Article

Roles of climate and functional traits in controlling toothed and untoothed margins

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Abstract

Premise of the study: Leaf-margin state (toothed vs. untoothed) forms the basis of several popular methods for reconstructing temperature. Some potential confounding factors have not been investigated with large data sets, limiting our understanding of the adaptive significance of leaf teeth and their reliability to reconstruct paleoclimate. Here we test the strength of correlations between leaf-margin state and deciduousness, leaf thickness, wood type (ring-porous vs. diffuse-porous), height within community, and several leaf economic variables. Methods: We assembled a trait database for 3549 species from six continents based on published and original data. The strength of associations between traits was quantified using correlational and principal axes approaches. Key results: Toothed species, independent of temperature, are more likely to be deciduous and to have thin leaves, a high leaf nitrogen concentration, a low leaf mass per area, and ring-porous wood. Canopy trees display the highest sensitivity between leaf-margin state and temperature; subcanopy plants, especially herbs, are less sensitive. Conclusions: Our data support hypotheses linking the adaptive significance of teeth to leaf thickness and deciduousness (in addition to temperature). Toothed species associate with the "fast-return" end of the leaf economic spectrum, providing another functional link to thin leaves and the deciduous habit. Accounting for these confounding factors should improve climate estimates from tooth-based methods.

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... Both approaches are extensions of an initial observation by Sinnott (1915, 1916) thatdwhen a flora is considered as a wholedthe form of woody dicot leaves is well correlated with some aspects of climate (see also Wolfe, 1971). Although some authors have recently questioned the causal relationships behind these correlations (e.g., Little et al., 2010;Peppe et al., 2011;Royer et al., 2012), temperature estimates made using leaf traits in fossil floras show general agreement with those derived from other palaeoclimate indicators, such as oxygen isotopes (e.g., Fricke and Wing, 2004;Kennedy et al., 2002), which reaffirms the utility of the approach. From initial observations of leaf form-climate correlations, two approaches to using physiognomy-climate relationships for palaeoclimate reconstruction have emerged. ...
... The parameters of the resulting regression lines vary depending on the number of sample sites, number of species recorded at each sample site, and geographic region, although the relative roles of these variables have not been parsed. Royer et al. (2012) reported that the presence of leaf teeth in individual species is linked with a variety of functional traits only indirectly related to climate and questioned the precision of climate estimation methods based on leaf margin. Similarly, Jordan (1997) noted that species of the Myrtaceae do not form leaf teeth even when growing in cold climates. ...
... An abundance of species in this family in a particular biogeographic region might skew MAT reconstructions based on margin character. Other leaf functional traits such as deciduousness, position in the canopy, gas exchange and hydraulic control may also influence the parameters measured to develop climate interpretations from leaves and thus confound climate interpretations ( Peppe et al., 2011;Royer, 2012;Royer et al., 2012). Royer (2012) went so far as to suggest a blanket ± 5 C uncertainty be applied to all leaf-based MAT reconstructions to accommodate these variables. ...
Article
The Soap Wash flora from the Cedar Mountain Formation of Emery County, Utah (Albian-Cenomanian bbuildary) consists almost entirely of angiosperms and is positioned Stratigraphically near the first appearance of flowering plants in this region. We applied both univariate (leaf margin analysis LMA, and leaf area analysis-LAA) and multivariate (Climate Leaf Analysis Multivariate Program CLAMP) methods to the 17 morphotypes recognized in the flora to reconstruct palaeoclimate. LMA produced a mean annual temperature (MAT) estimate ranging from 19 degrees C to 26 degrees C. CLAMP yielded 16 degrees C-18 degrees produced a mean annual precipitation (MAP) of 81 cm, while CLAMP generated a mean growing season precipitation of 134-187 cm, within the range of standard error for the LAA estimation. CLAMP also estimated a nine to ten month growing season with some temperature seasonality and substantial seasonality in precipitation. This reconstruction is broadly consistent with sedimentological data that suggested a semiarid to monsoonal precipitation regime for the region and with climate models that predict warm summers and strong winter seasonality in precipitation. Leaf physiognomic parameters of the Soap Wash flora fall within the range of variation circumscribed by the calibration sets of all three methods, so the differences in reconstructed MAT values cannot be explained exclusively by this kind of systematic error. We propose two alternative hypotheses: First, modern leaf form-climate relationships may not yet have evolved. This seems unlikely because CLAMP has been successfully applied to older material elsewhere. Second, the Soap Wash flora may be out of equilibrium with its prevailing climate due to contemporaneous rapid climate flux. If correct, this pattern may suggest a link between mid-Cretaceous environmental perturbations and the rapid diversification and geographic spread of flowering plants.
... On a global scale, Royer et al. (2012) used phylogenetically unstructured analyses of a pool of 3549 species to show that the fraction of woody species with toothed leaf margins decreases sharply with leaf thickness, and that-aft er controlling for mean annual temperature-species with toothed leaf margins are more likely to be deciduous and have thin leaves, high leaf N content, a low leaf mass per unit area, and ring-porous wood. Th e fi rst fi nding provides strong evidence for the support-supply hypothesis (see above). ...
... Th e latter fi ndings are consistent with the leaf economics spectrum ( Wright et al., 2004 ) and the functional integration of photosynthetic rate with stomatal conductance, transpiration rate, stem hydraulic conductance, xylem diameter, and wood density ( Wong et al., 1979 ;Bucci et al., 2004 ;Santiago et al., 2004 ). In contrast to the data for woody species, Royer et al. (2012) found no signifi cant latitudinal shift in the fraction of herbaceous species with toothed leaf margins. Royer et al. (2009) used phylogenetically structured analyses to show that the fraction and abundance of toothed woody species increase signifi cantly in moving from ridges to riparian habitats and from shallow to deep soils across 100 sites in Australian subtropical notophyll vine rainforest (their table 4, fi g. 6 ). ...
... Hydathodal teeth may thus be adaptive for cold temperate plants seeking to refi ll freeze-thaw embolisms ( Edwards et al., 2016 ). Toothed leaves are signifi cantly associated with ring-porous wood ( Royer et al., 2012 ), whose wide vessels can easily embolize during frosts or drought; entire margins are associated with diff use-porous wood with narrower vessels less susceptible to cavitation. However, large numbers of tropical plants possess hydathodes ( Roth, 1990 ), many arctic and alpine shrubs exposed to frequent frost lack teeth of any kind ( Bailey and Sinnott, 1916 ), species with toothed leaves oft en do not produce root pressure ( Edwards et al., 2016 ), most temperate plants produce root pressure only briefl y before the buds FIGURE 3 Leaf thickness and marginal type superimposed on the Qian-Jin molecular angiosperm phylogeny ( Qian and Jin, 2015 ), showing repeated evolution of thin leaves with non-entire margins. ...
Article
Premise of the study: A recent commentary by Edwards et al. (Am. J. Bot. 103: 975-978) proposed that constraints imposed by the packing of young leaves in buds could explain the positive association between non-entire leaf margins and latitude but did not thoroughly consider alternative explanations. Methods: We review the logic and evidence underlying six major hypotheses for the functional significance of marginal teeth, involving putative effects on (1) leaf cooling, (2) optimal support and supply of the areas served by major veins, (3) enhanced leaf-margin photosynthesis, (4) hydathodal function, (5) defense against herbivores, and (6) bud packing. Key results: Theoretical and empirical problems undermine all hypotheses except the support-supply hypothesis, which implies that thinner leaves should have non-entire margins. Phylogenetically structured analyses across angiosperms, the El Yunque flora, and the genus Viburnum all demonstrate that non-entire margins are indeed more common in thinner leaves. Across angiosperms, the association of leaf thickness with non-entire leaf margins is stronger than that of latitude. Conclusion: We outline a synthetic model showing how biomechanics, hydraulics, vein geometry, rates of leaf expansion, and length of development within resting buds, all tied to leaf thickness, drive patterns in the distribution of entire vs. non-entire leaf margins. Our model accounts for dominance of entire margins in the tropics, Mediterranean scrub, and tundra, non-entire margins in cold temperate deciduous forests and tropical vines and early-successional trees, and entire leaf margins in monocots. Spinose-toothed leaves should be favored in short-statured evergreen trees and shrubs, primarily in Mediterranean scrub and related semiarid habitats.
... This suggests that the leaf teeth-climate relationship observed in modern floras may reflect a combination of plants' responses on both short term (i.e., seasonal) and long term (i.e., evolutionary) time scales and processes of plant community assembly (Schmerler et al. 2012). Plant leaf life-span and leaf thickness also influence the occurrence of leaf teeth as both deciduous species and species with thinner leaves more commonly have teeth than evergreen species and species with thicker leaves (Royer et al. 2012). However, neither plant life-span (i.e., deciduous vs. evergreen) nor leaf thickness correlate strongly with MAT (e.g., Reich et al. 1999;Wright et al. 2004Wright et al. , 2005Royer et al. 2012), indicating that non-climatic factors also play a role in the occurrence of leaf teeth. ...
... Plant leaf life-span and leaf thickness also influence the occurrence of leaf teeth as both deciduous species and species with thinner leaves more commonly have teeth than evergreen species and species with thicker leaves (Royer et al. 2012). However, neither plant life-span (i.e., deciduous vs. evergreen) nor leaf thickness correlate strongly with MAT (e.g., Reich et al. 1999;Wright et al. 2004Wright et al. , 2005Royer et al. 2012), indicating that non-climatic factors also play a role in the occurrence of leaf teeth. The influence of phylogeny, leaf life-span, leaf thickness and other non-climatic factors on leaf physiognomic methods for reconstructing climate is unclear, but may inherently bias paleoclimate estimates (see Royer 2012a for more details). ...
... Significantly, since Wilf (1997), leaf margin type has been classified as toothed or entire (i.e., non-toothed). Although many factors confound the relationship between margin percentage and MAT, as discussed above and reviewed by others (e.g., Greenwood 2007;Jordan 2011;Peppe et al. 2011;Royer 2012a;Royer et al. 2012), the relationship between leaf margin and MAT is typically statistically significant and similar across geographic regions ( Fig. 13.2A). Based on these LMA regressions, LMA has been applied to numerous of Cretaceous and Cenozoic fossil floras to estimate MAT using fossil leaves (see for example studies cited in supplementary materials in Little et al. 2010). ...
Preprint
Full-text available
Plants are strongly influenced by their surrounding environment, which makes them reliable indicators of climate and ecology. The relationship between climate, ecology, plant traits and the geographic distribution of plants based on their climatic tolerances have been used to develop plant-based proxies for reconstructing paleoclimate and paleoecology. These proxies are some of the most accurate and precise methods for reconstructing the climate and ecology of ancient terrestrial ecosystems and have been applied from the Cretaceous to the Quaternary. Despite their utility, the relationships between plant traits and climate that underlie these methods are confounded by other factors such as leaf life-span and phylogenetic history. Work focused on better understanding these confounding factors, incorporating the influence of phylogeny and leaf economic spectrum traits into proxies, expanding modern leaf trait-climate and ecology calibration datasets to additional biogeographic areas and climate regimes, and developing automated computer algorithms for measuring leaf traits are important growing research areas that will help considerably improve plant-based paleoclimate and paleoecological proxies.
... For example, previous studies have indicated different leaf margin-temperature relationships for woody, herbaceous and ferny species. The leaf margin states of woody plants usually respond effectively to the macroenvironment because of the longer lifespan of such plants (Traiser et al., 2005), whereas those of herbaceous and ferny species are often less affected by climate due to their distinct hydraulic conductivity and leaf venation networks (Royer et al., 2012;Peppe et al., 2014). Similarly, Bailey & Sinnott (1916) found different percentages of entire-leaved species among trees, shrubs and herbs, and these percentages varied in tropical and temperate regions. ...
... Similarly, Bailey & Sinnott (1916) found different percentages of entire-leaved species among trees, shrubs and herbs, and these percentages varied in tropical and temperate regions. More recently, Royer et al. (2012) showed that the relationship between leaf margin state and temperature might differ between canopy and subcanopy plants, and this caused noise in the calibration of palaeotemperature. However, differences in the geographical patterns of leaf margin state and their relationship with climate across woody plant life-forms have rarely been evaluated in eastern Asia (Royer et al., 2012). ...
... More recently, Royer et al. (2012) showed that the relationship between leaf margin state and temperature might differ between canopy and subcanopy plants, and this caused noise in the calibration of palaeotemperature. However, differences in the geographical patterns of leaf margin state and their relationship with climate across woody plant life-forms have rarely been evaluated in eastern Asia (Royer et al., 2012). ...
Article
Full-text available
AimLeaf margin states have been found to be strongly related to temperature, and hence have been used to reconstruct palaeotemperatures. Here, we aimed to explore the uncertainties and conditions of use of this technique in China by testing the influences of plant life-form, precipitation and evolutionary history on the relationship between percentage of untoothed species and temperature. LocationChina. Methods Using distribution maps and leaf margin states (untoothed versus toothed) of 10,480 Chinese woody dicots and dated family-level phylogenies, we evaluated the phylogenetic signal of leaf margin state, and demonstrated the variation in the patterns of leaf margin percentage and the relationship with temperature across different life-forms (evergreen and deciduous; trees, shrubs and lianas), regions with different precipitation and species quartiles with different family ages. ResultsSignificant phylogenetic signals were found for the percentage of untoothed species within families. Relationships between leaf margin percentage and temperature were: (1) weak or insignificant for all woody dicots, shrubs, evergreen and deciduous dicots, but strong for trees and lianas; (2) significantly enhanced with increasing precipitation, and (3) significantly weakened for trees belonging to old families. Main conclusionsOur results showed the complete leaf margin spectrum found in China and revealed great uncertainties in its relationship with temperature induced by life-form, precipitation and evolutionary history. These findings suggest that analysis of leaf margins for palaeotemperature reconstruction should be done cautiously: (1) only dicot trees with a relatively young family age can be used and their leaf margin states are more strongly affected by winter cold than by mean annual temperature; (2) the transfer function between leaf margin percentage and temperature is only reliable in humid and semi-humid regions of China.
