Invasive non-native plant and animal species, both terrestrial and aquatic, are major threats to resources, ecosystems, habitat integrity, and biodiversity at Pictured Rocks National Lakeshore. Non-native species are those that originate in other regions of the world and have been brought to the United States (either accidentally or intentionally) through human activity.
Many have arrived in shipping crates, cargo, grain supplies, ship ballast water, construction materials, or the personal property of people traveling to the U.S. Early settlers and colonists brought various plant species from their home countries as garden and culinary plants, which then escaped over time into native ecosystems. Some invasive animals were originally pets or exotic game species that either escaped or were released by their owners into natural areas.
Non-native species are further transported by "hitchhiking" on vehicles, recreational equipment, hiking boots, firewood, and boats traveling from one waterway to another.
Many non-native species have little or no negative impact on the environment, but others called invasive species can do a great deal of damage. Invasive species spread quickly and aggressively out-compete native species for space and nutrients. Without the natural predators, diseases, competition, and environmental conditions that kept them in check in their native land, these species become robust "invaders" that can alter entire natural communities. They are more successful in a wider range of habitats than native species and they take advantage of disturbed environments.
Invasive species cause economic and environmental harm, and some are hazardous to human health. Once they get established, invasives are almost impossible to get rid of.
Beware Of Leafy Strangers
There are about 120 non-native plant species at Pictured Rocks. Most are benign but about a dozen are highly invasive and currently the target of intense control efforts by park staff. Of these, the worst culprits include spotted knapweed and garlic mustard.
Spotted knapweed, a plant native to eastern Europe, quickly overtakes dry and open habitats, invading the lakeshore's beach and dune systems and particularly threatening rare native plants in the pristine Grand Sable Dunes area. Each plant can produce as many as 4,000 seeds annually, and the seeds can remain viable in the soil for many years.
Garlic mustard, brought from Europe as an edible herb, is an aggressive invader of shady forests where it displaces native plants and reduces species diversity in wildflower communities. The impact of this invasive species is most noticeable in the Miners Castle area.
Other invasive plants affecting the national lakeshore include forget-me-not, goutweed, baby's breath, white sweet clover, and European swamp thistle. Invasive plants harmful to human health include wild parsnip, which can cause severe chemical burns if the sap gets on human skin in the presence of sunlight. (Giant hogweed, a highly toxic relative of wild parsnip, has not been found in the park.)
Battling invasive plants is one of the most important missions of the park's Science and Resource Stewardship Division. Control efforts include mechanical means (hand pulling) and targeted chemical treatment where appropriate. Since seeds from invasive plants can remain viable in the soil for decades, constant effective control will be needed for many years.
The park's interpretive and education staff recruit volunteers for public weed pulls as well as including forget-me-not weed pulling activities for school groups during spring field trips to the park.
Aquatic invasive species at Pictured Rocks range from tiny invertebrates to large aggressive fish. Spiny water fleas, which most likely entered Lake Superior through ballast water, have been found in Beaver Lake and Grand Sable Lake within the park. These tiny crustaceans upset the aquatic food chain by out-competing native invertebrates while having very few predators themselves.
The parasitic sea lamprey breeds in rivers throughout the Great Lakes, including several streams within the national lakeshore. A native of the Atlantic Ocean, the sea lamprey found its way into the Great Lakes through man-made shipping canals, and was in Lake Superior by the 1940's.
The U.S. Fish and Wildlife Service (USFWS) has conducted research and control efforts for several decades as part of a joint U.S./Canada endeavor, which has successfully reduced sea lamprey populations up to 90 percent in some areas. At Pictured Rocks, USFWS staff chemically treat several rivers each year where sea lamprey spawn and use traps to catch adults.
Other invasive fish of concern include round goby and Eurasian ruffe, both found in Lake Superior but not yet affecting park waters. Zebra and quagga mussels, which have devastated portions of Lake Michigan, have only been found in very limited numbers in Lake Superior, and currently are not found at the national lakeshore. However, they have been spreading in inland lakes and rivers throughout the Upper Peninsula.
Each summer, park staff conduct a survey of all the park's major inland lakes for invasive Eurasian watermilfoil and purple loosestrife, two highly aggressive freshwater plant species that damage aquatic ecosystems and crowd out native species. Neither plant has been found to date. A comparison chart shows the difference between Eurasian watermilfoil and similar native species found in the park.
Currently, insect and plant invasive species are the greatest concern at Pictured Rocks. The most serious threat to the park is Beech Bark Disease, which is caused by a tiny beech scale insect and fungal infection. This devastating disease has the potential to kill 80 to 90% of the park's mature beech trees.
Other invasive insects that affect the lakeshore's forests, but to a lesser degree, are gypsy moth and emerald ash borer. Gypsy moths have been trapped here before, but not in large numbers.
Emerald ash borer beetles have devastated ash populations in lower Michigan but since ash trees are not as common in this environment, the impact here has been considerably less. Park biologists survey for these and other invasive pests on an annual basis.
Invading insects "on the move" but not yet here at Pictured Rocks include the hemlock wooly adalgid and the Asian longhorn beetle. If these insects sweep through the national lakeshore in large numbers, they will have a profoundly negative impact on the forest ecosystem. Both the park's iconic hemlock groves and sugar maple uplands will be at risk. For now, the only defense is to prevent people from transporting these destructive insects into the area.
Another terrestrial invader impacting Michigan is the non-native fungus that causes white-nose syndrome in bats. Accidentally introduced to New York state from Europe in 2006, this fungus has spread to 33 states and seven Canadian provinces as of 2019. Bat populations within the national lakeshore are likely affected, and park staff conduct studies annually to monitor bat activity.
Little Things, Big Problems The Great Lakes Restoration Initiative (GLRI) has produced a series of short informative videos about invasive species in the Great Lakes entitled "Little Things, Big Problems." Take a look!
What YOU Can Do To Help
Prevention is the key! While recreating at Pictured Rocks National Lakeshore, you and your family can play a VERY important role in preventing the spread of invasive species to other parts of the park, and throughout the region.
Check for and remove all seeds, soil, insects, and eggs from tents, tent pegs, walking sticks, and other recreational equipment.
Stay on marked trails. Use boot brush stations if provided.
Clean and dry boats and all fishing equipment before visiting other lakes or water areas. (This is required by Michigan law.)
Use only approved bait; dispose of unused worms or other bait in the trash.
Burn wood where you buy it. Do not bring wood in from other areas.