Thus, by the early 19th century, the quality of rope materials made from New Zealand flax was known internationally, as was the quality of New Zealand trees which were used for spars and masts. The Royal Navy was one of the largest customers. The flax trade burgeoned, especially after male Māori recognised the advantages of trade and adapted to helping in the harvesting and dressing of flax which had previously been done exclusively by females. Driven by the desperate need for muskets and ammunition, many Māori moved to unhealthy swamplands where flax could be grown, and there devoted insufficient labour to the production of food, until any survivors were fully equipped, first with musket and ammunition, and then with iron tools. ""The taking of slaves increased – slaves who could be put to work dressing flax..."". A burgeoning flax industry developed with the fibres being used for rope, twine, matting, carpet under felt, and wool packs. Initially wild stands of flax were harvested but plantations were established with three in existence by 1851.