Reference for Eruvin 10:8
אִילָן שֶׁהוּא מֵסֵךְ עַל הָאָרֶץ, אִם אֵין נוֹפוֹ גָבוֹהַּ מִן הָאָרֶץ שְׁלֹשָׁה טְפָחִים, מְטַלְטְלִין תַּחְתָּיו. שָׁרָשָׁיו גְּבוֹהִין מִן הָאָרֶץ שְׁלֹשָׁה טְפָחִים, לֹא יֵשֵׁב עֲלֵיהֶן. הַדֶּלֶת שֶׁבַּמֻּקְצֶה וַחֲדָקִים שֶׁבַּפִּרְצָה וּמַחֲצָלוֹת, אֵין נוֹעֲלִין בָּהֶן, אֶלָּא אִם כֵּן גְּבוֹהִים מִן הָאָרֶץ:
A tree which bends over the ground, [i.e., whose boughs incline downwards all around] — if its boughs are not three tefachim above the ground, it is permitted to carry beneath if. [For since its boughs are not three tefachim above the ground, they are regarded as attached to the ground, and are, therefore, like partitions, for which reason it is permitted to carry beneath it. In any event, the space between the boughs and the ground must be filled with straw and stubble or the like, and the boughs must be tied so that they not be moved by the wind. For any partition that cannot withstand a normal wind is not a partition. And one may carry there only (the distance of) beth sa'atayim (seventy cubits and a remnant). For within any partition whose purpose is for "space" — that is, to guard the space of the fields and the vineyards, but not to dwell in — it is permitted to carry only beth sa'atayim.] If its roots are three tefachim above the ground, he may not sit upon them, [it being forbidden to make use of a tree (on Shabbath) — a decree, lest he come to tear from it. But if they are not three tefachim high, they are like the ground, and it is permitted to sit upon them.] The door of the muktzeh, [a space behind the houses, the door of which is not set in a socket, like other doors, but which stands against the opening, and is placed upon the ground when it is removed], and thorns in [i.e., filling] a breach, and [reed] mats — it is forbidden to close (the opening) with them unless they are above the ground. [All of these are not tied and not fixed in place, but when one comes to open (the enclosure), he places them on the ground. For this reason, he does not replace them, this giving the impression of "building" (a forbidden Sabbath labor) — unless they are above the ground, in which instance the impression of "building" is not given, and he may close (the space) with them.]