As far as feed though, not all feed is grown exclusively for cattle. I've worked with sugar companies in the past and the by-products of sugar production (molasses, raffinate, etc..) are sold as cattle feed. This is a billion dollar industry. These by-products are being produced regardless of whether we feed cattle or not.
Import control is an interesting idea, I haven't heard that before.
> The 2005 (FAO) Global Forest Resources Assessment ranked the United States as seventh highest country losing its old growth forests, a vast majority of which were removed prior to the 20th century.[3]
>For the 300 years following the arrival of Europeans, land was cleared, mostly for agriculture, at a rate that matched that of population growth.[7] During the 19th century, while the U.S. population tripled, the total area of cropland increased by over four times, from seventy-six million to three hundred nineteen million acres. For every person added to the U.S. population during this period, farmers put another three to four acres under the plow.[8] This trend continued until the 1920s when the amount of crop land stabilized in spite of continued population growth. As abandoned farm land reverted to forest the amount of forest land increased reaching a peak in 1963 of 753,000,000 acres (3,050,000 km2).[4]
It was estimated that there were 1,023,000,000 acres of forest in 1630, compared to 766,000,000 acres in 2012.
[1] https://www.washingtonpost.com/climate-solutions/2020/08/19/...
I would guess all cellulose-digesting animals (cow, sheep, goat, deer, elk, moose, antelope, buffalo, camel, rabbit, termite, ...) should produce about the same amount of methane the amount of cellulose they digest.
https://aggie-horticulture.tamu.edu/earthkind/landscape/dont...
Whereas a reduction in meat consumption would mean a reduction in total global land use for agriculture, allowing that land to be rewilded. Trapping carbon over a longer term and potentially providing numerous environmental benefits.
"The researchers report that grass-fed beef contributes very little to the global protein supply, accounting for just one gram of protein, per person, per day. In comparison, ruminants as a whole contribute 13g of protein to the global average protein intake, per person, per day."
"Despite making only a marginal contribution to global protein intake, grazed beef accounts for between a quarter and a third of all greenhouse emissions from ruminant livestock."
https://tabledebates.org/sites/default/files/2022-04/fcrn_gn...
A related interesting fact - 77% of the world's soy is used for feed:
https://ourworldindata.org/soy#:~:text=The%20majority%20(77%....
[1] https://extension.sdstate.edu/grass-fed-beef-market-share-gr....
Turns out you're right, the majority start out on pasture and then are transported to feed lots to fatten up once they reach maturity.
According to this[1], due to the fact that grass fed beef fatten up more slowly, end up at a lower overall weight at slaughter, and are kept alive and emitting longer, "a nationwide shift to exclusively grass-fed beef would require increasing the national cattle herd from 77 to 100 million cattle, an increase of 30%", and "the current pastureland grass resource can support only 27% of the current beef supply (27 million cattle)".
Further -
"Emissions of methane, a greenhouse gas with a large warming effect relative to carbon dioxide per molecule, come from beef cattle in the forms enteric fermentation and manure emissions. We calculated a 43% increase in methane from enteric fermentation (table 2), assuming that cattle finishing on grass had the same daily methane emissions as present-day stocker cattle, who have nearly identical ADG and are fed primarily on roughage."
Either way it seems as if grain is an indispensable part of animal agriculture currently, so we have to take that into account when talking about what would happen to land use with or without the cows around. Additionally, it seems that moving away from grain would potentially have even worse impacts on the climate.
[1]https://iopscience.iop.org/article/10.1088/1748-9326/aad401
"In aerobic composting, the more oxygen that is available, the more carbon dioxide (CO2) produced, the less methane (CH4), and the more complete the decomposition. As biological activity progresses, the oxygen concentration falls and CO2 concentration increases."
https://www.co2meter.com/blogs/news/8056965-co2-in-aerobic-a....
According to the FAO[1], grazing land for animals and cropland dedicated to producing animal feed represent almost 80% of all agricultural land globally. "Feed crops are grown in one-third of total cropland, while the total land area occupied by pasture is equivalent to 26% of the ice-free terrestrial surface"
Given food conversion ratios[2], where you lose roughly 90% of the energy you put into each step up the food chain, the lower we eat on it the lower the amount of energy input we need, which at the bottom of our food chain are those crops and grasslands.
Once we remove the heavily inefficient middlemen which are animals, we are left with a drastic reduction in the amount of agricultural land and output needed.
I'm not sure how many of these companies and farmers could find another use for their grassland and farmland, as it's not like people will be able to just up their consumption of food by several multiples, and I'm not sure what other sort of productive purposes beyond food production the majority would be able to find.
So yeah, once there's no demand and it's no longer profitable, a large amount of that agricultural land seems like it would just be allowed to lay fallow or be rewilded, which would be really beneficial to the environment for many reasons.[3]
[1]https://www.fao.org/animal-production/en/
[2]https://en.wikipedia.org/wiki/Trophic_level
[3]https://www.rewildingbritain.org.uk/explore-rewilding/what-i...