I'd start at the property line, the farthest corner on either side, left or right, because you have to have a starting point to get a basis for ones comparison. Then grab the nearest tree then look at all of the surrounding trees. if ones meet the criteria them mark them accordingly, if starting on the left side, move right go to next tree not in the set and repeat, making sweeping movements both left and right while moving forward repeating the sequence finding matches to the criteria. until you've covered the entire area. you'd also have to add that circumference of the tree that is being used to find the surrounding trees to put them into sets. that should also give you are moving forward part of the code. as in how far to move forward on your next sweep left or right, depending on which side one stared on.
