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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/230534874 Distribution, density and impact of invasiveplants in Lake Nakuru National Park, Kenya Article in African Journal of Ecology · November 2010 DOI: 10.1111/j.1365-2028.2009.01191.x CITATIONS 4 READS 604 3 authors: Caroline Ng'wenoUniversity of Wyoming 4 PUBLICATIONS 64 CITATIONS SEE PROFILE S.M. MwasiSchool for Field Studies 12 PUBLICATIONS 36 CITATIONS SEE PROFILE Jim KairuUniversity of Namibia 5 PUBLICATIONS 55 CITATIONS SEE PROFILE All content following this page was uploaded by Caroline Ng'weno on 16 January 2017. The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the srcinal documentand are linked to publications on ResearchGate, letting you access and read them immediately. Distribution, density and impact of invasive plantsin Lake Nakuru National Park, Kenya Caroline C. Ng’weno 1 , Shem M. Mwasi 1 * and Jim K. Kairu 2 1 Department of Environmental Biology and Health, School of Environmental Studies, Moi University, PO Box 3900, Eldoret 30100 and 2 Department of Wildlife Management, School of Natural Resources Management, Moi University, PO Box 1125, Eldoret 30100, Kenya Abstract Invasive plants have invaded swathes of grasslands in LakeNakuru National Park thus necessitating the Park man-agement to institute measures to control them. Despitethis, information on the status and impact of invasiveplants in these grasslands is lacking. Six grassland typeswere identified and assigned random numbers. Five studysites were then randomly selected from each grasslandtype. The Point-Centre Quarter method was used todetermine the distribution and density of seven majorinvasive plants, whilst their impact was assessed by com-paring biomass and crude protein content of importantforage grasses in invaded and noninvaded grasslands.Results show that the distribution of invasive plants didnot differ among the grasslands ( F 5, 30 = 1.47, P = 0.229)buttheirdensitiesdifferedamongtheplants( F 6,30 = 20.99, P < 0.001). The mean biomass in invaded and nonin-vaded grasslands (22 g m ) 2 versus 37.2 g m ) 2 ) wassignificantly different ( t -test, P < 0.05), while crude pro-tein content of grasses in invaded (7.73, % DM) andnoninvaded (9.3, % DM) patches was not significantlydifferent ( t -test; P > 0.05). Our results suggest that inva-sive plants lower grass production and hence might reducefood availability to grazers. Key words: biomass, crude protein, density, forage, grass-lands, invasive plants Re´sume´ Des plantes invasives ont envahi des e´tendues de prairiesdu Parc National du Lac Nakuru, ce qui oblige la gestiondu parc a` instaurer des mesures pour les controˆler. Malgre´cela, on manque toujours d’informations sur le statut etl’impact des plantes invasives sur ces prairies. On a iden-tifie´ six types de prairies et on leur a attribue´ un nume´ro auhasard. On a ensuite choisi au hasard cinq sites d’e´tudepour chaque type. La me´thode des quartiers par pointcentre´ fut utilise´e pour de´terminer la distribution et ladensite´ de sept plantes invasives importantes, tandis quel’on e´valuait leur impact en comparant la biomasse et lecontenu en prote´ine brute des herbes fourrage`res impor-tantes dans les prairies envahies et non envahies. Lesre´sultats montrent que la distribution des plantes invasivesne diffe´rait pas selon les prairies (F 5,30 = 1,47, P = 0,229), mais que leur densite´ diffe´rait parmi les plantes ( F 6, 30 = 20.99, P < 0.001). La biomasse moy-enne dans les prairies envahies et non envahies (22 g m ) 2 versus 37.2 g m ) 2 ) e´tait significativement diffe´rente (test de t : P < 0,05) alors que le contenu en prote´ine brutedans les ıˆlots de prairies envahies (7,73, % DM) et nonenvahies (9,3, % DM) n’e´tait pas significativement diffe´rent (Test de t: P > 0,05). Nos re´sultats sugge`rent que lesplantes invasives diminuent la production herbeuse etpourraient donc re´duire la disponibilite´ de nourriture pourles animaux qui broutent. Introduction The term invasive species refers to either indigenous ornonindigenous species that can heavily colonize a partic-ular habitat (Colautti & MacIsaac, 2004). Invasive plantsare known to be highly adaptable and have a diversity of survival strategies (Ivens, 1989). These plants havea competitive ability to spread into native ecosystems,displacing indigenous plants and creating ecologicalimbalances between grasses and shrubs in natural andagro-ecosystems (Pimentel, 2002), consequently affectingthe structure and function of these ecosystems by bringingabout changes in species composition, dominant life forms, * Correspondence : E-mail:
