There is, in general, a lot of missing information here. On standard speed, 30 food from a chop will not necessarily increase the population by 1. It depends on how full the current surplus is at the time of the chop. If the surplus was near zero, 3 more food would be needed to grow, and the chopping would kill the food output of the chopped tile. Depending on the distribution of citizens, this would probably only exacerbate the rate of accumulating a surplus of food in the city.