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DAMAGE STRATIFICATION ON Acacia drepanolobium at Ol Pejeta Conservancy Black Rhino habitat co-existence and survival: Interaction and effects of Mega-herbivores, fire and drought on Acacia drepanolobium in Ol Pejeta Conservancy, Kenya

By Joseph K. Makau Reg. No.: WM/16/06 Supervisor: Prof. G. M. Wahungu Moi University, Chepkoilel Campus School of Natural Resource Management Department of wildlife management P.O. Box 1125, ELDORET 30100, KENYA. Personal Contacts P.O. BOX 117, MACHAKOS. Email: jmvision2030@yahoo.com Phone No: +254-726-051-176. @2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy DISSERTATION A senior research project submitted to Moi University, the Department of Wildlife Management in partial fulfillment of the requirements for the award of a Bachelor of Science Degree in Wildlife Management.

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Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy DECLARATION I JOSEPH KYALO MAKAU solemnly declare that this research project is my original work, with assistance of my supervisor and without any form of plagiarism and that it has never been submitted to any university, or any other institution for the award of any certificate, diploma or degree.

Signature: …

Date: …29th May, 2010…

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Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy ACKNOWLEDGMENT I wish to express my heartfelt gratitude to the Ol Pejeta conservancy Earthwatch principal investigator, main financier of this project and my supervisor Prof. G. M. Wahungu for his continued support throughout the project period. I acknowledge the efforts of my lecturers: Dr. Karanja and Mr. Kimuyu for empowering me with the knowledge and skills on research methods. I thank the Ol Pejeta conservancy management for providing me with permission to do this research and the chance to be attached in the conservancy, especially the Ecological Monitoring Department staff; Mr. M. Mulama, Mr. Nathan, Mr. Mutisya, Miss. Ngw'eno and Mr. Kamaru. It is during the attachment period when I developed this research topic and the EMD staff assisted me in getting the background information as well as the literature review. I would also like to acknowledge, Lucy Mureu, Odera George, James Wambugu (the ranger), Mwangi Benson (the driver) and Mwaniki (research assistant) who enthusiastically supported and worked with me throughout the study period. Finally, this list will not be complete without acknowledging the Almighty God for His power and strength that has sustained me up to this far without which it would not have been possible.

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Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy DEDICATION I dedicate this proposal to my beloved family members: Mum; Philomena, Sisters; Frida, Noreen and Miriam, and my Brother; Stephen.

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Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy ABSTRACT

This study was carried out in Ol Pejeta Conservancy (OPC) which lies on the Laikipia plateau between Mt Kenya and the Aberdare mountains at an altitude of 1800 m. Damage stratification was examined in Acacia drepanolobium. The study was done in a period of eight months: June 2009 to February 2010. In total, 5722 Acacia drepanolobium trees were counted and measured in fourteen sampling plots and in two seasons (dry and wet). At the study site, Acacia drepanolobium form approximately 75% of the endangered black rhino diet. Frontiers The Acacia drepanolobium was subjected to three main treatments: burnt, unburnt and control plot (damage free zone). The 14 sampling plots were distributed on these treatments based on the relative size for a good replicate and representation of each treatment. Five radiating transects were laid originating from a marked center tree each measuring 100 x 2 m. All the Acacia drepanolobium trees were inspected for their damage status and various parameters measured and recorded. Rhinos, elephants, giraffes, small browsers, fire and natural death were recorded as the main damagers of Acacia drepanolobium. Both parametric and Non-parametric tests were used to test the hypotheses at a 0.05 significance level. Damage on the acacia trees was significant (p<0.00), with a damage level of 61% over the undamaged level of 39%. Natural damage was more in bunt areas (71%) than in unburnt areas (29%) hence Acacia drepanolobium trees are more susceptible to drought when burnt than when unburnt. Ol Pejeta conservancy Acacia drepanolobium population is composed of 73% seedlings, 17% saplings and 10% mature trees. Various levels of damage alters the Acacia drepanolobium population structure significantly (p<0.00). High damage level: burnt and other damage types combined maintained the Acacia drepanolobium trees short (48.58Âą73.51 cm), Medium damage level: Unburnt but with other damage types maintained the Acacia drepanolobium trees at a medium height (73.11Âą99.959 cm) while absence of damage made the Acacia drepanolobium trees grow tall (121.43Âą136.161 cm). Browsing by the other mega herbivores facilitates for the availability of rhino browse material. The conditions at the time of the study indicated significantly more Acacia drepanolobium trees in the conservancy had suffered some damage, and this damage was higher in the burnt areas and over the dry season. Key words: Acacia drepanolobium, mega herbivores, burnt and season. vi Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy TABLE OF CONTENTS DISSERTATION ....................................................................................................................... ii DECLARATION ......................................................................................................................iii ACKNOWLEDGMENT........................................................................................................... iv DEDICATION ........................................................................................................................... v ABSTRACT .............................................................................................................................. vi TABLE OF CONTENTS ......................................................................................................... vii LIST OF TABLES AND FIGURES.......................................................................................viii CHAPTER ONE ........................................................................................................................ 9 1.0 INTRODUCTION ............................................................................................................... 9 1.1 Background information ................................................................................................. 9 1.2 Problem statement ......................................................................................................... 10 1.3 Conceptual Framework ................................................................................................. 11 1.4 Justification of the Study ............................................................................................... 12 1.5 Research Objectives and Hypotheses ............................................................................ 13 CHAPTER TWO ..................................................................................................................... 15 2.0 LITERATURE REVIEW .................................................................................................. 15 2.1 Giraffe impacts on Acacia drepanolobium ................................................................... 15 2.2 Elephant impacts on acacia ........................................................................................... 16 CHAPTER THREE ................................................................................................................. 18 3.0 RESEARCH DESIGN ....................................................................................................... 18 3.1 Study area ...................................................................................................................... 18 3.1.1 Location...................................................................................................................... 18 3.1.2 Climate and hydrology ............................................................................................... 18 3.1.3 Wildlife ...................................................................................................................... 18 3.1.4 Vegetation and soil type ............................................................................................. 19 3.2 Research tools and equipment ....................................................................................... 19 3.3 Methodology ................................................................................................................. 21 CHAPTER FOUR .................................................................................................................... 23 4.0 DATA COLLECTION AND RESULTS .......................................................................... 23 4.1 Data collection .............................................................................................................. 23 4.2 Results ........................................................................................................................... 23 CHAPTER FIVE ..................................................................................................................... 36 5.0 DISCUSSION .................................................................................................................... 36 CHAPTER SIX ........................................................................................................................ 41 6.0 CONCLUSIONS AND RECOMMENDATIONS ............................................................ 41 6.1 Conclusions ................................................................................................................... 41 6.2 RECOMMENDATIONS .............................................................................................. 43 APPENDICES ......................................................................................................................... 44 Program of activities ........................................................................................................... 44 Data sheet ............................................................................................................................ 45 Key ...................................................................................................................................... 47 REFERENCE ........................................................................................................................... 49

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Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy

LIST OF TABLES AND FIGURES Figure 1; Map of the Ol Pejeta Conservancy Showing the Vegetation Types ........................ 19 Figure 2: Radiating transects ................................................................................................... 21 Figure 3: Acacia drepanolobium damage status in the fourteen sampled plots. ..................... 24 Table 1: Interaction between the habitat status and the damager ............................................ 24 Figure 4: Interaction of burning and the level of damage for each damager ........................... 25 Figure 5: Acacia drepanolobium population structure ............................................................ 26 Table 2 A general linear model; Univariate analysis of variance table of results ................... 26 Figure 6: Effects of fire on the Acacia drepanolobium population structure .......................... 27 Table 3: ANOVA table of results ............................................................................................ 28 Figure 7: Effects of fire on the Acacia drepanolobium density. .............................................. 28 Table 4: Damage stratification ANOVA test results ............................................................... 28 Figure 8: Damage stratification across the Acacia drepanolobium height structure ............... 29 Table 5: ANOVA test on the damagersâ&#x20AC;&#x2122; damaging diameter .................................................. 29 Figure 9: Acacia drepanolobium tree diameters for the various damagers. ............................ 30 Figure 10: Herbivore preference for sprouting Acacia drepanolobium trees. ......................... 31 Figure 11: The relationship between the symbiotic ants and the damager .............................. 31 Table 6: Effects of season on damage status ANOVA test resultâ&#x20AC;&#x2122;s. ........................................ 32 Figure12: Effects of season on the damage status ................................................................... 32 Table 7: The interaction between the season and the damager ................................................ 32 Figure 13; The interaction between season and damager ........................................................ 33 Table 8: Effects of damage on Acacia drepanolobium tree height structure ........................... 33 Figure 14: Effects of fire on Acacia drepanolobium tree height structure .............................. 34 Table 9: Effects of fire on Acacia drepanolobium diameter,................................................... 34 Figure 15: Effects of fire on the diameter of Acacia drepanolobium trees. ............................ 35

