Mapping and Controlling Invasive cacti in Northern Kenya ‘The species aren’t inherently bad, they are just in the wrong place’- David Lodge
Nelson Mwangi GIS Assistant Researcher, Save the Elephants Introduction: the problem – Opuntia stricta has been listed in the top 100 of the World’s Worst Invasive Alien Species (IUCN) – Opuntia was originated in tropical America, but has been introduced to other regions of the world, such as Europe (particularly the Mediterranean countries) and Africa (E.M. Yahia and C. Sáenz, 2011). – The plant was introduced in Mukogodo Division of Laikipia District by local landowners and colonial settlers in the early 1960s, as a life fence and as an ornamental plant (www.nation.co.ke, 2008) – Opuntia stricta and O.ficus indica are invasive in Laikipia and Tsavo East National Park and surrounds, where they have invaded more than 500 km2 (www.cabi.org).
Study Area: Samburu, Buffalo Springs and Shaba National Reserves
Laikipia-Samburu Ecosystems Common opuntia species in Kenya
Opuntia stricta: reddish fruits Opuntia ficus-indica (N. Pasiecznik, cabi.org, 2007) Introduction: the problem
– Elephants and baboons also eat the fruits of the prickly pear (Opuntia ficus- indica and Opuntia stricta/erect prickly pear) helping with the dispersal of the species (www.cabi.org). – Picture by STE media intern Robbie Labanowski, 2017
Introduction: the problem…
– When ingested, the small spines on the fruit, called glochids, get lodged in the throat, stomach or intestines of the animals (The Standard, 2015). – **Mr Peter Lekurtut, the manager of Oldonyiro Conservancies in Isiolo North, says that in the past five months, six elephants died after eating the plant (Daily Nation, July 2017). Introduction: Control Measures
– Mechanical control involves uprooting the plant and burning it. Chemical control should be avoided especially in National Parks and reserves to avoid killing native flora and fauna. – Save the Elephants has recently started using biological control of Opuntia. – We have a culture of the cochineal insect (Dactylopius The cochineal insect opuntiae) which we sustain by supplying fresh Opuntia (Wikimedia commons) stricta pads for the insects to feed on. – The cochineal is host-specific and Dactylopius opuntiae is specific to O. stricta (Stricta biotype) (Klein, 2002).
Introduction: Control Measures,
– Major elephants corridors in Northern Kenya made from Network theory and real-time GPS data from collared elephants – One of the most utilized areas is along the Ewaso Nyiro river
Introduction: Control Measures,
– Suspected origin of opuntia stricta into Samburu, Shaba and Buffalo Springs National Reserves – A need to eradicate the species from the Western side of the Ewaso Nyiro river
Area of heavy Opuntia stricta infestation Introduction: The benefits debate
– Economic benefits of prickly pears vs the ecological impacts of their spread vs the economic value of the cochineal bug as a dye – - Human consumption of opuntia fruits in various ways.
Objectives
1 2 3 4
To map out the To identify the To manually To harvest green distribution of type of Opuntia control invasive pads/cladodes Opuntia sp or species in cacti for our cochineal any evidence of Samburu-Buffalo culture it Springs National reserves Methodology: Data Collection
1 2
Garmin GPS Units and Collector for ArcGIS, paper forms! machete and wheelbarrows - In the 3 days, 41.561 Fields designed for quick data Km of data collection. - 2 days covered ~17km collection using collector Data Collection using collector for ArcGIS Results: 1st Phase
a. Individual sightings of opuntia cladodes and/or plants b. Point density of cladodes along Ewaso Nyiro River Results: 2nd Phase Heat map showing the distribution of opuntia and/or thorn cactus along Ewaso Nyiro river
Counts in first phase (n)=2,220
Counts in second phase (n)= 245. Second phase was more exhaustive with various aspects of opuntia being recorded using Collector for ArcGIS Results: 2nd Phase
High density areas were observed to be mostly on river bends where a lot of debris accumulates trapping any opuntia cladodes which then start growing Results: 2nd Phase
State of mapped opuntia cladodes and/or plants State 100
90
80 fresh
70
60
50
40
30
Growing 20 10
0 Fresh Growing Dry Rotting Fresh and rotting Results: 2nd Phase
Mechanically removed cacti Results
– From Fig 2 it is evident that we have an ‘Opuntia problem’ inside Samburu and Buffalo Springs National Reserves. – Most of these sightings were rooting cladodes and a few mature plant, there were also sightings of rotting pads and one instance of a cladode infested with the biological control bug. – Dominant species of the pads collected was Opuntia stricta plant with few from O. ficus indica and some from the thorn cactus. – Areas with a lot of debris had high densities of the cacti. O.ficus-indica was also sighted next to lodges with Samburu lodge having mature plants outside the gates and also inside the lodges. Results: The Database plan
– https://stegis.maps.arcgis. com/home/webmap/viewer. html?webmap=7bd5035eafa 64ea4bb53d1f915ff32d6 Goals: – A comprehensive photographic opuntia database that is frequently updated – Quick analysis using ArcGIS online
Conclusion and way forward
– We managed to mechanically control the cacti in most areas we surveyed at the same time collecting O.stricta cladodes. Plans have started to survey areas west of Westgate and in Archers post for O.stricta and hopefully use the biological control agent during the dry season. However, with O.ficus indica species we will continue using mechanical control since the cochineal is slow acting (or not acting at all) on this species. – The study was not exhaustive hence there is a need for more field to map out the different species and do an actual count of cladodes and mature plants which will in turn give us a comprehensive map, database and better view of the Opuntia problem. References
– E.M. Yahia,C. Sáenz 2011. Postharvest Biology and Technology of Tropical and Subtropical Fruits. Elsevier – https://www.standardmedia.co.ke/article/2000166495/kenya-tiny-insects-help- eradicate-killer-cactus-save-pasture – https://www.cabi.org/projects/controlling-invasive-species/ – Klein H. 2002. Biological control of Invasive cactus species (family cactaceae). ARC-Plant protection research institute, Pretoria. – https://www.nation.co.ke/lifestyle/dn2/Killer-cactus/957860-4010324- n7hx7hz/index.html
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