elevation as Nauta Formation forest (elevation greater than 251.103 m), and values of 0. (black) indicated areas ...... Thelypteris arcanum. (Maxon & Morton).
Geological Control of Floristic Composition in Amazonian Forests by Mark Higgins University Program in Ecology Duke University Date:_______________________ Approved: ___________________________ Dr. John Terborgh, Supervisor ___________________________ Dr. Kalle Ruokolainen ___________________________ Dr. Dean Urban ___________________________ Dr. Daniel Richter Dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the University Program in Ecology in the Graduate School of Duke University 2010
ABSTRACT Geological Control of Floristic Composition in Amazonian Forests by Mark Higgins University Program in Ecology Duke University Date:_______________________ Approved: ___________________________ Dr. John Terborgh, Supervisor ___________________________ Dr. Kalle Ruokolainen ___________________________ Dr. Dean Urban ___________________________ Dr. Daniel Richter An abstract of a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the University Program in Ecology in the Graduate School of Duke University 2010
Copyright by Mark Higgins 2010
Abstract Amazonia contains the largest remaining tracts of undisturbed tropical forest on earth, and is thus critical to international nature conservation and carbon sequestration efforts. Amazonian forests are notoriously difficult to study, however, due to their species richness and inaccessibility. This has limited efforts to produce the accurate, high‐resolution biodiversity maps needed for conservation and development. The aims of the research described here were to identify efficient solutions to the problems of tropical forest inventory; to use these methods to identify floristic patterns and their causes in western Amazonia; and propose new means to map floristic patterns in these forests. Using tree inventories in the vicinity of Iquitos, Peru, I and a colleague systematically evaluated methods for rapid tropical forest inventory. Of these, inventory of particular taxonomic groups, or taxonomic scope inventory, was the most efficient, and was able to capture a majority of the pattern observed by traditional inventory techniques with one‐fifth to one‐twentieth the number of stems and species. Based on the success of this approach, I and colleagues specifically evaluated two plant groups, the Pteridophytes (ferns and fern allies) and the Melastomataceae (a family of shrubs and small trees), for use in rapid inventory. Floristic patterns based on inventories from
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either group were significantly associated with those based on the tree flora, and inventories of Pteridophytes in particular were in most cases able to capture the majority of floristic patterns identified by tree inventories. These findings indicate that Pteridophyte and Melastomataceae inventories are useful tools for rapid tropical forest inventory. Using Pteridophyte and Melastomataceae inventories from 138 sites in northwestern Amazonia, combined with satellite data and soil sampling, I and colleagues studied the causes of vegetation patterns in western Amazonian forests. On the basis of these data, we identified a floristic discontinuity of at least 300km in northern Peru, corresponding to a 15‐fold difference in soil cation concentrations and an erosion‐generated geological boundary. On the basis of this finding, we assembled continent‐scale satellite image mosaics, and used these to search for additional discontinuities in western Amazonia. These mosaics indicate a floristic and geological discontinuity of at least 1500km western Brasil, driven by similar erosional processes identified in our study area. We suggest that this represents a chemical and ecological boundary between western and central Amazonia. Using a second network of 52 pteridophyte and soil inventories in northwestern Amazonia, we further studied the role of geology in generating floristic pattern. Consistent with earlier findings, we found that two widespread geological formations in western Amazonia differ eight‐fold difference in soil cation concentrations and in a v
majority of their species. Difference in elevation, used as a surrogate for geological formation, furthermore explained up to one‐third of the variation in plant species composition between these formations. Significant correlations between elevation, and cation concentrations and soil texture, confirmed that differences in species composition between these formations are driven by differences in soil properties. On the basis of these findings, we were able to use SRTM elevation data to accurately model species composition throughout our study area. I argue that Amazonian forests are partitioned into large‐area units on the basis of geological formations and their edaphic properties. This finding has implications for both the ecology and evolution of these forests, and suggests that conservation strategies be implemented on a region‐by‐region basis. Fortunately, the methods described here provide a means for generating accurate and detailed maps of floristic patterns in these vast and remote forests.
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To Leena, And those working to protect this world’s natural systems. “Rare is the enterprise which offers so little grounds for optimism and demands so much from our power to hope.” – Egbert Leigh Jr.