... This suggests that the leaf teeth-climate relationship observed in modern floras may reflect a combination of plants' responses on both short term (i.e., seasonal) and long term (i.e., evolutionary) time scales and processes of plant community assembly (Schmerler et al. 2012). Plant leaf life-span and leaf thickness also influence the occurrence of leaf teeth as both deciduous species and species with thinner leaves more commonly have teeth than evergreen species and species with thicker leaves (Royer et al. 2012). However, neither plant life-span (i.e., deciduous vs. evergreen) nor leaf thickness correlate strongly with MAT (e.g., Reich et al. 1999;Wright et al. 2004Wright et al. , 2005Royer et al. 2012), indicating that non-climatic factors also play a role in the occurrence of leaf teeth. ...
... Plant leaf life-span and leaf thickness also influence the occurrence of leaf teeth as both deciduous species and species with thinner leaves more commonly have teeth than evergreen species and species with thicker leaves (Royer et al. 2012). However, neither plant life-span (i.e., deciduous vs. evergreen) nor leaf thickness correlate strongly with MAT (e.g., Reich et al. 1999;Wright et al. 2004Wright et al. , 2005Royer et al. 2012), indicating that non-climatic factors also play a role in the occurrence of leaf teeth. The influence of phylogeny, leaf life-span, leaf thickness and other non-climatic factors on leaf physiognomic methods for reconstructing climate is unclear, but may inherently bias paleoclimate estimates (see Royer 2012a for more details). ...
... Significantly, since Wilf (1997), leaf margin type has been classified as toothed or entire (i.e., non-toothed). Although many factors confound the relationship between margin percentage and MAT, as discussed above and reviewed by others (e.g., Greenwood 2007;Jordan 2011;Peppe et al. 2011;Royer 2012a;Royer et al. 2012), the relationship between leaf margin and MAT is typically statistically significant and similar across geographic regions ( Fig. 13.2A). Based on these LMA regressions, LMA has been applied to numerous of Cretaceous and Cenozoic fossil floras to estimate MAT using fossil leaves (see for example studies cited in supplementary materials in Little et al. 2010). ...
Chapter
Full-text available
Plants are strongly influenced by their surrounding environment, which makes them reliable indicators of climate and ecology. The relationship between climate, ecology, plant traits and the geographic distribution of plants based on their climatic tolerances have been used to develop plant-based proxies for reconstructing paleoclimate and paleoecology. These proxies are some of the most accurate and precise methods for reconstructing the climate and ecology of ancient terrestrial ecosystems and have been applied from the Cretaceous to the Quaternary. Despite their utility, the relationships between plant traits and climate that underlie these methods are confounded by other factors such as leaf life-span and phylogenetic history. Work focused on better understanding these confounding factors, incorporating the influence of phylogeny and leaf economic spectrum traits into proxies, expanding modern leaf trait-climate and ecology calibration datasets to additional biogeographic areas and climate regimes, and developing automated computer algorithms for measuring leaf traits are important growing research areas that will help considerably improve plant-based paleoclimate and paleoecological proxies.
... Increased proportions of toothed margins within deciduous taxa have been well documented across a variety of floras in both northern and southern hemispheres (Greenwood et al., 2004;Peppe et al., 2011;Royer et al., 2012). However, it is unclear whether the same factors that encourage deciduous habits (e.g., temperature or greater seasonality driven by either temperature or precipitation, or both) lead to different proportions of toothed margins. ...
... The proposed hypotheses regarding tooth function could apply to any deciduous species with resting buds, including herbaceous species, so why herbaceous species have not been observed to show the same toothed-leaf correlation with cold climates as woody species is puzzling (Bailey and Sinnott, 1916;Royer et al., 2012). Bailey and Sinnott (1916) suggested that nonwoody plants are subject to microhabitats beneath the canopy that decouple them from selection pressures imposed by the broader regional climate. ...
... Bailey and Sinnott (1916) suggested that nonwoody plants are subject to microhabitats beneath the canopy that decouple them from selection pressures imposed by the broader regional climate. Citing the role of teeth in guttation, Royer et al. (2012) postulated that the lower stature of herbaceous plants would render them more sensitive to root pressure damage, thus selecting for increased teeth presence in all mesic environments. Because of Bailey and Sinnott's observation and lower prevalence of herbaceous species in the fossil record, these species have received much less attention in general, especially those in ecosystems other than temperate forests. ...
Article
Premise: The functional significance of leaf margins has long been debated. In this study, we explore influences of climate, leaf lobing, woodiness, and shared evolutionary history on two leaf margin traits within the genus Pelargonium. Methods: Leaves from 454 populations of Pelargonium (161 species) were collected in the Greater Cape Floristic Region and scored for tooth presence/absence and degree of lobing. Tooth density (number of teeth per interior perimeter distance) was calculated for a subset of these. We compared five hypotheses to explain tooth presence and density using mixed effect models. Results: Tooth presence/absence was best predicted by the interaction of leaf lobing and mean annual temperature (MAT), but often in patterns opposite those previously reported: species were more likely to be toothed with warmer temperatures, particularly for unlobed and highly lobed leaves. In contrast, tooth density was best predicted by the interaction of MAT and the season of most rain; density declines with temperature as consistent with expectations, but only in winter-rain dominated areas. Woody and nonwoody species within Pelargonium have similar associations between tooth presence/absence and MAT, contrary to the expectation that patterns within nonwoody species would be insignificant. Conclusions: We conclude Pelargonium leaf margins show predictable responses to climate, but these responses are complex and can contradict those found for global patterns across plant communities.
... Since then, leaf traits have been widely used as proxies for palaeoclimate reconstructions. For example, Leaf Margin Analysis exploits the statistically highly significant negative correlation between frequency of taxa showing toothed leaf margin and mean annual temperature (MAT) (Wolfe and Upchurch 1987;Wilf, 1997;Greenwood et al., 2004;Peppe et al., 2011;Royer et al., 2012). Another approach, the Climate Leaf Analysis Multivariate Program (CLAMP), includes numerous additional correlations between various leaf traits and climate parameters (Wolfe, 1993;Wolfe and Spicer, 1999;Yang et al., 2015). ...
... To demonstrate the potential for analysis of qualitative data, the distribution of leaf margin types was chosen as a first example. The leaf margin, toothed vs. untoothed, is one of the most widely applied plant traits in palaeobotany due to its extensive use as an environmental proxy for MAT Sinnott, 1915, 1916;Wilf, 1997;Greenwood et al., 2004;Su et al., 2010;Hinojosa et al., 2011;Royer et al., 2012). Altogether, approximately 3200 fossil specimens are currently available for determination of leaf margin characters. ...
Article
Full-text available
Morphometric characters of fossil leaves such as size and shape are important and widely used sources for reconstructing palaeoenvironments. Various tools, including CLAMP or Leaf Margin Analysis, utilize leaf traits as input parameters for estimating palaeoclimate, mostly based on correlations between traits and climate parameters of extant plants. During the last few years, the scope of information extracted from the morphology of fossil leaves has been further expanded by including leaf economics, which describe correlations between functional leaf traits and ecological strategies. The amount and quality of available data are essential for a successful palaeoecological analysis utilizing leaf traits. Here, the database MORPHYLL is described. This database is devised to offer a web-based resource for fossil leaf trait data. For this purpose, fossil leaves from various collections were digitized and morphometric traits extracted from leaf outlines. Besides metadata such as accession number, repository, fossil site or taxonomic information (for identified specimens), MORPHYLL offers queries for several morphometric parameters and derived ecophysiological traits (e.g., leaf mass per area). Currently, the database contains data from about 6000 fossil leaves from sites in Central Europe, spanning almost the entire Paleogene and part of the early Neogene. The application potential of the database is demonstrated by conducting some exemplary analyses of leaf traits for the Paleocene, Eocene and Oligocene, with the results indicating changes of mean leaf traits through time. For example, the results show leaf mass per area to peak during the Eocene, which is in accordance with general climate development during the Paleogene.
... While these proxies may not provide the detailed mean annual and seasonal records (growing season precipitation, three wettest month values, three driest month values, etc.) that leaf physiognomy proxies may provide, they rely less on wellpreserved whole-or almost-whole-leaf preservation, and so they can be sampled from more outcrops. It is also now fully appreciated that there are confounding factors in an uncritical application of leaf physiognomy [29][30][31][32][33][34][35][36][37], so we complement those data with additional geochemical analyses to attain a multi-proxy approach in our analysis. ...
... In the PCF, dinosaur skeletal remains are found in numerous bonebeds [5] (Table 3). Though plant diversity was low in the Early Maastrichtian of Northern Alaska [8], a combination of floristic analysis and CLAMP data [36] from both lower latitudes and earlier times allowed Spicer and Herman [11] to estimate a MAT of~6.7 • C at 80 • N for the Maastrichtian (Table 2). Salazar-Jaramillo et al. [41] calculated a MAP from δ 13 C of organic matter from paleosol Bt horizons from one measured section and obtained an average MAP value of 1250 mm year −1 . ...
Article
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The partially correlative Alaskan dinosaur-bearing Prince Creek Formation (PCF), North Slope, lower Cantwell Formation (LCF), Denali National Park, and Chignik Formation (CF), Aniakchak National Monument, form an N–S transect that, together, provides an unparalleled opportunity to examine an ancient high-latitude terrestrial ecosystem. The PCF, 75–85° N paleolatitude, had a Mean Annual Temperature (MAT) of ~5–7 °C and a Mean Annual Precipitation (MAP) of ~1250 mm/year. The LCF, ~71° N paleolatitude, had a MAT of ~7.4 °C and MAP of ~661 mm/year. The CF, ~57° N paleolatitude, had a MAT of ~13 °C and MAP of ~1090 mm/year. The relative abundances of the large-bodied herbivorous dinosaurs, hadrosaurids and ceratopsids, vary along this transect, suggesting that these climatic differences (temperature and precipitation) played a role in the ecology of these large-bodied herbivores of the ancient north. MAP played a more direct role in their distribution than MAT, and the seasonal temperature range may have played a secondary role.
... This trait is therefore widely established in paleoclimate research, either as single parameter in Leaf Margin Analysis or together with other traits in multivariate methods such as Climate Leaf Analysis Multivariate Program (CLAMP) (Wilf, 1997;Wolfe, 1993;Yang et al., 2015). The underlying functionality of this trait is still a matter of debate (Royer and Wilf, 2006), but there is various evidence that leaf teeth are advantageous particularly for deciduous leaves, and, in fact, taxa showing leaf teeth are more often deciduous than evergreens (Li et al., 2016;Royer et al., 2012). Leaf teeth represent sites with high gas exchange, and for various deciduous taxa a start of photosynthetic activity early in spring was shown to occur in leaf teeth, promoting assimilation soon after leaf expansion when the canopy is still quite open (Baker-Brosh and Peet, 1997). ...
Article
Numerous data based on extant vegetation reveal global patterns of relationships between functional leaf traits and climate. Leaf life span (LLS), i.e. evergreen vs. deciduous leaves, represents a central parameter linking functional traits related to the global leaf economics spectrum. Paleogene climate transitions are therefore expected to be reflected by functional leaf traits and leaf economics. In this study, fossil floras from six sites in Central Europe dating back to the Paleocene, late Eocene, Early and Late Oligocene are studied, addressing the following questions: 1) How does leaf economics and LLS change through the Paleogene? 2) How do various functional leaf traits change through the Paleogene, and how do they relate to leaf economics? 3) Are changes in leaf functional traits consistent with climate reconstructions from proxy data? As a proxy for LLS change, leaf mass per area (LMA) was determined indirectly. The results show the late Eocene site to stand out from all other sites, by tending towards lower leaf size/width, higher leaf mass per area (LMA), a tendency towards untoothed leaf margins, a high frequency of looped secondary veins, an almost complete absence of lobed leaves, and a low proportion of toothed pinnate leaves with non-looped secondaries. The LMA peak at the Eocene site is caused by untoothed leaf types tending to higher LMA and by an increase in LMA of toothed leaf types, compared to the Paleocene and Oligocene. The proportion of lobed leaves, which usually tend to lower LMA and therefore to deciduousness, increases from the older to the younger Oligocene sites. The results demonstrate that LMA data are valuable for evaluating functional/ecological contexts of architectural traits of fossil leaves. The results are consistent with a post-Eocene cooling trend with mild winters and the development of a drier season, both favoring a trend towards deciduous vegetation.
... Givnish and Kriebel performed two other analyses along these lines. First, they reduced a ~3500 species data set on leaf form, thickness, and habitat compiled by Royer et al. (2012) to ~600 species to repeat the original analyses in a phylogenetic context. As expected, they found a tight relationship between leaf thickness and margin type. ...
... Aquatic and herbaceous swamp plants (e.g. Limosella spuria, Eichhornia eocenica) are excluded from the dataset due to the uncertainty regarding the correlation of climate and toothness of species in these habitats (Royer et al., 2012). Herbaceous plants and mistletoe-like plants from Loranthaceae are excluded as well. ...
... Leaf teeth are sites of vigorous photosynthesis and transpiration in young leaves particularly during early growing season, accelerating growth relative to an equivalent untoothed leaf (Royer and Wilf, 2006). Previous studies have shown that in most regions of the world, the proportion of toothed woody eudicot species scales inversely with the mean annual temperature (MAT) (Peppe et al., 2011;Royer et al., 2012). This relationship has been used as the basis of a technique called leaf margin analysis for reconstructing MAT from fossil plants (Wilf, 1997). ...
