Li et al. BMC Ecol (2020) 20:7 https://doi.org/10.1186/s12898-020-00277-8 BMC Ecology RESEARCH ARTICLE Open Access Monitoring of the invasion of Spartina alternifora from 1985 to 2015 in Zhejiang Province, China Nan Li1 , Longwei Li2* , Yinlong Zhang1 and Ming Wu3 Abstract Background: Spartina alternifora is an invasive plant on the coast of China that replaces native vegetation and has a serious negative impact on local ecosystems. Monitoring the spatial distribution of S. alternifora and its changes over time can reveal its expansion mechanism, which is crucial for the management of coastal ecosystems. The purpose of this study was to map the distribution of S. alternifora in Zhejiang Province from 1985 to 2015 using a time series of Landsat TM/OLI images and analyze the temporal and spatial patterns of expansion of this species. Results: After analyzing the distribution of coastal vegetation, the vegetation index was calculated based on Landsat images for 4 years (1985, 1995, 2005 and 2015). According to a threshold determined based on expert knowledge, the distribution of S. alternifora in Zhejiang Province was extracted, and the temporal and spatial changes in the distribu- tion of S. alternifora were analyzed. The classifcation accuracy was 90.3%. S. alternifora has expanded rapidly in recent decades after being introduced into southern Zhejiang. Between 1985 and 2015, S. alternifora increased its area of distribution by 10,000 hm2, and it replaced native vegetation to become the most abundant halophyte in tidal fats. Overall, S. alternifora expanded from south to north over the decades of the study, and the fastest expansion rate was 463.64 hm2/year, which occurred between 1995 and 2005. S. alternifora was widely distributed in the tidal fats of bays and estuaries and expanded outward as sediment accumulated. Conclusions: This study reveals the changes over time in S. alternifora cover in Zhejiang and can contribute to the control and management of this invasive plant. Keywords: Dynamic change, Expert knowledge, Invasive plants, Landsat images, Spartina alternifora Background alternifora was intentionally introduced as an ecological Spartina alternifora Loisel. is a perennial halophyte that engineering species into China for sediment accumula- is native to the Atlantic and Gulf coasts of North America tion, land reclamation and saline soil amelioration [3]. and predominates in local salt marshes [1]. S. alternifora Experiments have shown that S. alternifora can per- is generally considered benefcial in ecological restora- form ecological functions and provide economic benefts tion because of its well-developed underground struc- [2, 4–6]. Coastal stabilization and land reclamation are ture, high salt tolerance, high reproductive capacity and the most important ecological functions of this species. rapid growth [2]. For this reason, in December 1979, S. A trial planting of S. alternifora was employed to solve river-shore crumbling near a sluice in Zhejiang Prov- ince in 1986. Te planting successfully solved this prob- *Correspondence: [email protected] lem, costing only 800 Yuan, and withstood typhoons and 2 School of Environmental & Resource Sciences, Zhejiang Agriculture foods [2]. Te S. alternifora marsh on the canal bank and Forestry University, Hangzhou 311300, China 3 Full list of author information is available at the end of the article prevented more than 100,000 m of sediment per year © The Author(s) 2020. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://crea- tivecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdo- main/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Li et al. BMC Ecol (2020) 20:7 Page 2 of 12 from migrating downstream [3]. In addition, Shen et al. our understanding of the invasion mechanism but also [7] proved the efcacy of this plant for saline soil ame- restricts the decision-making of government depart- lioration. Furthermore, S. alternifora is used as animal ments. To better understand the expansion mecha- fodder and fsh feed [2, 8, 9] and can be used to produce nism of S. alternifora and prevent its further invasion, green manure and biomineral liquids [1]. it is necessary to map its distribution and monitor its Since its introduction, S. alternifora has greatly dynamic changes. Terefore, this study employed a time expanded in distribution in the coastal salt marshes of series of Landsat Tematic Mapper (TM)/Operational China [1, 10]. An increasing number of studies have dem- Land Imager (OLI) images to monitor the