Effects of Exotic-Species Afforestation on the Understory Vegetation of Santo Antao, Cape Verde Islands

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

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

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.

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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.

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

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

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

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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 also tend to have small population sizes and limited geographical ranges, therefore native flora and fauna tend to be more sensitive to rapid environmental disturbances than their continental neighbors. On top of natural biological processes are the rapid and massive habitat modifications and species introductions that often accompany human colonization (Paulay 1994, Pimm 1996). ‘Naïve’ species and species that fill narrow ecological niches are typically not able to compete against invasive alien species, particularly generalists. Habitat modification even of small areas can be irredeemably harmful to geographically restricted island species, and climate change can alter the restricted habitats that characterize oceanic islands (Gillespie 2007).

Rates of species extinctions, richness, and composition on isolated oceanic islands are disproportionate across taxonomic groups (Sax and Gaines 2008). Birds have seen the highest extinction rates but richness often remains stable due to the increase of cosmopolitan species.

Isolated oceanic islands have few native mammal species, thus extinctions are rare and island mammal richness has generally increased. Species richness of vascular plants on oceanic islands has seen dramatic increases as many exotic species become naturalized and relatively few native

8 species have gone extinct (Sax and Gaines 2008). However, concerning vascular plants on isolated oceanic islands it is unclear if species saturation has yet to be reached, if species richness and composition are in equilibrium, or if drawn-out times to extinction are presently being observed (Sax and Gaines 2008). Thus conservation of unique and fragile populations of isolated oceanic island vascular plant populations merit significant conservation efforts and better understanding.

Biodiversity of Cape Verde and Santo Antão

The Cape Verde (CV) islands, the southern-most archipelago of the Macaronesian region, have less floral diversity than the Canary and Madeira Islands. The degree of floral endemism is similar to that of the Madeiras but lower than the Canaries, but much lower when compared on a per area basis (Table 1). Brochmann et al. (1997) attribute the lower level of floral endemism to less ecological diversity and a relatively young flora. However, the floral diversity of CV is still significant with 82 endemic vascular species and sub-species and one endemic genus,

Tornabenea (Brochmann et al. 1997, Arechavaleta et al. 2005). Floral diversity of CV is positively correlated with island area and maximum altitude, and the island of Santo Antão (SA) ranks second in CV in terms of area and altitude and thus supports a high percent of the flora of

CV. SA has 47 taxa (57%) of the total endemic flora of CV, 11 of which are restricted to the island of SA (Brochmann et al. 1997).

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).

Category Cape Verde Canary Madeira No. of islands 9 7 2 Total area (km2) 4034 7273 728 No. of endemic spp. 65 460 106 No. of endemic spp. per island 7.2 65.7 53 No. of endemic spp. per km2 0.016 0.063 0.146 Total no. of spp. in total flora 621 1800 1110 Total no. of spp. in native flora 224 1022 670 % endemic spp. in total flora 10.5 25.5 9.5 % endemic spp. in native flora 29 45 15.8

Of particular interest in regards to the biodiversity of CV is the role that SA plays in conservation. CV is no exception to the concept of islands as fragile environments, even though extinction rates are generally lower in northern Atlantic islands when compared to tropical

Pacific islands (Gillespie 2007). Leyens and Lobin (eds., 1996) list a large number of angiosperms of CV as threatened or extinct (Table 2). SA supports a large portion of the threatened species, and often at a lower level of threat than in CV as a whole (Leyens and Lobin, eds. 1996). The recognition of the significance of SA ecological communities by the international community has been manifested by a joint Capeverdean/UNDP project to establish four protected areas on the island (PRODOC: 4176 SPWA).

Table 2. Conservation status of angiosperms in Cape Verde (CV) and Santo Antão (SA) (adapted from Leyens and Lobin (eds.) 1996). Percent of all Capeverdean angiosperm species in parentheses.

No. of Species Status SA CV Extinct 1 3 Prolonged Absence - - Critically Endangered 3 4 Endangered 5 13 Vulnerable 10 18 Indeterminate 3 16 Rare 2 10 150 Total no. of indigenous spp. incl. endemics 240 (63) 24 64 No. of extinct or threatened spp. (38) (27) 50 Total no. of endemic spp. 84 (60) 16 45 No. of extinct or threatened endemic spp. (36) (54)

Plantation Forestry

Afforestations, and monotypic plantations common of afforestations, play an important role in meeting the world’s demand for fiber products and will likely continue to increase for the foreseeable future (Brockerhoff et al. 2008). The effect of afforestations on ecosystems and biodiversity, however, are not clearly understood and are hotly debated. Supporters of afforestations cite the artificial forests’ positive effects on habitat connectivity, buffer effects on adjacent native forests, increased biodiversity levels in comparison to more intensive land uses

(i.e. commercial agriculture and urban landscapes), lessened pressure on native forests to meet the demand for fiber products, and the presence of rare species in afforested lands (Brocherhoff et al. 2008). The net biodiversity effects of afforestation depend on the biodiversity of the new forest and the habitat that it replaces, preceding land use, what tree species are involved, and how

11 and for what purpose the afforestation is being managed, but afforestations typically decrease biodiversity when they replace original non-forest habitats (Brockerhoff et al. 2008, Finch 2005, van Halder 2007, Buscardo et al. 2008). Plantation forests common of afforestations typically are even-aged with simplified structure, undergo intensive management, and can alter soil chemistry and fertility, and available water yield (Le Maitre et al. 1999, Farley et al. 2005, van Halder

2007, Berthrong et al. 2009).

