The man closed the blinds. Then he opened the blinds. He closed and opened them again, with little effect: there was no longer that much light to keep out. For years he had shut the blinds on the front window every afternoon to intercept the path of the falling sun. But today it was unnecessary, because now there was a tree. There was a tree, though just this last Monday there was not a tree. In three days a tree had sprouted and grown tall enough to shade his window.

The man went outside to take another look at the tree. It was a normal enough tree, though the man had never before seen one of this particular species. It was just a tree, growing in the approximate middle of his front yard, with two distinguishing features: he had not planted it, and it had grown to be two stories tall in only a few days.

He wondered if he should do something about it. It wasn't causing any harm, and he had actually wanted a tree. There had been a tree in the yard once before, back when he was a child and the house had belonged to his parents. He used to like to climb it. But once the house became his own he didn't like raking up the leaves so he had cut it down, and though he had soon realized that this had been a mistake, he never got around to planting a new tree. Years had gone by with him missing the tree, and now he was so old that that was too late for him to plant a replacement that would reach appreciable height before he died. So this new instant tree was thus not unwelcome, and would have even made the man happy, except that there was something odd about the speed of its growth.

In other words though it was nice having a tree, he was suspicious. Nothing comes for free.

"I should probably call someone about this." He thought. But who could he call? The sheriff? The department of agriculture? Customs and immigration? The last would have been the most appropriate choice. Instead he phoned the sheriff.

"Well," said the sheriff after looking at the tree. "Can't say much about it. It's a tree and it's clearly on your property. That makes it your tree. If you don't like it cut it down."

"No. Guess I'll keep it."

"Don't know about eating the fruit though. Maybe you shouldn't."

Three large melon shaped objects were hanging in the higher branches.

"Right. I hadn't even noticed them until you mentioned them. "I wont eat any. But once they are ripe they might help me figure out what kind of tree it is."

The fruit ripened overnight. In the morning the man found only the shards of their peels on the ground.

"Who the hell ate my fruit," the old man said. Now that someone was stealing from the tree, the man was sure it was his.

.....

A figure crawled along the branch until it came to the trunk. There it met another figure huddled in a crook.

"Is it just us?"

"There is one more," the other said pointing. "He's still only halfway out."

"It looks like 02789."

"Probably." There was a small cracking sound, then a third figure fell through the canopy to the ground. The other two crawled down the trunk to meet it.

"That's it? Only us?"

"Until the next generation."

"Then we had better get busy. We should start looking at soils."

As the day broke, three sprouts walked, if such could be called their manner of locomotion, through the neighborhood.

"There are already many plants here," one said.

"I have heard the forests are even more crowded. But it shouldn't matter. Did you notice how much free carbon there is in the air?"

"Yes. But don't you think that is weird? There is more than enough for us to last 8 generations. Seems too good to be true."

"Yes, you may be right: our studies suggest that the parasites are treacherous here. Those parasites are presumably what is keeping the carbon levels high, but they are also the reason why it would be dangerous for us to stay for too many generations."

.....

The sheriff was back on the man's front porch. "Have you been seeing any of those unusual people around here?"

"What people?"

"Well, they're not quite people. They look like people, except they have a few more arms, and are covered with things that look like leaves."

"Sounds like trees."

"Yeah, but more shifty. A couple of them were hanging out at a construction site in town - standing around the porta-john. Then one of them was caught on camera stealing from the nursery."

"Which kind of nursery - baby or plant?"

"I'm not sure. Anyways, that was a couple days ago, and now there are a whole bunch of them all over the place. That's why I figured you would have seen some. That, plus they look like trees and you have this here invasive tree."

"I don't see the connection. This is a tree, rooted to the ground. You are talking about creatures, running around. How can a tree run around?"

"These ones have legs that they walk on - sort of look like roots, just not rooted. Whenever they stop they poke the tip of one of these legs into the dirt or a crack in the pavement. Looks like one of my kids dipping a toe into the wading pool."

"So is there something wrong with that? Are they causing trouble? When I showed you my tree you didn't think anything of it, why you so worried now?"

"They walk. They are trees. The combination seems suspicious."

"Is that such a bad trait to have in a tree? You can have shade wherever you want it at any time of day. And fruit delivered fresh by the source."

"Those things would be swell, but these trees don't follow directions from people. In fact they ignore us. I came on one of them in the middle of the street screwing around with a pothole and blocking traffic. I yelled at it to get out of the street but it wouldn't respond, so then I grabbed it to drag it. Have you ever tried to budge a tree? In the end it only moved after the sun was down. It just couldn't care less about the mess of traffic it caused. I tell you, these trees are lawless."

"What are you going to do about them?"

