Clipping response strategies of nine bunchgrasses native to the blue ash-oak savannah of the inner bluegrass region of Kentucky

Background/Question/Methods

Nine native bunchgrasses were used to do an experimental restoration/community assembly project of the Blue Ash-Oak Savannah of the Inner Bluegrass Region of Kentucky.  Since there are no existing reference systems of a native grassland matrix, nine native grasses were chosen for this project that were likely a part of this system.  These nine species include six C₃ species, and three C₄ species.  Four of the C₃ grasses are of the genus Elymus which is well documented in historic accounts.  Since disturbance is an important component to savannah systems, a greenhouse clipping experiment was completed the summer of 2010 that mimics disturbance in the form of simulated herbivory or clipping.  A factorial experimental design includes the 9 species, 2 clipping intensities (clipped 7.5 cm and 15 cm from the soil level), and 2 clipping intervals (1 week and 1 month between clippings).  A control treatment was included for comparison.  At each clipping, plant height, tiller number, number of flowering culms, and dried clip weight were recorded.  At the end of the experiment, dried shoot weight and root weight were recorded. 

Grasses have three major strategies to compensate for loss of defoliation due to herbivory: herbivory tolerance, herbivory avoidance, and herbivory deterrence.  I hypothesize that there are species’ differences in expressed traits of herbivory tolerance, herbivory avoidance, and herbivory deterrence in response to differing clipping regimes.  Herbivory tolerance traits include an increase in tiller number, a reduction in allocation/tiller, and an increase photosynthate in new or older leaves.  Avoidance traits include low growing or more prostrate plants, flowering or reproducing sexually at a shorter height, the ability to branch at intercalary meristems, and more allocation to root.  Deterrence traits include the accumulation of silica, lignin, and cellulose in response to clipping.  Plants that can deter herbivory are able to grow taller and become better competitors of light. 

Results/Conclusions

Over all species, an intensity effect was found but there were species differences.  Plants did worse at the 7.5 cm intensity than the 15 cm intensity clipping treatment.  The Elymus was most negatively affected by the 7.5 cm intensity.  The Elymus exhibit traits for herbivory tolerance at the 1/month clipping treatments, D. clandestinum exhibited traits for herbivory avoidance at the 15 cm 1/week clipping treatment, and the C₄ species exhibited traits for herbivory deterrence.