Afforestation has been a priority of CV government (under the Portuguese during colonial times before independence in 1975 and the Republic of CV after independence) during the 20th century. Various CV-specific publications cite the objectives of afforestation to include soil stabilization and improvement after traditional agro-pastoral practices denuded the vegetation cover, production of firewood and forage, hydrological regime regulation, fog capture, development of economic activities for rural populations, and reconstitution of a more complex biota (Sandys-Winsch and Harris 1992, Diniz and Matos 1999, Colaço and Morais

2008). In SA forest habitat types never existed where afforestations now exist during the present climatic period and all afforestations replace indigenous meso- and hygrophytic shrub- and grassland vegetation types, all planted tree species are exotic to CV, and intensive ground preparation is undertaken prior to planting (Frahm et al. 1996, Brochmann et al. 1997).

Objectives of current forest management on SA are still focused on establishing new afforestations although 30-70 years have elapsed since initial establishment meaning management practices are limited to removal of dead trees and limbs for fuelwood, thinning of aggressive species, and replacement plantings (van Melle 1990). No rotational cutting schemes are practiced although they were proposed (van Melle 1990). Various management practices for

12 biodiversity conservation in plantation forests have already been outlined by Hartley (2002) but none have been adopted by CV or SA forest managers.

An evaluation of the afforestations has not been completed to date, particularly in terms of the effect on understory species. Afforestations on SA are not just sources of exotic species introductions but also necessitate altering native habitats to a historically non-existing forest habitat. They are another source of pressure, in addition to intensive agriculture, pastoralism, and climate change, to native ecosystems. Therefore the central objective of this research is to determine the impact of exotic-species afforestations on the understory vegetation of the Planalto

Leste region of the island of Santo Antão.

STUDY AREA

Cape Verde

CV composes the southernmost archipelago of the Macaronesian region, which also encompasses the Açores, Madeiras, Canaries, and Selvagem archipelagos. CV is situated c. 500 km west of the African mainland (Senegal) and c. 1500 km south of the Canaries (Figure 1). CV is of volcanic origin and was never connected to a continental mass. The archipelago is composed of ten islands and eight islets which are divided into two groups according to their position relative to the dominant Northeast tradewinds- the northern, windward Barlovento group

(SA, São Vicente, Santa Luzia, São Nicolau, Sal and Boavista) and the southern, leeward

Sotavento group (Maio, Santiago, Fogo and Brava). Erosion has reduced the older eastern islands to low, flat and topographically monotonous bodies while the younger western islands are characterized by steep, high mountains and a rugged topography with deep river valleys

(Brochmann et al. 1997). Total land area is 4033 km2.

Figure 1. Geographic location of Cape Verde.

The climate of CV is dominated by the Inner Tropical Convergence where the northeast trade winds, the southern monsoon, and the hot, dry Harmattan from the Sahara meet

(Brochmann et al. 1997, Colaço and Morais 2008). The desiccating Harmattan can bring dry, dusty storms during the months from December to May. Multiple-year droughts occur regularly, with 28 between 1719 and 1984 (Frahm et al. 1996, Hiemstra 1986). The short rainy season is from August to October, but rains can also come during the cooler months from November to

February. Climate varies primarily with topography, aspect and altitude (Brochmann et al. 1997,

Diniz and Matos 1999), with higher elevation and north/northeast-facing slopes being the most humid and lower elevation, south/southwest-facing slopes being the most arid (Figure 2). In

15 comparison to the Canary and Madeira Islands, CV has fewer gradients of humidity due to comparatively less trade wind influence and much more gradual transition between ecological zones (Brochmann et al. 1997).

Figure 2. Climatic factors of Cape Verde (adapted from Rocha 2010).

Santo Antão and the Planalto Leste Region

SA is the westernmost island of CV, the second largest (779 km2), and one of the youngest islands, formed approximately 7.57±0.56 million years ago (Duarte et al. 2008). The most recent volcanic activity formed a 33 km long elevated central plateau, oriented east to west, ranging from 1000-1979m. The Planalto Leste (PL) constitutes the eastern portion of the central plateau from 800m upwards and is commonly dissected by steep north-south valleys (Figure 3).

Temperatures are cooler in the higher elevation PL than the rest of SA, with a maximum of

40°C, minimum of 5°C, and a mean monthly average of 20°C (Hiemstra 1986, van Melle 1989).

The result of the rain shadow effect are clearly seen on east-west transect of SA, as the further west one travels the drier the climate becomes. The eastern PL intercepts the moist northeast trade wind and the cooling air mass deposits the moisture in the form of precipitation in the rainy season and prolonged fog during the winter and spring months. Fog plays a critical role in PL by providing additional precipitation when condensed by foliage and decreasing surface temperature and potential evapotranspiration rates during the humid months from August to February

(Hiemstra 1986, Gils 1988, Duarte et al. 2008). Previous authors (Hiemstra 1986, Diniz and

Matos 1999, Colaço and Morais 2008, Rocha 2010) have divided the high altitude PL into three main bioclimatic zones – humid (601-1400 mm/year, more days with fog), sub-humid (300-600 mm/year, more days with fog) and semi-arid (150-250 mm/year, less days with fog). Actual bioclimatic boundaries, rainfall, and number of days of fog can vary significantly from year to year, and transitions can be severe in places with higher altitude (e.g. Moroços National Park on the western limit of PL ranging from 1400-1797m).

