[Katharine Nash Sudding]: When most people think about
an old-growth forest, they think of a
really unique and special place.
Huge mature trees, and all sorts of species interacting.
Old-growth grasslands are the same.
They have also taken centuries to develop,
and the grasses and the plants in those systems
are also really large, really old, but all their size is below ground.
[Narrator]: It’s hard to tell the difference
between an old-growth and young grassland.
But trained eyes can see key differences,
like higher biodiversity, and a world of wonder underground.
The deep roots, organs, and seed banks in grasslands
help them bounce back after disturbances.
[Katharine Nash Sudding]: We are getting more and more
information that the ecosystem services that grasslands
provide are as great as the ecosystem services
that forests provide.
We’re starting to understand the incredible carbon
that is stored below ground in grasslands.
[Narrator]: But these complex systems face significant threats.
In some regions, like the Cerrado in Brazil
and North America’s Great Plains,
more than half of grasslands have been cleared
for farmland and tree plantations.
So how do researchers restore damaged grasslands
to their former glory?
A review in Science lays out what scientists have tried so far,
and the questions yet to be answered.
[Elise Buisson]: There's a technique that's widely used in
temperate Europe – that's hay transfer.
That's when you collect the hay on one pristine grassland
to transfer it to another one that's degraded.
[Narrator]: Hay transfer is effective in grasslands with
annual species that produce viable seeds every year.
[Elise Buisson]: We also tried it in some
degraded grassland in Brazil.
It did not work at all over there.
Because in Brazil, the grasslands I worked in are
mainly composed of perennial species.
[Narrator]: Perennial species don’t have
the same regular cycles of seed production as annuals.
Some only create seeds on occasion, like after a fire.
Others rely more heavily on their root system to reproduce.
This makes establishing perennial plants
quite the challenge in grasslands.
[Katharine Nash Suding]: Those are ones that we're seeing
more and more that they need to be part of the grassland
system for a really successful recovery to occur.
So how do we do it?
Do we actually have to transplant individuals?
Do we have to put in some of those root fragments?
Those are all ideas that have potential value
[Narrator]: In addition to losing native species,
some grasslands have also lost the disturbances
that maintain them, like fire and grazing.
These are crucial to preserving their biodiversity
and preventing trees from colonizing.
[Elise Buisson]: It's very important to understand the rhythm
at which you have to apply this disturbance.
You cannot apply the disturbance regime that you understood
for the pristine grassland right away,
because the vegetation is not the same.
You're going to have to adapt your disturbance regime
as the restoration goes, and as species colonize,
or as you introduce species yourself.
There's one experiment where we grew some plants
for a number of months and years, and then we burned them
at different ages, to see what age they needed to be
to be transplanted in the wild and able to sustain fire.
Because it doesn't make any sense to transplant
six months seedlings that are going to die with
the first fire that we cannot control.
[Katharine Nash Suding]: There’s many ways to have to iterate
and have to intervene along that recovery trajectory
to have success.
And that just assembling, putting the desired elements,
and then walking away
probably won't be successful in many of these grasslands.
[Narrator]: As ecologists work out how to monitor and manage
restored grasslands, they also hope to preserve
old-growth grasslands that remain intact.
[Katharine Nash Suding]: I'm hoping that people think about
what type of agenda we can put forward
to actually better maintain and protect
these incredibly special old-growth grasslands
that are on the earth.