I live on the side of a steep hill. All the gardens are terraced with
retaining walls to support the various levels. One section of my
terrace is supported by an old, sturdy, stone retaining wall (which
looks to me as if it is in fine condition) topped by another, newer,
stone wall which isn't. The top section goes about a foot below the
soil level and the capping stones are about a foot above the soil so
this top section is about two foot high in total. Several large cracks
that go from top to bottom of this top section have appeared over the
winter and spring.

There used to be a tree in the corner. It had been cut down before but
the stump had sprung back into life again and I'm pretty sure that
this is what has caused the damage. I've now cut the trunk and the new
growth down again and the stump is still in the soil. My plan is to
remove the stump, dig a trench behind this top section of wall to take
off the pressure and then dismantle and rebuild this two foot upper
section.

Having seen some other local gardens where the soil has pushed the
retaining walls into gravity-defying distortions I suddenly wondered
whether the soil and roots might actually be holding it all together?
In which case I suppose the wall ought to be dismantled first - to
avoid stones dropping down into the next level.

Any thoughts about which way to approach this? Is it within the scope
of an amateur bricklayer like me or ought I call in someone with more
experience?

Thanks,

Nick