In terms of endemic vegetative diversity PL is located in some of the most diverse altitudinal and climatological ranges in CV and SA (Brochmann et al. 1997). The relatively recent volcanic origins of PL means that the soils of the PL are young, generally shallow, little developed and structured, and very susceptible to erosion. However, the soils’ youth also means that there is a good reserve of weatherable minerals, high nitrogen content, and a low carbon/nitrogen quotient (Hiemstra 1986). Infiltration capacity is high where shallow rock layers do not form impermeable layers but the siltier soils can naturally form surface crusts that impede infiltration. The most recent volcanic activity formed the central plateau and deposited

17 pyroclastic materials across the entire surface of PL, including ash, tuff, lapilli, and slag. Soils of the PL can generally be described by parent material- pozzolano, pyroclastic, basaltic, and phonolitic basaltic. Diniz and Matos (1999) provide a detail description and taxonomy of PL soils in relation to climatic and geomorphic situations, and according to FAO-UNESCO (1988).

Few records exist of the early history of CV or SA but an idea can be formed from the remarks of historians, anecdotes, place names, and inferred from the habitat preferences of native plant species in other localities within their natural distributional range. Specialized plant communities inhabit certain specialized geomorphologies such as springs, seeps, and steep rocky escarpments (Hiemstra 1986, Diniz and Matos 1999). Endemic and indigenous tree species of

CV (Table 3) are not capable of forming closed canopy forests throughout their natural distribution and thus were likely interspersed in a shrub- and grass-dominated landscape.

Within the Planalto Leste, large shrubs (Euphorbia tuckeyana, Echium stenosiphon ssp. stenosiphon, Periploca laevigata ssp. chevalieri, Artemesia gornoneum, Globularia amygdafolia), dwarf shrubs (Conyza spp., Nauplius daltonii ssp. vogelii, Helianthemum gorgoneum) and perennial grasses (Hyperrhenia hirta, Heteropogon contortus) form a dense cover (Frahm et al 1996, Hiemstra 1986, Diniz and Matos 1999, Brochmann et al. 1997). The natural vegetation of SA adapted to cyclical dry periods, but additional anthropogenic stressors likely aggravated species composition and distributions. Overgrazing by livestock (primarily goats), overharvesting of wood and medicinal plants, conversion to agriculture, climate change, and exotic species invasions have degraded natural vegetative communities (Frahm et al 1996,

Hiemstra 1986, Diniz and Matos 1999, Gomes et al. 2003). The uprooting of perennial grasses

18 for forage and roofing was a common practice, traditional agricultural practices entail removal of vegetation and humiferous topsoil (Sandys-Winsch and Harris 1992), and the wood of

Sideroxylon marginata and Ficus sycamorus ssp. gnaphalocarpa were especially valued for construction purposes. According to Hiemstra (1986) an increasing human and livestock population in combination with an extended dry period (1972-1983, only one wet year) virtually eliminated many shrub and perennial grasses from some zones within the PL. Today the remnant natural communities are found in steep, inaccessible escarpments at the higher elevations, although invasive alien species first introduced by the Portuguese and aggressive tree species used for afforestation are spreading there (i.e. Furcrea gigantea, Lantana camara, Acacia mollisima). Many plant species are ubiquitous ruderal species that are able to persist despite intense agricultural and pastoral pressure, and natural disturbance like torrential rains (i.e. Bidens pilosa, Tagetes minuta). MNP, in the western limit of PL, contains some of the largest quantities of native vegetative communities and lowest densities of spontaneous invasive species in SA.

Recently afforestation with exotic species has added yet another threat to the native vegetation

(Gomes et al. 1994, Frahm et al. 1996).

Table 3. Endemic and indigenous tree species of the Planalto Leste region of Santo Antão (Brochmann et al. 1997).

Species Status Acacia albida Indigenous Dracaena draco Indigenous Ficus sycamorus ssp. gnaphalocarpa Indigenous Phoenix atlantica Indigenous Sideroxylon marginata Endemic

Teixeira and Barbosa (1959) summarized the major dates of importance to the natural setting of SA (Table 4). SA was first discovered by the Portuguese in 1462 and was described as a rugged island with abundant trees and rivers. As was the common practice of sailors of that

19 time, goats and cotton seeds were released to reproduce on their own. Visitors would then return to SA periodically to cull goats and cotton to carry back to Portugal. Thus goats had at least 86 years to roam free and browse as they please. Permanent communities began to be established in

1548, at which time Valentim Fernandes remarked, “SA is tall and rugged, unpopulated, with many goats, much good water, and large dragon trees (Sideroxylon marginata)” (Teixeira and

Barbosa 1959). 1798 saw the first recorded introduction of tree species originating from Portugal and/or her colonies.

Table 4. Chronological summary of forestry-related events on the island of Santo Antão, Cape Verde.

