Annual mean estimates of aboveground net primary production (NPP) at 15 sites at Jornada Basin LTER, 1989-ongoing

[Note - revised version of this data record: https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-jrn&identifier=210011003 ]
This package contains values of mean annual aboveground net primary production (NPP, in grams per square meter per year) at 15 NPP study sites on Jornada Experimental Range (JER) and Chihuahuan Desert Rangeland Research Center (CDRRC) lands. Sites were selected to represent the 5 major ecosystem types in the Chihuahuan Desert (upland grasslands, playa grasslands, mesquite-dominated shrublands, creosotebush-dominated shrublands, tarbush-dominated shrublands). For each ecosystem type, three sites were selected to represent the range in variability in production and plant diversity; thus the locations are not replicates. At each site, a 1 hectare area was fenced in 1988 and a grid of 49 (48 at one playa location) 1m x 1m replicate quadrats was laid out when sampling began in 1989. In fall, winter, and spring periods aboveground biomass was calculated for each species and quadrat at each NPP site. These calculations rely on two data sources: 1) non-destructive horizontal cover and vertical height measurements of individual plants, or plant parts, within each quadrat, and 2) linear regression coefficients for each plant species derived from off-quadrat cover, height, and harvested biomass measurements. NPP is then calculated as the positive biomass increment between seasons. The annual totals in this dataset are derived by summing mean site NPP values for winter (October - February), spring (February - May), and fall (May - October) increments for a single calendar year. Data collection is ongoing with new annual NPP values calculated after the conclusion of each growing season.Attention:1) Calculated values in this data package have changed over time as the methodology for estimating biomass has changed. 2) Relating long-term NPP in this package with long-term precipitation is problematic given the importance of wet and dry periods and their effect on production in these ecosystems.See Notes 1 & 2 in the methods element for further details.
Resources in this dataset:
Resource Title: Website Pointer to html file.File Name: Web Page, url: https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-jrn&identifier=210011003Webpage with information and links to data files for download

[注：本数据记录修订版来源：https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-jrn&identifier=210011003]
本数据包包含霍纳达实验牧场（Jornada Experimental Range，缩写JER）与奇瓦瓦沙漠牧场研究中心（Chihuahuan Desert Rangeland Research Center，缩写CDRRC）管辖范围内15个NPP研究样地的年均地上净初级生产力（aboveground net primary production，缩写NPP，单位为克每平方米每年）数值。
样地选取旨在覆盖奇瓦瓦沙漠的5种主要生态系统类型：高地草原、干盐湖草原、牧豆树占优灌丛、石炭酸灌木占优灌丛、以塔布什为优势种的灌丛。针对每一类生态系统，各选取3个样地以涵盖生产力与植物多样性的变异梯度，因此这些样地并非重复样地。
1988年，每个样地内划定1公顷的围栏区域；1989年启动采样时，布设了由49个（其中一个干盐湖样地为48个）1米×1米重复样方组成的样方网格。
在秋季、冬季与春季采样时段，研究人员对每个NPP样地的各物种及各单样方的地上生物量进行计算。该计算基于两类数据源：1）对每个样方内的单株植物或植物器官开展无损的水平盖度与垂直高度测量；2）基于样方外的盖度、高度及收获生物量测量数据，推导得到各植物物种的线性回归系数。
NPP的计算值为季间的正生物量增量。本数据集的年度总量，通过单一日历年中冬季（10月至次年2月）、春季（2月至5月）与秋季（5月至10月）的样地平均NPP增量求和得到。
数据采集工作仍在持续，每个生长季结束后均会更新年度NPP计算值。
注意事项：1）由于生物量估算方法历经迭代，本数据包中的计算值随时间有所调整；2）鉴于干湿周期及其对这类生态系统生产力的重要影响，将本数据包中的长期NPP与长期降水数据进行关联存在一定局限性。详细信息请参阅方法部分的注释1与注释2。
本数据集包含以下资源：
资源标题：HTML文件网络指针。文件名称：网页，链接：https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-jrn&identifier=210011003，该网页包含数据下载所需的信息与文件链接。