Tracking Invasive Species with Pennsylvania iMapInvasives (Summer/Fall 2020)

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16 Tracking Invasive Species with

Pennsylvania iMapInvasives

Summer/Fall 2020 Edition

Letter from the Editor Dear Readers, The Pennsylvania iMapInvasives Program is pleased to bring you this newest edition of our triannual newsletter! In this edition, we are highlighting several stories with origins in northwest Pennsylvania. Jim Grazio, Great Lakes Biologist with the Pennsylvania Department of Environmental Protection, starts us off with a perspective on the current state of aquatic invasive species in the Great Lakes system. He emphasizes that if we are to keep the Great Lakes ecosystem functioning in good health, it’s crucial that we work to prevent the further spread of invasive species currently residing there. Next up, Tyson Johnston, Land Stewardship Coordinator with the Western Pennsylvania Conservancy, highlights efforts to protect a section of land along French Creek known as the Venango Riffle Natural Area by managing several terrestrial invasive species located there. Plantings of native species were also incorporated post-treatment to assist in promoting the ecological well-being of the area. Larissa Cassano-Hamilton, Watershed Specialist with the Mercer County Conservation District, highlights a particular aquatic invasive species found in Mercer County (as well as other locations in Pennsylvania): Eurasian water-milfoil. Known as a species that can easily spread by fragmentation on boats and other recreational equipment, she points to the need for vigilance in checking for this and other aquatic invasive species while out recreating at our local and state parks in order to prevent these species’ spread to new locations. Finally, Guy Dunkle, Forester with the Foundation for Sustainable Forests, wraps up our northwest-themed newsletter by discussing a handful of properties in Erie and Crawford counties where several terrestrial invasive species were managed in order to build up the resiliency of the forests located there. Throughout his story, Guy emphasizes that his expectation is not to eliminate invasive plants from the forest (an unrealistic goal), but rather to reduce their populations to a small enough number that the native flora and fauna can function effectively. Thanks to each of our contributors for taking the time to provide these important stories, and to each of you, our loyal readers, for keeping up with reading the stories we feel are important to share. Sincerely,

Amy Jewitt, Invasive Species Coordinator Pennsylvania Natural Heritage Program Cover: Dense understory of natives and multiflora rose at a site treated for invasive species by the Foundation for Sustainable Forests.

WHO WE ARE AND WHAT WE DO The iMapInvasives Program is an online reporting and data management tool used to track occurrences of invasive species. The goal of the Pennsylvania iMapInvasives Program is to assist natural resource professionals and citizen scientists by advancing their knowledge of species distributions in our state and provide a tool which stores both location and management details.

Invasive zebra mussels can attach to any hard surface.

TABLE OF CONTENTS AND CONTRIBUTORS Aquatic Invasive Species in the Great Lakes Written by Jim Grazio, Great Lakes Biologist

Conservancy Treats Terrestrial Invasive Species Along Important Waterway Written by Tyson Johnston, Land Stewardship Coordinator

Learning to Be Vigilant Written by Larissa Cassano-Hamilton, Watershed Specialist

Building Forest Resilience in Northwest Pennsylvania Written by Guy Dunkle, Forester

ENCOURAGING WORDS “Accurate mapping of invasive plant infestations at all scales – from within individual sites up to the statewide level – is critical to inform effective prioritization of control projects and allocation of resources. Staff within the Bureau of Forestry rely on the accurate, verified data that iMapInvasives provides to better understand how invasive plants are spreading on and off State Forest lands throughout Pennsylvania. I would encourage all land managers and folks engaged in invasive plant management across the state to fully utilize this resource while planning control projects.” - Kelly Sitch, Ecologist, PA DCNR, Bureau of Forestry

Written by James L. Grazio, Ph.D., Great Lakes Biologist with the Environmental Protection, Waterways and Wetlands Program –

