Not really. Trees plant themselves. If it’s not being actively used for something/mowed it’ll turn back into forest.
This isn't really true. Growing a forest is way more complicated than you might think - they don't just sprout spontaneously, as trees take a long time to grow and are easily kept down by fauna, landscape, nutrient levels, erosion, and many other factors.
I don't remember the details, but I believe it goes something like farm -> heath -> shrubland -> young forest -> mature forest, where each phase has a unique ecosystem of both plant species and animal life.
In an extremely heavily cultivated landscape like Denmark (seriously, look at a satellite photo), converting farmland back into forest is a multi-decade project requiring constant maintenance. Converting farmland into marshland (which is the "original" stone-age landscape in many areas) is a multi-century project.
Just like it was a multi-century project to convert it into farmland, by the way. Europe has been cultivated for millennia.
Exactly. It only takes a couple of decades for nature to reforest, which is an eyeblink, actually. And only a couple more decades to return to mature forest. No humans or projects needed. There is a lot more forest in New England (USA) now, than a century ago.
Tree planting in eroded/damaged ecosystems requires a helping hand - everything from site prep, germination, watering, etc.
Source: I’ve planted thousands of trees.
In the US that would be a bunch of only invasive species for a long time.
Eventually it returns to forest within a lifetime. In certain parts of the midwest you see fields of farmland and occasionally squares of trees in them. Chances are in the early 19th century all of what you saw was farmland and at one point not as much was actively farmed and certain fields no longer plowed. All the trees you find in that plot of what looks like the holdover of some carved up midwestern forest are actually all less than 100 years old and relatively recent growth.