|
|
|
|
|
26 July 2024
|
Featured FRI Magazine article: Testing multiple ignitions on a field scale to develop high intensity fires under mild weather conditions (low fire danger indices) for the control and/or eradication of invasive indigenous and alien plant species by Dr Winston Trollope (FRI Vol 2 no 7)
This week’s featured Fire and Rescue International magazine article is: Testing multiple ignitions on a field scale to develop high intensity fires under mild weather conditions (low fire danger indices) for the control and/or eradication of invasive indigenous and alien plant species written by Dr Winston Trollope (FRI Vol 2 no 7). We will be sharing more technical/research/tactical articles from Fire and Rescue International magazine on a weekly basis with our readers to assist in technology transfer. This will hopefully create an increased awareness, providing you with hands-on advice and guidance. All our magazines are available free of charge in PDF format on our website and online at ISSUU. We also provide all technical articles as a free download in our article archive on our website.
Testing multiple ignitions on a field scale to develop high intensity fires under mild weather conditions (low fire danger indices) for the control and/or eradication of invasive indigenous and alien plant species
By Dr Winston Trollope
Bush encroachment in natural grasslands and savannahs has become a major problem for livestock farmers and wildlife managers in South Africa, resulting in degraded rangelands with reduced carrying capacities and concomitant economic losses.
Dicrostachys cinerea (Sickle Bush) is one of the main encroaching plant species, particularly in savannah areas. There are multiple reasons for bush encroachment that include incorrect grazing and browsing management, a lack of or inappropriate fire management and recently it is also believed to be exacerbated by elevated levels of CO2 associated with global climate change (Buitenwerf et al, 2011). This encroachment of indigenous tree and shrub species is impacting on both commercial and small scale farmers and wildlife areas alike.
In addition, alien invasive shrub species such as Chromolaena (Chromolaena odorata), Lantana (Lantana camara) and Parthenium hysterophorus are invading extensive coastal forest and thornveld areas. Chemical and mechanical means of controlling invasive bush and alien species is very costly and labour intensive involving the investment of large amounts of capital on herbicides and/or mechanical treatments. Generally, this is a very expensive option as economic returns from increased carrying capacities generally do not meet or exceed the initial capital outlay. Fire is an alternative and more economically feasible method of reducing or controlling bush encroachment and alien invasive species but requires extreme weather conditions for the application of prescribed burns to have a significant effect in reducing the extent and degree of the encroachment.
Generally, fire will significantly reduce the structure of most plant species diminishing their height and size. This effect can be exploited through the introduction of domestic and wild ungulate browsing species to control the coppice growth of indigenous plant species. However, in the case of alien shrub species like Chromolaena odorata and Lantana camara, it is normally necessary to follow up with herbicide applications to control the regrowth. Nevertheless, using prescribed burning results in substantially less herbicide being required to spray the regrowth resulting in economic and ecological benefits to land owners and the environment respectively.
When burning to combat the encroachment of both indigenous and alien invasive plant species, high-intensity fires (>2000kJ/s/m) are necessary (Trollope, 2007) and necessitate burning under extreme weather conditions with grass fuel loads >4 000kg/ha that are fully cured ie amount of dry grass is >80%. The required weather conditions are air temperatures >30oC, relative humidity’s (RH) <20% and wind speeds between 10 and 15km/h. These guidelines translate into Fire Danger Indices (FDIs) of 60 to 70, ie orange conditions, which are dangerous and have a high fire risk requiring exceptionally well-trained manpower and adequate fire suppression equipment available. These weather conditions also result in the increased possibility of wildfires developing. As a possible alternative to this problem Chris de Bruno Austin, CEO of Working on Fire International, suggested after trials involving high intensity fires in the Kruger National Park during 2010, that more intense fires for controlling bush encroachment may be achieved under less extreme weather conditions by using multiple ignitions when applying prescribed burns. This would result in high-intensity fires being safely achieved under lower FDIs (50 to 55) as the potential for spotting would be considerably reduced and normal width firebreaks (50m) would be adequate for controlling the spread of the resultant high intensity fires.
