Anne frequently refers to how much she appreciates and enjoys nature. Why is nature so important to Anne? What does nature represent that she so desires? How do Anne’s passages on nature in the diary affect her mood and affect the mood of the diary?

Although forced to hide out in an attic annex for years on end, Anne still derives great solace from the little bit of nature she is able to experience. For example, she writes the following on February 23, 1944, after she and Peter are able to gaze out a window over Amsterdam and see the sunny sky:

"As long as this exists," I thought, "this sunshine and this cloudless sky, and as long as I can enjoy it, how can I be sad?"
The best remedy for those who are frightened, lonely or unhappy is to go outside, somewhere they can be alone, alone with the sky, nature and God. For then and only then can you feel that everything is as it should be and that God wants people to be happy amid nature's beauty and simplicity.
As long as this exists, and that should be forever, I know that there will be solace for every sorrow, whatever the circumstances. I firmly believe that nature can bring comfort to all who suffer.

As this passage conveys, nature is important to Anne because it represents her conviction that God wants people to be happy. This passage shows Anne's longing to be out in nature because nature is beautiful and simple. It provides a stark contrast to the stark terror of being a Jew hoping to stay alive in a Nazi-occupied country.
We can also see that because Anne is suffering—from fear, from boredom, from hunger, and from the general knowledge that world seems to be filled with evil, which she fights against every day—she longs all the more for an alternative world of peace, which she identifies with nature, God's creation. She will take what little bits of that world she can get and make the most of them. She has so little to cling to that even a strip of blue sky matters to her.