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Zooming in on fire history in Garden Route Fynbos

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A wild fire rages in the fynbos mountain catchments of the Garden Route National Park (Picture: Klaas Havenga)

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Controlled burning is undertaken in the Garden Route National Park (Picture: Jonathan Britton)

- Tineke Kraaij, SANParks Scientific Services, Garden Route

Fynbos vegetation is dependent on fire at appropriate intervals, and in the right season, in order to persist.

An understanding of the history of fire and its effects on the vegetation underpins current and future management for the purpose of biodiversity conservation. However, in newly established protected areas, such as the Garden Route National Park, historical information on fires is often lacking or not in a format that is readily available.

New database

To overcome this problem, a database has been compiled of fires reported by previous land managers in mountain catchment areas in the eastern Outeniqua and Tsitsikamma Mountains during the past century. The data were used to characterise the historical fire regime in the fynbos of the Park. An index of fire danger was furthermore calculated from daily weather data (from four weather stations in the region) since 1940 to explore the seasonality of fire-prone weather and to assess whether fire danger conditions have changed in the long term.

Short intervals between fires are a potential cause of concern if fires recur before the vegetation has produced sufficient seed to enable regeneration after fire.

Fires ranged in size from <1 to 41 902 ha, and the 1500 fires recorded collectively burnt 400 000 ha during the study period. Natural fires (ignited by lightning) dominated the fire regime, accounting for 60 % of the area burnt overall, and for more than 83 % of the area burnt in the Tsitsikamma region. Large numbers of man-made fires occurred, but these collectively burnt a relatively small area.

Seasonal impacts

Fires occurred in all seasons, unlike in the western part of the Fynbos Biome, where fires mostly occur during their dry summer-autumn period. The average interval between fires since 1980 was about 12 years in the eastern Outeniqua and eight years in the Tsitsikamma. The interval between fires in the Tsitsikamma portion of the Park is the shortest on record for any fynbos-dominated protected area.

The incidence of very large natural fires seems to have increased since the 1990s, resulting in a shortening of the interval between fires, and very limited areas of old fynbos existing in the park. Short intervals between fires are a potential cause of concern if fires recur before the vegetation has produced sufficient seed to enable regeneration after fire. Frequent large fires furthermore drive the rapid spread of fire-adapted alien invasive plants such as pines and Hakea, placing high demands on alien plant clearing initiatives shortly after fire.

Weather impacts

In terms of the weather, fire danger conditions peaked in winter (unlike in the western part of the Fynbos Biome), associated with low rainfall and regular occurrence of hot, dry (berg) winds. Low or moderate fire danger conditions were the norm year round, and even large fires occurred under these conditions.

A general lack of correlation between the seasonality of fire weather, lightning, and the incidence of fire, is interpreted as evidence for a largely non-seasonal natural fire regime in Garden Route fynbos. Fire danger conditions on average, as well as the number of moderate to very high risk days, increased in the long term, due to decreases in minimum relative humidity and rainfall, and increases in wind speed and maximum temperature.

These changes in climate are likely to manifest in increased fire frequencies and/or severity, some of which has already been observed.

Acknowledgements

SANParks, SAEON, the Nelson Mandela Metropolitan University and the CSIR funded this study. Climate and lightning data were made available by the South African Weather Service. This work has been submitted for publication to the International Journal of Wildland Fire.

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