Not many years ago，some farmers were worried because hawks were taking many of their chickens．The farmers didn’t know what to do．Finally they went to the country officials and asked for help．

“Kill the hawks，”the officials said．“We will even pay for them．”So the farmers began to think of ways to kill the hawks．

The farmers killed many hawks．They no longer had to worry about their chickens．But they now had a new worry．Field mice were eating up a lot of the farmers’grain．

How did this happen？

Hawks eat not only chickens but also field mice．They eat more field mice than chickens．But the farmers didn’t know this．When they killed a lot of hawks，they changed the balance．

When people move into a new place，they often destroy many wild plants．Often these plants are food for the animals．If the animals can’t find enough plants to eat，they will starve or have to leave the place．

In one part of the USA，for example，the deer there like to eat a certain kind of wild roses．The mountain lions there eat the deer．The number of deer，mountain lions and wild roses doesn’t change much if people leave things as they are．

But people killed many mountain lions in order to protect the deer．Soon there were so many deer that they ate up all the wild roses．Then the deer began to eat the green leaves of young trees．These trees were important to the farmers．So the farmers thought of ways to protect their trees．Now the deer had nothing to eat，and many of them died．This was another lesson from nature．

To keep the balance of nature is important for us to rememher．

Holly had another bad night. The owl didn’t come back, but there was an army of ants that decided to march all over her body. Eco got very excited and tried to eat them.

The next day, after breakfast, Holly waited for everyone to leave the house. Then she let down the rope ladder and took Eco for a walk. Eco loved it—he was happy to be on the ground again—and he ran and jumped and ran after other dogs.

Holly wanted to see her friends, but she couldn’t stay away from the oak tee for very long. She had to be there in case her father tried to cut it down.

Holly’s father tried to get her down from the tree again after work. This time he was ready for action! He walked up to the tree carrying a ladder. He leaned it against a branch.

“Right,” he said. “You’re going to come down from that tree right now.” “No way,” said Holly.

“OK, if that’s the way you want it, I’m going to come up and get you.”

But before her father could step on the ladder. Holly climbed onto the branch, and pushed it away. The ladder fell with a crash.

Then Holly saw her mother coming from the kitchen. She was carrying a tray with a bottle of fizzy water and a large mushroom pizza—Holly’s favourite. But Holly didn’t eat the pizza.

Her father took the tray and said, “Don’t think you’re going to get any more food from us while you’re up in that tree!”

And with that, he walked quickly back to the house and threw the pizza into the waste bin. Holly’s mother said sadly, “Oh, Holly, don’t be silly. Come down and have a nice dinner with us.” Holly didn’t answer.