DON RAKOW: Good evening to all of you. I'm Don Rakow, the Elizabeth Newman Wilds Director of Cornell Plantations.
Do some of you remember that show-- I think it was on CNN-- called Point/Counterpoint, in which two people with diametrically different views would debate furiously, and their faces would turn red? Well, you may recall that earlier this semester, we had a speaker, Carolyn Summers, who was advocating quite strongly and convincingly for people to plant just native species in their yards. We at Cornell Plantations believe in a diversity of viewpoints. And we're very pleased that this evening we're going to have a noted scientist who'll be presenting a somewhat different view.
We're very pleased that to introduce tonight's speaker, we have a noted member of the Department of Horticulture faculty, the Director of the Urban Horticulture Institute at Cornell, and coincidentally, my former principal advisor when I did my PhD at Cornell, professor Nina Bassuk.
NINA BASSUK: And I advised Don when I was 10 years old. So it was really--
It's just the way things happened.
It's really a pleasure to introduce Dr. Peter Del Tredici. Peter and I got to know each other-- we've seen each other on and off at conferences. And I've had the pleasure of having conversations with him over the years. I always learn something new, always have a different point of view, always hold on to his words.
Peter has a very, very varied background and came to his August position from not exactly the straight and narrow route. But many of us are that way. Bachelors in zoology, and then masters in biology. He worked at the Arnold Arboretum in various capacities. You may not know. He is one of the world experts on ginkgo biloba. I mean, that was his PhD thesis on ginkgo. And he's been editor of Arnoldia, the magazine at the Arnold Arboretum.
I have notes because there's so many things to say about Peter. Director of the Living Collections and research scientist, he's curator of the bonsai plants at the Arnold Arboretum. He teaches at the Department of Landscape Architecture at Harvard and is also the Scott Medal winner in 1999, which is a very prestigious award for horticulturists.
So Peter will speak on, I think, some very interesting topics about wild urban plants. We're very interested in urban at Cornell. And I'm dying to hear what he has to say. And so I hope you'll enjoy this talk by Peter Del Tredici. Please welcome him.
PETER DEL TREDICI: Is this working? Oh, great.
It is really a pleasure and an honor to be here at Cornell. I love coming to Plantations, particularly at this time of year. The weather is unbelievable. And I really like the array of speakers that they've set up for me. That is a first. Unfortunately, I forgot the soundtrack with this talk.
But I just published a book, Cornell University Press. It's called Wild Urban Plants. And that's essentially what this lecture is about. And from my best friends, I've made a CD that goes with the book. But if I'd known I was going to have these speakers here, I would have brought the CD. I call it the Weed CD. But I don't know. We've got to figure out some way to get that into circulation.
So as Nina mentioned, I essentially wear two hats. One, I've worked at the Arnold Arboretum for 30 years, over 30 years, working essentially on the woody ornamentals, woody plants, propagation, plant exploration, all aspects of woody plant horticulture. But since 1992, I've also been teaching at the Harvard Graduate School of Design in the core curriculum in landscape architecture. And this lecture tonight, and to a certain extent, the book, grows not out of my experience at the Arnold Arboretum as much as my experience at the Harvard GSD.
And I teach plants. I teach soils to the students. And I would take the students on field trips. And we'd be looking at plants. And my job was to teach them essentially the palette of horticultural plants that a landscape architect is going to use. And they would take an ecology class, so they'd learn their native species.
And in the course of the field trip, I would point to an ailanthus tree or some other plant that's growing out of a crack in the sidewalk. And I'd say, well, what's that? The most common plant in the urban area. And they'd have no idea what it is. And so I would berate them for not knowing anything at all. And they would feel badly, just the way I wanted it.
But at one point, one of the students said, well, listen, why don't we cover these plants? How come you don't cover them? I said, well, we have no time. We barely have enough time to cover 120 common ornamental species, let alone all the spontaneous vegetation. And she said, well, what if we were to work with you and we were to create a website or something like that, and we could learn it on our own? And I said, well, if you're really serious, I'd be happy to do that.
And it's really this interaction with the students and their desire to learn more about this most common vegetation that is all around us, but nobody pays any attention to, that first was the website and then ultimately became the book. It did take almost six years to produce that. But nevertheless, it's really what I'm going to-- that's the genesis of this. And I think it's really important to understand where these ideas come from.
So without further ado, I think I'll just jump right into the lecture. And as we go along, it's a narrative lecture. And so telling a story. And one of the things about studying the landscape is, everything is an artifact or an anachronism. It essentially comes from another era. And so understanding, being able to look at the landscape and understand what you see is a complex process.
And so this is a beautiful American elm, growing-- I don't know how many of you take Route 84 as it goes from Boston down to New York City. And it goes right through Hartford. And there's an underpass there where it says, Welcome to Hartford. Some of you may know that. Just as you emerge from that underpass, right in the middle of downtown Hartford, there's this massive American elm standing there. It's just a beautiful specimen, which is clearly an artifact of another era when American elm was the dominant street tree throughout Northeastern North America. That AIG sign-- that was just a happy accident.
And it's really a reflection of another era, mainly in the 1930s, when up to 50% of the street trees throughout many of the cities in the Northeast were the American elm. The Dutch elm disease, which was inadvertently introduced in the 1930s, put an end to that. And of course, the Depression was going on. So there wasn't a lot of money to replace street trees. And World War II happened, so there wasn't a lot of resources, again, available for street tree replacement. And it wasn't until, really, the soldiers came home, they're building the suburbs, they're putting new roads in, that the issue of replacing the American elm emerges to the forefront.
