Billy Hau-hang, a young botanist at the University of Hong Kong, hopes to restore Hong Kong's forests to their natural diversity. His efforts are being studied carefully in Beijing. Reforestation has risen to the top of the government's agenda after fierce flooding last summer, for which deforestation and consequential soil erosion were given much of the blame. One way to reforest a place is to fence it off and do nothing. Seeds will find their way in, and trees will grow. Experiments in the West, however, suggest that this takes about a century. That is a long time. Dr Hau aims to speed things up by planting a carefully crafted mixture of saplings, in the hope that they will grow reasonably rapidly (within 50 years say) into something resembling a natural forest. As a first step, he has presuaded the Kadoorie Farm, a conservation institution based in the New Territories to the north of Hong Kong island, to give him time and space for a native-tree nursery. His 150,000 seedlings are now in their second year.