonize an area. They are characterized by being large, slow-growing trees that can tolerate shade and require deep, nutrient-rich soil. The video gives examples such as maples and oaks, which take a long time to grow and are indicative of a mature ecosystem.

💡Disturbance

Disturbance in the context of the video refers to events that disrupt an ecosystem, clearing the way for secondary succession. Examples include wildfires, windstorms, or human activities like deforestation. The video explains that such disturbances leave the soil open for pioneer species to colonize and start the succession process anew.

💡Chemical Weathering

Chemical weathering is a process where rocks are broken down by chemical reactions, often catalyzed by organisms like moss and lichen. In the video, it is mentioned as a key mechanism in primary succession, where the secretion of acids by these pioneer species helps to break down rocks and release nutrients necessary for the formation of soil.

💡Data Analysis Skill

The video mentions practicing a data analysis skill at the end, which involves looking at a set of data and drawing conclusions based on observed trends. This skill is crucial for understanding ecological patterns and making informed decisions about environmental management. The video does not provide specific data but implies that such analysis would be an important part of studying ecological succession.

Highlights

Ecological succession is a series of predictable changes in a forest ecosystem.

There are two types of succession: primary and secondary.

Primary succession begins on bare exposed rock with no previously formed soil.

Moss and lichen are pioneer species in primary succession, growing directly on rocks.

Moss and lichen secrete acids to break down rocks and release nutrients.

Secondary succession starts in an area with established soil but cleared of plants by a disturbance.

Pioneer species in secondary succession include grasses, sedges, and wildflowers.

Succession is marked by the types of plant species that dominate each stage.

Pioneer species are followed by mid-successional species that require deeper, richer soil.

Mid-successional species include shrubs, bushes, and fast-growing trees like pine and cherry.

Late successional or climax community species are large, slow-growing trees tolerant of shade.

Maples and oaks are examples of late successional species.

Soil depth and richness are critical for the establishment of climax community species.

Primary succession can occur after volcanic eruptions or glacial retreats.

Secondary succession is faster than primary succession but can still take over 150 years.

The process of secondary succession is jump-started by disturbances like forest fires that enrich the soil.

Data analysis skill involves drawing conclusions from trends in data, such as the number of spruce trees over time.

