Oak Ridge Institute for Science and USDA Forest Service Pacific Northwest Research Station, Corvallis, Oregon, United States of America.
USDA Forest Service Pacific Northwest Research Station, Corvallis, Oregon, United States of America.
PLoS One. 2024 May 31;19(5):e0302823. doi: 10.1371/journal.pone.0302823. eCollection 2024.
Forest ecosystems store large amounts of carbon and can be important sources, or sinks, of the atmospheric carbon dioxide that is contributing to global warming. Understanding the carbon storage potential of different forests and their response to management and disturbance events are fundamental to developing policies and scenarios to partially offset greenhouse gas emissions. Projections of live tree carbon accumulation are handled differently in different models, with inconsistent results. We developed growth-and-yield style models to predict stand-level live tree carbon density as a function of stand age in all vegetation types of the coastal Pacific region, US (California, Oregon, and Washington), from 7,523 national forest inventory plots. We incorporated site productivity and stockability within the Chapman-Richards equation and tested whether intensively managed private forests behaved differently from less managed public forests. We found that the best models incorporated stockability in the equation term controlling stand carrying capacity, and site productivity in the equation terms controlling the growth rate and shape of the curve. RMSEs ranged from 10 to 137 Mg C/ha for different vegetation types. There was not a significant effect of ownership over the standard industrial rotation length (~50 yrs) for the productive Douglas-fir/western hemlock zone, indicating that differences in stockability and productivity captured much of the variation attributed to management intensity. Our models suggest that doubling the rotation length on these intensively managed lands from 35 to 70 years would result in 2.35 times more live tree carbon stored on the landscape. These findings are at odds with some studies that have projected higher carbon densities with stand age for the same vegetation types, and have not found an increase in yields (on an annual basis) with longer rotations. We suspect that differences are primarily due to the application of yield curves developed from fully-stocked, undisturbed, single-species, "normal" stands without accounting for the substantial proportion of forests that don't meet those assumptions. The carbon accumulation curves developed here can be applied directly in growth-and-yield style projection models, and used to validate the predictions of ecophysiological, cohort, or single-tree style models being used to project carbon futures for forests in the region. Our approach may prove useful for developing robust models in other forest types.
森林生态系统储存了大量的碳,它们可以是大气二氧化碳的重要来源或汇,而大气二氧化碳是导致全球变暖的原因之一。了解不同森林的碳储存潜力及其对管理和干扰事件的响应,是制定部分抵消温室气体排放的政策和情景的基础。不同模型对活树碳积累的预测方式不同,结果也不一致。我们开发了生长和产量模型,以预测美国太平洋沿岸地区(加利福尼亚州、俄勒冈州和华盛顿州)所有植被类型的林分水平活树碳密度随林龄的变化,该模型基于 7523 个国家森林清查样地。我们在查普曼-理查德方程中纳入了立地生产力和可蓄积量,并检验了集约管理的私有林与管理程度较低的公有林是否表现不同。我们发现,最好的模型将可蓄积量纳入控制林分容纳量的方程项,将立地生产力纳入控制生长率和曲线形状的方程项。不同植被类型的 RMSE 值范围为 10 到 137 Mg C/ha。在生产力较高的花旗松/西部铁杉区,标准工业轮伐期(~50 年)的所有权对其没有显著影响,这表明可蓄积量和生产力的差异很大程度上解释了归因于管理强度的变化。我们的模型表明,将这些集约管理土地的轮伐期从 35 年延长至 70 年,将使景观上储存的活树碳量增加 2.35 倍。这些发现与一些研究结果不一致,这些研究认为,对于相同的植被类型,活树碳密度随林龄的增加而增加,并且没有发现更长的轮伐期会导致产量(按年计算)增加。我们怀疑,差异主要是由于应用了从完全蓄积、未受干扰、单一物种的“正常”林分中开发的产量曲线,而没有考虑到不符合这些假设的森林的很大比例。这里开发的碳积累曲线可以直接应用于生长和产量模型,用于验证该地区森林碳未来预测的生理生态、林分或单木模型的预测。我们的方法可能对开发其他森林类型的稳健模型很有用。