Canberra, Australia's national capital, is a planned city established on grazing lands in the southern tablelands of New South Wales. Over the past nine decades it has grown into a garden city of 300,000 people. Landscaping was an early priority as much of the chosen site for the city was a treeless plain. Major tree planting began in the 1920's and today the urban forest on public lands contains 400,000 trees from over 200 species in streets and parklands. The species used have changed over time with exotic deciduous trees and conifers dominating early plantings. By the 1970's native species, mostly eucalypts, were planted. Today fewer species comprising an equal mix of native and exotics are used. Trees in the earlier plantings are now mature and given the harshness of the local climate many will come to the end of their ‘safe life’ in the early decades of this century. This provides new challenges for urban tree managers as to how to effect tree replacement that is aesthetically pleasing, ecologically sound and socially acceptable. To assist in this planning a tree data base and modeling system has been assembled. This system – Decision Information System for Managing Urban Trees or DISMUT – facilitates the development of forest-level management programs by allowing the projection of change and work requirements that the result from historical and current plantings over the entire urban forest.