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Comment by blablabla123 | Hacker News Reader

Most trees growing in Germany grow very fast. In areas with rainforests trees are much older and the ground on which they grow is very different from the ground in german forests. Once deforested it takes decades to just recover the ground, not to speak of the trees.

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Our trees in Europe can be very old if we let them, but the ground is different because it is young. The glaciers of the ice ages have given us great soil which still contains a lot of nutrients (and which is also still replenished from degrading minerals), while the big tropical forests are mainly located on depleted soil, so the nutrients are in the plant matter and easily lost if you remove it.

https://en.wikipedia.org/wiki/Loess

(On that topic, this is also interesting:

https://en.wikipedia.org/wiki/Terra_preta)

Trees grow fast in the rain forest too, and in rain forests and germany alike, it takes a long time to become an old growth forest, which stores a lot of carbon in the soil and organic layers.

I heard that rainforest soil is actually pretty poor, which to me sounds weird given how much grows (and dies / falls / decomposes) there.

Your comment intrigued me, so I looked it up--I found it pretty interesting, so thanks for the inspiration.

Looks like one of the main factors is due to the soil acidity being similar to the pH of the plant roots. Also, while there is a ton of dead organic material in the soil, the high temperatures and precipitation causes it to decompose so rapidly that most of the nutrients are lost.

Finally, the clay particles in the soil are poor for trapping the minimal nutrients remaining from the decomposing material, and what is trapped is frequently washed away from the precipitation.

Which is why you have a bootstrapping problem bringing back the forest. The soil is only poor because there is such a vibrant ecosystem that nutrients are constantly getting absorbed into living material as fast as they can be retrieved from dead material. The vibrancy consumes everything rapidly. But if you destroy the forest, you destroy the stored nutrients.

But as to raw material, surprisingly little of the physical bulk of trees actually comes from soil. It comes from the air! This is where the Carbon in the CO2 -> O2 process comes into play.

I think you are talking about the acidification of soil caused by pine trees. I've heard the same thing but a quick search suggests that this might be mostly rumour.

Certainly large mono-cultures of conifers are bad for numerous other reasons.

It's no rumor. Pine trees do acidify the soil, but a pH of 5 (which is typical) is not a problem as there are many other plants that are happy to thrive (and even require) a more acid soil. Blueberries are one such example.

I didn't commission a study or anything but the first page of results on Google suggested that pine needles are acidic because they prefer to grow in acidic soils but they have no method of acidifying the soil by themselves. Also pine needles can form a dense mat which tends to exclude other species.

Germany obviously old trees until they remove 80% of them...

If you look at a satellite image, you quickly see that there just isn't that much space left to nature. That is true for most of central Europe. Doesn't mean it isn't green, but pristine forests don't exist anymore. There are some spaces left to itself now, but they were still touched by human cultivation.

Pristine is a very high bar. There is archaeological evidence of semi-settled early agrarian existence where they would slash and burn an area to farm it and then once the soil depleted move on to a new segment of the surrounding forest and abandon their old settlement to be overgrown and renewed. Wasteful but the cycle was fully sustainable.

Even without human involvement we would see some "normal curves" to tree diameters via attrition of the oldest for varied reasons - but their ring count would be higher.

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