Soil warming alters seed-bank responses across the geographic range of freshwater Taxodium distichum (Cupressaceae) swamps.

PREMISE OF THE STUDY: Climate warming is predicted to have far-reaching effects on the distribution of species, but those effects may depend on the flexibility of regenerating species in responding to climate gradients. We conducted a study to determine whether the variation in the response of seed banks to temperature varied across the latitudinal range of Taxodium distichum swamps in North America.
METHODS: The soil was collected in a long-term research network and heated experimentally to three current-day spring normal soil temperatures (average maximum daily spring normal soil temperatures during May in Illinois, Arkansas, and Louisiana, USA, respectively: 22°, 25°, and 29°C). A "normal" is the mean temperature calculated over a 30-yr interval (1971-2000). Seed-bank density and biomass responses were examined in relation to latitude and difference in the soil temperature of the experiment and the spring normal. KEY
RESULTS: Using first- and second-order regression analysis, we determined that the variation in total germination density was lowest mid-range and in experimental soil temperatures similar to the spring normal. For some dominant species, the variance in germination density was higher in the northern (Cephalanthus occidentalis) or the southern part of the network (Saururus cernuus and Polygonum pensylvanicum). Overall, the variance of total biomass (root, shoot, whole plant) was higher if the experimental soil temperature was warmer than the spring normal.
CONCLUSIONS: Our results suggest that the regeneration of some populations of swamp species may have more flexibility to respond to climate warming than others.