Data from: Post-fire changes in forest carbon storage over a 300-year chronosequence of Pinus contorta-dominated forests

A warming climate may increase the frequency and severity of stand-replacing wildfires, reducing carbon (C) storage in forest ecosystems. Understanding the variability of post-fire C cycling on heterogeneous landscapes is critical for predicting changes in C storage with more frequent disturbance. We measured C pools and fluxes for 77 lodgepole pine (Pinus contorta Dougl. ex Loud var. latifolia Engelm.) stands in and around Yellowstone National Park (YNP) along a 300-year chronosequence to examine how quickly forest C pools recover after a stand-replacing fire, their variability through time across a complex landscape, and the role of stand structure in this variability. Carbon accumulation after fire was rapid relative to the historical mean fire interval of 150-300 years, recovering nearly 80% of pre-fire C in 50 years and 90% within 100 years. Net ecosystem carbon balance (NECB) declined monotonically from 160 g C m-2 yr-1 at age 12 to 5 g C m 2 yr-1 at age 250, but was never negative after disturbance. Decomposition and accumulation of dead wood contributed little to NECB relative to live biomass in this system. Aboveground net primary productivity was correlated with leaf area for all stands, and the decline in aboveground net primary productivity with forest age was related to a decline in both leaf area and growth efficiency. Forest structure was an important driver of ecosystem C, with ecosystem C, live biomass C, and organic soil C varying with basal area or tree density in addition to forest age. Rather than identifying a single chronosequence, we found high variability in many components of ecosystem C stocks through time; a > 50% random subsample of the sampled stands was necessary to reliably estimate the non-linear equation coefficients for ecosystem C. At the spatial scale of YNP, this variability suggests that landscape C develops via many pathways over decades and centuries, with prior stand structure, regeneration, and within-stand disturbance all important. With fire rotation projected to be < 30 years by mid century in response to a changing climate, forests in YNP will store substantially less C (at least 4.8 kg C/m2 or 30% less).

气候变暖可能会提升林分毁灭性野火（stand-replacing wildfire）的发生频率与强度，进而降低森林生态系统的碳（C）储量。理解异质景观下火后碳循环的变异特征，对于预测干扰频率增加背景下的碳储量变化至关重要。本研究沿300年的年代序列（chronosequence），对黄石国家公园（Yellowstone National Park, YNP）及其周边的77个扭叶松（Pinus contorta Dougl. ex Loud var. latifolia Engelm.）林分开展碳库与碳通量测定，旨在探究林分毁灭性野火后森林碳库的恢复速率、复杂景观下碳库随时间的变异特征，以及林分结构在该变异中的作用。相较于历史平均火间隔期150~300年，火后碳积累速率较快：林分在50年内即可恢复至火前碳储量的近80%，100年内恢复至90%。生态系统净碳平衡（Net ecosystem carbon balance, NECB）从林分12年生时的160克碳每平方米每年单调下降至250年生时的5克碳每平方米每年，但在干扰后始终未出现负值。相较于活生物量，本研究系统中枯木的分解与积累对生态系统净碳平衡的贡献极小。所有林分的地上净初级生产力均与叶面积呈显著相关；林分地上净初级生产力随林龄的下降，与叶面积和生长效率的双重降低相关。林分结构是生态系统碳库的重要驱动因子：除林龄外，生态系统总碳、活生物量碳以及有机土壤碳均随胸高断面积或林木密度发生变化。本研究并未采用单一的年代序列样地，而是发现生态系统碳储量的诸多组分随时间呈现出极高的变异性；若要可靠估算生态系统碳的非线性方程系数，需从采样林分中随机抽取超过50%的子样本。在黄石国家公园的空间尺度下，这种变异性表明景观碳库在数十年至数百年的时间尺度上通过多种路径形成，此前的林分结构、更新过程以及林分内的干扰均发挥了重要作用。根据气候变暖的预测结果，到本世纪中叶，火轮回期将降至30年以下，黄石国家公园的森林碳储量将大幅下降（至少减少4.8千克碳每平方米，降幅达30%）。