relationship of cumulative sums and moving averages of temperature to reproductive phenology in Clarkia

Flowering time (anthesis) differs among populations in the Clarkia unguiculata complex, and these differences appear to be adaptive with respect to avoiding the severe summer drought of the native habitats. As habitat elevation decreases, flowering time and soil drying occur earlier. Six populations of the C. unguiculata complex were grown in four temperatures to assess the effect of temperature on the timing of five developmental stages (phenophases). Regressions were calculated using the days from planting to a given phenophase (age) as the dependent variable, and values of 126 combinations of moving average lengths, cumulative sums, threshold temperatures and daily air temperature maxima, minima and means when the various phenophases occurred as the independent variables. The timing of all phenophases was significantly correlated more often with moving averages than with cumulative sums, and it took longer to reach a given phenophase at the lower temperatures. The absence of interpopulation and interphenophase differences suggests that the temperature environments of the native habitats during flowering are similar and that observed differences in flowering time in uniform culture are the result of different responses to other environmental factors such as insolation and soil water potential. Flowering and habitat characteristics are combined into a graphic model that illustrates the importance of flowering in response to temperature to avoid summer drought.