STOCKHOLM, Sept 30 (Reuters) - World number two truck maker Volvo said on Tuesday it was scaling back production and cutting about 1,400 jobs due to weaker demand in Europe, its biggest market. Volvo, which makes trucks under the Renault, Mack, Nissan Diesel and Eicher brands as well as its own name, said its Volvo Trucks arm would begin negotiations with unions regarding the staff cuts at plants in Belgium and Sweden.