Pennsylvania Department Great Lakes

The Laurentian or North American Great Lakes have been described as one of the most heavily invaded ecosystems in the world. Sturtevant et al. (2019) provided a recent and comprehensive review of over 180 non-native aquatic species which have become established into the Great Lakes. While most of these species are harmless,

Right: Quagga mussels in a laboratory setting. Opposite: Top two photos: Zebra mussels; middle two photos: Round goby; bottom two photos: Sea lamprey

a subset of these nonindigenous species cause environmental and/or economic harm – these are aquatic invasive species (AIS). Some, like the sea lamprey (Petromyzon marinus) and zebra/quagga mussels (Dreissena polymorpha & D. bugensis) have had truly extraordinary impacts since their introduction – dramatically altering food webs, 6

contributing to the collapse of important fisheries, and causing total economic impacts estimated to exceed $1 billion each year. Tens of millions of dollars are spent annually to suppress sea lamprey populations and prevent zebra mussels from clogging water pipes. However, for virtually all AIS, there is

no way to eliminate these highly destructive species from the lakes, and their impacts continue to this day.

There are many ways that nonindigenous species are spread from their donor to recipient regions. Two of the most important paths of entry into the Great Lakes have been the discharge of ballast water (and the aquatic organisms it contains) from trans-oceanic shipping and the construction of man-made interconnections and canals. Zebra mussels and a small, yet aggressive, fish known as the round goby (Neogobius melanostomus) are examples of highly destructive AIS that were introduced into the Great Lakes through ballast water releases in the 1980s and 1990s. The rate of AIS introduction via this pathway into the Great Lakes has slowed since the implementation of mandatory open-ocean ballast water exchange rules in 2006. However, the risk of further introductions via ballast water discharges still exists since ballast water exchange isn’t 100% effective at removing organisms from a ship’s tanks. Canals and waterway interconnections were among the first pathways for the spread of AIS. The installation of locks and dams on the St. Lawrence River, designed to allow for the passage of oceanic freighters, also allowed for the entry of coastal fishes like the parasitic sea lamprey from the Atlantic Ocean. Since the Chicago Sanitary and Ship Canal was built, the Great Lakes are hydrologically connected to the Mississippi River basin, allowing for the passage of AIS between these two waterways.

Above: A native mussel is covered in invasive zebra mussels.

As long as hydrologic interconnections remain and people continue to move vessels and equipment between bodies of water, the risk for further introduction of AIS will continue to persist. Even today, the “near-perfect” aquatic weed hydrilla (Hydrilla verticillata) and invasive Asian carp species are poised to invade the Great Lakes through existing canals and interconnections. Some researchers fear an “invasional meltdown”, whereby each successive invasion further destabilizes an ecosystem that has already been highly altered by AIS. Since there is no practical way to eliminate biological organisms from an 8

Above: Invasive round gobies. Right: Author, Jim Grazio, holding a 69 lb., 48” grass carp.

interconnected Great Lakes system containing 20% of the world’s surface freshwater, the prevention of further introductions and spread of AIS into and within the Great Lakes is essential to preserve both the natural heritage and economic vitality of the Great Lakes region.

• • • •

Great Lakes Aquatic Nonindigenous Species Information System (link) United States Geological Survey Nonindigenous Aquatic Species (link) Great Lakes Sea Grant Network (link) Great Lakes Panel on Aquatic Nuisance Species (link)

Jim Grazio is the Supervisory Great Lakes Biologist for the Pennsylvania Department of Environmental Protection. He is the agency’s lead scientist on Great Lakes issues and is a past Chair of the Great Lakes Panel on Aquatic Nuisance Species. Jim holds a Ph.D. in Wildlife and Fisheries Science from Penn State University and is an adjunct faculty member with Penn State Behrend’s School of Science. He can be reached at

Sturtevant, R. A., Mason, D. M., Rutherford, E. S., Elgin, A., Lower, E., & Martinez, F. (2019). Recent history of nonindigenous species in the Laurentian Great Lakes; An update to Mills et al., 1993 (25 years later). Journal of Great Lakes Research, 45(6), 1011-1035.

