Mapping salt marsh vegetation by integrating hyperspectral and LiDAR remote sensing

Jiansheng Yang, Francisco Artigas

Research output: Chapter in Book/Report/Conference proceedingChapter

24 Scopus citations

Abstract

Coastal wetlands or salt marshes are subjected to a high frequency of disturbances caused by hurricanes, storms, tidal cycles, ditching and draining which continuously affect the establishment, persistence, and distribution of plant species in marsh habitats. These areas retain sediments and provide the substrate that supports plants and creates buffer zones that help alleviate the impact of sea surges by reducing the impact of fl oods on coastal areas [1]. Disturbances have many ways of affecting how salt marshes look and function. In some cases, disturbances expose new sediment and create the opportunity for invasive species to establish and, as a consequence, the extent and type of the vegetation cover change [2]. Similarly, high-energy storms can signifi cantly alter the topography by exposing buried sediments, rerouting creeks and creating new saline intrusions that modify the intrinsic chemical properties of the sediments, which in turn has an effect on the distribution of wetland plants. Moreover, toxic insoluble metals that lack mobility when buried under anaerobic conditions may be stirred-up during a storm and exposed to the atmosphere making metals soluble and available to plants and animals up the food chain [3]. For this and many other reasons, monitoring and sampling wetland vegetation is a common and important activity. Wetland managers continuously monitor for invasive and opportunistic species such as the common reed (Phragmites australis), which is known to take over coastal wetlands in the northeastern United States and completely replace welladapted native species that support local wildlife [4]. Once established, these invasive species are diffi cult to remove and further alter the topography to promote their expansion. Wetland vegetation is also sampled to benchmark native species distribution at certain terrain elevations so that when restoring or establishing new wetlands, these benchmark species are used as references to recreate the natural environment at the correct elevations [5]. After restoration of new wetlands, monitoring continues for some years to make sure that there is adequate plant cover, there is no threat of invasive species, and ultimately to make sure that the community is self-sustaining. Newly established salt marshes are monitored by scientists that use fi eld methods designed to capture the extent of plant cover and the diversity of species in a given area [6]. One way to measure diversity is to randomly toss a 1 × 1 m quadrant square over a representative area and record all new species that fall within the quadrant after each toss. After several tosses, the number of new species starts to level-off and the approximate number of species present in the area is determined. A good fi eld biologist can describe wetland vegetation fairly accurately using these methods that are based on a series of samples measured in a given location within a site and extrapolated to characterize an entire area. Quadrants are usually laid out over points along transects where each one is divided into four subquadrants from where all species are counted and their density and percent cover estimated [7]. These fi eld methods to determine plant community composition are fairly accurate but are costly and labor intensive.

Original languageEnglish (US)
Title of host publicationEnglish Remote Sensing of Coastal Environments
PublisherCRC Press
Pages173-188
Number of pages16
ISBN (Electronic)9781420094428
ISBN (Print)9781420094411
StatePublished - Jan 1 2009
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Engineering(all)
  • Earth and Planetary Sciences(all)

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