Sea level rise (SLR) impacts coastal vegetation communities by increasing salinity and inundation, but there are few simple and accurate methods to quantify the spatial range of the SLR impact on vegetation. Quantifying the spatial range of the SLR impact is important in ecological conservation. For example, it can be used to determine the location and size of natural reservoirs.
In our study, SLR impact on vegetation was estimated by using leaf carbon isotope composition (δ13C) which increases with a greater growth stress associated with SLR. The leaf δ13C, as vegetation response to SLR, was incorporated into a coupled hydrology-vegetation simulation model, MANHAM, which projects effects of soil salinity on halophyte-glycophyte competition, to quantify spatial range of the SLR impacts. Our modelling approach described an innovative method of using small-scale leaf physiology response to estimate large-scale vegetation community change by SLR impacts. The connection between the two-scale dynamics is established by soil salinity effects on leaf stomas and leaf δ13C response to leaf stomas. In detail, higher salinity effect can decrease the opening of stomas, then the decreased opening leads to higher leaf δ13C values. On the basis of the interaction among salinity, stomas and leaf δ13C, we proposed a new version of MANHAM, called stoma-isotope based MANHAM, to quantify spatial range of SLR impacts. In addition, we applied the model to a stressed pine forest (loblolly pine, Pinus taeda) bordering the estuary of Waccamaw River in South Carolina. We sampled leaf, stem, soil and surface water samples along a transect from riverside (exposing to salinity stress) to inland areas (low salinity stress), and the leaf δ13C responses along the above transect with its associated gradient in salinity were simulated by the stoma-isotope based model.
Our study found that: (1) field observation indicate that leaf δ13C values decreased from inland to riverside, (2) the model showed a good agreement with the observed leaf δ13C pattern along the transect, and estimated threshold value of distance to river where the leaf δ13C response to SLR impact disappeared. Based on the same leaf δ13C pattern from both field and model study, our estimated threshold value of SLR impact spatial range can lead to a more informed conservation management.