This work was supported in part by the U.S. Department of Agriculture, Forest Service. The findings and conclusions in this publication are those of the authors and should not be construed to represent any official USDA or U.S. Government determination or policy. Effects of Climate Change on Invasive Species 4 Deborah M. Finch, Jack L. Butler, Justin B. Runyon, Christopher J. Fettig, Francis F. Kilkenny, Shibu Jose, Susan J. Frankel, Samuel A. Cushman, Richard C. Cobb, Jefrey S. Dukes, Jefrey A. Hicke, and Sybill K. Amelon over the next century combined with reductions in summer 4.1 Introduction precipitation in certain areas (Walsh et al. 2014). These changes will affect invasive species in several ways. Mean surface temperatures have increased globally by Furthermore, climate change may challenge the way we per- ~0.7 °C per century since 1900 and 0.16 °C per decade since ceive and consider nonnative invasive species, as impacts to 1970 (Levinson and Fettig 2014). Most of this warming is some will change and others will remain unaffected; other believed to result from increases in atmospheric concentra- nonnative species are likely to become invasive; and native tions of greenhouse gases produced by human activity. species are likely to shift their geographic ranges into novel Temperature increases have been greater in winter than in habitats. summer, and there is a tendency for these increases to be The ability to predict accurately how invasive species dis- manifested mainly by changes in minimum (nighttime low) tributions and their impacts will change under projected cli- temperatures (Kukla and Karl 1993). Changes in precipita- mate scenarios is essential for developing effective tion patterns have also been observed, but are more variable preventive, control, and restoration strategies. Climate vari- than those of temperature. Even under conservative emission ables are known to infuence the presence, absence, distribu- scenarios, future climatic changes are likely to include fur- tion, reproductive success, and survival of both native and ther increases in temperature with signifcant drying nonnative species. Environmental selection for traits that (drought) in some regions and increases in the frequency and enhance reproduction in warming climates will enable range severity of extreme weather events (IPCC 2007). For exam- expansion of some invasive species. Also, the availability of ple, multimodel means of annual temperature from climate “empty” niches in the naturalized range, an escape from projections predict an increase of 3–9 °C in the United States natural enemies, and a capacity to adapt to new habitats can D. M. Finch (*) U.S. Department of Agriculture, Forest Service, Rocky Mountain S. J. Frankel Research Station, Albuquerque, NM, USA U.S. Department of Agriculture, Forest Service, Pacifc Southwest e-mail: [email protected] Research Station, Albany, CA, USA J. L. Butler S. A. Cushman U.S. Department of Agriculture, Forest Service, Rocky Mountain U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Rapid City, SD, USA Research Station, Flagstaff, AZ, USA J. B. Runyon R. C. Cobb U.S. Department of Agriculture, Forest Service, Rocky Mountain Department of Natural Resources Management and Environmental Research Station, Bozeman, MT, USA Sciences, California State Polytechnic University, San Luis Obispo, CA, USA C. J. Fettig U.S. Department of Agriculture, Forest Service, Pacifc Southwest J. S. Dukes Research Station, Davis, CA, USA Forestry and Natural Resources and Biological Sciences, Purdue University, West Lafayette, IN, USA F. F. Kilkenny U.S. Department of Agriculture, Forest Service, Rocky Mountain J. A. Hicke Research Station, Boise, ID, USA Department of Geography, University of Idaho, Moscow, ID, USA S. Jose S. K. Amelon College of Agriculture, Food and Natural Resources, University of U.S. Department of Agriculture, Forest Service, Northern Research Missouri, Columbia, MO, USA Station, Columbia, MO, USA © The Author(s) 2021 57 T. M. Poland et al. (eds.), Invasive Species in Forests and Rangelands of the United States, https://doi.org/10.1007/978-3-030-45367-1_4 58 D. M. Finch et al. enhance an invader’s ability to respond positively to climate Similarly, management practices implemented in response to change (Jarnevich et al. 2014). effects of disturbances and climate can alter the susceptibil- In this chapter, we explain how the adaptive traits, genetic ity to invasions in positive or negative directions (Chapter 7). variability, and physiology of certain invasive species pro- For example, reseeding a disturbed area after a climate- vide them with the competitive ability to grow, reproduce, related event with seed contaminated with an aggressive and spread successfully