Some like it hot! Fire and the horsenettle

by Tom Kaye — last modified Feb 28, 2013

Research suggests short term benefit of fire on Parish’s horse-nettle

Parish’s horse-nettle and its habitat in the Applegate Watershed of southwestern Oregon
Parish’s horse-nettle and its habitat in the Applegate Watershed of southwestern Oregon

Parish’s horse nettle (Solanum parishii) is a rare plant in the nightshade family (Solanaceae) that is imperiled in Oregon.  Individuals typically grow in small populations (less than 10 plants) scattered across the landscape in chaparral habitat of southern Oregon and California.  Parish’s horse nettle is among a group of plants that may benefit from wildfires, but a clear understanding of how fire affects survival and reproduction of the species after controlled burns is lacking.

In 2009, IAE initiated a study working with the Bureau of Land Management (BLM), Medford District, to evaluate fire effects on this species through comparisons of burned and unburned plots at two sites in southern Oregon.  Controlled burns were lit by BLM fire crews in fall of 2010, and IAE followed up with data collection on plant size of Parish’s horse-nettle for the next two growing seasons.

Parish’s horsenettle plants were substantially larger the year following the burn at one of the two sites, while the plants in unburned areas stayed about the same size.  At the second site, burning had no effect on plant size.  Also, fire didn’t change the rate of flowering of the plants at either study location.

Two years after burning no effects of fire on Parish’s horsenettle were detectable.  The plants in burned and unburned areas were of equal size and bloomed the same amount.  In fact, the summer drought of 2012 seemed to outweigh any fire effects, with plants in that year growing much less than previously, regardless of fire treatments.

The short-term positive to neutral effects of prescribed burning on Parish’s horse-nettle suggest that this species tolerates fire and may have some ephemeral benefits in some locations.