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Ecological impacts of fire on the Cape Peninsula

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Silvermine valley looking towards Constantiaberg Peak (9 March, 2015)

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An open Protea cone and the released seeds collected in depressions in the soil (Peck's Valley, Muizenberg, 8 March 2015)

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Fire lilies (Cyrtanthus spp.) emerge within weeks of a fire, persist for a few days and are not seen again until the next burn (Cape Point, May 2014)

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Bobartia spp. at Silvermine resprouting after fire on 3 March (taken 9 March 2015)

By Dr Jasper Slingsby, Vegetation Scientist, SAEON Fynbos Node

"The fire behaviour conditions in the Western Cape were very high to extreme across the entire region before and during the veldfires... The veldfires were immediately preceded by two to five days of strong south-east winds accompanied by moderate to low humidity and temperatures...

"Midway through the fire episode the winds changed to the north and northwest and dropped in velocity. This shift brought with it record high temperatures and very low humidity. Veldfires became less driven by wind and more influenced by local topography and conditions [causing] previously inactive and unburned areas to flare up… While the rate of spread dropped, extremely low fuel moistures and humidity created localised instances of extreme fire behaviour.”


The quote is not a report on the March 2015 fire, but it may as well have been. This excerpt from a report on the January 2000 fires in the Western Cape by Fred Kruger and others highlights the strong similarity in conditions experienced during the two fire episodes.

While almost all of the natural vegetation on the Cape Peninsula is highly flammable and most of its extent has burnt in the past 50 years, the January 2000 and March 2015 fires are the biggest on record (see animation of 50 years of fire on the Cape Peninsula (1961-2011) .

Fire management on the Cape Peninsula

The January 2000 fires drew international attention to the issue of fire in Fynbos and stimulated the Ministries of Water Affairs & Forestry and Environmental Affairs to launch the Ukuvuka Fire Stop Campaign, aimed at managing and reducing the impact of fires through alien plant clearing and improved fire-fighting capacity.

Since 2000 the Volunteer Wildfire Services have been formed and various authorities on the Peninsula have combined forces to coordinate efforts through the Cape Peninsula Fire Protection Association, largely led by Working on Fire, SANParks and the City of Cape Town. This team has done an amazing job managing this and many other fires on the Cape Peninsula (at great expense!) despite extreme weather conditions and restrictive legislation.

One of the greatest challenges to managing Fynbos fires is the huge legal and financial disincentive to perform prescribed burns to reduce fuel loads and fuel continuity (and thus the likelihood of extreme fires), because one can be held liable for any damages should the burn get out of control (the same applies to the use of back burns used to halt fires). There are various efforts to ease this constraint underway, but the cost of prescribed burns is still prohibitively large and suitable conditions that are benign (i.e. not too hot and windy) but hot and dry enough to facilitate a fire are rare.

The second greatest challenge is the presence of invasive alien species such as pines, wattles and gum trees that increase the fuel load and/or are highly flammable, making fires much less manageable. Table Mountain National Park (TMNP) and the Working for Water campaign put serious effort into removing alien vegetation from the Park, but they are not responsible for private land. The majority of private houses lost in this and previous fires were surrounded by dense alien vegetation.

Despite these challenges, the fire protection services (and town planners) have maintained an amazing record relative to similar ecosystems elsewhere in the world. A comparison of severe fires across Mediterranean-type Ecosystems (Table 1) shows that some of the most damaging fires in Fynbos to date (the Peninsula fires of January 2000 and March 2015) pale in comparison to fires from other regions.

These differences are due, in part, to urban planners in Cape Town largely maintaining hard edges at the wildland-urban interface, with relatively few houses isolated within dense vegetation, and also to the greater severity of fires in other Med-type regions due to the large and highly flammable fuel loads formed by their natural vegetation (largely pines, wattles and gum trees).

In the Cape Peninsula, most houses are built at the bottom of slopes, not on hilltops or midslopes above flammable vegetation where they are far more vulnerable to fire. We need to take a very close look at where property was lost in the recent fire, where fire defense was difficult, and what we can do to improve the situation for future fires.

We are still losing property and many fires are occurring more frequently than is healthy for Fynbos ecosystems. Since fires will continue to occur in natural or alien vegetation irrespective of actions to prevent them, it is clear that we need to improve our ability to coexist with fire by learning to be more fire-wise about positioning our houses, managing our properties, reducing the risk of starting fires, and about how we respond when fires break out (see resources below).

