In Brazil, many ancient forests are very well preserves.

从语法上看应该是名词吧或者形容词。（做表语）
柯林斯字典里面有preserves的名词解释：
Preserves are foods such as jam and marmalade that are made by cooking fruit with a large amount of sugar and that can be stored for a long time .

不过仍然很费解阿。竟然是一种吃的。同时也没有，形容词的解释。

剑桥上面的说法，

preserve (KEEP)
verb [T]
1 to keep something as it is, especially in order to prevent it from decaying or being damaged or destroyed; to conserve:
to preserve the environment
We want to preserve the character of the town while improving the facilities.
The agreement preserved our right to limit trade in endangered species.
Putting varnish on wood is a way of preserving it.
I need to get out of the house from time to time just to preserve (= prevent me from losing) my sanity.
See also well-preserved.

上面提到了专有well-preserved这个词组我们也看看这个词组哈，

well-preserved
adjective
1 (especially of something old) kept in good condition:
It was a pret