I'm trying to find a book I read when I was young, roughly 25 years ago. I read it in German, which might complicate things, since sadly I don't know whether German was its original language or whether it was new when I read it.
The book contained multiple stories. The main story featured moles that had to go on a journey; at one point they built a raft to travel on a river.
Another story featured a tree (a weeping willow) and its friends. In a period of drought, the willow dug deeper than its friends and found a reservoir of water, but none of its friends believed it; in fact, they bullied it until they died of the drought. Later, new seeds appear and the new trees actually believe the willow.