C3C4 Dynamics during Glacial Interglacial Periods

The quantum-yield model predicts that important changes in the global proportions of C4 biomass occurred during the Pleistocene glacial-interglacial transitions. Figure 1 shows that at very low atmospheric C02 levels, C4 plants can be favored even at moderately low temperatures. The oscillation between glacial and interglacial conditions reflected an oscillation between about 180 and 280 ppmV (Fig. 2, middle), respectively, based on the CO, concentrations in the Antarctic ice cores (Petit et...

Photosynthetic Pathway Impacts Herbivores

Megafaunal changes are correlated with a shift between C3- and C4-dominated ecosystems. Several lines of evidence suggest relationships between turnover of mammalian grazing taxa and the shifts between C3 C4 vegetation types. Cerling et al (1998a) reported abrupt changes in mammalian lineages in East Africa asso- 813C tooth ename equid ( ) other ( ) FIGURE 9 Faunal Change Index from the Pakistan, represented by the number of first (nf) and last n ) occurrences, including only occurrences (n0),...

References

Historical development of gallery forests in northeast Kansas. Vegetatio 65, 29-37. Acocks, J. P. H. (1964). Karroo vegetation in relation to the development of deserts. In Ecological Studies of Southern Africa (D. H. S. Davis, Ed.), pp. 100-112. Dr. Junk Publishers, The Hague. Adamoli, J., Sennhauser, E., Acero, J. M., and Rescia, A. (1990). Stress and disturbance Vegetation dynamics in the dry Chaco region of Argentina. . Biogeogr. 17, 491-500. Ambrose, S. H., and Sikes,...

Global Soil Organic Carbon Pool

Introduction the Soil Carbon Pool and Global 2. Factors Affecting the Distribution of Soil Organic 3. Global Variations in the SOC 4. Limitations of Available Observational SOC 5. A Stratified Sampling 6. Conclusions Sandworld and 1. Introduction the Soil Carbon Pool and Global Change Estimates of the size of the global soil organic carbon (SOC) pool have ranged between 700 Pg (Bolin, 1970) and 2946 Pg (Bohn, 1976), with a value of around 1500 Gt now generally accepted as the most appropriate...

Global Expansion of C4 Ecosystems

Figure 5 shows that between 8 and 6 Ma there was a global expansion of C4 ecosystems (Cerling et al, 1997, 1998a). There is no conclusive evidence for the presence of C4 biomass in the diets of mammals before 8 Ma (Cerling et al, 1997 1998a), although the presence of small amounts of C4 biomass in diets is not excluded because of the uncertainty in the SI3C endmember for C, plants. By 6 Ma there is abundant evidence for significant C4 biomass in Asia (Cerling et al, 1993 1997 Morgan et al,...

Description of the Model

BIOME3.5 is an equilibrium terrestrial biosphere model based largely on the BIOME3 model of Haxeltine and Prentice (1996). BIOME3.5's main differences from its predecessor include the addition of a module to calculate isotopic discrimination during photosynthesis (Aleaf), the reparameterization of the original plant functional types (PFTs), and the addition of several new PFTs to reflect poorly represented vegetation types in the arctic and arid subtropics. Like BIOME3, BIOME3.5 is a coupled...

Summary and Conclusions

Observational data in combination with theoretical studies and modeling experiments suggest that the surface temperature of the Northern Hemisphere during the past 1000 years could be characterized as follows First, a slow ongoing cooling is by and large consistent with orbital forcing or the so-called Milankovitch effect. This amounts to an annual cooling of some 0.2 K over 900 years. Second, a rapid temperature increase starting at the beginning of the 20tli century remained more or less...

BuildUp of Carbon and the Evolution of Decomposers

By the Robinson (1990) hypothesis, effective lignin degradation did not appear until some 200 million years after lignin evolved with the appearance of basidiomycetes in the Pennsylvanian. This could explain the build-up of organic compounds during the late Mesozoic. With increasing oxygen content of the atmosphere, the increase in basiodimycetes and the evolution of angiosperms with lower lignin-content in the Late Cretaceous, carbon stores in the soils decreased. The events discussed so far...

Introduction Apples and Oranges

In December 1997, after nights of bargaining that culminated two years of hard negotiations, representatives of 160 governments wearily agreed in Kyoto, Japan, on a protocol to supplement the 1992 United Nations Framework Convention on Climate Change. It was hoped that the Kyoto Protocol would represent a major step forward by the international community to mitigate emissions of greenhouse gases that could alter future climate. Before long, however, doubts emerged on whether the treaty was...

Past and Future Forest Response to Rapid Climate Change

University of Minnesota, St, Paui, Minnesota 2. Long-Distance 3. Estimating Jump 4. Interactions with Resident Vegetation Constraints on 5. Interactions with Resident Vegetation Competition for Light and Resulting Constraints on Population Growth 7. Conclusions References In response to large changes of climate during the Ilolocene, geographical ranges of tree species shifted northward in eastern North America, with range extensions occurring at rates of 10-100 km per century. Long-distance...

Monitoring Compliance and Enforcement

It has been frequently emphasized that the effectiveness of international environmental law depends on establishing international procedures or mechanisms that may be used to ensure compliance.3, International environmental law has developed several such mechanisms, one of them being the obligation of states parties to regularly report the national measures undertaken to pursuent to the respective international agreement. However, international environmental law does not entrust particular...

Impulse Response Climate Models

For any complex, nonlinear system such as climate, it is permissible, for sufficiently small perturbations, to describe the response of the system to external forcing in terms of a linearized response model. In the case of the climate system, the linearization condition is approximately satisfied for the external forcing due to anthropogenic greenhouse gas emissions if the temperature change remains below about 2-3 C. Measured in Kelvin relative to absolute zero temperature at 273 C, the global...

The IGBP Transect Approach

Although new satellite images allow a more and more detailed observation of the earth surface (e.g., Defries et al., 2000), the ground truth remains essential. This was recognized by IGBP as a significant problem because it remains impossible to study processes with global coverage. Continental transects were suggested that represent the major climatic regions of the globe and allow repeated observations at the same time (Walker et al., 1999). Continental transects were suggested for the boreal...

Plant Compounds and Their Turnover and Stabilization as Soil Organic Matter

Czimczik, Christiane Kramer, Barbara L hkcr, and Michael W.I. Schmidt 2. Pathways of Soil Organic Matter 3. Stabilization of Soil Organic 4. Turnover of Soil Organic Matter The increase in atmospheric CO, because of fossil fuel emissions has been identified as a major driving force for global climate change. Soil organic matter (SOM) is expected to be an important sink for this carbon (Ciais et al., 1995 Schimel, 1995 Steffen et al., 1998). However, at higher mean...

Ecophysiological Information from Ae

It is well established that leaf carbon-isotope discrimination provides valuable information about the ratio of leaf assimilation to stomatal conductance (intrinsic water-use efficiency Farquhar et at, 1989). Based on field observations of Ac, Buchmann ct al. (1998) postulated that ecosystem discrimination might increase with decreasing ratio of ecosystem assimilation to canopy conductance (A Gc, in mol CO, per mol II,0). Using BIOME3.5, we tested this hypothesis for the 22 biomes simulated by...