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Map 1: Vegetation age (in days) in January 2000 and April 2011. The area affected by the March 2015 fire (within the black box) was predominantly 15 years old, but for a few small fragments. January 2000 saw the two largest fires on record at that time (both >3000 ha), burning approximately 8000 ha. The March 2015 fire is estimated to be >4000 ha, which would make it the largest single fire on the Peninsula on record. Areas like the Cederberg Wilderness Area have recorded fires as large as 80 000 ha, but do not have to contend with a large wildland-urban interface. Data courtesy of South African National Parks (SANParks)

We all need to think about what we can do to improve fire safety. Is our house close to the edge and how old is the veld the other side? Is anything on my property a hazard for spreading fire to the buildings or adjacent properties? Can fire protection services adequately access my property or the adjacent wildland-urban interface? Have I spoken to my neighbours and do we have a coordinated plan of action should a fire threaten our property? Of course, most homeowners bordering or near the park will be very fire-wise for the next year or two, but what about in 10-20 years’ time when the veld is ready for another round...?

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Ecological impacts of the March 2015 fires

"Great misapprehension prevails on the subject [of fire], caused mainly by looking at it from the point of view of an inhabitant of Northern Europe. The veldt fire here is not an incendiary disaster but a natural process, that usually is only dangerous when ignorantly interrupted or for some reason or other, too long deferred." - David Ernest Hutchins, 1893.

The vast majority of Fynbos plants have their lives intimately tied to fire. Most Fynbos vegetation must burn every 10-30 years or so (depending on where you are in the biome) otherwise it begins to senesce and become moribund. If you look at old stands of fynbos, there is a striking absence of seedlings and juvenile plants. Fynbos plants cue their reproduction to post-fire conditions when competition is low, and plant-eating animals are sparse.

There are a range of remarkable devices to get the timing right, including smoke- and heat-stimulated seed germination, post-burn flowering of many species recovering from bulbs, tubers and the like, and seed release from insulated cones. If fire is excluded for too long, some species begin to senesce without reproducing, eventually going locally extinct.

In contrast to the old stands, if you look at the blackened ‘ruins’ of today in a year’s time, you will see thousands of seedlings beginning their new cycle of life. Post-fire succession of Fynbos is a spectacular process with all kinds of beautiful botanical wonders like the fire lilies (Cyrtanthus spp.) that emerge within weeks of the fire, and a series of bulbs and rare orchids that are only seen in the first few years after fire, some of which put on mass displays that colour the mountain in pinks, yellows or orange.

Unfortunately, if Fynbos burns too frequently, some species do not have time to set seed and likewise go locally extinct. Fynbos thus needs fire within a certain range of return interval for diversity to be maintained.

While some of the vegetation burnt in this year’s fire may be less than ten years old, most of it last burnt in the huge fires of January 2000, falling perfectly within the 10-30 year range (see Map 1). The only pity (ecologically speaking) is that such a large tract of vegetation burnt in one go. Scientists widely believe that Fynbos plant biodiversity is maximized and best maintained if the vegetation is a mosaic of different aged stands that burnt at different times of year and under varied conditions.

Studies have shown that while almost all Fynbos species are adapted to cope with fire, each species has a different preference in terms of fire frequency and intensity and in weather conditions in the first few years after fire. Repeated extensive fires of high intensity like we have seen in January 2000 and March 2015 could have negative impacts on the flora.

Similarly, while little is known about the effects of fire on animal populations and species in Fynbos, the scarcity of large patches of remnant unburnt vegetation that would serve as refuge for the many animals displaced by the fire is likely negative. Of course some animals are killed in fire events, but by far the biggest impact is the transformation of habitat after a fire. For example, fynbos rodents that thrive in the cover of dense shrubs are now exposed to their bird and mammal predators while sunbirds and sugarbirds will have to wait years before nectar-producing flowers are abundant again.

But fynbos animals, like the plants, recover from fire. If they could not do so, they would have gone extinct when the current fire regime set in millions of years ago. The many individuals seen crossing roads away from fire and appearing in people’s gardens or houses indicates that many animals can get away from the fires, but suggests they need somewhere to go, and that fragmentation of their habitat by urban development limits their ability to get to unburnt sites. Biologists and animal lovers are asking homeowners to please be tolerant of these "visitors” as they will probably return to the veld once the fire has died and the ash cooled.

