The seed rain and seed bank of arctic dwarf birch,Betula glandulosa, were studied at Kuujjuaq, Que., and Tarr Inlet, near Iqaluit, N.W.T. At each site dispersing seeds were captured in sticky traps in three adjacent plots having locally high and low birch densities; soil cores were collected in parallel. Trap data indicate that birch samaras disperse principally during late fall and early spring. The number of samaras dispersed was significantly greater at Kuujjuaq than near Iqaluit and was greater in high- than in low-density areas. Samaras collected at Kuujjuaq were significantly heavier (xensp;=ensp;0.19ensp;mg) than those from Tarr Inlet (xensp;=ensp;0.10ensp;mg). Germination showed an asymptotic exponential weight dependence. From the weight distribution of samaras, we expected germination of 69.7 of samaras from Kuujjuaq. Few viable propagules were found in collections from the Iqaluit area; from their weight distribution 0.38 were expected to germinate. We predicted emergence from soil cores, using seed-trap and germination data, and tested predictions under greenhouse conditions. Observations and predictions agreed for low-density areas. At Kuujjuaq 248ensp;emergences/m2were predicted and 229 observed; at Iqaluit no emergences were predicted and none observed. In high-density plots at Kuujjuaq 9292ensp;emergences/m2were predicted and 2164 observed. Corresponding rates for Iqaluit were 2 and 17ensp;emergences/m2, respectively. Differences in seed banks and recruitment indicate differences in the structure, dynamics, and reproductive biology of populations at the two sites.
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