"Not sure yet. Think I will give it another day or two. Maybe by then they will have gone back to the forest."

.....

A tree walked over to the grove. "Now?"

"Yes. Did you locate suitable soil?"

"Yes. How many of us are there?"

"Roughly 100 at this point. Even factoring in parasites we should be above 100 trillion at generation 8."

The grove dispersed to plant.

.....

"Mom can we get a tree? Some of the kids at school got trees."

"Have. They have trees. And we have a tree."

"I mean one of the new ones. Like the one they had to cut down in the baseball field."

"Trees take a long time to grow. If we got a new tree you would be all grown up before it was."

.....

After the third generation, when there were thousands of new trees around town, the people called a meeting.

"They have to be cut down."

"They are just trees."

"At the rate we are multiplying, in a month there won't be an inch of bare ground left."

"The town needs more trees. And these don't require much watering."

"We don't need trees that walk around. That just goes against nature. The government should do something about it."

"The sheriff already talked to the feds. They told him all the agents in the region were busy keeping people from coming over the border from Mexico."

"I say we just cut them down."

"Not if they aren't on your own property. You can't go cutting down other people's trees."

.....

"Excuse me, mister trees? Do you want to come live in our yard? It's a big yard and the front faucet leaks into the lawn." The little girl said.

Two trees had been standing behind a car, hiding from a group of men with axes.

"Do you think it's a trap one tree said to the other." When the girl had spoke.

"Maybe. You can't trust these parasites. I have heard they have been using bags of fertilizer to lure our kind into the lumberyard."

"Please?" The girl said to the trees. "I want a tree swing. And a treehouse."

"Oh that sounds fun. I have never been on a swing before." One of the trees said.

"Don't let her fool you. A tree house? Do you know what they make their houses out of around here?"

.....

After the fifth generation the trees held a meeting.

"So far we have lost about 10 percent of our number to the parasites, but this was primarily due to individual outbreaks. Overall we are faring better than expected. Environmental resource availability is also still high. But now that our territorial spread is growing more concerted, well, it is a well know ecological principal that population growth carries an increase risk of parasites."

"This particular parasite does not seem like it could ever pose much of a threat to us. It's aggressive nature is tempered by a lack of organization. I don't think there is a risk of us not making it to generation 8.

"Has anyone ascertained why they are so aggressive towards us? Is wood that valuable here?"

"They apparently have a strategy of using atmospheric carbon to keep the planet warm. A significant proportion of their industry is involved with the processes of disinterring the remains of ancient flora and combusting these remains to transfer the carbon to their atmosphere. This puts our program in direct opposition to theirs."

"How strange. Should we not be afraid of an organism so strongly motivated by such an irrational purpose?"

I agree they are irrational. But that also contributes to their disorganized nature making them less of a threat."

.....

By around this time, several government bodies had almost come a consensus in agreeing that the trees should be cut down and burned. But there was still substantial public dissent, for example from corporations that felt the country should not fear that which we do not yet know how to make a profit from, and from a few liberal scientists who claimed that if the invasion continued global warming would be halted.

The eradication of the trees was therefor delayed while politicians, corporations, and environmentalists argued. Meanwhile, individuals with chainsaws continued their efforts, and firewood companies, fueled by patriotic advertising campaigns, saw their profits surge.

By generation seven, the impact of the trees on the landscape was global and not entirely unesthetic, and atmospheric carbon levels were lower than they had been for decades. But there was also the unavoidable fact that virtually every house on the planet now harbored at least one unregistered alien on its property. So it was finally decided that the trees must go.

On the eve of the assault, as military units across the globe were preparing for multilateral action, something changed: the trees all simultaneously bloomed. Each tree was suddenly covered in massive blossoms. This was particularly unexpected for while the trees had previously produced several crops of their strange fruit, this had always occurred without flowering.

The surprise and beauty of the blooms caused a last minute delay in the assault. Troops were mobilized, but told to hold their ground and wait for the signal to attack. So it was that the members of the soldier class of the planet, all gazing at the beautiful blooms, witnessed with awe as the flowers began to rotate slowly on their stems, until they all pointed up to the sky - not unlike radar dishes. The flowers stayed like this for several minutes - the soldiers oblivious to the microscopic pollen being broadcast out into the universe - and then the flowers all wilted and fell to the ground.

With the flowers gone, the worldwide attack was launched at dawn (well, at least it was dawn in some places) and within days the vast majority of the trees had been cut down. In the years that followed, through the use of various methods, most of the carbon from the tree invaders was returned to the atmosphere. Which was too bad, because the few trees that were spared - including at least a couple with tree swings - lived on for many decades as ordinary trees.