The impact of invasive alien Prosopis species (mesquite) on native plants in different environments in South Africa.

Abstract Many Prosopis species have been introduced to South Africa; some taxa and their hybrids have naturalised and become widespread invasive trees. These invasions have detrimental effects on biodiversity, ecosystem services and human livelihoods. Although several studies have documented these impacts, the studies have been limited to single sites or restricted areas. This study assessed the Prosopis population across the full invasive range of the genus in South Africa, and quantified the effects of invasions on native woody and herbaceous species. Basal areas of invasive Prosopis stands reached 9 m2/ha, and were on average higher along perennial rivers than along ephemeral rivers (mean basal areas of 3.2 vs. 1.4 m2/ha). Native woody species density, basal area, richness and diversity all decreased significantly as the basal area of Prosopis stands increased. For example, up to eight native woody species occurred at basal area of  4 m2/ha. The cover of native perennial grasses and herbaceous plants declined from 15–20% where the basal area of Prosopis was  4.5 m2/ha. The results highlight the widespread nature of the impacts across all invaded biomes. Current control of Prosopis has had limited success, and alternative, potentially more effective, options are controversial. In the light of the widespread impacts, we recommend that a thorough assessment of the problem be undertaken to inform policy.

[1]  Thomas Koellner,et al.  Ecosystem engineer unleashed: Prosopis juliflora threatening ecosystem services? , 2014, Regional Environmental Change.

[2]  Rieks D. van Klinken,et al.  Population Ecology of Hybrid Mesquite (Prosopis Species) in Western Australia: How Does it Differ from Native Range Invasions and What are the Implications for Impacts and Management? , 2005, Biological Invasions.

[3]  D. Maitre,et al.  An assessment of the effectiveness of a large, national-scale invasive alien plant control strategy in South Africa , 2012 .

[4]  A. El-Keblawy,et al.  Impacts of the invasive exotic Prosopis juliflora (Sw.) D.C. on the native flora and soils of the UAE , 2007, Plant Ecology.

[5]  B. Swallow,et al.  Invasion of prosopis juliflora and local livelihoods: case study from the Lake Baringo area of Kenya , 2005 .

[6]  D. Richardson,et al.  Challenges and trade-offs in the management of invasive alien trees , 2014, Biological Invasions.

[7]  Charlie M. Shackleton,et al.  The importance of dry woodlands and forests in rural livelihoods and poverty alleviation in South Africa , 2007 .

[8]  Mic Julien,et al.  Biological control of weeds in Australia. , 2012 .

[9]  D. Richardson,et al.  Trees and shrubs as invasive alien species – 2013 update of the global database , 2013 .

[10]  G. Mohren,et al.  Ecological impact of Prosopis species invasion in Turkwel riverine forest, Kenya , 2013 .

[11]  S. Milton,et al.  Avian assemblages in native Acacia and alien Prosopis drainage line woodland in the Kalahari, South Africa. , 2002 .

[12]  H. G. Zimmermann,et al.  Biological control of mesquite, Prosopis spp. (Fabaceae), in South Africa , 1991 .

[13]  F. X. Sans,et al.  Interspecific competition between alien and native congeneric species , 2007 .

[14]  R. Sosebee,et al.  Influence of mesquite control on soil erosion on a depleted range site , 1986 .

[15]  S. Chown,et al.  Influence of dense stands of an exotic tree, Prosopis glandulosa Benson, on a savanna dung beetle (Coleoptera: Scarabaeinae) assemblage in southern Africa , 1996 .

[16]  R. Lubke,et al.  Fuelwood harvesting and selection in Valley Thicket, South Africa , 2006 .

[17]  R. Poynton.  Report to the Southern African Regional Commission for the Conservation and Utilization of the Soil (SARCCUS) on tree planting in southern Africa. Vol. 2. The eucalypts. , 1979 .

[18]  A. El-Keblawy,et al.  Impacts of native and invasive exotic Prosopis congeners on soil properties and associated flora in the arid United Arab Emirates , 2014 .

[19]  D. Mazibuko.  Phylogenetic relationships of Prosopis in South Africa : an assessment of the extent of hybridization, and the role of genome size and seed size in the invasion dynamics , 2012 .

[20]  G. C. Bate,et al.  The occurrence of invasive Prosopis species in the north-western Cape, South Africa. , 1991 .

[21]  D. Richardson,et al.  Prosopis invasions in South Africa: Population structures and impacts on native tree population stability , 2015 .

[22]  R. Ostertag,et al.  Groundwater availability mediates the ecosystem effects of an invasion of Prosopis pallida. , 2014, Ecological applications : a publication of the Ecological Society of America.

[23]  D. Maitre,et al.  Costs, benefits and management options for an invasive alien tree species: The case of mesquite in the Northern Cape, South Africa , 2012 .

[24]  J. C. Tewari,et al.  The Prosopis juliflora - Prosopis pallida complex: a monograph , 2001 .

[25]  K. Armstrong,et al.  Benefits, threats and potential of Prosopis in South India , 2014 .

[26]  J. Zanuncio,et al.  The introduced tree Prosopis juliflora is a serious threat to native species of the Brazilian Caatinga vegetation. , 2014, The Science of the total environment.

[27]  Sebinasi Dzikiti,et al.  Water relations and the effects of clearing invasive Prosopis trees on groundwater in an arid environment in the Northern Cape, South Africa , 2013 .

[28]  A. Magurran,et al.  Measuring Biological Diversity , 2004 .

[29]  J. H. van den Berg,et al.  Detection, Quantification and Monitoring of Prosopis in the Northern Cape Province of South Africa using Remote Sensing and GIS , 2013 .

[30]  E. February,et al.  Impact of Prosopis invasion on a keystone tree species in the Kalahari Desert , 2013, Plant Ecology.

[31]  Inderjit,et al.  Community Impacts of Prosopis juliflora Invasion: Biogeographic and Congeneric Comparisons , 2012, PloS one.

[32]  D. Geesing,et al.  Management of introduced Prosopis species: can economic exploitation control an invasive species? , 2004 .

[33]  K. Esler,et al.  Impact of Prosopis (mesquite) invasion and clearing on the grazing capacity of semiarid Nama Karoo rangeland, South Africa , 2011 .

[34]  D. Maitre,et al.  The impact of invading alien plants on surface water resources in South Africa: A preliminary assessment , 2000 .

[35]  John H. Hoffmann,et al.  Biological Control of Mesquite (Prosopis Species) (Fabaceae) in South Africa , 2011 .

[36]  Milan Chytrý,et al.  The Vegetation of South Africa, Lesotho and Swaziland , 2008 .

[37]  D. Richardson,et al.  Stakeholder perceptions and practices regarding Prosopis (mesquite) invasions and management in South Africa , 2015, Ambio.

[38]  D. Richardson,et al.  Prosopis: a global assessment of the biogeography, benefits, impacts and management of one of the world's worst woody invasive plant taxa , 2014, AoB PLANTS.

[39]  Suresh Kumar,et al.  Impact of invasion by Prosopis juliflora on plant communities in arid grazing lands , 2014 .

[40]  J. Stromberg,et al.  Vegetation-Hydrology Models: Implications for Management of Prosopis Velutina (Velvet Mesquite) Riparian Ecosystems. , 1993, Ecological applications : a publication of the Ecological Society of America.

[41]  Cang Hui,et al.  Tree invasions: patterns, processes, challenges and opportunities , 2013, Biological Invasions.

[42]  L. Henderson.  Invasive, naturalized and casual alien plants in southern Africa: a sum- mary based on the Southern African Plant Invaders Atlas (SAPIA) , 2007 .