Presence records from iMapInvasives highlight documented occurrences of some of the aquatic invasive species (AIS) mentioned in Jim Grazio’s “Aquatic Invasive Species in the Great Lakes” story. Note: Each data record is available for viewing by anyone with a registered iMapInvasives user account. To look up one or more of these records, simply query the database using the Presence ID# listed for each.

On November 29, 2015, Mark Lethaby from the Tom Ridge Environmental Center, Curator of the Center’s Natural History Museum, observed round gobies (as well as invasive tubenose gobies) in Lake Erie at Presque Isle, near the West Pier Boat Ramp. Kyle Lambing (volunteer) assisted Mark in this survey effort. Together, they used a seine in order to observe these fish.


Round goby iMap Presence #934385

Hydrilla iMap Presence #934277

In 2015, Pete Woods from the Western Pennsylvania Conservancy/Pennsylvania Natural Heritage Program (WPC/PNHP) discovered the presence of hydrilla on two privately-owned properties in Girard, PA. This was the first discovery of hydrilla in Erie County, and the closest known infested location to the Great Lakes in Pennsylvania.

In 2013, Amy Jewitt from the Western Pennsylvania Conservancy/Pennsylvania Natural Heritage Program (WPC/PNHP) observed a zebra mussel along the shoreline of Lake Erie in State Game Lands 314, not far from the Pennsylvania/Ohio state line.

Zebra mussel iMap Presence #940131

Efforts to treat the hydrilla at these two locations has subsequently been underway by the WPC/PNHP and PA Sea Grant. Various treatment methods have been utilized including chemical methods and grass carp.

In September 2013, Christopher Tracey of the Western Pennsylvania Conservancy/Pennsylvania Natural Heritage Program observed the remnant of a dead quagga mussel along the shoreline of Lake Erie on Presque Isle. Note: This record was originally submitted to, and was later incorporated into iMapInvasives.


Quagga mussel iMap Presence #940010

Conservancy Treats Terrestrial Invasive Species Along Important Waterway Written by Tyson Johnston, Land Stewardship Coordinator with the Western Pennsylvania Conservancy In December 2019, the Western white pine, silver maple, sycamore, black Pennsylvania Conservancy was awarded a willow, box elder, silky dogwood, elderberry, grant from the Crawford Heritage and pin oak. While the native species that Community Foundation for the treatment of were planted began to grow, the invasive species in the Conservancy’s unwelcomed exotic invasive species also Venango Riffle Natural Area, an 8.5-acre quickly moved in. Multiflora rose, Morrow’s preserve protecting about 1,600 feet along honeysuckle, garlic mustard, dame’s rocket, French Creek in the borough of Venango, and Japanese barberry were all present on Crawford County. the site and in need of control. French Creek is documented as having Courtesy of the generous funding the highest level of aquatic biodiversity of provided by the Crawford Heritage any stream of its size in Pennsylvania and all Community Foundation, the Conservancy states to the northeast of was able to hire a local Pennsylvania. This reach of firm, Ecological Field “French Creek is documented French Creek is part of a Services, to provide foliar as having the highest level of longer segment containing herbicide treatment across aquatic biodiversity of any riffles, runs, and islands, stream its size in Pennsylvania the entire preserve. The and is an area identified as treatment occurred in and all states to the northeast one of the very highest May, and today the results of Pennsylvania.” priorities along French are hard to miss. Creek for the Conservancy Christian Maher, to protect. The waters here support stateExecutive Director of the Crawford Heritage listed fish species, state-listed freshwater Community Foundation, said, “As a mussel species, and federally-listed community foundation, we’re devoted to freshwater mussel species. improving our natural environment through The Venango Riffle Natural Area is grants to forward-thinking organizations comprised of two parcels; the first acquired like the Western Pennsylvania Conservancy. in 1995 and the second in 2012. In 2013, This is our third collaboration and we’re Conservancy staff and volunteers planted all excited to see how this will improve the of what had previously been maintained as watershed. lawn with native trees and shrubs, including (Story continued on following page.)

