I've started a new expedition. Our boys and caravan arrived in a sandy area with no trees to my light surprise and annoyance. After thinking for way too long about the solution (I didn't embark with wood) I had my miner dig down a few z levels where we found SHALE beyond the sand.
Using our new found shale, we quickly constructed two bridges to the other two areas that were cut off from us. One has plenty of plants, and one has many trees (great!) to exploit as well as a large hill which I have not yet named.
Our men have started digging down to which will indeed be our main beautiful home under the soil.