Canopy openness affects wiregrass reproduction
Our lab recently published a new paper on how tree canopy cover affects wiregrass reproduction (Baruzzi et al. 2021). This project was developed on the fly one fall morning after a perceptive undergraduate, Natalia Medina-Irizarry, made a very astute observation: There were more wiregrass plants flowering under pines than in the open. Well, what could be more exciting than a new question? So, we stopped what we had planned for the day, designed a new experiment, and started collecting data.
Crouched on hands and knees in the dry sandy soil, we inspected wiregrass plants along transects under pines and in the open. We checked each wiregrass plant to see if it was flowering and if so, how many flowering stems it had. There we are in the photo to the right, at the end of a long transect. Because the real measure of successful reproduction is the number of new baby grasses, we also collected seeds from wiregrass on the transects to germinate in the lab.
From past research, we know that fire season can affect wiregrass reproduction, so we also decided to place transects in pine stands that had been burned in different months of our sampling year: January (early dry season), March (mid-dry season), and June (wet season).
Our many hours of crawling along transects resulted in some exciting discoveries!
There are two main takeaways from the project:
Variation in the landscape, such as in canopy cover, affects wiregrass reproduction. In the dry site we studied, plants were more likely to flower and make seeds that could germinate when they were under some tree canopy than out in the open.
Wiregrass is sensitive to season of burn. We already knew this, but it is interesting that wiregrass appeared to reproduce after mid-dry season burns, but almost none of the seeds germinated.
We aren’t sure why wiregrass seems to reproduce more successfully when growing near tree cover. We guessed that plants under trees might have more water available and thus have more resources for reproducing. A greater abundance of flammable pine needles under pine trees might increase fire intensity and influence greater reproduction. Previous research by van Eerden (1997) found that wiregrass plants burned at hotter temperatures produced more flowering stems. It would be interesting to repeat this study in mesic pine savannas where water availability is likely higher, whether there are trees nearby or not. We anticipate more crawling around in pine savannas in our future!
References
Baruzzi, C., N. Medina-Irizarry, M.N. Armstrong, and R.M. Crandall. 2021. Fire season and canopy cover interact to affect reproduction of a pyrogenic bunchgrass, Aristida beyrichiana. Plant Ecology, DOI: 10.1007/s11258-021-01204-7.
Van Eerden, B.P. 1997. Studies on the reproductive biology of wiregrass (Aristida stricta Michaux) in the Carolina sandhills. Ph.D. Dissertation. University of Georgia.