[email protected] 2009 Blackwell Publishing Ltd, Afr. J. Ecol. , 48, 905–913 905 nutrient cycling, hydrology and decomposition (Oba et al. ,2000).Extensive reviews of invasive plants in African range-lands that would inform policy development by rangelandmanagers are generally lacking (White, 1980; Coppock,1994) with the most referred to study being that con-ducted in Kruger National Park in South Africa (Foxcroft &Richardson, 2003). In East Africa, few ecological studieshave focused on invasive plants (Sheil, 1994; Lyons, 2000;Coetzee et al. , 2007). Although studies on vegetation havebeen conducted in Lake Nakuru National Park byMutangah (1994) and Mwangi & Western (1998), none of them has focused on plant invasions despite invasivesbeing a major habitat management problem in the Park’sgrasslands at the moment.The extensive spread of invasive plants in the Park’sgrasslands has been worrying the Park management forsome time now prompting it to start thinking aboutmeasures to control it. Interaction between invasiveplants and indigenous grasses may lead to a decline inquality and quantity of forage grasses that might resultinto negative consequences for grazers. Lake NakuruNational Park is reported to have a high density of grazers (Mwasi, 2002) whose forage quality and quantityare likely to be compromised by invasive plants. Thepresent study thus investigated the density, distributionand impact of invasive plants in Lake Nakuru NationalPark. The results will provide baseline information on thecurrent plant invasion status of the grasslands and site-based ecological solutions to controlling and managinginvasive plants. Materials and methods Study area Lake Nakuru National Park lies between latitude 0 18 ¢ Sand 0 27 ¢ S; longitude 36 1.5 ¢ E and 39 9.25 ¢ E on the floorof the Kenyan Rift Valley with an approximate altituderange of 1760–2080 m above sea level. Five seasonalrivers (Njoro, Lamuriak, Makalia, Naishi and Nderit) drainthrough the Park (Fig. 1).Mean annual rainfall range between 876 and1050 mm distributed in a bimodal pattern, whereby twowet and two dry seasons occur during the year. The shortwet season starts in October and ends in December, whilethe long wet season starts in March and ends in June. Inbetween, are two dry seasons: short dry (January toFebruary) and long dry (July to September). The meandaily minimum and maximum temperatures are 8.2 and25.6 C respectively.The Park has undergone major changes in size since itwas gazetted in 1968. The srcinal size was 63.5 km 2 of which 42 km 2 was occupied by Lake Nakuru and itsshoreline (Mwasi, 2002). It was further expanded in 1973to the current 188 km 2 and enclosed in 1976 along itsperimeter by a chain link wire fence, which was laterreinforced by a perimeter electric fence in 1987 to protectthe then newly introduced black rhinoceros ( Dicerosbicornis L.).The Park has experienced changes in the densities of grazers over time, with those of the large-bodied grazers,especially buffalo ( Syncerus caffer Sparrman) and Burchell’szebra ( Equus burchelli Gray) increasing, while those of themedium and small sized grazers such as the defassawaterbuck ( Kobus defassa Ru¨ppell) and Bohor reedbuck( Redunca redunca Pallas) declining. However, there is a netincrease in the overall grazer density with the conse-quential effect of increased overgrazing in the grasslandsespecially during the dry season.Various types of vegetation are observed in the Park, themost dominant being grasslands (Fig. 2). Occasionalanthropogenic fires burn grasslands in the Park during thedry season, although the vegetation usually recoversduring the subsequent wet season.The growing period for most plants