A Kirwan blow-up and trees of vector bundles
  In the paper [MTT] a conceptuel description of compactifications of moduli spaces of stable vector bundles on surfaces has been given, whose boundaries consist of vector bundles on trees of sufaces. In this article a typical basic case for the projective plane is described explicitly including the constrution of a relevant Kirwan blow up. 
Guenther Trautmann
math.AG