Impacts of fire severity and cattle grazing on early plant dynamics in old-growth Araucaria-Nothofagus forests

Paola Arroyo-Vargas,Aníbal Pauchard,Bart Muys,Andres Fuentes-Ramírez

doi:10.1186/s40663-019-0202-2

Paola Arroyo-Vargas, Aníbal Pauchard + Show 2 more

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https://doi.org/10.1186/s40663-019-0202-2

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Abstract

BackgroundFire has historically shaped the dynamics of Araucaria araucana-Nothofagus pumilio forests in the Andean region of South America. Nevertheless, human disturbances and stronger drought events have resulted in increased occurrence and severity of wildfires. Regardless of their conservation relevance, the initial response to fire of Araucaria-Nothofagus forests has not been well documented. Through this research we tested the hypothesis that plant composition of Araucaria-Nothofagus forest after fire will initially differ in its recovery depending on fire severity, but over time, plant similarity will increase among areas with different levels of fire severity. The study was carried out in old-growth Araucaria-Nothofagus forests in south-central Chile (38°S) that were burned in 2015. We studied vegetation response to three levels of fire severity (low (LS), moderate (MS) and high (HS) severity), also including an adjacent unburned forest (UN), which were assessed one, two and three years after fire. We also evaluated the impact of cattle on plant recovery after fire. We measured species richness, abundance, plant diversity and origin of all vascular plant species.ResultsSpecies richness and plant abundance responded differently to fire severity. Time-since-fire had a significant effect on plant richness and abundance. Plant composition within LS areas was similar to UN areas, but MS and HS areas were significantly less diverse compared to UN and LS. In absence of other major disturbances, similarity in plant composition tended to increase over time across the different levels of fire severity, becoming more similar to UN. We also found a synergetic effect of cattle and fire on species richness. This interaction promotes the establishment of non-native species and limits the recovery of native species following fire.ConclusionsFire severity had a significant impact on the plant community of old-growth Araucaria-Nothofagus forests, especially in areas of high fire severity, where the native tree N. pumilio was completely absent. Nevertheless, plant communities can recover gradually, depending on fire severity, time-since-fire, and the absence of cattle grazing. Management actions should include the exclusion of cattle within fire-affected areas and afforestation with N. pumilio in areas high fire severity due to its unsuccessful recruitment after fire.

Highlights

Fire has historically shaped the dynamics of Araucaria araucana-Nothofagus pumilio forests in the Andean region of South America
Post-fire dynamics of vegetation Species richness In the unburned forest (UN), which we assume corresponds to the condition prior to fire, we recorded 31 vascular plant species
The common species that were found across the entire fire severity gradient, and for the three years of the study were A. araucana, Alstroemeria aurea Graham, Berberis microphylla G

Summary

Introduction

Human disturbances and stronger drought events have resulted in increased occurrence and severity of wildfires. Regardless of their conservation relevance, the initial response to fire of Araucaria-Nothofagus forests has not been well documented. Through this research we tested the hypothesis that plant composition of Araucaria-Nothofagus forest after fire will initially differ in its recovery depending on fire severity, but over time, plant similarity will increase among areas with different levels of fire severity. Disturbance regimes can be modified by climate change, but they could be amplified (i.e., increasing their frequency and severity) by human activities (Bowman et al 2009; Mundo et al 2013). On the other hand, when fire occurrence is relatively frequent, and is associated to the dynamic of the forest itself, there can be patchy patterns in the vegetation, with fire-tolerant species displaying adaptations (e.g., thick bark to protect the living tissues; Burns 1993; Keeley 2012), post-fire vigorous germination and resprouting, and rapid colonization after fire by fire-adapted non-native species (Bond and van Wilgen 1996)

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