Seedling recruitment and establishment of Lupinus perennis L. (wild blue lupine) in a mixed-management ecosystem

Background/Question/Methods

Seedling recruitment and establishment is a key stage 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 several endangered or threatened butterflies. Since L. perennis is known to respond favorably to fire, land managers use a mosaic of controlled burns and field mowings to improve habitat for both plant and butterflies. However, it is unknown whether lupine populations are successfully recruiting and establishing under this management. We measured natural lupine seedling recruitment and establishment throughout seven sites with known management histories in the Oak Openings region of Northwest Ohio. Seedlings were marked and followed in transects established in lupine populations. Because management varied and could not be experimentally manipulated, environmental measurements of light availability, soil moisture, pH, organic matter, litter depth, groundcover, and nearby vegetation were quantified at each seedling. Since lupines enter dormancy after seed dispersal in late June, we assumed that any seedling that had disappeared before July 1 was dead, while any missing after this date was assumed dormant and marked for further monitoring in 2008. Using logistic regression of seedling mortality, we determined relationships with environmental measurements and a site’s management history.

Results/Conclusions

Seedling density varied across the study sites, but did not have any relationship with management history. Additionally, there were few consistent effects of management on environmental factors. However, we did find a correlation showing litter depth decreasing with increasing management activity. Approximately 70% of all seedlings were alive as of July 1. We found that soil moisture, nearby ferns and grasses, and moss increased seedling survival while greater levels of light had the opposite effect. However, site-specific mortality patterns were not correlated with differences in these environmental factors (e.g. litter depth, soil moisture, and light levels). This information will aid land managers in identifying and creating conditions through which lupine populations can be self-sustaining and further bolster butterfly conservation programs.