This is The Family Tree by Sheri S Tepper (1998).
Police officer Dora Henry is investigating the bizarre murders of three geneticists. Meanwhile, strange things are happening everywhere she turns. Weeds are becoming trees; trees are becoming forests. Overnight, a city is being transformed into a wild and verdant place.
And, strangest of all, Dora can somehow communicate with the rampaging flora.
A potential civilization-ending catastrophe is in the making. The nearer Dora gets to a murderer--and to the truth--the more seemingly disparate events begin to entwine. And the answers she seeks today to the salvation of humankind may lie in afar distant future. . .one which is suddenly much closer than anyone imagines.
Book interleaves chapters set in Dora's time and the far future. Dora eventually is taken to the future, where we find the characters are talking animals and the beasts of burden are humans who chose that role to atone for what humans had done. The humans are waiting for fulfilment of a prophecy that would end their servitude. Enter Dora...