Turkana Region of Northern Kenya. A thesis presented to. the faculty of. the Voinovich School of Leadership & Public Affairs. In partial fulfillment

Transcription

1 Distribution and Density of the Invasive Plant Species, Prosopis juliflora, in the Western Turkana Region of Northern Kenya A thesis presented to the faculty of the Voinovich School of Leadership & Public Affairs In partial fulfillment of the requirements for the degree Master of Science Daniel K. Mwania August Daniel K. Mwania. All Rights Reserved.

2 2 This thesis titled Distribution and Density of the Invasive Plant Species, Prosopis juliflora, in the Western Turkana Region of Northern Kenya by DANIEL K. MWANIA has been approved for the Program of Environmental Studies and the Voinovich School of Leadership & Public Affairs by Nancy J. Stevens Professor of Functional Morphology & Vertebrate Paleontology Mark Weinberg Dean, Voinovich School of Leadership & Public Affairs

3 3 ABSTRACT MWANIA DANIEL K., M.S., August 2017, Environmental Studies Distribution and Density of the Invasive Plant Species, Prosopis juliflora, in the Western Turkana Region of Northern Kenya Director of Thesis: Nancy J. Stevens Prosopis juliflora is an evergreen plant originating from Central or South America that is highly invasive in Kenya. This fast-growing plant can thrive in harsh conditions including alkaline soils and areas with exceptionally low rainfall. Due to deliberate or accidental introduction in arid ecosystems, the plant is recorded in 129 countries globally and the invasion rate is projected to increase. Prosopis is now aggressively spreading in arid ecosystems throughout Kenya, where it forms impenetrable thickets that block access to waterways and disrupt livelihoods by serving as cover for thieves and dangerous animals and reducing suitable area available for grazing livestock. To inform management strategies for Prosopis juliflora, this study documented the extent of invasion near Lake Turkana and assessed the effect of soil substrate, distance from humans, and distance from water sources on presence, size and/or density of Prosopis juliflora in the arid ecosystem. More Prosopis was found in areas dominated by sand/silt, of proximity to areas of human activity and of proximity to Lake Turkana. These findings show that areas dominated by sand/silt, of proximity to human activity and of proximity to Lake Turkana as priority areas for any future mitigation strategies that may control/eradicate Prosopis juliflora.

4 4 DEDICATION I dedicate this work to my parents, Josephat Mwania and Mary Mwania and my siblings, Dennis Mwania, Davis Mwania and Dorcas Mwania. You offered me great support during the writing of this document. I will be forever grateful.

5 5 ACKNOWLEDGMENTS I would like to acknowledge the support of my advisor Dr. Nancy Stevens. Dr. Stevens offered immense support for this project since from conception and literature gathering, to data collection and writing of my thesis document. My committee members, Dr. Geoff Dabelko and Dr. Sarah Davis gave unwavering support and suggestions towards the writing of my thesis document. Your efforts are highly appreciated. The writing of this document could not have been possible without the support of Dr. Fredrick Kyalo, Mr. Rob Wiley, Dr. Ruhil, Dr. Miles, Onyango and Jeff. I thank the head of the West Turkana Paleo-project, Dr. Fredrick Kyalo, who offered logistical support during my data collection period. Mr. Rob Wiley assisted with my study design and equipment. Dr. Ruhil and Dr. Miles offered help in my statistical analysis. I also appreciate the support of the West Turkana Paleo project crew who offered support during my navigation in the field. Onyango and Jeff were particularly helpful by driving me to the field sites and setting up sample plots.

6 6 TABLE OF CONTENTS Page Abstract... 3 Dedication... 4 Acknowledgments... 5 List of Tables... 8 List of Figures... 9 Chapter 1: Introduction Colonization, spread and distribution of Prosopis juliflora Unpacking the costs and benefits of Prosopis juliflora for the environment and local communities Mitigation strategies employed for Prosopis invasion Objectives Chapter 2: Methods Study location and sampling parameters Study design Data analysis Chapter 3: Results Table Table Table Table Table Table Prosopis on different soil substrates Prosopis and distance from Lake Turkana Prosopis and distance from areas of human activity Do soil substrate grain size, distance from Lake Turkana and/or distance from areas of human activity predict the presence/absence of Prosopis? Relationships among variables measured in this study Chapter 4: Discussion... 50

7 7 4.1 Limitations References Appendix A: Data Collection Sheet Appendix B: Raw Count Data for Prosopis, Herbaceous Plants, Grasses and Shrubs... 60

8 8 LIST OF TABLES Page Table 1: Data on study sample plots showing Prosopis stem count (where presence/absence is indicated as 0/1), distance from Lake Turkana, distance from areas of human activity and soil substrate grain size categories...30 Table 2: Data on study sample plots showing how distance in meters from Lake Turkana(dislake) and distance in meters from areas of human activity(dishuman) for all 20 m plots Table 3: Table depicting results obtained from poisson regression analysis seeking to assess the significant effect of distance from lake ad distance from human on Prosopis stem count...39 Table 4: Table depicting results obtained from binary logistic regressions analysis seeking to determine whether any explanatory variable predicts presence of Prosopis across sampled plots Table 5: Table depicting results from Anova seeking to assess the effect of soil substrate grain size categories, distance from Lake Turkana and distance from areas of human activity on Prosopis stem count..40 Table 6: Table depicting exponentiated binary logistic regression coefficients interpreted as odds ratios to determine the probability of each of my variables affecting presence of Prosopis

9 9 LIST OF FIGURES Page Figure 1: Location of field site in Turkana Basin of Kenya..25 Figure 2: Presence/absence of Prosopis on sandy, gravel and rock soil substrates.41 Figure 3: Stem counts of Prosopis on sandy, gravel and rock soil substrates..41 Figure 4: Presence/absence of Prosopis and distance from Lake Turkana. (Very close=100 m 1 km, Close = 1-5km and Far = greater than 5 km)...42 Figure 5: Prosopis stem count at varying proximity from Lake Turkana 43 Figure 6: Presence/absence of Prosopis and distance from Lake Turkana. (Very close=less than 200 m, Close = 200 m 800 m and Far = greater than 800 m)...44 Figure7:Prosopis stem count at varying proximity from areas of human activity Figure 8: Soil substrate grain size categories vs distance from lake across sampled plots...47 Figure9: Soil substrate grain size categories vs distance from human activity across sampled plots..48 Figure10: Distance from the lake vs distance from human activity across sampled plots...49

