Australia 's home Ashes series began Johnson has taken 49 wickets in six Tests .
Which has triggered his bowling average to plummet - a legitimate description given he has played 57 Tests - from 30.93 to 27.5 .
Since Australia 's home Ashes series began Johnson has taken 49 wickets in six Tests , which has triggered his bowling average to plummet - a legitimate description given he has played 57 Tests - from 30.93 to 27.5 .