EFFECTS OF EXOTIC-SPECIES AFFORESTATION ON THE UNDERSTORY VEGETATION OF SANTO ANTAO, CAPE VERDE ISLANDS By: W. Scott Benton A Thesis Submitted in partial fulfillment of the requirements of the degree MASTERS OF SCIENCE IN NATURAL RESOURCES College of Natural Resources UNIVERSITY OF WISCONSIN – STEVENS POINT Stevens Point, Wisconsin April 2015 APPROVED BY THE GRADUATE COMMITTEE OF: _______________________________________________________ Dr. Ron Crunkilton, Committee Chairman Professor of Fisheries and Water Resources _______________________________________________________ Dr. Holly Petrillo Associate Professor of Forestry _______________________________________________________ Dr. Paul McGinley Professor of Fisheries and Water Resources ii ABSTRACT The nation of Cape Verde is an isolated, geologically young Macaronesian archipelago off the west coast of Africa. The westernmost island, Santo Antão, ranks second in the archipelago in terms of area and altitude, possesses high topographic relief, and thus harbors some of the highest levels of native plant diversity in Cape Verde. After a history of denudation, exotic-species afforestations were established in the high altitude regions of Santo Antão in the mid-20th century in an effort to combat erosion, re-establish vegetative understories, increase water yield and infiltration, and provide socio-economic opportunities for the local populace. An evaluation of the afforestations has not been completed, particularly in terms of the effect on understory species. The central objective of this research was to determine the impact of exotic- species afforestations on the understory vegetation of the Planalto Leste region of the island of Santo Antão across three bioclimatic zones – humid, sub-humid, and semi-arid. A total of 42 plots were sampled in both afforested and natural habitats, and the data were analyzed to ascertain the afforestation’s effect on understory richness, cover, and composition. Afforestations were observed to exert a negative effect on understory vegetation abundance and diversity, and the magnitude of the effect is likely attributable to the formation of closed canopies and thick leaf litter layers, inhibiting understory growth. Negative effects were most pronounced in the humid zone, less pronounced in the sub-humid zone, and not present in the semi-arid zone. The original goals of afforestation are evaluated, and some stand management suggestions are given to improve native understory plant conservation. iii ACKNOWLEDGEMENTS The list of people and organizations that allowed this project to be realized span many years and two continents. Thanks first go to Bobbi Kubish and the University of Wisconsin – Stevens Point and US Peace Corps for selecting me for the Masters International program and as a Peace Corps Volunteer. Thanks are owed to many Capeverdeans for their time, housing, food, knowledge, deep friendship, and for teaching me the definition of generosity; special thanks go to Domingos Fortes, João de Canda, Emitério Ramos, Silviana Roque, and Gilda Monteiro. Dr. Holly Petrillo and the other committee members provided valuable criticisms, and most importantly I am ever grateful to my intelligent, patient, witty, and supportive wife Melissa with whom I share all my adventures and who makes my life a joy. iv TABLE OF CONTENTS ABSTRACT ................................................................................................................................... iii ACKNOWLEDGEMENTS .......................................................................................................... IV LIST OF TABLES ........................................................................................................................ VI LIST OF FIGURES ..................................................................................................................... VII INTRODUCTION .......................................................................................................................... 8 Oceanic Island Biodiversity ............................................................................................................ 8 Biodiversity of Cape Verde and Santo Antão ................................................................................. 9 Plantation Forestry ........................................................................................................................ 11 STUDY AREA ............................................................................................................................. 14 Cape Verde.................................................................................................................................... 14 Santo Antão and the Planalto Leste Region .................................................................................. 16 METHODS ................................................................................................................................... 23 Plot Selection ................................................................................................................................ 23 Data Collection ............................................................................................................................. 25 Data Analysis ................................................................................................................................ 26 RESULTS ..................................................................................................................................... 30 Diversity Indices and Site Characteristics .................................................................................... 30 Rank Abundance Curves and Spearman Rank-Order Correlation ............................................... 31 Rarefaction Analysis ..................................................................................................................... 34 DISCUSSION ............................................................................................................................... 36 Cultural and Management Implications ........................................................................................ 38 Research Needs ............................................................................................................................. 42 LITERATURE CITED ................................................................................................................. 43 v LIST OF TABLES Table 1. Endemism of vascular plants of the Cape Verde, Canary, and Madeira islands; only islands >50 km2 are included (Adapted from Brochmann et al. 1997). ........................................ 10 Table 2. Conservation status of angiosperms in Cape Verde and Santo Antão (adapted from Leyens and Lobin (eds.) 1996). Percent of all Capeverdean angiosperm species in parentheses. 11 Table 3. Endemic and indigenous tree species of the Planalto Leste region of Santo Antão (Brochmann et al. 1997). .............................................................................................................. 19 Table 4. Chronological summary of forestry-related events on the island of Santo Antão, Cape Verde. ............................................................................................................................................ 20 Table 5. Definition of modified Braun-Blanquet cover-abundance classifications and conversion to average percent cover classes. .................................................................................................. 27 Table 6. Understory diversity, abundance, similarity and site characteristic metrics of the humid, sub-humid, and semi-arid bioclimatic zones. Significant values are in bold................................ 31 vi LIST OF FIGURES Figure 1. Geographic location of Cape Verde. ............................................................................. 15 Figure 2. Climatic factors of Cape Verde (adapted from Rocha 2010). ....................................... 16 Figure 3. Bioclimatic zones, national parks, afforested areas, and study plots of the Planalto Leste region of Santo Antão. Red points indicate natural plots and green points indicate afforested plots. ............................................................................................................................. 24 Figure 4. Rank abundance curves for natural and forest understory habitats in the a) humid, b) sub-humid, and c) semi-arid bioclimatic zones. The x-axis represents the ranked proportional abundances of understory species. ................................................................................................ 33 Figure 5. Rarefaction curves and upper and lower 95% confidence intervals for natural and forest habitats in the a) humid, b) sub-humid, and c) semi-arid bioclimatic zones. ............................... 35 vii INTRODUCTION Oceanic Island Biodiversity Insular oceanic islands have been of particular interest to scientists for centuries and are often viewed as ‘natural laboratories’ (MacArthur and Wilson 1967). Isolated oceanic islands often have a paucity of species compared to their continental neighbors but due to the rapid speciation of initial colonizers they generally have a high degree of endemism and adaptive radiations (Sadler 1999). While island ecosystems facilitate rapid diversification they also harbor high rates of extinction (Gillespie 2007, Pimm 1996, Sadler 1999, Paulay 1994, Sax and Gaines 2008). Isolated oceanic island species