10:45 AM - 12:15 PM
[HTT13-P04] LiDAR survey for understanding microtopography and 3D distribution of
tree species in mangrove forests
★Invited Papers
Keywords:mangrove, LiDAR, ALS, MLS
Mangrove forests inhabit within a limited elevation range above mean high tide in the intertidal zone. For that reason, mangrove forests exhibit zonation of species along the elevation gradient (Mochida et al., 1999). It has also been shown that habitats advance and retreat under the influence of sea level changes and tectonic movements (Fujimoto et al., 2015). Thus, mangroves are susceptible to relative sea level changes including influence of tectonic movement, and are strongly associated with topography. However, there are no cases of mangrove forests for which detail topographic data have been obtained over a wide area, and thus the quantitative relationship between mangrove elevation and species distribution is not yet known.
In this study, highly accurate and extensive mangrove topographic data were obtained for the Miyara River mangrove forest on Ishigaki Island, Okinawa Prefecture. The topographic data were acquired by using Light Detection And Ranging (LiDAR). LiDAR is a technology that captures objects as a point cloud by converting the time difference between the application of a laser beam to an object and the return of the reflected laser beam into a distance. Specifically, Airborne LiDAR Scanning (ALS), in which surveying equipment is mounted on a UAV and surveyed from the sky, and Mobile LiDAR Scanning (MLS), in which a backpack LiDAR is used to survey a forest area, were conducted in a mangrove forest. From the 3D point cloud data obtained from the LiDAR survey, a Digital Elevation Model (DEM) was created and tree species were sorted.
As a result of visual discrimination of individual mangrove tree species and mapping the distribution of tree species from the data obtained, about 5000 trees were detected in the study area. Relationship between DEM data and spatial distribution of mangroves showed that the range and peak of the height distribution of the habitat area differed depending on the tree species. Namely, the Rhizophora stylosa were found to exist at low elevations along rivers and creeks and at high elevations in the uppermost intertidal zone, surrounding the inland clumps of the Bruguiera gymnorrhiza. Comparing with Nakasuga (1976) report on mangrove distribution in this study area showed that Rhizophora stylosa was dominant in the 1970s, but is now dominated by Bruguiera gymnorrhiza. Past aerial photographs show that mangrove forests have increased both inland and along rivers since 1978, and that Rhizophora stylosa is now present in many of the increased areas when compared with tree species distribution. These results may be influenced by the fact that Rhizophora stylosa is a salt-tolerant, shade-intolerant tree, while Bruguiera gymnorrhiza is a shade-tolerant tree. The presence of Bruguiera gymnorrhiza may have led to a lack of light, causing Rhizophora stylosa to spread along rivers and forest streams at lower elevations that are prone to flooding, and inland at higher elevations where seawater evaporated and salinity is higher.
Thus, it is clear that mangroves are experiencing species turnover and a change in habitat range as a result of differences in species characteristics and changes in elevation.
This is the first study using both ALS and MLS in mangrove forests. Using LiDAR technology allowed a quantitative discussion of the relationship between mangroves and topography.
In this study, highly accurate and extensive mangrove topographic data were obtained for the Miyara River mangrove forest on Ishigaki Island, Okinawa Prefecture. The topographic data were acquired by using Light Detection And Ranging (LiDAR). LiDAR is a technology that captures objects as a point cloud by converting the time difference between the application of a laser beam to an object and the return of the reflected laser beam into a distance. Specifically, Airborne LiDAR Scanning (ALS), in which surveying equipment is mounted on a UAV and surveyed from the sky, and Mobile LiDAR Scanning (MLS), in which a backpack LiDAR is used to survey a forest area, were conducted in a mangrove forest. From the 3D point cloud data obtained from the LiDAR survey, a Digital Elevation Model (DEM) was created and tree species were sorted.
As a result of visual discrimination of individual mangrove tree species and mapping the distribution of tree species from the data obtained, about 5000 trees were detected in the study area. Relationship between DEM data and spatial distribution of mangroves showed that the range and peak of the height distribution of the habitat area differed depending on the tree species. Namely, the Rhizophora stylosa were found to exist at low elevations along rivers and creeks and at high elevations in the uppermost intertidal zone, surrounding the inland clumps of the Bruguiera gymnorrhiza. Comparing with Nakasuga (1976) report on mangrove distribution in this study area showed that Rhizophora stylosa was dominant in the 1970s, but is now dominated by Bruguiera gymnorrhiza. Past aerial photographs show that mangrove forests have increased both inland and along rivers since 1978, and that Rhizophora stylosa is now present in many of the increased areas when compared with tree species distribution. These results may be influenced by the fact that Rhizophora stylosa is a salt-tolerant, shade-intolerant tree, while Bruguiera gymnorrhiza is a shade-tolerant tree. The presence of Bruguiera gymnorrhiza may have led to a lack of light, causing Rhizophora stylosa to spread along rivers and forest streams at lower elevations that are prone to flooding, and inland at higher elevations where seawater evaporated and salinity is higher.
Thus, it is clear that mangroves are experiencing species turnover and a change in habitat range as a result of differences in species characteristics and changes in elevation.
This is the first study using both ALS and MLS in mangrove forests. Using LiDAR technology allowed a quantitative discussion of the relationship between mangroves and topography.