Life stage influences the resistance and resilience of black mangrove forests to winter climate extremes

Abstract

Abstract. In subtropical coastal wetlands on multiple continents, climate change-induced reductions in the frequency and intensity of freezing temperatures are expected to lead to the expansion of woody plants (i.e., mangrove forests) at the expense of tidal grasslands (i.e., salt marshes). Since some ecosystem goods and services would be affected by mangrove range expansion, there is a need to better understand mangrove sensitivity to freezing temperatures as well as the implications of changing winter climate extremes for mangrove-salt marsh interactions. In this study, we investigated the following questions: (1) how does plant life stage (i.e., ontogeny) influence the resistance and resilience of black mangrove (Avicennia germinans) forests to freezing temperatures; and (2) how might differential life stage responses to freeze events affect the rate of mangrove expansion and salt marsh displacement due to climate change? To address these questions, we quantified freeze damage and recovery for different life stages (seedling, short tree, and tall tree) following extreme winter air temperature events that occurred near the northern range limit of A. germinans in North America. We found that life stage affects black mangrove forest resistance and resilience to winter climate extremes in a nonlinear fashion. Resistance to winter climate extremes was high for tall A. germinans trees and seedlings, but lowest for short trees. Resilience was highest for tall A. germinans trees. These results suggest the presence of positive feedbacks and indicate that climate-change induced decreases in the frequency and intensity of extreme minimum air temperatures could lead to a nonlinear increase in mangrove forest resistance and resilience. This feedback could accelerate future mangrove expansion and salt marsh loss at rates beyond what would be predicted from climate change alone. In general terms, our study highlights the importance of accounting for differential life stage responses and positive feedbacks when evaluating the ecological effects of changes in the frequency and magnitude of climate extremes.

Quantifying how changing mangrove cover affects ecosystem carbon storage in coastal wetlands

“…Our research sites, and much of the western Gulf of Mexico, occupy low-rainfall, microtidal environments that create physiologically stressful, high-salinity conditions as salts accumulate (Zedler 1980), which limits plant productivity and biomass (Zedler 1982, Osland et al 2014. Mangrove aboveground biomass was also likely limited by stressful conditions, consistent with the general pattern that mangrove aboveground biomass tends to decrease towards the latitudinal limits of species ranges (Osland et al 2015). Mangrove aboveground biomass was also likely limited by stressful conditions, consistent with the general pattern that mangrove aboveground biomass tends to decrease towards the latitudinal limits of species ranges (Osland et al 2015).…”

“…Recent mangrove expansion has been particularly widespread in Texas, where mangrove cover has increased 74% since a series of freeze events in the 1980s (Armitage et al 2015). Mangroves are most vulnerable to freeze events near the edge of their range, where prolonged periods of freezing temperatures can cause partial or complete mortality of mangroves and create gradients in mangrove and marsh cover (Guo et al 2013, Osland et al 2015. The impacts on ecosystem structure and function as the proportion in marsh and mangrove cover changes are largely unknown (Guo et al 2017).…”

Climatic controls on the global distribution, abundance, and species richness of mangrove forests

“…Using data for eastern North America, several recent studies have quantified the importance of winter air temperature extremes in governing regional‐scale mangrove distribution and structure (Osland et al. , , , , Cavanaugh et al. , ; Gabler et al., ).…”

Salt marsh‐mangrove ecotones: using structural gradients to investigate the effects of woody plant encroachment on plant–soil interactions and ecosystem carbon pools

“…This ecotonal boundary consists of a dynamic mosaic of salt marsh and mangrove forest patches that is greatly influenced by the frequency and intensity of winter temperature extremes (Osland et al . , ).…”

“…; Osland et al . , , ). To our knowledge, there are only four published studies that have investigated the below‐ground effects of mangrove forest expansion in the northern Gulf of Mexico (Perry & Mendelssohn ; Comeaux, Allison & Bianchi ; Bianchi et al .…”