Model-based assessments of climate change effects on forests: a critical review

Model-based assessments of climate change effects on forests: a critical review While current projections of future climate change associated with increases in atmospheric greenhouse gases have a high degree of uncertainty, the potential effects of climate change on forests are of increasing concern. A number of studies based on forest simulation models predict substantial alteration of forest composition, forest dieback, or even loss of forest cover in response to increased temperatures associated with increasing atmospheric carbon dioxide concentrations. However, the structure of these computer models may cause them to overemphasize the role of climate in controlling tree growth and mortality. Model functions that represent the influence of climate on tree growth are based on the geographic range limits of a species, predicting maximal growth in the center of the range and zero growth (100% mortality) at the range limits and beyond. This modeling approach ignores the fact that the geographic range of a species reflects the influence of both climate and other environmental factors, including competition with other tree species, soil characteristics, barriers to dispersal, and distributions of pests and pathogens. These climate-response functions in forest simulation models implicitly assume that tree species occur in all environments where it is possible for them to survive (their fundamental niche or potential habitat) and that these potential habitats are entirely defined by climate. Hence, any alteration of climate must result in a fairly rapid decline of species near their range limits and rapid alteration of forest composition and structure. The climate-response functions that lead to these unrealistic conclusions have no basis in plant physiology or actual measurements of tree responses to climate stressors. Rather, these functions were chosen as a necessary expedient for modeling the climatic responses of many tree species for which there were limited or no ecophysiological data. There is substantial evidence, however, that some tree species can survive, and even thrive, in climatic conditions outside their present range limits. This evidence suggests that nonclimatic factors exclude some species from natural forests beyond their present range limits and that climate may not be the only determinant of these limits. Hence, there is reason to suspect that published projections of forest responses to climate change based on forest simulation models may exaggerate the direct impact of climate on tree growth and mortality. We propose that forest simulation models be reformulated with more realistic representations of growth responses to temperature, moisture, mortality, and dispersal. We believe that only when these models more accurately reflect the physiological bases of the responses of tree species to climate variables can they be used to simulate responses of forests to rapid changes in climate. We argue that direct forest responses to climate change projected by such a reformulated model may be less traumatic and more gradual than those projected by current models. However, the indirect effects of climate change on forests, mediated by alterations of disturbance regimes or the actions of pests and pathogens, may accelerate climate-induced change in forests, and they deserve further study and inclusion within forest simulation models. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Ecological Modelling Elsevier

Model-based assessments of climate change effects on forests: a critical review

Ecological Modelling, Volume 90 (1) – Sep 1, 1996

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Publisher
Elsevier
Copyright
Copyright © 1996 Elsevier Ltd
ISSN
0304-3800
eISSN
1872-7026
DOI
10.1016/0304-3800(96)83709-4
Publisher site
See Article on Publisher Site

Abstract

While current projections of future climate change associated with increases in atmospheric greenhouse gases have a high degree of uncertainty, the potential effects of climate change on forests are of increasing concern. A number of studies based on forest simulation models predict substantial alteration of forest composition, forest dieback, or even loss of forest cover in response to increased temperatures associated with increasing atmospheric carbon dioxide concentrations. However, the structure of these computer models may cause them to overemphasize the role of climate in controlling tree growth and mortality. Model functions that represent the influence of climate on tree growth are based on the geographic range limits of a species, predicting maximal growth in the center of the range and zero growth (100% mortality) at the range limits and beyond. This modeling approach ignores the fact that the geographic range of a species reflects the influence of both climate and other environmental factors, including competition with other tree species, soil characteristics, barriers to dispersal, and distributions of pests and pathogens. These climate-response functions in forest simulation models implicitly assume that tree species occur in all environments where it is possible for them to survive (their fundamental niche or potential habitat) and that these potential habitats are entirely defined by climate. Hence, any alteration of climate must result in a fairly rapid decline of species near their range limits and rapid alteration of forest composition and structure. The climate-response functions that lead to these unrealistic conclusions have no basis in plant physiology or actual measurements of tree responses to climate stressors. Rather, these functions were chosen as a necessary expedient for modeling the climatic responses of many tree species for which there were limited or no ecophysiological data. There is substantial evidence, however, that some tree species can survive, and even thrive, in climatic conditions outside their present range limits. This evidence suggests that nonclimatic factors exclude some species from natural forests beyond their present range limits and that climate may not be the only determinant of these limits. Hence, there is reason to suspect that published projections of forest responses to climate change based on forest simulation models may exaggerate the direct impact of climate on tree growth and mortality. We propose that forest simulation models be reformulated with more realistic representations of growth responses to temperature, moisture, mortality, and dispersal. We believe that only when these models more accurately reflect the physiological bases of the responses of tree species to climate variables can they be used to simulate responses of forests to rapid changes in climate. We argue that direct forest responses to climate change projected by such a reformulated model may be less traumatic and more gradual than those projected by current models. However, the indirect effects of climate change on forests, mediated by alterations of disturbance regimes or the actions of pests and pathogens, may accelerate climate-induced change in forests, and they deserve further study and inclusion within forest simulation models.

Journal

Ecological ModellingElsevier

Published: Sep 1, 1996

References

  • Air temperature, tree growth, and the northern and southern range limits of Picea mariana
    Bonan, G.B.; Sirois, L.
  • Relationship between life history characteristics and electrophoretically detectable genetic variation in plants
    Hamrick, J.L.; Linhart, Y.B.; Mitton, J.B.
  • Regional forest migrations and potential economic effects
    Hodges, D.G.; Cubbage, F.W.; Regens, J.L.
  • Ecological response surfaces for North American boreal tree species and their use in forest classification
    Lenihan, J.M.
  • The seasonal response of a general circulation model to changes in CO 2 and sea temperatures
    Mitchell, J.F.B.
  • Species migrations and ecosystem stability during climate change: The belowground connection
    Perry, D.A.; Borchers, J.G.; Borchers, S.L.; Amaranthus, M.P.
  • The potential for application of individual-based simulation models for assessing the effects of global change
    Shugart, H.H.; Smith, T.M.; Post, W.M.
  • Transient response of forests to CO 2 -induced climate change: Simulation experiments in eastern North America
    Solomon, A.M.
  • Computer-aided reconstruction of late-quaternary landscape dynamics
    Solomon, A.M.; Webb, T.

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