Article
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Diverse leaf forms ranging from simple to compound leaves are found in plants. It is known that the final leaf size and shape vary greatly in response to developmental and environmental changes. However, changes in leaf size and shape have been quantitatively characterized only in a limited number of species. Here, we report development of LeafletAnalyzer, an automated image analysis and classification software to analyze and classify blade and serration characteristics of trifoliate leaves in Medicago truncatula. The software processes high quality leaf images in an automated or manual fashion to generate size and shape parameters for both blades and serrations. In addition, it generates spectral components for each leaflets using elliptic Fourier transformation. Reconstruction studies show that the spectral components can be reliably used to rebuild the original leaflet images, with low, and middle and high frequency spectral components corresponding to the outline and serration of leaflets, respectively. The software uses artificial neutral network or k-means classification method to classify leaflet groups that are developed either on successive nodes of stems within a genotype or among genotypes such as natural variants and developmental mutants. The automated feature of the software allows analysis of thousands of leaf samples within a short period of time, thus facilitating identification, comparison and classification of leaf groups based on leaflet size, shape and tooth features during leaf development, and among induced mutants and natural variants.
... The inclusion of certain leaf morphological variables (e.g. variables of leaf-margin state), which are significantly correlated with the predicted climate, will improve the predictive power (Royer et al., 2012). Although some leaf traits exhibit multi-collinearity with each other, this multi-collinearity may not be a problem for the prediction. ...
Article
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Leaf physiognomy is climate-sensitive and used for quantitative climate reconstruction by applying leaf-climate correlations. Most studies have focused on site-level means of species sets in large-scale environments. The sensitivity of leaf physiognomy to habitat microclimate within species is poorly known, which limits our understanding of leaf-climate relationships and applications to cli mate proxies for forest monitoring. An experiment was performed in the present study to investigate the responses of leaf size, shape, and venation pattern in the seedlings of Quercus acutissima to different gradients of water and light availability. Multiple linear regressions and a contour extraction method were developed and their ability to predict microclimate was assessed by using variables derived from leaf physiognomy. The trends of leaf morphological variations along the gra dients share a general resource acquisition and conservation enhancement pattern. The synergy of leaf size, shape, and venation pattern optimized the tradeoff relationship between investment and return of restricted resources. The water-induced plasticity of leaves was lower compared to light-induced plasticity, which resulted in the predictive methods' poor ability to estimate water a vailability compared to their ability to estimate light availability. The contour extraction method was more precise, especially for combined predictions of extreme environments because multiple li near regressions exhibited overestimation and underestimation at lower and higher gradients, re spectively. The present study demonstrated that intraspecific variations of leaf physiognomy can provide a functional link to habitat, and climate proxies based on these relationships may con tribute useful information towards forest management.
... SLA and leaf N were primarily associated with cold tolerance and their assemblage means increased with maximum and minimum temperature, respectively. The increase in the proportion of angiosperm trees having high SLA and leaf N content per mass toward lower temperatures is consistent with previous findings (Cates & Orians, 1975;Royer, Peppe, Wheeler, & Niinemets, 2012;Wright et al., 2004). It is also in line with the hypothesis that trees from cold sites require high photosynthetic rates to adapt to a short growing season, whereas nutrient-limited subtropical sites from low latitudes favor evergreen species investing into leaf structure and associated nutrient conservation (Chabot & Hicks, 1982;Ordoñez et al., 2009). ...
Article
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Understanding how environmental change alters the composition of plant assemblages, and how this in turn affects ecosystem functioning is a major challenge in the face of global climate change. Assuming that values of plant traits express species adaptations to the environment, the trait-based approach is a promising way to achieve this goal. Nevertheless, how functional traits are related to species’ environmental tolerances and how trait spectra respond to broad-scale environmental gradients remains largely unexplored. Here, we identify the main trait spectra for US angiosperm trees by testing hypotheses for the relationships between functional traits and species’ environmental tolerances to environmental stresses, as well as quantifying the environmental drivers of assemblage means and variances of these traits. We analyzed >74,000 community assemblages from the US Forest Inventory and Analysis using 12 functional traits, five traits expressing species’ environmental tolerances and 10 environmental variables. Results indicated that leaf traits, dispersal traits, and traits related to stem hydraulics were related to cold or drought tolerance, and their assemblage means were best explained by minimum temperatures. Assemblage means of traits related to shade tolerance (tree growth rate, leaf phosphorus content, and bark thickness) were best explained by aridity index. Surprisingly, aridity index, rather than minimum temperature, was the best predictors of assemblage variances of most traits, although these relationships were variable and weak overall. We conclude that temperature is likely to be the most important driver of functional community structure of North American angiosperm trees by selecting for optimum strategies along the cold and drought stress trade-off. In turn, water availability primarily affects traits related to shade tolerance through its effect on forest canopy structure and vegetation openness.
... Owing to this covariation, there is a physiognomic aspect to the morphological variation in plants that can be exploited to provide information about the environments in which plants grow. This discovery has led, in turn, to the development of a number of proxybased methods for estimating climate parameters from leaf character-state data (e.g., Bailey andSinnott 1915, 1916;Wolfe 1993Wolfe , 1995Wilf 1997;Wilf et al. 1998;Spicer et al. 2000;Spicer 2008;Peppe et al. 2011;Royer et al. 2012). The principal application of these approaches has been in paleoclimatology, where the forms of fossil leaves are scored and then used to infer aspects of the regional paleoclimate at known intervals in earth history. ...
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Research into the relationship between leaf form and climate over the last century has revealed that, in many species, the sizes and shapes of leaf characters exhibit highly structured and predictable patterns of variation in response to the local climate. Several procedures have been developed that quantify covariation between the relative abundance of plant character states and the states of climate variables as a means of estimating paleoclimate parameters. One of the most widely used of these is the Climate Leaf Analysis Multivariate Program (CLAMP). The consistency, accuracy and reliability with which leaf characters can be identified and assigned to CLAMP character-state categories is critical to the accuracy of all CLAMP analyses. Here we report results of a series of performance tests for an image-based, fully automated at the point of use, leaf character scoring system that can be used to generate CLAMP leaf character state data for: leaf bases (acute, cordate and round), leaf apices (acute, attenuate), leaf shapes (ovate, elliptical and obovate), leaf lobing (unlobed, lobed), and leaf aspect ratios (length/width). This image-based system returned jackknifed identification accuracy ratios of between 87% and 100%. These results demonstrate that automated image-based identification systems have the potential to improve paleoenvironmental inferences via the provision of accurate, consistent and rapid CLAMP leaf-character identifications. More generally, our results provide strong support for the feasibility of using fully automated, image-based morphometric procedures to address the general problem of morphological character-state identification.
... Carlquist (1977) also proposed a Mesomorphy index (M ¼ Vulnerability Index multiplied by mean vessel length in mm), but this has a number of critics (for example Baas, 1987) because there does not appear to be a linear relationship between vessel volume and climate. There does appear to be a relationship between mesomorphic woods and evergreen habit (Wheeler and Baas, 1991;Royer et al., 2012). In the present study, measurements of vessel diameters and frequencies are used as a line of paleoenvironmental evidence. ...
Article
On the eastern side of Lake Turkana in northern Kenya are extensive Plio-Pleistocene deposits containing a rich diversity of fossil mammals, hominins and flora within the radiometrically dated tuffaceous, lacustrine and fluvial sequence. Reconstruction of this landscape and paleoenvironment are part of an ongoing multinational and multidisciplinary human evolution project in the eastern Turkana Basin. Today there is a huge lake in the Rift Valley but it has fluctuated since the early Pliocene. Silicified wood is fairly common in some areas of the Koobi Fora Formation. One such site is FwJj 14E, alongside one of the tributaries of the Ileret River. Hominin hand and arm bones have been excavated from here in the Okote Member and dated at 1.56-1.36 Ma. The fossils are associated with hominin and bovid footprints. Sixty of the over 100 wood specimens collected have been sectioned and studied. In general the woods have large vessels and an average vulnerability index of 40, which implies a mesic megathermal environment with no water stress. Taxonomically the woods belong to large African families: Caesalpiniaceae (Didelotia idae), Combretaceae (Anogeissus sp.), Putranjivaceae (Euphorbiaceae; Drypetes sp.), Lamiaceae (cf Premna sp.), Malvaceae (Heritiera sp.) and Sapindaceae (Sapindoxylon sp.). Most of these taxa do not occur in the area today because now it is much drier and the local vegetation is predominantly Acacia-Commiphora-Salvadora shrubland. The reconstruction of the paleovegetation supports the interpretation from the fauna, namely, a tall riverine forest with shady refuge trees, possibly some edible fruits, and wooded grassland and more open bushland in the vicinity.
... 、 南美(Kowalski, 2002)、欧洲南部(Traiser et al., 2005)、非洲热带地 区(Jacobs, 1999)、东亚(Wolfe, 1979;Su et al., 2010; Chen et al., 2014)、澳大利亚(Greenwood et al., 2004 Greenwood, 2005)乃至全球(Peppe et al., 2011;Royer et al., 2012)建立多个温度重建的转换方程。然而, 不同区域构建的转换方程在模型拟合度和回归斜率 上存在显著的差异(Greenwood et al., 2004 Adams et al., 2008;Peppe et al., 2011), 限制了转换模型的 普适性与外推。此外, 目前基于大尺度连续分布数 据的定量叶缘分析还很欠缺, 叶缘 组成对温度的响应及其潜在的生态影响因子尚需进 一步研究。 以往的叶缘分析主要关注叶缘组成与温度间的 关系(Gregory-Wodzicki, 2000;Royer et al., 2005Royer et al., , 2009aRoyer & Wilf, 2006;Peppe et al., 2011; Chen et al., 2014)。基于叶齿的生态学功能, 叶缘状态与 水分运输和利用率密切相关。在水分充足的湿润地 区, 叶缘可能更多地响应温度的变化(Adams et al.,Wiemann et al., 1998;Wilf et al., 1998;Peppe et al., 2011; Moles et al., et al., 2012;Peppe et al., 2014)。此外, 乔灌草也具有不同的叶缘-温度关系, 即乔木的叶缘状态对温度响应最敏感, 灌木居中, 草本最弱(Royer et al., 2012)。目前大尺度的叶缘分 析多以双子叶木本植物或被子植物为研究对象, 如 对欧洲阔叶树的叶缘研究(Traiser et al., 2005)、对全 球双子叶被子植物的研究(Royer et al., 2012)等; 部 分研究以双子叶乔木为研究对象, 如对北美(Adams et al., 2008)和对中国湿润地区(Chen et al., Dolph & Dilcher, 1980; Ackerly, 2004; Schmerler et al., 2012)及其与温度间的关系(Jordan, 1997; Little et al., 2010; Jordan, 2011)。Little等(Wilf, 1997; Adams et al., 2008; Peppe et al., 2011)。对北美乔木的叶缘分析发 Jacobs, 1999; Royer et al., 2005; Peppe et al., 2011)。 叶齿数目和大小均与 年平均气温呈负相关关系, 在寒冷的环境下, 叶片 通常具有更多、 更大的齿(Royer et al., 2005; Peppe et al., 2011)。 此外, 对Acer rubrum的研究发现, 叶齿数 目和叶裂程度对气候变化的响应非常敏感(Royer et al., 2009b)。在未来研究中, He et al., 2020)。小叶作为复叶的一部分, 并不是独立的单元, 复叶的小叶在某些生理功能上 类似于单叶的叶裂或叶齿(Xu et al., 2009)。 Niinemets et al., 2006; Wu et al., 2019), 这增加了侧 向生长的投入, 但相对于永久性枝条等木质结构, 复叶的叶轴比较"廉价", 可减少植株侧枝的生物量 分配, 从而更有效地促进垂直生长(Malhado et al., Niinemets, 1998), 在叶片光合、导水率等生理活动 上的差异(Yang et al., 2019a; 赵万里等, Niinemets, 1998;Warman et al., 2011;Wu et al., 2019)。与单叶相比, 复叶有相对较高的水分传导率 和光合速率, 因此具有较高的资源获取能力和相对 生长速率(Wu et al., 2019;Yang et al., 2019a)。此外, 有研究指出, 复叶在耐阴性和规避植食上与单叶相 比没有显著不同(Niinemets, 1998 Warman et al., Xu et al., 2009)。 在小尺度上, 复叶的小叶容易脱落, al., 1998Royer et al., 2005;Traiser et al., 2005; Peppe et al., 库 (TRY Plant Trait Database, https:// www.try-db.org/TryWeb/Prop0.php)和BIEN植物信息 与 生 态 网 络 (Botanical Information and Ecology Network, http://bien.nceas.ucsb.edu/bien/biendata/)两 ...
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Leaf is one of the important organs of plants to exchange water and air with surrounding environment. Leaves have various morphology and their traits directly affect the physiological and biochemical processes of plants, which reflects their adaptive strategies to obtain resource. Here, we focused on several leaf morphological traits, including leaf size, leaf shape, leaf margin (with or without teeth) and leaf type (i.e. single vs. compound leaf), and reviewed related research progress. We summarized the ecological function of leaf morphological traits, described geographical distribution of leaf morphology, and explored the behind environmental drivers, potential ecological interactions, and their effects on ecosystem functions. Current studies mainly focused on single or specific taxon in local regions to explore the distribution and determinants of leaf size and leaf margin state. Leaf development in morphology is under control of gene expression. Leaf morphology traits trade off with other functional traits, and their spatial variation is driven by both temperature and water availability. Leaf morphological traits, especially leaf size, influence water and nutrient cycling, reflect the response of communities to climate change, and can be scaling up to predict ecosystem primary productivity. Further study should pay attention to combine new approaches to obtain unbiased data in high coverage, to explore the long-term adaptive evolution of leaf morphology, and to generalize scaling in leaf morphology and its effect on ecosystem functioning. Leaf provides an important perspective to understand how plants respond and adapt to environmental changes. Studying on leaf morphological traits bridges individual fitness, community dynamics and ecosystem function, hence it improves our understanding of the research progress in related fields including plant community ecology and functional biogeography.
