By "Free Grazing" you mean Continuous Grazing, I assume. Yes
they can, because they pick the best plants to eat, and keep eating
them as they grow back, decreasing the population and vigour of
these desirable species, and enabling the less desirable species to
Yes, guinea pigs are grazing animals, and they need constant
supply of grass hay. When grazing, they prevent their teeth (which
are growing constantly throughout life) from over growing.
You can hear guinea pig grazing sound on the provided link.