Range and Richness of Vascular Land Plants: The Role of Variable Light

Published by the American Geophysical Union as part of the Special Publications Series. This is a research monograph and not a textbook. Here I demonstrate analytically how the observed, opposing, latitudinal gradients in the average range and richness of local vascular land plant species are (outside the moist-tropical zone, at least) driven primarily by the local temporal and spatial variability of shortwave radiative flux at the canopy top. (The term "richness" as used here means the local number of different vascular land plant species unlimited by the size of the area sampled.) The hypotheses are simplistic but are nevertheless convincingly accurate in extratropical latitudes when tested against observations over the continental land surfaces of the Northern Hemisphere, the only areas tested here.

Table of Contents:
Foreword xi Preface xiii Acknowledgments xvii Part I: Overview 1 Chapter 1: Introduction 3 Historical summary 3 Modeling philosophy 5 Bioclimatic basis for local community structure 7 Range 9 Richness 13 Major simplifications 14 Principal assumptions 15 Principal findings 15 Part II: Local Species Range and Richness 17 Chapter 2: Local Climate: Observations and Assessments 19 Major biomes of North America 19 Growing season 19 Solar radiation 20 Zonal homogeneity 27 Looking ahead 29 Chapter 3: Mean Latitudinal Range of Local Species: Prediction Versus Observation 31 Introduction and definitions 31 Range of local mean species as determined by local distributions about the mean 32 Theoretical estimation of the range with climatic forcing by SW flux only 36 Range of local modal species versus mean of local species’ ranges 39 Probability mass of the distribution of observed local species 42 Analytical summary for climatic forcing by SW flux only 43 Point-by-point estimation of range versus observation for North America 45 A thought experiment on the variation of SW flux in an isotropic atmosphere 49 Range of modal species at maxima and minima of the SW flux 51 Gradient estimation of range versus observation for North America 52 Point-by-point estimation of range versus observation for the Northern Hemisphere 55 Gradient estimation of range versus observation for the Northern Hemisphere 60 Low-latitude smoothing of range by latitudinal averaging of the growing season 62 Range as a reflection of the bioclimatic dispersion of species 63 A high-latitude shift in bioclimatic control from light to heat? 65 Extension of these range forecasts by use of multiple forcing variables 68 A look ahead 68 Chapter 4: Richness of Local Species: Prediction Versus Observation 69 Introduction 69 From continuous to discrete distribution of local species 72 Local SW flux as a stationary Poisson stochastic process 73 Distribution of C3 species–supporting radiation intercepted in a growing season 75 Moments of C 3 species–supporting radiation intercepted in a growing season 77 Moments of the number of C3 species–supporting cloud events in a growing season 78 From climatic disturbance to C3 species germination 79 Parameter estimation 80 Predicted potential richness versus observed richness 82 The theoretical tie between range and richness 84 Part III: Recapitulation 85 Chapter 5: Summary and Conclusions 87 Precis 87 Mathematical approximations in range calculation 89 Evaluation of range prediction 90 Evaluation of richness prediction 92 Finis 93 Part IV: Appendices: Reductionist DarwinianModeling of the Bioclimatic Function for C3 Plant Species 95 Appendix A: The Individual C3 Leaf 97 Photosynthetic capacity of the C3 leaf 97 Mass transfer from free atmosphere to chloroplasts 99 Assimilation modulation by leaf temperature and ambient CO2 concentration 104 Exponential approximation to the C3 photosynthetic capacity curve 104 Potential assimilation efficiency of C3 leaves 105 The state of stress 107 Darwinian operating state of the individual C3 leaf 107 The univariate bioclimatic function at leaf scale 108 Appendix B: The Homogenous C3 Canopy 111 Idealized geometry of the leaf layer 111 Darwinian heat proposition 113 Vertical flux of radiation in a closed canopy 113 C 3 species parameters 116 Bioclimatic function at canopy scale 117 Local evolutionary equilibrium: An hypothesis 118 Appendix C: Evaluation of the Evolutionary Equilibrium Hypothesis 121 The equilibrium hypothesis at leaf scale 121 The equilibrium hypothesis at local canopy scale 121 Summary 125 Notation 127 Glossary 137 Bibliography 141 Additional Reading 147 Author Index 149 Subject Index 151