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ARS Home » Plains Area » Las Cruces, New Mexico » Range Management Research » Research » Publications at this Location » Publication #380707

Research Project: Science and Technologies for the Sustainable Management of Western Rangeland Systems

Location: Range Management Research

Title: Thresholds and alternative states in neotropical dry forest in response to fire severity

item PEINETTI, RAUL - University Of La Pampa
item Bestelmeyer, Brandon
item CHIRINO, CLAUDIA - University Of La Pampa
item FLORENCIA, VIVALDA - University Of La Pampa
item KIN, ALICIA - University Of La Pampa

Submitted to: Journal of Applied Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2023
Publication Date: 12/10/2023
Citation: Peinetti, R., Bestelmeyer, B.T., Chirino, C.C., Florencia, V.L., Kin, A.G. 2023. Thresholds and alternative states in neotropical dry forest in response to fire severity. Journal of Applied Ecology. 34(2):e2937.

Interpretive Summary: We evaluated the response of a dry forest ecosystem to increasing fire severity to estimate a threshold at which forest resilience is lost. Threshold identification can help minimize undesirable forest transitions to shrub thicket states that have reduced utility for livestock production and other services.  Our results provide insights on fire-vegetation relationships that can guide the management of a critical South American forest ecosystem.

Technical Abstract: 1. Neotropical xerophytic forest ecosystems co-evolved with fires that shaped their resilience to disturbance events. However, it is unknown whether forest resilience to fires persists under a new fire regime influenced by anthropogenic disturbance and climate change. We asked if there is evidence for a fire severity threshold causing an abrupt transition from a forest to an alternative shrub thicket state.2. We studied a heterogeneous wildfire event to assess medium-term effects (~10 years) of increasing fire severity on a xerophytic Calden forest site in central Argentina. We conducted field vegetation surveys in patches that were exposed to low (LFS), medium (MFS), and high (HFS) fire severities, but had similar pre-fire woody canopy cover. Satellite images were used to quantify fire severity using a delta Normalized Burning Ratio (dNBR) and to map pre-fire canopy cover.3. Post-fire total woody canopy cover was higher in LFS and MFS than HFS patches, but the understory woody component was highest in HFS patches. The density of woody plants was over three times higher under high severity fire than moderate and low severity fire due to the contribution of short-statured woody plants to the total density. Unlike LFS and MFS patches, the short-statured plants in HFS patches were persistent, multi-stemmed shrubs that resulted from the resprouting of top-killed Prosopis caldenia trees, and more importantly, from young shrubs that probably established after the wildfire.Synthesis and applications. Calden forest structure proved to be resilient to fires of low to moderate severities but not too high severity fires. A fire event with dNBR values > ~600 increased the forest susceptibility to an abrupt transition to a shrub thicket state. Post-fire grazing and controlled fire treatments likely contributed to shrub dominance after high-intensity wildfire. Forest to shrub thicket transition may result in recurring high severity fire events. Repeated high severity fires combined with grazing can trap the system in a shrub thicket state. The abrupt transitions examined here occurred at local scales, but they illustrate the mechanisms of irreversible state change that are occurring across dry neotropical forests in response to the increasing severity of wildfires.