Opposite: French Creek in northwest Pennsylvania.


Above: Multiflora rose shrubs post-herbicide treatment next to a planted maple tree at the Venango Riffle Natural Area in Crawford County.

To learn more about this invasive species management effort conducted at the Venango Riffle Natural Area by the Western Pennsylvania Conservancy, please query the iMapInvasives database for Treatment Record #18998. By creating this query, you’ll be able to see the area treated as well as specific details about this management effort.

been employed by the Western Pennsylvania Conservancy since 2010 and Tyson Johnston has managed the Conservancy’s preserves across seven counties in northwestern Pennsylvania since 2016. Tyson currently resides near Meadville with his wife, Sarah, and daughters, Morgan and Ashley. He can be reached at

ABOUT THE AUTHOR Tyson Johnston holds a B.S. in Geography and Environmental Studies from Slippery Rock University. He has


Above and left: Views of the Venango Riffle Natural Area, located in Crawford County, in the borough of Venango.



‘ Hesperis matronalis L. Mustard family (Brassicaceae)

Origin Europe

Background Dame’s rocket, also known as dame’s violet and mother-of-theevening, was introduced as an ornamental around the time of European settlement. It continues to be widely used as an ornamental and can be found throughout North America.

Distribution and Habitat Habitats invaded include open woodlands, prairies, roadsides, ditches, and other disturbed areas.

Ecological Threat Dame’s rocket displaces native plant species.

Description and Biology • • • • •

Plant: herbaceous, biennial forb up to 4 ft. in height. Leaves: alternate, hairy, broadly lanceolate with toothed margins, sessile or nearly so, 2-6 in. long. Flowers, fruits, and seeds: flowers showy, fragrant, white to purple or pink with 4 petals in a cross; late spring; fruits slender, cylindrical and arch upwards. Spreads: by seed. Look-alikes: might be confused with wild blue phlox (Phlox divaricata), fall phlox (Phlox paniculata), and non-native annual honesty (Lunaria annua).

Prevention and Control Do not purchase or plant this species. Individual plants can be pulled by hand if soil is moist or dug up using a spade or shovel to loosen the soil and remove the entire root system. Re-sprouting may occur if entire root system is not removed. Systemic herbicides can be used to kill the entire plant including the roots.

Native Alternatives Ox-eye sunflower (Heliopsis helianthoides), Canada lily (Lilium canadense), wood lily (Lilium philadelphicum), Turk’s cap lily (Lilium superbum), and three-lobed coneflower (Rudbeckia triloba) are just a few showy native perennials that would make good substitutes for dame’s rocket.

Source This invasive species profile was provided by the “Plant Invaders of MidAtlantic Natural Areas, 4th Edition”, a field guide by authored by the National Park Service and the U.S. Fish and Wildlife Service and published in 2010.

A reminder to always be looking for aquatic ‘hitchhikers’ while recreating on the water. Written by Larissa Cassano-Hamilton, Watershed Specialist with the Mercer County Conservation District

In northwestern Pennsylvania, we are lucky to be surrounded by so much green (and blue) space – from farm fields, to game lands, to state parks with lakes and rivers. These great spots get more and more visitors that come and go throughout the season, especially now during the COVID-19 pandemic with outdoor recreation on the rise in the United States. However, sometimes visitors might accidentally take home more than just good memories and a nice-looking fish after visiting their local park or recreational area. Aquatic invasive species (AIS) are plants and animals that can get stuck on gear and vessels and be easily introduced into other bodies of water via movement by humans or waterfowl. AIS can accidentally be transported on boats, pets, and recreational gear, and it’s important for outdoor enthusiasts to be vigilant and check for aquatic hitchhikers whenever they are recreating in a water body. It’s also recommended to take note of posted signs that display information about aquatic hitchhikers. One species in particular, Eurasian water-milfoil (Myriophyllum spicatum), is an invasive aquatic plant that boaters and fishermen should be checking their gear for. Because it can spread via fragmentation, a single piece of this plant can begin a new population if transported to a new location.

