Is it permissible for a tenant/sharecropper to stipulate the yield of existing, minimal trees on the leased land?

Primary text

It is not permissible for the worker (sharecropper or lessee) to stipulate the fruit yield of existing, minimal trees on the land. This view is held by Al-Shafi'i and Ibn al-Mundhir. The justification is that the worker stipulated the entirety of the fruit yield, which is impermissible, similar to the case where the trees constitute more than one-third of the land.