Assessing change in ecosystem processes twenty four years after the 1988 Yellowstone Wildfires, 2013

The extent of young postfire conifer forests is growing throughout
western North America as the frequency and size of high-severity fires
increase, making it important to understand ecosystem structure and
function in early seral forests. Understanding nitrogen (N) dynamics
during postfire stand development is especially important because
northern conifers are often N limited. We re-sampled lodgepole pine
(Pinus contorta var. latifolia) stands that regenerated naturally
after the 1988 fires in Yellowstone National Park (Wyoming, USA) to
ask: (1) How have N pools and fluxes changed over a decade (15 to 25
years postfire) of very rapid forest growth? (2) At postfire year 25,
how do N pools and fluxes vary with lodgepole pine density and
productivity? Lodgepole pine foliage, litter (annual litterfall,
forest-floor litter), and mineral soils were sampled in 14 plots
(0.25-ha) that varied in postfire lodgepole pine density (1,500 to
344,000 stems ha-1) and aboveground net primary production (ANPP; 1.4
to 16.1 Mg ha-1 yr-1). Previous data collected 15 and 17 years
postfire (i.e., 2003 and 2005) provided a reference for assessing
change in ecosystem process rates over time. At that time, lodgepole
pine foliar nitrogen (N) concentrations had not yet suggested N
limitation, and tree density and net primary production strongly
influenced ecosystem carbon (C) and N stocks. These data were collected in 2012 and 2013 and are associated with the
following publication: Turner, M. G., T. G. Whitby, and W. H. Romme. 2019. Feast not famine:
Nitrogen pools recover rapidly in 25-yr old postfire lodgepole pine.
Ecology (In press).

北美西部的年轻火后针叶林分布范围正持续扩大，伴随高强度野火的发生频率与规模不断攀升，因此理解早期演替森林的生态系统结构与功能显得尤为关键。其中，厘清火后林分发育过程中的氮（Nitrogen, N）动态尤为关键，因为北方针叶林通常受氮限制。
本研究对美国怀俄明州黄石国家公园1988年火灾后自然更新的扭叶松（Pinus contorta var. latifolia）林分进行了重采样，旨在解答两个科学问题：(1) 在火后森林快速生长的十年间（火后15至25年），氮库与氮通量发生了何种变化？(2) 火后25年时，氮库与氮通量如何随扭叶松密度与生产力发生变化？
研究团队在14块面积为0.25公顷的样地中采集了扭叶松针叶、枯落物（年度枯落物、林地地表枯落物）以及矿质土壤样品。这些样地的火后扭叶松密度范围为1500至344000株·公顷⁻¹，地上净初级生产力（Aboveground Net Primary Production, ANPP）介于1.4至16.1 Mg·ha⁻¹·yr⁻¹之间。
2003年与2005年（即火后15年和17年）采集的前期数据，为评估生态系统过程速率随时间的变化提供了参照基准。彼时，扭叶松针叶的氮浓度尚未显现氮限制特征，且树木密度与净初级生产力对生态系统碳（C）与氮（N）储量具有显著影响。
本次研究数据采集于2012年与2013年，相关成果已关联发表于以下论文：Turner, M. G., T. G. Whitby, and W. H. Romme. 2019. 丰饶而非匮乏：火后25年的扭叶松林中氮库快速恢复. 生态学（Ecology）（即将刊出）。