We had a beautiful grafted hawthorn tree that had been in a plastic
tube thing, open to the ground, for a few years. The roots were well
established and the tree branches had grown to about 6 metres
diameter. Then we finally got around to the hard landscaping we had
planned, which included a 2 metre by 1.5 metre planter box around the
tree.

I think that the root system would have extended well beyond the
original plastic tube the tree was growing in.

This is a picture during the construction. The crazy paving was laid
on a 100mm slab where there had previously been grass.

http://tiny.cc/kexmg

This is what it looked like the next spring when it was in blossom.
Very healthy.

http://tiny.cc/u5xd2

Note that there are a couple of plants sharing the planter box with
the tree.

A year later it was dead. What changed?

The crazy paving over the grass and probably the root system.

The planter box gave the tree a much bigger volume of soil for the
roots to expand into. We thought that would help it.

We had a few days 40C and one day that hit 47C with a strong
northerly. That would have sucked all the moisture out.

We hadn't needed to water the tree much for years so we didn't start
watering it any more apart from the few days around the 40+ weather.

Ground cover was planted in the planter box. It grew vigourously and
soon covered the whole box and was flowing over the edges.

My view is that the ground cover sucked up all the available water and
was the major problem. What do you think?

--
Regards.
Richard.