> During the first half of the twentieth century, Soviet citrologists grew (sub)tropical plants in temperatures as low as minus 30 degrees Celsius – outdoors, and without the use of glass or any fossil fuel-powered assistance.
> Imported citrus varieties only survived in a few isolated points along the Black Sea coast, which enjoyed a particularly favourable microclimate. To better prepare citrus fruits for cold, Soviet citrologists followed a method called “progressive cold-hardening”. It allowed them to create new varieties which were adapted to local ecological conditions, a cultivation strategy which had originally been developed for apricot trees and grapes.
> The method consists of planting a seed of a highly valued tree a bit further north of its original location, and then waiting for it to give seeds. Those seeds are then planted a bit further north, and with the process repeated further, slowly but steadily pushing the citrus variety towards less hospitable climates. Using this method, apricot trees from Rostov could eventually be grown in Mitchurinsk, 650 km further up north, where they developed apricot seeds that were adapted to the local climate. On the other hand, directly planting the seed of the Rostov apricot tree in Mitchurinsk proved unsuccessful.
Sure, this is genetic selection. But citrus fruits reproduce sexually, so this could be entirely genetic. I don’t think the epigenetic traits follow so obviously.
Why doesn’t this process lead to much faster natural spread of plant life into more northern climates? Isn’t the process of “planting” seeds a bit further away exactly how any seed-producing plant spreads? Or is it just that humans are able to accelerate the process?
I'd say being outcompeted by already thriving local flora. When "planting" they must have made sure that the conditions were optimal for survival (soil condition, no competing crops etc.).
I suspect one factor is the range of an orange seed is pretty small in the wild. Some rodent grabs the fallen fruit and moves it a few dozen meters away. They're probably planting tens of miles away.
It seems to me there is a step missing: plant seeds further north, some plants survive better than others even reproduce, take those survivors and repeat further north.
So not the fruit from all trees but from the ones that are better adapted. This could happen naturally but probably more slowly and also would naturally have to compete with local species.
Very much accelerating, for instance by geographical spread. Also a plant might have a hard time "getting started" in a certain place, and not always end up in optimal conditions. The Soviets put plants in arrangements not found in nature.
The one thing that I can think of is that the natural rate of seed spreading is slow, at least for citrus plants. (Plants like dandelion likely spread much more quickly)
Off topic: I love this site, but it kills me how they could delete half a dozen CSS rules and HTML elements and make it actually readable. I use the following CSS:
https://solar.lowtechmagazine.com/2020/04/fruit-trenches-cul...
The most relevant part of that article...
> “Progressive cold-hardening”
> Imported citrus varieties only survived in a few isolated points along the Black Sea coast, which enjoyed a particularly favourable microclimate. To better prepare citrus fruits for cold, Soviet citrologists followed a method called “progressive cold-hardening”. It allowed them to create new varieties which were adapted to local ecological conditions, a cultivation strategy which had originally been developed for apricot trees and grapes.
> The method consists of planting a seed of a highly valued tree a bit further north of its original location, and then waiting for it to give seeds. Those seeds are then planted a bit further north, and with the process repeated further, slowly but steadily pushing the citrus variety towards less hospitable climates. Using this method, apricot trees from Rostov could eventually be grown in Mitchurinsk, 650 km further up north, where they developed apricot seeds that were adapted to the local climate. On the other hand, directly planting the seed of the Rostov apricot tree in Mitchurinsk proved unsuccessful.