Answer:

It can’t be done in two dimensions. Obviously, putting the trees on the four points of a square won’t do, as the diagonally opposite trees would be approximately 0.14 pasangs apart. But in three dimensions it is easy. The trees must be planted at the four corners of a tetrahedron (a triangular-based pyramid), and this can be done in several ways:

• Plant one tree on a mound (about 0.076 pasangs high) and the other trees in an equilateral triangle around it.
• Plant one tree in a crater (about 0.076 pasangs deep) and the other trees in an equilateral triangle around it.
• Plant two trees on a ridge (about 0.071 pasangs high) and the other two either side of it.
• Plant two trees in a small gully (about 0.071 pasangs deep) and the other two either side of it.

There are a few more esoteric solutions, which this writer leaves as an exercise for the creative solver.

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