Doug Morton: The forests of Puerto Rico are always changing.
Following Hurricane Maria, they've changed a lot.
But by taking measurements on the ground,
in the air, and from space,
we're able to not only identify those changes,
but also follow them through time
as these landscapes recover the lush tropical forests
they had before the storm.
Narrator: NASA scientists were in Puerto Rico
in early 2017, studying how forests grow and change.
They returned in 2018 to assess the forest recovery
after two hurricanes hit the island.
Doug: In many ways, Hurricane Maria has reset
patches of forest across the island.
Canopy trees normally have a large and
sometimes circular crown allowing them
to spread their leaves, photosynthesize, and
live in the top of the canopy.
Hurricane Maria came through and
ripped off many of those large branches,
leaving individuals standing almost like an individual stem.
What that means is they'll have to regrow
those leaves or give up that space in the canopy
to their neighbors as they regrow beneath them.
Narrator: The team returned to the specific plots
they measured the previous year,
hiking through the thick under brush that had grown
since the hurricane opened up the canopy.
A bit like this, Ian?
Doug: When this large tree fell,
it took out most of its neighbors
and created a large gap in the forest where sunlight
will now reach all the way down to the forest floor.
That will allow new, young trees to grow back in its place.
In contrast, on this side of the plot,
many of the large trees were stripped of their large branches
but they are still standing and most of them will recover
those leaves and grow back into the space they left behind.
Narrator: But with forests covering half of the island,
walking up to every tree was not practical.
Bruce: So, my name is Bruce Cook,
I'm from NASA Goddard Space Flight Center.
I'm here today in Puerto Rico, assessing damage
that was caused by both Hurricanes Irma and Maria.
And we're doing it with this instrument to my right,
which is called G-LiHT.
G-LiHT stands for Goddard's Lidar, Hyperspectral, and Thermal instrument.
And it’s using multiple sensors to actually understand
more about terrestrial ecosystems
Narrator: G-LiHT is installed on a small airplane
and flown at low altitudes to collect lots of measurements in one pass.
Bruce: The lidar is being used to measure changes
in the structure of the forest canopy,
how many branches were lost, how many trees were knocked over,
but we're also using other sensors that measure things
such as how much, or what changes in the amount of sunlight
that's being absorbed by these canopies and
how that's affecting their photosynthesis and growth these days.
Narrator: The lidar sends out five hundred thousand laser pulses
each second and can detect the physical structure of individual trees.
Doug: That laser energy from our lidar system
will intersect the top of the canopy,
smaller branches on the way down,
and all the way down to this understory vegetation on the ground
to help us construct a three-dimensional model of these forests
Narrator: But even though G-LiHT collects several types of data,
it's not enough to fully understand how forests react to changes.
Measurements from the ground level are a necessary complement.
Doug: The same laser technology on G-LiHT
can be put on a tripod on the ground
and make very detailed measurements of individual trees,
the vines and lianas that hang from those trees
as well as the damage that's occurred.
Bruce: This is a partnership and it involves
both the data from the ground,
but also the data from the airborne instrument,
as well as data from the satellite.
So we call this scaling, when we can scale
for ground measurements all the way up to satellites,
and it just helps us understand what is going on from a larger picture.
Doug: By being able to take information about the changes
and the recovery of these landscapes over time,
we're able to connect the changes in the carbon cycle,
the changes in tropical forests and their functioning,
even the changes in the strength and intensity of hurricanes
and understand how those changes observed today
help us understand and predict tomorrow's changes
as well as the imprint of that hurricane
in our atmosphere world-wide.
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