By Grace Bukowski-Thall

Biodiversity Losses Pose Huge Threats to Humankind
We are in the midst of the Anthropocene, a new geological era in which human beings have a profound and unprecedented influence on the natural world. In the past century alone, the human population has increased from 1.7 billion to 7.4 billion, the greatest rate of population growth that humankind has ever experienced. But as the human population surges, biodiversity has plummeted. Anthropogenic impacts have brought about the Earth’s sixth mass extinction; it is estimated that 11,000 to 58,000 species are lost annually (1) and a million more animal and plant species are facing extinction in the next decade. By the middle of this century, half of the species on Earth may be gone.

Rich biodiversity and healthy ecosystems are fundamental to life on Earth. Loss of biological diversity and destruction of ecosystems are currently two of the largest threats facing humanity.

Climate change is responsible for most biodiversity losses. Even slight changes in temperature and weather patterns pose large risks to the habitats of many species. For instance, in Australia, the endangered Mountain Pygmy Possum (Burramys parvus) burrows deep in the winter snow to keep warm during hibernation. The possum depends on at least one meter of snow for adequate insulation. Rising temperatures and snowmelt threaten their winter habitat, which is already less than 10 square kilometers.

*The mountain pygmy possum is facing extinction due to climate change. Photo: Fredy Mercay, ANT Photo Library*

Climate change and other human influences are also allowing invasive plant species to displace native plants, creating monocultures in previously diverse landscapes. Along with habitat destruction, infestation of invasive plants is a primary cause of biodiversity loss.

Invasive plants can also disrupt agricultural practices. For example, the leafy spurge (Euphorbia esula) has invaded many fields in the Great Plains Region, reducing the range of area for livestock to graze.

Threats to wildlife also negatively impact our economies. For example, the lobster industry in Maine provides employment for thousands of people and supplies over $1 billion to the state’s economy annually. But with rising ocean temperatures, lobsters are migrating away, to colder water habitats, thus threatening the livelihood of many Mainers.

So, what can be done about biodiversity losses on such a massive scale? To start, we need data on an equally massive level.

Traditional field surveys have been inadequate. They require a great amount of time and resources, and yield results based off low sample sizes taken in limited areas. This phenomenon called the “Linnean Shortfall,” is when there is a large gap between observations made, and the amount of species that actually exist. In order to more accurately gauge the effects that humans have on biodiversity, scientists must be able to obtain long-term, spatiotemporal, and global data. Fortunately, the advent of space-based, remote sensing technologies has allowed scientists to do just that.

Original Inspiration to Save the Planet
Images from space have heavily influenced environmental causes. The first image of the Earth captured by the Apollo 8 mission photographer, Bill Anders, in 1968 forever changed the way humans view their home planet and place in the universe.

*“Earthrise” by Bill Anders, 1968. Image: flickr*

After seeing the “Earthrise” photograph, people began to reckon with the finiteness of Earth and realized the need to protect it. Because of this, “Earthrise” is often accredited with initiating some of the first major environmental protection movements.

In the United States, many anti-littering and wildlife protection campaigns were created in the wake of the first Apollo missions. Commercial breaks on TV featured “Smokey Bear,” who told us to prevent wildfires, and “Johnny Horizon,” a park ranger character professed “This Land Is Your Land, Keep It Clean!”. In 1970, Earth Day was established as a national holiday. Some of these environmental campaigns were actually quite successful, evidenced by a 60% reduction in littering since 1969.

*Environmental stewardship campaign, “Johnny Horizon”. Image: flickr*

Remote Sensing of Biodiversity
In the 1970’s, scientists started using new methods to measure and track the dynamics of life on Earth. Satellites and other aircraft were equipped with technology to remotely acquire far greater amounts of data across vastly larger geographic areas. This helped close the gap between observations of species and the amount of species that actually exist. Scientists were able to more accurately gauge the effects that humans were having on biodiversity, and gain long-term, spatiotemporal, and global data from space-based, remote sensing technologies.

Four main methodological categories have been used for remote sensing of biodiversity: habitat mapping, species mapping, functional diversity, and spectral diversity. (2)

In the early days of remote sensing, the technology was mainly limited to mapping landscapes and habitats. Habitat mapping allowed scientists to assess species area curves and habitat heterogeneity, which was positively correlated with species diversity. This was an indirect way of evaluating biodiversity and only provided information about species that were restricted to a specific habitat.

With advancements, one effective technology that has allowed more detailed assessments of biodiversity, has been imaging spectroscopy and Light Detection and Ranging (LiDAR), which shines pulsing laser on target objects and creates 3D models by measuring differences in the laser’s return time and wavelength.