Year Event 1460 Discovery of Santo Antão :”Abundant trees, rivers” 1548 Santo Antão was populated, “very tall and inaccessible, unpopulated, with many goats, many good waters, and big trees” 1798 Introduction of pines (Pinus sp.), chestnut (Castanea sp.), oak (Quercus sp.), etc. 1954 Missão Silvícola (terminated 1972), Major forest development from 1955-1965 1975 Independence from Portugal 1982-91 SARDEP (Dutch-Capeverdean agreement), Period of major forest expansion and regulation  Legally established ‘Forest Perimeter’  Livestock and firewood harvesting rules  Forest Fund and economic arrangements

1992-Present Ministry of Rural Development (MDR), NGO’s, and international aid projects

The Portuguese began to realize some of the problems of a denuded landscape and forestry incentives began to appear in CV during Portuguese colonial rule in the early 20th century. SA did not receive much attention until the establishment of the Missão Silvícola

(Forestry Mission, or MS) in c. 1940-1972. MS completed major development works including roads, soil and water conservation (SWC) measures, animal husbandry development, and major forest development from 1940-1972. Afforestation activities initially focused on both drier, lower zones and the humid, high altitude eastern portion of SA. Planting efforts were mainly

20 focused on Pinus spp., Cupressus spp., Acacia spp., and Eucalyptus spp. A focus was placed on

Pinus spp. because they are pioneer species that are able to capture fog, grow without precipitation, produce good quality wood, and have proved to have a higher survival rate than other species (Litjens 1983). While the oldest forests of SA are relics of MS not all of their efforts were successful. The majority of the low altitude afforestation projects of MS have died off; some of those areas have been re-forested by later forestry programs (van Melle 1991).

Following independence from Portugal in 1975 Cape Verde has experienced an explosion of development- from one of the world’s 25 poorest countries in 1975 to their recent graduation to a Medium Developed Country today. Development of infrastructure (primarily in the areas of transportation, water storage, and utilities), education system, economic development, and technology have progressed quickly. An important aspect of this development in SA was the

Projecto Bilateral Cabo Verde e Holanda (Santo Antão Rural Development Project, or SARDEP) established in 1978 between the young CV government and Holland. The SARDEP Forest

Project initiated in PL in 1982 enacted far-reaching regulations and was a time of major forest development. SARDEP assisted the newly formed Ministry of Rural Development (MDR) with afforestation efforts, range land management, and soil and water conservation practices throughout the PL (Anonymous 1990). Extensive networks of low rock contour walls, check dams, water retention dykes, and other physical SWC methods were constructed, and forest management plans and agro-pastoral extension services were initialized until the project’s completion in 1990 (van Melle 1990). Tree and bush elimination trials were conducted and species most resistant to low precipitation, periodic dry periods, and repeated cutting were chosen for widespread planting (van Melle 1989). A saw mill was set up in 1989 that at one

21 point produced 6 m3 of board wood daily. SARDEP built capacity among natural resource technicians, and employment rate was high (Anonymous 1990). The first Forest Law, Forest

Perimeter, Forest Fund, and forest guards originated under SARDEP. A major shift in land tenure also occurred when the Forest Perimeter was established ─ before there were a small number of landowners with large tracts of land, after SARDEP there were more landowners with smaller tracts.

Sole responsibility of forestry activities and natural resource management was fully transferred to MDR in 1991. MDR initiated large afforestation projects in the lower altitudes of

SA in the early 1990s. DGASP published the results of the National Forest Inventory in 2013.

While MDR (now part of DGASP) remains the largest forestry-related entity in SA, various international aid groups (i.e. Food and Agriculture Organizations), non-governmental organizations, and occasionally local community associations are also major players. In 2011 the

Protected Areas Program of Cape Verde established two natural parks in heavily forested areas of SA.

METHODS

Plot Selection

All tree species used for afforestation in Cape Verde are exotic species and therefore any significant tree presence (>15% of canopy cover), whether by intentional planting or natural regeneration, constituted ´forest´ for the purposes of this study. Forested areas dominated by densely planted evergreen species such as Pinus spp. are visually distinctive from the surrounding natural and agricultural vegetation on aerial imagery and were easily delineated using ArcGIS 9.0. The deciduous and less dense Acacia-dominated forested areas required delineation on foot with a handheld GPS unit (Garmin eTrex). To select plots in the semi-arid bioclimatic zone a 50x50 meter grid system was then overlaid on the resulting map of PL in

ArcGIS and each grid line intersection was assigned a number. Forty numbers in total were selected randomly using a random number generator (Microsoft Excel 2007), 20 points in forested areas and 20 in natural areas. The study site within the semi-arid bioclimatic zone, primarily within the boundaries of Moroços National Park, contained a lower proportion of agriculture and degree of human influence as well as higher degree of safe accessibility than the humid and sub-humid bioclimatic zones and therefore a higher number of natural plot locations were able to be located (Figure 3).

Forest plots in the humid and sub-humid bioclimatic zones were initially selected in the same manner as semi-arid plots. However significant agro-pastoral activity has left few areas of the humid and sub-humid zones undisturbed and suitable natural plots are typically relict plant communities on very steep, dangerous cliff faces. Therefore the natural plots in these two zones were not selected randomly and the number of accessible, suitable natural plots was the limiting

23 factor on forest plots and ultimately sample size. Natural plot suitability criteria consisted of 1.

Safe accessibility and 2. Evidence of little to no grazing, pasture collection, or agriculture.

Ultimately, 10 plots were able to be located in the sub-humid bioclimatic zone, and 12 in the humid bioclimatic zone.

Data Collection

Plot characteristics: Elevation, aspect, slope, soil texture and type, soil conservation measures

(i.e. stone contour walls), and evidence of livestock browsing pressure and human activity (wood cutting, collection, fire, etc.) was noted for all plots. Plot characteristics were used to assist in a general habitat characterization but were not analyzed. A photo spanning the entire parcel was taken of each plot.

Vegetation: Each plot consisted of a 78.5 m2 circle with a five meter radius and contained two, 1 m2 subplots, one directly north and one directly south and both 2.5 meters from the plot center point. A comprehensive list of all observed plant species within the entire plot was compiled.

