Sectoral Impacts of Invasive Species in the United States and Approaches to Management

Invasive species have a major effect on many sectors of the U.S. economy and on the well-being of its citizens. Their presence impacts animal and human health, military readiness, urban vegetation and infrastructure, water, energy and transportations systems, and indigenous peoples in the United States (Table 9.1). They alter bio-physical systems and cultural practices and require significant public and private expenditure for control. This chapter provides examples of the impacts to human systems and explains mechanisms of invasive species’ establishment and spread within sectors of the U.S. economy. The chapter is not intended to be comprehensive but rather to provide insight into the range and severity of impacts. Examples provide context for ongoing Federal programs and initiatives and support State and private efforts to prevent the introduction and spread of invasive species and eradicate and control established invasive species.

Inventory and Monitoring of Invasive Species

Inventory and monitoring programs and high-quality distribution data are needed to manage invasive species and to develop quantitative ecological, economic, and social impact assessments. Strong inventory and monitoring programs provide valuable insights that help direct efforts to prevent and contain invasive species. Understanding where to focus management efforts, in addition to educational outreach, is key to developing economically efficient and ecologically relevant programs. As noted in Chap. 10.1007/978-3-030-45367-1_2, additional research is needed to address large-scale impacts and co-occurring impacts of multiple invaders. Inventory and monitoring efforts help to inform where this research can be most effectively applied by identifying areas where invasives are most abundant, most likely to spread, or most likely to be contained (Byers et al. 2002; Myers et al. 2000). Furthermore, as climate change continues to pose new and uncertain impacts on ecosystems, monitoring at the edge of invasive species’ ranges will become more important to management efforts (Hellmann et al. 2008).

Impacts of Invasive Species in Terrestrial and Aquatic Systems in the United States

The introduction, establishment, and spread of invasive species in terrestrial and aquatic environments is widely recognized as one of the most serious threats to the health, sustainability, and productivity of native ecosystems (Holmes et al. 2009; Mack et al. 2000; Pyšek et al. 2012; USDA Forest Service 2013). In the United States, invasive species are the second leading cause of native species endangerment and extinction, and their costs to society have been estimated at $120 billion annually (Crowl et al. 2008; Pimentel et al. 2000, 2005). These costs include lost production and revenue from agricultural and forest products, compromised use of waterways and terrestrial habitats, harm to human and animal health, reduced property values and recreational opportunities, and diverse costs associated with managing (e.g., monitoring, preventing, controlling, and regulating) invasive species (Aukema et al. 2011; Pimentel et al. 2005). The national significance of these economic, ecological, and social impacts in the United States has prompted various actions by both legislative and executive branches of the Federal Government (e.g., the Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990; the Noxious Weed Control and Eradication Act of 2002; Executive Order 13112 of 1999, amended in 2016).

Legislation and Policy

In the United States, biological invaders are managed by all Federal agencies that have responsibility for natural resources, as well as the States, territories, and occasionally regional entities. Federal agencies’ invasive species programs are implemented under the mandates and guidance provided by dozens of laws, which include statutes enacted by the Congress, Executive Orders issued by the President, and regulations adopted by the relevant agencies. Although there are numerous laws implemented by the States or occasionally regional entities, this chapter will focus on Federal legislation and regulations that guide work on all public and private forests, rangelands, and grasslands in the United States. There are three categories of laws: (1) laws to prevent introduction or initial spread; (2) laws for management or control of invasive species; and (3) more generally defined land management laws which serve as an umbrella for invasive species activities.

The Role of International Cooperation in Invasive Species Research

The root cause of the biological invasion problem is globalization, which has facilitated the planet-wide breakdown of biogeographic barriers to species migration (Mooney and Hobbs 2000). In order to understand and manage the problem, coordination on a global scale is essential, and international cooperation among affected countries as well as with countries of pest origin must therefore play a critical role in virtually all aspects of research on biological invasions (Chornesky et al. 2005; McNeely et al. 2001; Perrings et al. 2010; Wingfield et al. 2015). Here we discuss key aspects of research on biological invasions, where international collaboration and coordination are important, and what infrastructures play a role in this work.

Management of Landscapes for Established Invasive Species

Long-term management strategies are invoked once an invasive species has become established and spread beyond feasible limits for eradication or containment. Although an invasive species may be well-established in small to large geographical areas, prevention of its spread to non-affected areas (e.g., sites, regions, and cross-continent) through early detection and monitoring is an important management activity. The level for management of established invasive species in the United States has increasingly shifted to larger geographical scales in the past several decades. Management of an invasive fish may occur at the watershed level in the western States, with watershed levels defined by their hydrologic unit codes (HUC) ranging from 2 digits at the coarsest level to 8 digits at the finest level (USGS 2018). Invasive plant management within national forests, grasslands, and rangelands can be implemented at the landscape level (e.g., Chambers et al. 2014), although management can still occur at the stand or base level. Landscapes in this chapter refer to areas of land bounded by large-scale physiographic features integrated with natural or man-made features that govern weather and disturbance patterns and limit frequencies of species movement (Urban et al. 1987). These are often at a large physical scale, such as the Great Basin.

