Land-Use Intensification in Grazing Systems: Plant Trait Responses
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Land-Use Intensification in Grazing Systems: Plant Trait Responses and Feedbacks to Ecosystem Functioning and Resilience A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy in the University of Canterbury by Etienne Laliberté School of Forestry University of Canterbury 2011 To Ludovic and Sofia, the most significant results that emerged from this research. Table of Contents List of Figures v List of Tables vii Abstract vii Acknowledgments x Chapter 1: Introduction 1 1.1 Human Domination of the Biosphere . 1 1.2 Land-Use Change in Grazing Systems . 3 1.2.1 The Ecological Footprint of Grazing Systems . 3 1.2.2 Land-Use Intensification in Grazing Systems: An Un- avoidable Reality? . 3 1.3 Biodiversity and Ecosystem Functioning in Grazing Systems . 5 1.3.1 Does Species Richness Matter to Ecosystem Functioning? 5 1.3.2 The Response-Effect Functional Trait Framework . 8 1.4 Biodiversity and Ecosystem Resilience . 9 1.5 Thesis Outline . 12 Chapter 2: Measuring Functional Diversity 14 2.1 Summary . 14 2.2 Introduction . 15 2.3 A Flexible Distance-Based Framework . 16 2.4 Weighting the Traits . 19 2.5 Functional Dispersion . 20 2.6 Bridging the Gap Between Theory and Practice . 27 2.7 Conclusions . 29 Chapter 3: Comparison of Vegetation Sampling Methods 31 3.1 Summary . 31 3.2 Introduction . 32 3.3 Materials and Methods . 34 3.3.1 Study Area and Site . 34 3.3.2 Experimental Design . 34 3.3.3 Vegetation Sampling . 38 3.3.4 Statistical Analyses . 40 3.4 Results . 42 3.4.1 Sampling Method . 42 3.4.2 Treatment Effects . 45 3.5 Discussion . 48 3.6 Conclusions . 51 Chapter 4: Plant Trait Responses 53 4.1 Summary . 53 4.2 Introduction . 54 4.3 Materials and Methods . 59 4.3.1 Study Area and Study Site . 59 4.3.2 Experimental Design . 59 4.3.3 Vegetation Sampling . 59 4.3.4 Plant Functional Traits . 60 4.3.5 Statistical Analyses . 63 4.4 Results . 74 4.4.1 Relationships among Species Traits . 74 4.4.2 Shifts in Community-Weighted Traits . 76 4.4.3 Selective Advantage of Traits . 82 4.4.4 Species Richness . 89 4.4.5 Trait Over- and Under-Dispersion . 92 4.5 Discussion . 100 4.5.1 Relationships among Species Traits . 100 4.5.2 Shifts in Community-Weighted Traits . 103 4.5.3 Selective Advantage of Traits . 106 4.5.4 Trait Over- and Under-Dispersion . 112 ii 4.6 Conclusions . 116 Chapter 5: Feedbacks to Ecosystem Functioning 119 5.1 Summary . 119 5.2 Introduction . 119 5.3 Materials and Methods . 124 5.3.1 Study Area and Study Site . 124 5.3.2 Experimental Design . 124 5.3.3 Vegetation Sampling . 124 5.3.4 Plant Traits and Functional Diversity . 124 5.3.5 Aboveground Net Primary Production . 126 5.3.6 Belowground Net Primary Production . 127 5.3.7 Litter Decomposition . 127 5.3.8 Soil Respiration . 131 5.3.9 Soil Properties . 131 5.3.10 Statistical Analyses . 132 5.4 Results and Discussion . 139 5.5 Conclusions . 151 Chapter 6: Biodiversity and Ecosystem Resilience 153 6.1 Summary . 153 6.2 Introduction . 154 6.3 Materials and Methods . 157 6.3.1 Study Regions . 157 6.3.2 Plant Functional Traits . 158 6.3.3 Functional Redundancy and Response Diversity . 160 6.3.4 Meta-Analysis . 163 6.3.5 Null Models . 164 6.4 Results . 165 6.5 Discussion . 170 6.6 Conclusions . 173 Chapter 7: Conclusions 175 7.1 Summary . 176 7.1.1 Measuring Functional Diversity . 176 iii 7.1.2 Comparisons of Vegetation Sampling Methods . 177 7.1.3 Plant Trait Responses . 177 7.1.4 Feedbacks to Ecosystem Functioning . 178 7.1.5 Biodiversity and Ecosystem Resilience . 179 7.2 Future Directions . 180 7.2.1 Intraspecific Functional Diversity . 180 7.2.2 Modelling Trait Distributions . 180 7.2.3 Belowground Traits . 182 7.2.4 Extensions to the Maximum Entropy Model . 182 7.2.5 The Response-Effect Framework and Structural Equa- tion Modelling . 