Are temporal gaps necessary for the establishment of the native wildflower, Coreopsis tinctoria?

Coreopsis tinctoria (Asteraceae, goldenwave) is a widely-distributed early spring and early summer annual found primarily in disturbed areas (vegetational gaps). As a widespread, attractive native plant, C. tinctoria could be used in ecosystem restoration activities, however it is a poor competitor. Interspecific competition has been shown to reduce growth of C. tinctoria, apparently restricting it to vegetational gaps. The role of light levels in seed germination was investigated and there were no significant differences in germination at any tested light level. The effects of intraspecific competition on growth of C. tinctoria were explored in an increasing density series in a low-nutrient soil. As density increased there were significant increases in C. tinctoria mass per pot and mass per plant decreased. The effects of interspecific competition were examined by growing C. tinctoria with Bouteloua curtipendula (Poaceae, sideoats grama) in a replacement experiment using a total density of twelve plants per pot in a frequency series of 12:0, 10:2, 8:4, 6:6, 4:8, 2:10, and 0:12 (C. tinctoria: B. curtipendula) plants per pot. As the frequency of C. tinctoria increased, the shoot, root, and total dry mass per pot increased and mass per plant in those categories decreased. Increases in root mass per pot were not significant. As frequency of C. tinctoria increased, there were significant decreases in shoot mass per plant and total mass per plant. Five temporal gaps were simulated by planting C. tinctoria and B. curtipendula in the same pot, but varying the time between planting of each species: C. tinctoria planted 60 days before B. curtipendula (+60 day gap); C. tinctoria planted 30 days before B. curtipendula (+30 day gap); C. tinctoria planted at the same time as B. curtipendula (+0 day gap); C. tinctoria planted 30 days after B. curtipendula (-30 day gap); C. tinctoria planted 60 days after B. curtipendula (-60 day gap). Coreopsis tinctoria accounted for the majority of total pot biomass at all frequencies in the +60 day gap. In the +30 day and +0 day gaps C. tinctoria composed >50% of total pot biomass at frequencies 6:6 and higher. In -30 day and -60 day gaps, C. tinctoria accounted for 30% or less of total pot biomass. When C. tinctoria was grown with B. curtipendula, it produced the majority of pot biomass when given a 30 or 60 day germination advantage, suggesting that C. tinctoria is adapted to establish in temporal gaps that exists in early spring or early summer, before environmental conditions favor growth of B. curtipendula, a C4 warm-season grass.