And of course, after a long period of trial and error, the species that essentially becomes the de facto replacement for the American elm is the Norway maple. In the concept of the 1950s and '60s, this is the perfect tree. It's not nearly as aggressive in terms of lifting up the sidewalk and clogging drainpipes as the American elm. And it's highly salt tolerant, which made it very well adapted to the expanding highway system that was emerging in the 1950s and '60s.
What the horticulturists had not predicted, of course, is that Norway maple was so well-adapted to the urban environment that it began to spread into adjacent woodlands, such that as of January 1, 2009, in the state of Massachusetts, the possession with intent to distribute Norway maple is a more serious offense than the possession of marijuana. It is a remarkable turn of events. And I never would have predicted this in a million years.
So the search continues. You know, OK, now, we have to replace the Norway maple. Now, a little bit after the Norway maple comes to the fore, again, the Callery pear. Everyone is very familiar with the Bradford cultivar of the Callery pear. And I just absolutely can guarantee you that within five or 10 years-- this is in the mid-Atlantic region, where all of the post-agricultural land. Callery pear is everywhere as you go down the New Jersey Turnpike, that whole region. So I am certain that within five or 10 years, Callery pear will join the Norway maple as one of those species that is banned, at least in Massachusetts.
So there is this idea that somehow, things remain the same. That is, of course, a fantasy.
And this chart comes by way of the Harvard Forest. And it really doesn't relate so much to the topic of urban environments. But it's really important because it illustrates some really important principles. This green line represents the extent of forest cover in Massachusetts over 400 years. It reached its low point in terms of land coverage right before the Civil War, about 1840. And ever since then, it's been coming back, such that roughly 65% to 70% of the total land area in Massachusetts is now full forested. And the species that are most endangered are those species that require open land. That's what is totally endangered in New England.
You can see here how the deer reached a very low point sometime around 1780. Henry David Thoreau, who spent his entire life in the town of Concord, never saw a deer, a live deer in Concord. He once talked to somebody who saw a deer in Concord. I mean, that is incredible. There are now more deer in Massachusetts since the glaciers receded.
Beaver were hunted into extinction right around 1700. Reintroduced in 1920, 1930. And beaver are now inside the 95 belt. And although I haven't seen absolute proof, I'm sure they're within Suffolk County, the county where Boston is located.
You could put bear on here. You could put moose on here. And coyote, of course, which is not at all native to New England, made its way across Canada and then came down, arriving in New England, in Massachusetts, in the 1930s. So by strict definition, we would have to consider the coyote to be an invasive species.
What's important is-- oh, I'm going the wrong direction. There we go. What's important is to realize that not only do we see constant flux within our urban environment, but the non-urbanized environment has also gone through tremendous change over this period of time.
The American chestnut, which was known as the king of the forest, was wiped out by a blight introduced in the turn of the early 1900s, eliminated. It's now sort of a shrub in the understory of our forests. And most recently, the Canadian hemlock, at least in the southern part of its range, a significant percentage of the population has been wiped out by the hemlock woolly adelgid.
What's really important though to realize, when you sort of look at issues like this-- and if you keep your eye on this minus 5 degrees Fahrenheit line here, that's the temperature. This is the minimum temperature at which you get 98% mortality of the hemlock woolly adelgid nymphs. And that's essentially what keeps the population in check. That's why it hasn't spread into northern New England.
But you can also see that since about 1986, or I guess right here in 1987, we've really only had one, two, three winters where it's gotten below minus 5 degrees. And right here, which is around 1997, '98, when the adelgid was first reported in the Arnold Arboretum, we've only had one winter when the temperature got below minus 5 degrees. So the spread of the adelgid to a very strong extent, I think, can be considered a manifestation of climate change. So this is an insect that has been responding to this slow trend of the warming winters.
And so it's not so much that this invasive insect has come and been devastating our hemlock populations. It's that the climate has been warming steadily. And the ability of the adelgid to take hold is really a function of the changing climate.
What's interesting to me is that the species in southern New England that takes over when hemlock is removed is the black birch, Betula lenta. What's really interesting about Betula lenta is that this is a disturbance adapted species. It really doesn't matter whether the disturbances the adelgid, whether it's logging, or whether it's a hurricane. This is a species that benefits. And so throughout southern New England, we're seeing this massive increase in black birch in response to a variety of disturbance factors.
And I use this slide here. On the left-hand side is the distribution of paper birch, and on the right, river birch. These are from a series of maps produced by Albert Little from the US Department of Agriculture Forest Service representing the distribution of these species in 1977. We look at these maps and we think, this is the natural distribution of these species. But what they really are snapshots of where these plants were reported growing as of 1977. They say nothing about where these species are going to be occurring in the future.
And paper birch, under the influence of climate change, is one of those species that's predicted on the basis of a lot of data that's essentially going to be migrating north out of the Massachusetts. And river birch, Betula nigra, is one of those species, it's northernmost range are the Mystic River in northern Massachusetts. That's a species that's going to be moving right up into southern New England.
So there are clear winners and losers. And this idea that plants have these set ranges that represent a fixed entity is really a fantasy. And people forget that a good part of the Northeast was glaciated not more than 12,000 years ago. And in places, there was as much as a mile thick ice sheet. And so the vegetation, in response to that, it was driven south to these refugia, many of them in the mid-Atlantic Region. And then as the glaciers receded, these plants bounced back, if you will, from these areas in the mid-Atlantic Region to re-occupy the Northeast. And so again, during this process, we don't actually know, have these species reached the northern limit of extent? Or are they still in the process of expanding their range? And so understanding this flexibility of the range of these species, it's a really important concept for understanding what's happening in the world today.
And this really brings me to the main topic, which is urbanization. And I introduced these broad ecological concepts because I think they're really important for understanding what's happening in our cities very much today.