In addition to loss of habitat, some animals face food constraints induced by the fire, such as reduced nectar availability due to the lack of flowers. Dr Phoebe Barnard of the South African National Biodiversity Institute (SANBI) stated "the temporal resource bottlenecks faced by sugarbirds and sunbirds as a result of destruction of major Protea stands in Silvermine are probably severe, [resulting in] many more birds in the urban settlements than normal at the moment”.

The news isn’t all bad though. The flush of flowers in the first few years after fire provide a rich nectar resource, while new shoots provide good forage for herbivores. Indeed, some animal species prefer younger veld. "There is evidence that some [amphibians and reptiles] depend on fire-reduced vegetation [and] are not doing well on Table Mountain, which hasn't burnt in a long time,” said Dr John Measey, researcher at Stellenbosch University and Editor-in-Chief of African Journal of Herpetology.

Fire and soil erosion

Severe fires can alter soil properties resulting in severe soil erosion, which can clog culverts and road drains and damage houses that happen to be in vulnerable positions. By far the worst damage is where fires burn stands of alien trees or piles of brush where they have been felled. Pines, gum trees, and Australian acacias burn much more severely than fynbos and are invariably the source of severe erosion.

The Ukukuvuka campaign after the 2000 fires did an excellent job of clearing alien invasives from much of the urban/fynbos fringe. But some patches still remain and some of the worst flare-ups were in alien stands. If you are downslope of one of these hotspots, keep a watchful eye on possible sediment flows that might damage property or clog drains during the winter rains.

Fire and global change

Fire is determined by properties of the fuel, the weather conditions and an ignition source, all of which are influenced by humans and affect humans. This is termed the fire-climate-vegetation-human nexus and there are many complex feedbacks within and between the different components.

For example, climate affects both vegetation growth and fire weather. With changing climate we are seeing changes in the frequency and intensity of extreme fire weather (it has been suggested that March 3rd 2015 was the hottest day in Cape Town in 100 years, while the January 2000 fires included one of the hottest), but weather of this nature is also likely to alter plant growth and mortality or benefit invasive alien plants, leading to changes in vegetation fuel properties.

Predicting the potential outcomes of such feedbacks is no simple task and is the focus of much research locally and worldwide. The SAEON Fynbos Node is currently conducting and supporting various fire-related research projects. In 2014, SAEON held a symposium and panel discussion on "Fire, Biodiversity and Global Change in Fynbos” at the Fynbos Forum meeting in Knysna to outline the management and research problem, to highlight some of the skills and tools available, and to discuss potential for a unified research effort with applied outcomes.

Current SAEON projects involve monitoring the impacts of alien plants on fire intensity and post-fire vegetation recovery (both in terms of diversity and biomass); monitoring the effects of microclimate on post-fire recovery of biomass and exploring evidence for changes in post-fire recovery trajectories; and modelling the impacts of land cover transformation and weather on fire spread and fire frequency on the Cape Peninsula and in the Cederberg Wilderness Area.

For an animation of a basic model mimicking the March 2015 fire, click here.

Fire safety info links and further reading

 

Easy reading

  • Esler, Karen J., Shirley M. Pierce, Charl de Villiers. 2014. FYNBOS - Ecology and Management. Briza Books.
  • Pauw, Anton and Steve Johnson. 1999. Table Mountain, A Natural History. Fernwood Press.

 

Science publications

  • Forsyth and Van Wilgen 2008. The recent fire history of the Table Mountain National Park and implications for fire management. Koedoe. SANParks; 50(1):3-9.
  • Keeley, Bond, Bradstock, Pausas, Rundel 2012; Fire in Mediterranean Ecosystems. Cambridge.
  • Kraaij et al. 2014. Drivers, ecology, and management of fire in fynbos. In: Allsopp N, Colville JF, Verboom GA, editors. Fynbos: Ecology, Evolution, and Conservation of a Megadiverse Region. Oxford: Oxford University Press. page 47-72.
  • Moritz et al. 2014. Learning to coexist with wildfire. Nature; 515: 58-66.
  • Thuiller et al. 2007. Stochastic species turnover and stable coexistence in a species-rich, fire-prone plant community. PLoS One. Jan 2(9):e938.
  • Van Wilgen et al. 2012. The management of fire-adapted ecosystems in an urban setting: the case of Table Mountain National Park, South Africa. Ecol Soc;17

 

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