10 10 CHAPTER 1: INTRODUCTION Prosopis juliflora is an evergreen plant that is native to tropics of Central and South America (Pasiecznik et al., 2001; Mwangi & Swallow, 2005; Maundu et al., 2009), and perhaps the Caribbean (Ayanu et al., 2015). Broadly known as mesquite, this species is characterized by a short trunk that is often crooked or twisted, reaching a diameter of up to 65cm. The bark is grey-brown, rough and fibrous, varying from finely fissured to furrowed. Generally, Prosopis has crowns that are open and broader than the tree is high. Prosopis juliflora typically reaches a maximum height of 12 m, although trees 20 m in height are recorded in some locales (Pasiecznik et al., 2001). In addition, P. juliflora exhibits roots that develop rapidly following germination and can reach a depth of 40 cm in eight weeks. Prosopis juliflora is characterized by bi-pinnate leaves and pods that grow cm, that producing 10 to 30 seeds per pod (Pasiecznik et al., 2001). P. juliflora exhibits a broad ecological amplitude, making it well-adapted to a wide range of substrate types ranging from sand dunes to cracking clays (Pasiecznik et al., 2001). Its prolific seeds thrive in harsh conditions including arid and highly alkaline soils, making it a successful species in areas that are less habitable by other plants (Shiferaw et al., 2004). The resilience of this plant has led to its introduction by humans into a host of arid and semi-arid environments around the world, with goals including providing animal fodder and/or fuel wood, preventing soil erosion, lowering the water table in flooded settings, and acting as a windbreak, among other proposed beneficial services to society (Pasiecznik et al., 2001; Mwangi & Swallow, 2005; Ayanu et al., 2015). Prosopis is generally found in areas where water and poor soil fertility are the principle agents limiting plant growth, as

11 11 it can survive and even thrive on some of the poorest land, unsuitable for any other tree species (Pasiecznik et al., 2001). These features can also allow it to thrive at the expense of specialized native species in the extreme environments to which it has been introduced (Tegegn, 2008; Maundu et al., 2009). Due to deliberate or accidental introductions by humans, Prosopis juliflora now occurs in 129 countries globally (Shackleton et al., 2014). Previous studies have shown that the earliest introductions of P. juliflora on continental Africa may have been through Senegal, Egypt and South Africa in 1822, 1880 and 1900 respectively (Pasiecznik et al., 2001). Subsequent introduction into other parts of Africa remain undocumented. The timing and mechanisms of introduction of Prosopis into eastern Africa remains unclear, although some studies suggest that it may have been brought in by traders from India or South Africa or through livestock from South Africa that acted as seed dispersers (Pasiecznik et al., 2001; Mwangi and Swallow, 2005). In Kenya, the first documented introduction of P. juliflora was in the early 1970s with seeds sourced from Brazil and Hawaii (Johansson, 1985 cited in Mwangi and Swallow, 2005). As in other places, Prosopis introduction was intended to provide ecosystem services such by preventing soil erosion, restoring degraded ecosystems, and providing animal fodder and substrate for charcoal production. The ability of Prosopis to survive in areas with exceptionally low rainfall, with faster reproductive rates, and possessing seeds with high dormancy and ability to tolerate alkaline conditions were touted as features that made it a plant species selected in engineering ecosystems in these regions (Andersson, 2005; Mwangi and Swallow, 2005). A deeper discussion of the potential benefits of Prosopis is provided in Section 1.2.

12 12 The very same attributes that make Prosopis juliflora an attractive target for introduction into harsh habitats also makes it an invasive species in many of the areas to which it has been introduced (Shiferaw et al., 2004; Tessema, 2012). Invasive species are generally considered those not native to an area but that spread rapidly to the detriment of the environment, human health and/or the economy. According to Pejchar and Mooney, 2009 invasive species are defined as those non-native species that threaten ecosystems, habitats or species. In addition, they are also understood as naturalized taxa that have spread substantially from introduction sites. (Pysek et al., 2004 quoted in Shackleton et al., 2014). Features that enhance the invasive ability of Prosopis include its deep root system, together with its orthodox seeds exhibiting high levels of dormancy, and its ability to thrive in regions with alkaline soils and low precipitation (Andersson, 2005; Mwangi & Swallow, 2005; Shackleton et al, 2014; Ayanu et al., 2015). Perhaps as a result, Prosopis juliflora has invaded, and continues to invade, millions of hectares of rangeland in South Africa, eastern Africa, Australia and coastal Asia. In 2004, it was rated among the world s 100 least-wanted species (Mwangi & Swallow, 2005). In 2014, Wakie and colleagues reported that at that time over four million hectares on continental Africa had experienced invasion by Prosopis species, in a spreading wave that is critically threatening natural plant communities and agricultural lands. Because Prosopis reproduces at a rapid rate under harsh conditions and has a tenacious root system, it now poses a serious threat to the conservation of highly specialized native plant and animal communities throughout much of Africa. Indeed, Prosopis has been documented to

13 13 spread rapidly, reducing natural forest cover and altering natural ecosystem services (Mohamed, 1997; Choge et al., 2002; Maundu et al., 2009; Low, 2012). The long-term tendency for Prosopis invasiveness has serious implications for food security and livelihoods among agro-pastoralist communities (Anderson, 2005; Mwangi & Swallow, 2005; Bokrezion, 2008). Movements of people and livestock are limited by the formation of dense Prosopis thickets that are dominated by a dense network of short tough thorns. This threatens the livelihoods of agro-pastoralists by drastically reducing grazing land and limiting movements in the search for water and pasture for their livestock (Mworia et al., 2011; Shackleton et al., 2014). For instance, in Mali and Ethiopia, livestock herders are now fighting for reduced grazing land due to Prosopis invasion, whereas in South Africa, costs of managing Prosopis invasions are substantial, averaging $35.5 million per annum (Mwangi & Swallow, 2005; Ndhlovu et al., 2011; Shackleton et al., 2014). In the long term, the rapid colonization of Prosopis in introduced environments will have additional implications for food security by posing a threat to tracts of land currently used for food production (Ayanu et al., 2015; Maundu et al., 2009). A deeper discussion of additional costs of Prosopis is addressed in Section Colonization, spread and distribution of Prosopis juliflora The distribution and dispersal patterns of Prosopis juliflora pose a challenge to the control and mitigation of this invasive species. However, when they do succeed in introduced rangelands, their colonization and distribution patterns have been difficult to

14 14 monitor (Anderson, 2005). According to Anderson (2005, p. 6), A common phenomenon with introduced plant species is a so called time lag, where the plants only start to show invasive tendencies after a period of years to many decades. This is a feature exhibited in introduced species in their non-native environments whereby the invasive tendencies of plants are realized after a period of years to a couple of decades. Little information is available on the early introduction and spread of Prosopis juliflora in the non-native ecosystems of Kenya. The current spread and distribution of Prosopis juliflora is in part assisted by livestock and wildlife species (Muturi, et al., 2013). Mworia et al. (2011) investigated the dispersal of Prosopis along the Tana River, focusing on how wildlife and livestock species interact with the environment. They found livestock and wildlife have a role in the dispersal of Prosopis seeds. After analyzing their findings, it was evident that 80% of the invader seeds in the grazing areas (riverine woodlands) were introduced by livestock species (Mwangi & Swallow, 2008; Mworia et al., 2011). Seed production of Prosopis juliflora is estimated to be around 630,000 to 980,000 seeds per mature tree per year (Harding, 1988; Felker, 1979 cited in Mwangi & Swallow, 2005). Previous studies have demonstrated that seed dispersal is likely to be assisted by livestock that consume the sugary pods and the seeds are scoured while passing through the animal s gut (Mwangi & Swallow, 2005). This suggests that livestock-dominated landscapes should have a relatively higher density of Prosopis juliflora, but to date, no studies have examined whether human modified landscapes in northern Kenya facilitated the spread of Prosopis juliflora.

