Vegetation Assessment of Forests of Pagan Island, Commonwealth of the Northern Mariana Islands
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Vegetation Assessment of Forests of Pagan Island, Commonwealth of the Northern Mariana Islands Linda W. Pratt U.S. Geological Survey, Pacific Island Ecosystems Research Center Hawai`i Volcanoes National Park, HI 96718 December 2010 The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the opinions or policies of the U. S. Government. Mention of trade names or commercial products does not constitute their endorsement by the U. S. Government. ii TABLE OF CONTENTS Page LIST OF FIGURES ......................................................................................... iv LIST OF TABLES ........................................................................................... v EXECUTIVE SUMMARY .................................................................................. 1 INTRODUCTION ........................................................................................... 2 THE STUDY AREA ......................................................................................... 3 METHODS .................................................................................................... 5 Sampling Design ........................................................................................... 5 Data Compilation .......................................................................................... 9 RESULTS .....................................................................................................10 Coconut Forests of Northern Pagan ...............................................................10 Tree density, basal area, and dominance .............................................11 Density of understory woody plants .....................................................14 Ground cover .....................................................................................14 Coconut Forest of Southern Pagan ................................................................18 Tree density, basal area, and dominance .............................................18 Density of understory woody plants .....................................................18 Ground cover .....................................................................................20 Mixed Native and Alien Forest of Northern Pagan ........................................... 20 Tree density, basal area, and dominance .............................................21 Density of understory woody plants .....................................................24 Ground cover .....................................................................................26 Mixed Native Forest of Southern Pagan ......................................................... 28 Tree density, basal area, and dominance .............................................28 Density of understory woody plants .....................................................31 Ground cover .....................................................................................32 Ironwood Forest of Northern Pagan............................................................... 34 Tree density, basal area, and dominance .............................................35 Density of understory woody plants .....................................................37 Ground cover .....................................................................................37 Shrubland of Northern Pagan ........................................................................39 Grassland of Northern Pagan ........................................................................40 Species Composition of the Vascular Plant Flora of Pagan ............................... 41 Species not observed in 2010 ..............................................................42 New island records of plants ............................................................... 44 Vegetation of special areas .................................................................45 DISCUSSION ...............................................................................................47 Coconut Forests .................................................................................48 Mixed Native Forests .......................................................................... 50 Ironwood Forests ...............................................................................52 Shrublands and Grasslands .................................................................53 iii TABLE OF CONTENTS Page DISCUSSION (continued) Alien Plant Species .............................................................................54 Rare Native Plants ..............................................................................57 CONCLUSIONS ............................................................................................61 ACKNOWLEDGMENTS ..................................................................................62 LITERATURE CITED .....................................................................................63 APPENDIX I. UTM Coordinates for Vegetation Plots at Stations along Forest Bird Survey Transects and Supplemental Grass and Shrubland Plots. All Coordinates are in WGS84, UTM Zone 55 North ................................................................68 APPENDIX II. Vascular Plant Species of Pagan Island, Commonwealth of the Northern Mariana Islands .............................................................................69 LIST OF FIGURES Figure 1. Survey transects on Pagan Island, Mariana Islands (CNMI) in 2010 (Map by Fred Amidon, U.S. Fish and Wildlife Service.) ..................................... 6 Figure 2. Size class distribution of tree species in coconut forest of transect 6 on the northwest side of Pagan. ........................................................................13 Figure 3. Size class distribution of tree species in coconut forest of transect 8 on the northeast side of Pagan. .........................................................................13 Figure 4 Size class distribution of tree species in mixed native and alien forest of transect 1 on the southeast side of northern Pagan ........................................ 23 Figure 5. Size class distribution of tree species in mixed native and alien forest of transect 2 on the southeast side of northern Pagan .................................... 24 Figure 6. Size class distribution of tree species in mixed native forest of transect 9 on the southwest side of southern Pagan ....................................................30 Figure 7. Size class distribution of tree species in mixed native forest of transect 11-north on the upper plateau of southern Pagan ........................................... 31 Figure 8. Size class distribution of tree species in Casuarina equisetifolia forest of transect 4 on the southwest side of northern Pagan ....................................... 36 Figure 9. Size class distribution of Casuarina equisetifolia in forest of transect 5 on the west side of northern Pagan ...............................................................36 iv LIST OF TABLES Page Table 1. Density, Mean Basal Area, and Dominance of Tree Species in Plots (800m2/transect) of Coconut Forest on Northern Pagan .................................. 12 Table 2. Mean Number/100 m2 Plot of Woody Plant Species <2 m in Height along Transects in Coconut Forest on Northern Pagan .................................... 15 Table 3. Ground Cover (%) in Pooled Plots of Transects in Coconut Forest on Northern Pagan ...........................................................................................16 Table 4. Density, Mean Basal Area, and Dominance of Tree Species in Plots (800m2/transect) of Coconut Forest on Southern Pagan .................................. 19 Table 5. Mean Number/100 m2 Plot of Woody Plant Species <2 m in Height along Transects in Coconut Forest on Southern Pagan .................................... 19 Table 6. Ground Cover (%) in Pooled Plots of Transects in Coconut Forest on Southern Pagan ...........................................................................................21 Table 7. Density, Mean Basal Area, and Dominance of Tree Species in Plots (800m2/transect) of Mixed Native and Alien Forest on Northern Pagan ............. 22 Table 8. Mean Number/100 m2 Plot of Woody Plant Species <2 m in Height along Transects in Mixed Native and Alien Forest on Northern Pagan ............... 25 Table 9. Ground Cover (%) in Pooled Plots of Transects in Mixed Native and Alien Forest on Northern Pagan .....................................................................27 Table 10. Density, Mean Basal Area, and Dominance of Tree Species in Plots (600-800m2/transect) of Mixed Native Forest on Southern Pagan ..................... 29 Table 11. Mean Number/100 m2 Plot of Woody Plant Species <2 m in Height along Transects in Mixed Native Forest on Southern Pagan ............................. 32 Table 12. Ground Cover (%) in Pooled Plots of Transects in Mixed Native Forest on Southern Pagan ......................................................................................33 Table 13. Density, Mean Basal Area, and Dominance of Tree Species in Plots (800m2/transect) of Casuarina equisetifolia Forest on Northern Pagan .............. 35 Table 14. Mean Number/100 m2 Plot of Woody Plant Species <2 m in Height along Transects in Casuarina equisetifolia Forest on Northern Pagan ................ 37 v LIST OF TABLES (Continued) Page Table 15. Ground Cover (%) in Pooled Plots of Transects