Fire effects on the resprouting and total nonstructural carbohydrates of the highly invasive oriental bittersweet

Background/Question/Methods

Resprouting is an important evolutionary strategy for surviving disturbances such as fire.  Resprouting ability, in response to fire, is determined by resistance to burning, the location of protected meristems, and storage of reserves in roots for regrowth.  Total nonstructural carbohydrates (TNC) in the roots can be an important source of readily available reserves for rapid resprouting.   Oriental bittersweet (Celastrus orbiculatus) is a highly invasive liana that is migrating westward cross the central portion of North America.  This aggressive liana can girdle trees, reach and cover forest canopies, increase tree susceptibility to ice damage, and alter successional trajectories.  While it is known that this species can vigorously root sprout after a fire or from cutting, no quantitative study on this prolific resprouter has been conducted.  We conducted an eight block replicated experiment on sand and moraine soil substrates to examine the effects of burning, cutting, and cut-and-burn on resprouting and regrowth of Oriental bittersweet by season.  Oriental bittersweet density and cover were measured in four 1 m² subplots in each treatment plot (10 x 10m) with pretreatment in July 2009 and post treatment in July 2010 and 2011. Stems were classified into six size categories: seedlings, < 2.5 mm in diameter, 2.5 – 5.0 mm, 5.1 – 10 mm, 10.1 – 15 mm and > 15 mm.   We collected three root segments from each plot in March, May, and July, September 2010 for TNC analysis.  

Results/Conclusions

Burning and cut-and burn treatments reduced bittersweet cover more than just cutting and the control treatment; however, the reduction was less on the richer morainal soils than on sand.  We found that the cut-and-burn treatment had significantly greater numbers of resprouts compared to the cut treatment.  In addition, the number of resprouts increased with size class.  When we examined the percentage of plants that were killed in each size class we found, as expected, that the largest size class had the most survival overall.  The spring cut-and-burn had the most killed stems, but also had the highest number of resprouts.  Seasonally, TNC declined from a peak in March to moderate levels in May and then increased by July.  Cutting bittersweet in early July resulted in a 75% reduction in TNC compared to dormant TNC levels.  We discuss the implications of our results for developing effective strategies for controlling and eliminating Oriental bittersweet.