[biellls]

Monocultures of any kind are always fragile, you need diversity to have a resilient ecosystem. These projects should benefit from an understanding of permaculture, which is a discipline that aims to create the right conditions for healthy systems. Everything from succession (pioneer leguminous species that can fix nitrogen and improve soil, slowly replaced by other species), trying to slow down and catch water where it falls to prevent soil erosion and runoff and much more. I've heard (unsubstantiated) claims that initiatives in China have already started to take these into account and have succeeded where other monoculture forests failed.

A side effect is that you can end up with productive species. Imagine forests where many trees bear fruits, others have acorns that pigs can feed on, fruit vines and understory herbs that animals can graze on, large lakes with edible fish. This is the future I'd be excited for and it's all currently possible with the right policies.

[Retric]

Monoculture of very fast growing trees let’s them maximize the value per acre when sold as carbon indulgences. Actual impact is much lower, but by then they have moved to the next project.

That said, in areas that got deforested having any tree cover can make the area much more habitable for other trees. Thus single digit survival rates can still result in new forest over a few decades.

[tomrod]

The economic topic you're hinting at is externality. There is also the notion of Goodhart's Law, where any (single dimensional) measure gets gamed.

[jandrese]

Would it really be so hard to plant a mix of seeds? I can see a monoculture if the intention is to harvest the wood or fruit later, but if you're only planting to capture carbon or restore a forest then a mix of trees seems like a healthier option and shouldn't be any more effort. You don't need to be precise with the mix either, a just random chance should be fine.