| Year | Number of sites | Area (ha) |
|---|---|---|
| 1992 | 5793 | 1316800 |
| 1993 | 6100 | 1484300 |
| 1994 | 6370 | 1537300 |
| 1995 | 6446 | 1664900 |
| 1996 | 6576 | 2064800 |
| 1997 | 6620 | 2209000 |
| 1998 | 6728 | 2354164 |
| 1999 | 6808 | 2485406 |
| 2000 | 6939 | 2508731 |
| 2001 | 7010 | 2557816 |
| 2002 | 7087 | 2718281 |
| 2003 | 7120 | 2738145 |
| 2004 | 7169 | 2757427 |
| 2005 | 7243 | 2807056 |
| 2006 | 7279 | 2854477 |
| 2007 | 7346 | 2989956 |
| 2008 | 7424 | 3443960 |
| 2009 | 7608 | 3670447 |
| 2010 | 7739 | 3861420 |
| 2011 | 7870 | 3991386 |
| 2012 | 8029 | 4053313 |
| 2013 | 8101 | 4089632 |
| 2014 | 8154 | 4119041 |
| 2015 | 8184 | 4205632 |
| 2016 | 8245 | 4388099 |
| 2017 | 8296 | 4387522 |