15 15 Access to water is another environmental factor that likely affects the colonization, spread and distribution of P. juliflora. Prosopis has been found to thrive in dry coastal zones experiencing between 100mm mean annual rainfall (m.a.r.) and in the Andean region experiencing between 1500mm m.a.r. (Pasiecznik et al., 2001), although densities decreased in areas receiving over 1000mm m.a.r. (Pasiecznik et al., 2001). Relationships between seasonal water availability and Prosopis density were documented in a study conducted by Mworia et al. (2011) in the upper floodplain of Tana River. The floodplain featured prominently in the establishment and distribution of Prosopis juliflora around the region, such that density of P. juliflora was higher in the woodlands inside the floodplain than the outside (Mworia et al., 2011). According to Mwangi and Swallow (2005), Prosopis invasions in Australia and South Africa followed periods of high rainfall when conditions for germination and establishment were particularly favorable. This supports the notion that not surprisingly, timing and extent of moisture availability influence the success of Prosopis julifora in introduced range lands. The precise water conditions that favor Prosopis juliflora invasions into Kenya s seasonally wet Lake Turkana region ecosystems remains unknown. Elsewhere, Prosopis has been found to germinate during periods of seasonal rainfall, activating dormant seeds to sprout and grow into thickets in moist seasonal environments, accumulating more biomass in irrigated floodplains that have high levels of moisture than the dry lands (Ayanu et al., 2015), but this seemingly contrasts with findings mentioned earlier by Pasiecznik and colleagues in the Andean region, that documented decreased densities for Prosopis in

16 wetter areas. Clearly more study is required to understand the unique capabilities and tolerances of this invasive species in a diversity of ecosystems Unpacking the costs and benefits of Prosopis juliflora for the environment and local communities As mentioned above, Prosopis juliflora has been introduced for its potential benefits to humans in various arid ecosystems around the world (Tewari et al., 2001; Shiferaw et al, 2004; Mwangi and Swallow, 2005; Ayanu et al., 2015), providing income from charcoal production (Berhanu & Tesfaye, 2006), fodder for certain livestock species (Ayanu et al., 2005; Maundu et al., 2009), and preventing soil erosion (Muturi et al., 2013). In Mexico, Argentina and Peru, it has been used as a vital source of fodder for animal feed (Mwangi & Swallow, 2005). Moreover, reduced wind speeds were recorded in a Prosopis juliflora plantation in Sudan (Shackleton et al., 2014), offering respite from topsoil loss in areas of heavy aeolian activity. It has been used heavily by communities in Kenya for fencing and shade provision (Maundu et al., 2009). Notably, Prosopis can modify hydrological systems by exploiting the water table using both deep and superficial root systems (Ayanu et al., 2015), reducing soil salinity (Shiferaw et al., 2004; Muturi et al., 2013), and its flowers have even been exploited to increase honey production (Ayanu et al., 2015). For many of these reasons, it has been promoted by governmental and nongovernmental agencies in arid and semi-arid regions like those found in Kenya

17 17 (Anderson, 2005; Mwangi & Swallow, 2005; Mwangi & Swallow, 2008; Maundu et al., 2009, Shackleton et al., 2014). The potential benefits must be weighed against the numerous costs of introducing an invasive species. As noted above, Prosopis juliflora tends to outcompete native plant species in introduced ecosystems (Mohamed, 1997; Bokrezion, 2008; Choge et al., 2009; Tessema, 2012). This dominance is usually seen by the formation of impenetrable thickets which disrupt movement of people and livestock to water points, reducing growth and development of herbaceous plants and shrubs that are important to humans and wildlife, and generating social conflicts due to reduced grazing lands (Anderson, 2005; Shackleton et al., 2014; Ayanu et al., 2015). For example, the invasion of Prosopis julifora has been found to impact the growth of indigenous plants in Sudan, leading to complaints from farmers, as the invasive species colonized rangelands and the thorny branches caused harm to humans and their farm machinery (Njoroge et al., 2012). In Ethiopia, a range of pastoral lands, agricultural lands and protected ecosystems have been similarly threatened by the invasion of Prosopis juliflora (Mwangi & Swallow, 2005). In Kenya, the effects of Prosopis pods on animal teeth, loss of grazing and agricultural lands, and strong thorns that harm both people and animals are some of the main costs of Prosopis invasion that have caused alarm (Choge & Pasiecznik, 2009; Mworia et al., 2011). The loss of native plant and animal diversity is not often measured, occurring incrementally with increasing encroachment by this invasive species in relatively understudied areas (Maundu et al., 2009). But the currently understood state of Prosopis invasion has led conservationists and policymakers to project that Prosopis juliflora

18 18 can potentially grow in 85-90%... of Kenya s arid and semi-arid land areas although with less agility in more humid and highland areas. (Maundu et al., 2009, pg.49). The threat that Prosopis juliflora poses to society and the environment from the standpoint of food security and social conflict suggests that measures to reduce and/or eradicate the invasion of this plant are urgently required. 1.3 Mitigation strategies employed for Prosopis invasion The invasion of Prosopis has introduced myriad costs and changes to structure, function and future of socio-ecological systems in arid and semi-arid settings across the globe (Bokrezion, 2008; Shackleton, 2014; Ayanu, 2005), prompting a number of countries to devise management strategies aimed at preserving benefits and minimizing costs of this invasive species, with some mitigation strategies including efforts to completely eradicate the plant (Shackleton, 2014; Maundu, 2009). As of 2014, 23 countries with weedy species had implemented formal management of Prosopis and the approach varied according to the wealth of a given country and the invasive status of the plant (Shackleton et al., 2014). Wealthier countries that have milder invasions of Prosopis juliflora may opt to use mechanical or chemical control through physical cutting/burning and use of herbicides on plant parts (Shackleton et al., 2014). Middle income countries often utilize an integrated approach that includes both mechanical and chemical strategies together (Shackleton et al., 2014), whereas poorer countries may primarily try to control Prosopis through intensive harvest and utilization of the plant

