Real-time rendering of vegetation is currently a problem in need of a solution. The lack of plants and trees reduces the realism of outdoor scenes. The large number of polygons that form this kind of objects implies that current hardware cannot achieve interactive rendering of outdoor scenes. This paper deals with this problem and it presents a multiresolution scheme that allows us to represent the whole geometry of the trees and forests using both uniform and variable levels of detail. The method presented here models the trees using two multiresolution approaches, due to the different characteristics of the geometry that forms them. The trunk is modelled with a solution oriented towards representing continuous meshes, and the foliage is modelled with the multiresolution model Level of Detail Foliage, presented in a previous work. Both of them have been designed to take advantage of the graphics hardware by adapting the data structures and the rendering algorithms to make the visualisation time efficient. The main characteristic of Level of Detail Foliage is the fact that it classifies the leaves that form the foliage in independent clusters in order to improve the visualisation time. In this paper, it has been efficiently implemented and extended to allow us to change the level of detail in a variable manner, by adapting the resolution of the crown of the tree to certain criteria determined by the application.