CH 1 5 Soil + Vegetation Source

>[NICOLE KJERSTEN]
So we just spent a lot of time

in our last lecture talking about soils

and how the soil profiles change
across the state, depending on the biome.

So remember, soils are formed both
by the historical geological influences,

but also by the vegetation
that kind of forms of feedback, if you will.

The soil type supports
a certain amount of vegetation,

and that vegetation
contributes to the soil type.

And all of this is really
important for natural history,

and one way that it's important
is that soil actually helps us.

By studying the soil,

it actually helps us understand what organisms
(especially plant organisms)

were present in Minnesota in the past.

And so soil cores are really important tools

to understand
the natural history of the past.

This is a picture of folks taking a core
within a lake here in Minnesota.

Sometimes they take cores in the winter
so that they can stand on the ice

and stabilize themselves
when they're taking those cores.

But other times, there's different
devices that will help with the cores.

And this is a picture of some
different examples of cores,

and what you can see
are these different layers,

and of course, we know by now
that layers are an indication

of different aspects of geological
history and glacial activity

that caused different deposits
at different time periods.

And so what happens
is that within these layers,

there's not only
the inorganic part of the soil,

but there's also the organic parts.

And so this would include pieces
of wood or dead animals,

insect parts, organic material,

but also, we find fossils inside
of these sediment layers

and fossils that you might not quite
think about when you think about fossils.

And so I want to talk about
ways that plants disperse.

They will-- When plants reproduce,

they package their gametes either
into microscopic spores or pollen.

Spores and pollen are not the same thing.

Ferns and mosses produce spores,

whereas the evergreen trees,
the deciduous trees,

and angiosperms are the flowering plants,

they actually produce pollen.

And this differentiation between
spores and pollen is important

because it's a reflection

of the evolutionary history
of plants through time.

Spores have been around
for a whole lot longer than pollen.

Pollen is an evolutionary adaptation
that arose that actually had a huge impact

in plants being able to live
in areas with less water.

Anyways, I digress.

Here is a picture of pollen
grains under the microscope.

And it turns out that pollen grains have
unique shapes, unique morphologies

that are indicative of
what species they are.

Here are some pictures
of fossilized spores or pollen,

and there's different layers here.

And so this top layer here is showing you
the spores of different species of ferns.

The second layer is showing you
the pollen of different conifer species.

And then here is an example

of just the diversity of shape and texture in
the fossilized pollen grains of angiosperms.

And so we can use observations of
the quantity and the type of pollen

to create a pollen record which tells us
how vegetation changes over time.

And so I want to walk through this graph.

I know it's a lot to digest, but I also
think it's really, really fascinating.

And so, again,
we're looking at the pollen grains

that have been preserved in
the different layers of a soil core.

And this is an example of a soil core
that was taken and analyzed

from Itasca State Park near
Itasca State Park in Minnesota.

And so let's start over here on the left,

where we have the depth
in feet of the soil core.

This particular soil core
is about 30 feet long,

meaning that they were able to take
an intact core from 30 feet in the ground up.

So you can imagine that soil core
has a lot of different layers,

and you can date those layers.

That's what these lines are showing here,
based on radioactive carbon isotopes.

So plant material, they have
different ratios of isotopes,

and you can take the isotope
that plants have when they're dead

versus when they're alive

and look at that ratio to determine
how old that plant material is.

And so what they were able to do is,

they can say at this line, this was
about just under 3,000 years ago.

This line was just under 4,000 years ago,
plus or minus 100 years,

up to around, at the deepest layer,
they're saying is around 11,000 years ago.

And what they can do
across these different layers is,

they can pull out all the pollen grains.

So you're sorting through that soil,

pulling out all the pollen grains
under a microscope

and identifying them and quantifying them.

And so if we go back over to the left here,
we get the total amount of pollen

and what they're dividing this
between tree pollen and herb pollen.

And herb pollen,
we're just going to reference that

as the flowering plants
that are not trees.

So grasses, ferns (which this should
be a spore, not a pollen, but that's okay).

And they've also defined these as,

like, the ragweed plant
that causes a lot of allergies.

A lot of us are allergic to ragweed.

And if you look at the left here,
[corrects self] sorry, the right here,

this would mean that there's 100% of
all of the pollen grades in that sample.

And if we look at
these different columns,

what we can see is that—

let's just focus on this
bottom layer for a moment.

Most of that bottom layer
is made up of tree pollen.

But then what we see over time is,

um, around, oh, just over 8,500 years ago,

we see a reduction in amount of tree pollen
and an increase in herb pollen,

and that shifted again after
around 4,000 years ago,

we see more tree pollen until present-day,
maybe this is probably 500 to 100 years,

we see the emergence of more herbs

and these are just individual profiles
for those different species.

And what I want you to take away from this

is that the presence and quantity
of vegetation, it changes over time.

It comes and goes, it ebbs and flows,

and we could correlate this
to a lot of different things,

some of which--some of those factors
being changes in climate and precipitation,

changes in temperature over time.

The amount of pollen or spores
that a plant produces

is also going to be influenced by factors

such as competition
with other organisms.

This was taken in a bog,
so it was taken in a wet area,

and it's going to be influenced

by what can make it and
actually disperse to that area.

And there's a lot of different
factors that can affect dispersal.

All right.

And I believe that's where
I want to end it for now.

So thank you very much,
and I'll see you in the next video.