Alien tree invasions, fire, and restoration in the Cape Floristic Region (CFR)

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Patricia Holmes and David le Maitre

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The CFR is dominated by fire-adapted fynbos shrublands. Invasive alien trees cause major fynbos degradation, and fire is recognized as an important restoration tool. Serotinous invaders (Pinus, Hakea) can be managed using “Fell & Burn”: felling releases seeds after which seeds and seedlings are killed by fire. An alternative for serotinous species is short rotation burning, but this risks eliminating native serotinous species.  More challenging are long-lived, soil-stored invader seed banks, a feature of Acacia: in dense or long-term infestations fire stimulates germination, resulting in extremely dense recruitment which overwhelms recruiting native flora, and is difficult and prohibitively expensive to control. Postponing fire may simply delay the problem, but granivory can reduce invader seed banks after clearing. At lightly invaded sites, or in subsequent follow-ups of denser invasions, clearing must be integrated with fires – whether planned or accidental – to prevent invaders outcompeting the local flora.  Fire successfully suppresses germination of secondary invaders, such as weedy annual grasses, that otherwise benefit from Acacia’s legacy of increased soil nitrogen. Indigenous grasses also benefit from nitrogen and may suppress recruitment of other species, creating an undesirable alternative state dominated by herbaceous species. Post-fire timing of fynbos re-introduction is critical as exposure to wind and sun may kill seedlings where resprouter species have been lost. Sowing of fast-growing forbs and shrubs may partially counter this.  Management authorities remain reluctant to burn and prescribed fires are generally cool fires that are more easily managed and seldom the intense, summer fires ideal for restoration.

Resource Type:
Audio/Video, Conference Presentation, SER2019

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Society for Ecological Restoration