184 7.2.6 Response Diversity of Ecosystem Service Providers . 185 7.3 Final Conclusions . 185 Bibliography 188 iv List of Figures 2.1 Two artificial communities in a two-dimensional trait space . 21 2.2 Functional dispersion . 23 2.3 Simulation results, abundance data . 24 2.4 Simulation results, presence-absence data . 25 3.1 Aerial view of the experiment . 35 3.2 Comparison of vegetation sampling methods . 43 3.3 Non-metric multidimensional scaling biplot showing differences in community structure . 46 3.4 Canonical analysis of principal coordinates biplot showing dif- ferences in community structure among grazing treatments . 48 4.1 Scatterplot matrix of functional traits . 75 4.2 Principal component analysis biplots of functional traits and community-weighted traits . 76 4.3 Shifts in community-weighted traits, fertiliser treatments . 78 4.4 Shifts in relative abundances for groups of species . 79 4.5 Shifts in community-weighted traits, grazing intensity treat- ments . 81 4.6 Scatterplot matrix of community-weighted traits . 83 4.7 Differences in community-weighted traits, main effects . 84 4.8 Differences in community-weighted traits, interactions . 85 4.9 Predictive capacity of maxent models, uniform prior . 85 4.10 Maxent model results, uniform prior . 87 4.11 Maxent model results, with rare species removed . 88 4.12 Differences in λ-values, main effects . 90 4.13 Differences in λ-values, interactions . 91 4.14 Plant species richness . 92 4.15 Functional richness under increasing soil resource availability . 94 v 4.16 Abundance-weighted leaf [P] distributions . 95 4.17 Abundance-weighted leaf [C] distributions . 97 4.18 Abundance-weighted leaf area distributions . 99 5.1 Litter decomposition curves, incubation within plots . 129 5.2 Litter decomposition curves, incubation under standard soil conditions . 130 5.3 Relationship between soil resource availability and grazing in- tensity . 136 5.4 Differences in ecosystem processes among fertiliser levels . 140 5.5 Relationship between SLA and soil resource availability . 141 5.6 Cascading effects of land-use changes on functioning . 142 5.7 Relationship between leaf C:N and soil resource availability . 143 5.8 Interactive effects on functional diversity, ANPP, and litter decomposition . 145 5.9 Best causal path model, litter decomposition under standard soil conditions . 146 5.10 Soil surface carbon (0–20 cm depth) under increasing soil re- source availability . 148 5.11 Depth distribution of BNPP in 0–10 cm soil layer among fer- tiliser levels . 149 5.12 Soil carbon (60–80 cm depth) under increasing soil resource availability . 150 6.1 Map of study regions used in the meta-analysis . 156 6.2 Methodology for functional redundancy . 161 6.3 Methodology for response diversity . 162 6.4 Results of meta-analyis . 166 6.5 Associations between functional redundancy and response di- versity . 167 6.6 Null model results . 168 6.7 Changes in response diversity . 169 6.8 Changes in functional redundancy . 170 vi List of Tables 2.1 Differences between F_RED and dbFD . 28 3.1 List of species sown in 1982 . 36 3.2 Detailed ANOVA results . 44 4.1 List of species found in the 2007–2008 surveys . 61 4.2 List of plant functional traits . 64 4.3 Null model results . 93 4.4 Deviations from null distributions among fertiliser levels . 96 4.5 Deviations from null distributions among grazing intensities . 98 5.1 Description of variables . 123 6.1 Summary of data sets used in meta-analysis . 157 6.2 Effect and response traits . 159 vii viii Abstract Land-use change is the single most important global driver of changes in biodiversity. Such changes in biodiversity, in turn, are expected to influence the functioning of ecosystems and their resilience to environmental pertur- bations and disturbances. It is widely recognised that the use of functional traits and functional diversity.