This passage is excerpted from Joseph Mascaro, Gregory P Asner, Stuart Davies, Alex Dehgan, and Sassan Saatchi, “These Are the Days of Lasers in the Jungle,” ©2014 by Joseph Mascaro, et al.
Just as the Moon’s history was disrobed by laser ranging 50
years ago, Earth’s tropical forests are giving up their secrets to
the light. Airborne light detection and ranging—called LiDAR
—has over the last ten years become a key tool that ecologists
use to understand physical variation in tropical forests across
space and time. Like an MRI of the human brain, LiDAR
probes the intricate three-dimensional architecture of the forest
canopy, unveiling carbon that forests keep out of the
atmosphere, and also the mounting threats to that carbon
storehouse: drought, fire, clandestine logging and brash gold-
mining operations. Even the quintessential natural disturbance
of the sun-filled light gap—long thought to enhance the
incredibly high species diversity of tropical forests—has been
deconstructed by laser technology.
Laser ranging in tropical forests is such a game-changing
technology that science results can scarcely get through peer-
review before they are dwarfed by still larger-scale studies. In a
decade, laser power on commercial-grade LiDARs has
skyrocketed and costs have plummeted. These improvements
in LiDAR technology allow airplanes to fly faster, higher and
farther, covering more forest area in a single day than every
ground-based survey that has ever been collected in the history
of tropical ecology. To estimate the amount of carbon stored in
a 50-hectare tropical forest monitoring plot on the ground—the
largest field plot in the world—takes a team of 12 people about
eight months: a slog of rain and mud and snakes with tape
measures and data log books. Today’s airborne LiDARs can get
you to within about 10% of the same carbon estimate in eight
seconds.
It is this staggering contrast in scale between LiDAR and
fieldwork that led us here: Before this decade is out, we could
directly assess the carbon stock of every single square hectare
of tropical forest on Earth. We could do it just as well as if we
were standing there in the flesh with tape measures in hand.
And we could do it for far less than what we have already spent
to offset carbon emissions from forests. . . .
It is easy in principle, though logistically nightmarish, to
measure carbon in tropical forests. A strict constructionist
would cut, dry and weigh the biomass of the world’s forests.
But this is a self-defeating enterprise. As a result, it is likely
that no one has measured carbon over a single hectare of
tropical forest, even with the most detailed field surveys. For a
century ecologists and foresters have relied on allometric1
estimation in lieu of carbon measurements to translate field
surveys of tree diameters, heights and wood densities into
whole-forest carbon estimates. Given a volume with known
dimensions and density, one would estimate its mass in a
similar fashion.
As the new kid on the block, LiDAR has been tacked onto
the back end—initially thought of as kind of large-scale helper
to field surveys. Carbon estimates from the field have been
treated as something inherently closer to the real thing than
measurements made by LiDAR—ground “Truth” with a capital
“T”. This is perhaps understandable historically, but vis-à-vis
actual carbon, there is no such thing as ground truth: both field
and LiDAR efforts rely on allometry to convert measurements
into carbon estimates. Prior to using these measurements for
carbon estimation, they exist as standardized, spatially explicit,
archivable and verifiable data—the needed substrate for a
REDD2-type accounting program.
Due to the constancy of the underlying measurements, both
field and LiDAR data could provide the needed information if
they covered every hectare on Earth. But, in the case of field
surveys, this is impossible. The surveys that do exist measure a
tiny amount of actual forest, and so what might be verified is
widely spaced. And to avoid fraud and protect landowners,
many governments keep their plot locations secret. Satellite
LiDAR data remain sparse, providing only extrapolated,
coarse-resolution carbon estimates with very high
uncertainties, and there is no prospect of wall-to-wall coverage
in the near future. By 2020, airborne LiDAR could give us a
direct measurement of 3-D forest structure for every hectare in
the tropics: a standardized database from which to build a
carbon economy.
1 Pertaining to the study of changing proportions in part of an
organism or body resulting from growth.