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Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy

CHAPTER ONE 1.0 INTRODUCTION 1.1 Background information The Ol Pejeta conservancy was established in September 2004 after the merge of the SweetWaters Game Reserve and the Ol Pejeta ranch. The SweetWaters Game Reserve (SWGR) was established in 1989 mainly as a Black rhino sanctuary under a collaborative effort between Kenya Wildlife Service and Lornho East Africa. The establishment of the Game Reserve was necessitated by the rapid decline in black rhino population in Kenya in line with the governmentâ&#x20AC;&#x2122;s policy to intensively manage the remaining populations. Prior to 2004, much of the land was under cattle ranching. The ranch supported a variety of wildlife population ranging freely within and outside its boundary. In 2007 merging of the SWGR and the Ol Pejeta ranch was completed, together with the construction of an electric perimeter fence. This merging was after a recommendation from various stakeholders and high wildlife population pressure (mainly the elephants, giraffes, rhinos and other plain game like the buffaloes) within the former SWGR. Before the 2007 it was noted that the

Acacia drepanolobium habitat in the game reserve had

been severely damaged by herbivores while that in the cattle ranch side was free from browsing pressure and healthy. The expansion availed more food resources for herbivores and thereby reducing browsing pressure in the former SweetWaters Game Reserve and introduced herbivore damage to the Acacia drepanolobium habitat in the Ol Pejeta cattle ranch. The reserve was expanded almost three fold, thus bringing the current 75,000 acres (303.51Km2) into an integrated wildlife conservation area with livestock production. Although the conservancy is fenced all round, three wildlife movement corridors have been constructed to allow selective dispersal of all mammals except the rhinos. Acacia drepanolobium, which is a keystone species in the area, covers over 20% of the total area of the conservancy and it constitutes 40% of the trees population. The Acacia drepanolobium constitute approximately 75% of the black rhino diet. Giraffes in Ol Pejeta have been found to spend 90% of their feeding time browsing Acacia drepanolobium. The presence of the wildlife movement corridors makes the populations of elephants and giraffes populations to vary. However, it is estimated that the resident population is approximately 300 elephants, 300 giraffes 9 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy and the current black rhino population is 82 in total (Mutisya 2009). Currently with the assistance of the Earthwatch Institute, the Ol Pejeta conservancy ecological monitoring department monitors the Acacia drepanolobium growth rate, damage and mortality occasioned by elephants, rhinos and giraffes. Earlier studies by Birkett (2002) indicated that Acacia drepanolobium trees in the Ol Pejeta conservancy are generally maintained at less than 3m tall through browsing of the crown by giraffe or by having the stem broken off by elephants; however they can grow up to 20m once out of high herbivore browsing pressure. 1.2 Problem statement Herbivore damage on the Acacia drepanolobium trees across different height classes affects the habitat architectural structure. Browsing damage at various heights is known to affect the Acacia drepanolobium differently like decrease in browse availability. These effects if not well understood and active management interventions taken can compromise the objectives of conserving an endangered species. Studies conducted by Birkett (2002) in OPC indicated overstocking of elephants in the former SweetWaters Game Reserve (SWGR) lead to severe damage of the Acacia drepanolobium trees. As a result the rhino carrying capacity declined from estimated 90 to about 50 rhinos. Based on the recommendations of this study, a total of 56 elephants were trans-located from OPC to Meru national park in 2001. Consequently, Acacia drepanolobium mortality caused by elephants reduced significantly. The study also recommended that the game reserve be expanded and this was completed in April 2007. The former SWGR was expanded from 24,000 acres to the current Ol Pejeta conservancy 75,000 acres. The expansion availed more food resources for herbivores and thereby reducing browsing pressure. In addition to the expansion, three corridors were opened to the north of OPC, thereby enabling dispersal of elephants to the greater Laikipia ecosystem. Following the above major transformations, monitoring results showed that elephant induced mortality of Acacia drepanolobium declined (Wahungu & Mureu, 2008); this significant reduction was realized as a result of elephant redistribution due to the expansion and opening of the movement corridors. Habitat monitoring of Acacia drepanolobium woodland after the 2001 translocation showed gradual recovery of these habitat; 14% annual regeneration of Acacia drepanolobium recorded thereafter. A recent study on the interactions of herbivores and Acacia drepanolobium in OPC revealed that elephant related mortality in Acacia drepanolobium trees 10 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy was 35% and increased predictably with increase in tree height. Giraffe browse significantly reduced flowering and fruiting in Acacia drepanolobium but did not directly influence height increment. However, giraffe browsing increased susceptibility to drought. Rhinos browse on seedlings and trees below 2m thereby affecting the rate of recruitment of seedlings into trees (Wahungu & Mureu, 2008).This study is therefore, going to act as a post expansion examination of the damage status on the Acacia drepanolobium trees in the Ol Pejeta conservancy since 2007. 1.3 Conceptual Framework

FIRE

MEGAHERBI VORES

Acacia drepanolo bium

NATURAL DAMAGE

SMALL BROWS ERS

Mega herbivores, small browsers, fire and natural damage all interact interdependently in changing the architecture of the Acacia drepanolobium population.

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Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy 1.4 Justification of the Study Ol Pejeta conservancy strives to conserve the highly endangered black rhino (Diceros bicornis michaeli). Acacia drepanolobium makes up a high percentage (~75%) of the black rhinosâ&#x20AC;&#x2122; diet. As stated in the problem statement, the presence of the elephants and giraffes in Ol Pejeta possess a threat of compromising the standards of conserving the endangered black rhinos. The three mega-herbivores: rhino, elephants and giraffes, greatly affects the status of the Acacia drepanolobium (Wahungu & Mureu, 2008). The elephants kill trees entirely or reverse growth by breaking the main stem, giraffe affect flowering and fruiting and the rhinos reduce recruitment of seedlings to mature trees. There are other browsers like the elands and the impalas which browse on the seedlings hence having the same impacts as the rhinos. The need for a comprehensive understanding of elephants, rhinos and giraffes interactions with Acacia drepanolobium woodland in modeling the ecosystem at Ol Pejeta conservancy is necessary. Ol Pejeta conservancy is the south most and wettest of the ranches in the SamburuLaikipia ecosystem. Because of this, there has been an influx of wildlife particularly elephants escaping drought in the north (Samburu) into the conservancy. This has resulted in heightened elephant damage on the Acacia drepanolobium (Wahungu & Mureu 2008).

The corridor

movement of animals has made it difficult to accurately monitor the population demographics of the elephants, giraffes and other animals with the exception of the rhinos because the corridors are rhino proof. This may imply that the herbivore damage is high at certain seasons due to the opening of migratory corridors.

This study will give recommendations to the Ol Pejeta conservancy

management based on its findings in making decisions on the protection of the Acacia drepanolobium from extensive damage.

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Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy 1.5 Research Objectives and Hypotheses 1.3.1 Main objective

The main objective of the study was to assess the extent and the effects of damage on Acacia drepanolobium in the Ol Pejeta conservancy.

1.3.2 Specific objectives

The Specific objectives of this research were:

1) To assess the extent of damage on the Acacia drepanolobium in Ol Pejeta conservancy.

2) To examine the Acacia drepanolobium population structure at the Ol Pejeta conservancy. 3) To evaluate the effects of season on the Acacia drepanolobium in Ol Pejeta conservancy. 4) To examine the effects of fire on the Acacia drepanolobium population structure in Ol Pejeta conservancy.