To test this hypothesis that high-intensity fires can be achieved using multiple ignitions applied under mild weather conditions, the first phase of the multiple ignition trial was conducted at the Gustav Klingbiel Nature Reserve at Lydenburg, South Africa, from 18 to 30 June 2012. The trial was conducted on 200m by 200m plots in open grassland where multiple ignition capsules were dropped from a Bell 206 helicopter on trial plots using different ignition patterns.
The initial visual assessment of the resultant fires by both members of the research team and the participating Working on Fire project managers was that multiple ignitions do increase the intensity of a fire in comparison to normal perimeter ignitions. Data from infra-red cameras is currently being analysed to substantiate the visual assessment of the results of the trial. Two multiple ignition patterns were tested viz. Spiral and race course ignition patterns versus perimeter ignitions.
Testing multiple ignitions on a field scale to develop high intensity fires under mild weather conditions (low fire danger indices) for the control and/or eradication of invasive indigenous and alien plant species
By Dr Winston Trollope
Bush encroachment in natural grasslands and savannahs has become a major problem for livestock farmers and wildlife managers in South Africa, resulting in degraded rangelands with reduced carrying capacities and concomitant economic losses.
Dicrostachys cinerea (Sickle Bush) is one of the main encroaching plant species, particularly in savannah areas. There are multiple reasons for bush encroachment that include incorrect grazing and browsing management, a lack of or inappropriate fire management and recently it is also believed to be exacerbated by elevated levels of CO2 associated with global climate change (Buitenwerf et al, 2011). This encroachment of indigenous tree and shrub species is impacting on both commercial and small scale farmers and wildlife areas alike.
In addition, alien invasive shrub species such as Chromolaena (Chromolaena odorata), Lantana (Lantana camara) and Parthenium hysterophorus are invading extensive coastal forest and thornveld areas. Chemical and mechanical means of controlling invasive bush and alien species is very costly and labour intensive involving the investment of large amounts of capital on herbicides and/or mechanical treatments. Generally, this is a very expensive option as economic returns from increased carrying capacities generally do not meet or exceed the initial capital outlay. Fire is an alternative and more economically feasible method of reducing or controlling bush encroachment and alien invasive species but requires extreme weather conditions for the application of prescribed burns to have a significant effect in reducing the extent and degree of the encroachment.
Generally, fire will significantly reduce the structure of most plant species diminishing their height and size. This effect can be exploited through the introduction of domestic and wild ungulate browsing species to control the coppice growth of indigenous plant species. However, in the case of alien shrub species like Chromolaena odorata and Lantana camara, it is normally necessary to follow up with herbicide applications to control the regrowth. Nevertheless, using prescribed burning results in substantially less herbicide being required to spray the regrowth resulting in economic and ecological benefits to land owners and the environment respectively.
When burning to combat the encroachment of both indigenous and alien invasive plant species, high-intensity fires (>2000kJ/s/m) are necessary (Trollope, 2007) and necessitate burning under extreme weather conditions with grass fuel loads >4 000kg/ha that are fully cured ie amount of dry grass is >80%. The required weather conditions are air temperatures >30oC, relative humidity’s (RH) <20% and wind speeds between 10 and 15km/h. These guidelines translate into Fire Danger Indices (FDIs) of 60 to 70, ie orange conditions, which are dangerous and have a high fire risk requiring exceptionally well-trained manpower and adequate fire suppression equipment available. These weather conditions also result in the increased possibility of wildfires developing. As a possible alternative to this problem Chris de Bruno Austin, CEO of Working on Fire International, suggested after trials involving high intensity fires in the Kruger National Park during 2010, that more intense fires for controlling bush encroachment may be achieved under less extreme weather conditions by using multiple ignitions when applying prescribed burns. This would result in high-intensity fires being safely achieved under lower FDIs (50 to 55) as the potential for spotting would be considerably reduced and normal width firebreaks (50m) would be adequate for controlling the spread of the resultant high intensity fires.
