Complex sentence: The centre went in to decline in the 2000s due to competition from the more recently constructed Festival Place and many units are now vacant including the previously large department store unit located near the centre's Wilkinson's supermarket (Alders moved out in 2005).
Split into simpler sentences: The centre went in to decline in the 2000s due to competition from the more recently constructed Festival Place. As a result, some units are now vacant including the large department store unit located near the centre's Wilkinson's supermarket (Alders moved out in 2005).