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Climatic controls on the global distribution,
abundance, and species richness of mangrove
forests
Michael Osland
United States Geological Survey
Laura Feher
United States Geological Survey
Kereen Gri!th
United States Geological Survey
Kyle Cavanaugh
University of California, Los Angeles
Nicholas Enwright
United States Geological Survey
See next page for additional authors
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Climatic controls on the global distribution, abundance, and species
richness of mangrove forests
Abstract
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Disciplines
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Publication Details
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Authors
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1
Climatic controls on the global distribution, abundance,
and species richness of mangrove forests
MICHAEL J. OSLAND,
1,5
LAURA C. FEHER,
1
KEREEN T. GRIFFITH,
2
KYLE C. CAVANAUGH,
3
NICHOLAS M. ENWRIGHT,
1
RICHARD H. DAY,
1
CAMILLE L. STAGG,
1
KEN W. KRAUSS,
1
REBECCA J. HOWARD,
1
JAMES B. GRACE,
1
AND KERRYLEE ROGERS
4
1
Wetland and Aquatic Research Center, U.S. Geological Survey, Lafayette, Louisiana 70506 USA
2
Griffith Consulting Services, U.S. Geological Survey, Lafayette, Louisiana 70506 USA
3
Department of Geography, University of California, Los Angeles, Los Angeles, California 90095 USA
4
School of Earth and Environmental Sciences, University of Wollongong, Wollongong, New South Wales 2522 Australia
Abstract. 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 avail-
ability 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 distri-
bution, 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 lim-
its. 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.
Key words: abundance; climate change; climate gradients; climatic drivers; climatic thresholds;
distribution; ecological thresholds; mangrove forests; rainfall; range limit; species richness; temperature.
INTRODUCTION
Ecologists have long been interested in the influence of
climatic drivers (e.g., temperature and precipitation
regimes) upon the global distribution, abundance, and
diversity of ecosystems (Holdridge 1967, Whittaker 1970,
Woodward 1987). Climate- focused ecological research
and distribution modeling have been particularly useful
for elucidating climatic controls on ecosystem structure
and function (Whittaker 1960, Churkina and Running
1998, Jobbágy and Jackson 2000, Dunne et al. 2004,
Guisan and Thuiller 2005, Elith and Leathwick 2009).
Within the context of climate change, studies of the
ecological effects of climatic drivers are especially
important because they can help scientists and environ-
mental managers better anticipate and prepare for the
ecological consequences of changing climatic conditions
(Glick et al. 2011, Stein et al. 2014). In addition to
improved understanding of the influence of changing
mean climatic conditions, there is a pressing need to
advance understanding of the ecological implications of
changes in the frequency and intensity of climatic
extremes (e.g., freezing, drought, flooding; Jentsch et al.
2007, Smith 2011, IPCC 2013, Hoover et al. 2014).
In this study, we examined the influence of climatic
drivers upon the distribution, abundance, and species
Ecological Monographs, 0(0), 2016, pp. 1–19
© 2016 by the Ecological Society of America
Manuscript received 27 May 2016; revised 23 November 2016;
accepted 14 December 2016. Corresponding Editor: Aimée T.
Classen.
5
E-mail: mosland@usgs.gov
2
Ecological Monographs
Vol. 0, No. 0
MICHAEL J. OSLAND ET AL.
richness of mangrove forests. Mangrove forests are
freeze- sensitive tidal saline wetland ecosystems located
along sheltered tropical and subtropical coasts across the
world (Tomlinson 1986, Woodroffe and Grindrod 1991,
Saenger 2002, Alongi 2009, Spalding et al. 2010, Twilley
and Day 2012). Mangrove forests support ecosystem
goods and services that have been valued at up to
US$194 000·ha
−1
·yr
−1
(Costanza et al. 2014). In addition
to providing fish and wildlife habitat, mangrove forests
protect coastlines, support coastal fisheries, store carbon,
provide timber, improve water quality, and provide rec-
reational opportunities (Ewel et al. 1998, Barbier et al.
2011, Lee et al. 2014).
Despite the tremendous ecological and societal value
of mangrove forests, the influence of climatic drivers on
mangrove forest distribution, structure, and function has
not been well quantified in many parts of the world. The
mangrove literature contains many valuable observa-
tions and well- articulated hypotheses regarding the
influence of temperature and rainfall regimes on the
distribution, abundance, and diversity of mangrove
forests (e.g., Davis 1940, Lugo and Patterson- Zucca
1977, West 1977, Woodroffe and Grindrod 1991, Duke
et al. 1998, Saenger 2002, Ross et al. 2009, Saintilan et al.