... LMA is a method based on the single linear regression between the proportion of entire leaves in woody dicots within a flora and mean annual temperature (MAT) (Wolfe, 1993). However, many studies indicate that this correlation shows regional variations worldwide (Gregory-Wodzicki, 2000;Spicer et al., 2004;Adams et al., 2008;Su et al., 2010;Royer et al., 2012). Here we use the equation based on the Chinese dataset and the standard error of estimated MAT (SE) follows Miller et al. (2006). ...
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The paleoclimate of the late Pliocene Longmen flora from Yongping County located at the southeastern boundary of the Qinghai-Tibet Plateau was reconstructed using two leaf physiognomy based methods, i.e. Leaf Margin Analysis (LMA) and Climate Leaf Analysis Multivariate Program (CLAMP), to understand the paleoclimate condition and geographical pattern of monsoonal climate in southwestern China during the late Pliocene. The mean annual temperatures (MATs) estimated by LMA and CLAMP are 17.4 ± 3.3 °C and 17.4 ± 1.3 °C, respectively, compared with 15.9 °C at present. Meanwhile, the growing season precipitation (GSP) estimated by CLAMP is 1735.5 ± 217.7 mm in the Longmen flora, compared with 986.9 mm nowadays. The calculated monsoon index (MSI) of the Longmen flora is significantly lower than that of today. These results appear consistent with previous studies based on the coexistence approach (CA), and further suggest that there was a slightly warmer and much wetter climate during the late Pliocene than the present climate in western Yunnan. We conclude that the significant change of the monsoonal climate might have been resulted from the continuous uplift of mountains in western Yunnan, as well as the intensification of eastern Asian winter monsoon, both occurring concurrently in the post-Pliocene period.
... Leaf–climate relationships are weakened by the complicated responses of leaf physiognomy to the growing environment. For example, toothed margins of fossil leaves are usually related to temperature, but other factors such as local water, plant type (deciduous vs evergreen and woody vs non-woody), leaf thickness, and wood type (ring-porous vs diffuse-porous) (Peppe et al., 2011; Royer et al., 2012 ) are also closely linked to this trait. To further complicate matters, leaf shape, size, and margin are shown to be controlled by phylogeny and may not maintain the same climate–leaf characteristics relationship in the past as present (Little et al., 2010 ). ...
... 64 The approach is usually termed Leaf Margin Analysis (LMA) (Wilf, 1997). Globally, the proportion of 65 taxa showing toothed leaf margins is negatively correlated with mean annual temperature (MAT) (Bailey 66 and Sinnott, 1916;Royer et al., 2012). There is much discussion on the functional background of this 67 climate-dependent trait. ...
Article
Correlations of leaf traits with environmental conditions are widely used for reconstruction of palaeoclimate and to analyse the evolution of land plants. Evaluation of climate-dependent leaf traits of fossil floras can potentially contribute to our understanding of long-term responses of vegetation to changing climate. In this contribution, basic aspects and methods of palaeoclimate reconstruction by fossil leaf morphology, such as leaf margin analysis and CLAMP, are presented and discussed with respect to recent results on functional leaf traits. Also addressed is the use of stomatal data (density and size) for obtaining palaeoatmospheric CO2 as well as the (possible) interference of CO2 with other abiotic environmental parameters, leading to “non-analogue climates” which cannot be found today. There is much evidence that CO2, as an essential factor for gas exchange and therefore palaeoecophysiology, acted as an important driver in land plant evolution. For instance, elevated CO2 levels of the past and present are assumed to affect leaf shape evolution, because stomatal conductance is negatively correlated with atmospheric CO2 thereby affecting leaf heat dissipation. This topic is addressed in detail as an exemplary case of the interference of multiple environmental parameters. Results of a gas exchange model with coupled heat transfer indicate that the effect of elevated CO2 on leaf temperature may be minor, at least when water supply is not limited. This example demonstrates that ecophysiological analyses of trait–climate relationships can contribute to identifying adaptive features of leaf architecture and to evaluate predictions into the future as well as into the past.
... In addition, hierarchical partitioning analyses (HPAs) were applied to explore the independent effects of each environmental variables on CAPH using the R package 'relaimpo' (Chevan and Sutherland 1991;Groemping 2006). To eliminate the potential bias of sample size on the estimation of CAPH and the subsequent regression analyses, we excluded grid cells with species richness lower than 20 (for all woody plants, angiosperms, dicots, and dicots with different life forms) or 10 (for gymnosperms and monocots) following previous studies (Royer et al. 2012;Wolfe 1993). ...
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Aims Plant height is a key functional trait related to aboveground biomass, leaf photosynthesis and plant fitness. However, large-scale geographical patterns in community-average plant height (CAPH) of woody species and drivers of these patterns across different life forms remain hotly debated. Moreover, whether CAPH could be used as a predictor of ecosystem primary productivity is unknown. Methods We compiled mature height and distributions of 11,422 woody species in eastern Eurasia, and estimated geographic patterns in CAPH for different taxonomic groups and life forms. Then we evaluated effects of environmental (including current climate and historical climate change since the Last Glacial Maximum (LGM)) and evolutionary factors on CAPH. Lastly, we compared the predictive power of CAPH on primary productivity with that of LiDAR-derived canopy-height data from a global survey. Important findings Geographic patterns of CAPH and its drivers differed among taxonomic groups and life forms. The strongest predictor for CAPH of all woody species combined, angiosperms, all dicots and deciduous dicots was actual evapotranspiration, while temperature was the strongest predictor for CAPH of monocots and tree, shrub and evergreen dicots, and water availability for gymnosperms. Historical climate change since the LGM had only weak effects on CAPH. No phylogenetic signal was detected in family-wise average height, which was also unrelated to the tested environmental factors. Finally, we found a strong correlation between CAPH and ecosystem primary productivity. Primary productivity showed a weaker relationship with CAPH of the tallest species within a grid cell and no relationship with LiDAR-derived canopy height reported in the global survey. Our findings suggest that current climate rather than historical climate change and evolutionary history determines the geographical patterns in CAPH. However, the relative effects of climatic factors representing environmental energy and water availability on spatial variations of CAPH vary among plant life forms. Moreover, our results also suggest that CAPH can be used as a good predictor of ecosystem primary productivity.
... A large number of correlations have been proposed and widely used to qualitatively reconstruct palaeoclimate from Cretaceous to Cenozoic floras (Wolfe, 1979;Wing and Greenwood, 1993;Wilf et al., 1998;Jacobs, 1999;Gregory-Wodzicki, 2000;Greenwood et al., 2004;Traiser et al., 2007;Uhl et al., 2007;Peppe et al., 2011;Srivastava et al., 2012;Shukla et al., 2014;Herman et al., 2017;Bush et al., 2017;Ai et al., 2019). Although some factors, such as leaf life-span and historical genetic signals, have hampered palaeoclimate reconstructions (Jordan, Peppe et al., 2011;Royer et al., 2012), leaf physiognomy methods remain one of the most powerful and common tools to reconstruct terrestrial palaeoclimate (Bailey and Sinnott, 1916;Wing and Greenwood, 1993;Wilf, 1997;Peppe et al., 2011;Kennedy et al., 2014;Spicer et al., 2017). Previous studies have used single univariate methods to analyze the relationship between a single climatic parameter and a single leaf physiognomic character (Wolfe, 1971(Wolfe, , 1979(Wolfe, , 1993Dilcher, 1973;Givnish, 1984;Wing and Greenwood, 1993;Wilf, 1997;Jacobs, 1999;Gregory-Wodzicki, 2000;Greenwood et al., 2004;Malhado et al., 2009;Steart et al., 2010;Su et al., 2010;Chen et al., 2014;Li et al., 2016). ...
Article
In this paper, correlation between modern leaf physiognomy and climate in China are examined, to optimize the use of leaf characters as a palaeoclimate proxy. A large dataset was compiled, recording the distribution of leaf physiognomic characters among 3166 native dicot trees species across 732 calibration grids on a county level. Grids span a range of ecological environments (tropical rainforests to alpine shrubs) across humid areas. Thirteen climatic parameters were included for each grid and 22 leaf physiognomic characters were scored for each tree species. The correlation between leaf physiognomic characters and climatic parameters were calculated based on single linear regressions (SLR) and multiple linear regressions (MLR). Results indicate clear spatial distribution patterns, linked to latitude, exist for all leaf characters, with temperature (Coldest Month Mean Temperature, CMMT) and precipitation (Growing Season Precipitation, GSP) being the main climate controls. Moreover, because leaf characters are more closely correlated with Precipitation during the Three Wettest Consecutive Months (P3WET), rather than with Precipitation during the Three Driest Consecutive Months (P3DRY), seasonal variations in rainfall associated with the Asian Monsoon might especially influence leaf physiognomic characters. Closer correlations between leaf physiognomy and climate are seen using MLR compared with SLR; therefore Mean Annual Temperature (MAT) and Mean Annual Precipitation (MAP) based on MLR equations provide the most promising basis for palaeoclimate reconstructions in China.
... Leaf-climate relationships are weakened by the complicated responses of leaf physiognomy to the growing environment. For example, toothed margins of fossil leaves are usually related to temperature, but other factors such as local water, plant type (deciduous vs evergreen and woody vs non-woody), leaf thickness, and wood type (ring-porous vs diffuse-porous) (Peppe et al., 2011;Royer et al., 2012) are also closely linked to this trait. To further complicate matters, leaf shape, size, and margin are shown to be controlled by phylogeny and may not maintain the same climate-leaf characteristics relationship in the past as present (Little et al., 2010). ...
Article
Estimates of continental paleoelevation using proxy methods are essential for understanding the geodynamic, climatic, and geomorphoric evolution of ancient orogens. Fossil-leaf paleoaltimetry, one of the few quantitative proxy approaches, uses fossil-leaf traits to quantify differences in temperature or moist enthalpy between coeval coastal and inland sites along latitudes. These environmental differences are converted to elevation differences using their rates of change with elevation (lapse rate). Here, we evaluate the uncertainty associated with this method using the Eocene North American Cordillera as a case study. To do so, we develop a series of paleoclimate simulations for the Early (∼55–49 Ma) and Middle Eocene (49–40 Ma) period using a range of elevation scenarios for the western North American Cordillera.
... This study analysed herbaceous and woody species separately. Herbaceous plants are considered to be less sensitive to climate change compared to woody species, and only woody species are used in leaf-margin analyses (Bailey & Sinnott, 1916;Royer, Peppe, Wheeler, & Niinemets, 2012). Despite the small number of tree species in the European flora (Svenning & Skov, 2007), herbaceous and woody species showed similar trends in our study (see Appendix A). ...
Article
The percentage of dicotyledonous species with untoothed leaf margins is positively correlated with mean annual temperature across different continents and biomes. Paleobotanists commonly use this relationship as an index for inferring temperature in the past. However, leaf margin analysis often estimates cooler temperatures than alternative methods. Therefore, the following research hypothesis was stated: due to the observed climate warming, species with untoothed leaves are in better ecological status than species with toothed leaves. Responses of flora to global warming were studied for species with toothed vs. untoothed leaf margins after assigning species to the following categories based on data in the literature: 1) frequency; 2) population trends; 3) degree of endangerment; and 4) protected plants. A total of 2388 dicotyledonous woody and herbaceous plant species of Central Europe (separately from Germany and Poland) were analysed. The results were very similar in both analysed countries and for herbaceous and woody species. Contrary to assumptions, it was found that untoothed species clearly dominate in rare, disappearing, endangered, and protected plant groups. In contrast, plants with toothed leaf margins dominate in frequent and widespread species. The possible explanation is a delay in the response of local flora to climate change. This suggests a post-glacial relict nature of many species with untoothed leaves exists, persisting in local flora from the time of warmer periods. The constant error of underestimating past temperatures using the leaf margin method may explain the impact of today's flora in the models used because modern flora have more species with toothed leaves than expected. Taking into account the delayed reaction of flora to climate change may increase the accuracy of models predicting the climate in the past and in the future.
... Notably, some leaf traits can also be affected by microclimatic factors and abiotic factors, such as the exposure of leaves to the sun, and differ strongly between sun and shade leaves on a single plant (e.g., Uhl and Mosbrugger, 1999;Crifò et al., 2014;Uhl, 2014;Wright et al., 2017). Two semiquantitative methods have been established: (1) the Leaf Margin Analysis (LMA), which correlates proportions of toothed and untoothed leaves of woody dicots in a fossil assemblage to MAT values provided by meteorological data of similar extant vegetation (Wilf, 1997;Uhl, 2006; see Royer et al., 2012); and (2) the Climate Leaf Analysis Multivariate Program (CLAMP, e.g., Wolfe, 1993;Wolfe and Spicer, 1999;Yang et al., 2011Yang et al., , 2015 http://clamp.ibcas.ac.cn), which correlates 31 leaf physiognomic characters with those of extant assemblages and then projects the climatic requirements of the physiognomically most similar extant data set to the fossil assemblage. For both methods, specific calibrations were introduced (e.g., Su et al., 2010 for LMA;Teodoridis et al., 2012 for CLAMP) because differences between regions could not be gathered in a single comprehensive equation. ...