dynamic onstrated that although this exotic species can be benef- changes in S. alternifora in the coastal areas of Zhejiang cial, it has negative impacts on native coastal ecosystems Province, China. Specifcally, the spatial distribution of [11–14]. Once established, S. alternifora quickly expands S. alternifora in Zhejiang Province from 1985 to 2015 on bare beaches and competes with native plants, invad- was mapped, the spatial and temporal heterogeneities of ing their habitats and replacing them. Areas of Scir- S. alternifora expansion were analyzed, and the changes pus mariqueter Wang et Tang and Phragmites australis in S. alternifora in bays and estuaries were analyzed. Trin. ex Steud. and young mangrove swamps have been Tis study documents the temporal and spatial changes invaded by S. alternifora. Research shows that the spe- in S. alternifora invasion on the eastern coast of China, cies richness of benthic macroinvertebrates in S. alterni- providing important data for the ecological study of S. fora swamps is reduced because its invasion alters the alternifora. physicochemical properties of the sediment [15]. Some endangered birds are threatened because the density of S. Methods alternifora communities is too high and the altered habi- Study area tats are no longer suitable for them [16]. Terefore, the habitats of native plants, birds and benthic animals are Zhejiang Province is located in eastern China (Fig. 1a). It afected by S. alternifora, and biodiversity is reduced [17, has a subtropical monsoon climate with moderate annual 18]. In addition, the invasion of S. alternifora impedes temperatures and abundant sunshine and rainfall. Zheji- the development of local aquaculture and tourism and ang has abundant marine resources, with a coastline of hinders water-based transportation [19, 20]. Te signif- 6486.24 km, accounting for 20.3% of China’s coastline. cant negative impacts of this species have far exceeded According to the second wetland resource survey, the tidal fats are the largest natural wetland in the province, its ecological functions and economic benefts [12, 21, 2 22]. S. alternifora was listed as one of the top 16 inva- covering 1548.86 km . Te tidal fats are mainly distrib- sive alien species by the State Environmental Protection uted in Hangzhou Bay, Sanmen Bay and Yueqing Bay. Administration of China in 2003 [1, 23]. In 1983, S. alternifora was frst planted in the tidal fats Biological invasion has a strong infuence on Earth’s of Yuhuan County and then introduced to other places ecosystems and is considered one of the three most along the coast. Over the past 30 years, S. alternifora has pressing environmental issues [24–26]. S. alternifora rapidly expanded and become the main salt marsh veg- threatens local ecosystems and causes extremely large etation along the coast of Zhejiang Province. losses to the regional economy [11]. At present, from Guangxi Province (21° 33′ N, 108° 08′ E) to Liaoning Data collection and preprocessing ′ ′ Province (40° 20 N, 122° 35 E), S. alternifora can be Te data collected in this study included remote sensing found in most of China’s coastal areas [10, 27]. Accord- images, vector data such as administrative boundaries, ing to the Marine Environment Quality Bulletin of China, feld survey data and literature data. Remote sensing is this species invaded 12,400 ha of China’s coastal areas in an efective tool for monitoring changes in Earth’s surface 2006. Jianbo Lu [1] stated that it covered a total area of and is suitable for coastal wetland monitoring and vegeta- 34,178 ha in 2012. Hence, the invasion of S. alternifora tion monitoring [27–30]. Since 1972, NASA has launched has become a hot topic for ecologists and biologists at a number of Landsat series satellites, which are the most home and abroad. commonly used remote sensing data sources. Twenty-six Over the years, scholars have conducted many stud- scenes of Landsat TM/OLI images were obtained from ies on the invasion of S. alternifora in China’s coastal the U.S. Geological Survey Global Visualization data areas. However, there are few studies on the monitor- server (https ://glovi s.usgs.gov/app). Te principles of ing of changes in S. alternifora distribution, with most remote sensing image acquisition included (1) selecting such studies limited to monitoring the distribution of images taken between May and November, which is the S. alternifora in a given year. Te lack of long-term growth season of S. alternifora and (2) selecting high- sequential monitoring of S.