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In forests adapted to infrequent (> 100-year) stand-replacing fires, novel short-interval (< 30- year) fires burn young forests before they recover from previous burns. Postfire tree regeneration is reduced, plant communities shift, soils are hotter and drier, but effects on biogeochemical cycling are unresolved. We asked how postfire nitrogen (N) stocks, N availability and N fixation varied in lodgepole pine (Pinus contorta var. latifolia) forests burned at long and short intervals in Grand Teton National Park (Wyoming, USA). In 2021 and 2022, we sampled 0.25-ha plots that burned as long-interval (> 130-year) stand-replacing fire in 2000 (n = 3) or 2016 (n = 3) and nearby plots of shortinterval (16-year) fire that burned as stand-replacing fire in both years (n = 6 ‘reburns’). Five years postfire, aboveground N stocks were 31% lower in short- versus long-interval fire (77 vs. 109 kg N ha-1, respectively) and 76% lower than 21-year-old stands that did not reburn (323 kg N ha-1). However, soil total N averaged 1,072 kg N ha-1 and dominated ecosystem N stocks, which averaged 1,235 kg N ha-1 and did not vary among burn categories. Annual resinsorbed nitrate was highest in reburns and positively correlated with understory species richness and biomass. Lupinus argenteus was sparse, and asymbiotic N fixation rates were modest in all plots (< 0.1 kg N ha-1 y-1). Although ecosystem N stocks were unaffected, high-severity short-interval fire reduced and repartitioned aboveground N stocks and increased N availability. These shifts in N pools and fluxes suggest reburns can markedly alter N cycling in subalpine forests.
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Amazonian forest resilience inferred from fire-induced changes in carbon stocks and tree diversity
Abstract Understanding the resilience of tropical forests to fire is essential for evaluating their dynamics under climate change and increasing land-use pressures. Here, we assess how different fire frequencies and intensities influence tree mortality and carbon dynamics in southeastern Amazonia. Using a replicated randomized block design with 24 plots (40 × 40 m), we applied four treatments: unburned control, one burn in 2016 (B1), two burns in 2013 and 2016 (B2), and two burns with added fuel (B2+) to increase fire intensity. Forest inventories conducted from 2012 to 2024 measured tree mortality, diversity, composition, and aboveground biomass. Fire frequency and intensity significantly increased mortality, particularly among small trees, but impacts on forest structure and productivity were more nuanced. Aboveground biomass declined modestly in burned plots, with the greatest loss in B2+ (13%). Aboveground net primary productivity (ANPP) dropped immediately post-burn, especially in B2 and B2+, and partially recovered by 2022–2024. In contrast, leaf area index (LAI) and litterfall rebounded within a couple of years, suggesting a degree of structural and functional resilience. Species richness and composition remained relatively stable in the years following the first experimental fires, but gradually declined and shifted in B2 and B2+ plots beginning in 2014. These results indicate that the experimental forests’ resilience to low-intensity and infrequent fires can prevent widespread forest collapse, but repeated and intensified burns likely undermine long-term resilience by altering forest structure, composition, and carbon dynamics. With the southeastern Amazon forests projected to burn more often in the coming decades, our results highlight both the vulnerability and recovery potential of these ecosystems. Maintaining ecological integrity and minimizing additional disturbances that influence fuel availability will be critical for sustaining forest functions under future fire regimes.
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- PAR ID:
- 10607968
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Environmental Research Letters
- ISSN:
- 1748-9326
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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