Everyone wants plug and play plants for green stormwater infrastructure features. Two that are work horses, look good and are generally available in good quantities are Carex lurida and Liriope muscari. Can these two widely used species handle stressors that we know are coming because of climate change? Will they be able to continue to provide ecosystems services even during periods of extreme rain and drought? Do they require irrigation or other special management?
Plants were tested under simulated flooding and drought conditions in a ventilated greenhouse. Once plants were established, in the first experiment test plants experienced seven drought and five flooding periods. Stomatal conductance changed little during flooding periods, so for the second experiment, plants were only exposed to drought that was patterned based on real drought data for the Northeast US. Plants were exposed to four 27-day periods of drought with three-day recovery periods to simulate summer and fall months. Underground biomass was also documented to see if it could be correlated with stomatal conductance differences observed in the first experiment.
Both species are stressed in drought. But Liriope increased stomatal conductance (transpired) similar to non-stressed control plants during the recovery period. As also demonstrated in the first experiment, Liriope is more drought tolerant. On the other hand, Carex exchange more gas through leaves. Carex tended to show drought effects sooner and to take longer to recover than Liriope.
Both plants performed better in flooding than in drought. In both experiments, Carex had higher levels of stomatal conductance, which may mean that plants transpire at higher rates than Liriope. That could also mean Carex takes up more carbon dioxide than Liriope when the going gets tough.
While both plants did eventually show response to flooding, the time was much greater than the maximum allowable post-storm ponding time for green stormwater infrastructure features (48 hours in New York, NY and 72 hours in Philadelphia, PA).
When drought stressed Liriope recovers faster, returning to normal stomatal conductance quicker. Carex was not able to return to normal stomatal conductance levels following the first drought period. The authors speculated that Liriope may be the better option for areas where prolonged drought is expected to increase in the future.
Conclusion: The study “suggested tradeoffs between species resilience, and biomass production and stomatal conductance.” Both plants survived and performed following drought and flooding periods and are good choices for green stormwater infrastructure.
Potential climate change impacts on green infrastructure vegetation by Maria Raquel Catalano de Sousa and Franco Andre Montalto, Civil, Architectural, and Environmental Engineering, Drexel University, and Matthew I. Palmer, Ecology, Evolution and Environmental Biology Department, Columbia University in Urban Forestry & Urban Greening 20 (2016): 128-139. http://dx.doi.org/10.1016/j.ufug.2016.08.014