Tall Larkspur Monitoring at Ozark Riverways

Tall larkspur produces beautiful purple blooms, adding a splash of color to the forest floor.

Susan Farrington

By Dan Drees, Fire Ecologist
Updated by Jamie Ladner, Fire Ecologist

Ozark National Scenic Riverways (ONSR) is home to the largest inventoried and monitored population of the nationally rare tall larkspur (Delphinium exaltatum). The tall larkspur populations within the ONSR boundary represent over 94% of tall larkspur west of the Mississippi River and most of these plants grow in prescribed burn units.

This showy wildflower lives up to its name, with purple flowering stems reaching 6 feet tall. At ONSR, the largest populations are primarily found in open woodlands that receive strong sunlight at the edge of glades. Tall larkspur clearly prefers well-drained, but not drought-prone, soil that is high in calcium from nearby dolomite bedrock.

The greatest threat to tall larkspur is lack of sunlight, mostly due to woody encroachment by Eastern red cedar trees into the open woodland habitat that tall larkspur prefers. This attractive wildflower will persist naturally without fire for decades on some sunny steep slopes and the sunny banks of small high-gradient streams. This is especially true if windstorms, ice storms, or beavers thin the tree canopy.

However, only fire will prevent leaf litter accumulation from suppressing tall larkspur seedling germination over most of its preferred habitat. Our inventories and monitoring efforts confirm this, with 95% of the tall larkspur at ONSR growing in three prescribed burn units.

In 2010, a population of 2,481 tall larkspur plants was found at ONSR, near the park’s famous Alley Spring. This sparked monitoring efforts, and five plots were established in this large population. In total, nine monitoring plots were installed in 2010 and 2011: eight monitoring plots within three prescribed burn units, and one control plot.

 

Many of the park's favorite creatures rely on the biodiversity of burn units.

NPS Photo / Jamie Ladner

As of the 2022 data analysis, there are over 24,000 tall larkspur plants under fire management within the ONSR park boundary. Many of those plants are on Pioneer Forest land within the designated park boundary. The 2022 data from the eight managed plots show an increase of 270%, from 1,185 plants to 4,388 plants.

Tall larkspur population inventories at ONSR between 1984 and 2008 documented dramatic population declines at sites that were not favorable to prescribed burning due to highways or boundary issues. This decline is reflected by our unburned control plot, where the population decreased by 41% since 2010.

The results of ONSR’s fire management have led to this species being upgraded from “Imperiled” in Missouri, to “Vulnerable”. The ONSR fire management program has used prescribed fire to improve glade and woodland communities since 1994 and continues to implement prescribed fire to restore glades and woodlands. The positive impacts that prescribed fire has had on this species, and the woodlands it resides in, validates the NPS philosophy of trying to maintain the historical disturbances, including fire, that shaped the local biodiversity.

Contact: Jamie Ladner, Fire Ecologist for the NPS Ozark Highlands Park Group at [e-mail] for more information.