FCI RL E I MM AT AN E ACGHEAMNEGNET
PRESCRIBED FIRE? PLANNED BURNS, PLUS FUEL MANAGEMENT, MAY BE RX FOR WESTERN CAPE BY JENNIFER FILL AND BRIAN VAN WILGEN
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he all too familiar hue-and-cry was raised in Cape Town, South Africa, when wildfires erupted on the slopes of Table Mountain on April 18. The fires burned more than 600 hectares, tragically damaging numerous University of Cape Town buildings, including irreplaceable libraries and historical sites. Neighborhoods and university students evacuated, and more than 250 government and volunteer firefighters and resources were deployed to the scene. Stunned citizens and those watching around the world were asking: How did this happen? Large wildfires are a familiar anxiety not only for people living in South Africa, but also in places such as the western United States, Australia, Canada, Greece, and Spain. It seems that all it takes is one spark and thousands of hectares are burning. Although this observation might suggest that the way to control fire is to control the source of the spark, it takes more than just an ignition source to set the mountainside alight. All wildland fires depend on the right mix of three key ingredients: weather, fuel, and ignition. Hot, dry, and windy weather is ideal for fire ignition and spread. Regions such as the Western Cape of South Africa and the west coast of California have weather patterns that are very conducive to wildfires. Cool, wet winters alternate with hot, dry, and often windy summers. High temperatures and low humidity in summer allow vegetation to dry out, and once the fire has begun, high winds fan the flames. Temperatures on the day the Table 38
wildfire
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OCTOBER - DECEMBER 2021
Mountain fires started rose to more than 36 C with wind speeds of 45 km/hr, and relative humidity below 10 per cent. The 2015 Cape fires burned more than 6,900 hectares around Cape Town alone, when wind gusts were more than 100 km/hr. To put this in perspective, weather for lighting safe prescribed fires is roughly considered to be relative humidity above 25 per cent and wind speeds of five km/hr or less. Such gusty winds made the Table Mountain fire that much harder to contain and likely sent sparks flying dozens of meters to kilometers ahead of the flaming front. Not only did the weather set the stage, but the vegetation on Table Mountain was like a tinderbox under those conditions. The fynbos vegetation on the slopes of Table Mountain is a shrubby, biodiverse ecosystem unique to the Western Cape. It is structurally very similar to shrublands in other Mediterranean regions, like chaparral in California. Many fynbos species, including endemics (species unique to this ecosystem), are dependent on fires for reproduction, so fire is not always harmful from an ecological perspective. These shrublands are well known to be highly flammable and to recover rapidly after fire (witness the post-fire recovery of vegetation after the 2015 fires in the Western Cape). A much greater concern, however, is the alien pine trees that burn more intensely and result in greater fire severity
