This course surveys the diversity, structure and functioning of California’s ecosystems through time and the ways they have influenced and responded to human activities and stewardship. Topics include ecosystem drivers such as climate, soils, and land use history; human and ecological prehistory of the state; comparative marine, freshwater, and terrestrial ecosystem dynamics; and managed ecosystems such as range, fisheries and agriculture in California. The course also emphasizes important skills to understand as a scientist or consumer of scientific information, including data collection, natural history, and writing.
Franklin Point Dunes
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Из курса от партнера University of California, Santa Cruz
Ecosystems of California
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Erika ZavaletaProfessor
Ecology and Evolutionary Biology
[MUSIC]
I'm Erika Zavaleta and this is Ecosystems of California.
We're at Franklin Point between Half Moon Bay and
Santa Cruz on the California coast.
And the dune ecosystems at Franklin Point are a lot like many of the dunes in
California today.
Heavily affected by invasive plant species that have affected not only the native
plant and animal communities, but also the dynamics of the dune field themselves.
Let's go have a look at how it is that these dunes have changed in response to
the invasion, primarily of European beach grass, Ammophila arenaria.
Here's the Yellow bush Lupine, and it's past flowering.
And this individual is, so it's got it's little bean pods now.
It's going to seed.
Yellow Bush lupine.
Our typical shrubs as you get further into the back dunes in these dune fields
like here at Franklin Point.
So this is European Beach grass, Ammophila arenaria.
And it was actually introduced intentionally to
San Francisco in the 1860s.
And then later on down in the Pajaro Valley in the early- 9-teens.
It was introduced to stabilize dunes.
So, people knew what it was going to do.
It's native to Europe.
And it occur's all the way from Scandinavia down to the Mediterranean on
the coastal strand.
Here, in the California, in absence of all of its natural consumers and
pathogens, it does extremely well.
And Ammophila arenaria, or European beachgrass, it's kind of
a poster child for an invader that affects the ecosystem that it invades.
Because it not only changes the plant community,
but also really affects the geomorphology of these dunes.
So you can see that it forms these really, really dense stands.
And if you can imaging, being a beach strawberry, or
a little sand not being able to compete with this beach grass for
light, for space, and maybe also for soil resources.
This beach grass invades the four dunes.
It invades the dunes closest to the ocean,
which is also where you find the most dune adapted pioneer native species.
So there are at least six federally threatened or endangered species
that have been pushed out of many places by this invading beach grass.
Its growth habit is that it puts down these really, really deep roots, and
it spreads mostly by rhizomes.
Its seeds don't do very well in the shifting sand, but
it's able to spread really fast through those rhizomes.
It can go up to a meter every three months.
So, it can cover really really big areas quickly.
And with those deep rhizomes and all of these above ground biomass,
it captures a lot of sand blowing in from the beach and it stabilizes the sand.
The result is that the dune ridges get high and
steep like the ones you can see over here.
And the four dune facing the beach also gets really steep and unstable.
That makes that slope less usable by native plants like the beach bur.
And it also makes the dunes at the front of the dune field
block sand movement to the back.
So you get to the back dunes and there isn't sand coming in there so
much anymore.
And so those communities gradually shift away from the dune adapted
species to the more common grassland species, coastal sage shrub species.
And then invasive species of the inland terrestrial areas that typify
a lot of California's coast.
There are a lot of efforts underway to control European beach grass.
It has spread along most of the Pacific coast of the United States.
And it's especially dominant between Santa Barbara and the Pacific Northwest.
It's a really expensive plant to control.
Because it's so widespread, unless a more cost-effective way emerges,
it's probably never going to get eradicated.
So controlling European beach grass is all about heavy labor at this point.
It involves a lot of digging.
Because the first step is to try to dig up the entire rhizosphere,
all of those deep rhizomes connected to the plant.
And they go down deep.
They go down sometimes a meter or more.
And they're all connected to each other.
So I picked out some pretty small, pretty isolated heads here of the grass.
And so I'm able to get part of the plant out.
But I haven't got all of the rhizomes that connect this piece
to everything around it.
So I would have to after those two.
And it means some pretty serious excavation.
The cost of controlling European beach grass so far have been on the order of
20 or $25,000 a hectare to dig it up, pull it out.
And then come back repeatedly and remove or treat with herbicide the re-emerging
plants that come out over time from all the pieces that people missed.
There's also some work with fire to try to use fire as a way to try to reduce
the labor associated with having it come back through so many times and remove it.
At some point, there may be a biocontrol insect that makes it possible to tackle
European beach grass and restore these dunes without so much intensive labor.
And one of the most affected kinds of native
plants by this introduced beach grass are the native dune grasses.
They are typically in the exact same places up here on the foredune
closest to the beach.
But they're nowhere nearly as fast growing or as dense as the invader.
Partly because they have all of their pathogens and
herbivores here eating their seeds and preventing them from becoming so dominant.
[MUSIC]
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