CLIMATIC CHANGE AND THE BROAD-SCALE DISTRIBUTION OF TERRESTRIAL ECOSYSTEM COMPLEXES*
5. Conc lus ions
Comparison of the Holdridge Life-Zone Maps in Figures 2 and 4 provides an ini-tial test of the sensitivity of the distribution of major vegetation associations to temperature changes such as may result from increases in atmospheric C02 concentration. The indicated changes in global vegetation distribution are quite substantial and more complex shifts can be expected when additional factors are considered.
Even lhough one mighl predicL a large shifL in vegelalion in response Lo a change in climaLe, inspection of a smaller-scale subregion could demonstrate the presence of a wide range of vegetation al particular sites. One finds grass-land in fire-prone regions within foresLed grass-landscapes or riverine forests even in deserts. Such heterogeneity characterizes the present landscape, ancl we should expect il in landscapes thal mighl develop in response Lo a!Lered global climaLe.
With these considerations and an impression of the reliability of the Holdridge Classification and Maps in mind, it is appropriate Lo discuss the theoretical changes in global vegeLalion that might result from climatic warming (Figure 4)
The changes in carbon storage Lhal might resu!L from Lhese changes in vegetation distribuLion are sufficienlly large lo suggest that the feedback of climatic change on Lhe carbon cycle Lhrough Lhis mechanism may be important in understanding how atmospheric C02 concentration. will increase as further fossil fuel use occurs. Furthermore, the changes in land cover implied by Fig-ures 2 and 4 indicale significant changes in the Earth's albedo Lhat should be considered in simulating Lhe sensitivity of climate to changes in C02 concenlra -lion.
The most importanL facLor limiting Lhe realism of the exercise reporLed here is lhe absence of precipitation change in the analysis. The discussion above implies lhat the impacts of climatic change on nalural vegelalion distribution may be considerably differenl when moislure changes are also sLudied. Climate models now simulaLe changes in precipitation, although not as realistically as temperature, and the required analysis should be completed in lhe near future
Inconsislencies between the resolution of simulated climalic change and life-zone maps derived from meteorological daLa require refinements lo climale models lhat may not be practical for some time. The applicability of simulation results from climate models lo analysis of vegetalion pallerns associaled with seasonaliLy, topography, and transition zones is also restricted by the coarse resolution of climate models. Simulalion of climate at Lhe continental or regional scale with greater spatial resolution may provide Lhe firsl simulation resulls for studying the sensitivity of these more complex vegelalion pallerns . to climatic change. However, available methods for relating vegetation distribu -tion and climate, such as lhe Holdridge ClassiA.cation, also require refinemenL in this regard.
Acknowledgments
The authors wish to thank RV. O'Neill and J.R Krummel, Oak Ridge National Laboratory (ORNL), for review of early drafts of the paper. J.S. Olson (ORNL) pr o-vided review and guidance throughoul the work, and R.J. Renka (Ol~NL) developed the software used for interpolation and advised the authors on numerical problems associated with the research. Discussions and review by other participants in the Conference on The Sensitivity of Ecosystems and Society to ClimaUc Change held in Villach, Austria, in September 1983 were par-ticularly helpful in the preparation of the paper.
Climatic Change and Terrestrial Ecosystem Complexes 43
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