Jarvis, P.G. Ed. 1998. European Forests and Global Change: The Likely Impacts of Rising CO2 and Temperature. Cambridge University Press, Cambridge, United Kingdom.
It is important to understand how earth's plant life will respond to the ongoing rise in the air's CO2 content, because plants reside near the bottom of most food chains and are able to photosynthetically convert energy from the sun into the chemical energy that is ultimately used to support the existence of nearly all other organisms, including man. Trees are additionally important because they are long-lived and have the potential to remove vast amounts of carbon from the atmosphere and store it in their tissues or transfer it to the soil. Tree responses to atmospheric CO2 enrichment, therefore, need to be determined so we can better understand their role in the global carbon cycle. It was recently suggested, for example, that North America's forests might annually remove from the air all of the CO2 that the United States and Canada yearly put into it as a result of the burning of fossil fuels (see our Volume 1 Number 5 Editorial). We are thus most fortunate to receive this timely book from Paul Jarvis and a number of Europe's other leading CO2 researchers, which reviews the responses of several European forest trees to atmospheric CO2 enrichment and shows that they, too, provide a tremendous sink for atmospheric carbon dioxide.
The first chapter of the book describes the various methodologies that were used at study sites across Europe to increase the CO2 concentration around forest trees, including open-top and open-side chambers, miniature glasshouses and branch bags. The next four chapters investigate physiological responses of European forest trees to atmospheric CO2 enrichment, with emphasis being placed on photosynthesis, dark respiration, phenology, biomass and growth. Overall, photosynthetic rates of carbon uptake increased with atmospheric CO2 enrichment, while carbon losses from dark respiration were reduced. As a result, greater overall carbon sequestration occurred in trees exposed to elevated CO2 concentrations than occurred in trees exposed to ambient CO2 concentrations. Despite the large variability among the seven tree species utilized in the phenological studies, they all exhibited positive responses to elevated CO2 in terms of their relative growth rates. Elevated CO2 also either maintained or shortened, but did not extend, the growing seasons of all seven species; and it invariably increased their biomass production.
The following two chapters describe interactions between elevated CO2 and the availability of important resources with respect to European forest productivity. The first of these chapters discusses some of the mechanisms that lead to increases in water-use efficiency with atmospheric CO2 enrichment. It also provides data on the role that atmospheric CO2 enrichment plays in mitigating the negative effects of water stress on biomass production. The latter chapter similarly describes how soil nutrition influences biomass accumulation under conditions of atmospheric CO2 enrichment, which commonly is low for soils of poor nutrient status but substantial for soils of good fertility.
The next chapter deals with the interactive effects of elevated CO2 and temperature on the growth of three European tree species. In experiments with Scots pine, CO2-induced increases in water-use efficiency were enhanced by elevated temperatures. Likewise, annual net carbon assimilation in Scots pine increased by 40% in elevated CO2 alone, but rose by 58% when combined with high air temperature. On the other hand, the dry mass of sycamore seedlings increased with elevated CO2 by about the same amount at all treatment air temperatures; and beech seedling dry mass showed little response to either atmospheric CO2 enrichment or growth temperature until the highest treatment air temperature was reached, whereupon the positive effects of elevated CO2 began to be realized.
The following chapter describes the use of microcosms to determine ecosystem responses to elevated CO2. Miniature beech ecosystems were used to ultimately model increased photosynthetic rates of beech stands under conditions of atmospheric CO2 enrichment. This type of information is also used in the next chapter in an attempt to model total forest ecosystem productivity in response to increasing levels of atmospheric CO2. Two forest sites, one from Canada and one from France, had their productivities modeled for scenarios consisting of elevated CO2 and elevated temperature. For the French site, total forest carbon increased by 47% due to elevated CO2 alone, while high temperature alone destroyed the trees and replaced them with grasses. When evaluating elevated CO2 and temperature together, however, forest carbon sequestration was nearly unchanged from the productivity induced by enhanced CO2 alone. Thus, elevated CO2 ameliorated the deleterious effects of high temperature on growth and survival. Similar results were calculated for the Canadian site, but when CO2 and temperature were increased together, forest biomass more than doubled.
The final chapter of the book gives some perspectives on future research. Although much has been accomplished, much more remains to be done to better understand the roles of long-lived woody perennials in using and disposing of atmospheric CO2 in earth's great carbon cycle.
Reviewer: Dr. Keith E. Idso, Vice President
Last updated 1 January 1999