Vegetative cover was sampled in the subplots using a modified Braun-Blanquet scale (Table 5).

Maximum leaf litter depth was recorded in each sub-plot. In forested plots, basal area was measured to provide a measurement of forest cover. Total basal area (m2/ha) was calculated from the diameter at breast height (DBH) of every stem of the five nearest trees to the plot center point.

Understory physiognomy of each species, maximum understory vegetation height, percent cover of bare rock and soil, aspect, elevation, presence and classification of coarse woody debris, max tree height, and an ocular estimation of forest canopy cover were collected but not analyzed.

Data Analysis

Total understory species richness, endemic richness, Shannon-Weaver diversity indices, mean understory percent cover, and mean leaf litter depth was calculated for each assemblage to quantify species diversity, abundance, and understory characteristics. Importance values (relative abundance + relative frequency) were calculated for each species in each habitat type and bioclimatic zone. A Kolmogorov-Smirnov or Shapiro-Welk test for normality and Levene’s test for homogeneity of variance was applied to each data set to test the basic assumptions of paired t-test to test for differences between habitat types for each bioclimatic zone. Data sets were transformed as necessary to adjust for normality; if successful transformation was not possible the non-parametric Mann-Whitney Rank Sum test was used instead (SigmaPlot 12.5, 2013).

Cover values from the modified Braun-Blanquet scale were converted to percent cover values following a model similar to Maarel (1979). The species that covered less than five percent cover were grouped to two classifications to not over-weight rare species when calculating abundance, relative abundance, importance values, and Shannon-Weaver biodiversity indices (Table 5). Conversion of the modified Braun-Blanquet scale to average percent cover allowed for easier data analysis and is a common practice when using cover-abundance scales

(Maarel 1979).

Basal area calculations can not be extrapolated to the surrounding forest stands and may only be used as generalizations due to the methodology utilized. The total basal area of plots that contained five or fewer trees of the plot is accurate because all trees were measured, however in plots which had more than five trees not all stems were measured and the calculated total basal

26 area is lower than the total basal area of the stand. Plots with incomplete basal area measurements are relatively rare (16% of humid forest, 10% of sub-humid, and 15% of semi-arid plots, respectively), and therefore the mean basal area within each bioclimatic zone may be used as conservative estimates of the actual basal areas of those stands.

Table 5. Definition of modified Braun-Blanquet cover-abundance classifications and conversion to average percent cover classes.

Classification Definition Converted % Cover Value r ≤5% cover, ≤5 plants 2.5 p ≤5% cover, 6-15 plants 2.5 m ≤5% cover, 16-30 plants 5 a ≤5% cover, >30 plants 5 1 6-15.9% cover 10.5 2 16-25.9% cover 20.5 3 26-35.9% cover 30.5 4 36-45.9% cover 40.5 5 46-55.9% cover 50.5 6 56-65.9% cover 60.5 7 66-75.9% cover 70.5 8 76-85.9% cover 80.5 9 86-100% cover 93

Jaccard’s coefficient was calculated to compare understory species composition between habitat types of each bioclimatic zone; a score of 1 indicates that the two habitats are identical.

Jaccard’s coefficient measures similarity between sample sets and is defined as the size of the intersection divided by the size of the union of the sample sets:

Rank-abundance curves were calculated for natural plots and the understory species of forested plots in each bioclimatic zone to obtain a detailed and graphic description of abundance

27 distribution. The proportional abundance was calculated for each species present in the 1 m2 subplots (tree species not included), ranked by proportional abundance, and graphed. If more than one species had the same proportional abundance the average rank was used.

Rank-abundance curves do not consider the identity of the species ranked, in other words the curves do not show if the most abundant species in one habitat is the most abundant in another habitat. Therefore Spearman rank-order correlations of the proportional abundances of species shared in both habitat types within each bioclimatic zone was used to determine if species-abundance rankings varied in a similar way between habitat types (SigmaPlot 12.5,

2013). The Spearman rank-order correlation helped to determine if species-abundance relationships vary because or regardless of the habitat type.

Traditional biodiversity indices have some inherent problems, such as the loss of information associated with limited sampling (James and Rathbun 1981, Gotelli and Graves

1996), therefore sample-based rarefied estimates of species richness were calculated using

Analytic Rarefaction 1.3 calculator (Holland 2001). Rarefaction analysis allows richness and diversity to be compared after differences in abundance among samples has been standardized

(Simberloff 1972, Gotelli and Colwell 2001). Only the natural plot species and understory species of forested plots found in the 1 m2 subplots were ranked and graphed.

Total and endemic species richness was derived from species presence data within the entire 78.5 m2 plot area. The rank-abundance curves, rarefaction estimates, Spearman rank-order

28 correlation, Shannon-Weaver diversity index, Shannon’s equitability, mean understory percent cover, and mean leaf litter depth, were derived from the data obtained in the 1 m2 subplots.

