Vegan concerns for environment involve the ecological impact of livestock industry in terms of resource consumption (grains, land, water), pollution, greenhouse gases emissions and loss of biodiversity (see this answer).

However from personal conversations, were meat-eaters argue small scale farming is more sustainable, I got the doubt: is there any difference between small scale and industrial farming?

Of course I'm interested in the evaluation of ecological impact per unit or per ton of "product", since total impact is obviously different. Are there studies or publications assessing that small scale farming is more sustainable than industrial production? Or are the two forms equally destructive for the environment?