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Greenock Swamp wetland complex is one of few remaining natural wetlands in the Great Lakes region and, at 89 km2 in areal extent, is currently the largest hardwood swamp in southern Ontario, Canada. We present here pollen and sediment records from a kettle hole (Schmidt Lake) and adjacent Thuja occidentalis swamp to reconstruct regional paleoclimate and vegetation history, and to assess the timing and development of the swamp ecosystem and associated carbon stocks. Pollen-inferred paleoclimate reconstructions show the expected warming in the Early Holocene, and indicate the Mid-Holocene initiation of lake-effect snow. This enhanced snowfall may have maintained high water tables in the adjacent wetland since ca. 8300 years ago, promoting the establishment of a swamp dominated by Thuja occidentalis. Carbon accumulation rates in a >2-m-long peat core collected from a Thuja occidentalis stand adjacent to Schmidt Lake are 30-40 g C/m2/yr, which is higher than the average of northern high-latitude peatlands. Using topographic and hydrological parameters, we estimated that mean swamp peat thicknesses could exceed 2m. Thus, this study encourages future investigations on temperate swamps from the perspective of hitherto underestimated Holocene carbon sinks and shows the importance of regional hydroclimate in supporting swamp ecosystems. [ABSTRACT FROM AUTHOR]

Carbon-concentrating mechanisms (CCMs) in plants involve actively increasing CO2 concentrations near ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO). The assumption has been that terrestrial plants did not evolve CCMs for well over 300 million years, yet most marine plants probably evolved CCMs at the time when oxygenic photosynthesis first occurred in the Paleozoic. One primary reason for this assumption is that analysis of genetic mutations for phosphoenolpyruvate carboxylase (PEPc; an enzyme required for C4 and CAM photosynthesis) indicate a molecular age of no more than 65 Ma. Could the evolutionary response of both RuBisCO and PEPc to varying concentrations of atmospheric CO2 and O2 over geological time have obscured the real time when land plants first used PEPc during photosynthesis? [Copyright &y& Elsevier]

[1] High-resolution records of greenhouse gas concentrations from the Law Dome Antarctic ice core show small fluctuations in atmospheric CO2 and CH4, including a 10 ppmv decrease in CO2 and a 50 ppbv increase in CH4 during the Little Ice Age. Explanations for the biosphere-atmosphere carbon exchanges that caused these fluctuations, and their impacts on global climate, are lacking. We produce here a wetland index derived from the North American Pollen Database and show that for most of the past two millennia, this index is negatively correlated (antiphase) with atmospheric CO2 levels measured in the Law Dome ice core. Our analysis indicates the potential for global wetlands to act as carbon sinks, contributing to small fluctuations in atmospheric greenhouse gas concentrations, and thereby influencing submillennial-scale climatic change. Although our wetland index-CO2 relationship is statistically significant, the relationship between our wetland index-CH4 curve is not, possibly due to the confounding influence of wildfires on CH4. [ABSTRACT FROM AUTHOR]

The paleoenvironmental context of plant and animal species evolution (including glacial migrations and population separations) is based on a very patchy and incomplete paleo-phytogeographic record. It was our objective, therefore, to provide an additional source for paleovegetation comparison by presenting simulations from a state-of-the-art fully coupled earth system model (HadCM3LC). We simulated potential paleovegetation distributions following pre-Industrial and last glacial maximum (LGM) climate forcing for the continent of Africa. Our LGM simulations indicate that tropical broadleaf forest was not severely displaced by expanding grasslands within central Africa, although the outer extent of closed forest decreases, particularly in the north. Our simulations indicate that the structure of glacial forests may have been much different from today, in that LGM simulations indicate that forests were likely characterized by lower leaf area indexes, lower tree heights and lower vegetation carbon content. On the other hand, warmer interglacial climate (like our pre-Industrial climate scenario) results in simulated expansion of tropical forest from coast to coast across central Africa that we postulate could have acted as a barrier to plant and animal species migrations. We suggest that our modeling experiments have implications for the interpretation of phylogenetic data, including that of our own species, Homo sapiens sapiens. [ABSTRACT FROM AUTHOR]

Aim Using a Dynamic Global Vegetation Model (DGVM), we assessed the independent and co-varying effects of temperature, precipitation and atmospheric CO2 on nonlinear (threshold) responses in carbon-based processes, and evaluated whether these underlying process thresholds translate to the ecosystem-scale. Location Amazon Basin, South America. Methods The Lund-Potsdam-Jena model (LPJ) was employed to determine responses in net primary production (NPP), heterotrophic respiration (RH), vegetation carbon (CV), soil carbon (CS), and plant functional type (PFT) composition to variations in temperature (± 9 °C relative to the control), precipitation (up to 80% reduction in rainfall relative to the control) and atmospheric CO2 (± 100 p.p.m.v. relative to the control). Results Our modelling experiments show that increases in temperature result in lower and steeper NPP and RH curves, indicating a thermal threshold at current temperature conditions. Under a combination of temperature and precipitation change, CV responds more to precipitation, while CS closely follows temperature gradients. Ecosystem thresholds, measured in terms of PFT composition stability, are surprisingly few. Simulations indicate an ecosystem threshold occurring at 80% reduction in rainfall; however, due to modelling limitations, this threshold is likely to occur at earlier drought stress conditions. Further empirical research on abiotic stress tolerance levels in tropical ecosystems must be performed in order to refine PFT descriptions used in DGVMs. Main conclusion In evaluating simulation scenarios that promote major changes in PFT assemblage, we conclude that the ‘natural’ Amazonian rain forest is resilient to environmental change, particularly to decreases in temperature and precipitation. Determining to what extent anthropogenic pressures have altered this resiliency is of utmost importance in predicting the future fate of the Amazon Basin. [ABSTRACT FROM AUTHOR]

1. Physiological experiments have indicated that the lower CO[sub 2] levels of the last glaciation (200 µmol mol[sup -1]) probably reduced plant water-use efficiency (WUE) and that they combined with increased aridity and colder temperatures to alter vegetation structure and composition at the Last Glacial Maximum (LGM). 2. The effects of low CO[sub 2] on vegetation structure were investigated using BIOME3 simulations of leaf area index (LAI), and a two-by-two factorial experimental design (modern/LGM CO[sub 2] modern/LGM climate). 3. Using BIOME3, and a combination of lowered CO[sub 2] and simulated LGM climate (from the NCARCCM1 model), results in the introduction of additional xeric vegetation types between open woodland and closed-canopy forest along a latitudinal gradient in eastern North America. 4. The simulated LAI of LGM vegetation was 25-60% lower in many regions of central and eastern United States relative to modern climate, indicating that glacial vegetation was much more open than today. 5. Comparison of factorial simulations show that low atmospheric CO[sub 2] has the potential to alter vegetation structure (LAI) to a greater extent than LGM climate. 6. If the magnitude of LAI reductions simulated for glacial North America were global, then low atmospheric CO[sub 2] may have promoted atmospheric warming and increased aridity, through alteration of rates of water and heat exchange with the atmosphere. [ABSTRACT FROM AUTHOR]