NPP Multi-Biome: Gridded Estimates for Selected Regions Worldwide, 1989-2001, R1

Most field data for net primary productivity (NPP) are for relatively small field sites that are effectively points when considered at the 0.5 x 0.5 degree scale commonly used in global biogeochemical models. Thus, direct comparison between field data and coarse resolution model outputs can be misleading. Consistent estimates of NPP for 0.5x0.5 degree grid cells were developed from 15 studies representing NPP in croplands, sparse vegetation, shrublands, grasslands, and forests worldwide. The data set contains 3654 cells with a subset of 2335 cells in which outliers were removed and all replicate measurements were aggregated for each cell. The data set is a contribution to the Global Primary Production Data Initiative (GPPDI). Total NPP ranged from 3 gC/m2/yr for sparse vegetation to 1235 gC/m2/yr in forest, while aboveground NPP ranged from 3 to 890 gC/m2/yr (Zheng et al. 2003). Zheng et al. (2003) discuss the potential problems in such data-model inter-comparisons and identify issues that must be considered during the aggregation of field-scale data to coarser spatial resolutions, usually in the form of grid cells. They evaluated the data set by comparison with existing literature and the widely used Miami model. The file NPP_Gridded_3654_cells.csv is suitable for biome level and overall analyses because of larger sample size. The file NPP_Gridded_2335_unique_cells.csv was derived from the larger file; however, outliers were excluded, replicate measurements were averaged out for each unique geographic locations, and cells classified as water, bareground, and urban were excluded. It is more appropriate for model/data inter-comparisons.净初级生产力（Net Primary Productivity, NPP）的绝大多数野外实测数据均采集自相对狭小的野外样地，在全球生物地球化学模型常用的0.5×0.5经纬度格网尺度下，这些样地实质上仅相当于单个离散点。因此，直接将野外实测数据与粗分辨率模型输出结果进行对比，极易产生误导性结论。本数据集基于全球范围内覆盖农田、稀疏植被、灌丛、草地与森林的15项相关研究，生成了适用于0.5×0.5经纬度格网的统一NPP估算值。该数据集共包含3654个格网单元，其中包含一个由2335个格网单元组成的子集：该子集中已剔除异常值，并对每个格网单元的所有重复测量数据进行了聚合处理。本数据集是全球初级生产力数据倡议（Global Primary Production Data Initiative, GPPDI）的共建成果之一。据郑等（2003）的研究，总NPP取值范围为3 gC/m²/yr（稀疏植被）至1235 gC/m²/yr（森林），而地上部分NPP的取值范围则为3至890 gC/m²/yr。郑等（2003）探讨了此类实测数据与模型结果交叉对比中存在的潜在问题，并明确了将野外尺度数据聚合为通常以格网形式呈现的粗空间分辨率数据时所需考量的关键事项。该团队通过与已有文献资料及广泛应用的迈阿密模型（Miami Model）进行对比，对本数据集完成了评估验证。由于样本量更大，文件NPP_Gridded_3654_cells.csv适用于生物群系水平及整体层面的分析。文件NPP_Gridded_2335_unique_cells.csv由上述更大规模的数据集衍生而来：该文件剔除了异常值，对每个唯一地理坐标的重复测量数据进行了均值化处理，同时移除了被归类为水体、裸地及城市用地的格网单元，因此更适用于实测数据与模型结果的交叉对比分析。