Other immigrants became dominant from time to time but the same principles of woodland economy applied until the early twentieth century. By that time, the keeping of pigs there was long forgotten and local use of the woodland products had fallen away. Gas or coal was used for cooking and coal for heating. Building timber had by then, been imported from the Baltic for two hundred years. Coppice timber was no longer needed for tool handles and cottage roofs. The use of timber in locally built vehicles was about to drop away. Once the demand for wartime boatbuilding, trench construction, military camps and vehicles was done, the traditional forest products trade was nearly dead. The chipboard industry was in its infancy. Only bundles of hazel for sea defence and river training and large, straight timber suitable for mechanical processing were wanted. The latter was supplied by relatively impoverished estates' stripping out all the saleable timber. The Forestry Commission was set up by Parliament in 1919 to replenish the country's woodland after it was seen that most of the country's usable timber assets were gone and landowners were not in a position to begin to replace them rapidly. With forestry, maintaining cyclical replacement is an important matter. Many tens of years are needed to produce a commercially mature hardwood (broadleaf) tree of the sort now required. No matter how many trees might have been planted in 1920, they would not have begun to provide the sort of timber that was then demanded until 2000.