Potential climate change impacts on green infrastructure vegetation

Abstract

This study investigated the impacts of successive simulated droughts and floods on two plant species (Carex lurida and Liriope muscari) commonly installed in green-infrastructure (GI) sites built in the urban northeast USA. The instantaneous stomatal conductance, and belowground biomass growth (in a second drought experiment only) were used as metrics, since they are indicators of the ability of plants to provide ecosystem functions such as transpiration and carbon uptake. The results indicate that both species have greater tolerance for floods than for droughts. Signs of stress were only evident after a simulated flood exceeding the duration of 95% of all storms that occurred in this geographic region between 1950 and 2000. By contrast, simulated droughts had a more pronounced effect on both the instantaneous conductance measures during drought and the recovery following the cessation of drought in both species. Liriope subjected to drought treatments were all able to recover and to re-establish stomatal conductance levels similar to those displayed by a control group even after repeated drought treatments. By contrast, Carex showed reduced recovery after multiple droughts, in two separate rounds of experiments. However, regardless of moisture conditions and treatment, Carex generally displayed higher stomatal conductance than Liriope, indicating greater transpiration, and CO2 uptake than Liriope. The belowground biomass results supported this finding, i.e. Carex gained more belowground biomass than Liriope during all experiments. At the end of the experiment, the Carex subjected to drought had less than one sixth the belowground biomass of the control treatment, whereas for Liriope this ratio was only 50% (drought to control). The drought treatments, therefore, reduced the biomass of Carex more than it did Liriope, when compared to the respective control plants. Nonetheless, both species survived repeated cycles of droughts and floods, suggesting that these particular species are both likely suitable for use in GI facilities, despite projected future increases in the frequency and intensity of floods and droughts in this geographic region. From a practical perspective, the results suggest no need for irrigation or potential replacement of plants in GI systems in a changed climate.