Tropical Ecology 57(2): 333-341, 2016 ISSN 0564-3295 © International Society for Tropical Ecology www.tropecol.com Impact of African elephant on baobab along a surface water availability gradient in Mana Pools National Park, Zimbabwe 1 1* 1 2 ONIAS NDORO , CLAYTON MASHAPA , SHAKKIE KATIVU & EDSON GANDIWA 1Tropical Resource Ecology Programme, University of Zimbabwe, P.O. Box MP 167, Mount Pleasant, Harare, Zimbabwe 2School of Wildlife, Ecology and Conservation, Chinhoyi University of Technology, Private Bag 7724, Chinhoyi, Zimbabwe Abstract: An assessment of African elephant (Loxodonta africana) impact on baobabs (Adansonia digitata) was conducted along a surface water availability gradient in Mana Pools National Park, Zimbabwe. Data on baobab height, basal area, density and elephant damage were recorded from three strata with varying distance of 4 km, 26 km and 50 km from the Zambezi River. Rukomechi stratum which is furthest (50 km) from Zambezi River recorded tallest mean baobab height, largest mean basal area, highest mean baobab density and the least level of elephant induced damage on baobabs as compared to study sites on Sapi River and Fourways strata which are all less than 26 km from Zambezi River. It was concluded that there was high disturbance pressure on baobabs close to water sources and this seemed to influence baobab abundance and structure in Mana Pools National Park, Zimbabwe. Key words: Herbivory, proximity, tree density, Zambezi River. Handling Editor: Witness Mojeremane Introduction National Park, South Africa, Brits et al. (2002) recorded low shrub density closer to water sources The African elephant (Loxodonta africana) has and highest shrub density further away from significant impact on vegetation due to its large water sources, whereas, tree density did not show body size and foraging behaviour (Guldemond & much change with distance from water sources. van Aarde 2008). The generation of scientific infor- Gandiwa et al. (2012) recorded a decrease in woody mation on local elephant impact vegetation prefe- density with closeness to natural water sources, rences across relevant spatial and temporal scales suggesting woodland degradation around water is important for decision making in the manage- points in Gonarezhou National Park, Zimbabwe. ment of protected areas for the sustainability of Elsewhere, in northern Botswana, Ben-Shahar both elephants and woodlands (Loarie et al. 2009; (1998) reported that Colophospermum mopane Tafangenyasha 1997). Elephant impacts on woodlands subjected to excessive elephant damage vegetation near water sources has been recorded in had unchanged densities of trees. However, the many protected areas in African savannas (De concentration of elephants around watering points Beer et al. 2006; Gaugris & Van Rooyen 2010; exposes vegetation in the vicinity to herbivory or Gandiwa et al. 2011), and the factors causing trampling threats (Thrash & Derry 1999). differences in impacts are well understood Kupika et al. (2014) found that elephant (Gandiwa et al. 2016; Staub et al. 2013). In Kruger damage to baobabs (Adansonia digitata) was most *Corresponding Author; e-mail: [email protected] 334 ELEPHANT DISTURBANCE ON BAOBABS IN MANA POOLS, ZIMBABWE severe in areas located closer to water sources in concern that elephant induced annual baobab Gonarezhou National Park, southern Zimbabwe. mortality rate of 7.3 % in Mana Pools National Elephants usually encounter baobabs close to Park and observed that elephant foraging behavior permanent water sources. This increases the was a distinctly seasonal phenomena related to the chances of bark stripping and baobab damage as position of woodlands relative to perennial water recorded in several earlier studies (Brits et al. sources. Several factors could explain the spatial 2002; Gandiwa et al. 2011; Gandiwa et al. 2012; distribution of baobabs in African savanna as they Kupika et al. 2014; Mukwashi et al. 2012). are affected by a number of establishment factors, However, there have been suggestions that baobab such as herbivory (Mashapa et al. 2014), past populations are unaffected by elephants in certain human activities (O’Connor & Campbell 1986), habitats because of difficult access (Edkins et al. droughts (De Smedt et al. 2012), climate change 2007; Mpofu et al. 2012; Weyerhaeuser 1985). A (Sanchez et al. 2011) or soil type (Mashapa et al. better understanding of local factors influencing 2013). elephant impact on woody species is thought to be The increasing elephant population in important in the management of plant biodiversity northern Mana Pools National Park, Zimbabwe as well as other large herbivore species, which has been a cause for concern (Dunham & du Toit often congregate around perennial water sources 2012). As