In message , Broadback
writes

from a few days away to find that the Silver Birch which was about 3 to
4 metres tall with a trunk of around (pun there) 15 to 20 cm
circumference had keeled over. In doing so it had snapped the tree
support and broken the substantial rubber tie. The leaves were still
looking very healthy. I was particularly saddened as the trunk's bark
was just nicely showing the characteristic silver flaking. I tried to
support it back up, but in vain. Now my question is has anyone any
ideas as to what the problem may have been? I do not THINK that it is
lack of water as it was only a couple of feet above a pond, which,
though dried out, is still extremely wet. I hope the other varieties
will not be going the same way. There could, of course, have been very
strong winds (it had fallen towards the West)but the problem was the
trunk was bent (damaged but not snapped) about 30 cm above ground level.

Wind damage, unless it was placed where large animals or humans could
attack it. Has your area had thunderstorms while you were away? The
wind associated with a storm cell can do quite a bit of damage on a day
that's not otherwise windy.

If your measurements are correct your tree was rather thin in the trunk
for its height. This could be caused by being too close to other trees,
or by being tied to a support: tree stems that flex in the wind respond
by thickening, if you support them they rely on the support - and your
tree was let down suddenly when the support snapped.

If your other trees are also still staked after five years, consider
removing the stakes - do it in autumn after the leaves are off.

If your birch wasn't uprooted it'll regrow faster than a new one would
grow. If it's dead, don't replant the same species in the same place as
the soil will be tired of it.

--
Sue ]