RESULTS

Diversity Indices and Site Characteristics

Diversity indices and site characteristic metrics reveals parallel effects of afforestations on understory species of humid and sub-humid bioclimatic zones that vary only by the degree of magnitude. Total understory richness, Shannon-Weaver values, and mean understory percent cover were nearly double in natural plot understories than that of forest understories; endemic richness of humid natural understories was more than triple that of forest understories compared to only double in the sub-humid zone. Shannon’s equitability was higher in both bioclimatic zones than forest understories. Mean understory percent cover was significantly different between natural and forested understories in both humid and sub-humid zones. Mean leaf litter depth of the humid zone is more than twice as deep in forest understories than natural plots whereas sub-humid mean leaf litter depth is only slightly deeper (but still significantly so – t=2.58, P<0.01). Mean basal area in the humid zone was approximately four times that of the sub-humid and semi-arid zones. Natural regeneration of tree species was noted in the afforested areas. Pinus canariensis and Grevillea robusta were locally common in the humid zone, while juvenile A. mollisima were common throughout both the humid and sub-humid zones. Jaccard’s index did not display a strong degree of similarity, only 30% and 37% similarity in the humid and sub-humid zones, respectively. Table 6 summarizes the diversity, abundance, and site characteristic analytical results.

Conversely, the semi-arid metrics results display the similarity of natural and forested habitats. Total understory and endemic richness are only slightly higher in the natural plots;

Shannon-Weaver and Shannon’s equitability indices are actually higher in the forested plots.

Mean understory percent cover is slightly higher in natural plots, and mean leaf litter depth is nearly identical. Jaccard’s index reveals 57% similarity of species between natural forested plots, nearly double that of the humid and sub-humid zones.

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.

Humid Sub-Humid Semi-Arid Metric Natural Forest Natural Forest Natural Forest Total understory richness 49 24 46 28 39 33 Endemic richness 21 6 20 9 17 13 Shannon-Weaver 2.72 1.44 2.74 1.74 2.62 2.72 Shannon’s equitability 0.779 0.563 0.815 0.603 0.771 0.808 1Mean understory percent 74.5 30.5 82.3 46.4 75.1 64.0 cover (%) (27.4)* (46.6)* (29.3)† (29.7) † (29.4) (28.0) 1Mean leaf litter depth 2.8 7.6 1.4 2.0 1.5 1.7 (cm) (2.2)* (5.7)* (0.65) †† (0.83)†† (1.6) (1.9) 2Mean basal area (m2/ha) -- 0.24 -- 0.054 -- 0.056 (0.24) (0.052) (0.048) Jaccard’s index (%) 30 37 57 3Spearman’s rank order 0.14 (8) 0.39 (13) 0.78 (24)††† correlation *U = 126.0, n=24, P<0.001 †t = -3.85, n = 20, P < 0.001 ††t = 2.58, n = 20, P < 0.05 ††† rs = 0.776, n = 24, P < 0.001 1Mean corresponds to the average of the 1 m2 sub-plots (standard deviation in parentheses) 2Mean basal area corresponds to the average of the nearest 5 trees to the 10m-diameter plot center (standard deviation in parentheses) 3 Correlation coefficient, or rs (number of shared species in parentheses)

Rank Abundance Curves and Spearman Rank-Order Correlation

Natural plots in the humid bioclimatic zone have a greater number of species with intermediate abundances (Figure 4). The steeper slope of the rank-abundance of forested plots in the humid zone illustrates two main points: 1. Fewer species are present in exotic species afforestations and 2. The bulk of the understory abundance of afforestations is made up of a fewer number of species. The slopes and magnitudes of the sub-humid and semi-arid zones in

31 afforested areas mirror those of the natural areas. The one notable difference is the highest- ranked species in the sub-humid zone, Cynodon dactylon, whose abundance is nearly four times that of the next ranked species.

A Spearman correlation coefficient (rs) of +1 indicates a perfect association of ranks, conversely a rs of -1 indicates a perfect negative association. The closer rs is to zero, the weaker the association between ranks. The results of the Spearman rank-order correlations of the humid and sub-humid bioclimatic zones indicates weak, non-significant correlations between the abundance of shared species between natural and forested plots (Table 6), with the correlation of the humid zone (rs = 0.14) being nearly three times weaker than that of the sub-humid plots (rs =

0.39). Understory species in humid and sub-humid forested plots diminished their cover to relatively low values regardless of their percentage cover in the natural plots, meaning the ranking of plant species abundance in natural plots was not predictive of that in forested plots. A significant, predictive relationship (rs = 0.78, P < 0.001) was revealed between natural and forested understories in the semi-arid zone indicating that an abundant species in a forested plot would likely also be abundant in the natural plot.

a) 0.25 Humid 0.2

Natural 0.15 Forest Understory

0.1

0.05 Proportional Abundance Proportional

0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 Rank

b) 0.5

0.45 Sub-Humid 0.4 0.35 Natural 0.3 Forest Understory 0.25 0.2 0.15 0.1

Proportional Abundance Proportional 0.05 0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 Rank

c) 0.18

0.16 Semi-Arid 0.14 Natural 0.12 Forest Understory 0.1 0.08 0.06 0.04

Proportional Abundance Proportional 0.02 0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 Rank 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.

Rarefaction Analysis

Rarefaction curves represent the expected species richness for different frequencies of plant species. The curves in Figure 5 indicate that the low plant species richness recorded in humid and sub-humid forested plots was not merely a consequence of their low abundance – differences in species richness were still apparent after differences in abundance were accounted for. In other words, if a similar percent cover (abundance) of species were sampled in forested plots as natural areas the differences in species richness would still exist. A lower magnitude of difference in species richness is observed within the sub-humid zone than the humid zone. The semi-arid zone displays nearly identical rarefaction curves of natural and forested plots indicating little to no difference in expected species richness.

