Young bristlecone pine trees

Three bristlecone pine trees were included in amenity planting along Pace Street, not far from here. Unfortunately, one has died since I was here last and several branches on one of the others is turning brown. As I’m growing one successfully at home in New Zealand, I’m it sure what the problem is.

There has been some very cold weather here recently, but these trees grow at high elevation where it is very cold in winter. So I wonder whether it is the high summer temperatures, the large changes in temperature, or maybe excess moisture when the snow melts. I had been hoping to watch them grow.