INVASIVE SPECIES CONTROL

The control of invasive vegetation on Olifants West Nature Reserve, Balule 4th Quarter 2019

Chris Farren, 9th January 2019

Table of Contents

1.

Introduction

2.

Materials

3.

Method

4.

Invasive vegetation

4.1

Sweet prickly Pear

4.2

Queen of the Night

5.

Results

6.

Conclusion

1. Introduction A key aspect of reserve maintenance is the control of invasive vegetation within a reserve’s boundaries. Invasions by non-native flora has been widely studied in South Africa with the aim of eliminating invasive species and restoring ecosystems to their natural state through the reestablishment of natural biodiversity. Kruger National Park Management concluded that invasive vegetation is one of the largest threats to biodiversity. In 1997 the IUCN stated that invasive vegetation is the second largest threat to global biodiversity. Invasive vegetation competes for the same finite resources as indigenous vegetation and are a danger to a reserve’s natural flora impacting vegetation structure and biodiversity. Invasive vegetation faces no natural predators giving them a major advantage in outcompeting native vegetation. Olifants West Nature Reserve (OWNR) is occupied by a number of different invasive cactus species with the most abundant being sweet prickly pears (Opuntia ficus indica) and queen of the night (Cerus jamacaru) while jointed cactus (Opuntia aurantiaca), harrisia cactus or moon cactus (Eriocereus martinii), and boxing glove cactus (Cylindropuntia fulgida) can also be found within the reserve.

All of the invasive species recorded within Olifants West are category 1 plants according to CARA (Conservation of Agriculture Resources Act,1983) which states that under no circumstances may category 1 plants be allowed on any land or inland water areas outside of biological control reserves.

The responsibility of controlling category 1 plants lies with the land user. No person is permitted to grow or cultivate category 1 plants. Moreover, land users are legally required to control category 1 plants through several methods including; 1) mechanical removal – uprooting, cutting or burning the plant. 2) Chemical – treatment with a chemical designed to kill the plant. 3) Biological – control the plant using biological methods. 4) Combination of the previously mentioned methods (1), (2) and (3) in a way that the biological control is not tampered with to the point where the biological control is inactive. These methods must be completed in such a manner that category 1 plants are prevented from re-growing or spreading in any form. In order to accurately control category 1 plants, follow up procedures are obligatory to realize the achieve result. When dealing with category 1 plants, careful execution is necessary to have the least possible impact on the environment.

Figure 1 is shows historical locations of prickly pears and queen of the nights found within Olifants West. Transfrontier Africa has combated invasive vegetation since 2012 (not sure what year it actually started??) and this map includes data up until January 2019.

The data used for this is report was gathered between July 2019 and December 2019 through the use of a roadside survey for invasive vegetation with historical data on locations of invasive vegetation not considered. The data is logged into excel or on Avenza apps when conducting the roadside survey or when an invasive plant is found within the reserve. Historical data was ignored for this report in order to assess the roadside survey method accurately.

2. Materials In order to combat invasive species certain equipment is needed. The basic tools needed are tongs (to handle to invasive species), crates for transport of both biological control to the field and invasive species to the nursery, a knife to cut 6invasive species, MSMA (Monosodium methyl arsonate) which is the herbicide used to spray invasive species (used at a concentration of 5% mixed with water and liquid soap), spray bottles to apply the herbicide and biological control. Each species of biological control is unique to each invasive species. A nursery located at the Warden’s office of OWNR is used to store invasive species collected in order to cultivate biological control necessary to maintain an abundant supply of the biological control. The biological control cultivated in this nursery are the cochineal bug (host specific to sweat prickly pear) and the harissa mealybug (host specific to queen of the night).

3. Method There are 3 options in combating invasive vegetation; biological, chemical and mechanical. The biological and chemical methods are the most effective in combating invasive vegetation. The manual/mechanical removal of plants is not effective as every little piece of a plant that is not removed can regrow and is also labour intensive and costly. Biological treatment relies on a species of bugs which are host specific and only feed on the host species. The chemical used is MSMA (Monosodium methyl arsonate) and is used at 5% concentration mixed with water and a drop of liquid soap.