19 19 products (Shackleton et al., 2014). Control through utilization can have socio-economic benefits. For instance, as mentioned above, the tree may be used for charcoal production, fencing, animal fodder and so on (Ayanu, 2005; Maundu, 2009; Shackleton et al., 2014). Some countries have ventured into employing biological control mechanisms (Shackleton et al., 2014), such as the introduction of Algarobius prosopis against Prosopis in South Africa (Zimmermann,1991), with or without recognition that new biological agents, just like the introduction of Prosopis in the first place, can have unintended negative consequences, such as reduction of suitable material for livestock grazing (Choge et al., 2002), reductions of other types of biodiversity (Maundu et al., 2009), and other potential consequences for water availability (Mwangi & Swallow, 2005). It is notable that no country has been found to use biological methods exclusively (Shackleton et al., 2014). Biological control has been found to be used together with mechanical or chemical control methods (Shackleton et al., 2014), as is the case in countries like Australia and South Africa. However, there have been cases where biological agents have been found to occur without any deliberate introduction. For instance, in Egypt, native seed eating beetles were found to be controlling the population of various species of Prosopis by feeding on the seeds (Shackleton et al., 2014). Even with the application of multiple control strategies, Prosopis juliflora has remained a threat to a host of arid ecosystems globally (Mohamed, 1997; Shackleton et al., 2014). The primary challenge is to devise control strategies that would be effective at different scales of Prosopis invasion; i.e. small-scale or large-scale invasions require a combination of different utilization and control methods (Shackleton et al., 2014).

20 20 The control through utilization method is a management technique that simultaneously reduces the negative impacts of invasive plants and promotes local economic development (Choge & Chikamai 2004 cited in Shackleton et al., 2014). It entails pruning, harvesting, uprooting and thinning of P. julifora, but has generally been found to be ineffective in Kenya due to the rapid rate of recovery of the plant (Shackleton et al., 2014). However, some studies demonstrate effective management practices for control through utilization. For example, a study by Njoroge et al. (2012) within Marigat Division of the Baringo District in Kenya, found that an integrated approach was effective in mitigating the spread of Prosopis juliflora. The researchers embarked on harvesting, uprooting, stump burning, thinning and pruning as Prosopis juliflora management practices to aid in curbing the spread of this invasive plant. The authors documented that different management methods had different outcomes. Pruning led to pole production, leading to different possible methods of utilizing Prosopis after harvest, whereas thinning reduced the density of standing stock. The aggregate result was a decrease in the spread and distribution of Prosopis juliflora (Njoroge et al., 2012). Importantly, conclusions from the study described above (Njoroge et al., 2012) are somewhat limited, since the authors do not report on challenges associated with each of the mitigation strategies examined in the study. They also fail to project the long-term efficacy of these methods for Prosopis mitigation. Research from previous studies has documented that Prosopis can coppice after cutting and germinate after long dormancy once favorable conditions return (Mwangi & Swallow, 2005; Maundu et al., 2009). Mitigation strategies for curbing Prosopis juliflora invasion must be evaluated in the

21 21 specific context of local environmental conditions, with more information needed on the factors that favor the success of Prosopis juliflora in a broader range of arid ecosystems (El-Keblawy & Al-Rawai, 2007; Muturi et al., 2013). Conflict often exists between local communities and the government in mitigation strategies for Prosopis. Governments tend to advocate for intensified utilization of Prosopis as a means of reducing its spread, whereas local communities prefer attention to be devoted to control/elimination of Prosopis due to its dire effects on their livelihoods (Maundu et al., 2009). Some local communities have argued that the negative attributes of utilization outweigh the positive ones (Maundu et al., 2009). To date in Kenya, governmental agencies and conservation organizations have also strongly advocated finding alternative uses for Prosopis, rather than taking more extreme (and expensive) measures to control/eradicate the invasive plant. For example, the Kenya Forest Research Institute has even explored the idea of making edible flour from Prosopis plants. Unfortunately, after testing different formulations, researchers concluded that although the flour did have nutritional properties, it also contained mycotoxins harmful to humans (Maundu et al., 2009). Measures to control Prosopis can only be realized when environmental conditions that favor its success in arid ecosystems are better understood. Evaluation of the abiotic and biotic factors that favor Prosopis success (such as soil type, proximity to water, and agents of dispersal such as human settlements and livestock populations) in northern Kenya can help to inform mitigation strategies in this and other settings.

22 Objectives This study seeks to document the extent of Prosopis juliflora invasion into nonnative environments in northern Kenya, seeking to identify factors associated with the current presence and success of this invasive species. The study area is a semi-arid region in northern Kenya with low human population density, presently under invasion by Prosopis juliflora. This study seeks to determine whether soil substrate characteristics, distance from permanent water, and/or distance from human settlements correlate with the present size and density of Prosopis juliflora trees in this area. Results from this analysis will inform predictions about areas that are at the greatest risk of Prosopis spread and to inform and prioritize efforts to limit further invasion. 1.5 Hypotheses It is hypothesized that the following factors influence the presence, density, and height of Prosopis juliflora in the study area: 1) Soil substrate, as characterized by the dominant soil type (grain size on the ground surface) and composition (volcanic/sedimentary); 2) Moisture availability, as characterized by proximity to Lake Turkana (although clearly this is not the only source of moisture in the study area, it can serve as a proxy for most obvious permanent water source for the region); and 3) Proximity to human settlements (either due to deliberate introduction or through spread by livestock that accompany human settlements). In this study, higher Prosopis density and height are

23 expected closer to Lake Turkana, closer to human settlements, and on volcanic soil compositions of smaller grain size. 23

24 24 CHAPTER 2: METHODS 2.1 Study location and sampling parameters The study area is located west of Lake Turkana and north of the town of Lodwar in northern Kenya (latitude N to N; longitude E to E). Sampling locations were identified prior to field data collection using Google Earth (version bit) to characterize gross differences in substrate type, and select sampling areas at different distances from Lake Turkana, and from human settlements. Although practical limitations included the region s limited road access, and driving distance from secure camping, a total of m diameter plots and m plots were sampled for this study. The different sizes of the plots were sampled to cater for areas that have very dense thickets and hence pose a mobility challenge while sampling. 10 m plots were sampled in areas characterized by thickets posing mobility challenges whereas 20 m plots were sampled in areas that posed little or no mobility challenges.