1.3.3 Hypotheses 1. i) Ho: The occurrence of Acacia drepanolobium damage is independent of the sampling plots in Ol Pejeta conservancy. Ha: The occurrence of Acacia drepanolobium damage is dependent on the sampling plots in Ol Pejeta conservancy.

ii) Ho: There is no interaction between the habitat status and the damager. Ha: There is interaction between the habitat status and the damager. 2. i) Ho: Acacia drepanolobium population structure is independent of burning. Ha: Acacia drepanolobium population structure is dependent on burning.

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Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy ii) Ho: There is no difference in the Acacia drepanolobium density in the burnt and unburnt areas. Ha: There is difference in the Acacia drepanolobium density in the burnt and unburnt areas. iii) Ho: The damagers damage the Acacia drepanolobium trees at the same height. Ha: The damagers do not damage the Acacia drepanolobium trees at the same height. iv) Ho: All damagers damage Acacia drepanolobium trees of the same diameter. Ha: All damagers do not damage Acacia drepanolobium trees of the same diameter. v) Ho: The damager is independent of the sprouting status of the Acacia drepanolobium trees. Ha: The damager is dependent on the sprouting status of the Acacia drepanolobium trees. vi) Ho: The damager is independent of the symbiotic ants on the Acacia drepanolobium trees. Ha: The damager is dependent of the symbiotic ants on the Acacia drepanolobium trees.

3. i) Ho: Acacia drepanolobium damage status does not vary with season. Ha: Acacia drepanolobium damage status varies with season. ii) Ho: There is no interaction between the damager and the season. Ha: There is interaction between the damager and the season. 4. i) Ho: Fire does not affect the Acacia drepanolobium height structure. Ha: Fire affects the Acacia drepanolobium height structure. ii) Ho: Fire does not affect the diameter of Acacia drepanolobium. Ha: Fire affects the diameter of Acacia drepanolobium.

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Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy CHAPTER TWO 2.0 LITERATURE REVIEW Acacia drepanolobium is a swollen-thorn Acacia species native to East Africa. The Acacia drepanolobium trees have an average growth height of 2 meters and are covered with long thorns, some of which have large bulbous bases. These swollen thorns are naturally hollow and occupied by any one of the several symbiotic ant species. The common name of the plant is derived from this: when wind blows over the bulbous thorns in which ants have made entry/exit holes, they create a whistling sound thus the common name of the whistling thorn Acacia. Whistling thorn Acacia is the dominant tree in some areas of upland East Africa, sometimes forming a nearly monoculture woodland, especially on "black cotton" soils on impeded drainage with high clay content. It is browsed upon by the black rhinos, elephants and giraffes. 2.1 Giraffe impacts on Acacia drepanolobium Giraffa camelopardalis reticulata spend most of their feeding time within different areas of different diverse habitats however; they have a seasonal preference for certain plant species (Foster 1966). How these plant species are utilized depends on their tannin content and browsing pressure placed upon them. An increased disturbance on any given habitat takes long time and energy for equilibrium to be restored; this explains why there is a need to examine the herbivore damage extent and advice on management actions to be taken. A case study of the Nairobi national park shows that the Acacia drepanolobium has been severely affected by large herbivore browsing damage. As a result, they only grow to an average height of only 67cm, whereas outside the park they grow to 120cm because there is no browsing by specialist (Foster 1966). Species abundance is related to browsing pressure although some species can adapt to heavy browsing. Due to giraffe heavy browsing pressure in the Nairobi national park the Acacia drepanolobium have become smaller and short, but more numerous due to the absence of fires (Foster 1966). An indication of giraffes preferred food species is being over browsed is when they start feeding at a low level when they are adapted for reaching high levels (Foster 1966). It has been shown that there is clear stratification in the African browsing ruminants in which the male giraffe feed at a significantly higher level than females (Toit, 1990). This is accounted for by two theories, one being that this might imply the existence of competition between species 15 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy (Toit et al.,1990) and the other is that this competition is reduced by having different significant feeding levels (Sinclair and Norton Griffith 1979, Pellew 1983;). Booth (1997) reported that, giraffes in Ol Pejeta spend over 85% of their time budget feeding on Acacia drepanolobium. For a greater percentage of these feeding observations (86%), giraffes fed at the top soft crown of Acacia drepanolobium (Booth 1997). Severe browsing may have a considerable effect on Acacia drepanolobium and may alter the structure of the vegetation associations (Coe et al,. 1987). This is evident at OPC where distinct architectural difference exists in the Acacia drepanolobium habitats. Although moderate browsing by giraffe may stimulate sprouting in Acacia drepanolobium, severe browsing may reduce re-growth feed-back loop (Pellew, 1983). Although there is evidence to suggest that giraffe browsing is having an effect on the structure, the giraffes are still feeding at high levels and not utilizing all available food species in the conservancy. This indicates that the fitness of the Acacia drepanolobium is not being compromised. 'The diameter growth rate does depend on the general vigor of the tree' (New 1984), Booth (1997) found that the Acacia drepanolobium of SweetWaters were in good condition. However, they are maintained at a height of 2.8 m below their capacity of 4.8 m, with smaller canopy width and percentage leaf coverage as a result of giraffe browsing. She suggested that if over population of giraffe in the Game Reserve will occur, it would be expected that the preferred food source; Acacia drepanolobium, would be severely exploited and the vegetation to contain abnormal amounts of tannin due to an increased browsing pressure. This would result to mortality of those individuals with the weakest physiological tolerance. This study will therefore focus on assessing the structure and condition of Acacia drepanolobium in relation to the browsing pressure. 2.2 Elephant impacts on acacia Elephant damage on trees includes bark-stripping, breaking of branches and the main stem and uprooting of the complete tree. Van de Vijver et al., (1999); Ruess et al., (1990) and Croze (1974b) show that elephants push over tall mature trees (over 5m tall) but break branches and the main stem of smaller trees. Birkett (2002) showed that 72% of the trees sampled were below 3m in height and consequently the breaking of branches will be a significant mode of damage at 16 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy SweetWaters. Bond and Loffel (2001) assessed browse damage by recording the status of branch ends. Between 1998 and 2001, studies conducted by Birkett in OPC indicated overstocking of elephants in the former SweetWaters Game Reserve leading to severe damage of the Acacia drepanolobium trees. As a result the rhino carrying capacity declined from estimated 90 to about 50 rhinos. Based on the recommendations of this study, a total of 56 elephants were translocated from OPC to Meru national park in 2001 in conjunction with KWS. Consequently, Acacia drepanolobium mortality caused by elephants reduced significantly. The study also recommended that the game reserve be expanded and this was done in April 2007. The former SWGR was expanded from 24,000acres to 75,000 acres. The expansion availed more food resources for herbivores and thereby reducing browsing pressure. In addition to the expansion, three corridors were opened to the north of OPC, thereby enabling dispersal of elephants to the greater Laikipia ecosystem. Following the above major transformations, monitoring results showed that elephant induced mortality of Acacia drepanolobium declined from 4.4% to 2.5% (2005-2007); this significant reduction was realized as a result of elephant redistribution since the expansion and establishment of the movement corridors. Habitat monitoring of Acacia drepanolobium woodland after the 2001 translocation showed gradual recovery of these habitat; 14% annual regeneration of Acacia drepanolobium recorded there after. This study is therefore, going to act as an examination on the variations of the elephant damage to the Acacia drepanolobium since the establishment of the movement corridors in 2007. To accomplish this, secondary data from the EarthWatch institute on Acacia drepanolobium damage since 2007 will be used to compare and contrast with the data collected from this study.

