The development which culminated in the great west Norwegian clustered communities in the 18th and 19th centuries, such as we see at Havrå on Osterøy Island, actually first came into being in Viking times, with an incipient division of the farms into smaller units.
"Humus" is a word with great meaning. It is the soil we live from, in addition to the resources we get from the ocean. This layer of earth - sometimes appearing as loose fertile organic matter; other places as scanty and acidic soil - is found in varying thicknesses over the bedrock. It is the result of 10,000 years of breakdown and erosion following the last ice age, and then several thousand years of cultivation in more recent times. The soil we can buy at the garden centre is a different product than the "natural" humus layer, formed of processes occurring far under the earth's surface. If you dig your spade into the soil where it has not been ploughed before, you will see that there is a big difference in colour, soil structure, moisture and stone content. We might say that the soil is fertile and easily worked some places, whereas other places folk might have given up trying to grow anything on their small patches of land, which then become overgrown with birch and thicket. Modern agriculture does not have room for small stumps between the piles of stone. Nowadays, machines do the job, and they require a lot of space and flat ground.