A cost comparison of aerial and ground based approaches for the control of alien invasive pines in the Western Cape

Thesis (MSc)--Stellenbosch University, 2021.

ENGLISH SUMMARY : The rugged mountainous areas of the Western Cape fynbos are highly biodiverse, however alien invasive Pines remain a continual threat both in terms of its biodiversity and water supply as they are continually spreading and thriving uncontrollably. Felling has been the main clearing method; however, it has become too expensive and slow to use within these areas in comparison with the speed of the invasion. These environments are complex in that they can vary from site to site in terms of tree density, slope, surrounding obstructive vegetation and remoteness. These site properties often result in longer walk, removal and site access times which can significantly increase overall costs of labour-intensive methods such as felling. The problem is continuing to get worse over time and demands an investigation into alternative clearing methods. Chemical methods such as the Drill and Fill and Aerial Basal Bark Application (ABBA) method have increased the efficiency and scope of alien invasive Pine removal in other countries which have however not been tested for local conditions. The aim of this study was to determine under what site conditions these chemical control methods and the use of helicopters would be more cost effective compared to traditional felling which would encourage an integrated approach to managing the species. The study thus consisted of two novel clearing methods: the Drill and Fill method, the Aerial Basal Bark Application (ABBA) method and traditional felling currently used in practice. A work rate matrix was constructed which compared the financial implications of each clearing method at the various physical site combinations: tree density, slope, surrounding obstructive vegetation and remoteness. Expert knowledge was employed to validate the work rate and costing data. The study found that the higher productivity of the drill and fill teams outweighs their total daily team rate compared to traditional felling. The productivity of traditional felling was prevented by the mandatory higher safety and supervision requirements associated with chainsaw operation which resulted in the inclusion of unproductive team members, in contrast with all members of a drill and fill team using a drill from the added safety of drill operation. The relative lower weight of drill and fill equipment decreases walk times and increases productive working time. Consequently, most scenarios showed the drill and fill method is more cost-effective compared to traditional felling. The ABBA method is the preferred method at sites where isolated Pines are situated in dense fynbos with difficult access at slope gradients of 45° and higher. At these site combinations, ground teams experience longer walk times which reduces their productivity to such an extent that ABBA is comparatively more cost-effective. Additionally, at slope gradients of 45° and higher, high-altitude teams require specialized equipment which results in further reductions in their productivity. Helicopters should therefore target the species in their isolated spread stages before they reach reproductive maturity and spread large amounts of wind-blown seeds over considerable distances. The study assumed the helicopter had a high level of hours available per annum. In practice however this may not be the case due to unfavourable weather conditions in these mountainous areas which makes it risky for operators. Government must make use of a private contractor involved in agricultural crop spraying to prevent this from happening, as operations can be diverted to crop spraying in low lying areas when weather restricts invader tree eradication. This would allow the helicopter to work at a lower hourly rate than a government owned helicopter standing idle.

AFRIKAANSE OPSOMMING : In die ruwe bergagtige gebiede van die Wes-Kaapse fynbos bedreig die uitheemse indringer dennebome beide die biodiversiteit en waterafloop, omdat hulle aanhou versprei en onbeheers floreer. Die vernaamste uitroeimetode tot dusver is om die bome af te kap. Hierdie metode het egter te duur geword en neem te lank in vergelyking met die tempo van indringing. Hierdie omgewings is kompleks omdat hulle van plek tot plek verskil in terme van boomdigtheid, helling, omliggende versperrende plantegroei en afgeleënheid. Hierdie terrein kenmerke veroorsaak langer stap-, verwyderings- en toegangstye, wat die totale koste van arbeidintensiewe metodes soos afsaag aansienlik verhoog. Hierdie groeiende probleem vereis ’n ondersoek na alternatiewe skoonmaakmetodes. Chemiese metodes soos die drill and fill (boor en vul) en aerial basal bark application (ABBA) het die doeltreffendheid en omvang van die uitroeiing van uitheemse indringer dennebome in ander lande verhoog, maar is nog nie onder plaaslike toestande getoets nie. Die doel van hierdie studie was om te bepaal onder watter terreintoestande hierdie chemiese beheermetodes en die gebruik van helikopters meer koste-effektief sou wees in vergelyking met tradisionele afsaag, wat ’n geïntegreerde benadering tot die bestuur van die spesie sal aanmoedig. Die studie het gefokus op twee nuwe uitroeimetodes: die boor – en vul (“Drill and Fill”) metode en die Aerial Basal Bark Application (ABBA) metode, tesame met tradisionele afsaag soos tans in die praktyk gebruik word. ’n Werktempo-matriks is opgestel om die finansiële implikasies van elke uitroeimetode te bepaal vir terreine wat verskil ten opsigte van boomdigtheid, helling, omliggende versperrende plantegroei en afgeleënheid. Kundiges se kennis is verkry om die werktempo en kosteberekening te verifieer. Die studie het gevind dat ‘n boor- en vulspan meer produktief is as ‘n tradisionele afsaagspan. Die produktiwiteit van die tradisionele metode van indringerbome met ’n kettingsaag afsaag, is verlaag weens die insluiting van onproduktiewe spanlede a.g.v. die verpligte hoër veiligheids- en toesigvereistes, in kontras met ’n boor- en vulspan se lede, wat almal produktief is weens die groter veiligheid van die boor- en vulproses. Die relatiewe laer gewig van boor- en vultoerusting verkort staptyd en verhoog produktiewe werktyd. Gevolglik het die meeste scenario’s gewys dat die boor- en vulmetode meer koste-effektief is as die tradisionele afsaagmetode. Die ABBA-metode is die verkose metode op plekke waar geïsoleerde dennebome in digte fynbos voorkom wat moeilik toeganklik is as gevolg van steil hellings van 45° en meer. Hierdie liggingseienskappe vereis dat grondspanne vir langer tye moet stap om ʼn bepaalde area se indringerbome uit te roei, wat hulle produktiwiteit in so ’n mate verlaag het dat ABBA in vergelyking meer koste-effektief was. Verder vereis spanne wat teen hellings van 45° en meer werk gespesialiseerde toerusting, wat lei tot groter afnames in hulle produktiwiteit. Helikopters moet indringerbome teiken wanneer hulle nog in hulle geïsoleerde stadium is, voor hulle voortplantingsvolwasse word en groot hoeveelhede van hulle sade met wind oor groot afstande versprei. Helikopter ure per jaar word beperk deur ongunstige weerstoestande in die bergagtige gebiede, wat dit baie gevaarlik maak vir die operateurs. In plaas daarvan dat die staat self ʼn helikopter aanskaf wat slegs indringerbome uitroei, behoort die staat eerder gebruik te maak van ’n privaat helikopter kontrakteur wat landbougewasse bespuit in laagliggende gebiede wanneer die weer die bespuiting van indringerbome in die berge verhoed. Die helikopter in privaatbesit sal dus teen ’n laer uurlikse tarief kan werk as ’n helikopter in staatsbesit wat ʼn groot deel van ʼn jaar nie benut kan word nie.

Masters