Eurasian water-milfoil

Note: If you see a large, dense mat of a

Eurasian water-milfoil is a feathery, submerged aquatic plant that can quickly form thick mats in shallow areas of lakes and rivers in North America. These mats can then interfere with swimming and entangle propellers, which hinders boating, fishing, and waterfowl hunting. Heavy infestations may even reduce property values. Dense milfoil infestations can displace native aquatic plants, which negatively impacts fish and wildlife. Eurasian water-milfoil was first introduced to North America through the aquarium trade in the 1940s from a European/Asian origin. It has since spread to nearly every U.S. state and several parts of Canada. If a small piece of this plant remains on your gear, it could spread and establish in a new ecosystem if you frequent various waterbodies. Also, fragments of Eurasian water-milfoil that remain moist can be viable for weeks. The Pennsylvania Fish and Boat Commission and other agencies advocate “Check, Clean, Drain, Dry” when it comes to preventing the spread of AIS on recreational gear.

single aquatic plant in a water body, it might be a good indication to do some research and reach out to an agency for more information. It could just be an aquatic invasive species. Eurasian water-milfoil has already found in several bodies of water across Pennsylvania. According to data in iMapInvasives, almost two thirds of all Pennsylvania counties have documented occurrences of Eurasian watermilfoil.

• • • •


PA Sea Grant. Eurasian water-milfoil information fact sheet (link) PA Fish and Boat Commission. Clean your gear; prevent the spread of AIS (link) PA DCNR. Eurasian water-milfoil fact sheet; includes native look-alikes (link) iMapInvasives. Log your findings of Eurasian water-milfoil and other invasive species (link)

In this drawing from Minnesota Sea Grant, guidance is provided on how to correctly identify Eurasian water-milfoil.

Larissa Cassano-Hamilton is the Watershed Specialist with the Mercer County Conservation District (MCCD). In her free time, she enjoys creating recipes in the kitchen and spending time with her family. On weekends, she loves to explore the trails of Pennsylvania and beyond, together with her husband, and their pup, Duke. Larissa can be reached at

Below: A private property owner transported gear from a Eurasian water-milfoilinfested lake, and now, the homeowner’s pond is infested with invasive milfoil too.

Larissa Cassano-Hamilton

Building Forest Resilience In

Written by Guy Dunkle, Forester with the Foundation for Sustainable Forests

Forestland managers have a few prominent tools that are used in efforts to build vibrant, resilient ecosystems. Logging is the tool that catches everybody’s eye, generally because it’s messy, with treetops scattered around. However, to improve the health of forests, land managers use this tool because it restores the forest to a more natural condition. Logging allows for patches of light to access the forest floor, thus encouraging new growth of understory and mid-story plants. While it can be controversial and look unsightly in the short term, logging has direct benefits when implemented correctly. In recent years, another tool has seen an increase in popularity in our state; the use of herbicide. As invasive plant species spread, public and private landowners have ramped up efforts to address this concern. Suppressing invasive species with careful use of herbicides is a cost-effective and time-saving way to control large infestations of invasive plants compared to other methods. At the Foundation for Sustainable Forests (FSF), forest managers remove invasive species to restore native forests. The FSF is a small, not-for-profit land trust operating in the northern and western portions of Pennsylvania and adjacent regions of New York and Ohio. With a mission centered around harmonic utilization of forests, the Foundation has a mandate to actively manage and steward the lands that we protect. In addition to stewardship of the forestland we own, FSF has partnered with a handful of local organizations to assist them in the care of their forests. These partners include the City of Erie, the U.S. Army Corps of Engineers (USACE), and the Presque Isle Audubon Society. Our forestry process focuses on developing multiple age classes of trees, Right: FSF property with full understory. Previous page: Dense understory of natives and multiflora rose.

