JSON has become one of the most popular data formats. Yet studies on JSON data integration (DI) are scarce. In this work, we study one of the key DI tasks, nested mapping generation in the context of integrating heterogeneous JSON based data sources. We propose a novel mapping representation, namely bucket forest mappings that models the nested mappings in an efficient and native manner. We show experimentally the practicality of our approach over six real world data sets. Moreover, via intensive experiments over synthetic scenarios we demonstrate that our approach scales well to the increasing metadata complexity of DI scenarios.@en