New developments in CLAMP: Calibration using global gridded meteorological data

Climate Leaf Analysis Multivariate Program (CLAMP) is a versatile technique for obtaining quantitative estimates for multiple terrestrial palaeoclimate variables from woody dicot leaf assemblages. To date it has been most widely applied to the Late Cretaceous and Tertiary of the mid- to high latitudes because of concerns over the relative dearth of calibration sites in modern low-latitude warm climates, and the loss of information associated with the lack of marginal teeth on leaves in paratropical to tropical vegetation. This limits CLAMP's ability to quantify reliably climates at low latitudes in greenhouse worlds of the past. One of the reasons for the lack of CLAMP calibration samples from warm environments is the paucity of climate stations close to potential calibration vegetation sites at low latitudes. Agriculture and urban development have destroyed most lowland sites and natural vegetation is now largely confined to mountainous areas where climate stations are few and climatic spatial variation is high due to topographic complexity. To attempt to overcome this we have utilised a 0.5° × 0.5° grid of global interpolated climate data based on the data set of New et al. (1999) supplemented by the ERA40 re-analysis data for atmospheric temperature at upper levels. For each location, the 3-D climatology of temperature from the ECMWF re-analysis project was used to calculate the mean lower tropospheric lapse rate for each month of the year. The gridded data were then corrected to the altitude of the plant site using the monthly lapse rates. Corrections for humidity were also made. From this the commonly returned CLAMP climate variables were calculated. A bi-linear interpolation scheme was then used to calculate the climate parameters at the exact lat/long of the site. When CLAMP analyses using the PHYSG3BR physiognomic data calibrated with the climate station based MET3BR were compared to analyses using the gridded data at the same locations (GRIDMET3BR), the results were indistinguishable in that they fell within the range of statistical uncertainty determined for each analysis. This opens the way to including natural vegetation anywhere in the world irrespective of the proximity of a meteorological station

Climatic reconstruction of two Pliocene floras from Mexico

The role that climate plays in influencing the physiognomy of modern and fossil plant communities is widely acknowledged and forms the basis for several palaeoclimate proxies. In this work, both univariate Leaf Margin Analysis and multivariate Climate/Leaf Analysis Multivariate Program (CLAMP) were used for the climatic reconstruction of two fossil localities of the Atotonilco El Grande Formation. Using the predominantly North American and Asian calibration data set PHYSG3BRC, supplemented with new African material, results from two sites, Los Baños (present position 20°18′18″N, 98°42′44.4″W) and Sanctorum (20°18′18.5″N and 98°46′52.2″W), indicate that during the Pliocene a mesothermal climate existed with mean annual temperatures between 12 and 22°C, with the most likely being approximately 15°C, and a mean annual temperature range of 21°C. A distinct seasonal variation in rainfall is evident with a mean annual relative humidity of 60–70%. Differences between the sites can be explained by differences in depositional regime and spatial heterogeneity in the predominantly Quercus-dominated woodland. The continuous subsequent uplift of the Sierra Madre Oriental, the resulting development of a rain shadow, and the eventual disappearance of a palaeolake appear to have caused a transition to the modern xerophytic shrub vegetation

Leaf form-climate relationships on the global stage: an ensemble of characters

Aim Early in their evolution, angiosperms evolved a diversity of leaf form far greater than that of any other group of land plants. Some of this diversity evolved in response to varying climate. Our aim is to test the global relationship between leaf form in woody dicot angiosperms and the climate in which they live. Location We have compiled a data set describing leaf form(using 31 standardized categorical characters) from 378 natural or naturalized vegetation sites from around the world. Our data include sites from all continents except Antarctica and encompass biomes from tropical to taiga, over a range of elevations from 0.5 m to over 3000 m. Methods We chose the Climate Leaf Analysis Multivariate Program sampling, scoring and analytical protocols to test the relationships between climate and leaf form, which is based on canonical correspondence analysis. Cluster analysis evaluates the role of historical factors in shaping the patterns, and pairwise Pearson correlations examine the relationships among leaf characters. Results Woody dicot leaf characters form a physiognomic spectrum that reflects local climate conditions. On a global scale, correlations between leaf form and climate are consistent, irrespective of climate regime, vegetation type or biogeographic history. Relationships with temperature variables are maintained even when leaf margin characters, regarded as being particularly well correlated with mean annual temperature, are removed. Main conclusions In natural woody dicot vegetation an integrated spectrum of leaf form has developed across multiple leaf character states and species. This spectrum appears more strongly influenced by prevailing climate than biogeographic history. The covariation of leaf traits across species suggests strong integration of leaf form. New methods of exploring structure in multidimensional physiognomic space enable better application of leaf form to palaeoclimate reconstruction