2 Reduced Emissions from Deforestation and Degradation, a program
implemented by the United Nations Framework Convention on
Climate Change.
Just as the Moon’s history was disrobed by laser ranging 50
years ago, Earth’s tropical forests are giving up their secrets to
the light. Airborne light detection and ranging—called LiDAR
—has over the last ten years become a key tool that ecologists
use to understand physical variation in tropical forests across
space and time. Like an MRI of the human brain, LiDAR
probes the intricate three-dimensional architecture of the forest
canopy, unveiling carbon that forests keep out of the
atmosphere, and also the mounting threats to that carbon
storehouse: drought, fire, clandestine logging and brash gold-
mining operations. Even the quintessential natural disturbance
of the sun-filled light gap—long thought to enhance the
incredibly high species diversity of tropical forests—has been
deconstructed by laser technology.
Laser ranging in tropical forests is such a game-changing
technology that science results can scarcely get through peer-
review before they are dwarfed by still larger-scale studies. In a
decade, laser power on commercial-grade LiDARs has
skyrocketed and costs have plummeted. These improvements
in LiDAR technology allow airplanes to fly faster, higher and
farther, covering more forest area in a single day than every
ground-based survey that has ever been collected in the history
of tropical ecology. To estimate the amount of carbon stored in
a 50-hectare tropical forest monitoring plot on the ground—the
largest field plot in the world—takes a team of 12 people about
eight months: a slog of rain and mud and snakes with tape
measures and data log books. Today’s airborne LiDARs can get
you to within about 10% of the same carbon estimate in eight
seconds.
It is this staggering contrast in scale between LiDAR and
fieldwork that led us here: Before this decade is out, we could
directly assess the carbon stock of every single square hectare
of tropical forest on Earth. We could do it just as well as if we
were standing there in the flesh with tape measures in hand.
And we could do it for far less than what we have already spent
to offset carbon emissions from forests. . . .
It is easy in principle, though logistically nightmarish, to
measure carbon in tropical forests. A strict constructionist
would cut, dry and weigh the biomass of the world’s forests.
But this is a self-defeating enterprise. As a result, it is likely
that no one has measured carbon over a single hectare of
tropical forest, even with the most detailed field surveys. For a
century ecologists and foresters have relied on allometric1
estimation in lieu of carbon measurements to translate field
surveys of tree diameters, heights and wood densities into
whole-forest carbon estimates. Given a volume with known
dimensions and density, one would estimate its mass in a
similar fashion.
As the new kid on the block, LiDAR has been tacked onto
the back end—initially thought of as kind of large-scale helper
to field surveys. Carbon estimates from the field have been
treated as something inherently closer to the real thing than
measurements made by LiDAR—ground “Truth” with a capital
“T”. This is perhaps understandable historically, but vis-à-vis
actual carbon, there is no such thing as ground truth: both field
and LiDAR efforts rely on allometry to convert measurements
into carbon estimates. Prior to using these measurements for
carbon estimation, they exist as standardized, spatially explicit,
archivable and verifiable data—the needed substrate for a
REDD2-type accounting program.
Due to the constancy of the underlying measurements, both
field and LiDAR data could provide the needed information if
they covered every hectare on Earth. But, in the case of field
surveys, this is impossible. The surveys that do exist measure a
tiny amount of actual forest, and so what might be verified is
widely spaced. And to avoid fraud and protect landowners,
many governments keep their plot locations secret. Satellite
LiDAR data remain sparse, providing only extrapolated,
coarse-resolution carbon estimates with very high
uncertainties, and there is no prospect of wall-to-wall coverage
in the near future. By 2020, airborne LiDAR could give us a
direct measurement of 3-D forest structure for every hectare in
the tropics: a standardized database from which to build a
carbon economy.
1 Pertaining to the study of changing proportions in part of an
organism or body resulting from growth.
2 Reduced Emissions from Deforestation and Degradation, a program
implemented by the United Nations Framework Convention on
Climate Change.