Article
PREMISE: Fossil leaf traits can enable reconstruction of ancient environments and climates. Among these, leaf size has been particularly studied because it reflects several climatic forcings (e.g., precipitation and surface temperature) and, potentially, environment characteristics (e.g., nutrient availability, local topography, and openness of vegetation). However, imperfect preservation and fragmentation can corrupt its utilization. We provide improved methodology to estimate leaf size from fossil fragments. METHODS: We apply three methods: (1) visually reconstructing leaf area based on taxonspecific gross morphology; (2) estimating intact leaf area from vein density based on a vein scaling relationship; and (3) a novel complementary method, determining intact leaf length based on the tapering of the midvein in the fragment. We test the three methods for fossils of extinct Eotrigonobalanus furcinervis (Fagaceae) from two lignite horizons of the middle and late Eocene of central Germany respectively (~45/46 and 35/36 Ma). RESULTS: The three methods, including the new one, yield consistent leaf size reconstructions. The vein scaling method showed a shift to larger leaf size, from the middle to the late Eocene. CONCLUSIONS: These methods constitute a toolbox with different solutions to reconstruct leaf size from fossil fragments depending on fossil preservation. Fossil leaf size reconstruction has great potential to improve physiognomy-based paleoenvironmental reconstructions and the interpretation of the fossil record. KEY WORDS ecophysiology; Europe; morphometrics; paleobotany; paleoclimate; plant taphonomy; swamp forests.
... Previous research has demonstrated relationships between community-level trait composition and environmental variables, including for plant leaf margins (Nicotra et al., 2011;Peppe et al., 2011;Royer et al., 2012;Wolfe, 1979), herbivore teeth (Eronen, Polly, et al., 2010;Eronen et al., 2010a;Evans, 2013;Fortelius et al., 2016), and locomotor skeletal elements of bovids (Barr, 2017), carnivorans (Polly, 2010), and snakes (Lawing et al., 2012), but the estimation methods have varied. Wolfe (1979) used linear regression to demonstrate that areas with high mean annual temperatures are dominated by leaves with entire margins while areas with low temperatures are dominated by leaves with nonentire margins. ...
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• Ecometrics is the study of community‐level functional trait–environment relationships. We use ecometric analyses to estimate paleoenvironment and to investigate community‐level functional changes through time. • We evaluate four methods that have been used or have the potential to be used in ecometric analyses for estimating paleoenvironment to determine whether there have been systematic differences in paleoenvironmental estimation due to choice of the estimation method. Specifically, we evaluated linear regression, polynomial regression, nearest neighbor, and maximum‐likelihood methods to explore the predictive ability of the relationship for a well‐known ecometric dataset of mammalian herbivore hypsodonty metrics (molar tooth crown to root height ratio) and annual precipitation. Each method was applied to 43 Pleistocene fossil sites and compared to annual precipitation from global climate models. Sites were categorized as glacial or interglacial, and paleoprecipitation estimates were compared to the appropriate model. • Estimation methods produce results that are highly correlated with log precipitation and estimates from the other methods (p < 0.001). Differences between estimated precipitation and observed precipitation are not significantly different across the four methods, but maximum likelihood produces the most accurate estimates of precipitation. When applied to paleontological sites, paleoprecipitation estimates align more closely with glacial global climate models than with interglacial models regardless of the age of the site. • Each method has constraints that are important to consider when designing ecometric analyses to avoid misinterpretations when ecometric relationships are applied to the paleontological record. We show interglacial fauna estimates of paleoprecipitation more closely match glacial global climate models. This is likely because of the anthropogenic effects on community reassembly in the Holocene.
... Vitis acerifolia and V. aestivalis do not appear to be climatically sensitive, so their deviation from the expected correlation may be related to drivers other than changes in temperature or precipitation. These relatively climate insensitive responses may be due to the fact that Vitis is a liana, and lianas have been shown to have a weaker relationship with leaf margin state and climate than trees or shrubs (Royer et al., 2012). In addition, Vitis' preference for lowland and riparian environments is another potential confounding factor that may influence the leaf physiognomic-climate relationship (see discussion in Royer, 2012a). ...
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Premise: The size and shape (physiognomy) of woody, dicotyledonous angiosperm leaves are correlated with climate. These relationships are the basis for multiple paleoclimate proxies. Here we test whether Vitis exhibits phenotypic plasticity and whether physiognomy varies along the vine. Methods: We used Digital Leaf Physiognomy (DiLP) to measure leaf characters of four Vitis species from the USDA Germplasm Repository (Geneva, New York) from the 2012-2013 and 2014-2015 leaf-growing seasons, which had different environmental conditions. Results: Leaf shape changed allometrically through developmental stages; early stages were more linear than later stages. There were significant differences in physiognomy in the same developmental stage between the growing seasons, and species had significant differences in mean physiognomy between growing seasons. Phenotypic plasticity was defined as changes between growing seasons after controlling for developmental stage or after averaging all developmental stages. Vitis amurensis and V. riparia had the greatest phenotypic plasticity. North American species exhibited significant differences in tooth area:blade area. Intermediate developmental stages were most likely to exhibit phenotypic plasticity, and only V. amurensis exhibited phenotypic plasticity in later developmental stages. Conclusions: Leaves have variable phenotypic plasticity along the vine. Environmental signal was strongest in intermediate developmental stages. This is significant for leaf physiognomic-paleoclimate proxies because these leaves are likely the most common in leaf litter and reflect leaves primarily included in paleoclimate reconstructions. Early season and early developmental stages have the potential to be confounding factors but are unlikely to exert significant influence because of differential preservation potential.
... Aquatic and herbaceous swamp plants (e.g. Limosella spuria, Eichhornia eocenica) are excluded from the dataset due to the uncertainty regarding the correlation of climate and toothness of species in these habitats (Royer et al., 2012). Herbaceous plants and mistletoe-like plants from Loranthaceae are excluded as well. ...
Article
The Eocene, the world’s last global greenhouse period, shows distinct climatic developments through time, from subtropical towards warm-temperate conditions in Europe. The present paper investigates the response of five floras of the central German Weißelster Basin from different stratigraphic ages to terrestrial palaeoclimatic variations. The floras were selected from the Zeitz Floral Assemblage (“Florenkomplex”) and cover a time interval of ca. 3.5 Myr within the late Eocene, which is supposed to be a period of gradual decline of global mean annual temperatures. The Zeitz Floral Assemblage was characterized by mainly evergreen, notophyllous intrazonal vegetation, consisting of subtropical and warm-temperate elements. The five floras as well as the entire Zeitz Floral Assemblage have been analysed using the following quantitative techniques: leaf margin analysis (LMA), Climate Leaf Analysis Multivariate Program (CLAMP) and Coexistence Approach (CA). Furthermore, the results have been compared with previously published estimates for additional localities from the same area and age. The temperature estimates derived for the Zeitz Floral Assemblage are in a good agreement with those of previous studies i.e. mean annual temperature (MAT) 16.1 – 20.0 °C, warmest month mean temperature (WMMT) 24.9 – 26.4 °C, coldest month mean temperature (CMMT) 9.2 – 13.3 °C. Deviations have been determined for the calculated mean annual precipitation (MAP 1308 – 1335 mm) compared to previously published data, indicating values of about 2000 mm. Both CLAMP and CA reveal clear hints for seasonality in precipitation which is in agreement with previous phytosociological assumptions and palynological data. The estimates for the individual sites differ between the different techniques as well as among the individual sites, but generally indicate no temporal trends in temperature and precipitation development. Additionally, the applicability of these techniques for fluvial-estuarine plant assemblages, as well as the applicability of intrazonal vegetation for reconstructing transregional climate conditions are discussed. Taphonomic and methodical biases are also subject of debate.
... It is difficult to directly relate environmental selection pressures to the evolution and expression of leaf-shape controlling genes based on available evidence of the origin and relatedness of leaf-shape determining genes. Some investigators have attempted to address this area of research by examining how or if environmental factors have led to leaf-shape changes [4,[13][14][15][16]. Royer and Wilf [4] measured the seasonal patterns in photosynthesis and transpiration in relation to leaf-margin characteristics using 60 woody plants from two cold-climate regions in the north of the United States. ...
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The leaves of vines exhibit a high degree of variability in shape, from simple oval to highly dissected palmatifid leaves. However, little is known about the extent of leaf bilateral symmetry in vines, how leaf perimeter scales with leaf surface area, and how this relationship depends on leaf shape. We studied 15 species of vines and calculated (i) the areal ratio (AR) of both sides of the lamina per leaf, (ii) the standardized symmetry index (SI) to estimate the deviation from leaf bilateral symmetry, and (iii) the dissection index (DI) to measure leaf-shape complexity. In addition, we examined whether there is a scaling relationship between leaf perimeter and area for each species. A total of 14 out of 15 species had no significant differences in average ln(AR), and mean ln(AR) approximated zero, indicating that the areas of the two lamina sides tended to be equal. Nevertheless, SI values among the 15 species had significant differences. A statistically strong scaling relationship between leaf perimeter and area was observed for each species, and the scaling exponents of 12 out of 15 species fell in the range of 0.49−0.55. These data show that vines tend to generate a similar number of left- and right-skewed leaves, which might contribute to optimizing light interception. Weaker scaling relationships between leaf perimeter and area were associated with a greater DI and a greater variation in DI. Thus, DI provides a useful measure of the degree of the complexity of leaf outline.
... Previous studies have analyzed the presence of leaf teeth in samples that included both evergreen and deciduous species and temperate and (sub)tropical species (e.g., Royer et al., 2012;Edwards et al., 2016Edwards et al., , 2017Givnish and Kriebel, 2017). This mixing introduces confounding effects (cf. ...
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Premise The proportion of woody dicots with toothed leaves increases toward colder regions, a relationship used to reconstruct past mean annual temperatures. Recent hypotheses explaining this relationship are that (1) leaves in colder regions are thinner, requiring thick veins for support and water supply, with the resulting craspedodromous venation leading to marginal teeth (support–supply hypothesis) or that (2) teeth are associated with the packing of leaf primordia in winter buds (bud‐packing hypothesis). Methods We addressed these hypotheses by examining leaf thickness, number of primordia in buds, growing season length (mean annual temperature, MAT), and other traits in 151 deciduous woody species using georeferenced occurrences and a Bayesian model controlling for phylogeny. We excluded evergreen species because longer leaf life spans correlate with higher leaf mass per area, precluding the detection of independent effects of leaf thickness on leaf‐margin type. Results The best model predicted toothed leaves with 94% accuracy, with growing season length the strongest predictor. Neither leaf thickness nor number of leaves preformed in buds significantly influenced margin type, rejecting the support–supply and bud‐packing hypotheses. Conclusions A direct selective benefit of leaf teeth via a carbon gain early in the spring as proposed by Royer and Wilf (2006) would match the strong correlation between toothed species occurrence and short growing season found here using Bayesian hierarchical models. Efforts should be directed to physiological work quantifying seasonal photosynthate production in toothed and nontoothed leaves.
... ). The leaf mass per area was then 286 compared to modern sites(Peppe et al. 2011;Royer et al. 2012) to assess the ecological habitat. 287Univariate and multivariate methods were used to estimate mean annual temperature 290 (MAT) and mean annual precipitation (MAP) using Channel data. ...
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During the early Paleogene the Earth experienced long-term global warming punctuated by several short-term ‘hyperthermal’ events, the most pronounced of which is the Paleocene-Eocene Thermal Maximum (PETM). During this time, tropical climates expanded into extra-tropical areas potentially forming a wide band of ‘paratropical’ forests that are hypothesized to have expanded into the mid-latitude Northern Great Plains (NGP). Relatively little is known about these ‘paratropical’ floras, which would have extended across the Gulf Coastal Plain (GCP). This study assesses the preserved floras from the GCP in Central Texas before and after the PETM to define plant ecosystem changes associated with the hyperthermal event in this region. These floras suggest a high turnover rate, change in plant community composition, and uniform plant communities across the GCP at the Paleocene-Eocene boundary. Paleoecology and paleoclimate estimates from Central Texas PETM floras suggest a warm and wet environment, indicative of tropical seasonal forest to tropical rainforest biomes. Fossil evidence from the GCP combined with data from the NGP and modern tropics suggest that warming during the PETM helped create a ‘paratropical belt’ that extended into the mid-latitudes. Evaluating the response of plant communities to rapid global warming is important for understanding and preparing for current and future global warming and climate change.
... (2): the global LMA equation of Peppe et al. (2011), derived from a global set of 92 sites that represent more diverse vegetated environments than used to derive the original LMA equation, but with a much greater standard error ( Peppe et al. 2011). By using both equations we seek to counteract the regional variances noted between MAT and LMP of a flora ( Peppe et al. 2011;Royer et al. 2012). In Table 3, we provide MAT estimates derived from additional regional LMA calibration equations. ...
The late Paleocene to early Eocene sediments of Ellesmere and Axel Heiberg islands, Nunavut, of the Canadian High Arctic contain a rich fossil flora and fauna. Although the megafloral fossils have been known for more than a century, limited descriptions of the fossil flora have been presented. Here, we provide a comprehensive morphotype catalogue of fossil plants from multiple localities from Ellesmere and Axel Heiberg islands that form a systematic framework for establishing an early Paleogene polar flora from High Arctic latitudes in Canada. Described are 62 ‘dicot’ angiosperm morphotypes, three monocotyledonous angiosperms, 13 gymnosperms, and five pteridophyte morphotypes. This work presents a significant contribution to the understanding of north-polar diversity and environments during the warm greenhouse climate of the early Paleogene.
