Effects of prescribed fire for fuel reduction on Solanum parishii (Parish’s horse-nettle)
This project evaluated the effects of fire and fire intensity on Solanum parishii (Parish’s horse-nettle) through comparisons of replicated burned and unburned plots at two sites in southern Oregon. This report
This project evaluated the effects of fire and fire intensity on Solanum parishii (Parish’s horse-nettle) through comparisons of replicated burned and unburned plots at two sites in southern Oregon. This report also provides guidance for fuel reduction planning. Previous studies have shown that this species is among a group of plants that may benefit from wildfires (Copeland 2005), but a clear understanding of how fire affects survival and reproduction of the species after controlled burns is lacking.
In 2011, we found increases in size of S. parishii in burned plots at Hukill Hollow, and no differences at Woodrat Mountain (Gray et al. 2011). These results suggested that fire effects were likely light and patchy and that potentially a lag effect of fire on S. parishii might occur. In 2012, we observed no such lag-effect, and found no fire effects on mean size, reproductive status, or survival of S. parishii. In fact, time was the only factor to affect growth and reproductive status of S. parishii, suggesting that differences in climate between 2010 and 2012 were driving observed changes within these populations.
Solanum parishii exhibited more mortality in 2012 than combined mortality in 2010 and 2011, though this was unrelated to treatment. In addition, mean area of S. parishii decreased at Woodrat Mountain and reproductive effort declined substantially at both sites, compared to 2011 values. The significant effect of year across burned and unburned plots suggest that climate differences may have been driving population trends of S. parishii at Hukill Hollow and Woodrat Mountain.
Our data suggests that controlled fire could be a useful tool for managers as it was shown to have a neutral to positive effect on populations of this rare species, but implementing it as a management tool may be unwarranted and present risks of weed invasion. The variation in populations of this species through time coupled with the potential for seasonal variation in climate to affect the populations suggests that climate change should be a focus of management activities surrounding this rare species. In addition, the abundance of invasive species, especially annual grasses, points out the need for weed control in existing populations and surrounding habitats.