I also loved The Overstory, and have The Hidden Life of Trees by Peter Wohlleben on my shelf to read. It’s non-fiction so may not exactly scratch the same itch, but the premise looks great.
It looks at the forest as a “social network” and how trees behave like families, how they communicate and look after their sick.
Sorry that’s not an official recommendation, as I haven’t read it yet, but I hope it’s not too useless!