I fear that an increased temperature would cause water vapor to not create as much rain, or cause the jet stream to shift. Either one wouldn't be too good. It would either be really humid and the wind would blow all of the moisture away from the Midwest (maybe not Michigan and Ohio because of the Great Lakes). And the trees here are dying or getting cut down much faster than they are being replaced, and even if they were replaced, it takes 40-70 years for trees to grow big enough to be a normal forest.
The other possibility is that the level of pollution from Asia and elsewhere would cause acid rain to fall in greater acidity levels than it is already. If the rain is poison, all of the trees and smaller plants die off. Farms might be able to counter this with watering from the aquifer or the local lakes, but I'm not sure how many of them would be able to switch quickly if something happened that they couldn't get water from those sources. And with all the dry dead plant material, forest fires would be an issue.
And a simple heat wave, with farmers not planting crops that could handle drought conditions (an not having the modern watering capabilities), and a lack of trees to stop the wind caused the dust bowl in the 30s. And just because we can get water from other sources today to grow food in the Midwest if another heat wave and drought comes, doesn't mean that it will always be the case or as easy as it is today.
1936 North American heat wave - Wikipedia, the free encyclopedia