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Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy CHAPTER THREE 3.0 RESEARCH DESIGN 3.1 Study area 3.1.1 Location Ol Pejeta Conservancy (OPC) is located in central Kenya, 230km north of Nairobi, near Nanyuki, on the equator at longitude 36°56'E. It lies on the Laikipia plateau between Mt Kenya and the Aberdare mountains at an average altitude of 1800m. 3.1.2 Climate and hydrology Ol Pejeta conservancy is in a semi-arid area with an average annual rainfall of 739 mm with peaks from March to May, and from October to December. There is a smaller peak in August with an average of 78mm. The annual average maximum and minimum temperatures are 28ºC and 12ºC respectively. Two permanent rivers; Ewaso Nyiro and Ng’obit which traverse OPC and several seasonal rivers and streams (lagga), man-made dams, troughs and pipelines provide water to wildlife, livestock and staff. 3.1.3 Wildlife Ol Pejeta conservancy is home for approximately 68 species of mammals. The conservancy is currently the largest Black rhino Sanctuary in East Africa with a population of 82 black rhinos (Diceros bicornis). Other large mammal herbivores at the study site include elephants (Loxodonta africana), giraffes (Giraffa camelopardalis), cape buffalos (Syncerus caffer), elands (Taurotragus oryx), Grevy’s zebras (Equus grevyi), Burchell’s zebras (Equus burchelli), Beisa oryx (Oryx beisa), Jackson’s hartebeests (Alcelaphus buselaphus jacksoni), Waterbuck (Kobus defassa), Grant’s gazelles (Gazella granti), steinbucks (Raphicerus campestris) and domestic cattle. Predators include Lion (Panthera leo), leopard (Panthera pardus, cheetah (Acinonyx jubatus), wild dog (Lycaon pictus), Silver-backed jackal (Canis mesomelas) and Spotted hyena (Crocuta crocuta). Primates include Olive baboon (Papio anubis), Patas monkey (Erythocebus patas), Vervet monkey (Cercopithecus aethiops) and Lesser bushbaby (Galago senegalensis).

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Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy 3.1.4 Vegetation and soil type Ol Pejeta conservancy has got four distinct habitats; a mosaic of grassland, Acacia drepanolobium mixed woodland, Euclea bushes (Euclea divinorum), and Riverine woodland (Acacia xanthophloea). The Grasslands are dominated by Themenda triandra and Penisetum mezianum grass species. The Acacia drepanolobium is mixed with shrubs of Euclea divinorum, Carissa edulis, Psidia punctulata and Scutia myrtina. The dominant soil type is black cotton soil. Figure 1 below shows the habitat distribution map of the Ol Pejeta conservancy courtesy of the OPC Ecological Monitoring Department.

Figure 1; Map of the Ol Pejeta Conservancy Showing the Vegetation Types (Map adopted from Olpejeta Earthwatchâ&#x20AC;&#x2122;s Black rhino habitat Project)

3.2 Research tools and equipment A computer with Geographical information system software 19 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy A

global

positioning

system

unit

(GPS)

measuring

tape

A 100 m measuring tape A

30

m

steel

Measuring

rod

Prismatic

compass

Stationeries

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Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy 3.3 Methodology A Geographical information system (GIS) map of OPC showing the vegetation types (shown above) was used to identify Acacia drepanolobium habitat. Within these habitats, fourteen sampling plots were selected to cover the main sectors/blocks of the conservancy. Each plot was circular in shape with a radius of 100 m and covering 31428.57 m2. Four plots were set in areas that had a record of burning in past two or three years. One control plot was also established in an enclosure free from herbivore and fire damage: Morani and the remaining nine sampling plots were distributed in the rest of the Acacia drepanolobium habitat with mixed types of damages. For each sampling plot an Acacia drepanolobium tree was identified, marked and its position marked as a way plot in a GPS unit for subsequent identification and measurements. For each plot the marked tree was used as the starting plot to lay down five radiating transects each measuring 100m as shown in figure 2 below.

720 2m 100m

Figure 2: Radiating transects The first transect was oriented straight in to any direction with help of a leader at the end of transect and a follower at the starting point to position the leader. Then its bearing was measured using a prismatic compass held by the follower in order to get the bearing of the next transect by adding 72°. The same procedure was repeated respectively to lay down all transects. Once transect was laid down all the Acacia drepanolobium trees within a belt of 2m (i.e. 1m on either side of transect) were given a number and several variables were measured and recorded against its number. First, the tree height was measured, its breast height diameter and its damage status; whether present or absent were recorded against the treeâ&#x20AC;&#x2122;s number. Once an Acacia drepanolobium tree

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Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy was identified as damaged, the damage height was measured and recorded. The type of damage was described as whether the main stem was broken, snapped off/ secateursâ&#x20AC;&#x2122; type of cut, side branch broken or snapped off, the tips snapped off, tree leaning or uprooted, tree burnt, tree drying from the top or tree dry/dead stamp. The age of the damage was estimated by direct observation of the damage site, Croze (1974 b) stated that the age of damage could be categorized by inspection of the color and condition of the wood at the damage site. Birkett (2002) stated that elephant damage older than 18 Months was frequently missed due to the subsequent growth of the branch. Damage over 18 months old was therefore not sampled due to the relatively low probability of encountering representative samples.

The cause of the damage was identified and recorded. Elephant damage was distinguished from rhino damage through inspection of the mode of breakage (Laws 1970; local information) where the branch or the main stem appeared to have been ripped of, the damage was attributed to elephants. Where a secateurs type of cut was identified, that was attributed to rhino. Selective removal of the soft twigs at the crown of tall Acacia drepanolobium trees was attributed to giraffe browsing and that on short Acacia drepanolobium trees was attributed to small browsers like Impalas. Where the Acacia drepanolobium trees were seen to be drying from top this was attributed to natural damage either because of prolonged droughts, age or nutrients deficiency. The identification of damage signs was backed up by information from the accompanying security guards who have good knowledge on the local vegetation and animal behavior. Also the presence of the symbiotic crematogaster antsâ&#x20AC;&#x2122; species was observed and recorded. Any other relevant information such as whether the tree was sprouting, regenerating, flowering or bearing seeds (pods) was recorded as an additional comment.

22 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy CHAPTER FOUR 4.0 DATA COLLECTION AND RESULTS 4.1 Data collection The data was collected in two seasons starting from June 2009 to December 2009: dry season and January 2010 to February 2010: wet season.

The collected data was first entered in

Microsoft office excels spreadsheet, and coded for analysis with the statistical package for social sciences (SPSS).

The data was then analyzed using parametric tests in case of a normal

distribution and where the sample number was equal to or greater than the total number of trees sampled. Non-parametric tests were used where the data did not follow a normal distribution. The hypotheses were tested at a 0.05 significance level. 4.2 Results In total 5,722 Acacia drepanolobium trees were counted and measured in fourteen sampling plots. Each sampling plot was measured twice in the entire study period: in dry and wet seasons. 2,770 Acacia drepanolobium trees were sampled in the dry season and 2,952 Acacia drepanolobium trees in wet season. Out of the fourteen sampling plots four of them were in areas which had been burnt two years before and the total number of Acacia drepanolobium trees sampled in these plots was 2,104. Nine sampling plots were located in unburnt areas where a total of 3,259 Acacia drepanolobium trees were sampled. One control sampling plot was set up in an enclosure free from herbivore damage and also unburnt; in this plot 359 Acacia drepanolobium

trees

were

sampled.

A Pearson chi-square test indicated that the occurrence of Acacia drepanolobium damage was dependent on the sampling plots in Ol Pejeta (Ď&#x2021;2 =5.793; DF = 13, P <0.00). This study showed that 61% (N= 3467) of the Acacia drepanolobium trees had some of damage from either herbivore browsing, fire or drying naturally and 39% (N= 2255) were intact and without any form of damage. Out of the 14 plots 12 of them the level of damage was higher than the undamaged. The control (plot 10) and plot 13 had very low damage level: the number of damaged trees was less than the undamaged ones therefore; Acacia drepanolobium damage is

23 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy distributed all over the Ol Pejeta conservation area with some areas highly damaged than others (Figure 3 below).

600 500 400 300

Damaged Undamaged

200 100 0 1

2

3

4

5

6

7

8

9 10 11 12 13 14

Sampling plots

Figure 3: Acacia drepanolobium damage status in the fourteen sampled plots. A general linear model; Univariate analysis of variance indicated that there was a significant interaction between the habitat status and the damager (Table 1 below). Table 1: Interaction between the habitat status and the damager Tests of Between-Subjects Effects Dependent Variable: Plot number Type III Sum Source of variance of Squares

DF

Mean Square

F

Sig.

