Innovations

Conservation in 3D

LIDAR SYSTEMS put everything into perspective

Forecologists, seeing the forest for the trees is a constant dilemma. Satelliteand airplane images provide an overall picture of the forest and its boundaries.But the aspects of the forest typically crucial to the health of the localdenizens, such as the age, height and density of the trees, often remainhidden. To obtain these particulars, researchers must lug measuring tape,rope, and surveying equipment into the woods and painstakingly performmeasurements on individual trees.

A new tool may help put everythinginto perspective. Known as light detection and ranging (LIDAR) systems,these instruments can provide not only a two-dimensional picture of theextent of the forest but also a full three-dimensional view of the shrubsand trees within. The device has already proven it can identify everythingfrom spotted owl habitat to forest conditions suitable for spawning salmon.

All airborne LIDAR systems operatein pretty much the same way. A pulsing infrared laser is attached to anairplane’s underside. As the plane whirrs along, the laser blinks on andoff like a strobe light, sending pulses of light toward the ground. A detectormounted on the plane picks up the light after it reflects off the land.By observing the time difference between when pulses leave and return,researchers deduce the height of objects on the ground.

The first LIDAR systems, built byNASA in the seventies and eighties, used a narrow-beam laser to simplyobtain elevation data from directly under an aircraft. LIDAR has evolved since then, and now systems can gleandata on large swaths of land with one pass. The most common of the moderncommercial LIDAR systems use scanning mirrors to continuously spray the groundto each side of the airplane with a narrow-beam laser—like an automatic sprinkler. Even more cutting-edgedevices shine big, house-sized spots of infrared laser light below the plane.Detectors record the many photons from this spot of light as they bounceoff the terrain. The result is essentially a plaster relief of the land madefrom light.

Over the years, LIDAR has primarilybeen employed as a tool for crea-ting topographic maps. In the late nineties,foresters realized the systems not only retrieved elevation readings ofthe ground but also of tree tops, low-level vegetation, and everythingin between. In short, LIDAR technology provided three-dimensional viewsof forests and shrubland.

Researchers, like Michael Lefsky atColorado State University, began to analyze LIDAR data to see whether itcould reveal more of what lies hidden beneath forest canopies. They found,among other things, that they could extract readings on the diameter oftrees, the relative forest age, and even the amount of sunlight hittingthe forest floor. In one study, Lefsky used LIDAR to classify 22 plots of land as young, mature, or old-growth forest,with 100 percent accuracy. To obtain the same accuracy in situ, hewould have had to wrap a tape measure around large samples of trees and thenbring in ropes, laser rangefinders, and other survey instruments to measuretree height and the depth and extent of the crowns.

Withits extensive capabilities validated, LIDAR is now finding its way intothe hands of ecologists. Ralph Dubayah, a geographer at the Universityof Maryland, recently employed LIDAR to measure spotted owl (Strixoccidentalis) habitat. In the Pacific Northwest and California, spotted owl populations continue to dropdue to the degradation of their old-growth forest habitat. Identifying andmapping owl habitat, however, has always been dismayingly difficult. UsingLIDAR, Dubayah and his research team found that owls thrive in forests withtall trees, plenty of canopy cover, and thick vegetation. When these factorsfall below specific levels, owl populations plummet. Armed with this knowledgeand an advanced LIDAR system, conservationists could now conceivably mapremaining owl habitat in North America.

Although they are less infamous thanthe spotted owl, great tit (Parus major) populations have been waningacross England. One of many reasons for the decline of these and othersmall woodland birds could be the continued development of the Englishcountryside, which gives rise to woodlands that don’t differ much in heightor structure. Ross Hill and his colleagues at the Centre for Ecology andHydrology at Bath Spa University College in the U.K. used LIDAR to examinethe relationship between tree height and nestling weights in relativelyuntouched deciduous forests near Bath. The study revealed that after acold spring, great tit babies grow bigger faster where trees are loweron average. Conversely, nestlings thrive in taller trees after a warm spring.These results suggest the birds have a better shot in the long run wherecanopy height varies. The researchers plan to examine other woodland areaswith LIDAR to gain further insights into the decline of bird populations.

LIDAR’s potential extends well beyondbird conservation and could aid in research involving everything from butterfliesto bears. David Nash, a geographic information systems (GIS) specialistfor Kitsap County, Washington, is monitoring tree cover along salmon- spawningstreams to see whether the trees are well-enough developed both to shadesalmon eggs and shed ample woody debris, which is needed to form spawningpools. And in Florida, John Brock at the U.S. Geological Survey Centerfor Coastal and Watershed Studies is using LIDAR’s topographic abilitiesto precisely map beaches, grasslands, and even shallow coastal waters alongEast Coast national parkland. One goal is to study the impact storms,human activity, and climate change have on coastal ecosystems, includingshallow coral colonies.

Downthe road, LIDAR may even be able to do much more than just monitor individualanimal habitats. Long-standing ecological theories have linked forest structureand biomass to biodiversity. Dubayah and his team are now testing thesetheories. Over the next few years, they will be flying LIDAR over ecologicalresearch areas where extensive plant and animal data have been collected.They will try to uncover relationships between forest attributes measurableby LIDAR and the level of species richness. The goal is to use LIDAR oneday to measure biodiversity.

Another somewhat futuristic applicationof LIDAR is forest restoration. LIDAR could be used to map and identifythe characteristics that make old-growth forests “old growth.” Then, employinghorticultural techniques, researchers could direct the development of newerforests to obtain essential old-growth characteristics in a fraction ofthe time it would take naturally.

Before LIDAR can become widespread,costs will have to come down significantly. Even basic LIDAR systems gofor hundreds of thousands of dollars, and many researchers are still unableto pay for them or the data. Compounding the problem, remote-sensing organizationssuch as the Management Association for Private Photo-grammetric Surveyors(MAPPS) are lobbying to ensure that everyone from budget-constrained scientiststo big logging corporations must buy systems and data from the privatesector. Given the remarkable abilities of LIDAR to aid in conservation,however, in the long run it will likely become a standard instrument forecologists, regardless of such obstacles.

About the Author:

John Weier is a freelance writer based in Seattle, Washington.