Abstract
Taijiang National Park (TNP) of Taiwan is the northernmost geographical position of mangrove habitats in the Northern Hemisphere. Instead of occupying a vast region with a single species, the mangroves in TNP are usually mingled with other plants in a narrow corridor along the water or in groups on a small sandbank. The multi-spectral images acquired from the spaceborne platforms are therefore limited in mapping the abundance and distribution of the mangrove species in TNP. We report the work of mapping pure mangrove patches in small corridors and sandbanks in TNP using airborne Compact Airborne Spectrographic Imager (CASI) hyperspectral imagery. Bu considering the similarity of spectral reflectance among three species of mangrove and other plants, we followed the concept of supervised classification to select a few training areas with known mangrove trees, where the training areas are determined from the detailed map of mangrove distribution derived from the field investigation. The Hourglass hyperspectral analysis technique was employed to identify the endmembers of pure mangrove in the training areas. The results are consistent with the current distribution of mangrove trees, and the remarkable feature of a “mangrove desert” highlights a fact that biodiversity can be easily and quickly destroyed if no protection is provided. Some remnant patches located by this research are very important to the management of mangrove trees.
Highlights
Thriving in a transition zone between land and sea in intertidal coastal regions, mangroves act as a pioneer of coastal ecology and an indicator of climate change
Even within a well-defined training area with pure mangroves such as the red, cyan and yellow boxes enlarged in Figure 12, there are still some pixels dominated by the tree shadows or small water pits
By examining the spectral features illustrated by the MNF bands (Figure 11) and the false-color composite of the MNF-transformed image, the three endmembers retrieved from the training areas provide the required spectral characteristics to differentiate the three species of mangrove and other plants
Summary
Thriving in a transition zone between land and sea in intertidal coastal regions, mangroves act as a pioneer of coastal ecology and an indicator of climate change. Since mangroves represent a significant sink in carbon, their response to climate change may result in either negative or positive feedback [2]. It is estimated that about 36% of the total global mangrove habitat area was lost during the last two decades [5]. Polidoro et al [7] collected species-specific data to determine the probability of extinction for all 70 known species of mangroves. They concluded that several species at high risk of extinction may disappear well before the decade if existing protective measures are not enforced. Retrieving up-to-date information of the extent and condition of mangrove ecosystems, is an essential aid to management and policy- and decision-making processes [3]
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