Habitat Status

1218.365

1

1218.365

105.238

.000

Damager

7841.844

6

1306.974

112.891

.000

Status * Damager 689.762

5

137.952

11.916

.000

Error

5709

11.577

66094.738

24 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy Relatively herbivores preferred browsing on burnt Acacia drepanolobium habitat i.e. 55% in burnt areas over 45% in unburnt areas. However, of all damages recorded, others; small herbivores like the impalas, elands, zebras and hartebeest had the highest preference for burnt habitat with 60% of their total damage being on burnt habitats and 40% on the unburnt areas. Black Rhino had the second high preference for burnt habitats with 55% on the burnt Acacia drepanolobium habitat and 45% on unburnt habitats. 70% of the elephant damage was found on unburnt areas while only 30% was on burnt areas. Natural damage was more in bunt areas (71%) than in unburnt areas (29%) hence Acacia drepanolobium trees were more susceptible to drought when burnt than when unburnt (Figure 4 below). 1200 1000 Mean damage

800 600 burnt 400

unburnt

200 0

-200

Figure 4: Interaction of burning and the level of damage for each damager Ol Pejeta conservancy Acacia drepanolobium population is composed of 73% seedlings, 17% saplings and 10% mature trees (Figure 5 below).

25 Joseph K. Makau @ 2010


No. of sampled trees

Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy 4500 4000 3500 3000 2500 2000 1500 1000 500 0 Seedling (1-50 cm) Sapling (51-200 cm) Mature Trees (>200 cm)

Figure 5: Acacia drepanolobium population structure A general linear model; Univariate analysis of variance indicated that there was a significant interaction between the Acacia drepanolobium population structure and burning (table 2 below). Table 2 A general linear model; Univariate analysis of variance table of results Tests of Between-Subjects Effects Dependent Variable: Plot No. Source of

Type III Sum

variation

of Squares

Habitat Status * Age class Error

Df

Mean Square

12669.651

5

21770.336

3778

F

2533.930 439.735

Sig. .000

5.762

Burning increased the seedlings of Acacia drepanolobium by 8% in a period of two years. Fire was more detrimental on the Acacia drepanolobium saplings where there was a 6% decrease; burning also decreased the mature Acacia drepanolobium trees (Figure 6 below).

26 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy 300

Mean No. of A. drep

250 200 150

burnt

100

unburnt

50 0 -50

seedling (1-50 cm)

sapling (51200)

mature trees (>200)

-100

Figure 6: Effects of fire on the Acacia drepanolobium population structure An ANOVA test indicated that there were significantly more trees in burnt areas (mean 58Âą 39) than in unburnt areas (mean 48 Âą 33) (table 3 below).

27 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy Table 3: ANOVA table of results ANOVA Number of trees per transect Source of

Sum of

Mean

variation

Squares

DF

Square

F

Sig.

Habitat status

92920.395

1

92920.395

68.719

.000

Error

5113962.476 3782

1352.185

Fire increased the density of the Acacia drepanolobium by an average of 24% after a recovery

Mean No. of Trees Per transect

period of two years (figure 7 below) 120 100 80 60 40 20 0 burnt

unburnt

Figure 7: Effects of fire on the Acacia drepanolobium density. An ANOVA test illustrated that the damagers significantly damaged the Acacia drepanolobium trees at different heights (Table: 4 below). Table 4: Damage stratification ANOVA test results ANOVA Tree damage height Source of

Sum of

variation

Squares

Damager

15522790

DF

Mean Square F

Sig.

6

2587131.698 1.1613

.000

28 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy Error

1.273E7

5715

2227.799

The rhino browsing intensity was concentrated below 50cm (Mean 22.13±26.83 cm), other browsers like the Impalas and the hartebeests also fed at the same height as the rhinos (Mean 22.14±31.54 cm), the elephants were found to browse the Acacia drepanolobium between the heights 30- 200 cm (Mean 118±85.94 cm), fire mostly affected the Acacia drepanolobium measuring up to 160 cm (mean 76.6381.84 cm), natural damage affected the Acacia drepanolobium trees of 180 cm and above (Mean 179±149 cm) , giraffes browsed Acacia drepanolobium trees measuring >200 cm(mean 223.21±110.1 cm) in height (Figure 8 below).

Mean Damage height (cm)

400 350 300 250 200 150 100 50 0 -50

Rhino

Others

Fire Elephant Natural Damager

Giraffe

Figure 8: Damage stratification across the Acacia drepanolobium height structure An ANOVA test indicated that all damagers damaged Acacia drepanolobium trees of significantly different diameters (table 5 below)

Table 5: ANOVA test on the damagers’ damaging diameter ANOVA Tree Diameter mm Source of

Sum of

variation

Squares

Mean DF

Square

F

Sig.

Damager

1767934.836 6

294655.806 631.904 .000

Error

2664895.810 5715

466.298 29

Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy

Small browsers like Impalas and hartebeests were found to damage Acacia drepanolobium trees with an average of 9.8±13.76 mm diameter, rhinos; 11.88±10.72 mm, natural damage; 46.12±33.63 mm, giraffe; 57.65±24.68 mm, fire; 58.56±17.44 mm and elephant; 59.92±37.83 mm (figure 9 below).

A. drep. Average diameter (mm)

120 100 80 60 40

20 0 -20

Others

Rhino

Natural

Giraffe

Fire

Elephant

Damager

Figure 9: Acacia drepanolobium tree diameters for the various damagers. A Pearson Chi-Square indicated that the damagers were dependent on the sprouting status of the Acacia drepanolobium trees (χ2 =18.737; DF = 6, P =0.005). Most of the sampled sprouting Acacia drepanolobium trees were intact without any form of damage on them. Black Rhino showed the highest preference for browsing on the sprouting Acacia drepanolobium trees followed by the elephants, other browsers, natural and giraffe, respectively, as shown in Figure 10 below.

30 Joseph K. Makau @ 2010


Mean No of sampled sprouts

Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy 160 140 120 100 80 60 40 20 0 -20

No damage

Rhino Elephant Others Natural Giraffe Damage Cause

Figure 10: Herbivore preference for sprouting Acacia drepanolobium trees. Pearson Chi-Square indicated that the damager was dependent on the Symbiotic ants on the Acacia drepanolobium trees (Ď&#x2021;2 =27.124, DF =6; P <0.000). Most Acacia drepanolobium trees hosting the symbiotic ants had not been damaged. Rhino damaged the highest number of Acacia drepanolobium trees with symbiotic ants, elephants damaged relatively lower number of Acacia drepanolobium trees hosting the symbiotic ants compared to rhinos followed by other browsers, natural damage and giraffe in a descending

No. of Trees with Symbiotic Ants

order. No burnt Acacia drepanolobium tree that had hosted the symbiotic ants (Figure 11 below). 350 300 250 200 150 100

50 0 No damage

Rhino Elephant Others Natural Giraffe

Fire

Damage cause

Figure 11: The relationship between the symbiotic ants and the damager

31 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy An ANOVA test indicated that damage status on Acacia drepanolobium trees varied significantly with season (Table 6 below). Table 6: Effects of season on damage status ANOVA test results. ANOVA Tree damage status Source of

Sum of

Mean

variation

Squares

DF

Square

F

Season

84.568

1

84.568

377.396 .000

Error

1281.753

5720

0.224

Sig.

