The English word "nature" means something like: the natural world, the natural environment, the force of nature. Here are some definitions of the word "nature" which I have taken from Kenkyusha's Luminous English-Japanese dictionary:
Here are some natural English sentences using the word "nature":
1) We can see the beauty of nature in a single grain of sand.
2) We do not understand all the the laws of nature.
3) Some people believe in God, and some people believe in Nature.
4) There are many lessons we can learn from nature.
5) We should spend more money on nature conservation.
Therefore many Japanese sentences using the word "自然" often do not sound very natural when translated into English using the word "nature" (like "There is a lot of nature in Nagano.").
There are a variety of expressions which can be used to translate "自然". Here are some examples:
5) In some parts of Tokyo the natural environment remains.
6) Although this is a large city, much of the wildlife remains [many of the wild animals and the original plants remain].
7) This park is full of greenery.
8) This zoo is returning many animals to the wild.
9) The hotel is located in a natural setting.
10) Much of the natural landscape of Nagano remains.
11) There are many parts of Nagano which retain their natural beauty.
12) The countryside in Nagano is unspoilt.
So, as a general rule, if you want to talk about trees, and animals, and the beautiful countryside, try to avoid the word "nature"; and instead try to use some of the suggestions above.
a grain of sand：1粒の塩
believe in ～：～の存在を信じる
spend money on ～：～にお金を使う
a variety of ～：さまざまな
a natural setting：自然な環境