Index: src/main/java/hudson/plugins/mercurial/MercurialSCM.java
===================================================================
--- src/main/java/hudson/plugins/mercurial/MercurialSCM.java	(revision 23700)
+++ src/main/java/hudson/plugins/mercurial/MercurialSCM.java	(working copy)
@@ -345,11 +345,16 @@
                 listener.error("Failed to clobber local modifications");
                 return false;
             }
-            if (launcher.launch().cmds(findHgExe(listener), "--config", "extensions.purge=", "clean", "--all")
-                    .envs(build.getEnvironment(listener)).stdout(listener).pwd(workspace).join() != 0) {
-                listener.error("Failed to clean unversioned files");
-                return false;
-            }
+            if(!forest){
+		if(!cleanRepository(build, launcher, workspace, listener, workspace.toString()))
+		    return false;
+	    }
+	    else{
+		for(String tree : getTrees(build, launcher, workspace, listener)){
+		    if(!cleanRepository(build, launcher, workspace, listener, tree))
+			return false;
+		}
+	    }
         }
         FilePath hgBundle = new FilePath(workspace, "hg.bundle");
 
@@ -516,6 +521,26 @@
         return createEmptyChangeLog(changelogFile, listener, "changelog");
     }
 
+    private String[] getTrees(AbstractBuild<?,?> build, Launcher launcher, FilePath workspace, TaskListener listener) throws InterruptedException, IOException {
+	ByteBuffer bb = new ByteBuffer();
+        ArgumentListBuilder args = new ArgumentListBuilder();
+        args.add(findHgExe(listener), "ftrees");
+	if(launcher.launch().cmds(args).envs(build.getEnvironment(listener)).pwd(workspace).stdout(bb).join()!=0){
+	    listener.error("Failed to get trees");
+	    return null;
+        }
+        return bb.toString().trim().split("[\\r\\n]+");
+    }
+
+    private boolean cleanRepository(AbstractBuild<?,?> build, Launcher launcher, FilePath workspace, TaskListener listener, String repository) throws InterruptedException, IOException {
+	if (launcher.launch().cmds(findHgExe(listener), "-R", repository, "--config", "extensions.purge=", "clean", "--all")
+	    .envs(build.getEnvironment(listener)).pwd(workspace).stdout(listener).join() != 0) {
+		listener.error("Failed to clean unversioned files in repository " + repository);
+		return false;
+	}
+	return true;
+    }
+
     @Override
     public void buildEnvVars(AbstractBuild build, Map<String, String> env) {
         MercurialTagAction a = build.getAction(MercurialTagAction.class);