Vegetation feedback

Harvey, L. D. D. (1989b). Milankovitch forcing, vegetation feedback, and North Atlantic deep-water formation. /. Climate 2, 800-815... 

TEMPO. (1996). Potential role of vegetation feedback in the climate sensi-tiviy of high-latitude regions A case study at 6000 years B. P. Global... 

Since neither land-surface nor ocean-surface feedbacks alone arc sufficient to explain the observed expansion of the African monsoon during the mid-Holocene, synergistic feedbacks involving land-atmosphere-ocean interactions are likely to be involved (GanopoLski ct al., 1998 Braconnot et al., 1999 Berger, in press). There have been only two attempts to examine this question. In simulations with an intermediate-complexity model, GanopoLski et al. (1998) showed that vegetation feedbacks were more important than ocean feedbacks in the amplification of the African monsoon. This simulation may not be realistic, however, because the ocean model does not re-... 

Levis, S., Foley,. A., and Pollard, D. (1999b). Potential high-latitude vegetation feedbacks on CO,-induced climate change. Geophys. Res. Lett. 26, 747-750. 

Predicting the effect of the terrestrial vegetation response to C02-induced climate change for a particular site involves explicit treatment of feedbacks. These are diagramed in Figure 3. The balance between decomposition + autotrophic respiration and gross primary production (GPP) determines the net storage and release of carbon to atmosphere. Climate meets each of these... 

A positive feedback between vegetation and atmospheric CO2 will occur if biomass declines. This will happen to the extent that climatic warming causes increased water stress, either through decreased precipitation or increased evap-otransporation, particularly on soils of low water-holding capacity. Decreases in soil nutrient availability, either directly caused by drought or indirectly caused by replacement with taxa with more recalcitrant litter, may further decrease the net release of carbon from the biosphere to the atmosphere. Positive feedback will also arise if the current standing biomass of trees is replaced by small trees, shrubs, and herbs that store less carbon. 

The effects that changes in vegetation have on soil carbon pools and nutrient availability are also difficult to evaluate. However, several models have been successful in predicting vegetation-soil nutrient relationships because they assume that such changes occur as a result of different rates of decomposition and nutrient release from leaf litter of different taxa 50, 60), Such predictions could be tested and the models refined or parameterized for new taxa by measuring soil nutrient availability and respiration in stands of different species on the same soil type. For example, fifty years ago the U.S. Civilian Conservation Corps (CCC) established such stands as species trial plots measurements in some indicate large differences in soil nutrient availability (48), Further measurements in these stands would now occur at the same time-scale at which we expect the feedback between species replacement and soil processes to occur. 

Information on the response of taxa to climate and the feedback between vegetation and soil nutrient availability should be synthesized and used to construct computer models operating at the same scale as GCM output 61). Such models should be able to do the following ... 

Kutzbach, J., Bonan, G., Foley, J. and Harrison, S. P. (1996). Vegetation and soil feedbacks on the response of the African monsoon to orbital forcing in the early to middle Holocene, Nature 384, 623-626. 

The complex of feedbacks controls interactive exchange with energy, water, and carbon between the atmosphere and the Earth s surface causing a response of these fluxes to disturbances such as transformation of land cover or pollution of the World Ocean with oil. Substantial feedbacks are physiological responses of vegetation communities to changes in temperature and humidity of the atmosphere and soil. 

Graetz R. D. (1991) The nature and significance of the feedback of change in terrestrial vegetation on global atmospheric and climatic change. Clim. Change 18, 147-173. 

Figure 4. Feedbacks in a vegetation - atmosphere system described by Went (1960).

Last but not least come the environmental feedbacks that link atmospheric chemistry, the biosphere and climate change. Isoprene is a major biogenic trace component of the atmosphere. It was more than 40 years ago when Went (1960) discussed a specific relation between plant emissions and a blue haze observed above the countryside vegetation on sunny... 

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