Reference for Bava Batra 48:11

אלא אי איתמר דרב כהנא אסיפא איתמר אם האילן קדם קוצץ ונותן דמים ולימא להו הבו לי ברישא דמי והדר איקוץ אמר רב כהנא קידרא דבי שותפי לא חמימא ולא קרירא:

must not be turned into cultivated field nor cultivated field into suburb? — The rule had to be stated here to meet the view of R. Eleazar, who said that cultivated field may be turned into suburb, and suburb may be turned into cultivated field; even on his view trees must not be planted [close to the town], so as not to spoil the amenities of the town. And the Rabbis too who said that a cultivated field may not be turned into suburb nor suburb into cultivated field, meant this to apply only to the sowing of vegetables but not to the planting of trees; yet here they too would prohibit on account of the amenities of the town. What ground have you for saying that there is a difference [in this respect] between vegetables and trees? — Because it has been taught: 'If an enclosure, big enough to sow more than two se'ahs in, is fenced round for dwelling purposes, then if the greater part of it is sown with vegetables, it is reckoned as a vegetable garden and it is forbidden [to carry in it on Sabbath], but if the greater part of it is planted with trees it is reckoned as a courtyard and it is permissible [to carry in it on Sabbath].<span class="x" onmousemove="('comment',' 'Er. 23b. This shows that vegetables turn ground into a 'field', but trees do not. ');">¹⁰</span>

Jastrow