Total Carbon Flux in the Northeastern U.S.

These datasets were formed from the ratios of two runs of PnET , a forest ecosystem model (see Parent DIF). It represents a grid of pixels in New England and eastern New York at spatial resolution of 60 arc seconds (about 2 kilometers). One model run used ambient levels of CO2, precipitation and temperature, and the other run used modified levels. Rapid and simultaneous changes in temperature, precipitation and the atmospheric concentration of CO2 are predicted to occur over the next century. Simple, well-validated models of ecosystem function are required to predict the effects of these changes. This model is an improved version of a forest carbon and water balance model (PnEt-II) and the application of the model predicts stand-level and regional-level effects of changes in temperature, precipitation, and atmospheric CO2 concentration. PnET-II is a simple, generalized, monthly time- step model of water and carbon balances (gross and net) driven by nitrogen availability as expressed through foliar N concentration. Improvements from the original model include a complete carbon balance and improvements in prediction of canopy phenology, as well as in the computation of canopy structure and photosynthesis. The model was parameterized and run for 4 forest/site combinations and validated against available data for water yield, gross and net carbon exchange and biomass production. The validation exercise suggests that the determination of actual water availability to stands and the occurrence or non-occurrence of soil-based water stress are critical to accurate modeling of forest net primary production (NPP) and net ecosystem production (NEP). The model was then run for the entire New England/New York (UAS) region using a 1 km resolution geographic information system. Predicted long-term NEP ranged from, -85 to +275 g C /m^2/yr for the 4 forest/site combinations, and from 150 to 350 g C /m^2 /yr for the region, with a regional average of 76 g C /m^2/yr. A combination of increased temperature (+6 deg C), decreased precipitation (-15%) and increased water use efficiency (2X, due to doubling of CO2) resulted generally in increases in NPP and decreases in water yield over the region.

本数据集源自森林生态系统模型PnET（详见Parent DIF）的两组模拟结果之比。其数据覆盖新英格兰与纽约东部区域的像素网格，空间分辨率为60角秒（约2千米）。其中一组模拟采用环境背景水平的二氧化碳、降水与温度参数，另一组则采用修改后的参数水平。据预测，未来百年内全球将出现温度、降水与大气CO₂浓度的快速协同变化。为精准预测此类变化带来的生态影响，亟需构建经过充分验证的简易生态系统功能模型。本模型是森林碳水平衡模型PnET-II的改进版本，可用于模拟温度、降水及大气CO₂浓度变化对林分尺度与区域尺度生态系统的影响。PnET-II是一款简易通用的月时间步长模型，用于模拟水分与碳平衡（包括总碳平衡与净碳平衡），其驱动因子为基于叶片氮浓度表征的氮素可利用性。相较于原始版本，该模型的改进之处涵盖完整碳平衡模块、冠层物候预测精度提升，以及冠层结构与光合作用计算方法的优化。研究针对4种森林/样地组合完成了模型参数化与模拟，并利用已公开的水量、总碳交换、净碳交换以及生物量生产数据对模型进行了验证。验证结果表明，准确获取林分实际水分可利用性以及判断土壤水分胁迫是否发生，对于精准模拟森林净初级生产力（Net Primary Production, NPP）与生态系统净生产力（Net Ecosystem Production, NEP）至关重要。随后，研究利用空间分辨率为1千米的地理信息系统（Geographic Information System），对新英格兰与纽约全域（UAS）开展了模型模拟。针对4种森林/样地组合的长期NEP模拟结果范围为-85至+275克碳/平方米/年，区域尺度的模拟结果范围为150至350克碳/平方米/年，区域平均水平为76克碳/平方米/年。当同时满足温度升高（+6℃）、降水减少（-15%）以及水分利用效率提升2倍（因CO₂浓度翻倍）这三个条件时，该区域整体的NPP将呈现上升趋势，而水量产出则会出现下降。