Now, this is a range map for my book. It essentially covers the area from Montreal to Boston to Washington, DC to Detroit. It's a rather large geographical area. And you can see just by looking at this map a very significant proportion of the land area is fully urbanized. Here, urbanization is defined as a density of 500 people or more per square mile.
And when you fly over a city-- in this case, like Los Angeles-- you realize somewhere down there, there is a river. You can talk about what used to grow in Los Angeles.
But the concept of native species, that somehow there are some species that are native to Los Angeles I think is a crazy idea. Nothing is native to the urban environment. In order to build that city, everything had to be wiped out. And then essentially, certain plants will come back. They may or may not have been there before. But you can talk about what used to grow in the urban environment. But the concept, the whole concept of a native species in an urban environment does not make a whole lot of sense to me. And it's easy to pick on Los Angeles.
But in point of fact, in many of our suburban areas, you have these big box malls. This is one that's on Cape Cod. From a vegetation point of view, you can see that, in fact, whenever you have paving and structure, you essentially have urbanized conditions. And again, from the plant's point of view, when you have as much land that is paved or covered with some form of structure as you have open land, you essentially have an urbanized situation. So many of our suburbs, even though in terms of the density of human population that we consider them non-urbanized, from a biological point of view, they are very much urbanized.
Some of the attributes of urban environments that are distinguishing is on this vertical axis here, this is the temperature difference between a rural area and an adjacent urban area. And you can see, this is degrees centigrade. So we're talking about 12 degrees centigrade. That's over 20 degrees Fahrenheit. So this is the population of the urban area. The squares are US cities. The circles are European cities. And you can see here how as the size of the city increases, the temperature difference between the rural and urban area dramatically increases. Now, this is the maximum temperature difference. So this would be on a calm night in summer. But nevertheless, this urban heat island effect is a dramatic illustration of the fact that the conditions in our urban areas are dramatically different from those of the surrounding areas.
And from the perspective of wanting to study and think about climate change, urban areas are actually the perfect place to do climate change research because they have already heated up to the extent that is predictive for the surrounding areas. So you can very easily get a preview of coming attractions in terms of the environmental impact of climate change by looking at what's happening in our cities.
There are certain characteristics, again, from a vegetation point of view, the urban island, if you like. This is a typical planting of Norway maple. And when these two trees fully exploit the soil that's available to them, they will essentially die. That's maybe 10, 15 years. That's it. I view them as they're like bonsai plants. They're going to be there. They're containerized. When that soil is fully exploited, they will die.
And you can see, if you look closely, all over our cities where there used to be trees. I call these ghost trees. And in many, many cities, there are as many ghost trees as there are real trees. It's sad. And I like to say to my students here, if I ever catch you writing a spec for a 3 by 3 foot tree pit, and you plant a tree in there, I'm going to go into the records and I'm going to change your grade to an F.
And why we know that this doesn't work-- these trees live 10 to 12 years. And yet, you could see new developments going in. And time and time again, this is what they give the trees. It's sad. And it says a lot about the values in our society.
Other aspects of urbanization that are very common and important is the quality of the soil. Sometimes in urban areas, you do have remnants and patches of native soils. But in many cities, particularly a city like Boston, where well over half of the land area is fill, the soil is brought from another area. And in many cases, it consists of rubble from prior structures that were on there. So the soil, more often than not, is a serious problem that plants have to deal with in the urban environment. And it's not an easy situation for them.
And of course, the problem of soil compaction-- I view the heavy equipment that is always brought in-- even the small jobs now, they bring in heavy machinery. It completely destroys the soil structure. And it's analogous to glaciation. I really think that you have to view urbanization as a form of a modern day glaciation. It comes in there, and it wipes everything out in its wake. And what does it leave behind but compacted glacial till.
So when you start talking about the urban environment, you're really talking about primary succession. These are plants. There's no remnant of any vegetation left there at all. And vegetation has to start from ground zero. And that's the reality of life in the big city for plants that are growing essentially on their own.
Now, many of the species that do well, the spontaneous vegetation, are very well-adapted to these urban conditions. Here's the Kentucky blue grass here. Here's the walking path. And then there's a gradation of compaction that's intense right here. And then it diminishes as you get further away from the path. And right in this area here, this is where the prostrate knotweed grows. So that's a species that the weed scientists will tell you is an indicator of soil compaction. And what I like to say is, it's actually adapted to soil compaction and does extremely well.
Another ubiquitous element in your environment is road salt. Nobody wants to compromise human safety for the sake of a few plants. And so we use it with impunity.
And not to scare you, but this is a chart. This is sodium chloride input up there. And the impacts are massive, starting with the shrinkage of the soil. It essentially draws the water out of the soil, causing it to shrink. It increases the sodium saturation, which effectively elevates the pH. So it's analogous to spreading limestone on the soil. And then finally, it increases the osmotic potential of the soil, which makes it very difficult for plants to actually get water out of the soil, creating conditions of osmotic drought for plants. So this very simple act of spreading salt completely alters the ecology. And what's really interesting is that certain plants are-- I use the term "adapted." But in fact, the correct term is "pre-adapted." These are plants that come from areas that naturally experience conditions that are similar to those found in the urban environment.
So this mugwort, Artemisia vulgaris, is adapted to high pH soils in Europe, meadow-type situations. And you'll find it typically growing in vacant lots that are mulched with rubble, concrete and brick, because it likes the high pH from the concrete. But you also find it along heavily salted streets because the salt has elevated the pH. So this is an example of a plant that, actually, over the last 20 or 30 years, has left the urban environment and migrated out into the countryside along our interstate highways, following the bands of salt that border our highways.
