Fig. 4. The ecological hierarchy of (a) the DFEH from 2000 to 2012 (b) the DFEH excluded the self-driving effect from 2000 to 2012. Subscripts 1, 2, 3, 4, 5, 6 represent the result of 2000, 2002, 2005, 2007, 2010 and 2012, respectively. A and M belong to Level 1; Level 2 is made up of the PM and ET; Level 3 is composed of AM; Level 4 includes the TI and C. Different components are depicted by different color bar in this figure.