Shifting Baselines: Invasive Species in a Changing Climate

Two people in bug nets looking at a GPS in the woods
Two U.S. Fish and Wildlife Service (USFWS) biologists surveying for invasive species. 📷 Deborah Kornblut/USFWS

Climate change and invasive species are the leading causes of biodiversity loss. While often addressed separately, these two environmental stressors interact and introduce significant challenges in Alaska.

Alaska’s geographic location and environmental conditions make it difficult for invasive species to arrive and spread, but also make the state particularly vulnerable to climate change. Over the past six decades, Alaska’s average air temperature has increased roughly 4oF — more than twice that of the lower 48 states. The shifting climate opens new entry points for invasive species and creates ways for invasive species to arrive and survive here.

“The climate is a regional trend affecting events like droughts or extreme weather, and then all those things interact with the species on the landscape,” said Dawn Magness, a landscape ecologist for the Kenai National Wildlife Refuge. “These are going to be complex interactions, and there’s potential for an invasive species to be a part of that.”

Graphic illustrating the relationship between invasive species and climate change using illustrations of extreme weather, species movement, increased ship traffic, and changing growing seasons
An illustration of the relationship between invasive species and climate change. Adapted from Bradley et al. 2020 by Grace Rodgers/USFWS.

What are Invasive Species

Invasive species are broadly defined as plants or animals that are:

1) introduced, often by humans,

2) non-native,

3) and cause harm to lands, waters, economies, or human health.

Plants or animals may become invasive if they consume or outcompete native species, often by reproducing and spreading quickly. Invasive species can impact landscapes, infrastructure, food security, livelihoods, and cultural values. Management costs drastically increase when the invasive species spreads. Compared to native species, invasives are better prepared for a changing climate because of their ability to survive in varying environmental conditions, such as with temperature rise.

Most species never receive the ‘invasive’ status because undisturbed environments can sometimes prevent or slow the spread of a non-native species. However, climate change is altering the playing field.

Woman in a USFWS baseball hat inspects a white swetclover plant growing on a gravelly slope
White sweetclover, an invasive plant, growing along a roadside in Interior Alaska. 📷 Deborah Kornblut/USFWS

How Climate Change and Invasive Species Interact

As the climate changes, native and invasive species may grow in areas where they were previously not able to survive or reproduce. Rising temperatures, extreme weather, wildfires, drought, flooding, deforestation, urbanization, pollution, and other landscape-scale disturbances increase opportunities for invasive species to arrive in new areas. For example, as temperatures rise and sea ice melts, marine shipping routes may expand and new pathways — the routes by which invasive species spread — could become available.

A few invasive species likely to take advantage of climate change in Alaska include the European green crab, Elodea, and white sweetclover.

European Green Crab

Person holding a live European green crab
As of February 2022, there were no known European green crabs (Carcinus meanas) in Alaska. 📷 USFWS

The European green crab (Carcinus meanas) is a small shore crab known for its opportunistic feeding and aggressive behavior. Recognizable by the five prongs on each side of the front of its body, the crab is often listed among the world’s worst invasive species. Its large appetite can have dramatic negative impacts for native shore crab, clam, and oyster populations, which further disrupts food webs for other native animals.

“If the ocean water warms or the chemistry of the ocean water changes due to the increased runoff from glaciers, that can alter coastal marine systems,” said Ben Wishnek, a U.S. Fish and Wildlife Service Invasive Species Biologist in Alaska . “If these areas become more suitable for European green crabs, there is a greater likelihood of negative impacts to important coastal environments.”

While they are not known to be in Alaska, European green crabs were spotted just south of the state in December 2020. Unlike native crabs, this invasive species can tolerate a wide range of salinities and temperatures, allowing them to survive in a changing climate. With warming marine temperatures in Alaska, biologists generally agree it’s only a matter of time until the species arrives.


Hand holding a healthy fragment of Elodea above a waterbody
A healthy fragment of Elodea found in Anchorage. 📷 Deborah Kornblut/USFWS

Elodea (Elodea spp.) is another invasive species that is perhaps already taking advantage of climate change. Alaska’s first aquatic invasive plant, Elodea was brought into the state through the aquarium trade. The first documentation of Elodea in the wild was in Cordova in 1982, likely after somebody dumped an aquarium tank into the local waterways.

Elodea’s leaves are arranged in groups of threes and the plants create large, tangled masses below the surface of lakes and streams in Southcentral and Interior Alaska. These masses can encroach on salmon habitat and spoil recreational opportunities by fouling equipment such as boats and floatplanes. If left unmanaged, research says Elodea could cause $159 million annual damages to Alaska’s commercial sockeye fishery.