... It has been hypothesized that plants from higher latitudes develop thinner leaves with greater dissection, marginal serration and/or increased number of lobes. This may potentially maximize the leaf surface:volume ratio and impact gas exchange (Baker-Brosh and Peet, 1997;Royer and Wilf, 2006;Royer et al., 2012;McKee, 2017). Similar attention has not been paid to ferns, a lineage that is remarkable for variation in overall leaf morphology (Vasco et al., 2013), and the association between leaf architecture and ecological adaptation in ferns has remained unexplored. ...
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The thelypteroid fern genus Stegnogramma s.l. contains around 18–35 species and has a global, cross‐continental distribution ranging from tropical to temperate regions. Several genera and infrageneric sections have been recognized previously in Stegnogramma s.l., but their phylogenetic relationships are still unclear. In this study, we present a global phylogeny of Stegnogramma s.l. with the most comprehensive sampling to date and aim to pinpoint the phylogenetic positions of biogeographically and taxonomically important taxa. Based on the reconstructed historical biogeography and character evolution, we propose a new (infra)generic classification and discuss the diversification of Stegnogramma s.l. in a biogeographical context. New names or combinations are made for 12 (infra)species, including transferring the monotypic species of Craspedosorus to Leptogramma. Finally, we discuss a possible link between leaf architecture and ecological adaptation, and hypothesize that the increase in leaf dissection and free‐vein proportion is an adaptive feature to cool climates in Stegnogramma s.l.
... The Leaf Margin Analysis (LMA) regression equations used here are the classic LMA equation (3) from Wolfe (1979) and Wing and Greenwood (1993). As a number of studies have shown that the correlation between the proportion of untoothed leaves in a flora and the MAT show regional variations world-wide (Gregory-Wodzicki, 2000; Greenwood et al., 2004; Spicer et al., 2004; Royer et al., 2012 ), the global LMA equation (4) from Peppe et al. (2011) was also applied. Standard error for classic LMA is calculated from the number of morphotypes in a flora as per the Wilf (1997) equation (5) where r is the number of morphotypes. ...
Article
The early Eocene was the warmest interval of the Cenozoic, and included within it were several hyperthermal events, with the Paleocene–Eocene Thermal Maximum (PETM) the most pronounced of these. These globally warm climates extended into the Arctic and substantive paleobotanical evidence for high Arctic precipitation (MAP >150cm/yr) is indicative of an Arctic rainforest, which contradicts some climate models that show low Arctic precipitation. Prior studies of Arctic early Eocene wood stable-isotope chemistry, however, have shown a summer peak in precipitation, which suggests modern analogs are best sought on the summer-wet east coast of the Asia (e.g., China, Japan, South Korea), not the winter-wet west coasts of the Pacific Northwest of North America). Furthermore, some prior modeling data suggest that highly seasonal ‘monsoon-type’ summer-wet precipitation regimes (i.e., summer:MAP >55%) characterized certain mid and lower latitude regions in the early to mid-Eocene. Presented here is a new analysis using leaf physiognomy of 3 leaf megafloras (Split Lake, Stenkul Fiord and Strathcona Fiord) and palynofloral Bioclimatic Analysis from the Margaret Formation from Ellesmere Island, placed stratigraphically as early Eocene, possibly occurring during or following one of the early Eocene hyperthermals. These new data indicate high summer precipitation in the Arctic during the early Eocene, which in part corroborates the results from Eocene wood chemistry. Nevertheless, in contradiction to the wood analysis, monsoonal conditions are not indicated by our analysis, consistent with current modeling studies. High summer (light season) and winter (dark season) precipitation in the Eocene Arctic during hyperthermals would have contributed to regional warmth.
... (2): the global LMA equation of Peppe et al. (2011), derived from a global set of 92 sites that represent more diverse vegetated environments than used to derive the original LMA equation, but with a much greater standard error (Peppe et al. 2011). By using both equations we seek to counteract the regional variances noted between MAT and LMP of a flora (Peppe et al. 2011;Royer et al. 2012). In Table 3, we provide MAT estimates derived from additional regional LMA calibration equations. ...
Article
Paleogene sediments of the Huntingdon Formation, a correlative to the Chuckanut Formation of neighboring Washington State, USA, are exposed in the greater Vancouver area, British Columbia, Canada. Palynology and plant macrofossils suggest the Kanaka Creek section is Paleocene rather than Eocene in age. Detrital zircon dating is less decisive, yet indicates the Kanaka rocks are no older than Maastrichtian. Analyses of plant macro- and microfossils suggest an early to middle Paleocene age for the Kanaka fossil flora. Paleocene indicators include macrofossils such as Platanus bella, Archeampelos, Hamamelites inequalis, and Ditaxocladus, and pollen taxa such as Paraalnipollenites, Triporopollenites mullensis, and Duplopollis. Paleogene taxa such as Woodwardia maxonii, Macclintockia, and Glyptostrobus dominate the flora. Fungal spores including the Late Cretaceous Pesavis parva and the Paleogene Pesavis tagluensis are notable age indicators. Physiognomy of 41 angiosperm leaf morphotypes from Kanaka Creek yields mean annual temperatures in the microthermal to lower mesothermal range (11.2 ± 4.3°C to 14.6 ± 2.7°C from LMA; 14.8 ± 2.1°C from CLAMP), with mild winters (cold month mean temperature 3.9 ± 3.4°C). Paleoclimate was cooler than the upper Paleocene and Eocene members of the Chuckanut Formation. Mean annual precipitation is estimated at ~140 cm with large uncertainties. The Kanaka paleoflora is reconstructed as a mixed conifer-broadleaf forest, sharing common taxa with other western North American Paleocene floras and growing in a temperate moist climate. Kanaka Creek is a rare coastal Paleocene plant locality that provides new insights into coastal vegetation and climate prior to the Paleocene-Eocene Thermal Maximum.
... Although teeth may enhance gas exchange and improve carbon production, limitation of the attendant water losses is more important (Royer and Wilf, 2006). This balance between carbon production and water loss explains the lower untoothed% from valleys than from ridges in P-zone is related to the humidity condition, which is secondary to the influence of MAT (Royer and Wilf, 2006;Wolfe, 1993).In the present study, the r value of the untoothed%-MAT relationship for shrubs was lower than that for trees, which agrees with the observation that the sub-canopy microclimate surrounding lowerpositioned shrubs within a community is more disjointed from regional climate than the canopy microclimate surrounding trees and lianas (Bailey and Sinnott, 1916;Royer et al., 2012). The difference between sub-canopy microclimate and canopy microclimate depends upon soil moisture availability and vapour pressure deficit, for example, when the free air mass is dry but the soil is wet, sub-canopy microclimate can be up to 5°C cooler than regional climate (Fritts, 1961). ...
Article
Models based on the relationship between leaf morphology and climate parameters of different regions have been used for paleoclimate estimation. Information from Japanese floras has been included in some of these models; however, variation in the distribution pattern of leaf margin within Japan caused by the effect of topography and East Asian Monsoon has not been reflected in these previously published leaf margin analysis models. In this study, we investigate the relationship between leaf characters and climate parameters under different climate conditions within a small geographical scale and, in doing so, improve the accuracy of leaf physiognomy-based paleoclimate reconstruction. We use the local flora in central Japan as an example to determine the distribution pattern of leaf margin (toothed and untoothed) and habit (evergreen and deciduous) characteristics under monsoon climate conditions. In areas along the Pacific Ocean (P-zone), the leaf margin and habit types correlated with the temperature parameters and growing season precipitation. The P-zone includes more toothed species than in other regions of the world obtained with published models at a given mean annual temperature. In the areas along the Sea of Japan (J-zone) with deeper snow cover during the winter, the percent of sub-canopy evergreen shrubs increases, especially at higher altitudes. No significant relationship between leaf margin characters and climate parameters was observed in this area. As heavy snow was a feature of this region since late Early Pleistocene times, paleoclimate estimation based on leaf margin of fossil assemblages younger than Early Pleistocene from these areas might be less reliable. In addition, we found that the leaf margin of woody shrub species is less sensitive to the mean annual temperature than tree species.
... The global LMA equation (eq. 3) of Peppe et al. (2011) was also applied in our analysis, and it is derived from a global set of 92 sites that represent more diverse vegetated environments than used to derive the original LMA equation, but it has a much greater standard error (Peppe et al. 2011). This is intended to counteract the regional variances that have been observed between MAT and the proportion of untoothed leaves found in a flora (Gregory-Wodzicki 2000; Greenwood et al. 2004;Royer et al. 2012). ...
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Early Eocene fossil floras from British Columbia are a rich resource for reconstructing western North American early Cenozoic climate. The best known of these floras reflect cooler (MAT ≤ 15 °C) upland forest communities in contrast to coeval (MAT ≥ 18 °C) forests in lowland western North American sites. Of particular interest is whether Early Eocene climates were monsoonal (highly seasonal precipitation). The McAbee site is a 52.9 ± 0.83 Ma 0.5 km outcrop of bedded lacustrine shale interbedded with volcanic ash. In this report two historical megaflora collections that were collected independently from different stratigraphic levels and (or) laterally separated by ∼100–200 m in the 1980s (University of Saskatchewan) and 2000s (Brandon University) are investigated to (i) assess whether they represent the same leaf population, (ii) assess whether a combined collection yields more precise climate estimates, and (iii) reconstruct paleoclimate to assess the character of regional Early Eocene precipitation seasonality. Combined, the two samples yielded 43 dicot leaf morphotypes. Analysis of leaf size distribution using ANOVA showed no difference between the two samples, and thus they were combined for climate analysis. Climate analysis using leaf physiognomy agrees with previous estimates for McAbee and other regional megafloras, indicating a warm (MAT ∼8–13 °C), mild (CMMT ∼5 °C), moist (MAP > 100 cm/year) ever-wet, non-monsoonal climate. Additionally, we recommend that climate analyses derived from leaf fossils should be based on samples collected within a stratigraphically constrained quarry area to capture a snapshot of climate in time rather than time-averaged estimates derived from multiple quarry sites representing different stratigraphic levels within a fossil site.
Article
Land plants exhibit a wide variety of defences that deter the consumption of leaves and stems, including trichomes (hairs), thorns, and thick cuticles. In many plants, trichomes are hooked or inclined to the leaf or stem surface, and the teeth on leaf margins point either apically or more rarely toward the base. The role of these anisotropic structures as potential defences has been largely ignored. In the present study, it is proposed that apically oriented surface features function as ratchets directing the movements of small herbivores toward the leaf ends and ultimately off the leaf, whereas basally oriented protrusions interfere with the ascent of consumers to the upper parts of the plant. These proposed defencive functions do not exclude other potential benefits of anisotropic features, such as self-cleaning of surfaces. The proposed defencive role of apically oriented trichomes and teeth may represent an unusual class of physical defences that speed up rather than slow down encounters between enemies and their plant victims.
Article
Leaf physiognomy (size and shape) in fossils is commonly used to reconstruct terrestrial paleoclimate. Physiognomic leaf-climate methods are underpinned mostly by the covariation between toothed margins and mean annual temperature (MAT) and between leaf size and mean annual precipita-tion. Digital leaf physiognomy, a multivariate method based largely on variables that are functionally linked to climate and that can be measured by computer algorithm, minimizes many of the deficiencies present in other approaches. Nevertheless, the relationships between MAT and many physiognomic vari-ables, especially tooth-related variables, are confounded by leaf thickness, leaf habit (deciduous vs. ever-green), and phylogenetic history. Until these factors are properly accounted for, a minimum error in MAT of ±4 °C for digital leaf physiognomy and ±5 °C for other methods should be assumed.
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The variability of leaf margin serration of Populus nigra L. in conditions of industrial dumps (coal mines dumps and overburden dumps) and city park is estimated. The value of this indicator is in the range from 1.25 to 1.76 and significantly increases along the gradient: coal mines dumps – overburden dumps – city park. From the number of selected gradations of P. nigra leaf blades, the gradation with values of 1.45-1.55 is most pronounced according to the analyzed index for industrial dumps, for the park – with the values of 1.55-1.65. The degree of serration of edge leaf blade is characterized by low values of variation – coefficient of variation is less than 10.0%. We registered the significant positive correlation between the average values of leaf margin serration and the length of P. nigra leaf blade.
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Plant leaf morphological traits adapt to the environment through long-term evolution and are closely related to the basic function of plants. In this study, we examined the responses of leaf morphological traits of broadleaved woody plants to the climatic gradient of Changbai Mountain in northeastern China. We measured plant leaf morphological traits from 13 altitudes in Changbai Mountain, including leaf length, leaf width, leaf perimeter, leaf area, the ratio of leaf length to width (LW) and the ratio of leaf perimeter to area (PA). Correlation analysis and standardized major axis were used to investigate the relationships between plant leaf morphological traits and climate factors, as well as correlations among leaf morphological traits, and general linear model and variation partition were used to partition leaf trait variation and to analyse the leaf traits in relation to environmental factors and species identities. Leaf length, width, perimeter and leaf area decreased significantly with increased altitudinal gradient and decreased annual temperature, while the perimeter/area and length/width ratios increased, which helps increase the leaf boundary layer resistance and decrease heat dissipation from leaves. Variations in leaf morphological traits in this study are largely explained by species identity, with its independent explanatory power between 47.08% and 76.07%. Environmental factors also have a significant impact on leaf morphological traits, but by itself explained only 1.22%-3.82% of variation.
