PRODUCTIVITY OF CAMEL THORN (Acacia. erioloba) AND ANA TREE (Acacia albida) SPECIES AND THE FACTORS THAT MAY LIMIT MAXIMUM PRODUCTION: AN INDEX'

Transcription

1 PRODUCTIVITY OF CAMEL THORN (Acacia. erilba) AND ANA TREE (Acacia albida) SPECIES AND THE FACTORS THAT MAY LIMIT MAXIMUM PRODUCTION: AN INDEX' NAME OF STUDENT: HELMUTH TJIKURUNDA NAME OF SCHOOL: POLYTECHNIC OF NAMIBIA DEPARTMENT: NAME OF TUTOR: DUTY STATION: RESEARCH CENTRE SUPERVISOR: DATE: NATURE CONSERVATION DA VE JOUBERT GOBABEB TRAINING AND JOH HENSCHEL OLA VI MAKUTI JUL Y/OCTOBER 2002

2 CONTENTS PAGE NO. 1. Abstract 1 2. Intrductin Objectives Methds Study area 4 6. Results Discussin Cnclusins and Recmmendatins Acknwledgements References Appendix Appendix 2 15

3 PROJECT REPORT PRODUCTIVITY OF THE CAMEL THORN (Acacia erilaba) AND ANA TREE (Acacia albida) SPECIES IN THE KUISEB RIVER A D THE FACTORS THAT MAY LIMIT MAXIMUM PRODUCTION: AN INDEX I. ABSTRACT A study was dne n the prductivity f tw tree species, Acacia erilba and Acacia albida, in the river. The aim f the study was t determine factrs affecting the prductin f flwers and pds f the tw species and t create an index fr lng-term mnitring f the vegetatin in the river with emphasis n these tw species. These factrs are height f tree, canpy width f tree and water availabil ity in the river. Other factrs such as phenlgy, river prfile and utilisatin f the trees by animals were als studied. It was fund that canpy width plays an imprtant rle in the flwer and pd prductin f these species. These species has a specific preference fr river prfile and prduce better in certain areas than in thers. Bth species have well-develped deep tap rt systems that reach grund water. Animals playa rle in the prductivity f these trees as they feed n the tree and its prducts. 2. INTRODUCTION The Gbabeb Training and Research Centre was established t further understanding f the desert envirnment. The Centre (23 33'S, 15 02'E) is situated in the basin f the Kuiseb River. The Kuiseb River is the primary surce f life fr many species in the desert (Henschel pers.cm, 2002). The mean annual relative humidity is 50 % and the mean temperature is 21.1 C (Henschel et a/2000). Flds riginating frm distant rainfalls are the surce f water and nutrients that keep the riparian frest alng the Kuiseb River alive (Jacbsn et a/1995). Accrding t Jacbsn et al (1995) these frests are very sensitive t changes in runff frm upstream regins caused by climate change r dam building. Abstractin f water fr human activities is by far the mst threatening factr fr the survival f many species in ephemeral rivers (De Klerk, 2002). Water is harvested extensively in the upper catchments thrugh damming (De Klerk, 2002). This culd reduce water availability in lwer catchments where it is further reduced by abstractin. De Klerk (2002) highlighted that the

4 damming in the upper catchments f the Kuiseb has had a tremendus effect n the areas dwnstream and that dead trees in the river are ne factr indicating such effect. Jubert, pers.cm (2002) pinted ut that ephemeral rivers are mre affected by upstream events than variatin in rainfall in the desert. Pd and flwer prductin f vegetatin in the Kuiseb River might pssibly be affected by this abstractin, as water is an essential cmpnent f plant life (Kramer, 1980). Plants are primary prducers (Smith, 1980) and frm the basis f the fd chain in any ecsystem and are imprtant cmpnents f the ecsystem (Chapman & Reiss, 1992). Accrding t Smith (1980) the animals rely n fd stred in the seeds. Therefre, the prductivity f trees can largely determine and regulate the ppulatin f animals. A brehle was drilled in the river t supply the water needs f the Gbabeb Centre. If used unsustainably, the water level in the brehle might fluctuate and cntribute t the changes in prductivity f river vegetatin. Studies dne by Wd (1989), shwed that Acacia albida have lng rts that extend deep int the grund t access grund water. Phenlgy culd be used as an indicatr f bth the ecsystem health and grund water level fr the study f pd and flwer prductin f the vegetatin in the Kuiseb River. The presence f animals might als affect the prductin f the trees in the river. Birds and insects feed n the seeds and flwers f trees (Wd, 1989) as d livestck, thus it may appear t sme eclgists that trees have a lwer prductivity during their bservatin than is the case. It was decided that an index be develped t study the vegetatin fr these trees. This determinatin will serve as the basis fr lng-term mnitring f the vegetatin in the river. 3. OBJECTIVES PROJECT OBJECTIVES 1. T estimate the pd and flwer prductin f Acacia erilba and Acacia albida and create an index f ttal cunts fr prvisin f baseline data fr further mnitring f these vegetatin. 2. T relate the pd and flwer prductin f the tw trees t height and canpy width as well as water availability in the area. 3. T review literature n the phenlgy f the tw species and cmpare the rt structures f the tw species in terms f water accessibility and relate the findings t their pd and flwer prductin. 2