25 25 Figure 1. Location of field site in Turkana Basin of Kenya (Red square indicates inset on zoomed map; red circle on the right shows study area in the African continental map). 2.2 Study design To sample across substrate types, sampling areas were first distinguished using satellite imagery based on the color of the surface. Darker soils are typically igneous

26 26 (mineral-rich volcanics) in origin, and lighter soils are more often sandy to silty soils of sedimentary/metamorphic origin. Another important aspect of substrate/soil type is grain size, from sandy/silty soils to surfaces dominated by rocks and boulders, with smaller grain sizes expected to enhance the likelihood for Prosopis germination. Grain size variability was built into sampling design upon ground-truthing sampling areas in the field. Substrates in the sampling plots were defined as follows: Sand/Silt = surface dominated by grains less than 2 mm, Pebbles/Gravel = grain size larger than sand/silt but smaller than 5 cm, Rocks/Boulders = surface dominated by rocks exceeding 5 cm. The density of Prosopis was predicted to be higher in richly mineral volcanic soils dominated by smaller (sand/silt) grain size. Ninety two plots, seventeen plots and forty one plots were sampled in the sand/silt, mostly gravel/pebbles and mostly rocks/boulders soil substrate grain size categories respectively. To assess the impact of human activity on the density of Prosopis, sampling plots were established at varying distances from villages. The communities in these villages occupy parcels of land of various shapes ranging from 400 m 2 to 1600 m 2. Livestock keeping and charcoal burning are the most important economic activities in this region, and both could be expected to incorporate the use of Prosopis. Sampling plot distances from human settlements were measured in World Imagery in Arc Map software (version ), with proximity to human settlement defined as follows: Very close = < 200 m, Close = 200 m 800 m, Far = > 800 m. The density of Prosopis was predicted to be higher closer to human settlements, and to decrease in more distant sampling plots. Thirty plots per category were identified and sampled, for a total of 90 plots sampled.

27 27 To assess the impact of water availability on the density of Prosopis, sampling plots were first conservatively established at varying distances from the region s only truly permanent water source, Lake Turkana. Sampling plot distances from the lake were measured in World Imagery in Arc Map software (version ) with proximity to permanent water defined as follows: Very close = between 100 m and 1 km from the lake, Close = 1-5 km from the lake, Far = > 5 km from the lake. The density of Prosopis was predicted to be higher closer to the lake, and to decrease in more distant sampling plots. Thirty plots per category were identified and sampled, for a total of 90 plots sampled. 2.3 Vegetation sampling Within each sampling plot, the following variables were recorded: number of Prosopis stems, number of stems of other trees, number of stems of herbaceous vegetation and any occurrence of other plants (like grasses, where stems were not counted but were rather included as a total percentage of ground cover). Prosopis was identified using morphological features such as thorns, pods, tree form and flowers (Pasiecznik et al., 2004). The dominant plant species were noted for each sampling plot, and species of woody vegetation including Prosopis were recorded according to the following height classes: 0-1 m, 1-5 m, 5-10 m, m and more than 15 m. Lengths of individual pieces of woody debris were also measured and categorized into five classes; less than 2 cm, 2-5 cm, 6-10 cm, cm and greater than 20 cm. Finally, the overall percentage of ground cover was

28 28 recorded, to assess the present area available for Prosopis colonization. This will assist in documenting the spread of this species in the future. All field data were recorded on field data forms (provided in Appendix A) and supplemented by electronic recording equipment such as Infinix hot X507 digital camera and a Trimble Juno 3B Data collector (with Terrasync software) global positioning system. 2.4 Data analysis GPS coordinates recorded in the field were converted into shapefiles using Trimble Path Finder software (version 5.1). Converted shapefiles were clustered into a single dataset in ArcGIS (version ). Prosopis stem counts were standardized by dividing the number of Prosopis by the area of the sample plot (either 10 m 2 or 20 m 2 ). Prosopis densities for each sample plot were then visualized in ArcGIS (version ) to explore their relationships with distance from human settlements, and distance from Lake Turkana. Using World Imagery in Arc Map software (version ), polygons were drawn around areas of human influence, defined here as places with homesteads and/or livestock sheds. Clearly humans have influence in places without homesteads or livestock sheds, but these serve as a convenient proxy for sustained human impact. Distance from sample plots to the nearest area of human influence were measured using ArcGIS software, recorded in meters. Plots within area of human influence were recorded as zero since they fell within the delineated polygons. Distance between each plot and the edge of Lake Turkana were

29 29 also measured in ArcGIS, and recorded in meters to establish measures to examine Prosopis density in relation to distance from permanent water. To visualize data, pie charts were constructed in Excel (version 2010), to explore presence/absence of Prosopis on soil substrates of different grain size, at varying proximity from Lake Turkana and at varying proximity from areas of human activity. Next, box plots were constructed in R (version ), to assess variation in Prosopis stem count among plots that recorded the presence of Prosopis across different soil substrate grain size categories, at varying proximity from Lake Turkana and at varying proximity from areas of human activity. For all 20 m plots, poisson regressions were conducted in R s glm () function (version ) to determine whether distance from Lake Turkana and/or distance from areas of human activity significantly influence Prosopis stem count. Next, a binomial logistic regression was conducted in R s glm () function (version ), with presence of Prosopis as a binary outcome variable indicating presence/absence (1/0), to determine whether any explanatory variable predicts presence of Prosopis across sampled plots. Coefficients results from binomial logistic regression were exponentiated and interpreted as odds ratios to determine the probability of each of my variables affecting presence of Prosopis. Finally, ANOVA was conducted in R (version ) to assess the effect of soil substrate grain size categories, distance from Lake Turkana and distance from areas of human activity on Prosopis stem count

30 30 CHAPTER 3: RESULTS The table below depicts for each plot, Prosopis presence/absence (indicated as 1/0), distance from Lake Turkana, distance from areas of human activity, and soil substrate grain size categories (1= Mostly sandy, 2=Mostly gravel/pebbles, 3=Mostly rocks/boulders) 3.1 Table Table 1. Data collected in this study Prosopis stem count Dislake Dishuman Soilsub

31 Table 1: continued

32 Table 1:continued

33 33 Table 1: continued

34 34 Table 1: continued The table below depicts Prosopis stem count, distance in meters from Lake Turkana (dislake), and distance in meters from areas of human activity (dishuman) for all 20 m plots. 3.2 Table Table 2. Data collected in this study prosopisstemcount dislake dishuman

35 35 Table 2: continued

36 36 Table 2: continued

37 37 Table 2: continued

38 38 Table 2: continued The table below depicts results obtained from poisson regression analysis seeking to assess the significant effect of distance from lake and distance from human on Prosopis stem count.

