CREATE TABLE table_28237 ("NSG Nr." FLOAT, "Name of the nature reserve" CLOB, "District / Town" CLOB, "Area  ( ha ) " CLOB, "Date established" CLOB)

When was Stellbrookmoor established?
SELECT "Date established" FROM table_28237 WHERE "Name of the nature reserve" = 'Stellbrookmoor'
SELECT "Date established" FROM "table_28237" WHERE "Name of the nature reserve" = 'Stellbrookmoor'