Restoration of Landscapes and Habitats Affected by Established Invasive Species

Preventing invasions of aquatic and terrestrial habitats is the preferred and most cost-effective approach to address the invasive species threat (see Chap. 10.1007/978-3-030-45367-1_6). However, when prevention efforts fail, invasive species can become widespread and deeply embedded in native ecosystems, causing severe impacts (see Chaps. 10.1007/978-3-030-45367-1_2, 10.1007/978-3-030-45367-1_3, and 10.1007/978-3-030-45367-1_4). In such cases, invader control (see Chap. 10.1007/978-3-030-45367-1_7) accompanied by restoration facilitates recovery of native species and prevents reinvasion (e.g., Pearson et al. 2016). Here, we summarize the current state of restoration science and highlight critical information gaps that must be overcome to advance ecosystem restoration in terrestrial and aquatic systems affected by invasive plants, insects, diseases, and vertebrates.

Future Invasive Species Research Challenges and Opportunities

Introductions of new invasive species continue with ever-expanding global trade, and the increase in invasive species does not show any sign of saturation for most taxonomic groups. However, some non-native species may arrive in an area and fail to become established or have no measurable impact. Thus, the protection of valued ecosystems depends on reliable knowledge about the species that are or might be invading, the ecosystems that are being invaded, the potential magnitude of different types of harm, the availability and effectiveness of management responses, and the desired state of ecosystems under protection. Primary research is a vital means of gathering that knowledge.

Effects of Climate Change on Invasive Species

Mean surface temperatures have increased globally by ~0.7 °C per century since 1900 and 0.16 °C per decade since 1970 (Levinson and Fettig 2014). Most of this warming is believed to result from increases in atmospheric concentrations of greenhouse gases produced by human activity. Temperature increases have been greater in winter than in summer, and there is a tendency for these increases to be manifested mainly by changes in minimum (nighttime low) temperatures (Kukla and Karl 1993). Changes in precipitation patterns have also been observed, but are more variable than those of temperature. Even under conservative emission scenarios, future climatic changes are likely to include further increases in temperature with significant drying (drought) in some regions and increases in the frequency and severity of extreme weather events (IPCC 2007). For example, multimodel means of annual temperature from climate projections predict an increase of 3–9 °C in the United States over the next century combined with reductions in summer precipitation in certain areas (Walsh et al. 2014). These changes will affect invasive species in several ways. Furthermore, climate change may challenge the way we perceive and consider nonnative invasive species, as impacts to some will change and others will remain unaffected; other nonnative species are likely to become invasive; and native species are likely to shift their geographic ranges into novel habitats.

Early Intervention Strategies for Invasive Species Management: Connections Between Risk Assessment, Prevention Efforts, Eradication, and Other Rapid Responses

Managing invasive species becomes increasingly difficult and expensive as populations of new pathogens, plants, insects, and other animals (i.e., pests) spread and reach high densities. Research over the past decade confirms the value of early intervention strategies intended to (1) prevent invasive species from arriving within an endangered area or (2) detect and respond quickly to new species incursions (Baker et al. 2009; Ewel et al. 1999; Holden et al. 2016; Leung et al. 2014). The goal of such biosecurity approaches is to keep or return the density of invasive species to zero so that damages from those pests might be prevented or to confine populations to localized areas so that damage from those species might be limited (Magarey et al. 2009). Prediction, prevention, early detection, eradication, and other rapid responses, all components of proactive management, are less costly and more effective than reactive tactics (Epanchin-Niell and Liebhold 2015; Leung et al. 2002; Lodge et al. 2006; Rout et al. 2014) (Fig. 6.1). Prediction is achieved through risk assessment (a process to forecast the likelihood and consequence of an invasion) and pathway analysis (a process to evaluate the means by which invasive species might be brought into an area of concern). Prevention is achieved through a variety of measures including regulations and quarantine treatments. Indeed, pathway analyses and subsequent regulation of those pathways are considered “the frontline in the prevention of biological invasions” (Hulme 2009) and cost-effective approaches (Essl et al. 2015; Keller et al. 2007; Leung et al. 2002; Tidbury et al. 2016). Surveillance is fundamental to early detection, and if a target species is detected, the primary rapid responses are eradication, containment, or suppression (reviewed in Beric and MacIsaac 2015). Early intervention strategies often operate at spatial scales that are much greater than the scale at which most land managers operate. Success thus requires effective coordination among researchers, regulators, and managers at international, national, sub-national, and local levels.