73% of the Acacia drepanolobium trees had been damaged during the dry season while 49% of

Average No. of A. drep

the Acacia drepanolobium habitat had been damaged in wet season (figure 12 below). 2500 2000 1500 Present 1000

Absent

500 0 Dry

Wet

Figure12: Effects of season on the damage status A general linear model; Univariate analysis of variance indicated that there was a significant interaction between the season and damager (Table 7 below) Table 7: The interaction between the season and the damager Tests of Between-Subjects Effects Dependent Variable: Plot number

32 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy Type III Sum Source

of Squares

DF

Mean Square F

Sig.

season * Damager 12450.418

12

1037.535

.000

Error

5708

12.099

69058.558

85.757

Elephant damage was high over the dry season; 58% compared to 42% in wet season, Rhino damage was relatively constant over the two seasons (i.e. 51% in dry and 49% in wet). Giraffe damage was very high in wet season; 70%, and low in dry season; 30%. Most small browsers preferred the Acacia drepanolobium habitat in dry season; 75%, than in wet season; 25%. Natural damage on the Acacia drepanolobium habitat was very high in dry season; 74%, and low in wet season; 26%. Damage by fire was constant over the two seasons since there was no burning during the study period (Figure 13 below). 14

Mean damage

12 10 8 6

Dry

4

Wet

2 0

Figure 13; The interaction between season and damager An ANOVA test indicated that fire significantly affected the Acacia drepanolobium height structure (Table 8 below). Table 8: Effects of damage on Acacia drepanolobium tree height structure ANOVA Tree height (cm)

33 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy Source of

Sum of

variation

Squares

Treatment

1898440.592 2

949220.296

Error

5.054E7

8839.587

DF

5718

Mean Square F

Sig.

107.383 .000

High damage level (burnt areas with other damage types) maintained the Acacia drepanolobium trees short (Mean 48.58±73.51 cm; seedling height), medium damage level (Unburnt areas but with other damage types) maintained the Acacia drepanolobium trees at a medium height (Mean 73.11±99.959 cm; sapling height) while absence of damage (control plot) made the Acacia drepanolobium trees grow tall (Mean 121.43±136.161 cm; mature trees’ height) (Figure 14 below).

300

Mean tree height

250 200 150 100

50 0 -50

Burnt & other damages Unburnt but with other Control: Un damaged damage types

Figure 14: Effects of fire on Acacia drepanolobium tree height structure An ANOVA test showed that the diameter of Acacia drepanolobium varied significantly with the level of damage (Table 9 below). Table 9: Effects of fire on Acacia drepanolobium diameter, ANOVA Tree Diameter mm

34 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy Source of

Sum of

variation

Squares

DF

Mean Square F

Sig.

Treatment

97480.844

2

48740.422

.000

Error

4335349.801 5719

64.296

758.061

High damage level (burnt areas) maintained Acacia drepanolobium trees of small diameter (15.732Âą21.581 mm), medium level of damage (unburnt) maintained Acacia drepanolobium trees of relatively larger diameter (22.538Âą30.3606 mm) while the absence of damage maintained large diameters (30.532Âą31.3912 mm) (Figure 15 below). 70

Mean tree Diameter (mm)

60 50 40 30 20 10 0 -10

Burnt & other damages

-20

Unburnt but with Control: Un damaged other damage types treatment

Figure 15: Effects of fire on the diameter of Acacia drepanolobium trees.

35 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy CHAPTER FIVE 5.0 DISCUSSION Woodlandâ&#x20AC;&#x201C;grassland ecosystems are inherently dynamic (Dublin, 1995) with factors such as browsing, fire and rainfall being critical in determining whether the habitat will be stable or subject to change (Cumming, D.H.M. (1982)). Norton-Griffiths (1979) and Dublin (1995) reported that fire and browsing pressure impact the vegetation structure of Serengeti- Mara ecosystem and limit the natural regeneration of East African woodlands. Elephants have been reported to cause spectacular changes in vegetation structure and in composition of savannahs in Africa (Cumming, 1982; Ruess & Halter, 1990). Furthermore, elephants have been reported to kill large Acacia trees (Western & Praet, 1973; Croze, 1974), resulting in disappearance of woodland. However, Western & Praet (1973) recognized that some trees in Amboseli were dying without appreciable elephant damage, while apparently healthy trees were able to tolerate significant amounts of debarking and branch removal. Their study suggested that long-term climatic change was also a more fundamental cause of tree mortality.

In this study, the Acacia drepanolobium woodland was exposed to the conditions of wet and dry seasons, different levels of browsing by large herbivores (mainly elephants, giraffes and black rhinoceros) and subject to fire. These impacts appeared to be sufficient to cause rapid reductions in tree density, height and canopy. Dry season, burning, low rainfall and intense browsing pressure reduced tree growth. Growth retardation was height and canopy specific, whereas growth increment was diameter specific. The present study has found that in the burnt and browsed area, there was a low average growth rate in plant height and canopy compared with the trees in the fenced plot (control area). The results show that heavy browsing pressure on Acacia trees resulted in lower average incremental growth in the height and canopy cover of the trees in the damaged areas as compared to the fenced and protected plot. Hence, the impact of heavy browsing pressure on Acacia trees in the damaged area resulted in a lower average growth in diameter as compared to the fenced plot where average growth in stem diameter was higher.

Therefore, high damage pressure (burning combined with herbivore browsing) decreased growth in stem diameters of the trees and growth of tree height and canopy. Although the impact of

36 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy browsing on the height and canopy of Acacia trees was considered to be high, it did not kill trees, and seedlings and saplings were found growing in all plots, with the exception of the few instances where the elephants uprooted the all tree. Birkett (2002) studying the impacts of giraffes, rhinos and elephants within the black rhino sanctuary habitat in the Sweet Waters Game Reserve in Kenya found that Acacia drepanolobium trees subject to high levels of giraffe browsing and low rainfall grew by only 7.5 Âą0.5 cm/year in an unprotected area as compared to 19.1Âą 2.1 cm/year in a protected area. This study reported extensive damage of trees due to elephant destruction. Ruess & Halter (1990) observed vegetation changes in Serengeti National Park due to the combined effects of fire, elephants and giraffes, reporting a high degree of stem and branch damage that resulted in high mortalities among trees.

A recent study on the interactions of herbivores and Acacia drepanolobium in OPC revealed that Elephant related mortality in Acacia drepanolobium trees was 35% and increased predictably with increase in tree height (Wahungu & Mureu, 2008). Giraffe browse significantly reduced flowering and fruiting in Acacia drepanolobium by selectively browsing on the soft flowering and seed bearing shoot tips. However, giraffe browsing increased susceptibility to drought hence did not directly influence height increment (Wahungu & Mureu, 2008). Rhinos browse on seedlings and trees below 2m thereby affecting the rate of recruitment of seedlings into trees (Wahungu & Mureu, 2008).

In this study, significant differences were found in the average damage level in Acacia trees in both rainy and dry seasons. This shows that Acacia drepanolobium is highly preferred by all browsers in dry season due to the unavailability of other alternative browse materials in OPC. Low rainfall not only lowered the rate at which trees were replaced but also slowed grass and herb growth. Elephants eat a mixture of grass and browse in the wet season but increase the browse proportion during the dry season (Field & Ross, 1976; Dublin, 1995). Similarly, rhinos will eat more woody species (Oloo, Brett & Young, 1994) as the availability of herb species decreases during dry periods. Green grass biomass peaks within a month of the rains starting and then grass quantity and quality decline (Dublin, 1995) during the dry period. The crude protein content of grasses was reported to fall from 11 to 3% during a 3-month dry period (Pellew, 1984). Woody species retain their high protein levels (Pellew, 1984). This accounted for the high 37 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy preference of Acacia drepanolobium in OPC which is an enclosed reserve. Elephant damage was recorded the highest in dry season and also higher than that of the other damagers. This can be attributed to the fact that elephants are in competition for the available grass with other grazers such as zebras and buffaloes. Zebras in particular can browse grass to such a low height that elephants have difficulty feeding. The higher the density of competing grazers, the earlier in the dry season elephants will be forced to switch to trees and seedlings, hence the more they will damage trees. During this study several buffaloes died during the six months drought and there were clear signs that the rest of the other big mammals had lost weight.

Fire increased the density of the Acacia drepanolobium by an average of 24% after a recovery period of two years. The increment was on the Acacia drepanolobium seedlings by 8%. However, fire was more detrimental to the Acacia drepanolobium saplings and mature trees. Most mature trees, especially those above 3 m tend to have desiccated bark and colonies of lichen that make them very susceptible to fire than shorter trees. Also the high woody content of the mature trees increases their vulnerability to fire. These trees were seen to dry from top and drop off chunks of their canopy after the first year of burn (Wahungu et. al., 2009). The burnt trees were also more susceptible to breakage by animals rubbing and scratching against them. All these factors lead to rapid reductions in heights and mortality (Wahungu et. al., 2009).