And another example, even more dramatic, is a native species, the seaside goldenrod, which is a coastal dune species. And it's been well-documented that over the last 20 years, this species has also left the coastal dunes and followed the interstate highways. And now, you can find it halfway across the state of Massachusetts along the Massachusetts Turnpike. It's not that it requires salt. But when salt is present, it has a competitive advantage.
So again, it's this concept of pre-adaptation. It's not all about invasive species doing this, but our own native species are actually behaving in much the same way. So again, this whole idea that somehow, these species have fixed ranges, and this is where God put them, and this is where God wants them to stay is really a denial of the reality of what is actually happening in the world. And the plants know what's happening. And they're responding to it very dramatically.
So like any good botanist, I have to have my own taxonomy. And the urban environment is very patchy. You have a variety of different ecotypes or habitats within the urban areas. My general classification are remnant, natural urban landscapes, which consist mainly of native woodlands and wetlands, persisting from times of early settlement. These are dominated by a mix of native and invasive species-- and this is absolutely key-- on relatively undisturbed soils.
And that means that if you really want to have a native ecosystem, you really need native soils. They go together. You can't really separate one from the other.
Then you have managed functional landscapes. These would be parks, gardens, lawns, ball fields, cemeteries, dominated by cultivated plants on rich modified soils. And they have, of coarse, medium to high maintenance requirements.
And then the ones that interest me most and are really what I'm going to be talking about for the rest of the lecture are the ruderal, or abandoned, landscapes, postindustrial vacant lots, infrastructure edges, dominated by spontaneous vegetation on compacted filled soil, and zero to low maintenance requirements.
And this last little line here-- whoops, excuse me. This is important. If you define sustainability as essentially the ecological services that you get in relationship to the resources that you have to put in to maintain those plants, some of the spontaneous vegetation is going to score very high on that sustainability index because of these low maintenance requirements.
Just some examples of these different types of landscapes-- this is the Hemlock Hill section of the Arboretum, considered to be not a primordial forest, but it was logged in the early 1800s. And the hemlock trees that dominate the site have been there, essentially, since the early 1800s. But as you can see from this stump right here, it's not as though we just leave it alone. We had to remove that tree because it was a hazard.
And of course, what you can't see is the fact that every one of these trees we've treated with the insecticide Merit. We've injected it in the soil. And had we not done that, all of these trees would have been destroyed by the hemlock woolly adelgid. So much for your low maintenance native landscape.
The poster child, of course, for the managed landscape is Central Park. Everybody loves Central Park. And I gave a talk in New York City a couple of years ago. And I thought, oh, this is great. I'm going to get to walk across Central Park in early spring. And maybe I'll get to see what kind of weeds are growing in Central Park. Well, needless to say, there are no weeds in Central Park. It is a remarkable experience to go across it.
And it took me a while to figure out exactly why there were no weeds in Central Park. But I realized they use a special kind of mulch there. What you do-- if you take dollar bills and you grind them up very fine and then you just spread them out about two inches thick, that will suppress all weed growth. And don't be afraid to try this at home, because I can pretty much guarantee success with it.
And of course, the spontaneous, or the ruderal landscape-- I love the word "ruderal." It comes from the Latin word meaning "rudis," "broken stone or rubble." So these are plants that grow on the ruins.
And if you're interested in spontaneous urban woodlands, the place to go is Detroit. And here you see. This is an abandoned-- there probably was a factory here at one point. Large parts of Detroit, they were initially abandoned following the riots in the late 1960s. So you're talking about land that's been abandoned for upwards of 40 to 50 years.
So you're beginning to see in a lot of these sites actual forest development. And it's very interesting. Because in most cities, particularly cities that have a thriving economy, land may stay vacant for five, 10, or even 20 years. But eventually, somebody is going to come in, wipe it all out, and put something there. So the presence of spontaneous vegetation is very much a socioeconomic indicator of how vital the economy of the city is. And when you go into a place like Detroit and you see spontaneous forests that are 30 or 40 years old, you realize that that's a city that is in deep, deep trouble.
How much vegetation in your average city is-- how much spontaneous vegetation is there in the average city? This is Somerville, Massachusetts. It's a relatively small city. So I picked this as a project for my students. And using GIS technology-- and then because it's small, we were able to ground truth all of this. But the yellow represents surface railroad lines. The large red patches, that's abandoned industrial land. And then the smaller red patches are vacant residential lots. And the figure for Somerville is 9.5% of the total land area in Somerville is dominated by spontaneous vegetation. That is not an insignificant figure.
So we're not talking about plants that grow in sidewalk cracks here. We're talking about there's more spontaneous vegetation in Somerville than there is parkland. So it's not a trivial amount.
And then you, again, look at a city like Detroit. Here, red represents abandoned buildings. And the green represents abandoned property. 40% of the total land area in Detroit is abandoned. It's a remarkable statistic. And you know, what is going to happen to this land? Well, it's not going to be converted into parks. Because who's going to maintain them? And it's not going to be converted to urban agriculture because a lot of it is intensely contaminated.
So this idea that somehow this urban land is a valuable resource, and there's lots of things we can do for it is really, when you get into some of the Rust Belt cities in the Midwest, it's a serious issue that nobody really has a handle on what to do about it.
The technical name, it's called shrinking cities. And these are cities that have essentially lost half of their population with no prospect of the jobs coming back that will bring those people back. They are looking at a future that is essentially half the size of what it once was. And then what happens to the rest of the land?
