ARIA:
We told you about the island simulation, right? Footprint Island. I was wondering what advice you have for us? In particular, I'm just thinking about the introduction of animals, you know, farm animals to this environment.

CLAYTON:
A couple of things to keep in mind. An excellent, excellent point. A fellow working years ago at the University of Washington wrote a good description of what a lot of us sense but never really think about - and that is, that there's this constant war between plants and animals.

The plant develops an adaptation so it isn't eaten, or its seeds aren't eaten, okay? But what does the animal do? The animal then adapts some ability to overcome the plant's adaptation. So you can think of it as this war going on.

Well, the plant communities on your island - your forests, your grasslands, and so on - if they have not evolved with certain types of animals, they are not going to have defenses against them. It's like what we've been talking about here, with your compromised immune system against viruses. Its ability to deal with animal impact is going to be compromised.

So, if your island has never had large grazing animals - like elk, bison, elephants - you should probably not put sheep and cattle on there, because the plant community can't deal with them.

CHRISSY: So what's a horse...?

CLAYTON: Somebody's got a horse?

[Everyone laughing.]

MERIAH: We have a horse.

CHRISSY: Chrystal.

CLAYTON:
What you're going to have to do is, when you bring Chrystal onto the island, is to manage where your horse eats, and how long it eats very, very closely.

CHRISSY: That was my plan…

CLAYTON:
If you do that, then no problem. But you'll also have to understand how that plant community responds to the loss of material.

For example, in the Hawaiian Islands, heavy grazing was carried out by birds. Birds do a lot of heavy grazing on the plants. If the Hawaiians had brought birds over, it would have been okay. But when they brought sheep and cattle, sheep and cattle eat things differently than birds do, and the plant community fell apart.

The other thing you have to keep in mind is, keep a good stand of vegetation on your soils… By "good" I mean both the density of plants and the amount of plant cover over ground. Which means, the cleaner your water will be, and the more even your water flow in your streams will be. When you or your animals denude the landscape, and open it up too much, then you have more sediment in your water, and your river flows become more erratic. You get tremendous volumes coming down your rivers that are very destructive, and then they go dry until the next rain event.

Vegetation protects the soil from immediate raindrop impact, plus then it shades the soil, so sunshine doesn't evaporate the water out. And thirdly, it slows the flow of water down across the surface, so it isn't as erosive, and the water has time to soak into the soil. Water that soaks into the soil enters the geology and comes out into the river, four or five days or months later. So you get this very continuous river flow. If you lose vegetation, then the water impacts the surface, it's running fast, it erodes things, adding more sediment, and it all comes out immediately, and nothing gets into the soil.

MERIAH:
We haven't cut down very many trees. So far.

CLAYTON:
So now, if you guys want to have it real easy, your island has been grazed by large herbivores now for a million years, like the East African plains. And all the plant communities are extremely grazing tolerant, and, in fact, actually need heavy grazing to be healthy.

ZEUS: It's not that way.

[Everyone laughs.]

CLAYTON:
If it's like British Columbia, you have very few, if any, large herbivores, so you have a very fragile ecosystem there.

CHRISSY: We have deer.

CLAYTON:
Yeah, but you see, deer are opportunistic. The way deer feed is they only want to take a little bit off the plant, so that the plant isn't triggered into making an adaptation to stop grazing. So they take a little bit here, and they go and take a little bit there. So, you'd have to either domesticate the deer, live off deer as hunters, or introduce a form of domestic livestock that eats the same way.

JEFF:
Such as?

CLAYTON:
Probably domestic sheep come the closest to doing that. Horses, on the other hand… Horses and bison, they deal with plant adaptations by overpowering them. They just say, "Hey, I'm big, I'm tough. I'll eat it all," and they'll eliminate the adaptation of the plant. Cattle are much like that, too. Water buffalo, cape buffalo. Certainly elephants.

MERIAH:
What about free-range chickens? What effect would they have?

CLAYTON:
Okay, now, chickens may have little impact on the plant itself, but they may have a lot of impact on regeneration of the plant community. Why?

IVY:
They love those little sprouts.

CLAYTON:
They love little sprouts, and they love seeds.

So you'd have to know how many little sprouts have to survive to replace the big plants that die, and how many seeds have to survive to make enough little sprouts. And then anything in excess of that, you can let your chickens have.

JEFF:
Now how do we keep our cattle away from the water source without fences, so their fecal material doesn't get into it?

CLAYTON:
Again the easiest way is to have cattle that have evolved over time to that system. The reason cattle are so hard on water systems in the western United States, is that the cattle we run here evolved in a very humid environment. To survive in their original environment, they had to stay in one area and heavily graze on it so it doesn't grow up taller than them and become unusable. But the western United States is very arid. Bison, who evolved here, move all the time. So what ranchers here have to do is make their cattle act like bison, and keep them moving all the time. And that's what you'll have to do - keep your cattle moving all the time. That will minimize their impact on both the plant community and your water supply.