To test this hypothesis that high-intensity fires can be achieved using multiple ignitions applied under mild weather conditions, the first phase of the multiple ignition trial was conducted at the Gustav Klingbiel Nature Reserve at Lydenburg, South Africa, from 18 to 30 June 2012. The trial was conducted on 200m by 200m plots in open grassland where multiple ignition capsules were dropped from a Bell 206 helicopter on trial plots using different ignition patterns.
The initial visual assessment of the resultant fires by both members of the research team and the participating Working on Fire project managers was that multiple ignitions do increase the intensity of a fire in comparison to normal perimeter ignitions. Data from infra-red cameras is currently being analysed to substantiate the visual assessment of the results of the trial. Two multiple ignition patterns were tested viz. Spiral and race course ignition patterns versus perimeter ignitions.
The spiral ignitions were spectacular and the resultant chimney effect resulted in the spiral ignition lines being drawn into the centre of the plot causing increased rates of spread, flame heights and resultant higher fire intensities. The racecourse ignition pattern was also observed to enhance the intensity of the fire, but only after the open sides of the burn plots were closed off with ignition lines also resulting in a chimney effect and causing the parallel ignition lines to converge with one another resulting in increased rates of spread, flame heights and fire intensities. The different types of fire behaviour resulting from the spiral, racecourse and perimeter ignitions are illustrated in Figure 2.
Spiral ignition pattern
|
Racecourse ignition pattern
|
Perimeter ignition
|
Figure 2: The different types of ignition patterns and resultant fire behaviour.
On reflection and arising from the initial multiple ignition trial at Lydenburg, another method that can be used to determine whether multiple ignitions result in increased fire intensities in comparison to perimeter ignitions is to burn areas under similar weather conditions and then record the effect of the fires on the trees and shrubs in terms of the reduction in live woody phytomass expressed in tree equivalents per hectare (TE/ha).
This procedure has been effectively demonstrated in a trial conducted at the Mun-Ya-Wana Private Game Reserve in KwaZulu-Natal using perimeter ignitions. Prior to burning the phytomass of trees and shrubs in an area that was being burnt to control bush encroachment was estimated using the Adapted Point Centre Quarter Method developed by the Working on Fire research and development section at Nelspruit (Trollope et al, 2012). The area was then resurveyed after the application of a high intensity fire to determine the reduction in phytomass of trees resulting from the topkill of stems and branches. The surveys showed that the phytomass of trees and shrubs prior to the fire was 1 915TE/ha and this had been reduced by the high intensity perimeter burn to 96TE/ha ie a 95% reduction in the phytomass of the trees and shrubs. This reduction in phytomass in the trial in the Mun-Ya-Wana Game Reserve is illustrated in Figure 3.
This procedure has been effectively demonstrated in a trial conducted at the Mun-Ya-Wana Private Game Reserve in KwaZulu-Natal using perimeter ignitions. Prior to burning the phytomass of trees and shrubs in an area that was being burnt to control bush encroachment was estimated using the Adapted Point Centre Quarter Method developed by the Working on Fire research and development section at Nelspruit (Trollope et al, 2012). The area was then resurveyed after the application of a high intensity fire to determine the reduction in phytomass of trees resulting from the topkill of stems and branches. The surveys showed that the phytomass of trees and shrubs prior to the fire was 1 915TE/ha and this had been reduced by the high intensity perimeter burn to 96TE/ha ie a 95% reduction in the phytomass of the trees and shrubs. This reduction in phytomass in the trial in the Mun-Ya-Wana Game Reserve is illustrated in Figure 3.
