Unfortunately, we're in 2019, and it's already happened. You're stuck with homogenous forests.
It's very, very simple: stop doing that.
No, we can't easily get back the old-growth forests in the US, as that ship has sailed, but there's more to the planet than the US, and we can stop causing even more damage. But we don't want to.
The environments that we assumed to be in place when we look back and describe these 'ancestral' states are rapidly changing. The timing and duration of rain events, winter snow levels (elevation, depth, duration), high heat events, Santa Ana winds; all of these things are quite rapidly changing their patterns of predictability.
Forests are dynamical systems with non-linearity in many of the ways they interact with and respond to the environment. How forests have responded to climate change, to anthropogenic interactions, hunting and extinction of large herbivores (and predators), create feedbacks that further impact how forests (or really, vegetation at large), respond to the environment.
I think my point here is that there is questionable utility in trying to run the clock in reverse. Its more important to understand where we're at and how things respond now than it is to contrast them with some ancestral state that is impossible to return to.
There's no un-baking the cake. The 'climate' (read: entire earth biosphere), has changed/ is changing.
The 'climate', and the species that can live in it, also change and continue to change- the wooly mammoth couldn't survive many places right now, to be honest.
I feel like a lot of people miss the idea that the planet itself shifts over time- Hawaii hasn't been there forever, and most of the land on the earth has shifted a lot from where it first was in Pangaea.
Humans stopping climate change feels a lot like getting in front of a moving train- it is absolutely futile- it also makes sense to try to shift the rails themselves around, but I don't even know how feasible that is, either.
But in situations with complex dynamics of nature, such as the one in the comment you replied to, there are often unforeseen laws of nature or physics or government that make things more complicated, that only the experts really know about, so that our solutions often aren't grounded in the facts that would make them very useful or practical.
Of course, as usual with stupid humans, when there's a very simple solution to a problem, they absolutely refuse to do it, usually because some selfish person is benefiting from the action that's causing the problem, and countless other people are perfectly happy to enable that person.