World-wide and regional Red List categories have recently been drawn up using quantitative criteria which describe the past, present and expected future viability of populations. A past reduction in national populations has probably been the most frequently used criterion in global and regional Red Lists but detailed historical distribution data is lacking for many species, e.g. inconspicuous cryptogams. The projected or suspected decline in populations can then be a valuable alternative in the process of at-risk designation. We describe a method for assessing the future decline of a national population according to Red List criteria based on the size structure of local, independent populations. This method uses a spatially implicit, individual-based model of the extinction process of dispersal limited local populations of epiphytic lichen species such as L obaria pulmonaria. A small tree harvest considerably increases the vulnerability of small populations and a harvest intensity considered sustainable in terms of tree harvesting inevitably leads to the extirpation of even large L. pulmonaria populations. Estimating future decline in national populations identified 12 vulnerable and 1 endangered species. For another 81 species, A3 confirmed the threat category assigned to other Red List criteria.