"By the end of 2012/13, this financial year, we will have achieved an 11.9% real-terms reduction in the SPCB's budget compared to the baseline 2010/11 budget. This means that we will have delivered the four-year percentage savings target for the overall Scottish budget in just half that time."
Mr McArthur, a Liberal Democrat MSP, said further modest real-terms savings - which take inflation into account - will be achieved in the final two years of the four-year plan.
"The profile of our annual budget reduction is considerably steeper in the first two years of the UK Comprehensive Spending Review than the overall Scottish Budget, as we deliver our savings early," he told MSPs.
"It levels off in the remaining two years, although it still shows a further modest real-terms saving in each of the final two years, finishing at a cumulative real terms reduction of 12.7%, 1.1% below the 11.6% target for the overall Scottish budget."
The reductions have been reached in part through staffing cuts, a pay freeze for Parliament staff and a freeze on MSPs' pay and expenses until the end of March next year.