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Tropospheric ozone is considered the most detrimental air pollutant for vegetation at the global scale, with negative consequences for both provisioning and climate regulating ecosystem services. In spite of recent developments in ozone exposure metrics, from a concentration-based to a more physiologically relevant stomatal flux-based index, large scale ozone risk assessment is still complicated by a large and unexplained variation in ozone sensitivity among tree species. Here we explored whether the variation in ozone sensitivity among woody species can be linked to interspecific variation in leaf morphology. We found that ozone tolerance at the leaf level was closely linked to leaf dry mass per unit leaf area (LMA) and that whole-tree biomass reductions were more strongly related to stomatal flux per unit leaf mass (r(2) = 0.56) than to stomatal flux per unit leaf area (r(2) = 0.42). Furthermore, the interspecific variation in slopes of ozone flux-response relationships was considerably lower when expressed on a leaf mass basis (coefficient of variation, CV = 36%) than when expressed on a leaf area basis (CV = 66%), and relationships for broadleaf and needle-leaf species converged when using the mass-based index. These results show that much of the variation in ozone sensitivity among woody plants can be explained by interspecific variation in LMA and that large-scale ozone impact assessment could be greatly improved by considering this well-known and easily measured leaf trait. This article is protected by copyright. All rights reserved.
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The first chapter explores relationships between a suite of six functional leaf traits and leaf-level reflectance spectra in a unique biogeographical region, the Greater Cape Floristic Region (GCFR). Leaf level reflectances were measured for 1,862 leaves (1,120 species) sampled across communities in the GCFR. Functional traits were measured from populations of the same species from each sampling location. We show that the leaf reflectance spectra have vary and can be classified based on differences in leaf trait magnitudes, taxonomic group and sampling region. Second, we compare two statistical methods, Penalized Functional Regression (PFR) and Partial Least Squares Regression (PLSR) in their ability to predict leaf traits from spectra. PFR outperformed PLSR in prediction with significantly lower mean RMSE values when models were validated and compared in ten fold cross validation. Based on RMSE values from the model validation, PFR lowered model bias up to 39% in certain regressions suggesting significant improvements in prediction. We also introduce a new cross-validation method that structures folds of data based on spatial autocorrelation. Our results suggest that physical proximity of observations did not affect predictability for PFRs. The second chapter focuses on leaf margins within a single genus. The function and purpose of leaf margins are still under debate. Most botanical work on the subject has primarily focused on temperate woody species in the northern hemisphere. In the second chapter, the leaf margins of the genus Pelargonium, a recent radiation centered in South Africa, were evaluated for their linear relationships with a wide suite of variables related to climate, growth form, and evolutionary history (represented by clade). We found that Pelargonium margins are not a significant predictor of mean annual temperature, which is the linear correlation often cited as a method of predicting paleo-climates from fossil leaf assemblages. In a multivariate regression, where variables were selected to best predict the mean leaf tooth density, we found that a combination of temperature range, seasonality, growth form categories and clade yielded the best model explaining 28% of the variation in tooth density. This generates interesting hypotheses of the true purpose of leaf margins within Pelargonium since they seem to be related to broad climatic features but filtered by growth form and evolutionary relationship.
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Проведено определение минимальных размеров выборок, необходимых для информативного сравнения показателей изрезанности листовой пластинки Рopulus nigra L. s.l. в условиях городских экосистем. Материал собран в 2012–2017 гг. на территории г. Донецка с древесных растений зрелой стадии генеративного периода во время листопада. Для оценки степени изрезанности листовой пластинки применяли два различных подхода, ранее используемых исследователями. Минимальные размеры выборок, необходимые для информативногосравнения с использованием t-критерия Стьюдента показателя изрезанности как отношения периметра листовойпластинки к длине окружности, ограничивающей круг, площадь которого равна площади листовой пластинки,значительно ниже, чем для сравнения показателя изрезанности как отношения периметра листовой пластинкиР. nigra к её площади.
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PREMISE OF THE STUDY: The size and shape (physiognomy) of woody, dicotyledonous angiosperm leaves are correlated with climate and these relationships have been used to develop paleoclimate proxies. These proxies assume that leaf morphology plastically responds to meteorological conditions and that leaf traits change isometrically through development. METHODS: We used Digital Leaf Physiognomy (DiLP) to measure leaf characters of multiple Vitis species from the USDA Germplasm Repository in Geneva, NY from the 2012-2013 and 2014-2015 growing seasons. These growing seasons had different temperature and precipitation. KEY RESULTS: We found three primary results: (1) there were predictable significant differences in leaf characters in leaves of different developmental stages along the vine, (2) there were significant differences in leaf characters in leaves of the same developmental stage between the growing seasons, and (3) there were significant differences in leaf characters between growing seasons. CONCLUSIONS: We found that Vitis leaf shape had the strongest relationship with growing season meteorological conditions in taxa growing in their native range. In addition, leaves have variable phenotypic plasticity along the vine. We interpret that the meteorological signal was strongest in those leaves that have completed allometric expansion. This is significant for leaf physiognomic-paleoclimate proxies because these leaves are most likely to be preserved in leaf litter and reflect the type of leaves included in paleoclimate reconstructions. We found that leaf development does have the potential to be a confounding factor, but it is unlikely to exert a significant influence on analysis due to differential preservation potential.
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Plant functional indicators of vegetation response to climate change, past present and future: I. Trends, emerging hypotheses and plant functional modality. Flora, 254, 12-30. https://doi.org/10.1016/j.flora.2019.03.013 Highlights  Uncertainties in paleo-habitat definition limit adequate vegetation reconstruction.  Plant functional indicators are of limited value for paleovegetation reconstruction.  Biome scale analyses of functional types rarely apply to plant communities.  Underlying basis for whole-plant modal PFT construction and use is described.  Modal PFTs are more functionally informative than individual traits. Abstract Plant functional traits are widely applied in models that simulate the effects of climate change on biodiversity and resource management. Here the aim is to examine the potential role of specific plant functional traits and their whole-plant syndromes (Plant Functional Types or PFTs as specific 'modal' trait assemblages) as indicators of vegetation response to climate change, past, present and future. Because plant functional characteristics have evolved through time, it is widely argued that models of vegetation performance under future climates should benefit from a study of plant response under previous climates. This paper presents an overview first, of developmental concepts underlying the current use of PFTs as indicators of plant response to environmental change, second, implications arising from species acclimation and third, process-based models used in reconstruction of vegetation under mainly Holocene environments but also with respect to present and future climates. In this regard the role of individual functional traits in 'biomization' procedures in vegetation response models is briefly discussed. It is concluded that, while PFTs possess limited indicator value at biome scale, uncertainties in the delimitation of local paleohabitats greatly restrict their use as indicators for paleovegetation reconstruction at community level. Emerging hypotheses are: 1) A whole-plant system of modal PFTs based on a novel set of functional traits can provide an improved alternative to PFTs and traits used in models of vegetation response to climate change, 2) Modal PFTs are potentially more efficient indicators of vegetation response to climate change than individual traits, 3) Improved plant functional selection criteria can lead to more efficient parameterization of Earth System and Dynamic Global Vegetation Models. Previous article in issueNext article in issue.
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The uppermost Eocene lacustrine Florissant Formation in central Colorado preserves a diverse flora and fauna at a key time in Earth history immediately preceding the Eocene-Oligocene boundary. Laminated shales in the Florissant Formation record impression fossils of woody non-monocot angiosperm leaves that were used to estimate paleoecological and paleoclimatic parameters using leaf physiognomic methods (leaf mass per area (MA), digital leaf physiognomy (DiLP), leaf margin analysis (LMA), and leaf area analysis (LAA)). The majority (58%) of the morphotypes analyzed for MA suggested a semi-evergreen leaf lifespan, whereas another 27% indicated a deciduous habit and just 15% an evergreen habit. There was no significant relationship between MA and insect damage based on a small subset of Florissant's leaves. Higher MA values (~73% of leaves ≥ one-year lifespan), coupled with a tendency toward long and narrow leaf shapes and small leaf areas, support the presence of sclerophyllous vegetation at Florissant. Using the global regression for mean annual temperature (MAT), the DiLP estimate of MAT was anomalously cold: 5.5 ± 4 °C. However, using a ‘Northern Hemisphere’ regression the DiLP MAT estimate of 11.6 ± 3.3 °C was more plausible. Using DiLP, mean annual precipitation (MAP) for Florissant was estimated at 740 + 608/−334 mm∙yr⁻¹, which supports dry conditions. Estimates for MAT and MAP using the univariate LMA and LAA methods overlapped within uncertainty of the DiLP results. In addition, Florissant taxa classified as growing in wet areas (riparian) had significantly more teeth than non-riparian taxa. These paleoclimatic and paleoecological results suggest that outside the riparian forest, the Florissant flora sampled a seasonally dry temperate sclerophyllous shrubland to woodland, perhaps similar to modern chaparral forests, in the Western Interior of the USA just before the transition into the cooler Oligocene.
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Precise estimates of past temperatures are critical for understanding the evolution of organisms and the physical biosphere, and data from continental areas are an indispensable com- plement to the marine record of stable isotopes. Climate is considered to be a primary selective force on leaf morphology, and two widely used methods exist for estimating past mean annual temperatures from assemblages of fossil leaves. The first approach, Leaf Margin Analysis, is uni- variate, based on the positive correlation in modern forests between mean annual temperature and the proportion of species in a flora with untoothed leaf margins. The second approach, known as the Climate-Leaf Analysis Multivariate Program, is based on a modern data set that is multivariate. I argue here that the simpler, univariate approach will give paleotemperature estimates at least as precise as the multivariate method because (1) the temperature signal in the multivariate data set is dominated by the leaf-margin character; (2) the additional characters add minimal statistical precision and in practical use do not appear to improve the quality of the estimate; (3) the predictor samples in the univariate data set contain at least twice as many species as those in the multivariate data set; and (4) the presence of numerous sites in the multivariate data set that are both dry and extremely cold depresses temperature estimates for moist and nonfrigid paleofloras by about 2 8C, unless the dry and cold sites are excluded from the predictor set. New data from Western Hemisphere forests are used to test the univariate and multivariate meth- ods and to compare observed vs. predicted error distributions for temperature estimates as a func- tion of species richness. Leaf Margin Analysis provides excellent estimates of mean annual tem- perature for nine floral samples. Estimated temperatures given by 16 floral subsamples are very close both to actual temperatures and to the estimates from the samples. Temperature estimates based on the multivariate data set for four of the subsamples were generally less accurate than the estimates from Leaf Margin Analysis. Leaf-margin data from 45 transect collections demonstrate that sampling of low-diversity floras at extremely local scales can result in biased leaf-margin per- centages because species abundance patterns are uneven. For climate analysis, both modern and fossil floras should be sampled over an area sufficient to minimize this bias and to maximize re- covered species richness within a given climate.
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Leaf mass per area (MA) is a central ecological trait that is intercorrelated with leaf life span, photosynthetic rate, nutrient concentration, and palatability to herbivores. These coordinated variables form a globally convergent leaf economics spectrum, which represents a general continuum running from rapid resource acquisition to maximized resource retention. Leaf economics are little studied in ancient ecosystems because they cannot be directly measured from leaf fossils. Here we use a large extant data set (65 sites; 667 species-site pairs) to develop a new, easily measured scaling relationship between petiole width and leaf mass, normalized for leaf area; this enables MA estimation for fossil leaves from petiole width and leaf area, two variables that are commonly measurable in leaf compression floras. The calibration data are restricted to woody angiosperms exclusive of monocots, but a preliminary data set (25 species) suggests that broad-leaved gymnosperms exhibit a similar scaling. Application to two well-studied, classic Eocene floras demonstrates that MA can be quantified in fossil assemblages. First, our results are consistent with predictions from paleobotanical and pa- leoclimatic studies of these floras. We found exclusively low-MA species from Republic (Washington, U.S.A., 49 Ma), a humid, warm-temperate flora with a strong deciduous component among the an- giosperms, and a wide MA range in a seasonally dry, warm-temperate flora from the Green River Formation at Bonanza (Utah, U.S.A, 47 Ma), presumed to comprise a mix of short and long leaf life spans. Second, reconstructed MA in the fossil species is negatively correlated with levels of insect herbivory, whether measured as the proportion of leaves with insect damage, the proportion of leaf area removed by herbivores, or the diversity of insect-damage morphotypes. These correlations are consistent with herbivory observations in extant floras and they reflect fundamental trade-offs in plant-herbivore associations. Our results indicate that several key aspects of plant and plant-animal ecology can now be quantified in the fossil record and demonstrate that herbivory has helped shape the evolution of leaf structure for millions of years.
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Bringing together leaf trait data spanning 2,548 species and 175 sites we describe, for the first time at global scale, a universal spectrum of leaf economics consisting of key chemical, structural and physiological properties. The spectrum runs from quick to slow return on investments of nutrients and dry mass in leaves, and operates largely independently of growth form, plant functional type or biome. Categories along the spectrum would, in general, describe leaf economic variation at the global scale better than plant functional types, because functional types overlap substantially in their leaf traits. Overall, modulation of leaf traits and trait relationships by climate is surprisingly modest, although some striking and significant patterns can be seen. Reliable quantification of the leaf economics spectrum and its interaction with climate will prove valuable for modelling nutrient fluxes and vegetation boundaries under changing land-use and climate.