In order to accurately and efficiently treat invasive vegetation within OWNR, a roadside survey is conducted along the road network of OWNR. The roads are grouped according to the 1KM2 grid references with the grids covered systematically. This allows for an accurate and detailed record of what areas of the reserve have been covered. The roads and grids covered during the survey are tracked and monitored using a GPS and Avenza maps in the field and recorded in Quantum GIS (QGIS). QGIS allows for the area of the reserve covered through the roadside survey and the area that has not been surveyed. Areas that were not surveyed are neither visible or accessible by road and will be needed to be surveyed on foot in search of invasive species.

While conducting the road surveys there must be s driver and at least 2 spotters in the car besides the driver. When an invasive species is located from the car, data is collected on the invasive plant.

The data collected is the GPS location, species, size (if the plant is small enough for successful mechanical removal then this is conducted in order to store the plant at the nursery and cultivate more biological control), and if the plant shows signs of previous biological or chemical treatment.

Once this information has been gathered the plant is treated chemically and then biologically. In order to effectively treat the plant, small slits are cut into the plant to allow the chemical (MSMA) to seep in the to plant but also to use as a place to insert the biological control onto the plant. Once this is complete, a 50-metre area around the plant is surveyed on foot in search of other invasive species. If any other invasive plants are found during this walk the same method (data collection, treatment and 50 metre walk around the plant) is applied.

4. Invasive vegetation There are 5 known invasive species within OWNR. These species are both harmful to the indigenous flora and fauna within the ecosystem as invasive species can outcompete native vegetation for resources therefore changing the structure of the ecosystems vegetation and adversely affecting ecosystem health and stability.

Table 1 shows the 5 known invasive species within OWNR. Scientific Name Cereus jamacaru Cylindropuntia fulgida Eriocereus martini Opuntia aurantiaca Opuntia ficus-indica

4.1.

Common Name Queen of the night Boxing glove cactus Moon cactus/Harrisia cactus Jointed cactus Sweet prickly pear

Sweet Prickly Pear (Opuntia ficus-indica)

The most abundant invasive species within OWNR is the sweet prickly pear. This species is native to Mexico and invades areas that are rocky or dry, and fruits during the months of January to May. This plant highly adapted to colonizing areas and if one modified leaf, or cladode, falls off a plant it can develop roots and grow into a whole new plant. Biocontrol has been proven as an effective method to control sweet prickly pear in Kruger National Park. The biocontrol used is the cochineal bug (Dactylopius opuntiae) which is host-specific to sweet prickly pears, and is the same biological control used in OWNR.

Figure 2 (above left) shows a sweet prickly pear that has died from chemical treatment (MSMA), while Figure 3 (above right) shows a dense sweet prickly pear found in OWNR.

Figure 4 shows the spread of the cochineal bugs on a sweet prickly pear plant.

Figure 5: sweet prickly pears located and treated in OWNR. The roadside survey has proven an effective and viable method for locating sweet prickly pears. In addition, more sweet prickly pears have been found and treated while investigating prickly pears found during the roadside survey.

In total 138 individual sweet prickly pear plants were located during the roadside survey, with 85 found while driving and 34 found while walking. 15 of the prickly pears found were small enough to be successfully removed to the nursery.

Table 2: prickly pear plants located and treated KMs driven

Total found

Found Found while while driving walking

140

137

118

19

Treated with biological control only 1

Treated with chemical control only 32

Treated with both

Removed to nursery

Dead

88

10

10

The detection rate of prickly pears (i.e. prickly pears found while driving vs. found while walking) is 118:19 for a total of 137 prickly pears identified.

4.2.

Queen of the night (Cereus jamacaru).

The queen of the night is the second most abundant invasive vegetation species found within OWNR. This species is an erect cactus that has a woody, succulent stem that can grow to enormous sizes (15m +). The queen of the night is a highly invasive species to South Africa and is indigenous to South America and the Caribbean. Like the sweet prickly pear this species is able to colonize areas very quickly as any stem that comes into contact with soil is able to sprout roots. Mechanical removal is not viable for this species as the roots are deeply imbedded in the soil and the plants can grow to massive sizes making manual removal seemingly impossible. Biological agents are the preferred method to control the queen of the night and the best suited biological control agent for this species is the harissa mealybug (Hypogeococcus pungens).

Z

Figure 6 (above left): a queen of the night that has been chemically treated. Figure 7 (above right): a dense queen of the night plant found in OWNR. Figure 8 (left): is a quuen of the night that has been successfully infected with biological control.