39 Table Table 3. Poisson Regressions results Estimate Standard error Z value P value (Intercept) 4.795e e <2e-16 *** Dislake e e <2e-16 *** Dishuman e e <2e-16 *** The table below depicts results obtained from binary logistic regressions analysis seeking to determine whether any explanatory variable predicts presence of Prosopis across sampled plots 3.4 Table Table 4.Binary logistic regression results Estimate Standard error Z value P value Intercept e-10 *** Dislake e-08 *** Dishuman ** Soilsub Soilsub The table below depicts ANOVA results obtained from binary logistic regressions analysis seeking to assess the effect of soil substrate grain size categories, distance from Lake Turkana and distance from areas of human activity on Prosopis stem count

40 Table Table 5. ANOVA results Df Deviance Residue Df Residue Dev Null Dislake Dishuman Soilsub The table below depicts coefficients results from binomial logistic regression were exponentiated and interpreted as odds ratios to determine the probability of each of my variables affecting presence of Prosopis 3.6 Table Table 6. Exponentiated binary logistic regression coefficients Intercept Dislake Dishuman Soilsub2 Soilsub Prosopis on different soil substrates The pie charts below depict Prosopis presence/absence in plots situated on different soil substrate types. 66% of plots dominated by sand/silt substrates contained Prosopis, 41% of plots dominated by gravel/pebble substrates contained Prosopis and 21% of plots dominated by rocks/boulders contained Prosopis. (Fig.2)

41 41 Figure 2: Presence/absence of Prosopis on sandy, gravel and rock soil substrates The boxplot below depict variation in Prosopis stem count in all 20 m plots that contain Prosopis in the three substrate grain size categories. Highest Prosopis stem counts were observed on sand/silt substrates, with lower stem counts on gravel/pebble substrates and rocks/boulders substrate. (Fig.3) Figure 3: Stem counts of Prosopis on sandy, gravel and rock soil substrates

42 Prosopis and distance from Lake Turkana The pie charts below depict presence/absence of Prosopis in plots at different distances from Lake Turkana. 90% of plots between 100 m 1 km from Lake Turkana contained Prosopis, 91% of plots between 1-5 km from Lake Turkana contained Prosopis and only 5% of plots greater than 5 km from Lake Turkana contained Prosopis. (Fig.4) Figure 4: Presence/absence of Prosopis and distance from Lake Turkana. (Very close=100 m 1 km, Close = 1-5km and Far = greater than 5 km) The scatterplot below depicts Prosopis stem counts in all 20 m plots containing Prosopis as a function of distance from Lake Turkana. The highest Prosopis stem counts were observed in plots located around 2km from Lake Turkana. Lower Prosopis stem counts were observed in plots beyond 4km from Lake Turkana (Fig 5). Poisson regression analysis indicates that distance from Lake Turkana is a significant influence upon Prosopis stem counts (p < 0.05)

43 43 Prosopis stem count Distance from Lake Turkana(in meters) Figure 5: Prosopis stem count at varying proximity from Lake Turkana 3.9 Prosopis and distance from areas of human activity The pie charts below depict presence/absence of Prosopis in plots at varying distances from areas of human activity. 93% of plots within or less than 200 m from areas of human activity contained Prosopis, 63% of plots between 200 m and 800 m from areas of human contained Prosopis and only 16% of plots greater than 800 m from areas of human activity contained Prosopis. (Fig.6)

44 44 Figure 6: Presence/absence of Prosopis and distance from areas of human activity. (Very close=less than 200 m, Close = 200 m 800 m and Far = greater than 800 m) The scatterplot below depicts variation in Prosopis stem count in all 20 m plots containing Prosopis as a function of proximity to areas of human activity. Highest Prosopis stem counts were observed in plots located directly within areas of human activity (0-500 m). A drastic reduction in Prosopis stem counts is observed in plots beyond 1.5km from areas of human activity (Fig 9). Poisson regression analysis indicates that distance from human activity is a significant influence upon Prosopis stem counts (p < 0.05).

45 Prosopis stem count Distance from areas of human activity(in meters) Figure 7: Prosopis stem count at varying proximity from areas of human activity 3.10 Do soil substrate grain size, distance from Lake Turkana and/or distance from areas of human activity predict the presence/absence of Prosopis? Results from binary logistic regression found that distance from Lake Turkana, distance from areas of human activity and sand-dominated soil substrates predict presence or absence of Prosopis (Table.4). Logistic regression coefficients suggest that holding all else constant, as distance from Lake Turkana increases by a factor of 1, Prosopis stem counts in 20 m plots decrease by In addition, these findings demonstrate that holding all else constant, as distance from areas of human activity increases by a factor of 1, Prosopis stem counts in 20 m plots decrease by

46 46 This indicates that there is a higher reduction of Prosopis stem count with increasing distance from Lake Turkana compared to an increasing distance from areas of human activity. Findings from exponentiated regression coefficients were interpreted as odd ratios, providing a value slightly less than one for both distance from Lake Turkana (0.9992) and distance from areas of human activity (0.9994). This indicates that for a one unit increase in distance from the lake, the odds of having a Prosopis stem count is In addition, for a one unit increase in distance from areas of human activity, the odds of having a Prosopis stem count is Interpretations from exponentiated regression coefficients reveal that the probability of encountering Prosopis decreases with distance from Lake Turkana and from areas of human activity (Table.6). Moreover, there is a relatively lower probability of encountering Prosopis further from the Lake Turkana than at distant proximity from areas of human activity, suggesting that location in relation to permanent water is the strongest influence upon Prosopis Relationships among variables measured in this study The boxplot below depicts the relationship between soil substrate grain size (where 1 = mostly sandy, 2 = mostly gravely, 3 = mostly rocky) and distance from the lake (in meters) across sampled plots. Plots dominated by sand occur between 2 km and 8 km from

47 the lake, plots dominated by gravel occur between 2.5 km and l0 km close to the lake and plots dominated by rock occur between 8 km and 10 km far from the lake. 47 Figure 8: Soil substrate grain size categories vs distance from lake across sampled plots The boxplot below depicts the relationship between soil substrate grain size (where 1 = mostly sandy, 2 = mostly gravely, 3 = mostly rocky) and distance from areas of human activity (in meters) across sampled plots. Plots dominated by sand and gravel occur within areas of human activity (between 0 km 2 km). Plots dominated by rock occur between 1 km and 2.5 km far from areas of human activity.

48 48 Figure 9: Soil substrate grain size categories vs distance from human activity across sampled plots The scatterplot depicts the relationship between distance from the lake and distance from areas of human activity across my sampled plots. Almost all plots sampled in this study were less than 6 km from areas of human activity. All sampled plots were less than 14 km from from Lake Turkana.