2009, 2014, Asbridge et al. 2015). Unfortunately, a lack
of relevant and easily accessible climate and/or ecological
data has meant that many of these relationships have not
been fully tested or quantified. Data constraints have
sometimes resulted in the use of the best- available
surrogate variables. For example, latitude and sea surface
temperatures have often been used as proxies for winter
air temperature extremes (e.g., Woodroffe and Grindrod
1991, Duke 1992, Twilley et al. 1992, Saenger and
Snedaker 1993, Ellison 2002, Alongi 2009, Twilley and
Day 2012), sea surface temperatures have been used
instead of rainfall (e.g., Duke 1992, Duke et al. 1998), and
mean monthly air temperatures have been used as proxies
for extreme minimum daily air temperatures (e.g.,
Quisthoudt et al. 2012, Record et al. 2013, Hutchison
et al. 2014, Jardine and Siikamäki 2014, Rovai et al. 2016,
Ximenes et al. 2016). Although these surrogate variables
are helpful for showing that general relationships are
present, the use of proxies can potentially be misleading
without adequate discussion and characterization of the
relevant physiological mechanisms responsible. Using
proxies also makes it difficult to identify ecologically rel-
evant climatic thresholds, which are needed to anticipate
and prepare for future change.
In recent years, the quality and availability of global-
scale climate and mangrove distribution data have been
improving (Polidoro et al. 2010, Spalding et al. 2010, Giri
et al. 2011, Osland et al. 2013, Cavanaugh et al. 2014,
Armitage et al. 2015). As a result, there is potential to
more directly quantify the influence of climatic controls
upon mangrove forests. In this study, we used recent
climate and mangrove ecological data to investigate the
following questions: (1) at the global and regional range
limit scale, how do air temperature and rainfall regimes
influence the distribution, abundance, and species
richness of mangrove forests; (2) given the historic
emphasis on sea surface temperatures in portions of the
mangrove ecological literature, what are the linkages
between sea surface temperatures, air temperatures, and
rainfall regimes; and (3) how and where is climate change,
in the form of warmer air temperatures and altered
rainfall regimes, expected to affect the distribution, abun-
dance, and diversity of mangrove forests?
Although sea surface temperatures are often used to
describe the global distribution of mangroves, we postu-
lated that minimum air temperature and mean annual
precipitation regimes are more directly relevant vari-
ables, and that these two climatic variables would be
tightly correlated to sea surface temperatures. These
hypotheses stem from a literature review of mangrove
range limits across the world (Table 1). Mangrove forests
are highly sensitive to freezing and chilling temperatures,
which can lead to mortality and/or damage (Lugo and
Patterson- Zucca 1977, Woodroffe and Grindrod 1991,
Stuart et al. 2007, Lovelock et al. 2016). Our literature
review identifies range limits near transitions zones
between tropical and temperate climates where man-
grove ecologists have noted that winter air temperatures
play an important ecological role (in Table 1, see range
limits with temperature minima included as a driver). In
addition to air temperature extremes (i.e., freeze events),
mangrove mortality and/or damage can also be induced
by hypersaline conditions, which are most common and
intense along arid and semiarid coasts (Saenger 2002,
Saintilan et al. 2009, Semeniuk 2013, Asbridge et al. 2015,
Lovelock et al. 2016). Our review identifies range limits
near transition zones between arid and humid climatic
zones where ecologists have noted that precipitation
regimes and hypersaline conditions play an important
ecological role (in Table 1, see range limits with rainfall
included as a driver). Throughout the manuscript, we use
the terms rainfall and precipitation interchangeably, as
mangroves are not present in regions with large amounts
of colder forms of precipitation (e.g., snow or sleet).
We hypothesized that climatic thresholds associated
with temperature and rainfall would be lower for man-
grove presence than for abundance and/or species richness
because mangrove individuals can be present in physically
stressful regions (i.e., colder and/or more arid regions)
without being abundant or species rich (Fig. 1). For
example, along the northern Gulf of Mexico coast, there
are three common mangrove species. Within the coldest
coastal reaches that contain mangroves, only isolated
individuals of the most freeze- tolerant species (Avicennia
germinans) are present (in these areas, mangroves are
present but not abundant or species rich). In contrast,
where the frequency and intensity of temperature extremes
decreases, all three species (A. germinans, Rhizophora
mangle, and Laguncularia racemosa) can be present (in
these areas, mangrove forests are present, abundant, and
species rich). We expected similar patterns in presence,
abundance, and richness to occur at all range limits.
