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The Ring - CCxA

Entangled Landscapes: The effects of invasive species on mycorrhizal fungi and soil health



Dog strangling vine affects the mycorrhizal fungi in the soil. IMAGE/ Leslie J. Mehrhoff

Phaedra Maicantis (PM): Could you give a synopsis of your research?

Richard Dickinson (RD): I’m examining the effects of invasive plants, primarily dog strangling vine (DSV), on the mycorrhizal fungi in the soil, and, in turn, what effect that has on native vegetation. Nobody has really looked at this in terms of the native plants growing in the immediate area around DSV and compared it to native plants in a similar habitat where DSV is not found.

PM: In a recent presentation [at the Ravine Symposium, Toronto Botanical Garden, November 2018], you talked about how non-native species such as DSV alter soil properties, and how that can result in potential failure of restoration efforts.

RD: DSV connects to the common mycorrhizal network (where other plants are connected, too) and produces allelopathic chemicals that are transported throughout the mycorrhizal community. Some of these chemicals are detrimental to native plants, so DSV is attacking plants through their own nutrient uptake system. In addition, we’ve found that not only is DSV changing the mycorrhizal community, it’s also changing the nutrient availability to native plants and the pH of the soil. Once established, DSV starts to take over the ecosystem. It’s managing the ecosystem so it can grow farther.

PM: Is it possible to reverse that?

RD: Soil reclamation is paramount. If you’re planting into soil that has previously been inhabited by invasive plants such as dog strangling vine, phragmites, buckthorn, or garlic mustard, the allelochemicals these invasives produce will still be in the soil. The micro-flora in the soil are unfamiliar with those chemicals, and so the breakdown is really slow and they remain in the soil for a long time (certainly much longer than any of the native plants that release their allelo-chemicals, which are broken down readily because they’ve evolved with the micro-flora in that soil).

PM: Some people — including many landscape architects — argue that we should accept non-native species as part of the ecosystem now. What is your take on that?

RD: In the urbanized parts of southern Ontario, reversing the spread of non-native, invasive plants is a daunting task. But in other parts of the province, such as central Ontario where invasive species are just starting to spread, I think it’s very important to be proactive and manage those sites so the invasives don’t spread farther.

In urban areas, such as Toronto, I think you would need to focus on the tree canopy and on getting rid of the larger invasive trees such as Norway maple, and then focus on the ground vegetation. There are native plants that can stand up to invasive plants, but over time, they become overwhelmed, so if you can slow that down in conjunction with soil remediation, I think it’s possible to control the spread of invasives. But at the scope of a city such as Toronto, that’s a massive project.

One thing that municipalities can do, though, is public education. And if you can educate the public, funding will come when you have enough people becoming part of a movement to do something about the problem with invasive species.

PM: What do you think landscape architects can do in terms of moving forward on these issues?

RD: The training of landscape architects needs to include a lot more of a focus on soil and on the mycorrhizal components of soil. Five percent of soil is organic matter, and there’s a huge number of mycorrhizal species within that five percent, and the molecular technology for identifying mycorrhizae in soil has improved dramatically. There are some good, recent scientific papers about inoculating disturbed sites with soil from a pristine site.

PM: What other applications do you see your research having, beyond restoration projects?

RD: I’m working on a project with garlic mustard, and looking at how it seems to reach a certain point in its invasion, and then it drops back a bit, so I’m going to be looking at the mycorrhizal content of the soil and see if there’s any difference there. All invasives can’t be painted with the same brush, but the more invasive ones are definitely using fungal pathogens in their spread. I’m pretty sure that phragmites and garlic mustard are going to be quite similar in that, too.

PM: Are there any plant species that can overcome DSV, in conjunction with soil restoration efforts?

Goldenrod (Solidago sp.). IMAGE/ Liz West

RD: The goldenrods are pretty tough. Ironically, they’re classified as invasive in Europe and in China; so, goldenrods are probably doing the same thing to the native plants of Europe and China as what DSV is doing here, because goldenrod definitely has allelopathic chemicals. Another tough native is black-eyed Susan (Rudbeckia hirta). If you look through the urbanized areas of southern Ontario and you see both DSV and some native plants, those are the natives that are a little more resilient. There may be other native plants that could grow in soil that’s been reinoculated with some of the native mycorrhizal components.

PM: What are the barriers, then, stopping people from just planting goldenrod and black-eyed Susans together to deal with the dog strangling vine issue?

RD: Once you get rid of the DSV, the seed bank lasts for three years, so you’re going to have to deal with DSV coming back. And I wonder if people don’t plant goldenrod because it’s just everywhere. They tend to plant plants that look nice, I guess. But goldenrod is native and we all know how it spreads, so I think it would be a prime candidate for regeneration projects. If you plant goldenrod and other resistant or resilient-type native plants, in time that soil is going to be remodified back to a natural soil, and then you can plant Virginia mountain mint and Penstemon hirsutus and other showy plants.

PM: In terms of the landscape architecture profession, let’s say we’re given a site: What should be our first course of action? Do we call in an ecologist to examine the soil for us?

RD: Yes, go in and do a biophysical inventory and see what plants are there, native and non-native. And then maybe look at the mycorrhizal fungi community and see how damaged it is. Unfortunately, though, it’s not like CSI where you put a little sample in one end of the machine and it comes out the other with an answer. It’s quite laborious and expensive, but it does give you a good idea. For years, we’ve been so attuned to doing an inventory of a site or an ecological assessment, but we just look at everything that’s above ground. We don’t really look at the other part, which is soil.

PM: Many landscape architects don’t have the ecology background to do that, and even if they did, not many of them will have the scientific expertise to do it themselves.

RD: That’s where we get into partnering projects and research with colleges and universities, because they’ve got that expertise.