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Quantitative statistical sampling of plant debris entombed within deltaic sediments of a Holocene fluviolacustrine environment at Silwood Lake, Berkshire, demonstrates that patterns of deposition exist that can be used to reconstruct the relative spatial distributions of species within the source vegetation. Samples of unconsolidated sediment, each 0.5 x 0.5 x 0.02 m in volume, were collected from subaerial deltaic deposits, using a regular sampling matrix, and examined for their content of plant material. Density and cover measurements were made of both whole and fragmented recovered leaves and the data subsequently analyzed using principal components analysis and correspondence analysis ordination methods. Both theoretically and practically, correspond- ence analysis proved the more useful technique and revealed that the pattern offragment deposition, unlike that of whole leaves, is associated with stream distributaries. The various species compositions of the whole-leaf and fragmented-leaf distribution over a single bedding surface can be used to reconstruct the relative positions of the source species within the vegetation. Sorting by long-distance wind transport favors small sun leaves; in open-lake environments the deposited leaf size population can depart significantly from that exhibited by the growing source vegetation. The vertical pattern of plant-debris deposition was revealed by coring. A lower leaf bed represents lake-bottom deposition, an upper leaf bed was formed by direct aerial transport of leaves, fruits, seeds, and other material to the subaerial deltaic sediments as well as by collective settling at the top of the foreset slope of stream-transported material. Theoretically, these two distinct leaf beds differ in species composition such that the lower leaf bed reflects the vegetation immediately surrounding the basin of deposition, and the upper a deposit enriched by plant material derived from more distantly growing upstream vegetation. Preferential feeding by invertebrate organisms and differential microbiological breakdown may seriously distort this pattern, but the effect may be compensated for by exam- ining leaves preserved in relation to rapidly deposited sediments. Rapid deposition limits the biological degradation that can take place and that may totally destroy susceptible species under more normal conditions. Most information of paleoecological value is in the fragmented material rather than the more complete "museum specimens." Vertical differences in the species composition of plant-fossil beds may reflect special species distributions in the source vegetation rather than floristic changes with time.
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There are many methods for inferring terrestrial palaeoclimates from palaeontological data, including the size and species diversity of ectothermic vertebrates, the locomotor and dental adaptations of mammals, characteristics of leaf shape, size, and epidermis, wood anatomy, and the climatic preferences of nearest living relatives of fossil taxa. Estimates of palaeotemperature have also been based on stable oxygen isotope ratios in shells and bones. Interpretation of any of these data relies in some way on uniformitarian assumptions, although at different levels depending on the method. Most of these methods can be applied to a palaeoclimatic reconstruction for the interior of North America during the early Eocene, which is thought to be the warmest interval of global climate in the Cenozoic. Most of the data indicate warm equable climates with little frost. Rainfall was variable, but strong aridity was local or absent. The inferred palaeoclimate is very different from the present climate of the region and from model simulations for the Eocene. This suggests that models fail to incorporate forcing factors that were present at that time, that they treat the heat régime of continents unrealistically, and/or that model inputs such as sea surface temperature gradients or palaeotopography are incorrect.
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Australia has numerous fossil floras suitable for paleoclimatic analysis, with potential to improve understanding of Southern Hemisphere climatic evolution. Leaf-margin analysis (LMA) is a widely used method that applies present-day correlations between the proportion of woody dicot species with untoothed leaves and mean annual tempera-ture to estimate paleotemperatures from fossil megafloras. Australia's unique history and vegetation imply that its leaf-margin correlation might differ from other regions; these possible differences are investigated here to improve paleo-climatic interpretations. Australian rainforest vegetation shows nearly the same regression slope as recorded in East Asia and the Americas, indicating a globally convergent evolutionary response of leaf form to temperature. However, Australian sites tend to have fewer toothed species at localities with the same tem-perature as Asian and American sites. The following factors, singly or in combination, may account for this difference: (1) Australia's Cenozoic movement into lower latitudes, insulation from global cooling, and isolation from high-latitude cold-tolerant vegetation sources; (2) lack of high mountains as sources and refuges for cold-adapted taxa; (3) Pleistocene extinctions of cold-adapted taxa; and (4) the near absence of a cold-climate forest ecospace in Australia today. Application of Australian LMA to Australian Cenozoic floras resulted in cooler temperature estimates than other LMA regressions. However, Australian paleotemperature estimates should account for the relative importance of cold-deciduous taxa. The timing and magnitudes of the extinctions of cold-adapted lineages are not known, and the most conservative approach is to use Australian LMA as a minimum and non-Australian LMA as a maximum temperature estimate.
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Analyses of physiognomy of Late Cretaceous leaf assemblages and of structural adaptations of Late Cretaceous dicotyledonous woods indicate that megathermal vegetation was an open-canopy, broad-leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year, with a moderate increase at about 40–45°N. Many dicotyledons were probably large, massive trees, but the tallest trees were evergreen conifers. Megathermal climate extended up to paleolatitude 45–50°N. Mesothermal vegetation was at least partially an open, broad-leaved evergreen woodland (perhaps a mosaic of woodland and forest), but the evapotranspirational stress was less than in megathermal climate. Some dicotyledons were large trees, but most were shrubs or small trees; evergreen conifers were the major tree element. Some mild seasonality is evidenced in mesothermal woods; precipitational levels probably varied markedly from year to year. Northward of approximately paleolatitude 65°N, evergreen vegetation was replaced by predominantly deciduous vegetation. This replacement is presumably related primarily to seasonality of light. The southern part of the deciduous vegetation probably existed under mesothermal climate. Comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational-climatic patterns suggested from North American data. Limited data from equatorial regions suggest low rainfall.
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The sizes and shapes (physiognomy) of fossil leaves are widely applied as proxies for paleoclimatic and paleoecological variables. However, significant improvements to leaf-margin analysis, used for nearly a century to reconstruct mean annual temperature (MAT), have been elusive; also, relationships between physiognomy and many leaf ecological variables have not been quantified. Using the recently developed technique of digital leaf physiognomy, correlations of leaf physiognomy to MAT, leaf mass per area, and nitrogen content are quantified for a set of test sites from North and Central America. Many physiognomic variables correlate significantly with MAT, indicating a coordinated, convergent evolutionary response of fewer teeth, smaller tooth area, and lower degree of blade dissection in warmer environments. In addition, tooth area correlates negatively with leaf mass per area and positively with nitrogen content. Multiple linear regressions based on a subset of variables produce more accurate MAT estimates than leaf-margin analysis (standard errors of ±2 vs. ±3°C); improvements are greatest at sites with shallow water tables that are analogous to many fossil sites. The multivariate regressions remain robust even when based on one leaf per species, and the model most applicable to fossils shows no more signal degradation from leaf fragmentation than leaf-margin analysis.
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Teeth are conspicuous features of many leaves. The percentage of species in a flora with toothed leaves varies inversely with temperature, but other ecological controls are less known. This gap is critical because leaf teeth may be influenced by water availability and growth potential and because fossil tooth characters are widely used to reconstruct paleoclimate. Here, we test whether ecological attributes related to disturbance, water availability, and growth strategy influence the distribution of toothed species at 227 sites from Australian subtropical rainforest. Both the percentage and abundance of toothed species decline continuously from riparian to ridge-top habitats in our most spatially resolved sample, a result not related to phylogenetic correlation of traits. Riparian lianas are generally untoothed and thus do not contribute to the trend, and there is little association between toothed riparian species and ecological attributes indicating early successional lifestyle and disturbance response. Instead, the pattern is best explained by differences in water availability. Toothed species' proportional richness declines with proximity to the coast, also a likely effect of water availability because salt stress causes physiological drought. Our study highlights water availability as an important factor impacting the distribution of toothed species across landscapes, with significance for paleoclimate reconstructions.
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Present-day correlations between leaf physiognomic traits (shape and size) and climate are widely used to estimate paleoclimate using fossil floras. For example, leaf-margin analysis estimates paleotemperature using the modern relation of mean annual temperature (MAT) and the site-proportion of untoothed-leaf species (NT). This uniformitarian approach should provide accurate paleoclimate reconstructions under the core assumption that leaf-trait variation principally results from adaptive environmental convergence, and because variation is thus largely independent of phylogeny it should be constant through geologic time. Although much research acknowledges and investigates possible pitfalls in paleoclimate estimation based on leaf physiognomy, the core assumption has never been explicitly tested in a phylogenetic comparative framework. Combining an extant dataset of 21 leaf traits and temperature with a phylogenetic hypothesis for 569 species-site pairs at 17 sites, we found varying amounts of non-random phylogenetic signal in all traits. Phylogenetic vs. standard regressions generally support prevailing ideas that leaf-traits are adaptively responding to temperature, but wider confidence intervals, and shifts in slope and intercept, indicate an overall reduced ability to predict climate precisely due to the non-random phylogenetic signal. Notably, the modern-day relation of proportion of untoothed taxa with mean annual temperature (NT-MAT), central in paleotemperature inference, was greatly modified and reduced, indicating that the modern correlation primarily results from biogeographic history. Importantly, some tooth traits, such as number of teeth, had similar or steeper slopes after taking phylogeny into account, suggesting that leaf teeth display a pattern of exaptive evolution in higher latitudes. This study shows that the assumption of convergence required for precise, quantitative temperature estimates using present-day leaf traits is not supported by empirical evidence, and thus we have very low confidence in previously published, numerical paleotemperature estimates. However, interpreting qualitative changes in paleotemperature remains warranted, given certain conditions such as stratigraphically closely-spaced samples with floristic continuity.
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Leaf margin characters are strong predictors of mean annual temperature (MAT) in modern plant communities and widely used tools for reconstructing paleoclimates from fossil floras. However, the frequency of nonentire-margined species may vary dramatically between different habitats of the same forest. In this paper we explore the potential for this habitat variation to introduce error into temperature reconstructions, based on field data from a modern lowland forest in Amazonian Ecuador.The data show that the provenance of leaves can influence temperature estimates to an important degree and in a consistent direction. Woody plants growing along lakes and rivers underestimated MAT by 2.5°-5°C, while those in closed-canopy forest provided very accurate predictions. The high proportion of liana species with toothed leaves in lakeside and riverside samples appears to be responsible for a large part of the bias. Samples from closed-canopy forest that included both lianas and trees, however, were more accurate than tree-only or liana-only samples.We conclude that paleotemperature reconstructions based on leaf margin characters will be misleading to the extent that fossilization provides a better record of certain habitats than others. The preponderance of lake and river deposits in the angiosperm fossil record suggests that underestimation of mean annual paleotemperature may be common.
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Broad scaling relationships between leaf size and function do not take into account that leaves of different size may contain different fractions of support in petiole and mid-rib. The fractions of leaf biomass in petiole, mid-rib and lamina, and the differences in chemistry and structure among mid-ribs, petioles and laminas were investigated in 122 species of contrasting leaf size, life form and climatic distribution to determine the extent to which differences in support modify whole-lamina and whole-leaf structural and chemical characteristics, and the extent to which size-dependent support investments are affected by plant life form and site climate. For the entire data set, leaf fresh mass varied over five orders of magnitude. The percentage of dry mass in mid-rib increased strongly with lamina size, reaching more than 40 % in the largest laminas. The whole-leaf percentage of mid-rib and petiole increased with leaf size, and the overall support investment was more than 60 % in the largest leaves. Fractional support investments were generally larger in herbaceous than in woody species and tended to be lower in Mediterranean than in cool temperate and tropical plants. Mid-ribs and petioles had lower N and C percentages, and lower dry to fresh mass ratio, but greater density (mass per unit volume) than laminas. N percentage of lamina without mid-rib was up to 40 % higher in the largest leaves than the total-lamina (lamina and mid-rib) N percentage, and up to 60 % higher than whole-leaf N percentage, while lamina density calculated without mid-rib was up to 80 % less than that with the mid-rib. For all leaf compartments, N percentage was negatively associated with density and dry to fresh mass ratio, while C percentage was positively linked to these characteristics, reflecting the overall inverse scaling between structural and physiological characteristics. However, the correlations between N and C percentages and structural characteristics differed among mid-ribs, petioles and laminas, implying that the mass-weighted average leaf N and C percentage, density, and dry to fresh mass ratio can have different functional values depending on the importance of within-leaf support investments. These data demonstrate that variation in leaf size is associated with major changes in within-leaf support investments and in large modifications in integrated leaf chemical and structural characteristics. These size-dependent alterations can importantly affect general leaf structure vs. function scaling relationships. These data further demonstrate important life-form effects on and climatic differentiation in foliage support costs.
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Floras of predominantly wet-soil environments show a greater than expected proportion of toothed leaves, affecting the outcome of leaf physiognomically based temperature estimates. New analyses of foliar physiognomy of plants growing in predominantly wet soils in modern forests suggest that current methods of inferring paleotemperatures from fossil floras yield underestimates of 2.5-10 degrees C. The changes we propose bring terrestrial paleotemperature estimates into agreement with temperatures inferred from other biological and geological proxies and strengthen the use of leaf physiognomy as a method for climate reconstruction.
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Cohesion-tension transport of water is an energetically efficient way to carry large amounts of water from the roots up to the leaves. However, the cohesion-tension mechanism places the xylem water under negative hydrostatic pressure (P x), rendering it susceptible to cavitation. There are conflicts among the structural requirements for minimizing cavitation on the one hand vs maximizing efficiency of transport and construction on the other. Cavitation by freeze-thaw events is triggered by in situ air bubble formation and is much more likely to occur as conduit diameter increases, creating a direct conflict between conducting efficiency and sensitivity to freezing induced xylem failure. Temperate ring-porous trees and vines with wide diameter conduits tend to have a shorter growing season than conifers and diffuse-porous trees with narrow conduits. Cavitation by water stress occurs by air seeding at interconduit pit membranes. Pit membrane structure is at least partially uncoupled from conduit size, leading to a much less pronounced trade-off between conducting efficiency and cavitation by drought than by freezing. Although wider conduits are generally more susceptible to drought-induced cavitation within an organ, across organs or species this trend is very weak. Different trade-offs become apparent at the level of the pit membranes that interconnect neighbouring conduits. Increasing porosity of pit membranes should enhance conductance but also make conduits more susceptible to air seeding. Increasing the size or number of pit membranes would also enhance conductance, but may weaken the strength of the conduit wall against implosion. The need to avoid conduit collapse under negative pressure creates a significant trade-off between cavitation resistance and xylem construction cost, as revealed by relationships between conduit wall strength, wood density and cavitation pressure. Trade-offs involving cavitation resistance may explain the correlations between wood anatomy, cavitation resistance, and the physiological range of negative pressure experienced by species in their native habitats.