A trip to Detroit, it's really eye opening. I was totally unprepared to see. Maybe one in six or seven houses is still standing. They knocked them down into their own foundations. They run over them with a backhoe. They push them down. They spread some topsoil on it. And they sow orchard grass. You could be in the middle of the countryside, yet you're only a mile away from downtown Detroit. All the street trees are there. The sidewalks are there. The telephone poles are there. But the houses are gone.
And of course, here's a good example of a wetland up on the second story of a building. Obviously, the willow has found the leak, if you will.
Now, a lot of this, people look at these plants, and they say, well, these are weeds. Weed, of course, it's not a biological concept. It's a human value judgment. It just is a plant that competes with something else we're trying to grow. So it really has no biological meaning. And it, of course, has very negative connotation. So in an effort to change that dynamic, I've come up with a concept of cosmopolitan urban vegetation to help change the way people think about this.
And once you start looking at it, it's really remarkable. This is from New London, Connecticut. And again, this concept of pre-adaptation is really important. This is a species that grows commonly on limestone cliffs throughout central China. And what is a deteriorating brick building but a limestone cliff? So the plant has found the exact analogy to its native habitat. Or in this case, Ailanthus on the Great Wall in China. These are these dry limestone hills all around the city of Beijing. And then on the right, of course, the Great Wall of the Arbor Way adjacent to the Arnold Arboretum.
And so this concept of pre-adaptation really is important to understanding why certain plants do so well in urban environments and why others don't.
This is my little schematic for thinking about succession in an urban environment. It's driven by disturbance, competition, and habitat stress. And essentially, as opposed to thinking about succession to some steady state climax, a situation, essentially, disturbance periodically is essentially driving the succession cycle back to zero. And so you have much more of a cyclical succession process in your urban environment as opposed to some trajectory that's leading to stability over time.
And again, this is right from the book. When you start looking at cities, and you can sort of treat it as a real ecosystem, and you begin to look at characteristic habitats just like you would any other ecosystem, you realize that there are some very characteristic habitats within the urban environment, not the least of which is the chain link fence. If you said to yourself, I really want to do something for plants, like, you know, plants they really have it tough, and I just want to do something to make it easier for plants, you couldn't have done anything better than invent the chain link fence. This is heaven for plants. It allows them to get up over the competition. It just exposes them to full sun. And so there's a whole suite of species that are pre-adapted to growing on the chain link fence. And in ecological terms, the chain link fence is a safe site for seedling establishment.
So this American elm, the maintenance crews would love to remove this plant. They cannot do it. It's so enmeshed with the chain link fence that it essentially avoids destruction-- its predators, if you will. So you think about the maintenance crews as predators. And the chain link fence allows the plant to escape.
And what's really interesting is in a lot of cities where you see these very weird lines of trees in strange places, I guarantee you, that's always where there used to be a chain link fence. That row of trees got established. And then they removed the chain link fence. It's an extremely common sight for tree establishment in urban areas.
Or the urban meadow, in this case, curly dock and mugwort. This is just a typical vacant lot. There was nothing but rubble on the surface. And here are the same plants growing in Tuscany. The urban meadow, again, its high pH, compacted soils-- except in Tuscany, of course, we have to pay a lot of money to go there and admire it. And in our own cities, it's a sign of dereliction.
Or the median strip, or as it's known in New Orleans as the neutral zone. This is near the Arboretum. And I watched them build this. It's about three feet across. And they dutifully sowed it with Kentucky bluegrass. And then all of it died within two months, as soon as summer came. And of course, what's growing there now is crabgrass. You know, what this median strip, it's the ideal habitat for crabgrass. It's a summer annual. It doesn't even grow until the temperatures get above 70 degrees. The hotter it is, the more it grows. There's no water there. There's high temperatures. And if you wanted to actually design a habitat for crabgrass, I don't think you could have done a better job.
So a lot of what you see is really-- these are the biological characteristics, but the drivers are human behavior. And that's really a very, very important idea here. The difference between urban ecology and natural systems ecology, you have to account for people and their behavior when you study urban ecology. You can't leave them out of the picture.
Or how about this one? I like to say-- and Peter Trowbridge, I hope you won't wince when I say this. But if you look at this picture, you see-- it took me a while. I didn't actually even recognize this when I was just taking the picture. But you realize that the grass is only growing on the short end of the brick. OK? It looks like a landscape architect planted this is what I like to say.
And I show this picture, and I say, you know, obviously something is going on here, but I don't know what it is. And finally, there was a physicist in the audience. And he said, well, if masonry is anything like metal, the amount of contraction and expansion is a function of length. And so the brick is going to contract more in this dimension than it is in this dimension. And therefore, just that little bit of an opening, it's wider at the narrow end of the brick than it is here. In fact, that difference probably has to do with the size of the seed. And that seed is able to get between the bricks in this dimension, but not in that dimension. So this is a very sophisticated ecology that's actually going on here. But who would have recognized-- This, of course, Eragrastis spectabilis, this is a native species. But who's going to take the time to get down on their hands and knees and actually identify this plant?
So the environment is filled with examples like this. The sidewalk crack is the ubiquitous habitat in the urban environment. We think of cracks as being very stressful environments. But in fact, if you visualize water sheeting across the parking lot, and as soon as it gets to the crack, it goes straight down, the crack is where the resources collect. And if you define the oil the drips off the bottom of our cars as a resource once it's been digested by bacteria, the crack becomes a sink where resources accumulate. And all of a sudden, the crack becomes a very rich site for the establishment of plants. And again, fall panicum and path rush, those are both native species.
And of course, wherever you have more than one kind of paving material in contact with another one, you always have a seam. You're going to have a crack develop there, because these paving materials expand and contract at different rates essentially, according to the temperature. And so whenever you have two types of paving material next to each other, they always separate. And I call this the trifecta of cracks. You have blacktop. You have granite. And you have cement all together. So this is a crack that's expanding in all dimensions, providing excellent opportunities for plant establishment.
