Invasive Plants - Part I

by Dave Wilson

Dave Wilson brings us part one of a series on the negative impact of invasive non-native plants.

Today we're going to discuss invasive plants in Maryland and the challenges they present for both people and biological diversity in the state. In my 20 years of working in conservation I feel like they've become a bigger threat than people realize. And we'll explore that today.

In the studio we're lucky to have Wes Knapp, a botanist with the Maryland Department of Natural Resources Wildlife & Heritage Program. He's worked for DNR for the past 15 years as the Eastern region heritage ecologist. Kerri Kyde is the invasive plant ecologist. She's responsible for the invasive plant assessment and control on some 475,000 acres of state land. With over 20 years of experience she was the founding member of the Maryland Invasive Species Council and is chair of the Maryland Invasive Plant Advisory Committee. Welcome to you both.

How big of a problem for wildlife are invasive plants and is it getting worse?

Kerri Kyde:
"The answer is yes it is getting worse and it's a huge problem for a number of reasons, primarily because invasive plants have the capacity to change habitats. They can change ecosystem processes like nutrient cycling and strata, community composition, the way forests for instance have layers. They can change community diversity. They can change species richness. They can change food webs and the way species interrelate. So for all those reasons invasive plants are a problem for wildlife."

Is there a particular region of the state were invasive plants are worse? For example, is Western Maryland in worse shape than the Delmarva Peninsula?

Kerri Kyde:
"Wow. I'd say not. Invasive species are a problem across the state. Certainly it is the case that less disturbed areas have fewer since mostly we move them either inadvertently or on purpose. So habitat that doesn't have as many people generally has fewer invasive plants. So magic, secret places on Delmarva and magic, secret places in Garrett County are going to have fewer invasive species."

Wes, I want to talk to you a little bit about wetland plants. I know Japanese stiltgrass has invaded wetlands and Japanese honeysuckle has hit upland forests. What are some of the invasive plants that are impacting wetlands?

Wes Knapp:
"That all depends on what type of wetlands you want to talk about. Our open marsh systems have phragmites which is a really common grass that dominates, but the real up-and-comer is a forested wetland plant Murdannia keisak and this is horrible because it's truly invading high quality forest systems. We recently found this in the beautiful bald cypress swamps of the Pocomoke and it's acres of forest understory. And it's really uncontrollable already. It got here so recently. These are the types of weeds we're facing. And they're going to just change our systems."

Is there anything we can do about it? Do we have any recourse to stop these plants?

Wes Knapp:
"That is a beautiful question. And we are a major vector for invasive species. And I know Kerrie can talk more about the recent laws to control species that are coming into the state and are being sold in the state. Wildlife move invasive species. There's really nothing we can do about that. Waterfowl move invasive species through seeds. Most of our aquatic species are moved like that. Deer are a major vector. Humans, deer, and waterfowl are the larger factors I can think of."

People might not have a good idea of how hard these species are to control. It's not just a matter of going out in your backyard and ripping something out. We are talking about hundreds, and in some cases, thousands of acres of these plants taking over huge swathes of forest and I know that's a problem here the Eastern Shore and large parts of Western Maryland.

Kerri Kyde:
"That's true. In many cases invasive plants, and invasive species of all taxa actually although it's very characteristic of invasive plants, arrive here and don't automatically become problems. There's something in the scientific literature called the Rule of Tens and it works roughly for plants. What it means is for every thousand species that are introduced or brought here 10% will actually establish; 10% of those will start reproducing and spreading; and 10% of those will become a real problem. So it's not very many species that become a problem and I got to say many of our food plants are exotic, but they're not invasive. Control of the few that do become problems is hugely expensive and time-consuming. Most of the plants that become invasive have what's called lag meaning the time between their introduction and the time they start spreading can be 50 to 100 years".

Is there a historical date by which botanists judge plants to be native or non-native?

Kerri Kyde:
"The cutoff date that we use is sort of pre-Columbian although indigenous people who populated this part of North America brought their own plants with them. But the huge influx of plants and other invasive species begin with European colonization."

Read the rest of this series:Find out more:
Invasive Species of Concern in Maryland
Maryland Invasive Plant Advisory Committee
Delmarva's Rare Plants with Wes Knapp Part I
Delmarva's Rare Plants with Wes Knapp Part II
Maryland Department of Natural Resources Wildlife & Heritage Program
Maryland Biodiversity Project
Maryland Biodiversity Project on Facebook
Maryland Plant Atlas