XXX 2016 3CLIMATIC CONTROLS ON MANGROVE FORESTS
We also expected that global- and regional- scale
linkages between climatic conditions and mangroves
would be well characterized by nonlinear sigmoidal equa-
tions with abrupt ecological thresholds across climatic
gradients (Osland et al. 2016). We anticipated that dif-
ferent regional range limits would have different climatic
regimes, and that the role of extreme events (e.g., freeze
events) would be particularly important in certain
regional range limits. For example, mangrove range
limits in eastern North America and eastern Australia
have different winter air temperature regimes. In eastern
North America, winter air temperature extremes are
approximately 12°C colder than in eastern Australia;
however, annual mean winter air temperatures in eastern
North America are occasionally warmer than in eastern
Australia. Stuart et al. (2007) noted that, due to these
different temperature regimes, mangroves in eastern
North America have different growth rates, xylem vessel
diameters, and temperature sensitivities compared to
their counterparts in eastern Australian. Winter air tem-
perature and precipitation regimes greatly influence man-
grove physiology (Clough 1992, Lovelock et al. 2016),
and observations in the literature indicate that freeze and
drought sensitivity are range limit dependent (Table 1).
Hence, we expected that climatic thresholds for man-
grove presence, abundance, and species richness would
be range limit specific (i.e., lower in some range limits and
higher in others).
METHODS
Study area
We first created a seamless global grid of cells with a
resolution of 0.5° (i.e., ~50 km at the equator). Next, we
created polylines representing coastlines using the
perimeter of the Shuttle Radar Topographic Mission
(SRTM) v4.1 global digital elevation model data at a
resolution of 250 m (Reuter et al. 2007). We used these
coastline polylines to identify and retain cells that inter-
sected the coast. We excluded 192 227 cells that did not
intersect the coast. To avoid cells with minimal potential
coastal wetland habitat, we used the SRTM raster data
to remove an additional 1056 coastal cells that contained
less than or equal to 5% coverage of land. We also
removed 176 cells that did not have suitable climate data;
most of these cells were removed because they either did
not have minimum air temperature data (i.e., no values
at all) or they had unrealistic low or high minimum air
temperature data relative to their neighboring cells.
Collectively, these steps produced a grid (hereafter,
study grid) that contained a total of 4908 cells at a reso-
lution of 0.5°.
TABLE 1. The 14 mangrove distributional range limits evaluated in this study.
Range limit name Hypothesized climatic driver Literature sources for hypothesized climatic driver
Eastern North America (1) temperature minima West (1977), Osland et al. (2013), Cavanaugh et al. (2014)
Western Gulf of Mexico (2) rainfall and temperature minima Lot- Helgueras et al. (1975), Montagna et al. (2011),
Osland et al. (2016)
Western North America (3) rainfall and temperature minima Felger et al. (2001), Turner et al. (2005)
Western South America (4) rainfall (D&H) West (1977), Woodroffe and Grindrod (1991),
Saintilan et al. (2014)
Eastern South America (5) temperature minima (D&H) Schaeffer- Novelli et al. (1990), Soares et al. (2012),
Ximenes et al. (2016)
Northwest Africa (6) rainfall Woodroffe and Grindrod (1991), Saenger (2002),
Spalding et al. (2010)
West central Africa (7) rainfall Woodroffe and Grindrod (1991), Saenger (2002),
Spalding et al. (2010)
Southeast Africa (8) temperature minima (D&H) Macnae (1963), Saenger (2002), Quisthoudt et al. (2012)
East central Africa (9) rainfall Saenger (2002), Spalding et al. (2010)
Middle East (10) rainfall and temperature minima Saenger (2002), Spalding et al. (2010)
Eastern Asia (11) temperature minima Chen et al. (2010), Wang et al. (2011)
New Zealand (12) temperature minima Woodroffe and Grindrod (1991), Morrisey et al. (2010)
Eastern Australia (13) temperature minima (D&H) Saenger (2002), Duke (2006), Stuart et al. (2007),
Saintilan et al. (2014),
Western Australia (14) rainfall and temperature minima (D&H) Saenger (2002), Duke (2006), Semeniuk (2013)
Notes: These range limits are illustrated in Fig. 2, and the numbers in parentheses correspond to the numbers in that figure. In
the climatic driver column, (D&H) indicates that dispersal constraints and/or lack of potential habitat are also expected to influence
mangrove distributions near that range limit.
FIG. 1. A generalized illustration of the hypothesized
relationships between climatic drivers and mangrove forest
presence, abundance, and species richness. The climatic drivers
examined in this study include minimum air temperature and
mean annual precipitation.