Or this little plant, carpetweed, Mollugo verticillata, an annual from Central America, existing exclusively on air conditioner drip. OK? So you turn the air conditioner on in June. The condensation causes it to drip. It's an annual. The seeds germinate. It grows. They flower. They set their seeds. We turn the air conditioner off in September. The water stops. The plant dries up, leaves its seeds behind, and disappears. It's an ephemeral species. It's found the perfect microclimate.
And it's just a matter of changing how you think about what you see. And actually what it is, it's thinking about what you see. Most people never take the time to actually look at what's going on.
Or the urban Krakatoa-- I like to think about how--
If you squint-- I hate to keep asking you to squint. But you could be on the big island in Hawaii and the [INAUDIBLE] could be the silversword plant.
And when you think about what the temperatures are on this in July and what's the water that's available, you really have to admire the tenacity of these species and their ability to survive and flourish under these conditions.
This, of course, is my favorite, from Detroit, the loading dock wetland. Obviously, the drain is clogged up. It fills with water. The phragmitis comes in. There are red-wing blackbirds there. I'm not sure about the fish. I didn't see any fish. But I would guarantee you there's probably frogs in there. And it's an actual functional wetland.
So this ability of vegetation to interact with human structure is much more powerful than people realize. And it's actually very scary if you're on the maintenance side of things because if you let the plants get a foothold, they can really take that landscape apart. Of course, and again, using an analogy with natural systems ecology, corridors are critically important for understanding ecological systems, particularly in urban areas, the river corridor that runs through most of our cities.
River corridors and stream corridors are naturally disturbed areas because the water level, it's always fluctuating. It's high in the spring. It's very low in the summer. And the plants that grow naturally in river areas are well-adapted to disturbance. And so these river corridors become a haven for disturbed and adapted species of all sorts, both native and exotic species. And this is one of the main avenues for the migration of species, both into and out of the city.
And of course, our rail corridors are similarly important, especially, I think, for wildlife. We have a train line that comes up from the south to the Forest Hills Station that is right near the Arnold Arboretum. And as it comes into the station, it abuts the Peters Hill section of the Arboretum. And I am sure that coyotes that we have, the fox that we have, the deer that we have, are all migrating up and down this rail corridor. So it's just like in natural systems ecology. These corridors are a critically important piece of the puzzle.
And since you've gone as far as you have with me in this lecture, we might as well go all the way and talk about the environmental functions of spontaneous urban vegetation. Because I believe in an urban context, a lot of these plants are actually providing environmental benefits or services. This is, of course, the list. And as I said, this is straight from the book.
And the poster child for this, this is the New Jersey Meadowlands. This is the Vince Lombardi exit, you know, this old bridge there you go over. And you can get an overview of the Meadowlands. And you could either look at this-- you could say, oh, my god, the invasives are taking over. Or you could say, this is a landscape of landfills. There is over 500 landfills in the New Jersey Meadowlands taken as a whole. And the phragmitis is actually helping to clean up this area. Phragmitis is one of the most efficient plants known for absorbing nitrogen and phosphorus, dissolved elements in the water that are very difficult to remove. Phragmitis is very effective at getting rid of it.
But even if your goal was to get rid of the phragmitis, OK? Let's just say, OK, we want those cattails back, then the prescription is very straightforward. It's very simple. You remove the New Jersey Turnpike. You reestablish the tidal flow in the Meadowlands. And I guarantee you, the cattails will come back. But in the meantime, when you have impeded flow of water, and you have brackish water conditions, you're going to have phragmitis. That's just the way it is.
And so a lot of these plants, when you see them, it's not that they're causing environmental degradation. I like to say, they're symptomatic of degradation. They are not the cause. And it's really important that you think clearly about what is actually going on in terms of other examples of services. All trees, it really doesn't matter where they come from, they create shade. They lower temperatures, end of the story.
I sent a memo to Mayor Bloomberg. I said, you know, you want to plant a million trees in New York City. Well, if you actually just start counting Ailanthus, maybe you only have to plant 500,000. Because we're actually getting a tremendous amount of ecological value out of this tree. But nobody counts it. And I think that says a lot.
You know, in terms of stabilization, this is the Charles River, not too far from my house. Those are some American elms there. There are some river birch. And of course, there's Norway maple. And without those trees there, we'd have some very serious erosion problems.
Or Rosa rugosa, the seaside rose, for stabilization of dunes just behind the high water mark. Besides some of the native sea grasses, there's no shrub that occupies this niche in our native New England coastline. This is a plant that is a very important tool for mitigating coastal erosion. We need this plant. This plant is actually-- and there is no native species that is actually performing the same function. So it's really important not to put everything in terms of good and bad based on a plant's nativity.
Many of you will recognize this plant. I worked on the vegetation of roadsides in the 1970s. And that was during the Johnson administration, when the interstate highway system was being expanded. And the deal was the feds would build the highway, and the states had to beautify it. That was Lady Bird Johnson's little contribution to it.
And so in Massachusetts and Connecticut, especially Elaeagnus umbellata was the plant that was going to save the world. It fixes nitrogen. The birds love the seed, so it provides food and habitat for wildlife. And of course, you can make jelly out of the seeds. Tell me what the problem is. So millions of these plants were planted along our roadsides. And then 20 years later, my god, it's spread everywhere. It's an invasive species. Well, it's not as simple as that. There was actually a policy that set the table for this.