LiDAR increases the dimensionality of biological data and yields images with high spatial resolution and provides detailed spectral and structural information. (3) Airplanes and helicopters are typically used to collect LiDAR data over a large area. Different types of LiDAR systems are used to map land and underwater features. Topographic LiDAR, which uses a near-infrared laser, is used to create terrestrial maps, whereas bathymetric LiDAR, which uses water-penetrating green light, is used to collect underwater data.

*LiDAR can be used to compare the structure of a new growth forest (left) to an old growth forest (right). Image by Sarah Frey, Oregon State University*

LiDAR systems can be used for species mapping by measuring physiological or chemical traits that distinguish different species. For example, an invasive plant species may have a different 3D structure than a native plant. LiDAR can also distinguish between plant species based on biochemical composition such as pigment content or nitrogen fixation abilities. (4)

In addition to being used for species mapping, airborne LiDAR and other spectral imaging sensors like HyMap (Hyperspectral Imaging Sensor) and AVIRIS (Airborne Visible Infrared Imaging Spectrometer) can assess plant functional diversity. Functional diversity describes the aspects of biodiversity that allow ecosystems to function. Measuring the biochemical, physiological, and structural functional traits of plants reveals how different species respond to their environment. Measurements of plant functional variation give researchers insight into the health of the ecosystem. (5) Since there is a high correlation between plant and animal biodiversity, 3D vegetation structure data such as tree canopy height, canopy cover, canopy complexity, and understory density can be used to evaluate animal ecology. (6)

Remote sensing can also be used to assess spectral diversity, which can be used to distinguish between species based on both structure and function. For instance, in plants, differences in leaf spectra have been found to increase with both functional and evolutionary divergence. As a result, spectral diversity data from remote sensing can be used to predict ecosystem function. (7)

In addition to measuring terrestrial biodiversity, remote sensing can be used to determine oceanic biodiversity by measuring amounts of sunlight absorbed or emitted by different marine species and habitats. This technique is typically utilized to determine the biodiversity of organisms like algae, seagrass, coral, and phytoplankton. (8) For example, ocean reflectance is directly linked to phytoplankton biomass, so ocean color satellite imagery can be used to determine phytoplankton biodiversity levels in surface waters. (9) Phytoplankton reside at the bottom of most marine food webs, making them an essential part of the ocean ecosystem. Additionally, phytoplankton have a large role in regulating global climates as they are responsible for a majority of CO2transportation from the atmosphere to the ocean. As a result, it is highly important to keep tabs on phytoplankton population size and diversity.

*Phytoplankton and algae bloom seen from above in Finland. Image: flickr.*

Conclusions
In the midst of the Earth’s sixth mass extinction, remote sensing has proven to be a valuable conservation tool. Remote sensing allows conservationists and scientists to identify and monitor spatiotemporal changes in habitats and biodiversity. Remote sensing data can help us prepare for climate change as well as plan landscape management to improve biodiversity. The uses of remote sensing of biodiversity have been recognized globally. Many countries, research institutions, and government agencies keep their own remote sensing databases.

Proving the global importance of using remotely sensed data for biodiversity, the Group on Earth Observations has recently founded global Biodiversity Observation Network (GEO BON) that combines remote sensing datasets from around the world to create a framework for biodiversity and ecosystem management policies. This demonstrates just how comprehensive a tool remote sensing is, and how images from space continue to possess a unifying power on Earth.

References
(1) Dirzo, R. et al. Defaunation in the Anthropocene. Science 345, 401–406 (2014).
(2) Wang, R. & Gamon, J. A. Remote sensing of terrestrial plant biodiversity. Remote Sens. Environ. 231, 111218 (2019).
(3) Ustin, S. L., Roberts, D. A., Gamon, J. A., Asner, G. P. & Green, R. O. Using Imaging Spectroscopy to Study Ecosystem Processes and Properties. BioScience 54, 523 (2004).
(4) Asner, G. P. et al. Invasive plants transform the three-dimensional structure of rain forests. Proc. Natl. Acad. Sci. 105, 4519–4523 (2008).
(5) Fusco, G. & Minelli, A. Phenotypic plasticity in development and evolution: facts and concepts. Philos. Trans. R. Soc. B Biol. Sci. 365, 547–556 (2010).
(6) Davies, A. B. & Asner, G. P. Advances in animal ecology from 3D-LiDAR ecosystem mapping. Trends Ecol. Evol. 29, 681–691 (2014).
(7) Schweiger, A. K. et al. Plant spectral diversity integrates functional and phylogenetic components of biodiversity and predicts ecosystem function. Nat. Ecol. Evol. 2, 976–982 (2018).
(8) Canonico, G. et al. Global Observational Needs and Resources for Marine Biodiversity. Front. Mar. Sci. 6, 367 (2019).
(9) Bracher, A. et al. Obtaining Phytoplankton Diversity from Ocean Color: A Scientific Roadmap for Future Development. Front. Mar. Sci. 4, (2017).