Modelling Holocene peatland dynamics

Dynamic global vegetation models (DGVMs) are designed for the study of past, present and future vegetation patterns together with associated biogeochemical cycles and climate feedbacks. However, current DGVMs lack functionality for the representation of peatlands, an important store of carbon at high latitudes. We demonstrate a new implementation of peatland dynamics in a customised "Arctic" version of the dynamic vegetation model LPJ-GUESS, simulating the long-term evolution of selected northern peatland ecosystems and assessing the effect of changing climate on peatland carbon balance. Our approach employs a dynamic multi-layer soil with representation of freeze-thaw processes and litter inputs from a dynamically-varying mixture of the main peatland plant functional types; mosses, dwarf shrubs and graminoids. The model was calibrated and tested for a sub-arctic mire in Stordalen, Sweden, and validated at a temperate bog site in Mer Bleue, Canada. A regional evaluation of simulated carbon fluxes, hydrology and vegetation dynamics encompassed additional locations spread across Scandinavia. Simulated peat accumulation was found to be generally consistent with published data and the model was able to capture reported long-term vegetation dynamics, water table position and carbon fluxes. A series of sensitivity experiments were carried out to investigate the vulnerability of high latitude peatlands to climate change. We found that the Stordalen mire may be expected to sequester more carbon in the first half of the 21st century due to milder and wetter climate conditions, a longer growing season, and CO2 fertilization effect, turning into a carbon source after mid-century because of higher decomposition rates in response to warming soils.

动态全球植被模型（dynamic global vegetation models, DGVMs）旨在研究过去、当前及未来的植被格局，以及与之相关的生物地球化学循环与气候反馈机制。然而，当前的DGVMs尚未具备模拟泥炭地的功能——泥炭地是高纬度地区重要的碳储存库。本研究在定制化的"北极版"动态植被模型LPJ-GUESS中实现了全新的泥炭地动力学模块，以此模拟选定的北部泥炭地生态系统的长期演化过程，并评估气候变化对泥炭地碳平衡的影响。本研究采用的方法包含动态多层土壤模块，可模拟冻融过程，同时纳入了主要泥炭地植物功能型（包括苔藓、矮灌木和禾本科植物）的动态混合枯落物输入。该模型已在瑞典斯托尔达伦（Stordalen）的亚北极沼泽中完成校准与测试，并在加拿大梅尔布卢（Mer Bleue）的温带泥炭沼泽站点完成验证。研究还对模拟的碳通量、水文过程与植被动力学开展了区域尺度评估，覆盖了斯堪的纳维亚半岛的多个额外站点。模拟得到的泥炭积累量总体与已发表的数据相符，且模型能够复现已报道的长期植被动态、地下水位位置与碳通量变化。本研究开展了一系列敏感性试验，以探究高纬度泥炭地对气候变化的脆弱性。研究发现，由于气候更温和湿润、生长季延长以及二氧化碳施肥效应，斯托尔达伦沼泽在21世纪上半叶或将吸收更多碳；但到本世纪中叶后，由于土壤变暖导致有机质分解速率提升，该区域将转变为碳源。