40 a) Humid

30 25 Natural 95% conf. int. Natural 20 95% conf. int. Natural 15 Forest 95% conf. int. Forest

Species Richness Species 10 95% conf. int. Forest 5

10 70

250 130 190 310 370 430 490 550 610 670 730 790 850 910 970

1390 1030 1090 1150 1210 1270 1330 1450 1510 1570 1630 1690 1750 Percent Cover

35 b) Sub-Humid

25 Natural 20 95% conf. int. Natural 15 95% conf. int. Natural Forest Understory

10 95% conf. int. Forest Species Richness Species 5 95% conf. int. Forest

10 60

460 110 160 210 260 310 360 410 510 560 610 660 710 760 810 860 910 960

1010 1610 1060 1110 1160 1210 1260 1310 1360 1410 1460 1510 1560 Percent Cover

c) 35

25 Natural 20 95% conf. int. Natural 95% conf. int. Natural 15 Forest Understory 10 95% conf. int. Forest Species Richness Species 95% conf. int. Forest 5

0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 Percent Cover 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.

DISCUSSION

The effects of exotic-species afforestations on the understory vegetation of the Planalto

Leste region of Santo Antão could best be thought of as a continuum. The effect is greatest in the easterly humid zones where natural plot richness, diversity, and abundance is higher than afforested understories and differences are often statistically significant. Afforestations in the semi-arid zones do not relate to any significant differences in the variables measured, and natural and afforested understories have comparable richness, diversity, and abundance. The sub-humid zones are not in the exact middle of the continuum; afforestation affects understory vegetation negatively but not as severely as in humid zones.

Rarefaction and rank-abundance curves for the humid and sub-humid zones suggest that reductions in the richness caused by plantations also relate to reductions in the evenness of the understory assemblages. Rank-abundance curves and Spearman’s correlation coefficients indicate that humid and sub-humid afforested understories support fewer species with intermediate abundances and a severe reduction in abundance in general. Since closed canopy forests likely never existed at high elevations of Santo Antão, but only shrubs and grass- dominated rangelands, the majority of native plant species are not adapted to low-light environments while a handful in the PL region are. When ranked by importance value (relative abundance + relative frequency) Brachypodium distachyon and Cynodon dactylon are within the top 8 important species in all habitat types. In fact C. dactylon is the most important species in all afforested habitats. When paired with rarefaction and rank-abundance curves, importance values indicate that some species are affected by afforestations more than others, some positively and some negatively.

The mechanisms by which afforestations affect understories on Santo Antão appear to be similar as in other areas of the world (Brockerhoff et al. 2003, Paritsis et al. 2008) and include the degree of canopy cover, formation of thick leaf litter, and stand age. These factors are clearly linked to climate and time; given sufficient time (~50 years) afforestations in the more favorable, humid eastern areas that intercept the moist tradewinds are able to thrive, forming closed canopies and deep, dense mats of leaf litter. As the climate becomes less favorable and drier in the sub-humid zone afforestations are unable to form closed canopies and the leaf litter layer is less complete. Moisture is sparse (50-250 mm/year) in semi-arid zones and afforestations are unable to form closed canopies or thick leaf litter. Brockerhoff et al. (2003) observed in New

Zealand in P. radiata plantations that increased stand age correlated with increased understory diversity due to an increase in shade tolerant, late seral species adapted to closed canopy forest conditions. However CV has no native closed canopy forest conditions and thus no shade tolerant, late seral species.

Some consideration must also be given to tree species characteristics and forest establishment practices. Commonly planted tree species in the humid zone in CV (P. canariensis, P. radiata) are able to form closed canopies in their native ranges. For example,

Arévalo et al. (2005) observed P. canariensis forests with 60% canopy cover and basal area reaching 14.56 m2/ha in areas with just 600 mm/year in the Tamadaba National Park of Gran

Caranaria Island, Canary Islands. Henry (2005) observed canopy closure of more than 80% and basal area of up to 35 m2/ha in native P. radiata stands in coastal California (USA). In CV, these species were originally planted with close spacing in the climatically favorable areas, while those

37 planted in the less favorable semi-arid zone do not typically form closed canopies and were planted less densely to maximize water harvesting abilities of the low contour walls. Sub-humid afforestations consist of a mix of mesic- and dryland tree species whose spacing depended on aspect and microclimates (MDR, personal communication), thus are sometimes able to form closed canopies and sometimes not.

Cultural and Management Implications

Based on the data from this research, exotic species afforestations are detrimental to the richness, diversity, and abundance of understories within the more favorable habitats, especially those of the humid zones. However, the same afforestations provide valuable soil and water conservation, employment, fuelwood, structural building materials, an aesthetically pleasing landscape, and give local residents a sense of pride. Moving forward, an evaluation of the original goals of forest planners and incorporating new management techniques would be helpful for all stakeholders.

All afforestation entities that are or have been active in SA share four main goals:

1) Provide soil erosion control by mechanical and vegetative methods;

2) Increase infiltration, fog capture, and water availability;

3) Increase biodiversity and vegetative cover; and

4) Increase economic aspects of forests such as firewood, employment, and timber.

SA has met with success in meeting goal 1; the forestry practices utilized in SA do a good job of controlling soil erosion (Haagsma 1990). Mechanical SWC structures are abundant and generally well-maintained, and many current development projects focus on constructing more. Forests have been successfully established and maintained for more than 60 years.

