McDonnell T C, Clark C M, Reinds G J, Sullivan T J, Knees B
E&S Environmental Chemistry, Inc., PO Box 609, Corvallis, OR 97339.
US EPA, Office of Research and Development, National Center for Environmental Assessment, Washington DC, 20460, USA.
Environ Adv. 2022 Jul 28;9:1-13. doi: 10.1016/j.envadv.2022.100271.
Forest understory plant communities in the United States harbor most of the vegetation diversity of forests and are often sensitive to changes in climate and atmospheric deposition of nitrogen (N). As temperature increases from human-caused climate change and soils recover from long term atmospheric deposition of N and sulfur (S), it is unclear how these important ecosystem components will respond. We used the newly developed US-PROPS model - based on species response functions for over 1,500 species - to evaluate the potential impacts of atmospheric N deposition and climate change on species occurrence probability for a case study in the forested ecosystems of the Great Smoky Mountains National Park (GRSM), an iconic park in the southeastern United States. We evaluated six future scenarios from various combinations of two potential recoveries of soil pH (no change, +0.5 pH units) and three climate futures (no change, +1.5, +3.0 deg C). Species critical loads (CLs) of N deposition and projected responses for each scenario were determined. Critical loads were estimated to be low (< 2 kg N/ha/yr) to protect all species under current and expected future conditions across broad regions of GRSM and these CLs were exceeded at large spatial extents among scenarios. Northern hardwood, yellow pine, and chestnut oak forests were among the most N-sensitive vegetation map classes found within GRSM. Potential future air temperature conditions generally led to decreases in the maximum occurrence probability for species. Therefore, CLs were considered "unattainable" in these situations because the specified level of protection used for CL determination (i.e., maximum occurrence probability under ambient conditions) was not attainable. Although some species showed decreases in maximum occurrence probability with simulated increases in soil pH, most species were favored by increased pH. The importance of our study is rooted in the methodology described here for establishing regional CLs and for evaluating future conditions, which is transferable to other national parks in the U.S. and in Europe where the original PROPS model was developed.
美国森林林下植物群落承载着森林中大部分的植被多样性，且往往对气候和氮（N）的大气沉降变化敏感。由于人为导致的气候变化使温度上升，以及土壤从长期的氮和硫（S）大气沉降中恢复，尚不清楚这些重要的生态系统组成部分将作何反应。我们使用新开发的美国植物反应预测系统（US-PROPS）模型——基于1500多种物种的物种反应函数——来评估大气氮沉降和气候变化对大雾山国家公园（GRSM）森林生态系统案例研究中物种出现概率的潜在影响，GRSM是美国东南部一个具有标志性的公园。我们评估了六种未来情景，这些情景来自土壤pH值两种潜在恢复情况（无变化、升高0.5个pH单位）和三种气候未来情景（无变化、升高1.5、升高3.0摄氏度）的各种组合。确定了每种情景下氮沉降的物种临界负荷（CLs）和预测反应。据估计，临界负荷较低（<2千克氮/公顷/年），以在GRSM的广大区域保护当前和预期未来条件下的所有物种，并且在各情景中的很大空间范围内这些临界负荷都被超过。北方硬木林、黄松林和栗栎林是GRSM内发现的对氮最敏感的植被地图类别。未来潜在的气温条件通常导致物种最大出现概率下降。因此，在这些情况下临界负荷被认为是“无法达到的”，因为用于确定临界负荷的指定保护水平（即环境条件下的最大出现概率）无法实现。尽管一些物种随着模拟土壤pH值的增加最大出现概率下降，但大多数物种受pH值升高的青睐。我们研究的重要性源于此处描述的用于建立区域临界负荷和评估未来条件的方法，该方法可应用于美国和欧洲其他国家公园，美国植物反应预测系统（PROPS）模型最初就是在这些国家公园开发的。
