Impacts of spring temperature on the duration of high light prior to canopy closure for three forest herbs

Differential sensitivities of species’ phenologies to climate warming have the potential to alter species’ interactions, but this has rarely been studied for interactions among plant species. Over 12 years in a forest dominated by Acer saccharum in southern Québec, Canada, we studied the timing of canopy closure and of leaf-out and flowering in three understory herbs that depend strongly on the short period of high light in spring. For two species, Erythronium americanum and Trillium erectum, the duration of the period between leaf emergence (or flowering) and canopy closure was insensitive to spring temperature. However, for Claytonia caroliniana, leaf-out and flowering showed greater sensitivity to temperature compared to the canopy, resulting in an increase in the duration of high light with warmer temperatures. Leaf emergence and flowering showed similar temperature sensitivities for T. erectum and C. caroliniana. However, for E. americanum, leaf-out was more sensitive to temperature than flowering, thus challenging an assumption invoked in previous studies to estimate leaf-out dates from flowering dates. Overall, our results suggest that the strategy of “phenological escape” (emergence prior to canopy closure) will not be compromised by climate warming, with the potential for extended periods of high light for some species.