Scaling mangrove aboveground biomass from site‐level to continental‐scale

Feher

Griffith

et al. 2017

Ecological Monographs

230

204

Mangrove forests are highly productive tidal saline wetland ecosystems found along sheltered tropical and subtropical coasts. Ecologists have long assumed that climatic drivers (i.e., temperature and rainfall regimes) govern the global distribution, structure, and function of mangrove forests. However, data constraints have hindered the quantification of direct climate–mangrove linkages in many parts of the world. Recently, the quality and availability of global‐scale climate and mangrove data have been improving. Here, we used these data to better understand the influence of air temperature and rainfall regimes upon the distribution, abundance, and species richness of mangrove forests. Although our analyses identify global‐scale relationships and thresholds, we show that the influence of climatic drivers is best characterized via regional range‐limit‐specific analyses. We quantified climatic controls across targeted gradients in temperature and/or rainfall within 14 mangrove distributional range limits. Climatic thresholds for mangrove presence, abundance, and species richness differed among the 14 studied range limits. We identified minimum temperature‐based thresholds for range limits in eastern North America, eastern Australia, New Zealand, eastern Asia, eastern South America, and southeast Africa. We identified rainfall‐based thresholds for range limits in western North America, western Gulf of Mexico, western South America, western Australia, Middle East, northwest Africa, east central Africa, and west‐central Africa. Our results show that in certain range limits (e.g., eastern North America, western Gulf of Mexico, eastern Asia), winter air temperature extremes play an especially important role. We conclude that rainfall and temperature regimes are both important in western North America, western Gulf of Mexico, and western Australia. With climate change, alterations in temperature and rainfall regimes will affect the global distribution, abundance, and diversity of mangrove forests. In general, warmer winter temperatures are expected to allow mangroves to expand poleward at the expense of salt marshes. However, dispersal and habitat availability constraints may hinder expansion near certain range limits. Along arid and semiarid coasts, decreases or increases in rainfall are expected to lead to mangrove contraction or expansion, respectively. Collectively, our analyses quantify climate–mangrove linkages and improve our understanding of the expected global‐ and regional‐scale effects of climate change upon mangrove forests.

Section: Discussionmentioning

confidence: 99%

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

Feher

Griffith

et al. 2017

Ecological Monographs

230

204

“…Across precipitation gradients that span the transition from humid to arid climates, there is often: (a) a decrease in the coverage of coastal wetland plants (Bucher & Saenger, ; Gabler et al, ; Longley, ; Montagna, Gibeaut, & Tunnell, ; Osland et al, ; Osland, Feher, et al, ); (b) a decrease in coastal wetland plant canopy height (Feher et al, ; Gabler et al, ; Lot‐Helgueras, Vázquez‐Yanes, & Menéndez, ; Méndez‐Alonzo, López‐Portillo, & Rivera‐Monroy, ); (c) a decrease in aboveground biomass (Gabler et al, ; Hutchison, Manica, Swetnam, Balmford, & Spalding, ; Rovai et al, ); and (d) a shift in coastal wetland plant functional group dominance, from plant communities dominated by graminoid and/or mangrove plants to plant communities dominated by succulent salt marsh plants and/or microbial mats (i.e., wetlands that lack vascular plants; unvegetated salt flats) (Gabler et al, ; Saenger, ; Yando et al, ).…”

Section: Discussionmentioning

confidence: 99%

Climate and plant controls on soil organic matter in coastal wetlands

Gabler

Grace

et al. 2018

Global Change Biology

122

Coastal wetlands are among the most productive and carbon-rich ecosystems on Earth. Long-term carbon storage in coastal wetlands occurs primarily belowground as soil organic matter (SOM). In addition to serving as a carbon sink, SOM influences wetland ecosystem structure, function, and stability. To anticipate and mitigate the effects of climate change, there is a need to advance understanding of environmental controls on wetland SOM. Here, we investigated the influence of four soil formation factors: climate, biota, parent materials, and topography. Along the northern Gulf of Mexico, we collected wetland plant and soil data across elevation and zonation gradients within 10 estuaries that span broad temperature and precipitation gradients. Our results highlight the importance of climate-plant controls and indicate that the influence of elevation is scale and location dependent. Coastal wetland plants are sensitive to climate change; small changes in temperature or precipitation can transform coastal wetland plant communities. Across the region, SOM was greatest in mangrove forests and in salt marshes dominated by graminoid plants. SOM was lower in salt flats that lacked vascular plants and in salt marshes dominated by succulent plants. We quantified strong relationships between precipitation, salinity, plant productivity, and SOM. Low precipitation leads to high salinity, which limits plant productivity and appears to constrain SOM accumulation. Our analyses use data from the Gulf of Mexico, but our results can be related to coastal wetlands across the globe and provide a foundation for predicting the ecological effects of future reductions in precipitation and freshwater availability. Coastal wetlands provide many ecosystem services that are SOM dependent and highly vulnerable to climate change. Collectively, our results indicate that future changes in SOM and plant productivity, regulated by cascading effects of precipitation on freshwater availability and salinity, could impact wetland stability and affect the supply of some wetland ecosystem services.

“…Macroclimatic variables such as temperature and precipitation are important in controlling the distribution, abundance and diversity of mangroves (Duke et al, ; Hutchison, Manica, Swetnam, Balmford, & Spalding, ; Rovai et al, ). In the case of temperature, it appears that extremes (e.g.…”

Section: Discussionmentioning

confidence: 99%

“…This is not to say that temperature and precipitation are unimportant in these regions. Mangrove species richness near each of these range limit regions is strongly correlated with temperature or precipitation (Osland, Day, et al, ), and global mangrove biomass is correlated with both of these climatic factors (Hutchison et al, ; Rovai et al, ). Rather, it is possible that there is an interaction between climate and dispersal limitation at these range limits.…”

Section: Discussionmentioning

confidence: 99%

Sensitivity of mangrove range limits to climate variability

Cavanaugh

Bardou

et al. 2018

Global Ecol Biogeogr

Aim Correlative distribution models have been used to identify potential climatic controls of mangrove range limits, but there is still uncertainty about the relative importance of these factors across different regions. To provide insights into the strength of climatic control of different mangrove range limits, we tested whether temporal variability in mangrove abundance increases near range limits and whether this variability is correlated with climatic factors thought to control large‐scale mangrove distributions. Location North and South America. Time period 1984–2011. Major taxa studied Avicennia germinans, Avicennia schuaeriana, Rhizophora mangle, Laguncularia racemosa. Methods We characterized temporal variability in the enhanced vegetation index (EVI) at mangrove range limits using Landsat satellite imagery collected between 1984–2011. We characterized greening trends at each range limit, examined variability in EVI along latitudinal gradients near each range limit, and assessed correlations between changes in EVI and temperature and precipitation. Results Spatial variability in mean EVI was generally correlated with temperature and precipitation, but the relationships were region specific. Greening trends were most pronounced at range limits in eastern North America. In these regions variability in EVI increased toward the range limit and was sensitive to climatic factors. In contrast, EVI at range limits on the Pacific coast of North America and both coasts of South America was relatively stable and less sensitive to climatic variability. Main conclusions Our results suggest that range limits in eastern North America are strongly controlled by climate factors. Mangrove expansion in response to future warming is expected to be rapid in regions that are highly sensitive to climate variability (e.g. eastern North America), but the response in other range limits (e.g. South America) is likely to be more complex and modulated by additional factors such as dispersal limitation, habitat constraints, and/or changing climatic means rather than just extremes.