Places that used to be forested and are not productive farmland. There’s lots of places like this, just maybe not in Denmark.
Quick history lesson: After the war, with Prussia in 1864, Denmark lost about 33% of it's area. That part was some of the most suited to agriculture. To compensate for those loses Denmark started a process of turning previously unusable land in to farmland. So lakes where drained, the the moors were drained, areas with sandy soil, good for nothing but growing common heather, was heavily fertilised and forests where cut down. There where even suggestion to drain parts of the sea between Denmark and Sweden.
In some sense it was good, and basically help shape modern Denmark, but it's just not needed anymore, and has come at the cost of wildlife, native plants and sea creatures. It didn't start out like that, but when you add modern intensive farming on top of killing of most of your nature areas, then things starts to go very wrong. Denmark has almost nothing of it's original nature left.
> just maybe not in Denmark
exactly, and we're talking about Denmark, after all
That last bit is correct, there aren’t many places like that in Denmark. So the original question remains, where would be a better place for them specifically to plant these trees?
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.