The results of meeting goal 2 are more ambiguous. The forests of SA, especially the mature pine forests of the PL, likely increase infiltration and definitely capture large amounts of fog. van

Melle (1989) report multiple tree species capturing an amount of fog ≥200% more than the surrounding precipitation levels. The increased fog capture can possibly have a great effect on water availability as Scholl et al. (2002) report that fog drip is a major component of stream flow and shallow groundwater at higher altitudes in similar habitats. However afforestation can have both positive and negative consequences on the hydrology of an area (Allen and Chapman 2000,

Farley et al. 2005, Le Maitre et al. 1999). Greater uptake of soil water by trees and increased water holding capacity of forest soils can diminish groundwater recharge, reduce surface runoff, and negatively impact groundwater quality, especially in semi-arid and arid climates where rainfall is unevenly distributed throughout the year (Sahin and Hall 1996). Reduced recharge rates and altered groundwater quality in turn negatively impacts the quantity and quality of drinking and irrigation water. Additionally, altered acidification, nitrification, and nutrient cycling processes under afforested areas can cause imbalances in soil nutrients, especially when the mineral weathering process of young, volcanic soils like SA’s is restricted by forest cover

(Berthrong et al. 2009). The effects of afforestations on the hydrology and soil nutrients of SA are not well understood; few to no studies have been conducted but the need is great.

Goal 3 states the intention of afforestations to increase biodiversity and vegetative cover.

Data from this thesis indicate that afforestations actually have a detrimental effect on understory diversity and abundance in the favorable humid and sub-humid zones that allow closed canopies to form, but have virtually no effect on semi-arid understories. The effects on total vegetative cover are likely not as severe as tree cover likely replaced shrub and grass cover in humid and sub-humid zones. van Melle (1990) believed the intense land preparation with contour walls could actually be destructive to biodiversity in the long term due to high level of soil disturbance and uprooting of vegetation. Soil disturbance is particularly devastating in drier environments like SA. The effects of forest establishment-related soil disturbance on understory vegetation diversity and abundance is beyond the scope of this thesis, but I believe forest management practices have played a significant if not greater role.

The forests of SA do provide increased economic resources (Goal 4). As of 2012 MDR currently employs 155+ individuals in SA related to forest maintenance who would otherwise be searching for work in other sectors. MDR generates income from the sale of wood (large diameter stumps, poles, and small diameter firewood). People are able to gather firewood if accompanied by a forest guard and MDR laborers can sell extra bundles of firewood they are given as compensation if they choose. The forests create a greener landscape, are undoubtedly pleasing to the eye, and as such provide a draw for tourists. However the economic potential of

SA forests is much higher. Increased timber harvesting could potentially meet a large portion of the timber demand of SA and possibly the nearby island of São Vicente. Many secondary economic benefits are possible but are underutilized, such as charcoal and artisanal crafts.

Additionally, tourism agencies relying on the ruggedness and natural beauty of SA are all based

40 in São Vicente or the coastal SA urban centers. The economic benefits of tourism rarely make it into the hands of the rural residents residing in forested areas.

High habitat heterogeneity typically translates to high levels of biodiversity, and lower forest canopy cover often translates to higher species richness. The single best correlation between animal species diversity and afforestation structure is the amount of native vegetation present (Hartley 2002). Original forest management plans called for varying levels of management for different stands based on carrying capacity of soils, aspect, slopes, and susceptibility to erosion (Briel 1984, Duiker 1983, Fraiture et al. 1983, Ruks and Tielens 1984).

Prescribed thinning and ‘cleaning’ (trimming of lower branches) were prescribed for all stands to promote forest establishment, followed by harvest rotations ranging from ~20 years to never in forest stands intended for soil protection. In reality forest management never progressed from the forest establishment phase. Excepting hazard trees and particularly aggressive species (i.e. A. mollisima), live trees are not harvested. Only trees that die naturally are removed. Hartley

(2002), Brockerhoff et al. (2007), and Lindenmayer et al. (2006) describe stand-level management techniques that could improve biodiversity conservation and not compromise soil stability or production. Some recommendations are currently adhered to, e.g. leaving slash/residues when forests are ‘cleaned’, but most are not. I believe ‘leave strips’ are particularly suitable to PL afforestations as trees are already planted following contour lines.

Rows of trees of varying lengths could be removed along existing contour walls, one or two contours wide. The resulting gaps would increase canopy heterogeneity, increase sunlight on the forest floor, and provide space for native understory vegetation (Hartley 2002, Brockerhoff et al.

2007, Moore and Allen 1999). Care would need to be taken to prevent the establishment of aggressive invasive species (especially Lantana camara), but leave strips would most likely

41 result in increased biodiversity without compromising soil stability and potentially improve the local economy by temporarily increasing timber production. Education of all stakeholders involved would be necessary and vital.

Research Needs

This research project did not attempt to analyze anthropogenic effects of high disturbance soil and water conservation measures (e.g.. rock contour walls), pasture collection, and grazing because those practices are fairly consistent across all study areas (personal observation). While ubiquitous agro-pastoral activities made it difficult to find natural areas, the main research question of effects of exotic-species afforestations on understory vegetation can be answered with less risk of confounding variables. Anthropogenic effects are present but consistent.

Caution should also be exercised when only investigating one bioindicator group; evaluation of additional groups (epigeal beetles, arachnids, reptiles, birds) would provide a more complete picture to aid in management. Further research could explore the effects of exotic species afforestations on soil chemistry and nutrient cycling, the effects on hydrology and water availability, and stand management techniques that increase understory diversity and still promote soil stability, erosion control, invasive species suppression, and production.

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