Decreasing meat consumption would dramatically decrease the amount of land amount used for crop agriculture, not increase it. 85% of the UK's landmass is grazing land and crops grown specifically as animal feed[1].

In 2010, the British livestock industry needed an area the size of Yorkshire just to produce the soy used in feed. But if global demand for meat grows as expected, the report says, soy production would need to increase by nearly 80% by 2050. [2]

From a completely theoretical standpoint, if humans were to stop consuming meat we would actually need to close 1000's of crop farms, not open them on rolling hills, even when accounting for our dietary increase in plants. I'd therefore argue that it's a shame the land has to be used for agriculture at all. Better would be to maintain them as national parks and the like.

[1]http://www.sciencedirect.com/science/article/pii/S0959378017...

[2] (PDF WARNING) https://www.wwf.org.uk/sites/default/files/2017-10/WWF_Appet...