As for climate change, Elodea could benefit from shifts in water temperatures and growing seasons. Changes to the Elodea’s spread would be especially visible in Interior Alaska where conditions would invite new growth due to shortened and more mild winters.

White Sweetclover

Two hands holding the top of a healthy white sweetclover plant before it has flowered
White sweetclover before it has flowered. 📷 Deborah Kornblut/USFWS

Climate change also affects invasive plants found on land. The invasive plant white sweetclover (Melilotus albus) is commonly found alongside roads and other places near human activity in Southcentral and Interior Alaska. Growing up to six feet, the aromatic flower is a major competitor with native plants due to its ability to change soil chemistry. In its second year of growth, a single plant can produce up to 350,000 seeds, allowing for a rapid spread.

As temperatures rise due to climate change, warmer winters mean that the seeds have a higher chance to survive until the next growing season. Places like Kanuti or Tetlin National Wildlife Refuges may face greater impacts of white sweetclover due to their proximity to highways.

“That’s something we’re seeing here in northern Alaska along the Dalton Highway. As the climate warms, white sweetclover is moving steadily northward partly because it’s assisted by people, but partly because it’s now able to survive. It’s just not getting as cold,” said Lisa Dlugolecki, another USFWS Invasive Species Biologist working in Alaska.

What the USFWS is Doing in Alaska

Empty crab pot during a low tide with two people walking away from the pot in the background
USFWS staff set crab pots in Cold Bay in 2021 as part of an effort to monitor for European green crabs. 📷 Deborah Kornblut/USFWS

By exploring linkages between climate change and invasive species, we can better understand and address these challenges that have the potential to threaten wildlife, lands and waters, and our communities. Working with partners to prevent and manage invasive species in Alaska’s rapidly changing climate is especially important.

Today, we are collaborating with partners to conduct habitat suitability modeling under current and projected conditions, assess pathways of new introductions, and horizon scanning to evaluate which invasive species could spread to Alaska. Information from these activities helps managers and biologists make informed decisions on how and where to direct resources for early detection of invasive species and quick response to infestations.

Our decision-making process also adopts the Resist-Accept-Direct (RAD) framework, a concept that helps resource managers respond to ecological changes resulting from climate change.

“RAD strategies need to be contextualized within a real landscape. We have to make choices about which landscapes we can protect. It’s not enough just to document change,” said Magness.

What You Can Do

Group of adults and children walking through the woods with their weed clippers to remove invasive species from their local community
Volunteers of all ages can help remove invasive species, like during this event to remove the surrounding invasive bird cherry trees. 📷 Deborah Kornblut/USFWS

Everybody in Alaska has a unique opportunity to address the spread of invasive species before they have an irreversible impact on the places we love and respect. Together, we can make a difference in keeping Alaska wild and free of invasive species by learning more about the invasive species in our local areas, checking and cleaning gear and equipment (including boots and clothes), and reporting invasive species. Reports from members of the public are critical for early detection and effective response. Reports with an image and location can be submitted via the Invasive Species Hotline (1–877-INVASIV) or via the Alaska Department of Fish & Game Online Reporter.

To learn more or to get involved, check out the National Invasive Species Awareness Week, contact your local invasive species management organization, and stay tuned for events during Alaska Invasive Species Awareness Week (mid-June).

Additional Resources:

Magness et al. (2022). “A Multi-Scale Blueprint for Building the Decision Context to Implement Climate Change Adaptation on National Wildlife Refuges in the United States,” Earth. Vol. 3: No. 1, PP 136–156.

National Research Council. (2011) “Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia,” The National Academies Press. Washington, DC.

Schwoerer, Tobias; Little, Joseph M.; and Adkison, Milo D. (2019) “Aquatic Invasive Species Change Ecosystem Services from the World’s Largest Wild Sockeye Salmon Fisheries in Alaska,” Journal of Ocean and Coastal Economics: Vol. 6: Iss. 1, Article 2.

In Alaska we are shared stewards of world renowned natural resources and our nation’s last true wild places. Our hope is that each generation has the opportunity to live with, live from, discover and enjoy the wildness of this awe-inspiring land and the people who love and depend on it.

Story compiled by Grace Rodgers, Climate Fellow with Alaska External Affairs, and Deborah Kornblut, Regional Invasive Species Outreach Coordinator.



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