Of great importance to note in this study was the great significant difference in the damage caused by drought between the burnt and the unburnt areas. Acacia drepanolobium trees were more susceptible to drought when burnt than when unburnt. Although, fires caused mortalities to adult Acacia drepanolobium, the most significant effect was tree reversals into seedling height class as trees resprouted. Although fire may increase browse biomass of A. drepanolobium available for black rhino, it is not an appropriate black rhino habitat management tool because burnt areas attract many seedling predators that lower seedling recruitment into adult trees (Wahungu et. al., 2009).

This study also found similar observations whereby, burnt plots

attracted small browsers such as the impalas, Jacksonâ&#x20AC;&#x2122;s hartebeest, elands and zebras. The small browsers predate on Acacia drepanolobium seedlings hence lowering the rate of seedling recruitment into saplings and mature trees. This signifies that burning of Acacia drepanolobium habitat should be discouraged. Burning makes the acacia trees more vulnerable to drought 38 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy especially in this era of drastic climate change characterized by prolonged droughts. Mega herbivores: the elephants and the giraffe do not prefer feeding on burnt Acacia drepanolobium plots. This probably is due to the absence of their browse material, since fire maintains short Acacia drepanolobium trees which are below their browsing level. There was no relationship between damage by rhinos and rainfall. Tree deaths that appeared to be caused by drought increased steadily during the study and continued to increase even after the rains began.

It is noted that the current browser population of ~300 elephants, ~300 giraffes and 82 rhinoceros in the vast 303.51Km2 area of the Ol Pejeta conservancy has not reached a critical level to cause much negative impacts on the Acacia drepanolobium trees. Findings of this study showed that although heavy browsing reduced the height and canopy of Acacia trees, seedling regeneration took place simultaneously with higher rate of regeneration in burnt area and over the wet season but with very little seedling regeneration in undamaged areas (control plot). The results clearly indicated that most of the damage took place in the height above 50 cm. Pellew (1983) in Serengeti National Park, reported more giraffe browsing impact on Acacia tortilis trees of 200â&#x20AC;&#x201C;300 cm height class, but Birkett (2002) observed that giraffes browsed extensively in the 250â&#x20AC;&#x201C;450 cm height class, whereas black rhino concentrated on lower <200 cm height class. This clear height stratification of the level at which each browser browses leads to forage facilitation. Facilitation allows species to co-exist in a community, especially where one species increases resource access by another through its feeding behavior. Vessey Fitgerald (1960) established that trembling and feeding by elephant exposed medium height grass to buffaloes which in turn through their feeding activities generated shorter grass for topi. This study found out that rhino, elephant and giraffe damage were well stratified across the height and diameter structures. Natural and giraffe damages maintained the acacia trees short (~200cm) such that the elephants could access. Elephants damaged the Acacia drepanolobium trees by breaking the main stem or the side branches at an average height of ~150cm. The feeding behavior of the elephants then reverses the Acacia drepanolobium trees to a height which is accessible to the rhino. Elephants also facilitated the accessibility of rhino browse material by breaking the main stems or side branches of mature Acacia drepanolobium which later resprouted producing fresh browse for the rhino.

39 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy Elephants, giraffes and natural death damaged the Acacia drepanolobium trees with diameters larger than that of the browsing level of the rhino. This reversed the trees to the rhino browsing level hence maintaining maximum browse availability for the black rhino. Absence of damage allowed the acacia trees to grow large and tall far above the browsing level of the rhinos hence making the browse material for rhino inaccessible.

Despite the presence and impacts of large herbivore damage, fire, and natural damages, results of this study indicated that the Acacia drepanolobium habitat was still at a balance. The addition and recruitment of seedlings into saplings was at a relatively high rate except in burnt areas where saplings had been reduced by 6%. The conditions at the time of study indicated that the damage in Acacia drepanolobium habitat was significant, and was serious in burnt areas and over the dry season. This was a warrant for management intervention to look for alternative methods of pasture management other than burning.

It will be of high importance for the management to monitor the fluctuating populations of the elephants and giraffes within the conservancy. This is necessitated by the fact that Ol Pejeta conservancy is the south most and wettest of the ranches in the Samburu-Laikipia ecosystem. This caused an influx of wildlife particularly elephants escaping drought in the North into the conservancy through the wildlife movement corridors. This has resulted in heightened elephant damage on the Acacia drepanolobium during dry seasons.

40 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy CHAPTER SIX 6.0 CONCLUSIONS AND RECOMMENDATIONS 6.1 Conclusions The Acacia drepanolobium habitat in the 303.51Km2 area of the Ol Pejeta conservancy in Kenya is being altered as populations of elephant, giraffe and black rhino increase. Damage heightspecific impact data was recorded for a period of eight months in a total number of 5,722 trees of the dominant species, the whistling thorn; Acacia drepanolobium. Rhinos, elephants, giraffes, small browsers, fire and natural death were recorded as the main causes of damage on the Acacia drepanolobium habitat. Damage on the Acacia trees was significant (p<0.00), with a damage level of 61% over the undamaged level of 39%. Natural damage was more in burnt areas than in unburnt areas indicating that Acacia drepanolobium trees are more susceptible to drought when burnt than when unburnt. Burnt plots attracted more Acacia drepanolobium seedlings predators (rhino and small browsers such as the impalas, Jacksonâ&#x20AC;&#x2122;s hartebeest, elands and zebras). This has the implications that the rate of seedling recruitment into saplings and mature trees is lowered in the burnt areas. In Ol Pejeta conservancy the population structure of Acacia drepanolobium is pyramidal where seedlings dominate the population followed by the saplings with mature trees being the least. This indicated that the habitat type is still in balance with the addition of recruitment of seedlings and saplings except in burnt areas where the saplings were reduced by 6%. Fires caused mortalities to mature Acacia drepanolobium trees. The most significant effect of fire was tree reversals into seedling height class as trees resprouted hence more seedlings in burnt areas than in unburnt. The damagers were well stratified across the Acacia drepanolobium height and diameter structures. This clear height stratification of the damage level of each damager leads to forage facilitation. Facilitation allows species to co-exist in a community, especially where one species increases resource access by another through its feeding behavior. Natural and giraffe damages maintained the acacia trees short such that the elephants could access. The feeding behavior of the elephants then reverses the Acacia drepanolobium trees to a height which is accessible to the 41 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy rhino and other small browsers. Elephants also facilitated the accessibility of rhino browse material by breaking the main stems or side branches of mature Acacia drepanolobium which later resprouted producing fresh browse for the rhino. There was a significant interaction between the season and the damager (p<0.00) such that damage level increased over the dry season and decreased in wet season. Acacia drepanolobium therefore, is a highly preferred browse by browsers in dry season at OPC. The elephants and the other browsers such as the impalas, elands, zebras and the Jacksons hartebeests switched to Acacia drepanolobium diet during the dry season. This indicated that Acacia drepanolobium in OPC is under great browse pressure in dry season. In contrast, the giraffes fed more on Acacia drepanolobium in wet season than in dry season.

Various levels of damage altered the Acacia drepanolobium population structure significantly (p<0.00). High damage level: burnt and other damage types combined together maintained the Acacia drepanolobium trees short at seedling height. Medium damage level: Unburnt but with other damage types maintained the Acacia drepanolobium trees at a medium height a health structure with more saplings than old mature trees. While absence of damage made the Acacia drepanolobium trees grow tall with very few seedlings and saplings growing.

42 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy 6.2 RECOMMENDATIONS Fire is very detrimental to the Acacia drepanolobium saplings. Also, fire increases the treesâ&#x20AC;&#x2122; vulnerability to drought especially in this era of climate change characterized by prolonged droughts and unpredictable seasons. These conditions are unsustainable and will result in habitat change and may affect rhino breeding and population growth in OPC. Therefore, based on the findings of this study I recommend that: 1. Burning as a tool of pasture management should be practiced away from Acacia drepanolobium dominated or mixed woodlands. Alternative method of pasture management should be adopted and use of controlled fire should be practiced in open grasslands only.

