There is no regulatory guidance on this as of yet that I'm aware of and recently I have seen a couple of opinions posted that 226.35 would require taxes on the 40 acres to be escrowed based on the following.
(3) Escrows--(i) Failure to escrow for property taxes and insurance. Except as provided in paragraph (b)(3)(ii) of this section, a creditor may not extend a loan secured by a first lien on a principal dwelling unless an escrow account is established before consummation for payment of property taxes and premiums for mortgage-related insurance required by the creditor, such as insurance against loss of or damage to property, or against liability arising out of the ownership or use of the property, or insurance protecting the creditor against the consumer's default or other credit loss.
However based on the following from the Commentary:
1. Section 226.35(b)(3) applies to principal dwellings, . .
I have taken the stance that you only need to escrow for the items directly associated with the primary dwelling.
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The opinions expressed are mine and they are not to be taken as legal advice.