PRETORIA, Sept 7 (Reuters) - The South African economy grew 1.2% in the second quarter compared to the previous three months in seasonally adjusted but non-annualised terms, statistics agency data showed on Tuesday. Economists polled by Reuters had forecast gross domestic product (GDP) growth of 0.7%, versus a revised 1.0% increase in the first quarter. (Reporting by Alexander Winning Editing by Nqobile Dludla) Our Standards: The Thomson Reuters Trust Principles.