49 Distance from human activity(in meters) Distance from the lake(in meters) Figure 10: Distance from the lake vs distance from areas of human activity across sampled plots

50 50 CHAPTER 4: DISCUSSION Distance from Lake Turkana, distance from areas of human activity and different soil substrate grain size each seemed to have a significant effect on Prosopis presence and stem count. This finding is supported by the relatively higher number of plots (61%) containing Prosopis in sand dominated substrates (Fig.2), higher number of plots (90%) containing Prosopis within one kilometer of Lake Turkana (Fig.4) and higher number of plots (93%) containing Prosopis within two hundred meters of areas of human activity (Fig.7). Soil substrate was expected to influence the establishment of Prosopis in the study area, functioning in providing nutrients, substrate, and water retention required for germination and establishment of mature seedlings. The assessment of different soil substrate grain sizes, did show significant differences with respect to Prosopis stem count. Mostly sand/silt soil substrate category seemed to have the highest Prosopis stem count followed by the mostly rocks/boulders and mostly gravels/pebbles soil substrate categories. This finding seems to differ, at least in the Turkana region, from previous studies stating that Prosopis inhabits a broad ecological amplitude adapted to a very wide range of soils ranging from sand dunes to cracking clays (Pasiecznik et al., 2001). In particular, distance from permanent water was expected to influence the establishment of Prosopis in my area of study. Water is a key requirement for germination, breaking seed dormancy and also acting as an agent of dispersal. As highlighted in previous studies (Ayanu, 2005; Pasiecznik., 2001 & Shiferaw., 2004), Prosopis produces many small seeds that assume dormancy until favorable conditions. The lake likely provides

51 51 favorable conditions for Prosopis seedlings to germinate hence the high Prosopis stem count in plots of proximity to Lake Turkana. A previous study conducted by Anderson, 2005 examining the pattern of Prosopis spread in Baringo found increased spread of Prosopis from his sampled plots to one of the dams in his study area. He also found that Prosopis was thriving in water-fed areas and had started to invade estuaries in his study area (Anderson, 2005, pg.22). Further analysis of my data using logistic regression model showed that distance from Lake Turkana seemed to have a strong influence on Prosopis stem counts. In addition, ANOVA results show that distance from the lake is the strongest predictor of Prosopis presence in my study area (Table 3.5). The high occurrence of Prosopis closer to Lake Turkana might be explained by the inundation of seasonal pools observed in my study area within four kilometers from the lake. Further work is needed to reveal the extent of subsurface water, and the role that plays in Prosopis invasiveness. Higher Prosopis stem counts were also expected near areas of human activity. Since the communities in my study area are agro-pastoralists, the presence of livestock near human settlements can serve as agents of dispersal, and perhaps largely influence the spread of Prosopis throughout the region. High Prosopis stem counts were indeed found in areas of proximity to human activity. People may preferentially plant Prosopis for use in fencing and firewood. In addition, as noted in previous studies (Geesing et al., 2004, Anderson, 2005), the spread of Prosopis is propagated by goats that eat palatable mature pods which disperse the seeds over long distances. The passage of the seed pods facilitates germination of Prosopis seedlings, and feces serve as fertilizer during the initial stages of Prosopis establishment (Shiferaw, 2004). Data collected in this study do not provide a

52 52 direct assessment of the extent to which livestock grazing was associated with areas of human influence, but anecdotal observations suggest a strong relationship that could be examined in future studies. 4.1 Limitations Due to practical limitations including road access and logistical/financial constraints of the study, the study sample contains different numbers of individual observations (plots) in each treatment group. And although this study focused on collecting plot data on Prosopis, it could be augmented with future studies incorporating questionnaires or interviews to explore how local communities, non-governmental organizations and the Kenyan government respond and contribute to the spread of Prosopis. Questionnaires would be useful in gathering information to assess the feelings, beliefs, experiences and attitudes of different stakeholders towards the introduction, distribution and spread of Prosopis. Interviews could be useful in gathering reliable and valuable information about the historical context, key drivers of Prosopis establishment and any possible attempts by different stakeholders to eradicate or curb the spread of Prosopis. Going forward, both kinds of information will contribute to a better understanding of how different stakeholders understand the historical context of Prosopis

53 invasion in northern Kenya, negative or positive attributes of Prosopis today, and the success of ongoing mitigation strategies Conclusions Prosopis juliflora is an aggressive weed that has both positive and negative attributes in arid ecosystems. As a plant that can survive in harsh environments, the plant has been deliberately introduced in arid ecosystems in a bid to engineer the environment. However, the attributes that make it a preferred species for arid ecosystems also make it invasive. Production of many small seeds with high levels of dormancy, ability to survive in alkaline conditions and coppicing after cutting the plant are some of the key features that make Prosopis a plant that thrives at the expense of native plant communities. This study predicted that Prosopis stem count would be higher in areas with sandy soils, with high water availability and closer proximity to human settlements. Perhaps because of germination requirements, Prosopis stem count appears to be highest on sandy/silty substrates. Areas dominated by sand could be preferable for human settlement as they provide suitable areas for digging water wells and providing pasture for grazing livestock. Perhaps not surprisingly, distance from the permanent water source seems to be a dominant environmental variable affecting the density of Prosopis in this study area. The interaction effect of humans and livestock likely contribute to high Prosopis stem count in areas of proximity to human settlements. Future work should explore the interactive effect of livestock and the agropastoralist communities on the density of Prosopis. Questionnaires and interviews of agro-

54 54 pastoralist communities can provide valuable information. Since these communities use temporary settlements, their movements could reveal informative patterns on future distribution and spread of Prosopis. In addition, more information is needed to explain the high Prosopis seedlings stem count closer to the lake compared to the relatively lower stem count of taller Prosopis plants dominating areas relatively distant from the lake. Interviews and questionnaires with government, regional, national and international organizations are needed to effectively shape Prosopis mitigation strategies. Based on the results of this study, mitigation efforts formulated to control or completely eradicate Prosopis in the Turkana region should prioritize sandy areas closer to permanent water and human influence.

55 55 REFERENCES Andersson, S. (2005). Spread of the Introduced Tree Species Prosopis juliflora (Sw.) DC in The Lake Baringo Area, Kenya (Doctoral Dissertation, Slu). Ayanu, Y., Jentsch, A., Müller-Mahn, D., Rettberg, S., Romankiewicz, C., & Koellner, T. (2015). Ecosystem Engineer Unleashed: Prosopis juliflora Threatening Ecosystem Services? Regional Environmental Change, 15(1), Berhanu, A., & Tesfaye, G. (2006). The Prosopis dilemma, impacts on dryland biodiversity and some controlling methods. Journal of the Drylands, 1(2), Bokrezion, Harnet. "The ecological and socio-economic role of Prosopis juliflora in Eritrea." Academic Dissertation, Johannes Gutenberg-Universität Mainz, Germany, (PhD report) (2008). Choge, S., & Pasiecznik, N. (2009). The challenges of eradicating Prosopis in Kenya. Choge, S. K., Ngunjiri, F. D., Kuria, M. N., Busaka, E. A., & Muthondeki, J. K. (2002). The status and impact of Prosopis spp in Kenya. Choge, S. K., N. M. Pasiecznik, M. Harvey, J. Wright, S. Z. Awan, & P. J. C. Harris. "Prosopis pods as human food, with special reference to Kenya." Water Sa 33, no. 3 (2007). El-Fadl, M. A. (1997). Management of Prosopis juliflora for use in agroforestry systems in the Sudan (No. 16). Department of Forest Ecology, University of Helsinki. El-Keblawy, A., & Al-Rawai, A., Impacts of the invasive exotic Prosopis juliflora (Sw.) DC on the native flora and soils of the UAE. Plant Ecology, 190(1), pp