And similarly, kudzu, if any of you-- I'm sure some of you have seen this in the South. Everybody disparages this plant. But very few people realize that in the 1930s and '40s, when soil conservation was the highest environmental issue of the day, the government subsidized the planting of kudzu to the tune of $0.10 per plant, mainly along railroad right-of-ways. That's 13 million plants that were planted of kudzu.
So you cannot actually explain the kudzu phenomenon if you don't account for people. It's actually not a biological phenomenon. It's a sociological phenomenon. And as long as we perceive it as, oh, my god, nature's out of control, we're not actually correctly analyzing the situation.
The problem is us. It's really easy to blame the plant. Oh, if we just get rid of this plant, everything is going to be fine. And it just is not true. The native vegetation is not going to come back because the underlying soil conditions, the climate, everything is different.
So the way the world used to be, that was terrific. But I think we have a better chance of restoring the economy of the 1700s than we have of restoring the ecology of the 1700s. And I mean that, because at least the economy is a human invention. The ecology is an incredibly complex system involving the interaction of thousands of different types of organisms.
Now, of course, you can't talk about the urban environment without talking about the cultural significance of the plants. How did they get here? What are they doing? And so this is the list of cultural uses of plants.
Purslane, you're all familiar with this. And nobody even knows where this plant comes from. Maybe India, that's the best guess. But what they know is that every archeological site involving early human remains, the Homo sapiens remains, you find the seeds of this plant. This was a very important food source that either followed people around, or was actually cultivated by people. And it actually contains-- purslane has the highest concentration of omega 3 oils-- that's what you find in carnivorous fish like salmon-- than any other plant.
And everywhere you go in a Third World country, this plant is actually typically eaten. It's even served in restaurants, because it's a very valuable food resource. And I'm happy to say that in the latest edition of Johnny's seed catalog, you can now buy red and yellow leaf cultivars of purslane for your very own garden.
Or this plant, mulberry, this is a plant that is a reflection of the 1820s, when the United States was trying to compete with China on the production of silk. Well, that didn't work out very well. That never happened. But the mulberry remains as a echo of this period in time. And so this is one of the really interesting-- all the plants in the urban environment are reflections of different eras in the social economic history of that urban area. And so being able to recognize that is really important.
Or you all know this plant. This was sort of in vogue in the 1850s. It was introduced in the 1850s. And then William Robinson in The Wild Garden waxed eloquently about this beautiful plant from Japan and thought it was wonderful in the perennial border. And then in the 1880 edition, he says, well, maybe it's a little aggressive. Maybe you put it a little bit in the back of the border. And then in the 1890 edition, he said, well, actually don't put it in a garden, maybe in the driveway leading up to your garden. But by then, of course, it's too late and this plant is everywhere.
But who realizes? You've all heard, if you drink enough red wine, you will live forever. Right? Everybody knows that. And who can tell me what the compound in red wine is that it's responsible for this health effect?
SPEAKER 1: Resveratrol.
PETER DEL TREDICI: Resveratrol, right. So do you think that they can make these resveratrol tablets that you can buy in health food stores-- do you think they take this really good French wine, they boil it down to make those resveratrol tablets? Yeah, right.
Well, what they do is this is this species, this and its cousin, the giant knotweed, Polygonum sachalinense-- so be thankful you don't have that plant in your backyard. This is the source of resveratrol. This is the species that has more resveratrol in it than the red wine grape. But you know who would have thought that?
Or my last example, this beautiful combination in mid to late summer, chicory-- both European plants. Chicory, of course, you toast the root. You can mix in with coffee to stretch the coffee and/or make what's called New-Orleans-style coffee.
And then Queen Anne's lace, which the ancient Greeks, going back at least 2,000 years to the time of Dioscorides, recognized that this was a plant that was effective for birth control purposes. And it's not an abortifacient. It actually can be taken as a morning after pill. You grind up the seeds, drink it down. And that isn't to say-- I don't want you to try this at home.
Then you fast forward to the 1970s, where a researcher named John Riddle from University of North Carolina is investigating the medicinal uses of plants by people in Appalachia, out-of-the-way corners of Appalachia. And he would talk to the women. And they all knew that Queen Anne's lace was a birth control pill. And they used it as a morning after drink.
And the question is, well, how did you know this? They'd say, well, my mother told me. And how did she know it? Her mother told her. So this is information that passed directly through the maternal line, crossed the ocean by word of mouth, and landed in the New World, essentially through midwifery channels.
So who would have-- we've forgotten all of this information. And these plants are really part of who we are as human. They make us human actually. And to just disparage them. Oh, my god, it wasn't here when Columbus landed. Therefore, it is a bad plant. I just do not accept that as a very complete view of the world in which we live.
I mean, we are human beings after all. We are the most incredible weed that has ever existed.
There's no two ways about that.
And this is the last part of the talk actually. And this is because of my design school students. They say, OK, we buy what you say. All right, I can see that they have ecological value. I can see that they're historically really interesting. But you know, a lot of these plants are really ugly. What about the aesthetic issue here? So I have to take this on directly because of my students.
And this is Fisher's Island off the coast of Connecticut. What people don't realize-- nobody even knows this island exists because it's actually part of New York State, a little part of New York that is off the coast of Connecticut.
So I was giving a talk there. And the woman who was my host said, oh, I want to show you this beautiful wildflower area. And she took me here. And it was actually very beautiful. But the fact of the matter is, there wasn't a native species in there. Yet, it's filled her concept of what was a beautiful wildflower area.
And what this illustrates to me is the contextual issue here, which is in the context of Fisher's Island, looking out to sea, these are wildflowers. The same plants growing in a vacant lot in downtown Boston are weeds. And our aesthetic judgments are totally contextual. They're not absolute. It really depends upon our perception of reality. They don't actually describe anything besides an emotional reality.
