Climate shift means that none of the old records make any sense anymore and attempts at replication have ended in failure. Everyone assumes that either the ancients were talking out their asses, were straight up mistaken, or something funky is going on. Most of the best scholars assume the first two and thus don't make serious attempts to replicate it, since obviously the mistakes of the past are not worth replicating when you have the tools of an enlightened society to show you the way.
Like, part of the issue is that there was a lot of stuff that never got written down because why would you be specific, everyone knows what you are talking about. So there were old records and recommendation for action by later generations, but they assumed that there was active management the whole time and that the references being made would be understood because the reader was part of the same sacred forest temple maintenance tradition. Like, the best way to understand the records is to understand them as being written in LOLcat speech: if you don't understand the in-jokes and references it makes no bloody sense. Same with those ancient records, they have all of these internal references that a combination of loss of living tradition and linguistic shift makes even methodological recovery essentially impossible with your current toolset. Independent redevelopment will take considerable other efforts.
The People do still care a lot about forestry, just not as much as they once did.