5 4. T determine ther factrs that might cause changes in the pd and flwer prductin f the tw species, such as psitin in relatin t the riverbed and the utilisatin PERSONAL by animals. OBJECTIVES T gain experience in cnducting research and write scientific reprts T cnvert my theretical knwledge btained frm schl int practice 4. METHODS AND MATERIALS 1. T estimate the flwer and seed prductin f the camel thrn and the ana tree and create an index. A map f the river cmpiled by Grieve et al (2001) including the species name, number f tree, heights and canpy widths f trees was used t select the study area. Cunting was dne in three sites and the number f trees was cnsidered, as the study was nt a sampling study but ttal cunt. The ttal number f flwers and pds frm individual trees were cunted. Cunting was dne using a tally cunter as utlined belw: In the case f tall trees where ttal cunting was impssible the methd was mdified in the fllwing way: ne branch within reach f the bserver was cunted as yu wuld cunt a flck f flying birds r a grup f running springbks. All branches that have the same size as the cunted branch were cunted. The ttal number f flwers as cunted frm the first branch was multiplied by the number f branches t give an estimate f ttal numbers f flwer per tree. In the case f seeds (pds), all pds that are visible t the bserver were cunted. The methd is nt cmpletely standardised and can be imprved when used with ther methds f vegetatin surveying such as fixed-pint phtgraphy. 2. T relate the pd and flwer prductin f these trees t height and canpy width, as well as water availability in the area: A study was dne in the river by Grieve et al (2001), where the height and canpy widths f all trees were measured in the fllwing way: The bserver wh's arm was measured, mved away frm the tree hlding a ruler at shulder height. When the ruler was level with the tip f the tree the distance frm bserver t tree was 3

6 measured. The ruler reading was taken as height f the tree in centimetres. All readings were cnverted t meters and actual heights were btained using the fllwing frmula, (AxR)7D, where A is Arm length, R is ruler reading and D is distance frm the tree t the bserver. The reasn was t establish a lng-term mnitring strategy f the vegetatin in the river. The infrmatin was used in this study t relate the height and canpy width f these species t their pd and flwer prductin. Data n the brehle depth and river flw as well as rainfall was used t relate pd and flwer prductin f the tw species t water availability. Literature n water requirement f the tw species was reviewed. 3. T review literature n the and phenlgy f the tw species and cmpare the rt structures f the tw species in terms f water accessibility and relate the findings t their pd and flwer prductin: Relevant literature was reviewed t ascertain the rt structure with regard t water abstractin and cnductin f the tw species. This infrmatin was used t relate the phenlgy f the tw species t their pd and flwer prductin and water. The river prfile in which the tree is grwing was als recrded t determine if the psitin where the tree is grwing affects its prductin. 4. T determine ther factrs that might cause changes in the pd and flwer prductin f the tw species such as the psitin in relatin t the riverbed and utilisatin by animals: During the cunting f the seeds and the flwers, the presence f bird, insects, mammals and tracks f dmestic animals were bserved during every cunt. This was dne by lking fr animals physically, signs such as faeces, sunds and tracks as well as signs f brwsing n the branches. Literature n the uses f trees was reviewed t supplement this data. 5. STUDY AREA (SEE APPENDICES 1 & 2) The study area was in the middle part f the Kuiseb River in Gbabeb Training and Research Centre (23 33'S, 15 02'E) situated in the Central Namib Desert. The Kuiseb River acrss the desert savannah transitin Giess (1971) is ne the ephemeral rivers in the western part f Namibia. 4