improving native species diversity, At that time, we utilized a tractor-mounted maintaining a “full” understory with dense herbicide sprayer to control dense thickets plant cover, and enhancing the vigor of of multiflora rose and release native plants. trees. Over time, this management style Fast forward to the year 2020, and now builds resilience in the forest system – much of the area treated in 2012 has had healthy, vigorous trees and plants of diverse native plant regeneration. There are thickets species and age are better able to bounce of tree seedlings and saplings, and only back from the disturbances of extreme scattered multiflora rose bushes are still weather, introduced pests, and invasive present. However, in several areas, the species. native plants are being out-competed by So far in 2020, we have embarked on several invasive plants that were able to invasive plant control reestablish themselves. projects covering 60 acres To combat this issue, “Our expectation is not to of forestland. These have we contracted with eliminate invasive plants from the involved partner Ecological Field Services, forest; that seems to be an properties such as the based in the nearby town unattainable goal. Rather, our USACE’s Union City Dam of Waterford, to handle in Erie County, Presque this round of herbicide objective is to reduce invasive Isle Audubon’s Laura application. The crew was plants to a small enough presence Olsen Memorial Sanctuary composed of five hardthat native components and in Crawford County, and a working folks toting processes are able to function property owned by FSF backpack sprayers effectively.” located near Platea in Erie through the forest. County. At the Platea As they wrapped up Forest, the most problematic invasive plant work at the Platea Forest, they drove an is multiflora rose (Rosa multiflora). In ATV-mounted sprayer into the densest addition, there are populations of garlic patch of multiflora rose bushes and were mustard (Alliaria petiolata) and common able to thoroughly treat what had privet (Ligustrum vulgare) near an appeared to be an impenetrable bramble. abandoned farmyard site. Our expectation is not to eliminate Our control work this year was the invasive plants from the forest; that seems continuation of efforts begun in the summer to be an unattainable goal. Rather, our of 2012, when we embarked on a largeobjective is to reduce invasive species to a scale habitat improvement project through small enough presence that native a partnership with Ducks Unlimited and the components and processes are able to National Fish and Wildlife Foundation. function effectively.

Opposite: Ecological Field Services crew working at Platea Forest.


A view of presence data points entered into iMapInvasives by Guy Dunkle. Each represents an observation of an invasive plant species, many of which are discussed throughout the author’s story. Clockwise from top: Platea Forest, Union City Dam, Laura Olsen Memorial Sanctuary, private land with a large infestation of knotweed, and the author’s farm along Federal Run.



Oak seedlings at USACE Union City Dam

Another very important consideration for us is maintaining the fullness of the forest understory. As the saying goes, “Nature abhors a vacuum”, and forests with open understories and very few plants growing at ground level seem to be ripe for invasion by non-natives. Therefore, we pair our control efforts with strategic thinnings of the forest canopy (aka logging). By releasing light onto the ground, we are able to bolster the health and density of wildflowers, tree seedlings, shrubs, and other desirable ground cover. As the understory fills with desirable plants, there is less space available for non-natives to occupy. Then, through selective herbicide applications, we reduce the invasive species to a small, lowimpact component of the forest. Thankfully, this process also reduces the impact of deer browse, spreading the damage across many plants in a dense, lush understory. In pursuit of a vibrant, resilient forest ecosystem, managers have a variety of tools available. Implementing these tools successfully requires observation, thoughtfulness, and intimacy with the forest.

