In my region one of the most beneficial plants for our soil is a weed with roots that can go as deep as 30 feet into dry hard subsoil and bring nutrients up to the surface that other plants cannot reach. The plant then dies back in winter and forms a layer of organic material and this process repeats.
Over time barren soils are broken up into more friable material, enriched and they start to support grasses, which give way to shrubs and small trees, which are then able to survive and thrive on the plot of land, that has been worked and enriched by the plants over time.
The plant I am thinking of does poorly in fertile acidic soils, but does well in dry alkaline soils, so as it alters an environment over time and enriches it, this action of enrichment then causes the land to favor other plants and the original species dies off.
The plant is Convolvulus arvensis and I have watched it colonize barren soils and turn them into tree filled groves in less than a decade. It has amazing abilities to help soil though animals like cattle or sheep prevent the effects of enrichment and this type of effect is not observed on grazed lands, which decrease in fertility over time.
