Fire-driven alternative vegetation states across the temperate Andes.

Abstract

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 of fires would stabilize pyrophobic forests. However, to confirm this hypothesis, it must be demonstrated that 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) to obtain an indicator of the fire activity at micro-basin scale (percentage of the cumulative burned area (PBA); the higher the PBA the higher the fire activity). 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.This article is part of the theme issue 'Novel fire regimes under climate changes and human influences: impacts, ecosystem responses and feedbacks'.