The human relationship to food has gone through two major stages. The first was Hunting and Gathering in which we extracted food from the wilderness while leaving the wilderness intact. This strategy involved keeping our population density below carrying capacity. This strategy could only support relatively low population densities except in exceptional bioregions. Even then, the populations had to remain semi-nomadic in order to avoid over utilizing areas in most environments.
However, in some bioregions, humans were able to settle and build villages while hunting and gathering because the food sources were so rich. The Tigris, the Euphrates, the Nile, the Yangtze, the west coast of British Columbia. In these areas, fishing provided highly concentrated food sources and allowed settlement without farming. We still use hunting and gathering today to collect fish directly from the wild. However, eventually the settled populations outgrew there food sources (exceeded the carrying capacity of the wilderness). In the past, hunters and gatherers just moved on when that happened but, in these cases, they had already build large structures and created significant masses of material belongings. Instead of moving, and abandoning the structures and belongings, they began to cultivate the land and a second relationship to food was born; agriculture.
Agriculture involved the replacement of wilderness with farms. Farms are large areas of land where all species are excluded except those that serve human purposes. Industrial agriculture takes this to extremes, poisoning the land to kill off all but the plants and animals that serve as food for humans. Agriculture has led to a massive drop in the diversity of life on Earth and, at the same time, a massive increase in the population of humans. If this trend continues, eventually, only species that serve humanity will exist. Industrial agriculture has also led to reduced diversity of even these species so that the numbers of crop species and the numbers of varieties of each crop species have both dropped in recent decades.
Diversity of Earthlife can only be increased slowly, either by evolution over periods of time greater than the lifespans of civilizations, or through genetic engineering with great effort and uncertain results. Diversity can be decreased quickly as we have seen. Therefore, the continued decrease in diversity is likely to lead to a situation where, instead of millions of species at each trophic level, there will be just a handful and then, eventually, just one species at one of trophic levels. At that point, especially if the critical trophic level of plants or detritovors is the level with just one species, the continued existence of Earthlife will be unlikely. A single catastrophic event or disease, will then cause the total collapse of the ecosystem and we will lose 600 million years of complexity and be returned to a planet occupied only by bacteria and protists.
However, we cannot return to hunting and gathering. Human populations are too high and a return to hunting and gathering would cause both an even more rapid loss of biodiversity and a rapid die off of humanity. So we need to find a new relationship to food. A candidate is unfarming.
In Unfarming, the wilderness is left intact but careful extraction is used to gather its productivity from existing species intensely. The key enabler of unfarming will be the use of food which is inedible to humans without processing. The key food will be wood. Wood is produced in very large quantities by forests which are the natural climax ecosystems over much of Earth's surface. Wood is made largely of cellulose which is a polymer of sugar. So it is possible to convert wood into sugar industrially and also using various organisms which are capable of digesting cellulose. The key, of course, is to avoid an agricultural attitude toward forestry. Unfarming is not clear-cutting forests in order to obtain wood. It isn't even cutting down trees except at a rate far below the sustainable limit.
The key is to think of trees and cellulose creating machines. If you had a factory where robots built automobiles for you, would you design the robots so that once the car was built you would have to destroy the robot to get the automobile and then build a new robot to build the next automobile. That would be crazy. We should not treat trees that way either. Instead, we can simply prune branches off of trees to get our cellulose. With most species of tree, this will encourage them to grow more branches, most of which we can also harvest. The technologies to gather this harvest would need to be solar robotic-AI.