Seedling recruitment and establishment are key stages in the growth and maintenance of viable plant populations. Lupinus perennis (Wild blue lupine) is a long-lived oak savanna indicator species and the sole larval food source for endangered or threatened butterflies. While the seeds of this species typically overwinter and germinate in May, seedlings may appear later when conditions are favorable for germination. Usually, these plants are believed to contribute little to population size, however, in September 2007, we observed a large number of naturally-dispersed lupine seedlings emerge in two remnant oak savannas in Northwest Ohio. In order to determine whether this cohort could add to local population viability, we measured each seedling’s size and marked them in the field to determine whether any would establish into juvenile plants the following spring. These results were then compared with a concurrent study examining recruitment and establishment for lupine seedlings that had emerged in spring 2007.
Results/Conclusions
88 new seedlings were marked in one remnant savanna, while 111 more were marked in the other. In May 2008, 45% and 69% of these seedlings reemerged in the study sites, respectively. These establishment rates were generally larger than those rates seen for the spring seedling cohort (18 – 50%), however, juvenile plant size was found to be no different between the spring and fall lupine cohorts. This evidence aids restoration practitioners who manually seed their lupine populations in the fall and burn them the following spring, as it is now know that these plants can grow to become juveniles over a short period of time. However, it remains inconclusive whether fall recruitment pulses can substantially contribute to population viability if these events only occur at low frequencies. Ultimately, climatic factors, such as rainfall and temperature, will influence the likelihood of these outcomes. However, in a climate change scenario where these habitats become wetter, these events may become more widespread. At the very least, this study yields valuable information to lupine restoration programs concerned with the success of fall seedlings, as we now know that large numbers of these plants can become established before winter’s arrival.
