Life-History responses of Solidago canadensis to fire and grazing

Background/Question/Methods

It has long been understood that fire and grazing have an important impact on prairie plant populations.  Individual plants can alter their life history traits such as biomass allocation patterns and growth architecture in order to maximize fitness.  Improving our understanding of how individuals adjust their life history in response to disturbance regimes could help elucidate the mechanisms behind population-level responses.  To examine the impact of burn frequency, burn timing, and grazing on plant life history, individuals of Solidago canadensis were harvested from five different burn and grazing regimes at Konza Prairie Biological Station: unburned/ ungrazed, 2-year spring burn/ ungrazed, 2-year summer burn/ungrazed, 2-year spring burn/ grazed by bison, and 1-year spring burn/ grazed by bison. This study sought to address two main questions: 1) How does disturbance regime influence plant architecture (height, size, leaf and rhizome number)? 2) How does disturbance regime influence biomass allocation patterns, particularly allocation to sexual and asexual reproduction?

Results/Conclusions

Plant size was greater in the 2-year burned than in annually burned grazed plots (F=5.83, p=0.02) and greater in the presence of grazers (F=8.29, p<0.01).  Reproductive effort (allocation to rhizomes and inflorescence) was significantly greater in the summer burn than in the spring burn (F=4.03, p=0.049; F=6.65, p=0.01).  Stem allocation was greater in the spring burn than in the summer burn despite similar height.  In grazed treatments, leaf and rhizome number were greater in the 1-year burn than in the 2-year burn; leaf and rhizome number were also significantly greater in grazed than in ungrazed 2-year burns.  These results suggest that plant growth and allocation patterns are significantly influenced by grazing and burning timing and frequency, so further study along these lines may help improve our understanding of the mechanisms behind prairie plant population responses to fire and grazing regimes.  This an important question since fire and grazing are important management regimes for tallgrass prairie, an endangered ecosystem.