Learn Farsi: علی‌رغم مشکلات، کشاورزان به درختکاری ادامه می‌دهند. - Despite the problems, the farmers continue tree planting.

The compound verb ادامه دادن (to continue) requires the preposition به (to) when it is followed by a noun or a long infinitive. Literally, the farmers are giving continuation to tree planting.

Is there a hidden ezāfe after علی‌رغم?

Yes, علی‌رغم (despite) requires an ezāfe to link it to the noun that follows. You must pronounce it as علی‌رغمِ مشکلات (ali-raghm-e moshkelāt).

How is the noun درختکاری (tree planting) constructed?

It is built from درخت (tree) + کار (the present stem of کاشتن, to plant) + ی (a suffix that creates abstract nouns). Together, they form a verbal noun that functions perfectly with the ادامه دادن به structure.

If I wanted to use a verb for planting instead of the noun درختکاری, how would the sentence change?

You would drop the preposition به and use the subjunctive form of the verb. The second half of the sentence would become ادامه می‌دهند که درخت بکارند (they continue to plant trees). Using به + noun is often preferred in formal written Farsi for its conciseness.