Reid's paradox of rapid plant migration

Reid hypothesized that diffusion was not a possible explanation for the observed paradox, and supplemented his hypothesis by noting that birds were the likely cause of long range seed dispersal.

[2] The dispersal of seeds from a parent tree are initially occurs as a normal distribution, as predicted by a standard diffusion equation.

[2][3][5] In order to resolve Reid's Paradox, the vector(s) of seed-dispersal, which give the dispersal kernel a fat-tail, must be identified.

[1][3] Small populations of plants may have grown closer to the ice sheets in microhabitats that possessed the habitat characteristics needed for growth and reproduction.

In North America, there is some genetic evidence of cryptic northern refugia for sugar maple and American beech.