And this is a quote. I'm going to read it just, so those of you who can't maybe read it. This is this from the first guidebook to Central Park that was written in 1869. "Blessed dandelions in such a beautiful profusion as we have never seen elsewhere, making the lawns in places like green lakes, reflecting a heaven sown with stars." That is quite a statement about dandelions. There are no dandelions in Central Park anymore. They have been eliminated. And so really, this whole concept of what constitutes beauty, it's a very, very tricky issue.
And so it's with great trepidation that I present this slide to you. I call this the cosmopolitan urban meadow. This is a low-growing, long-lived perennial species tolerant of full sun and poor soil. And essentially, there's a meadow mix-- I call it my vacant lot mix-- for essentially taking abandoned urban land, doing a minimum amount of site preparation, sowing it. And these species will hold that land until you have something better to do with it.
And in the meantime, these plants are actually helping to remediate some of the contamination conditions that exist there. They require minimal maintenance. You're going to have to mow it once a year. And they are actually aesthetically much more beautiful than a random collection of spontaneous vegetation that might otherwise be there.
Now, this isn't to say-- I'm very, very tolerant about most plants. But this is not to say that I love all plants. Some plants have no redeeming social value, the bittersweet being the plant-- you know, I've engaged in hand-to-hand combat with this plant over many years. Its root sucking capacity is just not to be believed.
And you know the problem with the bittersweet and a lot of other vines is their goal in life is to destroy trees, that the vine is a parasitic life form. It doesn't bother to invest any resources in building a trunk of its own. It just takes over somebody else's trunk. That is the nature of what a vine is. So if you're interested in trees and you want to grow trees, it's very hard to figure out how to incorporate the vines into that mix, because that is what vines really do.
And even our native grape, once it gets up into the crown of a tree, can actually do a lot of damage, particularly when it gets loaded up with ice and snow. The crown gets breakage.
So the issue then is, how do you manage some of the spontaneous vegetation? And the concept-- this was introduced by a man named Frank Egler, a wonderful book from the 1960s called The Wild Garden and the Wild Landscape. And he called the process intaglio after the engraving process where you create a positive image by removing material. So you create the landscape not by going in there and planting, but by removing weak plants, diseased plants, plants that may be problematic, vines and things like that. So it's a very different concept. It's a management concept. And you manage it to increase not only its ecological functionality, but also its aesthetic potential.
And so I believe that this is a very important way that we have to start thinking about these wild urban woodlands that are beginning to appear in many of our cities, as opposed to saying, oh, my god, it's all invasive species. We have to remove them all and put in a native forest. I think that there's different ways that we have to begin thinking about this that really require much less drastic disturbance of the landscape.
And the place to go if you actually want to see examples of this, of course, is Berlin. On the left, you can see, it's a wonderful park. It's an abandoned railroad yard. It was abandoned in the 1960s, Sudgolande. And it's been converted into a park, a public park.
And those white birches-- again, Peter, my apologies. It looks like a landscape architect did that. Who could have envisioned putting white birches like that, just between the railroad tracks? And then they put a little bit of wood chips in the railroad tracks. And you've got this wonderful path. It looks like, Naumkeag.
And then one part of the area is this grassland. They found 40 species of beetle in there. So they put a boardwalk in there, essentially so people wouldn't trample it. But amazingly high biodiversity in some of these abandoned sites.
And I think we have a lot to learn about it. Unfortunately, one of the lessons-- the High Line, I call it the artifice of abandonment. This is the most expensive landscape to maintain per square foot basis in all of New York City. And what is it? It's nothing but a copy of Sudgalande that grew spontaneously in the railroad. So I must been asleep when copying abandonment became a high aesthetic goal. But nevertheless, that's what seems to have happened.
It's really remarkable. This is what High Line used to look like. It looks like a desert, actually. This is old ballast. And there's a crabapple that's at least 20 years old and maybe three feet high, a very dramatic landscape. But of course, most of that is all gone now.
I mean, it's easy to knock the High Line. But people really love it. It's very effective. But what it is not is sustainable. The resources that go in to preserve and maintain that landscape are off the charts. So it's a very complicated issue that we really have to come to grips with.
And again, going back to the German model, this famous area-- it's not really a park. It's like a cathedral of industry, the Ruhr area, which is the German equivalent of Pittsburgh. This is where the steel and coal industry was located, abandoned, like in Pittsburgh in the 1970s. And essentially, they've just left everything there. It's clearly remarkable. And the vegetation, they just left the spontaneous vegetation grow up in the middle of this industrial complex. It's truly remarkable what they've done.
It's all open to the public. The coal bunkers have become rock climbing venues. The big gasometers, the gas tanks for storing manufactured gas, they've filled them with water. Those have become diving tanks. It's remarkable to see what imagination can do.
And it actually covers a huge area, 30 different towns, 600 kilometers of bike paths, monuments, sculptures everywhere. And it's all connected by this network of spontaneous vegetation. It really represents a totally different way of thinking about it. And I think we actually have a lot to learn from it.
So this is my very last slide. And it's my final message. So I just want to thank you very much for your attention.
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Dr. Peter Del Tredici explores the natural and cultural history of the plants that grow spontaneously in our cities, focusing on the cosmopolitan nature of this flora and its ability to adapt to the stresses that dominate our urban ecosystems.
Dr. Del Tredici defines a forward-looking approach to the issue of spontaneous urban vegetation that encourages us to see these plants - the natural vegetation of the urban environment -- with fresh appreciation and understanding. His ideas on the subject have been published in the book, "Wild Urban Plants of the Northeast: A Field Guide."