Monitoring the Invasion of Spartina alterniflora Using Multi-source High-resolution Imagery in the Zhangjiang Estuary, China

Mingyue Liu,Lin Li,Zongming Wang,Chunyan Lu,Huiying Li,Mingming Jia,Weidong Man

doi:10.3390/rs9060539

Abstract

Spartina alterniflora (S. alterniflora) is one of the most harmful invasive plants in China. Google Earth (GE), as a free software, hosts high-resolution imagery for many areas of the world. To explore the use of GE imagery for monitoring S. alterniflora invasion and developing an understanding of the invasion process of S. alterniflora in the Zhangjiang Estuary, the object-oriented method and visual interpretation were applied to GE, SPOT-5, and Gaofen-1 (GF-1) images. In addition, landscape metrics of S. alterniflora patches adjacent to mangrove forests were calculated and mangrove gaps were recorded by checking whether S. alterniflora exists. The results showed that from 2003–2015, the areal extent of S. alterniflora in the Zhangjiang Estuary increased from 57.94 ha to 116.11 ha, which was mainly converted from mudflats and moved seaward significantly. Analyses of the S. alterniflora expansion patterns in the six subzones indicated that the expansion trends varied with different environmental circumstances and human activities. Land reclamation, mangrove replantation, and mudflat aquaculture caused significant losses of S. alterniflora. The number of invaded gaps increased and S. alterniflora patches adjacent to mangrove forests became much larger and more aggregated during 2003–2015 (the class area increased from 12.13 ha to 49.76 ha and the aggregation index increased from 91.15 to 94.65). We thus concluded that S. alterniflora invasion in the Zhangjiang Estuary had seriously increased and that measures should be taken considering the characteristics shown in different subzones. This study provides an example of applying GE imagery to monitor invasive plants and illustrates that this approach can aid in the development of governmental policies employed to control S. alterniflora invasion.

Highlights

Biological invasions are important components of global change that challenge the conservation of biodiversity and negatively affect ecosystem functioning [1,2,3]
When considering the categories of water body and intertidal mudflat, the confusion may be attributed to the tidal activity, which can lead to turbid water in littoral areas
Another advantage is that researchers can flexibly select images of different resolutions from Google Earth based on the scale of the study area, because the spatial resolution of GE imagery depends on the spatial resolution of the original image provided by the commercial image operators, and on the zoom level of Google Earth

Summary

Introduction

Biological invasions are important components of global change that challenge the conservation of biodiversity and negatively affect ecosystem functioning [1,2,3]. Invasive plants can directly compete with native species, indirectly cause economic losses, and formidably threaten local ecological environments by altering dominant vegetation types, soil properties, biogeochemical cycles, patterns of herbivory, and disturbance regimes [4,5]. S. alterniflora, an invasive plant, was first introduced to China from the Atlantic Coast of the U.S. in 1979 [6]. For the purpose of ecological engineering, it was used to protect coastal dikes, promote siltation, purify water quality, and ameliorate soil, etc. With its strong adaptability, high productivity, and rapid growth, introduced S. alterniflora expands rapidly in the intertidal zones [8,9,10]

Objectives

Methods

Results

Discussion

Conclusion