Year: 2024
Type: dissertation
Abstract: This dissertation aims to assess the impact of invasive species on coastal wetlands and urban Forest ecosystems, and proposes an approach for understanding and devising management strategies. The study of invasive species, which can lead to disrupt ecosystems, is vital for maintaining ecosystem stability and preserving biodiversity. Ecosystem stability relies on the complex network of interactions among various species. However, the introduction of invasive species has the potential to disturb these interactions, ultimately resulting in the destabilization of ecosystems. Understanding the impact of invasive species is crucial for safeguarding ecosystem stability. Invasive species also pose a threat to biodiversity by displacing or causing the extinction of native species. In this study, the term "Invasive Species" refers to biological invasions from species to ecosystem to global dimensions. Specifically, Invasive Species encompasses the concept of ecosystem-disturbing species and harmful wild animals as regulated in South Korea, taking into consideration human impact, ecological factors, as well as economic and socio-economic aspects. This dissertation encompasses three research studies. Chapters 2 and 3 delve into the impact and management of Spartina anglica, an invasive plant species in coastal wetlands. Chapter 4 focuses on assessing the habitat suitability models of harmful wild animals, specifically water deer and wild boar, in urban forests, along with examining the impact of fencing. The summary of each chapter is as follows. \nChapter 2. Spartina anglica Impact on Tidal Flat Macrofauna: \nSpartina anglica is an invasive perennial marsh grass that has a significant negative impact on tidal flat ecosystems. Few studies have examined the effects of S. anglica patch size on macrofauna. In this study, we conducted a field experiment to identify the effects of S. anglica patches that appeared ≤ 5 years after invasion on macrofauna assemblages. The survey area was divided into two regions: Suaeda japonica vegetation 0–60 m from the embankment and bare mudflats 60–90 m from the embankment. S. anglica patches were categorized into small (1–4 m2),medium(5–11m2),and large(13–40m2)sizes,with four replicates per section.The ratio of below- to above-ground biomass was significantly higher in small S. anglica patches than in medium and large patches, indicating that more resources were allocated to rhizomes in smaller patches with a shorter invasion history (1–2 years). Macrofauna richness (70%), Shannon–Wiener diversity (80%), and density (67%) decreased following S. anglica invasion, whereas the abundance of the infaunal deposit-feeding polychaete Perinereis linea, and epifaunal gastropods Batillaria cumingi and Lactiforis takii, increased. An ordination of the macroinvertebrate assemblages clearly distinguished the S. anglica invasion habitat from the adjacent uninvaded tidal flatand Suaeda japonica habitats. The results of this study offer significant insight into the early invasion strategies of the aggressive plant invader S. anglica, which may facilitate coastal wetland management and sheds light on the impact of Spartina anglica invasion on macrofaunal assemblages. \nChapter 3. Management Strategies for Spartina anglica: \nS. anglica, an invasive marsh grass, was designated as a harmful marine organism in 2016 due to its ability to stabilize mudflats and reduce macrobenthic diversity. To control such invasive species, physical, chemical, or biological methods can be applied while chemical methods are prohibited by law due to ecological disruption. However, the preferred methods of soil tillage, cutting, and native plant restoration for managing S. anglica have rarely been analyzed. To compare the methods, we performed 9 treatments with four replicates, comprising control, different frequencies of clipping (once and twice) and tilling (once and twice), and different densities (50 and 100 seedling)of restoration of the native plants Suaeda japonica and Phragmites australis. To evaluate the severity of disturbance, we measured coverage, stem density, average plant height, and above-ground biomass for two years. We found P. australis and S. japonica did not successfully establish or survive due to niche differences and the inherent biological features of Spartina. However, physical removal had a stronger effect than interspecific interaction. Two cutting treatments in the early and the late growing season reduced plant height and biomass of S. anglica by 6% and 34%, respectively, compared with the control treatment at the rapid vegetative growth stage in the following year. We also found that two tillage treatments reduced biomass, plant cover, and stem density by 32%, 38%, and 83%, respectively, in the following year.In the study site, managing invasive species such as S. anglica demands complete physical destroy by several attempts of soil tillage while attempt to restore native species had marginal control effects. \nChapter 4. Wildlife Incursions and Fencing Effectiveness: \nForest fragmentation and habitat loss are increasing human–wildlife conflict. The use of fencing to reduce wildlife incursions into agricultural areas, particularly through optimizing fence locations, is gaining interest. However, the spatiotemporal predicted movement patterns of animals relative to hotspot fencing have received scant study. This study evaluated how effectively a single fence reduces seasonal incursions into an agricultural zone by crop-damaging mammals. The seasonal predicted distributions of wild boar (Sus scrofa Linnaeus)and water deer (Hydropotes inermis argyropus) were evaluated, along with the effect of a short fence on their spatial behavior at a junction of a forest fringe and fields during different seasons. Seasonal habitat suitability models were constructed using unmanned aerial vehicle and camera trap data for the environmental predictor variables. Connectivity analysis utilizing habitat suitability models was applied to assess the effects of fencing on wildlife. The seasonal movements of water deer and wild boar were found to be primarily constrained by trails and roads, while fencing was the most important variable for wild boar following fence erection. A high permeability area of wild boar disappeared at the fencing location, while that of the water deer was maintained. \nCollectively, these studies underscore the pervasive impact of invasive species on diverse ecosystems and emphasize the critical need for effective management strategies. The insights gained from investigating Spartina anglica early invasion strategies contribute to the broader understanding of coastal wetland ecosystems. Additionally, the comparative analysis of management methods for Spartina anglica highlights the importance of complete physical destruction for successful control. In the context of human-wildlife conflicts, the evaluation of fencing effectiveness provides valuable guidance for optimizing fence locations, particularly in areas prone to incursions by wild boar and water deer. These findings contribute to the ongoing efforts to mitigate conflicts between agricultural activities and wildlife. \nOverall, they provide a robust foundation for policymakers and environmental managers to formulate strategies aimed at preserving biodiversity and ecosystems threatened by invasive species.
Author: 신원협
Institution: Seoul National University
Language: English
Subfield: Nature and Landscape Conservation
Field: Environmental Science
Domain: Physical Sciences
SDG: Life on land
Open Access status: green
OpenAlex ID: W6982682652