elephants become increasingly confined during the dry season (Chamaillé-Jammes et al. to smaller fragmented landscapes coupled with 2009; Gandiwa et al. 2012). African elephant their increasing densities there is concern over the distribution is suggested to be regulated by surface modification of the vegetation and biodiversity water availability (Redfern et al. 2003), with herds (Gandiwa et al. 2011; Loarie et al. 2009). The staying less than 10 km radius from permanent present study sought to understand the effect of water sources on average during the dry season elephant browsing pressure on baobabs along a (Loarie et al. 2009; Stokke & du Toit 2002). surface water availability gradient in Mana Pools The African baobab is a deciduous woody- National Park, Zimbabwe, given that the influence succulent plant native to dry regions of sub- of elephant impact on woody species can be site Saharan Africa (Wickens & Lowe 2008). Lack of specific and vary across space and time according recruitment seems to threaten the baobabs, as to elephant density and/or among other factors (De little natural regeneration has been reported in Smedt et al. 2012; Mashapa et al. 2013, 2014; different parts of Africa (e.g., Edkins et al. 2008; O’Connor & Campbell 1986; Sanchez et al. 2011). Schumann et al. 2010). Low natural regeneration The specific objectives of the study were: (i) to of baobabs has been partially related to high investigate baobab density, height and basal area frequents of drought events in dry lands of Africa in relation to distance from a major perennial (Sanchez et al. 2011; Wickens & Lowe 2008). water source, and (ii) to determine elephant Baobabs are mainly dispersed by elephants and induced baobab damage in relation to distance baboons (Papio spp.), and are under considerable from a major perennial water source. pressure due to use by humans for different purposes (Dovie 2003; Schumann et al. 2010; Materials and methods Wickens & Lowe 2008). Bark harvesting for small- scale commercial sale of mats was reported being Study area done un-sustainably in Zimbabwe (Dovie 2003). The baobab plant is of conservation importance in Designated as a United Nations Educational, Africa mainly because it is keystone species of Scientific and Cultural Organization World Heri- ecological significance of the important ecosystem tage Site in 1984, Mana Pools National Park function it plays (Buchmann et al. 2010; (2,196 km2) is located in northern Zimbabwe, Schumann et al. 2010; Symes & Perrin 2004; between latitudes 15° 40 to 16° 20 S and longi- Wickens & Lowe 2008). tudes 29° 08 to 29° 45 E (Heath 1986; ZPWMA In Zimbabwe, elephant foraging behavior, and 2011). To the north, the park is bordered by the impacts on baobabs have been studied in Mana Pools Zambezi River which forms the international National Park, northern Zimbabwe (Swanepoel boundary with Zambia and to the south it is 1993; Swanepoel & Swanepoel 1986) and bordered by Mukwichi Communal Land. The soils Gonarezhou National Park, southern Zimbabwe of Mana National Park are described by Guy (e.g., Kupika et al. 2014; Mashapa et al. 2014; (1977). The area located between the Chitake Mpofu et al. 2012). Swanepoel (1993) noted with River and the Zambezi escarpment is charac- NDORO et al. 335 terized by colluvial deposits. Alluvial deposits are defined study strata. The following variables were restricted to the larger rivers (Rukomechi and measured and/or recorded: baobab height, basal Sapi) and are especially pronounced and older circumference and elephant induced damage on along the Zambezi Valley, forming the Mana Pools baobabs following the methods as outlined by “floodplain”, covered by what is referred to as Kupika et al. (2014) and Mashapa et al. (2014). Zambezi riverine vegetation. The gneissic derived Baobab height was measured by placing a calib- soils on and above the escarpment are generally rated 6 m pole against a baobab plant. For baobab shallow, medium-grained lithosolic sands (Thompson trees > 6 m, the pole was manually uplifted and & Purves 1978). height visually estimated by observing it at a ZPWMA (2011) recognised twelve vegetation distance away from the tree. For multi-stemmed communities in Mana Pools National Park, inclu- baobabs, only the height of the tallest stem was ding riparian vegetation dominated by Faidherbia considered. The basal circumference at breast albida woodlands, dry deciduous Commiphora- height (1.3 m above the ground level) of each Combretum thickets, and Colophospermum mopane baobab tree was measured using a 50 m tape woodland, which is the most extensive vegetation measure. For baobab saplings, the basal circum- type which is common with baobab stands. In ference of each stem was measured just above the Mana Pools National