Knowing pioneer plants can help us understand how colonization of new land can occur.
These strong plant can colonize our properties in hopes of restoring disturbed soil to create green organic matter, to enrich the soil.
Furthermore, if we look at the earliest pioneer plants, probably they can mine for their own nutrients, be potassium, calcium or nitrogen.
Usually, colonization of newly land (rock, gravel or sand) depends in both type of soil, temperature and humidity. For example, a desert, a volcanic island, exausted soil, or highly disturbed soil.
In Iceland, we have often newly land when eruptions happen and cover large tracts with either ash deserts, or newly formed lava rocks. These can be large areas many kms wide.
I frequently see creeping thyme (thymus praecox) as one of the pioneer species of acidic soils. Especially when it is deposited gravel (for example volcanic pumice), and not even a lichen or moss has grown before there. Thus, I must assume that creeping thyme fixes nitrogen, otherwise it wouldn't be able to grow there!
When mosses grow, then blueberries, crowberries often grow. Highly acidic and poor soils. But I guess that the mosses and lichens have fixed the nitrogen for the berries. Still, they grow their roots between the moss and rock (there is actually no soil, only newly formed peat moss). I have also seen bluberries growing out of sole volcanic rock, so they might be also able to fix some degree of nitrogen.
In gravel plains I often see armeria maritima (thrift), large colonization by the n-fixer Nookta lupin (a perennial and very cold hardy, but agressive invasive), silene acaulis (widespread in new gravel and sand).
There is also a volcanic island created off the coast of Iceland in 1963. No human was ever allowed there, except scientists, to see how plants colonized the newly formed soil. The sucession was like this: sea rocket (a radish-like plant), orache (you probably know this one), sea sandwort (a succulent), oyster plant (borage family) and lyme grass (the orage and oyster are probably edible) appearing after 5 years, following this birds started to establish there (after 10 years) and the original plants grew more abundantly. The original plants probably could get their nitrogen from symbiotic fungi (because the soil was obviously without nitrogen), the potassium, calcium and phophorus were naturally occuring in the rock, and probably leached by rain or bacteria (and probably the plants needs were not that big).
30 years later, northern rock cress (Cardaminopsis petraea), sea campion (Silene uniflora) and thrift arrived in sandy plains (but probably already containing nutrients from the birds) and within the sites of bird colonies, many flowering species arrived there (and only there - therefore they need the nitrogen from the bird excrements!), this includes species like chamomiles, grasses, chickweeds and willows (seeds were probably there for a long time, but only grew when they had the necessary nitrogen).
Maybe this can give you an idea about how important it is for us, in Permaculture, to keep an idea about pioneer plants, the nutrient cycle, the importance of animals and ecological sucession and habitat placement.
in Portugal, sheltered terraces facing eastwards, high water table, uphill original forest of pines, oaks and chestnuts. 2000m2
in Iceland: converted flat lawn, compacted poor soil, cold, windy, humid climate, cold, short summer. 50m2
Don't forget about Cyanobacteria. Amazing things happen at the smallest of levels before plant species are able to thrive. It is interesting how it seems like they are pioneering the area into soil that is more amenable to the next generation of plant (animal) species to come, but often it just seems to be the opportunistic nature of life itself. Add water, nutrient (mineral), and sunlight and hey presto, the air born fungi and bacteria see dinner. Life truly is the dragon eating its own tail, with each plant (animal) devouring the one before till eventual balance seemingly takes hold, the point at which excess nutrient has been held in check by the organisms themselves in relation to the light and water that is available to keep it in motion.
In regards to the plant kingdom, I think we have a lot to do to change our perception about weeds and "excess" biological material in any of its forms. True wisdom is knowing how to manipulate the species around us in a way that encourages their (and our) ongoing existence. Diversity appears to be nature's end result as niches are created and filled. We must allow nature some breathing room in order to carry on with the process of evolution. When allowed to be, nature is the most bountiful of providers we have. It makes me sick when I hear farmers complaining about over-abundance of produce effecting their market price, and in the end allowing the fruit to rot on the tree because it is not worth picking. The same with kangaroos over-breeding and threatening the environment with their grazing. We must learn to be more amenable to organic systems and stop treating the earth like a spreadsheet. Monetary profit is a most dangerous ideology, as it brings value to scarcity.
We need to reduce our population, and only look at developing in the degraded places of the world that we have left as deserts in the wake of our "progress". Our biggest problem as a species is our tendency to the simplification of systems we create that encourage monopolization of economic, cultural, and biological processes. All this does is make the system of life itself more fragile. In the end it's not a question of how many people can the world support. It's about how many does our species truly need to survive, let alone "progress".
I do hope that one day we as a species will be able to value the diversity of our planet and of each other. It would be sad to think that in the days ahead we will be the sole-surviving species, a parasite with nothing left to feed on but each other.
I think our culture, the current dominant culture, is not humanity. Our cultural values are not the values of the entire human species, in my opinion. There is evidence of humans having other values and living in a way which fosters diversity.