7 6. RESULTS A ttal f 52 Acacia erilba were cunted but nt all trees had flwers and r pds. The results shwed that there is a relatinship between canpy width f this species and the number f flwers bserved as shwed n (figure la). The number f flwers and pds f Acacia erilba des nt relate t its height (figure Ib). Scatterplt (helmuth.sta 10v*53c) NO_FLOW (L)= *x+eps NO_PODS (R)= *x+eps Ul 4000 Q; :: ""0 z _----tj' C,-' '.. NO_FLOW (L: -1000O-~~~~--~~~~--~--~--~~~~----~ -500 a '0... NO_PODS (R) ~,..--- Width (m) i!l. ~,., a. -" ", z Figure la: Number f flwers and pds f Acacia erilba in relatin t its canpy width. The Acacia albida did nt have pds during the study. Therefre, results were nt cmpared t Acacia erilba. Results btained shws that bth the height and canpy width f Acacia albida have an influence n the number f flwers bserved (figure l c & Id). 5

8 Scatterplt (helmuth.sta 10v'53c) NO_FLOW (L)= *x+eps NO_PODS (R)= *x+eps c [I> 4000 Q) i: = '0 ci 2000 z , {l a '0 z 0~ ~ Cl. --~-;;~-~ ~--fclc~~~~gi~~~c~ cr---~ u---~~--~------~----~------~------~~ NO_FLOW(L '0... NO_PODS (R) Height (m) Figure I b: Number f flwers and pds f Acacia erilba in relatin t its height. A_WIDTH vs. A_FLOWER (Casewise MD deletin) A_FLOWER = A_WIDTH Crrelatin: r = ' [I> Q) i: 0 0= '0 ci z »->: '0... Regressin 26 95% cnfid Canpy width (m) Figure Ic: Number f flwers f Acacia albida in relatin t its canpy. 6

9 A_HEIGHT vs. A_FLOWER (Casewise MD deletin) A_FLOWER = * A_HEIGHT Crrelatin: r = !'! 1000 Q) >: 0 -= ill Ll E :::J 400 Z Regressin /0 cnfid Height (m) Figure ld: Number f flwers f Acacia albida in relatin t its height. The average number, height and canpy widths f the tw species as well as their average number f flwers and pds are shwn (table 1). The table shws a high average flwer prductin fr the Acacia erilba. The pds f Acacia albida were unavailable during the study perid. The table als shws that Acacia albida grws taller than Acacia erilba but have a smaller canpy. Table 1: Summary f average number f trees, flwers, pds, height and width f Acacia erilba and Acacia albida. Species Average n. f Average n. f A verage height Average canpy Flwers pds (rn) width (m) (inflrescence) Acacia erilba Acacia albida 216 Nt available The table is nt a cmparisn f the tw species but rather a summary due t unequal number f individuals cunted fr0111each species. Number f flwers and pds in relatin t river prfiles are shwn n (figure 2a & 2b) in percentages. There was a high number f bth the flwers and pds f Acacia 7

10 erilba cunted alng the main channel f the river but lw in the riparian frest (figure 2a). O%f101.er prcuctkn % seed prcx:luctin.--.. ~ ~ 60.00%- :.g 50.00% ::J '840.00%... :: % Q) ~ 20.00% ;:;:::: ' % c r 0.00% '0 8.. River bank l'v'einchannel Riparian frest River pufile Figure 2a: Percentage f flwer and pd prductin f Acacia erilba in relatin t river prfile. 8

