hmm.. you will do some thing else.
you will add two fields one for year2001 and the other for year 2011
then in Year 2001 field you will divide NLCD2001 by the total of study area ( use statistics for COUNT field and get the Sum ).
then do the Previous step with new field Year 2011.
the Equation will be same but change to new fields
( (Year2011 - Year2001) / Year2001 ) * 100