The impact of change in climate, human demography, and other social factors on the fire regime of the Kogelberg Nature Reserve.

Abstract

Background. Fire is a dominant ecological factor in the Fynbos Biome in the Western Cape, and changes in the fire regime have important consequences for the biodiversity conservation of the landscape. Fire regimes in the Western Cape are known to have changed over the past decades due to factors such as changing climate, resources for fighting fires, sources of ignition and human demography. Fire regimes at any given site are never fixed, occurring at varying intervals, in different seasons and at different intensities. Each event is therefore unique and the ecological consequences will depend on both the burn parameters and the nature of the fires that preceded it. Over time, it has been difficult to accurately and consistently quantify fynbos fire regimes and the impact of change in climate, human demography and other social factors because of the unavailability of accurate fire data and records. An understanding of the trends in fire regime and the impact of changes in climate, human demography and other social factors is important to maintain biodiversity and the co-existence of species. There is an urgent need to find effective approaches for assessment of fire regime conditions that balance scientific credibility, spatial continuity and quick delivery. This study seeks to determine the trends in the fire regime (frequencies, return interval, veld age and seasonality) of the Kogelberg Nature Reserve and the impact of changes in climatic patterns, fire-fighting resources, sources of ignition and population increase. Methods. The study site was the Kogelberg Nature Reserve in the Western Cape Province because of its exceptional conservation significance. It is regarded as the floristic heart of the globally unique Cape Floral Kingdom since it appears to have the highest levels of plant species richness and endemism in the Fynbos Biome. Fifty-four years of fire data records were analysed to determine the trends in the fire regime. The study period was divided into two management periods; 1952-1980 and 1981-April 2006 for analysis of the historical fire regime, with the former being a period when there was less pressure of human settlement and before the reserve was proclaimed a mountain catchment area. The latter period was when the reserve had been declared a nature reserve and more people were settling in the neighbouring towns, the fire risk was increasing and allegations of climate change were being made. To test for the impact of climate change on the fire regime of the Kogelberg Nature Reserve, weather data (temperature, wind speed, relative humidity and rainfall) from a weather station in the vicinity of the nature reserve were analysed to determine fire danger indices for a period of 33 years. The United States of America National Fire Danger Rating System as adapted for South African conditions was used to formulate burning indices from the weather data. A relationship between the fire days and the fire data was established. To test for the impact of the changes in fire fighting resources and sources of ignition, data were obtained from the fire records. To investigate the impact caused by population increase on the fire regime of the Kogelberg Nature Reserve population, data were obtained from Statistics South Africa. Available records for each factor were analysed to test for changes in that factor, and each factor was compared with the trends in fire frequency in the study site. Logistic regression was used to test for the relationships in the changes in fynbos fire regimes and its adaptation to changes in climate and social factors. A multivariate analysis was done to tie the four causing variables namely; fire numbers, fires sizes with population density and burning indices. Results. Analysis of data indicated a significant increase in the frequency and size of fires during the period 1981-2006 compared to the period 1952-1980. There has been an increase in the burning of veld younger than 6 years, and the total area burnt has increased significantly in the period 1981-2006 coupled with an increase in the number of fires. However, the size per individual fire has decreased significantly in the period 1981-2006. This study found that the conditions for starting fires improved significantly during the period 1989-2005, due to burning indices increasing from the period 1989-2005 which resulted in conditions for starting fires becoming more conducive than the previous era although fires in the reserve started under all environmental conditions. The population size of people staying in the neighbouring towns and villages has more than doubled during the period 1996-2006. Multivariate analysis showed that there was a significant correlation between number of days when fires burnt and area burnt and population with numbers of fires. Finally, since 1988 Cape Nature has not been able to comply with the minimum requirements for fire prevention due to lack of capacity and resources. Conclusions. The Kogelberg Nature Reserve has been negatively impacted by the increased conditions of ignitions associated with climate change, increased unplanned fires associated with increase in population growth and lack of capacity and resources to prevent and control veld fires. These results could negatively impact biodiversity of the Kogelberg Biosphere Reserve if no actions are taken to address these shortfalls.