Guy Dunkle

Guy Dunkle is a practicing forester based out of Crawford County. He is a professional member of the Forest Stewards Guild and serves on the Board of Directors for the Foundation for Sustainable Forests. Most of Guy’s education has come from time spent in the forests, streams, and fields of northwest Pennsylvania, including a degree from Allegheny College’s Environmental Science department. He and his family raise sheep, Christmas trees, and chickens on a farm at the confluence of Muddy Creek and Federal Run in Crawford County. Guy can be reached at 33

Photo Credits COVER PAGE Dense understory of natives and multiflora rose. Credit: Guy Dunkle, Foundation for Sustainable Forests (FSF)


Zebra mussels. Credit: Julie Mida Hinderer, (link)

PAGE 11 Round goby. Credit: Eric Engbretson, USFWS, (link)

Letter from the Editor (photo of Amy Jewitt). Credit: Aaron Jewitt

Round goby. Credit: USGS, (link)


Sea lamprey. Credit: USFWS, (link)

Invasive zebra mussels can attach to any hard surface. Credit: Missouri Department of Conservation (link) Encouraging Words (photo of Kelly Sitch). Provided by: Kelly Sitch

PAGES 4-5 Global view of the Great Lakes. Credit: Pixabay (link)

PAGE 6 Quagga mussels in a laboratory setting. Credit: Rebekah D. Wallace, University of Georgia, (link)

PAGE 7 Left to right, beginning at the top. Zebra mussel. Credit: Amy Benson, USGS, (link)

Fishing seine (graphic). Credit: Wikimedia Commons (link)

Sea lamprey. Credit: Great Lakes Fishery Commission (link)

PAGE 8 Unionid mussel covered in invasive zebra mussels. Credit: PA DEP

PAGE 9 Round gobies, upside down in clear dish. Credit: PA DEP Author (Jim Grazio). Credit: PA DEP

PAGE 10 Map of Presque Isle. Credit: Google maps

Round goby. Credit: Wikimedia Commons Peter van der Sluijs / CC BY-SA

(link) PAGE 12 Maps. Credit: Google maps Zebra mussel. Credit: Amy Jewitt, Western Pennsylvania Conservancy (WPC) & PA Natural Heritage Program (PNHP) Hydrilla. Credit: Pete Woods, WPC & PNHP

PAGE 13 Map of Presque Isle. Credit: Google maps Quagga mussel. Credit: Christopher Tracey, WPC & PNHP

PAGE 14 French Creek, near the mouth at Franklin. Credit: Wikipedia – Finetooth / CC BY-SA (link)

Photo Credits PAGE 16


PAGES 32-33

Multiflora rose shrubs postherbicide treatment. Credit: Andrew Zadnik, WPC

Eurasian water-milfoil (line drawing). Credit: Minnesota Sea Grant (link)

Oak seedlings at USACE Union City Dam. Credit: Guy Dunkle, FSF

Author (Tyson Johnston). Provided by: Tyson Johnson

Author (Larissa CassanoHamilton). Provided by: Larissa CassanoHamilton


PAGE 17 Maps of Venango Riffle Natural Area. Provided by: Jessie Smucker, WPC

PAGE 18 Dame’s rocket. Credit: Rob Routledge, Sault College, (link)

PAGE 19 Dame’s rocket. Credit: Richard Gardner, (link) Dame’s rocket (line drawing). Credit: The New York Times – Bobbi Angell (link)

PAGES 20-21 Eurasian water-milfoil (mosaic). Credit: Alison Fox, University of Florida, (link)

PAGE 22 Eurasian water-milfoil. Credit: Alison Fox, University of Florida, link)

Eurasian water-milfoil on picnic bench (3 pictures total). Credit: Mercer County Conservation District

PAGE 24 Dense understory of natives and multiflora rose. Credit: Guy Dunkle, FSF

PAGES 26-27 FSF property with full understory. Credit: Guy Dunkle, FSF

PAGE 28 Ecological Field Services crew working at Platea forest. Credit: Guy Dunkle, FSF

PAGES 30-31 Presence data points in iMapInvasives. Credit: iMapInvasives – NatureServe, 2020 (link)

Author (Guy Dunkle). Credit: Annie Maloney, FSF

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