Sensitivity of mangrove range limits to climate variability

Abstract

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.

Temperature thresholds for black mangrove (Avicennia germinans) freeze damage, mortality and recovery in North America: Refining tipping points for range expansion in a warming climate

“…How do these thresholds compare to those for other mangrove species on other continents? The freezing temperatures affecting mangroves in the southeastern United States are the coldest temperatures reported globally; thus, the northern range limit of A. germinans in eastern and central North America is the coldest mangrove range limit in the world (Cavanaugh et al, ; Lovelock et al, ; Osland, Feher, et al, ; Stuart et al, ). Temperature thresholds for other mangroves near poleward range limits on other continents are expected to be warmer than the thresholds identified here.…”

“…Winter temperatures greatly influence the ecological structure, function and distribution of mangrove forests in North America, Asia, Australia, New Zealand, South Africa and eastern South America; however, the ecological influence of winter temperature extremes (i.e. discrete freezing and/or chilling events) is strongest in eastern and central North America (Cavanaugh et al, 2018;Lovelock, Krauss, Osland, Reef, & Ball, 2016;Osland, Feher, et al, 2017;Stuart, Choat, Martin, Holbrook, & Ball, 2007). In North America, the black mangrove (Avicennia germinans; hereafter, black mangrove or A. germinans) is the most freeze-tolerant mangrove species.…”

Is the central‐marginal hypothesis a general rule? Evidence from three distributions of an expanding mangrove species, Avicennia germinans (L.) L

“…Mangrove abundance and species richness decrease towards poleward range limits, as climatic variables (i.e., temperature, precipitation) become more marginal (Osland, Feher, et al, ). Range cores generally remain stable, unless impacted by stochastic weather events (e.g., Smith, Robblee, Wanless, & Doyle, ) or anthropogenic changes (Valiela, Bowen, & York, ); whereas range limits are highly mobile due to climatic thresholds specific to individual geographic regions (Cavanaugh et al, ; Osland, Feher, et al, ).…”

“…Although these three coastlines share many commonalities, there is a strong dichotomy between climatic factors controlling mangrove distributions in Texas compared to neighbouring Louisiana, and to Florida. Mangrove abundance and distributional limits in Florida and Louisiana are controlled by latitudinal gradients in minimum winter temperatures, whereas inverse latitudinal gradients in both minimum temperatures and precipitation control mangroves across Texas (Cavanaugh et al, ; Osland, Feher, et al, ) (Appendix details this climatic information). Mangroves in the USA are most abundant in South Florida (with an assemblage of three principal species), transition into a mangrove‐salt marsh ecotone along both Florida coastlines, and are eventually replaced by salt marsh as freeze events become more common (Kangas & Lugo, ) (Figure a,b).…”

“…Southern range core mangroves are relatively stable in Florida (but see Ross, Ruiz, Sah, & Hanan, ; Zhang, Thapa, Ross, & Gann, ) and Texas (but see Lonard & Judd, ) compared to highly‐mobile range margins (Cavanaugh et al, ). Periodic extreme freeze events lead to declines in mangrove cover at USA range margins and a cyclical pattern of expansion and contraction over time across the region (Giri & Long, ; Osland, Day, et al, ; Rodriguez, Feller, & Cavanaugh, ; Rogers & Krauss, ).…”