Modeling the Invasion of Holly (Ilex aquifolium): Spatial Relationships and Spread Trajectories

Abstract

In this study, we investigated the environmental factors associated with the establishment of invasive English holly (Ilex aquifolium) and the spatiotemporal trajectories of its potential spread. We collected georeferenced presence and absence and demographic data of holly between 2011 and 2014 in Saint Edward State Park, Washington. We analyzed them through a spatially explicit framework that combines multiple logistic regression, cellular automata, and bivariate quadratic modeling. Results showed that the presence of holly is influenced by the proximity to evergreen coniferous vegetation and forest edge, distance to streams, forest structure, and slope direction. Our study confirmed that local environmental conditions, species characteristics, and vegetative and dispersal mechanisms play a significant role in determining the rate and success of holly establishment across the different phases of invasion. Invasive species management plans should consider both species characteristics and their habitat and the interactions among them when planning long-term strategies for control and eradication.

我们于本研究中, 探讨与入侵的英国冬青树 (Ilex aquifolium) 定殖有关的环境因素, 及其潜在扩散的时空轨迹。我们蒐集华盛顿州的圣爱德华州立公园自 2011 年至 2014 年间, 以地理坐标为参考的冬青树存在及缺席与统计数据。我们透过结合多元逻辑迴归、细胞自动机与二元二次式模式化的明确空间架构, 分析上述数据。研究结果显示, 冬青树的存在, 是受到与常青针叶林及森林边缘的邻近性、与溪流的距离、森林结构和坡向带的影响。我们的研究确认了地方环境与条件、物种特徵和植栽及分布机制, 在决定冬青树在不同入侵阶段的定殖比率及成功中, 扮演了显着的角色。入侵物种管理方案, 在规划控制与根除入侵物种的长程策略时, 应同时考量物种特徵及其栖地, 以及两者之间的互动。

En este estudio investigamos los factores ambientales asociados con el establecimiento de la planta invasora acebo inglés (Ilex aquifolium) y las trayectorias espaciotemporales de su dispersión potencial. Recogimos datos demográficos de la presencia y ausencia georreferenciadas del acebo entre 2011 y 2014 en el Parque Estatal Saint Edward, en Washington. Analizamos esos datos por medio de un marco espacialmente explícito que combina modelaje de regresión logística múltiple, autómata celular y cuadrática bivariable. Los resultados mostraron que la presencia del acebo es influida por la proximidad a vegetación de coníferas de hoja perenne y el borde del bosque, distancia a las corrientes de agua, estructura del bosque y dirección de la pendiente. Nuestro estudio confirmó que las condiciones ambientales locales, las características de la especie y los mecanismos vegetativos y de dispersión juegan un papel significativo en determinar la tasa y éxito de la fijación del acebo a través de las diferentes fases de la invasión. Los planes de manejo de las especies invasoras deben considerar tanto las características de la especie como sus hábitats, y las interacciones entre éstos, cuando se planeen estrategias de control y erradicación a largo plazo.

Key Words:

• cellular automata
• Ilex aquifolium
• invasive species
• multiple logistic regression
• Pacific Northwest

关键词:

• 细胞自动机
• 冬青树
• 入侵物种
• 多元逻辑迴归
• 太平洋东北岸。

Palabras clave:

• autómata celular
• Ilex aquifolium
• especies invasoras
• regresión logística múltiple
• Pacífico del Noroeste

Acknowledgments

This research was conducted under Washington State Parks Research Permit # 110101. We thank Washington State Parks and the staff of St. Edward State Park for their assistance with the project. We also thank Joanna Mead, Amy Vondette, and Katrina Fisk for help with GIS data processing and collection; and Elliot Church, David Cronkright, Caitlin Campbell, Rachel Phillips, Jenna Beverly, Justin Bales, Dexter Chan, Michael Crepps, Shannon Kehoe, Evan Kreklow-Carnes, Chuong Pham, and James Watson for help with the field work. We also thank the Editor, Barney Warf, and two anonymous reviewers for their helpful comments on the article.

Funding

Fieldwork was made possible in part through a grant to support undergraduate participation in research from the University of Washington.

Additional information

Notes on contributors

Santiago López

SANTIAGO LOPEZ is an Assistant Professor in the School of Interdisciplinary Arts and Sciences at the University of Washington Bothell, Bothell, WA 98011. E-mail: [email protected]. His research interests include geographic information science, land use and land cover changes in the Americas, and issues related to the human dimensions of global environmental change.

David L. Stokes

DAVID L. STOKES is an Associate Professor in the School of Interdisciplinary Arts and Sciences at the University of Washington Bothell, Bothell, WA 98011. E-mail: [email protected]. He is an ecologist and conservation biologist whose current research focuses on animal movement and migration, conservation and restoration of endangered populations, and invasive species spread.