ISLSCP II ECOSYSTEM ROOTING DEPTHS

The goal of this study was to predict the global distribution of plant rooting depths based on data about global aboveground vegetation structure and climate. Vertical root distributions influence the fluxes of water, carbon, and soil nutrients and the distribution and activities of soil fauna. Roots transport nutrients and water upwards, but they are also pathways for carbon and nutrient transport into deeper soil layers and for deep water infiltration. Roots also affect the weathering rates of soil minerals. For calculating such processes on a global scale, data on vertical root distributions are needed as inputs to global biogeochemistry and vegetation models. In the Project for Intercomparison of Land Surface Parameterization Schemes (PILPS), rooting depth and vertical soil characteristics were the most important factors explaining scatter for simulated transpiration among 14 land-surface models. Recently, the Terrestrial Observation Panel for Climate of the Global Climate Observation System (GCOS) identified the 95% rooting depth as a key variable needed to quantify the interactions between the climate, soil, and plants, stating that the main challenge was to find the correlation between rooting depth and soil and climate features (GCOS/GTOS Terrestrial Observation Panel for Climate 1997). In response to this challenge, a data set of vertical rooting depths was collected from the literature in order to construct maps of global ecosystem rooting depths.

The parameters included in these data sets are estimates for the soil depths containing 50% and 95% of all roots, termed 50% and 95% rooting depths (D50 and D95, respectively). Together, these variables can be used to calculate estimates for vertical root distributions, using a logistic equation provided in this documentation. The data represent mean ecosystem rooting depths for 1 by 1 degree grid cells.

Related data sets: The ORNL DAAC offers related data sets by Jackson et al. (2003), Gordon and Jackson (2003), Schenk and Jackson (2003), and Gill and Jackson (2003).

This data set is one of the products of the International Satellite Land-Surface Climatology Project, Initiative II (ISLSCP II) data collection which contains 50 global time series data sets for the ten-year period 1986 to 1995. Selected data sets span even longer periods. ISLSCP II is a consistent collection of data sets that were compiled from existing data sources and algorithms, and were designed to satisfy the needs of modelers and investigators of the global carbon, water and energy cycle. The data were acquired from a number of U.S. and international agencies, universities, and institutions. The global data sets were mapped at consistent spatial (1, 0.5 and 0.25 degrees) and temporal (monthly, with meteorological data at finer (e.g., 3-hour)) resolutions and reformatted into a common ASCII format. The data and documentation have undergone two peer reviews.

ISLSCP is one of several projects of Global Energy and Water Cycle Experiment (GEWEX) [http://www.gewex.org/] and has the lead role in addressing land-atmosphere interactions -- process modeling, data retrieval algorithms, field experiment design and execution, and the development of global data sets.

本研究旨在基于全球地上植被结构与气候数据，预测植物根系深度的全球分布格局。垂直根系分布格局会影响水、碳与土壤养分的通量，以及土壤动物的分布与活动。根系可向上输送养分与水分，同时也是碳与养分向深层土壤运移、深层水分入渗的通道。此外，根系还会影响土壤矿物的风化速率。在全球尺度上模拟上述过程时，需将垂直根系分布数据作为全球生物地球化学与植被模型的输入参数。在陆面参数化方案比较计划（Project for Intercomparison of Land Surface Parameterization Schemes, PILPS）中，根系深度与垂直土壤特征是解释14个陆面模型模拟蒸腾量离散程度的最重要因素。近期，全球气候观测系统（Global Climate Observation System, GCOS）的气候陆地观测专家组将95%根系深度列为量化气候、土壤与植物间相互作用的关键变量，并指出当前的主要挑战是厘清根系深度与土壤、气候特征之间的关联（GCOS/GTOS Terrestrial Observation Panel for Climate 1997）。为应对这一挑战，研究团队从文献中收集了垂直根系深度数据集，以绘制全球生态系统根系深度分布图。

本数据集包含的参数为包含50%和95%总根系的土壤深度估算值，分别称为50%根系深度（D50）与95%根系深度（D95）。结合本文档提供的逻辑斯蒂方程，可利用这两个变量估算垂直根系分布情况。数据集数据为1×1度网格单元的平均生态系统根系深度。

相关数据集：橡树岭国家实验室分布式主动存档中心（Oak Ridge National Laboratory Distributed Active Archive Center, ORNL DAAC）提供了Jackson等人（2003）、Gordon与Jackson（2003）、Schenk与Jackson（2003）以及Gill与Jackson（2003）的相关数据集。

本数据集是国际卫星陆面气候计划第二阶段（International Satellite Land-Surface Climatology Project, Initiative II, ISLSCP II）数据合集的产物之一，该合集包含1986至1995年十年间的50套全球时间序列数据集，部分数据集的时间跨度更长。ISLSCP II是一套统一整合的数据集合集，基于现有数据源与算法编译而成，旨在满足全球碳、水与能量循环领域建模者与研究者的需求。数据源自多家美国及国际机构、大学与科研院所。全球数据集采用统一的空间分辨率（1、0.5和0.25度）与时间分辨率（月度，气象数据采用更高分辨率，如3小时）进行制图，并统一格式为ASCII格式。数据集与相关文档已通过两轮同行评审。

国际卫星陆面气候计划（International Satellite Land-Surface Climatology Project, ISLSCP）是全球能量与水循环实验（Global Energy and Water Cycle Experiment, GEWEX）的多个项目之一，在陆-气相互作用研究中发挥主导作用，涵盖过程建模、数据反演算法、野外实验设计与实施以及全球数据集开发等方向。