I used to work in a native plant program, where we’d replant denuded and eroded areas with seedlings and cuttings. With the seeds, they always warned us we had to be careful about noting where exactly we got them from, because if we planted something that came from a plant just a few hundred yards away we’d be “contaminating the gene pool”. I never understood why this was important unless a specific population had some very distinct traits that set it apart from other members. The claimw as that the pollen would contaminate the local stock (even though animals like bees and other insects probably carry the pollen just as far). I also came across this quote from a webpage on the subject:
I personally don’t see how adding in a new influx of genes from the same species is harmful, if the plants aren’t very distinct. Like I said, I can kind of see why with sub-species that are distinct (like the Poppy example given above), but for populations that grow very close in proximity, I don’t see what the big deal is.
It really shouldn’t be a big deal at all, if as you say in your first paragraph the plants are from only a few hundred yards away. That’s within the normal range of pollen and seed dispersal, so it shouldn’t cause any genetic problems. Perhaps whoever was in charge of the problem was being excessively careful.
In certain circumstances it *might * be possible for certain plants to develop some very localized populations adapted to very specialized habitats over a short scale, but this isn’t the typical case.
I would note, however, that plants can be genetically rather different even if they look the same, so you can’t necessarily go by appearance alone.
In the National Park I used to work in, the rules were that restoration programs had to use seeds from within the same watershed. I’m not certain if the rules were relaxed for air-dispersed seeds or not.
I got the impression that the fear was destruction of part of the genetic diversity of the population.
For example, if you want to replant Valleys A, B, C with California Poppies, but you get all your source seeds from Valley D, you might wipe out genetic diversity in the A, B, and C subpopulations with the introduced Poppies. Then later on, what if a virus comes along to infect the Poppies and Valley D variant Poppies are especially susceptible? You’ve just wasted a lot of work, especially if the valley B variant happened to have unusual immunity.
The basic principle is that genetic diversity within a population is healthy. The specific rules for maintaining genetic diversity may need to be a little arbitrary since it would be more trouble to measure the genetic diversity than it is to follow rather arbitrary rules.