So I sent Ben Law an email and asked him. His response:
Hello Paul,
Really flat out here at present, just completing book and about to start a
really interesting build at sustainability centre.
The new book is 'Roundwood Timber Framing' and it is a practical manual on
building roundwood timber frames, including new jointing techniques,
suitable timber species, suitable tools, case studies and galleries of
roundwood projects, over 300 photos, line drawings etc
Species selection suitable for USA and Europe, published August 2010