2. It is important for the OPC management to monitor and control the fluctuating populations of the elephants, giraffes and zebras within the conservancy especially during the dry season.

3. An extensive case study on the population dynamics of the Acacia drepanolobium habitat in Ol Pejeta conservancy should be carried out to determine the population density, growth and mortality factors. This will be very useful in projecting future Acacia drepanolobium population trends.

43 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy APPENDICES Program of activities Activity

Time

Research topic , literature review, proposal writing and May- June 2009 approval by supervisor Data collection fieldwork

June 2009-feb 2010

Data analysis

March 2010

Report writing

March and April 2010

Defending before a university panel

April 2010

44 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy

Data sheet STRATIFICATION OF HERBIVORESâ&#x20AC;&#x2122; DAMAGE ON ACACIA DREPANOLOBIUM Investigator

_____________

__________Transect

number

________

Date

&

Time____________________________ Plot

No.___

GPS

Coordinates

X_________

Y_________

Local Name ______________________________________

Tr No

Transec

height

Diamete Dam

Descri

Dama

D.

t No.

(cm)

r (mm)

ption

ger

height e age

commen

(cm)

ts

age

status (type)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 45 Joseph K. Makau @ 2010

Damag

Ants &


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy 20

46 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy

Key Growth stage 1) Seedlings: 0-0.5m height 2) Saplings: 0.51-2.0m height 3) Mature trees: Above 2m height 4) Regeneration: Sprout with tree stump present Damage status P- Present A- Absent Damage description MSB = Main stem broken off BB = side branch broken or ripped off. TSB = Terminal shoot bitten/ browsed. TU = Tree up-rooted TL = Tree leaning sideways Others = any other form of damage apart from the above mentioned which should be explained in the comments column. The comments column should include the trees condition such as; Seedling, Sprout, Flowering, Bearing seeds and any other observable condition that will be useful in understanding and explaining the observed data. Damage identification I)

Rhino damage: secateurs type of cut.

II)

Elephant damage: Branch ripped off, main stem broken, or the all tree uprooted.

III)

Giraffe damage: selective removal of the upper soft twigs at the tree crown.

IV)

Other: small browse marks at the supple tips at low levels by small browser mammals. 47

Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy

Damage aging i) Fresh; within 48 hours after browsing, white and wet/green ii) Recent: Two weeks to 12 months old, dry and yellow to brown in color iii) Old: 18 months old; brown to dark color and some recovery of the bark. Crematogaster antâ&#x20AC;&#x2122;s species The head thorax and abdomen colors: R: red, B: black. 1. RRB 2. RBB 3. BRB 4. BBR

48 Joseph K. Makau @ 2010


Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy REFERENCE i) Anon. (1999). Kenya’s black rhinos. Handbook for Earthwatch volunteers. ii) Barnes, R.F.W., Barnes,K.L., and E.B. Kapela. 1994. The long-term impact of elephant browsing on

baobab trees at Msembe, ruaha National park, Tanzania. Afr.J.

Ecol.32:a77-184. iii) Birkett, A.(2002). The impact of giraffe, rhino and elephant on the habitat of a black rhino sanctuary in Kenya. Afr. J. Ecol.40:276-282. iv) Birkett, Alan; Stevens-Wood & Barry; May 2005. 'Effect of low rainfall and browsing by large herbivores on an enclosed savannah habitat in Kenya.' Afr. J. Eco., Volume 43, Number 2, pp. 123-130(8) v) Bond,W.J., and D. loffell. 2001. Introduction to changes of acacia distribution in a South African savanna. Afr. J. Ecol.39:286-294. vi) Coe, M. & Coe, C. (1987) Large herbivores, Acacia trees, and bruchid beetles. South Afr. J. Sci. 83, 624–635. vii) Croze, H.(1974b) The Seronera bull problem. I I. E. Afr.Wild. J.12,29^47. viii)

Cumming, D.H.M. (1982) The influence of large herbivores on savanna structure

in Africa. In: Ecology of Tropical Savannas (Eds B. J. Huntley and B. H. Walker). Springer-Verlag, New York. ix) Dublin, H.T. (1995). Vegetation dynamics in the Serengeti-Mara ecosystem: the role of elephants, fire, and other factors. In: Serengeti II: Dynamics of Ecosystem (Eds A. R. E. Sinclair and P. Arcese). University of Chicago Press, Chicago. x) Du Toit, J.T., Bryant, J.P. & Frisby, K. (1990) Regrowth and palatability of shoots following pruning by African savanna browsers. Ecology 71, 149–153. xi) Dublin, H.T., Sinclair, A.R.E. & McGlade, J. (1990) Elephants and fires as causes of multiple stable states in the Serengeti–Mara woodlands. J. Anim. Ecol. 59, 1147– 1164. iii) Field, C.R. & Ross, I.C. (1976) The savanna ecology of Kidepo Valley National Park. II Feeding ecology of elephant and giraffe. E. Afr. Wild. J. 14, 1–15. iv) Laws, R.M. (1970). Elephants as agents of habitat and landscape change in East Africa. Oikos . 21: 1-15.

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Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy v) Mutisya S. Ngw'eno C. & Douglas K. 2009 The Ecological monitoring department 2nd quarter report (unpublished June 2009). Nanyuki; OPC. vi) McNaughton, S.J. (1979). Grazing as an optimization process: grass-ungulate relationships in the Serengeti. Am. Nat.113, 691-703. vii) Norton-Griffiths, M. (1979). The influence of grazing, browsing and fire on the vegetation dynamics of the Serengeti. In: Serengeti, Dynamics of an Ecosystem (Eds A. R. E. Sinclair and M. Norton-Griffiths). University of Chicago Press, Chicago. viii)

Oloo, T.W., Brett, R. & Young, T.P. (1994) Seasonal variation in the feeding

ecology of black rhinoceros (Diceros bicornis L.) in Laikipia, Kenya. Afr. J. Ecol. 32, 142–157. ix) Pellew, R.A. (1984) The feeding ecology of a selective browser, the giraffe Giraffa camelopardalis tippelskirchi. J. Zool. 2-02, 57–81. x) Pellew, R.A. (1983) The impacts of elephant, giraffe and fire upon the Acacia tortilis woodlands of the Serengeti. Afr. J. Ecol. 21,41^74. xi) Pellew, R.A. (1983b) The giraffe and its food resource in the Serengeti.I. Composition, biomass and production of available browse. Afr. J. Ecol. 21, 241^267. xii) Pellew, R.A. (1983c) The giraffe and its food resource in the Serengeti.I I. Response of the giraffe population to changes in the food supply. Afr. J. Ecol. 21, 269^283. xiii)

Ruess, R. W.&Halter F.L. (1990) The impact of large herbivores on the Seronera woodlands, Serengeti National Park, Tanzania. Afr. J. Ecol. 28, 259^275.

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Ruess, R.W. & Halter, F.L. (1990) The impact of large herbivores on the Seronera

woodlands, Serengeti National Park, Tanzania Afr. J. Ecol. 28, 259–275. xv) Van de Vijver, C. A. D. M., Foley, C. A. & Olff, H.( 1999) Changes in the

woody

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www.conbio.org/activities/meetings/2008/program/MONDAY_14_July.pdf 50 Joseph K. Makau @ 2010

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Damage stratification on Acacia drepanolobium at Ol Pejeta conservancy xvii)

Wahungu G. M., Mureu L. K. and Macharia P. G (2009) Variability in survival

and mortality of Acacia drepanolobuim Sjøstedt following prescribed burning at Ol pejeta conservancy, Kenya (Early release; Afr. J. Ecology) xviii) Walter, H. (1971) Ecology of Tropical and Subtropical Vegetation (Ed. J. H. Burnett) transl. by D. Muller-Dombois. Oliver and Boyd, Edinburgh. xix)

Western, D. & Praet, C.V. (1973) Cyclical changes in the habitat and climate of

an East African ecosystem. Nature: 241, 104â&#x20AC;&#x201C;106.

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Joseph Makau BSc Dessertation on Acacia Drepanolobium survival