in the Park is tiedwith the wet season with the maximum herbaceous phy-tomass occurring in the middle of the long wet season(May) and the lowest at the end of the short dry season(February). All forage grasses are synchronous in theirsprouting, growth and drying up phases. Description of invasive plantsSolanum incanum L. This is a small, low perennial shrub,usually 60–150 cm high with leaves densely or less den-sely covered with hairs (usually very white-velvety). Someraces appear to be indigenous in dry areas and othersintroduced and found only in cultivated and waste places(Ivens, 1989). It is a poisonous plant (Verdcourt & Trump, 1969). Cattle and sheep do not eat it, but goats eat theleaves when no better browse is available. Sida schimperiana Hochst. ex A.Rich. This is a dwarf annual or perennial shrub 15–60 cm high with short hardbranches and small simple leaves. It is a widespread rud-eral with sporadic distribution and provides additional906 Caroline C. Ng’weno et al. 2009 Blackwell Publishing Ltd, Afr. J. Ecol. , 48, 905–913 grazing for goats and sheep in denuded areas where grazeis scarce (Agnew & Agnew, 1994). Lippia javanica (Burm.f.) Spreng. This is an erect, highlybranched, small (sometimes woody) shrub, which canreach a height of 2 m. The stems are covered with shortstiff hairs and have a square appearance when looked at incross-section (Le Roux, 2004). This plant grows in opengrassland, in the bush, as well as on forest margins. It isknown to colonize disturbed areas as a pioneer plant. It ishardy and thus able to grow under harsh conditions withlittle maintenance.It is possible that its aromatic leaves protect it frombrowsing. A study on black rhinoceros diet in NairobiNational Park (Muya & Oguge, 2000) showed thatalthough L. javanica was the most available plant inthe Park, it was only moderately browsed by blackrhinoceros. Urtica massaica Mildbr. This is an erect, almost un-branched, perennial herb that grows wild in nitrogen-richsoils on the edge of fields, stream banks, waste places andclose to cattle kraals and human habitations. Its hairy,erect, single stalks grow in dense clusters giving the plant a LegendRiversNRoadsLake NakuruPark Boundary 30°02’E 0 ° 2 9 ’ S 0 ° 2 7 ’ S 30°02’ E30°12’ E 0 ° 2 7 ’ S 0 ° 2 9 ’ S 30°12’ E R. L a m u d i a k R. N a i s h i R . N d e r i t M . M a k a l i a R. N j o r o Kilometers10864202 Fig 1 Map of Lake Nakuru National Park Plant invasion in grasslands 907 2009 Blackwell Publishing Ltd, Afr. J. Ecol. , 48, 905–913 bushy look. Leaves are dark green on the top and palegreen on the underside. The plant grows to about 1.2 m(Verdcourt, 1992). Ocimum gratissimum L. This is an aromatic, erectperennial herb or soft shrub, up to 2 m tall. The stem isround-quadrangular, much branched, with no hair on thesurface, woody at the base, often with epidermis peeling instrips (Le shu, 1994). Achyranthes aspera L. This is an erect to sprawling, an-nual or sub-woody perennial herb, 0.5–2.0 m in height,with a woody base, upper leaf surface dark green than theunderside (Verdcourt, 1992). It is commonly found inopen, dry places, and in disturbed habitats (e.g. roadsides)and wastelands, where it can form monospecific carpets,but can also be found in forests, from the seashore to2100 m asl (Ivens, 1989). Lantana trifolia L. This is a scrambling herbaceousperennial shrub – introduced into Africa from tropicalAmerica (Verdcourt, 1992) – with hispid stems, stoutrecurved prickles and strong odour that typically grows to2 m tall (Agnew & Agnew, 1994). It requires plenty of sunshine and is drought resistant. Leaves are poisonous to 1012345Kilometers LEGEND Bushed Themada triandra grassland (G1) Cynodon niemfluensis grassland (G3) Chloris gayana grassland (G4) Sporobolus spicatus grassland (G5) Cynodon - Chioris - Themada grassland (G6) Cynodon niemfluensis - wooded acacia xanthophloea grassland (G7)BushlandLocation of TransectsLake NakuruWoodland 30°02’ E30°12’ E30°02’ E30°12’ E 0 ° 2 7 ’ S 0 ° 2 7 ’ S 0 ° 2 9 ’ S 0 ° 2 9 ’ S N Fig 2 Vegetation types and study sites inLake Nakuru National Park 908 Caroline C. Ng’weno et al. 2009 Blackwell Publishing Ltd, Afr. J. Ecol. , 48, 905–913
