Seasonal non-destructive vegetation measurements at 15 net primary production (NPP) study sites at Jornada Basin LTER, 1989-ongoing

This data package contains non-destructive quadrat measurements
collected for the long-term Net Primary Production (NPP) study at
the Jornada Basin LTER. Data here include measurements of horizontal
cover and vertical height of plants observed at permanent NPP
quadrats at 15 study sites. 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 1m x 1m replicate quadrats was laid out
when sampling began in 1989. Grids consist of 49 quadrats arranged
in a square 7 x 7 pattern, with quadrats 10 m apart (P-COLL has 48
quadrats in a 3 x 16 pattern). Standing vegetation in quadrats is
sampled three times a year: in winter (February - March), before
shrubs begin spring growth; in spring (May), when shrubs and spring
annuals have reached peak biomass; in fall (late summer; October),
when summer annuals have reached peak biomass but before killing
frosts. Additional observations of plant count and phenological
stage are also made. This dataset is subsequently used to determine
quadrat biomass and net primary production. Details and linked data
packages are described in the methods element. This is an ongoing
dataset with new quadrat measurements collected in the spring, fall
and winter of each year. Attention: 1) For most species, these data are
not appropriate for estimates of percentage cover because of the way
the data are collected. See Note 1 in the methods element
for further details.

本数据集套件包含为霍罗纳德盆地长期生态研究站（Long-Term Ecological Research, LTER）的净初级生产力（Net Primary Production, NPP）长期研究采集的无损样方（quadrat）测量数据。本次收录的数据涵盖15个研究样地的永久性NPP样方中观测到的植物水平盖度与垂直高度测量结果。
研究样地的选取旨在代表奇瓦瓦沙漠的5类主要生态系统类型，即高地草原、干盐湖草原、牧豆树占优灌丛、石炭酸灌木占优灌丛以及塔布什灌丛（tarbush）。针对每类生态系统，各选取3个样地以覆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，各研究样地均划定1公顷范围并设置围栏；1989年启动采样工作时，布设了1米×1米的重复样方网格。网格采用7×7的正方形布局，包含49个样方，样方间距为10米；其中P-COLL样地采用3×16布局，共包含48个样方。
样方内的现存植被每年采样3次：分别为冬季（2月-3月，此时灌木尚未启动春季生长）、春季（5月，此时灌木与春季一年生植物的生物量达到峰值）以及秋季（夏末10月，此时夏季一年生植物生物量达到峰值但尚未遭遇霜冻致死）。此外还会开展植物数量与物候阶段的补充观测。
本数据集后续将用于计算样方生物量与净初级生产力。详细说明与关联数据集套件可参见方法模块内容。本数据集为持续更新的数据集，每年春、秋、冬三季均会采集新的样方测量数据。
注意事项：1）由于数据采集方式的限制，本数据集的多数物种数据不适用于百分比盖度估算。详细说明可参见方法模块中的注释1。