The Hoonah Native Forest Partnership (HNFP) is a highly unique effort at the confluence of land management, collaboration, subsistence lifestyle, and cutting-edge data. In particular, a highly detailed data-set of landscape characteristics and forest structure was captured by implementing Light Imaging, Detection, and Ranging (LiDAR) throughout the study area. The survey technique provides scientists and land managers data to generate research questions and test hypotheses. This introduction to LiDAR and overview of the HNFP LiDAR data-set will help frame the intent of some of the fish surveys and vegetation surveys, and demonstrate the utility of this data-set.
Extensive LiDAR data-sets within Alaska are still fairly rare as they can be cost prohibitive. The HNFP collaboration benefited from financial support from Hoonah Indian Association and the Natural Resource Conservation Service (NRCS) to conduct the LiDAR flights. Flights occurred in August of 2015 resulting in 865 square kilometers of LiDAR data. Processing and quality control of the data was completed by the U.S. Forest Service PNW Forest Sciences lab and the GIS lab at the University of Washington.
The Hoonah Native Forest Partnership study area covers 865 kilometers and a significant chunk of Chichagof Island. The border encompasses 8 (HUC 10) watersheds on both the east and west side of Port Frederick.
What is LiDAR?
Before going any further it is necessary to understand what LiDAR is. Traditional methods of surveying landscape topography have employed RADAR which beam radio waves down at the ground. The results give an accurate representation of structures and elevation changes. Instead of using radio waves, LiDAR beams light at the ground. The faster rate of return (light speed) enables the collector to know the exact position on the earth that the beam was sent out and received at. For every square meter of land 10 beams of light are sent down and the light bounces off the first object it encounters. In a forest that means "returns" from leaves and trees or the ground. The returns are placed into a point cloud of the point's elevation from sea level. The resulting point cloud point cloud (8.7 trillion points in the HNFP study area) provides a three-dimensional structure of a forested landscape - a tremendous advantage over RADAR. It also provides high resolution; traditional RADAR techniques can detect a bus while LiDAR can detect the tire on the bus.
This small snippet of LiDAR demonstrates the point cloud generated during the surveys. Colors are correlated to height. This cross-section of the data is outside of the Hoonah Harbor spanning the mainland and Huckleberry Island.
LiDAR Products
With proper processing, the results of LiDAR data-sets can create a suite of data layers to be utilized in GIS. Hydrology data-sets were derived by Terrain Works using the NetMap program. Among other things, the hydrology analysis yielded a high-resolution stream network, accurately delineated watersheds, and potential barriers to fish.
A cross-section of LiDAR data just outside of Hoonah Alaska demonstrating its ability to look at the 3D structure of the forest. Blue values represent the ocean and red values higher elevation.
LiDAR can generate highly details (1m resolution) digital elevations modesls (DEMs). A small section of the LiDAR data shows the abrupt rise to Elephant Mountain near Hoonah, Alaska. You can also easily visualize small tributaries.
Because of its high accuracy and resolution, LiDAR data-sets greatly improved our understanding of watershed boundaries. By using LiDAR and NetMap through Terrain Works the HNFP was able to build an extensive stream network. Identification of these small tributaries are important for stream restoration and fish rearing habitat.
Raw LiDAR data is just a series of geo-referenced points.
The Next Steps
The HNFP seeks to use the LiDAR dataset to its fullest potential and is focusing on three primary objectives with the LiDAR data this summer.
- Using NetMap modeling potential barriers to fish were identified. Crews are surveying the barriers for fish to determine if they are passable. If the LiDAR can be calibrated correct, barriers to passage may be identified across the watershed.
- Vegetation survey crews are sampling forest types to use LiDAR to identify stand characteristics and biomass for deer.
- Surveyors are also surveying density of fish in streams to verify results of an "intrinsic potential" model of fish habitat based on slope and riparian characteristics.
Aside from current surveys LiDAR also documents the state of the forest. Another unique perk of this data-set is the ability to monitor change over time. "If they re-fly the same area 10 years from now we'll be able to compare stand heights and look at site productivity", stated Conor Reynolds, Forestor at The Nature Conservancy. A new flight in the years to come could also monitor the results of land management decisions that come as a result of the HNFP and "shed light" on stand characteristics which are intensive to survey using traditional methods. LiDAR is pivotal to the HNFP and future community forest projects may also reap the benefit of landscape assessment by taking advantage of this unique and powerful data.
Article by : Ian Johnson, Hoonah Indian Association and Sustainable Southeast Partnership. Edited by: Bob Christensen