Figure 9: queen of the night plants located and treated within OWNR. Although not many queen of the night plants have been located through the roadside survey this method is still viable in controlling the population of this invasive species as it is not labour intensive and an effective method of surveying the entirety of OWNR. As with the sweet prickly pears, the queen of the night plants located during the roadside survey have allowed more queen of the night plants to be located on foot.

In total 29 individual queen of the night plants were located during the roadside survey, with 23 found while driving and an additional 6 found while walking. 3 of the queen of the night plants found were already infected with biological control. None of the plants found were mechanically removed to be stored at the nursery as the sizes of the plants did not allow for successful removal without risking spreading the plant more. However, parts of the plant were cut off and stored in the nursery to cultivate biological control.

Table 3: queen of the night plants located and treated.

KMs driven

140

Total Found Found Treated while while with only driving walking biological control 23 17 6 0

Treated with only chemical control 12

Treated with both 11

The detection rate for queen of the nights (i.e. queen of nights found while driving vs. found while walking) is 17:6 for a total of 23 located and treated.

5. Results OWNR in total is 8500 hectares. Of this 1574 hectares have been covered during the roadside survey during the period of August 2019 to December 2019. OWNR is split into many different landowner properties with the properties surveyed so far being Oxford (883 hectares), Cambridge 1 and Cambridge 2 (combined total of 936 hectares). Therefore, the roadside survey within Oxford, Cambridge 1 and Cambridge 2 covered 1574 hectares of the total 1819 hectares meaning 87% of the land in these properties were covered during the roadside survey. The remaining 254 hectares will be surveyed on foot.

In total 137 prickly pears have been located and treated. Of these prickly pears found certain plants were revisited opportunistically and 10 were found to be dead from chemical treatment while other plants had been successfully infected with biological control.

Table 4: Density per hectare of prickly pear plants in OWNR. Total plants Oxford density/ha Cambridge 1&2 density/ha OWNR density/ha 137 0.075 0.074 0.016 23 queen of the night plants located and treated. Of these queen of the night plants identified certain plants were revisited opportunistically and 3 were found to be dead from chemical treatment while other plants had been successfully infected with biological control.

Table 5: Density per hectare of queen of the night plants in OWNR. Total plants 23

Oxford density/ha 0.015

Cambridge 1&2 density/ha 0.010

OWNR density/ha 0.003

Up to December 2019 1574 hectares (18%) of OWNR has been covered with 6926 hectares (82%) of the reserve still needing to be surveyed. This method will be continued until the entire road network of OWNR has been covered allowing the areas that need to be surveyed on foot to be determined.

6. Conclusion Invasive vegetation is a significant threat to the biodiversity of an ecosystem as invasive species compete with native vegetation for limited resources. These invasive species do not have natural predators within OWNR allowing them to outcompete native vegetation that is under stress from herbivores. Even if animals do feed on the invasive species, this will do little damage to the plant and in fact just spread the species more as seeds will be dispersed by animals. Using biological control that is host specific allows for a concentrated control of the invasive species leading to a healthier ecosystem as native vegetation will have less species to compete with. Biological control agents are able to spread to other nearby invasive species that have not been treated. Therefore, it is important to revisit plants that have been treated (both biologically and chemically) to track the progress of the control agents but also to search for any new invasive species that have sprouted since the last search. In order to accurately record the effect of biological and chemical control methods on invasive vegetation plants will be revisited every 6 months with the aim of revisiting plants during winter as there is a higher visibility. During this revisitation process invasive species will be examined for the impact from the control retreated if necessary.

For the roadside survey to be effective, the entire road network of OWNR will need to be driven systematically in order to accurately locate and treat the invasive vegetation within the reserve. Very few of the roads have been driven so far yet plenty of invasive species plants have been located and treated. This method will be continued until the entire road network has been covered. As there are areas of the reserve that are not accessible by road, once the road network has been driven QGIS will be used to determine both the area covered through the roadside survey and the area that has not been covered. The areas within the reserve that are not covered are noted as areas that need to surveyed on foot. These areas can be determined using a visibility index on QGIS. While this method of driving to spot invasive species is not labour intensive, OWNR is a large nature reserve. Therefore, the assistance of lodges and landowners is required. As the control of invasive vegetation is a legal requirement by a landowner. Together landowners, lodges and OWNR managers can act to identify locations of invasive vegetation and prevent the landscape from becoming completely homogenised by invasive vegetation.