There's no mention of diversity of tree species, or efforts to match species with local conditions.
Mass tree planting efforts can be relatively unsuccessful, see China's Great Green Wall Project [1] which has resulted in large monocultures where nothing else can grow and greatly lowered groundwater levels.
Also the history of the equivalent in Africa, which this planting is a part of [2].
It still seems like a net positive. Environments change an order of magnitude more quickly than ecosystems, and many orders of magnitude more quickly than evolution. But if you build it they will eventually come. Life abhors a vacuum...
Forestry is hard. If you plant the wrong species, in the wrong soil, with the wrong fertilizer or in the wrong climate, you are likely to completely fail. Early attempts at forestry often ended up with every single one of the planted trees dying.
Luckily forestry is a pretty seasoned science by now and people mostly know what they are doing. I trust that the Ethiopian forestry scientists did their job though before this and they end up far more successful then these early attempts, before the science was known.
I've noticed this as well in the redwoods in northern California. Some groves are completely silent. I'm not sure why that is. These are natural forests, so I'm puzzled as to why there aren't many birds.
I live in a redwood forest and it is noticeably quieter of insect and bird sounds compared to nearby down out of the forest a bit, but not as silent as in an old growth grove.
The redwood canopy blocks out a lot of light, the thicker it is, the harder for any plants to grow down below. The redwood leaves acidify the soil over time as they fall, there is a limited range of plants that can handle it. And then the trees themselves are highly insect resistant, there are no insects living in bark for example.
So basically: bottom of the food chain for birds isn't there, especially not down on the floor in old growth with so much light blocked out.
Birds still need a sure and high area to nest so can easily move some Km to feed and return to the forest later. Some birds stop singing after nesting.
I don't think it's accurate to say it wasn't successful for China. It has reduced ground water, yes, but that doesn't seem to have been a major issue. Nor was a desire for biodiversity. Instead their goal was providing timber and slowing the growth of the Gobi Desert, both of which seem to have had at least modest levels of success. So it might not have accomplished what other people would want, but it does seem to have met China's goals.
Mass tree planting efforts can be relatively unsuccessful, see China's Great Green Wall Project [1] which has resulted in large monocultures where nothing else can grow and greatly lowered groundwater levels.
Also the history of the equivalent in Africa, which this planting is a part of [2].
[1] https://en.m.wikipedia.org/wiki/Three-North_Shelter_Forest_P...
[2] https://www.smithsonianmag.com/science-nature/great-green-wa...