11 Figure 2b shws results f the number f flwers f ana tree. There was a high number f flwers cunted in the riparian frest but lw in the ther tw prfiles f the river. (f) % (i) 9000% 3: 80.00% 0 ;;: 70.00% % % 0 Z ~ 40.00% - (i) 30.00% OJ r % (i) 10.00% > j <{ 0.00% 1- - River bank Main channel Riparian frest River prfile.% flwer prductin Figure 2b: Percentage f flwer prductin fr the Acacia albida in relatin t the river prfi Ie. 7. DISCUSSION Prductin in relatin t height, canpy width f tree and water avai lability Acacia erilba The number f flwers and pds f Acacia erilba is related t its canpy width (figure Ia & 1b). There are a number f reasns t explain this relatinship. A tree might be tall but if it des nt have a large canpy it will nt have a high prductin f pds r flwers. Thus, trees that are widely spaced have a better chance f spreading their crwns and prducing many pds and flwers. A crwn f was recrded fr this species during the study and in ther studies, it was recrded at 17.5m (Carr, 1976). This is just ne but pssible reasn why canpy is related t number f flwers and pds. This species was in full blm and many pds had still nt drpped during the study (table 1). Timberlake et al. (1999) did a study n Acacia erilba and fund ut that it des nt rely n rainfall but its grwth is necessitated by the availability f grundwater. The rt system is structured in a way that it can reach grundwater. Mean annual rainfall in this area is very lw (llmm) (Henschel et ai, 2000). This amunt f rain is nt sufficient if trees have t depend n it, which explains why the rts f trees in the desert have t adapt in sme ways t harvest grund water. 9

12 Acacia albida The study fund ut that there is a relatinship between height and canpy f this species and the number f flwers fr the few trees that still had flwers (figure 1c & 1d). Pssible reasn is that Acacia albida grws very tall but canpy is relatively small, at average f 8.6m as recrded during the study. The branches grw almst alng the entire height f the stem r trunk as bserved during the study. The Acacia albida is dependent n sme frm f misture and in sme instances, catastrphic flds are necessary t create new sandbanks fr its establishment (Timberlake et. al, 1999). Hwever, during perids f ttal absence f rain, high temperature, lw humidity and high evaptranspiratin, the rt system has a taprt that grws rapidly until it reaches a zne f adequate misture. This explains why ana trees thrive in the Kuiseb River. Prductin in relatin t Lcatin/River prfile Acacia erilba in the main channel f the river prduces a high number f bth pds and flwers (figure 2a). A high number f this tree was bserved alng the river banks and away frm the river. The few trees that are grwing in the main channel are very large and have big canpies, which is why there was a high number f flwers recrded in the main channel f the river. Acacia albida prduced a high number f flwers in the riparian frest. The reasn fr high prductin f flwers fr the Acacia albida culd be as a result f the high ppulatin f this tree in the riparian frest. Prductivity in relatin t Phenlgy Acacia erilba is semi-deciduus and can lse leaves fr a shrt perid Rdt (1998). It flwers frm the end f August thrugh t Octber, as bserved during the study. Accrding t Rdt (1998), it btains water by penetrating the rts deep int the sil t a great depth. This accunts fr the green fliage thrughut the year, she added. A study referred by (Rdt, 1998) shws that the rts f the Acacia erilba reached a depth f 46 m. This slwer grwing but mst lng-lived acacia f all is desert adapted and grws well prvided that there is sufficient grundwater (Fagg & Barnes. 1990). Acacia erilba des nt ndulate naturally but it gets mst f its nutrients frm grundwater and nt thrugh bilgical fixatin (Timberlake et al, 1999). This explains the reasn fr its deep taprt, which is fanned during the first 10

13 year f its grwth, he added. While camel thrn des well in the dry sandy sil, Acacia albida is fund t d well in riverine r drainage line (Timberlake et al, 1999). As frm Timberlake et al (1999), Acacia albida is deciduus and lses leaves during the entire wet seasn and starts new leaves during the dry seasn (April/May). This strange and rather unique phenlgy led mst taxnmists t be cnfused regarding its classificatin and ended up classifying it in its wn class. The rts f Acacia albida grw rapidly and were recrded at a depth f 40 m r mre depending n the accessibility f grundwater and may even reach the water table Wd (1989). A study dne by (Wd, 1989) n the develpment f rts f yung Acacia albida shwed that the rts reach a depth f 60 ern in 60 days. Prductivity and utilisatin by animals Owing t the high nutritinal cntent in these tw species, they are highly used by almst a wide variety f rganisms. Gats as bserved in the river specifically prefer the Acacia albida, whereas the dnkeys eat the pds f Acacia erilba Wd (1989). Wildlife uses the trees extensively. The name Camel Thrn was given after evidence that giraffes (Came/pardalis giraffaei brwse extensively n this species (Rdt, 1998). 8. CONCLUSIONS AND RECOMMENDATIONS Height is nt as imprtant as canpy in the prductin f Acacia erilba, but plays a rle in the prductin f Acacia albida. Prductin differs by lcatin f the species in the river. Acacia erilba is nt directly dependent n free water near the surface and grws away frm the river. Acacia a/bida depends very much n misture thus grws nly in r near the river. Acacia erilba has high number f flwers and pds in the main channel f the river and Acacia albida has high number f flwers in the riparian frest. Bth species have a well-develped rt system t reach grund water. Animals use the trees and this shuld be cnsidered when studying the pd and flwer prductin f these species. T mnitr the pd and flwer prductin f these species, ttal cunts must be dne n the whle tree. Large trees must be mnitred in the manner as utlined in the methds. The technique used in determining the index is based n the judgement f the bserver and shuld be used in cmbinatin with ther II

