>> Hello, students. This is Plants and Animals of Southern California. Today we are in Cheeseboro Canyon which is in Agoura Hills, California. We're at the northern range of the Santa Monica Mountains National Recreation Area. And today we're going to talk about invasive species but focus mainly on invasive plant species, invasive alien plant species. And I think Paul wanted me to talk about that with you today because I am a biological technician for the park service and I've spent a lot of time out here in Cheeseboro Canyon dealing with the weeds out here. They are an introduced species that have the ability to cause some kind of adverse effect to either economy -- so it could be, for example, in agricultural areas, we have a lot of invasive alien plant species that overwhelm these areas. And we spend billions of dollars annually trying to control these weeds so that we can grow our crops. It could be impacts to human health. So there's some invasive species, those are castor bean and poison hemlock, and they cause harm to human health if they're ingested. They can kill people. In fact, poison hemlock is what killed Socrates, yeah, because he wasn't getting with the program with religion back in the day. And then what we're interested in mainly in this class is the impacts that it has to ecological areas, and that's what I deal with here at the park. So, invasive species can displace native species or alien plant species, the invasive ones can increase by a frequency -- in fact, I think in California, the thought is that invasive alien plant species are probably one of the worst if not the worst threat to the remaining native populations and communities, because they're so aggressive and they spread so rapidly. So let's look at some other definitions. So, non-native was mentioned. A non-native species is a species that has evolved in a different geographic area. So, the distribution, the natural distribution of its range occurs in a different geographic region. So, for example, the Mediterranean plants that are here, they evolved in the Mediterranean region, somewhere else, and they've been introduced here. So they're a non-native species, and they're invasive because of the fact that they cause harm. But some species don't cause harm; they just are not native. So, for example, if you were to go to the grocery store, you go and you buy some plants that are in pots, and you put them around your kitchen or in the front yard, put them in your garden, those are also non-native. A lot of those plants actually are tropical plants, but they don't have the ability to cause harm, so we call them non-native plants that are ornamental, maybe, because they're used mainly for decoration. And if you were to come out here and plant them out here in some natural areas, they probably wouldn't survive because they need human care, intensive human care to keep them alive. But there are non-native species that can survive out here in the wild areas, in natural areas, but they don't cause harm. And so those we call naturalized species. So maybe a good example of that would be like Mexican cactus, probably, which is the same genus as our native cacti, opuntia, but it doesn't really cause harm, and it doesn't have the spines that our native cacti have. It looks a little bit different, it's a bit bigger. It can reproduce on its own, but it usually occurs in areas where people have planted it and the offspring don't generally stray too far from the parent plant, so it doesn't really spread and cause the same kind of harm that invasive species can. So, what is it about an invasive species that makes it invasive? Like why is it that there are certain introduced species that have this ability to -- a lot of the invaders have these common physical traits that make them superior invaders. Certain areas have higher invasibility [phonetic] than other areas. So it has to do with physical traits, area, they lack competitors, oftentimes; that could be a reason why. So it gives them an advantage. Another thing that really helps invasive species out is the rate of introduction. So we can call that propagule pressure. Propagule being the part -- the material of the plant that's responsible for reproduction. So this would be like the seeds and the spores. If you just -- this last one's probably easy to imagine if you just think about the world that we live in now with our trade, travel, our roads and freeways, the propagule pressure is very high and some of these species have been intentionally introduced here for particular reasons. A lot of them accidentally, as well. But we're jumping contents on a daily basis. You guys are probably carrying a bunch of seed in your shoes right now and you're going to go to the next field trip and maybe disperse some of that. But then you can imagine on even a greater scale, vehicles driving millions of miles every day, carrying a bunch of weed seed and -- that's why you'll see some of these species that you see today that we pointed out, if you keep your eyes open on the roads, you'll see them on the sides of the roads too, because vehicles bring them in their engines and they drop them on the road and it rains and the rainwater brings these seeds off to the side. And we also trade different animals and plants, and some of those are invaders, and a lot of them are hitchhikers. So that's high propagule pressure. Also, like I mentioned, some of the species were intentionally brought here. And this first started mainly with the European settlers who came out here. So, when the European settlers came out here, for example, like in Cheeseboro Canyon, this has, I think, 150 years of ranching history. So they had a lot of grazing animals, domestic animals like cattle, because more and more people were coming over here. And so this was becoming a business and -- so they selected a lot of our native grasslands because cattle are really good at grazing through native grasslands. But additionally, they also selected areas that had more shrubby stuff, like coastal sage scrub, for example, and they would remove those shrubs and they would bring a lot of their invasive species here and