Transcripts

hey everybody it's mr smeeds and today

we'll be covering topic 2.7

which is ecological succession our

objective for today's video is to be

able to describe what ecological

succession is

but also to describe the different

effects that ecological succession has

on an ecosystems

structure the skill that we'll be

practicing at the end of today's video

is a data analysis skill

and it will involve looking at a set of

data and trying to draw conclusions

based on the trends we see in those data

so ecological succession refers to a

series of predictable changes

that occurs in a forest ecosystem

there's two different types

and the first type is referred to as

primary succession

in primary succession the area has only

bare exposed

rock so there's no previously formed

soil

the process involves moss and lichen

which are species of plants that have

their seeds or their spores dispersed by

the wind

so the wind carries in those seeds and

moss and lichen are actually uniquely

adapted to grow directly on

rocks they're able to break the rocks

down by secreting acids

which releases the nutrients that they

need to grow and so if we look at a

diagram what we'll see here

is that we start with this bare rock

then as the wind carries in those seeds

the moss and the lichen are able to

colonize or start going on the rock

that breaks the rock down into smaller

bits and eventually forms soil

over time in secondary succession on the

other hand

we're starting in an area that already

has previously established soil

but the plants in that ecosystem have

been cleared away by some sort of large

disturbance

so that could be a wildfire could be a

wind storm

or even a human disturbance like

clearing an area of land

to use for agriculture we're also going

to see

some pioneer species or some initial

species move in

similar to in primary succession but the

big difference

is that these first species to arrive

are going to be grasses

sedges and wildflowers and these are

species that are quick growing

and they have their seeds dispersed by

the wind or by animals

so if we look at a diagram of secondary

succession you'll notice the big

difference

is that there is established soil

already existing

it's just that a disturbance has cleared

out the existing plant community

and that leaves the soil open for these

pioneer species to come in

and start to take up root now we'll talk

about the basic steps of succession

which are common to both primary and

secondary so really the only difference

between those two

is the starting stage whether or not

there's already established soil

after that it's relatively the same

process so it's important to understand

that these stages of succession or this

process is marked

by which types of plant species dominate

the ecosystem during each stage

and that's because different species are

adapted to the different conditions

that occur in each phase or each stage

of succession

so we always start with pioneer or early

successional species

these are the first species to appear in

the area

and they are able to become established

either on the bare rock

if we're talking about primary

succession or in the recently disturbed

soil if we're talking about secondary

succession

they share some characteristics which is

that they are dispersed by the wind

meaning that their seeds are often

carried by the wind to the area

or by animals who may eat the seeds and

then disperse them

in their waste or the seeds may get

stuck to the animal's fur so we have a

picture here of the wind blowing seeds

to help us remember

that pioneer species need to be able to

be dispersed by the wind

or by animals some examples would be

moss and lichen

if we're talking about bare rock that

occurs in primary succession

or wildflowers plants that produce

berries like raspberries or grasses and

sedges if we're talking about secondary

succession

pioneer species are always followed by

mid-successional species

mid-successional species appear after a

couple years where the pioneer species

have built up the soil

so it's a little bit deeper and a little

bit more nutrient-rich

and so what happens is those pioneer

species as they grow and die

grow and die their biomass or their

organic matter gets added to the soil

and that increases the richness of the

soil and increases the depth over time

which eventually enables the mid

successional species to come in

those mid-successional species share

some characteristics as well

they're going to be fast growing they're

going to be a little bit larger than the

pioneer species

so they're going to grow a little bit

slower they're typically going to need a

little bit deeper soil with more

nutrients

than those pioneer species were able to

tolerate but they're also

able to be tolerant of full sunlight and

that's because there's no shade in the

ecosystem yet

if we look at a diagram we can see here

that it takes some time for the shrubs

and the smaller trees which are

mid-successional species to arrive

because those pioneers have to build up

that soil depth for them

and they're also just species that grow

a little bit more slowly so these

trees you know take years to start to

develop and so they're not going to be

seen

right you know the first or second year

after a disturbance

if we want some examples to remember we

can think of shrubs

and bushes you know things that take a

couple of years to start developing

same thing with trees that are fast

growing so pine

and cherry are two great examples of

mid-successional species

and then we have late successional

species which as their name implies

are the last species to colonize or to

start going in an area

we also sometimes call these members of

a climax community

because a climax is at the end of the

transition and so it takes them quite a

while to arrive

so they are going to be able to start

growing after the soil has been deepened

and enriched further by this process of

the early and mid successional species

dying

and having their biomass and their

nutrients added to the soil

all of these late successional species

share some characteristics

those would be that they are large slow

growing trees

that are tolerant of shade now they take

a long time to grow and develop but

they're able to develop in the shade

of these mid-successional species that's

an important characteristic of them

and they need deep nutrient-rich soil to

anchor their roots because they're

oftentimes

very large trees that can grow to

hundreds of feet tall

maples and oaks are great examples as

well as other large trees that reach

heights of hundreds of feet

and if we look at this diagram here what

i like about this is it helps us

remember

that we need this soil to be built up

over time so we would not have deep

enough soil

you know a couple years or even 10 or 20

years after primary succession

it takes hundreds of years to get soil

deep enough to support the roots of

these

large shade tolerant and slow growing

trees

and so again we would call this here a

climax community because it's at the

end of succession it takes hundreds of

years for the soil to be built up

and for these trees to grow and emerge

from the canopy

of the mid-successional trees so as a

reminder

that early mid to late successional

process is common to both

primary and secondary succession

the main difference is just the starting

material of those two

and so primary succession you'll

remember starts from fair rock

this is an ecosystem that has not

previously had soil present

and this can also often occur after a

volcanic eruption

or after a glacial retreat that's

because those are both events that will

leave

bare rock without soil on top of it

and so very important to remember that

moss and lichen are the colonizers or

the pioneer species

in primary succession and that's because

their spores or their seeds

are easily blown in by the wind but then

also they're uniquely adapted to grow

on rock they have a unique adaptation

that enables them to secrete acids

into the rock those acids will actually

break down or chemically weather the

rock

so that the minerals in those rocks that

have the nutrients that the moss and

like you need will be released

and those moss and liking can then

absorb the nutrients into their bodies

so these are things like potassium

phosphorus and nitrogen

and again this is really critical to

primary succession

starting without this chemical

weathering we wouldn't have the

formation of soil

so as the rock starts to break down

there are smaller bits of rocks

that mix together with the dead biomass

or the dead organic matter from

the moss and the lichen as they

eventually die and all of that kind of

miscon

mixes together and forms this initial

rocky

shallow soil so if we look at this

picture here

we can see this is a lava flow where

there is exposed rock

after the lava has cooled and it's going

to be colonized first by these lichen

and then we have this diagram that we

did look at before but it's a great

reminder that we have this bare rock

and then eventually the rock is starting

to be broken down by the secretion of

the acid by moss and lichen

and eventually we get just the very

beginnings of really rocky shallow soil

here

and then from there the process is the

same as we've discussed we have our

pioneers

our early successional species followed

by our mid-successional species

followed by our late successional or

climax community species

and finally we'll wrap up by focusing in

a little more detail on secondary

succession

so remember this isn't an area where

there's already established soil

but most of the plant community has been

removed by some sort of disturbance

so pioneers are still going to be the

first species to arrive in this area

and they're going to be plants that have

their seeds dispersed either by the wind

or by animals and they're going to be

fast growing and sun tolerant

but they're going to be wild flowers

grasses and sedges

as opposed to the moss and lichen who

are our pioneers or colonizing species

in primary succession important to point

out

that the soil is already established

here and sometimes it's even enriched if

the disturbance was a forest fire

now that's because forest fires burned

down the previous plants that were in

the area and they return a lot of the

nutrients that those plants have been

storing

back to the soil so soil in the wake of

a forest fire is often actually very

nutrient rich

and really jump starts the process of

secondary succession

so if we look at this diagram here i

know we've seen this one before but it's

a great reminder that we do start with a

disturbance of some sort

often a forest fire but it could be a

human disturbance like clearing land for

agriculture

or even just a wind storm or a flood

anything

that dramatically reduces the plant

community and basically

enables these pioneer species to come in

and dominate so remember our pioneer

species in this case are going to be

grasses

sedges weed species that have their

seeds to source by the wind

they're also going to be very fast

growing they're going to be full sun

tolerant so they can handle that full

sunlight

they colonize the area they eventually

die and build up the soil a little bit

deeper for our mid successional species

who are faster growing trees bushes and

shrubs and then finally we have our late

succession or our climax community

species

i do want to point out that this process

of secondary succession is faster than

primary succession

but it can still take upwards of 150

years

for this climax community reform that's

because these late successional species

are very slow growing

they need deep roots with a lot of

nutrient-rich soil to

nourish those huge trees that are going

to grow and anchor them and so it

is still a relatively slow process to

reach

a climax community so for practice frq

2.7 today we're going to practice the

skill

of analyzing data and drawing

conclusions from those data

so we have here is a graph showing the

number of spruce trees per hectare

in an ecosystem as time goes on after a

glacial retreat

so based on this graph i want you to

explain whether or not you think the

spruce tree

is an early middle or late successional

species and remember that with explain

you need to justify your reasoning for

this