I did the math. A standard cremation takes 2-3 hours at a temperature of 1400° Fahrenheit. This would require at least 12lbs of charcoal briquettes. Charcoal is made using a 3:1 ratio with wood (36lbs of wood) and a standard lolblolly pine harvests 470lbs of usable wood. (48 per day.) There were 6 million jews killed in the Holocaust across 4 years (1941-1945) averaging 1.5 million a year across 6 camps. Given the number of hours in a day, the time to heat and cool and other factors such as breaks, each oven reasonably cremated a max of 4 bodies per day.
That means each camp had approximately 1,028 ovens averaging 171.3 ovens per camp burning a total 49,344lbs of charcoal per day per camp, equaling 18,010,560 per year, and 72,042,240 across the entire four years totaling 432,253,440lbs for all camps. This would have been created from the equivalent of 1,296,760,320lbs of wood harvested from approximately 2,759,064.6 trees. A little over 500,000 more trees than compromise the entirety of the Atlantic forest in Brazil (2.2 million) a mass of wood that's approximately 7 times larger than Italy or in other words a mass of wood the size of Mexico. Even removing the ovens from the equation you would need just as much, if not more wood when factoring in the surface area and loss of heat due to the open air environment and that's without even getting into the storage and transportation of the wood or how it would be continuously fed into the pit.
Also, officially they only had 15 ovens at Auschwitz.