intentionally try to make grasslands out of these areas. They knew the species that they had from their home area, and a lot of these species they thought, "Hey, you know, let's try it out. Let's bring it over here and see if it works here," and so it became food for their animals. And so they changed plant communities from one type to another, and when that happens, we call that a type conversion. A lot of the grasses that you see here on the hills, that was -- that's probably there because of some form of disturbance, most likely a lot of it is from grazing and perhaps from some of the early ranchers intentionally trying to introduce these European grasses, because they know how they work, they know what they do. And that's why sometimes if you look, you'll see little pockets of coastal sage scrub on some of the really steep cliffs where the cows couldn't get to. But additionally, it may have something to do with fire as well and the increase of fire frequency when European settlers came here, just from human activity. So, we mentioned some things about the physical traits of the invader, too. A lot of these plants, they evolved in areas where there was agriculture. So like in the Mediterranean region, they had been doing agriculture there for over 1,000 years when they came over here, but when they first started doing agriculture here, they brought those species over, these species had evolved with agriculture, so they're used to high amounts of water, high nutrient levels, and they do well in disturbed areas. And when they came out here and carried out their agriculture, those species just took off and felt right at home. So a lot of them are very fast-growing. They germinate early, like the mustards that I was pointing out. Those come up right after the first rains, they form these blanketing effects, and there's only so much light, water and nutrients to go around, and so they crowd out and displace the native species. They reproduce very fast, generally. A lot of them are annual species, so they live for about a year, and they may have a very high dispersal ability. So they put out a whole lot of seeds, thousands and thousands of seeds, and a lot of them have evolved adaptations that allow them to bring, to disperse seeds far from the parent plant. So, they can spread very quickly. And we've seen a lot of that in California, this exponential growth of the range of these different invaders, like tecolote, for example. Back in the '80s, you know, no one was really thinking about this species, but now it's all over the place, in the same way [inaudible]. I think it was like a million acres in California in the '90s, and now it's at like seven or eight million acres. So they spread very rapidly. A lot of them have phenotypic plasticity. They can take a number of different morphologies and adapt to a number of different environments. So they're generalists, basically, and a lot of the invasive plant species can carry out what's called ecological facilitation. What this means is that they change the ecology of an area in some way to better suit themselves. So, a good example of this would probably be like eucalyptus trees that put out the allopathic effects. They drop chemicals that inhibit germination of native plants. And so it facilitates their existence. A couple of other ones, tamarisk in the desert; it grows along creeks, it can reduce water tables dramatically. And water is a really valuable resource in the desert, right? But it sucks up all that water and it just transpires it, and so native animals can't use those areas as water sources. And also it reduces the soil moisture habitat and so native plants that, in the desert, that really need that water don't have it. So, yeah, usually you see invaders at least starting out and heavily infesting disturbed areas. So, these would be areas, for example, grazing, that's one form of disturbance, that's probably why we see a lot of the invaders out here, maybe coupled with fire. With human settlement came an increase in fire frequency, and a lot of these plant communities have evolved with fire, but the rate at which fire happens is really important. And so human beings have increased that frequency to the point where -- and sometimes intentionally -- but to the point where the native communities don't have enough time to recover from the effects of fire. And you guys probably learned something about that when you looked at fire ecology. Like for example chaparral communities need, I think, an interval of about 15 to 25 years after a fire, after they've been burned down to the ground, to re-sprout or to germinate from seed, and to grow up, put out enough seeds so that, when the next fire comes through, they can do it all again. But some of these areas in the Santa Monica Mountains have burned 12 times in the last hundred years. So that's a fire once every, like, eight or nine years. So, what kind of community do you think is going to do better? The chaparral community that needs at least, you know, 20 years or so to recover, or these invasive grasses that put out thousands of seeds? A single plant can put out thousands of seeds every year. I mean, the grasses and the forbs. The Italian Thistle species, for example, they can put out -- a single plant in a season can put out I think like 20,000 or 30,000 seeds. Well, you can burn that area five -- like once every five years, probably, and those invaders are going to come right back. And so, sure enough, in these areas where we see high fire frequencies, we usually see tight convergence as well. So a change from chaparral, for example, to annual grasses. That kind of sums up what I wanted to talk about. Mainly when we see invaders, we usually see them in disturbed areas. It's something about the physical traits of the invader, the area it's invading and the fact that we have such high propagule pressure that we see invasive species where we see them. And like I said, this is probably the worst threat to our native -- remaining native populations and communities here in California. So make sure you clean your shoes before you leave, I guess. And that's all I have to say about that.