14 methds such as fixed-pint phtgraphy. This will nt nly accunt fr biases but als give a visual estimate n the changes f the vegetatin ver a lng perid. 9. ACKNOWLEDGEMENTS I wuld like t thank the fllwing peple fr their supprt and cntributin twards this reprt: Dr. Jh Henschel, Executive Directr f Gbabeb Training and Research (GTRC) Centre, Olavi Makuti, Research Technician at GTRC, Dave Jubert, Eclgy Lecturer at Plytechnic f Namibia, Vernika Drausnick, German Internatinal Student, Nadia Manning & Emily Westergaard, Grinnell fellws, Thmas Nergaard, PhD student, University f Zurich, Switzerland, Lesley Parenzee, Data manager f Desert Research Fundatin f Namibia (DRFN) and all the staff members fgtrc anddrfn. 10. REFERENCES Carr, J.D The Suth African Acacias. Cnservatin Press (Pty) Ltd. Jhannesburg, Suth Africa. 323 pp. Chapman, ll & Reiss, M.l Eclgy Principles and Applicatins. Press Syndicate f the University f Cambridge. Cambridge, England. 293 pp. Fagg, C.W., Barnes, R.D AFRICAN ACACIAS: A STUDY AND ACQUISITION OF THE GENETIC RESOURCE. Final Reprt. Oxfrd Frestry Institute. University f Oxfrd. Oxfrd De Klerk, M Aquatic Ecsystem Management, Study Guide. Windhek: Plytechnic f Namibia. Grieve, c., Makuti, 0., Oetjens, M., Meinhld, K., Unger, H., Madrell, G., Muller, M., Hensel, N Vegetatin mapping f the Kuiseb River. Unpublished reprt. Gbabeb Training and Research Centre: Desert Research Fundatin f Namibia Henschel, J Persnal cmmunicatin. Executive Directr, Gbabeb Training and Research Centre. Namibia. Henschel, L, Pallett, l, Parenzee, L., Makuti, 0., Mtuleni, Y., Seely, M.K Fauna and Flra f Gbabeb with a Descriptin f the lng-term Pitfall Trapping Prject. Unpublished reprt. Desert Research fundatin f Namibia. Gbabeb. Namibia. 12

15 Jacbsn, P.J.,Jacbsn, K.M and Seely, M.K Ephemeral Rivers and their Catchments: Sustainable Peple and Develpment in Western Namibia. Desert Research Fundatin f Namibia, Windhek. 160 pp. Jubert, D Persnal cmmunicatin. Eclgy Lecturer, Plytechnic f Namibia. Windhek. Namibia. Kramer, P.l. & Turner. N.C Adaptatins f Plants t Water and High Temperature Stress. A Wiley-Interscience Publicatin and Sns, Inc. New Yrk. U.S.A. 482 pp. Rdt, V Trees and Shrubs f the Okavang Delta. Published by Shell Btswana (Pty) Ltd. Gabrne. Btswana. 213 pp. Smith, R.L Eclgy and Field Bilgy. Harper & Rw Publishers. New Yrk U.S.A. 835 pp. Timberlake, J, Fagg, C, & Barnes, R Field Guide t the Acacias f Zimbabwe. CBC Publishers. Harare, Zimbabwe. 160 pp. Wd, P.J Faidherbia Albida: A Mngraph. Oxfrd Frestry Institute. Oxfrd, England. 66 pp. 13

16 11. APPEN DIX 1: Map 0f Kuise. b River shwmg. lcatin 0fGbabeb. 14

17 12. APPENDIX 2: MAP OF RIVER, SURVEYED AREA ONLY, SHOWING THE STUDY SITE (shaded area). 15