This is a literature review of the relationship between the abundance of tree seeds and the productivity, survival and dispersal of Holarctic tree squirrels. Causal links between changes in tree seed supplies and changes in squirrel numbers are often masked by various factors including intraspecifk and interspecific competition for seed, weather, predation and seed hoarding; density-dependent relationships have not been clearly established. Tamiasciurus and Sciurus species have different seed-hoarding strategies which are associated with differences in their social and spatial organization. Average squirrel densities in the long-term are discussed in relation to forest habitat type, and directions for future research indicated.