Salt Marsh Plant Community Structure Influences Success of Avicennia germinans During Poleward Encroachment

Abstract

Along the Florida coast, decreasing freeze events are promoting the range shift of the mangrove species Avicennia germinans northward into temperate salt marsh wetlands. Although plant species’ ranges are tightly linked with their climatic tolerances, there is considerable variability in the magnitude by which biotic factors like competition and facilitation may also influence range shifts. Changes in mangrove and marsh plant abundance can alter both the above and belowground environment, which may in turn influence ecosystem services typically associated with these systems such as storm surge abatement and carbon storage. Therefore, it is key to understand (1) how the above and belowground environment of established salt marshes influences establishment of mangroves, and (2) how above and belowground environments shift in response to mangrove encroachment. Using a semi-natural mangrove planting experiment, we investigated the impact of four distinct marsh plant community structures ( Batis maritima, Spartina alterniflora , mixture of B. maritima and S. alterniflora , mudflat) on mangrove survivorship and decomposition rate. In mixed marsh plots, mangrove survivorship was 42 % higher compared to survivorship in mudflat plots, and decomposition rate was 47 % greater in mixed marsh plots compared to mudflat. However, percent cover of vegetation differed across treatments, and was highest in mixed marsh plots. High survivorship in mixed marsh plots is likely due to increased protection from physical stressors by the dense aboveground cover, and belowground plant root-driven effects such as nutrient availability and oxygen delivery. Our findings suggest that above and below ground differences in salt marsh plant community structure can have an impact on the survival of encroaching mangroves, which may have implications for predicting future mangrove encroachment and improving mangrove restoration techniques.

Warming drives poleward range contractions of Beringian endemic plant species at high latitudes

“…That is, for some species, warming presents the opportunity for range expansion with no significant shrinkage at their trailing edges (e.g. Adgie & Chapman, 2021; Bebber et al, 2013; Parmesan et al, 1999), whereas other species are tracking cooler climates; shrinking on the trailing edge and advancing on the leading edge (e.g. Brito‐Morales et al, 2018; Kuhn & Gégout, 2019; Lesica & McCune, 2004).…”

Using vulnerability assessment to characterize coastal protection benefits provided by estuarine habitats of a dynamic intracoastal waterway

“…Overall, results suggest that current estuarine habitats offer the lowest levels of coastal protection in the north Reserve. The image classification techniques employed by this study to characterize the current distribution of estuarine habitats indicate that mangroves are less abundant in the northern section of the Reserve, perhaps due to slower infill or different marsh vegetation ( Adgie & Chapman, 2021 ). Consequently, fewer biogenic habitats (especially mangroves and oyster beds) are distributed throughout this area to buffer wave action ( Figs.…”

Coastal Wetland Soil Carbon Storage at Mangrove Range Limits in Apalachicola Bay, FL: Observations and Expectations

“…However, we also hypothesize that the regional-scale findings of no difference between vegetation type are not necessarily at odds with the global findings that there is a difference. Both "within site" lateral expansion and mangrove poleward range expansion are forecasted to continue (Chapman et al, 2021), facilitated by warming (Coldren et al, 2019;Sturchio et al, 2021), especially at their poleward range limit (Chapman et al, 2021), decreased frequency of damaging or mortality-inducing freezes (Cavanaugh et al, 2014), and the availability of optimal abiotic characteristics, often mediated by saltmarsh vegetation (i.e., Adgie and Chapman, 2021). Though the regional data do not yet support the claim that mangrove encroachment of saltmarshes will increase blue C storage (Table 3 and Supplementary Table 1), there is context to surmise that these comparisons will change as mangrove range expansion continues.…”