Complex sentence: Rothschild was the founder of the Society for the Promotion of Nature Reserves (SPNR), which in 1919, leased Meathop Moss for use as a nature reserve.
Split into simpler sentences: Rothschild was the founder of the Society for the Promotion of Nature Reserves (SPNR). In 1919 Meathop Moss was leased for use as a nature reserve.