56 56 Esther Mwangi & Brent Swallow, June 2005, Invasion of Prosopis juliflora and local livelihoods: Case study from the Lake Baringo area of Kenya. ICRAF Working Paper no. 3. Nairobi: World Agroforestry Centre. Kahi, H. C., Ngugi, R. K., Mureithi, S. M., & Ng'ethe, J. C. (2009). The canopy effects of Prosopis juliflora (dc.) and acacia tortilis (hayne) trees on herbaceous plants species and soil physico-chemical properties in Njemps flats, Kenya. Tropical and Subtropical Agroecosystems, 10(3), Geesing, D., Al-Khawlani, M., & Abba, M. L. (2004). Management of introduced Prosopis species: can economic exploitation control an invasive species. Unasylva, 217(55), Low, T. (2012). In denial about dangerous aid. Biological Invasions, 14(11), Maundu, P., Kibet, S., Morimoto, Y., Imbumi, M., & Adeka, R. (2009). Impact of Prosopis juliflora on Kenya's semi-arid and arid ecosystems and local livelihoods. Biodiversity, 10(2-3), Muturi, G. M., Poorter, L., Mohren, G. M. J., & Kigomo, B. N. (2013). Ecological Impact of Prosopis Species Invasion in Turkwel Riverine Forest, Kenya. Journal of Arid Environments, 92, Mwangi, E., & Swallow, B. (2008). Prosopis juliflora invasion and rural livelihoods in the Lake Baringo area of Kenya. Conservation and Society, 6(2), 130. Mworia, J. K., Kinyamario, J. I., Omari, J. K., & Wambua, J. K. (2011). Patterns of Seed Dispersal and Establishment of the Invader Prosopis juliflora in the Upper

57 57 Floodplain of Tana River, Kenya. African Journal of Range & Forage Science, 28(1), Ndhlovu, T., Milton-Dean, S. J., & Esler, K. J. (2011). Impact of Prosopis (mesquite) invasion and clearing on the grazing capacity of semiarid Nama Karoo rangeland, South Africa. African Journal of Range & Forage Science, 28(3), Njoroge, E., Sirmah, P., Mburu, F., Koech, E., Mware, M., & Chepkwony, J. (2012). Preference and Adoption of Farmer Field School (FFS) Prosopis juliflora Management Practices: Experiences in Baringo District, Kenya. Forestry Studies in China, 14(4), Pasiecznik, N.M., Felker, P., Harris, P.J.C., Harsh, L.N., Cruz, G., Tewari, J.C., Cadoret, K., & Maldonado, L.J. (2001) The Prosopis juliflora - Prosopis pallida Complex: A Monograph. HDRA, Coventry, UK. Pp.172. Pasiecznik, NM, PJC Harris., & SJ Smith Identifying Tropical Prosopis Species: A Field Guide. HDRA, Coventry, UK. ISBN Pejchar, L., & Mooney, H. A. (2009). Invasive species, ecosystem services and human well-being. Trends in ecology & evolution, 24(9), Pimentel, D., Lach, L., Zuniga, R., & Morrison, D. (2000). Environmental and economic costs of nonindigenous species in the United States. BioScience, 50(1), Shackleton, R. T., Le Maitre, D. C., Pasiecznik, N. M., & Richardson, D. M. (2014). Prosopis: A Global Assessment of the Biogeography, Benefits, Impacts and Management of One of the World's Worst Woody Invasive Plant Taxa. Aob Plants, 6, Plu027.

58 58 Shackleton, C. M., McGarry, D., Fourie, S., Gambiza, J., Shackleton, S. E., & Fabricius, C. (2007). Assessing the effects of invasive alien species on rural livelihoods: case examples and a framework from South Africa. Human Ecology, 35(1), Shiferaw, H., Teketay, D., Nemomissa, S., & Assefa, F. (2004). Some biological characteristics that foster the invasion of Prosopis juliflora (Sw.) DC. at Middle Awash Rift Valley Area, north-eastern Ethiopia. Journal of Arid environments, 58(2), Stave, J., Oba, G., Bjorå, C. S., Mengistu, Z., Nordal, I., & Stenseth, N. C. (2003). Spatial and temporal woodland patterns along the lower Turkwel River, Kenya. African Journal of Ecology, 41(3), Tegegn, G. G. (2008). Experiences on Prosopis management case of Afar region. FARM- Africa, London. Tessema, Y. A. (2012). Ecological and economic dimensions of the paradoxical invasive species-prosopis juliflora and policy challenges in Ethiopia. Journal of Economics and Sustainable Development (www. iiste. org), 3(8). Tewari, J. C., Harris, P. J. C., Harsh, L. N., Cadoret, K., & Paseicznik, N. M. (2001). Managing Prosopis julifora (Vilayati babul)-a technical manual. Zimmermann, H. G. (1991). Biological control of mesquite, Prosopis spp.(fabaceae), in South Africa. Agriculture, ecosystems & environment, 37(1-3),

59 58 APPENDIX A: DATA COLLECTION SHEET SAMPLE FORM: MEASURING PROSOPIS JULIFLORA INVASION NEAR LAKE TURKANA, KENYA (May-June 2016) Date: Aspect (AZM): Weather: Plot Number: Plot Temperature: Time: Slope (%): Diameter: Most dominant Pebbles/Grave soil substrate Sand/Silt l Igneousdominated Sedimentary/Metamorp hic Land Position/Shape Upland Lowland Foot slope Channel Lake Edge Hydrology Active Channel Seasonal Pool Dry 10M 20M Rock/Boulde rs Disturbed Undisturbed Woody Debris <2 CM 2-5 CM 6-10 CM CM >20 CM Percent Ground Cover: <1% 1-10% 10-20% 20-40% >40% Vegetation Type: Low mat-forming Herbaceous Shrubs <1 M Shrubs <1 M Shrubs 1-2 M Trees Shrubs 2-3 M Shrubs>3 M Trees 3-5 M Trees 5-10 M M Trees>15 M Vegetation Cover <1% 1-10% 10-20% 20-40% >40% Number Species/Plot Herbs: Grasses: Shrubs: Trees:

60 59 Dominant Life Form Herbs Grasses Low Shrubs Tall Shrubs Trees Tally of Woody Vegetation Species Code 0-1m 1-5m 5-10m 10-15m >15m Other Notes/Photographs Taken:

61 60 APPENDIX B: RAW COUNT DATA FOR PROSOPIS, HERBACEOUS PLANTS, GRASSES AND SHRUBS Plot diameter Overall Prosopis stem Herbs Approximate Shrubs count count Grass count count

62

63

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