2.2.1 Fire regime data analysis
Fire records of the study site were used to determine trends in the fire frequency (number of fires over time), fire return interval (number of years between fires), fire sources, seasonality and evidence that the presence of young vegetation limits the spread of fires.
The fire records were analysed for different periods to determine the trend in the fire regime of the Kogelberg Nature Reserve. Since the fire regime is built over a period of time and changes over time as well, it was important that the changes (if any) were analysed. The periods of analysis were as follows:
1952-1980 - this period was the longest period analysed since the accuracy of the records was less precise and also because the pressure of human settlement around the Kogelberg was of limited significance.
1981-2006 - during this period, the reserve had been declared a nature reserve area.
More people were settling around the neighbouring towns and the fire risk was increasing and allegations of climate change were made. CapeNature was in charge of the water catchment areas of the Western Cape with limited resources for fire management.
2.2.2 Fire data records
Fire records analysed for this study were from the beginning of 1952 until April, 2006. Analysis of all the fire data (up to April, 2006) was carried out to address the question of whether the fire regime is changing and if so, to what degree these changes are driven by climate change, changes in human population density and the availability of resources to manage fires.
Using the NFDRS, the weather data from Boontjieskraal weather station from the period January 1973 to December 2005 was analysed using Fire Family Plus 3 software to derive burning indices. The burning indices period was broken into 3 periods of roughly equal lengths (1973-1985, 1986-1995 and 1996-2005) and the threshold values for the burning indices that delimit categories of fire danger (Categories extreme, high, moderate, low and insignificant) were established. A comparison of the categories per period was made to determine any changes in the fire danger indices above 50.
Information and data on all fires that occurred on the Kogelberg Nature Reserve from the beginning of 1952 to April, 2006 were extracted from fire reports, maps, aerial photographs, block files and Department of Water Affairs archives. The fire database stores both the fire report and the fire boundary. The records for the fires used in this study included the following: fire identity, years, months, dates started, dates extinguished, locality type, veld age and number of hectares burnt. For the fire return interval, Thresholds of Potential Concern were also used as described by van Wilgen (2001) to define the upper and lower levels along a continuum of change that indicates whether or not an acceptable degree of variation is being achieved.
Note: The reports were not always complete for the period 1952-1969, but usually provided data on locality, year, month, area burnt and occasionally the cause.
Completeness and accuracy of the data recording improved from 1970-2006. Sketch maps of area burned, usually at the scale 1:50 000 were available with increasing completeness and accuracy over time.
2.2.3 Data analysis
The fire data were analysed to determine:
1. Fire frequency - number and size of fires over time 2. Fire return intervals - number of years between fires 3. Fire seasonality - months in which fires burnt
2.2.3.1 Objective one
Fire Frequency at Kogelberg Nature Reserve
The fire records were analysed for different management periods to identify differences in the fire regime of the Kogelberg Nature Reserve. Since the regime is built over a period of time and it changes over time as well, it was important that the changes, if any, were identified. The management periods were analysed for the periods 1952-1980 and 1981-2006.
2.2.3.2 Objective two
Fire return interval: number of years between fires in the Kogelberg Nature Reserve
Analysis of all the data (from 1952 up to April 2006) was carried out to identify changes in fire frequency over the period of the study. Intervals of 1952-1980 and
1952-2006 were allocated respectively to the data.
To calculate the fire interval for all the fires that occurred in the Kogelberg Nature Reserve, GIS Arc view 3.3 and Excel were used to join multiple fire dates into polygons for a particular area using the method described by De Klerk et al. (2005)
2.2.3.3 Objective three Seasons of burn
Brown et al., (1991) describes the natural fire season for fynbos as November to April, with a peak between November and February. All the fires that burnt at the Kogelberg Nature Reserve in the two management periods of the study were analysed to determine in which months they burnt the total area that burnt during those months and if there were any shifts in the season of burn.
GraphPad Prism 5® (GraphPad Software, San Diego California USA), Arc view GIS 3.3 and Microsoft Excel were used to analyse the data. As the fire data were not normally distributed, the median was used as a more appropriate indication of the central tendency rather than the mean. Non parametric Mann–Whitney U tests (GraphPad Prism 5) were used for statistical analysis. The test was two-tailed and P- values ≤ 0.05 were considered significant.