Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
UNC Health Care System, 1025 Think Place, Morrisville, NC, USA.
Sci Total Environ. 2022 Feb 1;806(Pt 4):151482. doi: 10.1016/j.scitotenv.2021.151482. Epub 2021 Nov 4.
Fire disturbance has increased in some tundra ecosystems due to anthropogenic climate change, with important ramifications for terrestrial carbon cycling. Assessment of the potential impact of fire-regime change on tundra carbon stocks requires long-term perspectives because tundra fires have been rare historically. Here we integrated the process-based Dynamic Organic Soil version of the Terrestrial Ecosystem Model with paleo-fire records to evaluate the responses of tundra carbon stocks to changes in fire return interval (FRI). Paleorecords reveal that mean FRIs of tundra ecosystems in Alaska ranged from centennial to millennial timescales (200-6000 years) during the late Quaternary, but projected FRIs by 2100 decrease to a few hundred years to several decades (70-660 years). Our simulations indicate threshold effects of changing FRIs on tundra carbon stocks. Shortening FRI from 5000 to 1000 years results in minimal carbon release (<5%) from Alaskan tundra ecosystems. Rapid carbon stock loss occurs when FRI declines below 800 years trigger sustained mobilization of ancient carbon stocks from permafrost soils. However, substantial spatial heterogeneity in the resilience/sensitivity of tundra carbon stocks to FRI change exists, largely attributable to vegetation types. We identified the carbon stocks in shrub tundra as the most vulnerable to decreasing FRI because shrub tundra stores a large share of carbon in combustible biomass and organic soils. Moreover, our results suggest that ecosystems characterized by large carbon stocks and relatively long FRIs (e.g. Brooks Foothills) may transition towards hotspots of permafrost carbon emission as a response to crossing FRI thresholds in the coming decades. These findings combined imply that fire disturbance may play an increasingly important role in future carbon balance of tundra ecosystems, but the net outcome may be strongly modulated by vegetation composition.
由于人为气候变化，一些冻原生态系统的火灾干扰有所增加，这对陆地碳循环产生了重要影响。评估火灾发生频率变化对苔原生态系统碳储量的潜在影响需要从长远角度考虑，因为历史上苔原火灾很少见。在这里，我们将基于过程的陆地生态系统模型的动态有机土壤版本与古火灾记录相结合，以评估火灾回归间隔（FRI）变化对苔原生态系统碳储量的响应。古记录表明，在第四纪晚期，阿拉斯加苔原生态系统的平均 FRI 范围从百年到千年（200-6000 年），但到 2100 年，预计 FRI 将缩短至几百年到几十年（70-660 年）。我们的模拟表明，改变 FRI 对苔原生态系统碳储量有阈值效应。将 FRI 从 5000 年缩短至 1000 年，仅导致阿拉斯加苔原生态系统释放出少量的碳（<5%）。当 FRI 缩短到 800 年以下时，就会引发多年冻土土壤中古老碳储量的持续释放，从而导致碳储量的快速损失。然而，苔原生态系统碳储量对 FRI 变化的恢复力/敏感性存在很大的空间异质性，这主要归因于植被类型。我们发现，灌木苔原的碳储量最容易受到 FRI 减少的影响，因为灌木苔原的可燃烧生物量和有机土壤中储存了大量的碳。此外，我们的研究结果表明，碳储量较大且 FRI 相对较长的生态系统（如布鲁克斯山麓）可能会因未来几十年内越过 FRI 阈值而向多年冻土碳排放热点转变。这些发现表明，火灾干扰可能在未来苔原生态系统的碳平衡中发挥越来越重要的作用，但植被组成可能会强烈调节净结果。