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Contents Abstract .........................................................................................................................................iv List of Tables................................................................................................................................xii List of Figures .............................................................................................................................xiv Acknowledgements ...................................................................................................................xix Chapter 1. Introduction................................................................................................................ 1 Chapter 2. Rapid tropical forest inventory: a comparison of techniques using inventory data from western Amazonia.................................................................................................... 10 Summary................................................................................................................................ 10 Introduction........................................................................................................................... 11 Methods ................................................................................................................................. 15 Inventory data..................................................................................................................... 15 Creation of abbreviated inventories ................................................................................ 16 Evaluation of inventory abbreviations ............................................................................ 20 Results .................................................................................................................................... 23 Inventory data..................................................................................................................... 23 Creation of abbreviated inventories ................................................................................ 23 Evaluation of inventory abbreviations ............................................................................ 25 Occurrence metric analyses .......................................................................................... 25 Taxonomic resolution analyses.................................................................................... 25 Diameter‐class analyses at species or genus resolution ........................................... 26 Taxonomic scope analyses............................................................................................ 28 viii
Discussion.............................................................................................................................. 30 Evaluation and comparison of inventory abbreviations .............................................. 30 Presence‐absence occurrence metric ........................................................................... 30 Genus resolution ............................................................................................................ 31 Diameter classes at species or genus resolution ........................................................ 32 Taxonomic scope............................................................................................................ 33 Optimizing tropical forest inventory............................................................................... 35 From inventory to conservation planning ...................................................................... 36 Acknowledgements.............................................................................................................. 37 Chapter 3: Are floristic and edaphic patterns in Amazonian rain forests congruent for trees, pteridophytes and Melastomataceae? ........................................................................... 48 Summary................................................................................................................................ 48 Introduction........................................................................................................................... 50 Materials and methods ........................................................................................................ 53 Study sites............................................................................................................................ 53 Floristic inventories............................................................................................................ 54 Soil sampling....................................................................................................................... 56 Computing of distance matrices ...................................................................................... 57 Mantel tests and ordinations ............................................................................................ 59 Multiple regressions on distance matrices...................................................................... 60 Results .................................................................................................................................... 62 Floristic inventories............................................................................................................ 62 ix
Soils ...................................................................................................................................... 62 Congruence between plant groups.................................................................................. 63 Congruence between floristic, environmental and geographic patterns ................... 65 Discussion.............................................................................................................................. 68 Determinants of floristic patterns .................................................................................... 68 Are these results reliable?.................................................................................................. 71 Practical implications......................................................................................................... 73 Acknowledgements.............................................................................................................. 75 Chapter 4: Long‐term Sub‐Andean Tectonics Control Floristic Composition in Amazonian Forests ..................................................................................................................... 87 Summary................................................................................................................................ 87 Introduction........................................................................................................................... 89 Results .................................................................................................................................... 93 Discussion.............................................................................................................................. 98 Materials and Methods ...................................................................................................... 104 Landsat image mosaics and image interpretation ....................................................... 104 SRTM mosaics and elevation calculations .................................................................... 105 Pteridophyte and Melastomataceae transect analyses................................................ 106 Tree plot analyses ............................................................................................................. 107 Acknowledgements............................................................................................................ 109 Chapter 5. Geological control of floristic composition in western Amazonia ................. 130 Introduction......................................................................................................................... 130 x
Methods ............................................................................................................................... 135 Study area.......................................................................................................................... 135 Satellite imagery acquisition and interpretation.......................................................... 136 Field data collection ......................................................................................................... 138 Data analyses .................................................................................................................... 140 Results .................................................................................................................................. 145 Satellite image interpretation.......................................................................................... 145 Data analyses .................................................................................................................... 146 Discussion............................................................................................................................ 151 Overview ........................................................................................................................... 151 Relationships between elevation, soils, and floristic composition ............................ 152 Evolution of the western Amazonian biota .................................................................. 156 Implications for conservation planning ........................................................................ 157 Chapter 6. Conclusion .............................................................................................................. 182 References .................................................................................................................................. 185 Biography................................................................................................................................... 198
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List of Tables Table 1: Characteristics of presence‐absence and taxonomic resolution abbreviations for nine sites near Iquitos, Peru....................................................................................................... 39 Table 2: Characteristics of diameter classes at species resolution for nine sites near Iquitos, Peru. a.............................................................................................................................. 40 Table 3: Characteristics of diameter classes at genus resolution for nine sites near Iquitos, Peru. a.............................................................................................................................. 41 Table 4: Characteristics of taxonomic scope abbreviations for nine sites near Iquitos, Peru. a ............................................................................................................................................ 42 Table 5: Characteristics of taxonomic scope combinations for nine sites near Iquitos, Peru. a ............................................................................................................................................ 43 Table 6: Results of floristic inventories made in three regions in lowland western Amazonia. Floristic similarity between sites is calculated both with the Steinhaus index (Steinh.) (abundance data) and with the Sørensen index (Søren.) (presence‐absence data). ....................................................................................................................................................... 77 Table 7 : Results of chemical and physical analyses of soils within three regions in lowland western Amazonia. Cation concentrations are given in cmol(+) kg‐1, LOI (loss on ignition) and sand content in %........................................................................................... 78 Table 8: Mantel correlations between floristic differences based on three different plant groups in three western Amazonian regions. Partial Mantel tests, where the effect of geographical distances has been removed before computing the correlation between the two floristic distance matrices, are shown in parenthesis. Sørensen index uses species presence‐absence data, Steinhaus index abundance data. Statistical significances were obtained by a Monte Carlo permutation test using 999 permutations: *** P