Fire-driven alternative vegetation states across the temperate Andes

The theory of alternative stable states as applied to terrestrial ecosystems, suggests that, under common environmental conditions, different vegetation types may remain stable by contrasting feedback processes. In the temperate Andes, forests and shrublands of Nothofagus species have been proposed as fire-driven alternative vegetation states (AVS): while high fire frequency would promote the stability of pyrophilic shrublands, the absence fires would stabilize pyrophobic forests. However, to assert that they are AVS we need to demonstrate that the fire-vegetation feedbacks occur under the same environmental conditions. We aimed to (i) identify to what extent Nothofagus forests and shrublands occur in the same environmental conditions across the temperate Andes and (ii) to understand how the fire regime explains the distribution patterns of these states. We used global environmental databases and local fire data to (i) estimate the environmental niche overlap of forests and shrublands, and (ii) obtain an indicator of the fire activity at micro-basin scale (percentage of cumulative burned area of forests and shrublands relative to the burnable area; PBA). The environmental niches of forests and shrublands overlapped by more than 70%. Shrublands become more frequent as PBA increases, suggesting that stabilizing fire-vegetation feedbacks promote their persistence. Our results provide broad-scale evidence of fire-driven AVS beyond the tropics.