By packed solid, I mean it has very fast growing vines and bushes everywhere like on non-desert living land plus lead crud and hidden small holes so movement is severely restricted. Similar on swallow water areas. Vegetarian food is grown in tiny scattered bushes and the vines and lots of animals on the vines to kill hence no such thing as large scale food production (people probably have no concept of large scale food production). Cities are similarly restricted by having a dense population of people to constantly cut back these invasive vines. The question is how this version of Earth's people be like culturally?
The vines and bushes have some fire retardant properties otherwise natural processes (lightning initiated fires) would have removed them long ago. Also these vines etc. are not smothering types of plants- such plants would be eradicated. The vines are synergistic with your main food plants.