LiDAR use in Forest Inventory
Knowing the structure of your forest and the patterns that exist across your ownership are the most critical aspects needed to manage the resource. The development of this information for the past century has been accomplished through traditional forest inventory, most commonly known as Variable-Radius Plot (VRP) data collection. Often sampling intensity is 1 plot per 3 or 5 acres. These data necessary for forest growth & yield models that provide the foundation for forest volume and appraisal valuations.
Variable-Radius Plot (VRP) data collection was developed in 1947 by Walter Bitterlich and applied in 1952 by Lewis Grosenbaugh. Northwest Management, Inc. has provided inventory services for nearly four decades with plot totals reaching 50,000 to 70,000 a year for the last decade. The importance of accurate field data and the nature of where forests grow has continued to apply pressure on the inventory workforce industry-wide. The result is a continued decline in inventory personnel despite an increase in our Nation’s desire to “increase the pace and scale of forest restoration” (USFS Chief Vicki Christiansen). As technology enters the forest industry, and particularly harvesting and silviculture, field inventory has become the most costly and time-consuming part of forestry.
Arguably, one of the most influential new technologies is Light Detection and Ranging (LiDAR or Lidar). Lidar is a box the size of a medium-sized desktop printer bolted to the bottom of a fixed-wing airplane that has a high-powered laser scanner sending out 50,000+ shots/pulses per second. As each laser pulse bounces off the ground or vegetation it provides a “signature” to the printer on the plane that includes a GPS position. A Lidar scan on 100 acres can have more than 5-million GPS points with 3D coordinates.
Dr. Corrao is the technology manager at NMI and an adjunct faculty at the University of Idaho in CNR and Ag Sciences.
The movement of Lidar into the forestry sector about 15-years ago is now significantly affecting the way many land managers, and Northwest Management, Inc., are looking at gathering forest inventory. The 3D point data of a forest scanned by Lidar can be processed through to identify individual trees, heights, DBH, volume, trees-per-acre, roads, streams, fire fuels and wildlife habitat conditions. If high-resolution imagery is included in the processing of the Lidar measures of forest health, species, mortality and forest change detection can be accurately mapped.
Despite these advances in technology, highly accurate field data is still needed to validate the results of the Lidar and Imagery. The advantage to landowners from this new technology is that instead of 5 personnel completing an inventory on 20,000 acres in 2 months, the same 5 personnel can inventory 200,000 acres in the same time. The other advantage of this technology is the versatility of it to provide information across the landscape for natural resources; fire, water, forest, wildlife and is not constrained to silviculture.