|
|
Figure 3: Before and after photographs of the burnt area on the Harrowgate section of the Mun-Ya-Wana Game Reserve illustrating the 95% reduction in phytomass of bush expressed in TE/ha (1915 TE/ha reduced to 96 TE/ha) caused by the high intensity fire (4 204 kJ/s/m) applied on 23 July 2010
It is therefore proposed that this procedure be used on multiple ignition test burn sites in the Mun-Ya-Wana Private Game Reserve in Zululand, the Barberton Nature Reserve near Nelspruit and the six wooded experimental burn sites in the Gustav Klingbiel Nature Reserve at Lydenburg. The hypothesis to be tested will be that multiple ignitions applied as spiral and race course generate more intense fires under mild weather conditions than perimeter ignitions as reflected by a greater reduction in the phytomass of tree and shrub vegetation expressed in tree equivalents per hectare. Permission has been obtained to conduct cooperative trials in these areas using the spiral and race course ignition patterns and comparing them with perimeter ignitions to control the encroachment of indigenous tree and shrub species with particular reference to Dichrostachys cinerea (sickle bush) and the alien plant species Chromolaena odorata and Lantana camara.
Preliminary results from the first replicate of the multiple ignition trial conducted at the Gustav Klingbiel Nature Reserve at Lydenburg during 2012 clearly demonstrated that multiple ignitions generated more intense fires than perimeter ignitions – see Figure 4.
It is therefore proposed that this procedure be used on multiple ignition test burn sites in the Mun-Ya-Wana Private Game Reserve in Zululand, the Barberton Nature Reserve near Nelspruit and the six wooded experimental burn sites in the Gustav Klingbiel Nature Reserve at Lydenburg. The hypothesis to be tested will be that multiple ignitions applied as spiral and race course generate more intense fires under mild weather conditions than perimeter ignitions as reflected by a greater reduction in the phytomass of tree and shrub vegetation expressed in tree equivalents per hectare. Permission has been obtained to conduct cooperative trials in these areas using the spiral and race course ignition patterns and comparing them with perimeter ignitions to control the encroachment of indigenous tree and shrub species with particular reference to Dichrostachys cinerea (sickle bush) and the alien plant species Chromolaena odorata and Lantana camara.
Preliminary results from the first replicate of the multiple ignition trial conducted at the Gustav Klingbiel Nature Reserve at Lydenburg during 2012 clearly demonstrated that multiple ignitions generated more intense fires than perimeter ignitions – see Figure 4.
The results in Figure 4 clearly demonstrate the more intense fires generated by multiple ignitions (spiral and race course) compared to perimeter ignitions. These results are currently being investigated in field trials conducted during July/ August 2013 in the Gustav Klingbiel Nature Reserve and the Barberton Nature Reserve in Mpumalanga and the Mun Ya Wana and Zulu Nyala Private Game Reserves in KwaZulu-Natal.
In this case, the effects of the fire intensities generated by the different ignition patterns is being recorded in terms of the reduction in phytomass of the tree/shrub vegetation expressed in TE/ha as described and illustrated in Figure 4.
Interestingly, the preliminary results of the trial in terms of the response of the tree and shrub vegetation recorded in KwaZulu-Natal also clearly showed that the multiple ignitions generated more intense fires than the perimeter ignitions with the spiral ignitions resulting in the most intense fires.
These are very promising results considering the very serious encroachment of Chromolaena odorata, Lantana camara and Dichrostachys cinerea in the wildlife areas of this region and the major objective of Working On Fire in this trial is now to operationalise these results so that they can be used at a field scale in controlling these encroaching species.
In this case, the effects of the fire intensities generated by the different ignition patterns is being recorded in terms of the reduction in phytomass of the tree/shrub vegetation expressed in TE/ha as described and illustrated in Figure 4.
Interestingly, the preliminary results of the trial in terms of the response of the tree and shrub vegetation recorded in KwaZulu-Natal also clearly showed that the multiple ignitions generated more intense fires than the perimeter ignitions with the spiral ignitions resulting in the most intense fires.
These are very promising results considering the very serious encroachment of Chromolaena odorata, Lantana camara and Dichrostachys cinerea in the wildlife areas of this region and the major objective of Working On Fire in this trial is now to operationalise these results so that they can be used at a field scale in controlling these encroaching species.