| Year | Number of sites (cumulative) | Total area (ha) |
|---|---|---|
| 1929 | 2 | 135709 |
| 1958 | 3 | 160197 |
| 1961 | 5 | 200127 |
| 1990 | 12 | 200313.7 |
| 2000 | 14 | 429857 |
| 2001 | 14 | 429857 |
| 2002 | 14 | 429857 |
| 2003 | 17 | 565956 |
| 2004 | 18 | 592366 |
| 2005 | 19 | 603820 |
| 2006 | 18 | 698701 |
| 2007 | 19 | 699496 |
| 2008 | 20 | 735755 |
| 2009 | 43 | 876031 |
| 2010 | 43 | 880774 |
| 2011 | 43 | 880774 |
| 2012 | 44 | 892546 |
| 2013 | 44 | 892546 |
| 2014 | 44 | 892546 |
| 2015 | 44 | 892546 |
| 2016 | 44 | 892546 |
| 2017 | 44 | 892546 |
| 2018 | 44 | 892860 |