Rodents as seed dispersers in a heath - oak wood succession

In a Danish heathland invasion of oak shrub has taken place, the succession rate being approximately 300 m during the last 100 years. The colonisation has occurred in steps related to the delay time between seedling stage and fertility stage. Seedlings are often found in clusters originating from caches probably made by seed-eating rodents. Apodemus sylvaticus, A. flavicollis and Clethrionomys glareoles. These rodents reached autumn densities of 25-50 individuals per ha. Radioactive acorns were scatterhoarded by the rodents, which mainly deposited the acorns singly up to at least 34 m from the oak shrub (mean 15.3±8.2 m), and preferably under Empetrum nigrum mats in the walls of runways Seedlings originating from radioactive acorns were found next summer at distances of 4-37 m from the oak shrub. In early summer caches containing new seedlings had a mean size of 2.0±2.2 acorns, range 1-16; mean distance of seedlings to nearest crown projection was 24.0±23.6 m, range 1-137. Thus, rodent acorn dispersal can explain the observed succession rate of oaks into the heathland.