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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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Variation of key elements in soils and plant tissues in subalpine forests of the northern Rocky Mountains, USA
The essential elements for the structure and function of forest ecosystems are found in relatively predictable proportions in living tissues and soils; however, both the degree of spatial variability in elemental concentrations and their relationship with wildfire history are unclear. Quantifying the association between nutrient concentrations in living plant tissue and surface soils within fire-affected forests can help determine how these elements contribute to biogeochemical resilience. Here, we present elemental concentration data (C, N, P, K, Ca, Mg, S, Fe, Mn, Zn) from 72 foliar and 44 soil samples from a network of 15 sites located in the fire-prone subalpine forests of the northern Rocky Mountains, USA Plant functional type is strongly correlated with carbon (C) and nitrogen (N) – C concentrations are highest in coniferous needles, and N concentrations are highest in broadleaved plant species. The average N / P ratio of foliage among samples is 9.8 ± 0.6 (μ ± 95 % confidence). This suggests that N is the limiting nutrient for these plants, however several factors can complicate the use of N / P ratios to evaluate nutrient status. Average C concentrations in organic soil horizons that were burned in regionally extensive fires in 1910 or 1918 CE are lower than those from sites that burned prior to 1901 CE (p < 0.05). This difference suggests that wildfires reduced the pool of soil C and that the legacy of these fires can be measured a century later. Our results help aid in modeling how changing wildfire regimes will influence biogeochemical cycling in subalpine forests.
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- Award ID(s):
- 1655121
- PAR ID:
- 10162999
- Date Published:
- Journal Name:
- Biogeosciences Discussions
- ISSN:
- 1810-6285
- Page Range / eLocation ID:
- 1 to 19
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/bg-2018-443