under conditions of climate change. invasive plant like cheatgrass (Bromus tectorum) can unin- Our chapter offers examples of biological responses, distri- tentionally promote its spread. butional changes, and impacts of invasive species in relation This chapter covers the genetic basis of, and environmental to climate change and describes how these vary among selection on, several factors including (1) adaptive traits of plants, insects, and pathogens, as well as by species, and by invasive species, (2) evolutionary trends of invasive species in type and extent of change. We also review attributes of changing climates, and (3) interacting drivers and evolution- plants, insects, and pathogens that enhance their ability to ary responses of ecological communities to invasion. Climate adapt to changes in hosts, native species, and environments change and invasive species are drivers of global environmen- affected by climate change. tal change that interact across biological communities in ways Our assessment of the literature reveals that, for a given that have eco-evolutionary consequences. Successful inva- invasive species at a given location, the consequences of cli- sions are dependent on the genetic makeup of a species. High mate change depend on (1) direct effects of altered climate levels of additive genetic variation tend to be linked to suc- on individuals, (2) indirect effects that alter resource avail- cessful invasions (Crawford and Whitney 2010) and the ability ability and interactions with other species, and (3) other fac- of an invader to evolve in response to novel environments or tors such as human infuences that may alter the environment changing conditions. Rapid adaptation to local climates can for an invasive species. Manipulative experiments on inva- facilitate range expansions of invasive species (Colautti and sive species, while uncommon, have shown that some spe- Barrett 2013), even beyond the climatic distributions in their cies respond strongly to elevated carbon dioxide (CO2) (e.g., native ranges (Petitpierre et al. 2012). Dukes et al. 2011) but less so to temperature and precipita- We discuss and provide examples of how and why carbon tion (Dukes et al. 2011). Insects are not directly affected by cycling and carbon storage change, their relationship with elevated CO2, but they can be affected indirectly by responses insect outbreaks, and how climate can infuence those of plants to CO2. However, increasing temperatures can posi- changes. Insect and disease outbreaks can affect ecosystem- tively affect invasive insects by infuencing their movements, level carbon cycling and storage by reducing growth, sur- growth rates, phenology, dispersal, and survival. Conversely, vival, or distribution of trees. Under climate change, invasive elevated temperatures also have the potential to affect inva- organisms are likely to vary in their impact and rate of sive insects negatively by disrupting their synchrony with spread, depending on their sensitivities to climate variation their hosts and altering their overwintering environments. and on the extent and type of climate change. Climate change can directly affect invasive pathogens In order to manage invasive species under a changing cli- through effects on formation of spores, host infection suc- mate, it is important to anticipate which species will spread cess, or selection pressures. For example, some invasive to new habitats and when, and to understand how the charac- pathogens are sensitive to changes in timing and amount of teristics of specifc invaders may disrupt or have the potential precipitation and to changes in ambient temperature or to disrupt invaded ecosystems. Of utmost importance in con- humidity, whereas others are more responsive to changes in taining the spread of invasive species, managers must have host stress. Briefy, effects of climate change on pathogens the ability to (1) predict which species will positively respond vary depending on how the change is expressed and how to climate change, (2) predict and detect sites likely to be hosts are affected. invaded, and (3) deter incipient invasions before they are We describe and provide examples of how indirect effects beyond control. We outline methods for developing the capa- of climate change are mediated through changes in habitats, bility to predict and monitor invasive species in order to fore- hosts, other disturbances, trophic interactions, and land use cast their spread and increase their detection. Key fndings or management. Our chapter provides information on how and key research needs are included for each section. host-invasive species relationships and trophic interactions can be modifed by climate change while recognizing that important knowledge