Arson burn on LTER-I transect plant line intercepts - LT series (percent cover)

On March 19, 2000, an arson burn occurred of 2.5 acres of the upper
grassland area on the Summerford bajada just below the powerline
road. The area affected included portions of the LTER-I Transect
Plant Line Intercept study that was begun in 1982. To evaluate the
impact of the burn on those lines, the line intercepts were read
for the upper grassland area extending from immediately above the
creosotebush fringe to the base of Summerford Mountain. The
stations measured were C73-C89, T75-T90, and X76-X91 (Control,
Treatment, and Alternate Control, respectively). Measurements were
made immediately after the burn, after the spring growing season,
and after the fall growing season in 2000 only. In the initial
sampling period, the burn area intercepted by the line was noted in
the data set using a "species" code of BURN.

Average percent coverage of each plant species per 5-meter segment
along a 30-meter line intercept perpendicular to each of 91 stations
on each of the three LTER-I permanent transects. Data consists of
week number, transect, station number, species, carbon reduction
pathway, habit, form, and average percent cover. It is sorted by
transect, station number, then plant species.

Measurements are made on 30-meter line intercept transects located
perpendicular to each of 91 stations on each of the 2.7 km long
Control, Treatment, and Alternate Control Transects established at
the beginning of LTER-I. Following January 1, 1987, spring line-
intercepts will only record cover of annual species. All perennial
cover data will be limited to fall samples. Both annuals and perennials
are measured during the fall. Measurements were made biannually from
1982 - 1988. After this they are measured every 5 years. Annuals are
measured through 1998; however, after this only perennials are measured
and only in the fall. Each plant line transect is divided into 6
5-meter segments. Annuals are measured only in the first meter of
segments 1, 2, and 3 and in the last meter of segments 4, 5, and 6.
Perennials are measured for the full length of all segments.

BACKGROUND.
In the spring of 1982, as part of the establishment of
the Jornada Long-Term Ecological Research site in southern
New Mexico, a 135 ha portion of a 1500 ha, internally
drained, watershed was exclosed from grazing by domestic
livestock. Prior to exclosure the watershed, as well as the
rest of the Jornada basin, had been moderately to heavily
grazed for the past 100 years. Concurrent with grazing, the
vegetation had undergone a dramatic change from desert
grassland, with an almost continuous cover of C4 perennial
grasses, to isolated patches of the original grassland in a
mosaic with desert shrub dominated plant communities
(Buffington and Herbel, 1965).
The exclosure lies along a northeast facing piedmont
slope at the base of a steep isolated mountain peak, and
covers a variety of component landforms from the foot of the
mountain to the basin floor. This provided the opportunity
to investigate the response of vegetation with respect to
landscape characteristics as well as release from grazing.

2000年3月19日，萨默福德山麓冲洪积扇（Summerford bajada）紧邻输电线公路下方的上部草原区域发生纵火焚烧事件，过火面积达2.5英亩。受影响区域包含1982年启动的LTER-I样带（Long-Term Ecological Research I Transect，LTER-I样带）植物样线截距研究的部分区段。为评估此次火烧对这些样线的影响，研究人员对从杂酚灌丛（creosotebush）带正上方直至萨默福德山山麓的上部草原区域开展了样线截距读数工作。此次测量的样点为C73–C89、T75–T90及X76–X91，分别对应对照样带、处理样带与替代对照样带。测量分别在火烧后即刻、2000年春季生长季结束后以及2000年秋季生长季结束后完成。在初始采样阶段，数据集采用"BURN"物种代码标记样线所截获的火烧区域。

本数据集记录了3条LTER-I永久样带各91个样点处，垂直于样带的30米样线截距上，每5米区段内各植物物种的平均盖度百分比。数据包含周次、样带、样点编号、物种、碳同化途径、生活型、形态以及平均盖度百分比，按样带、样点编号、植物物种排序。

测量工作在LTER-I启动时设立的全长2.7千米的对照、处理及替代对照样带的91个样点处开展，每条样线均垂直于对应样点。1987年1月1日起，春季样线截距调查仅记录一年生植物盖度，多年生植物盖度数据仅收录于秋季采样；秋季采样则同时记录一年生与多年生植物盖度。1982年至1988年期间，每半年开展一次测量；此后改为每5年测量一次。1998年之前均会调查一年生植物，1998年之后仅测量多年生植物，且仅在秋季采样。每条植物样线均划分为6个5米区段：一年生植物仅在区段1、2、3的第一米以及区段4、5、6的最后一米范围内测量，多年生植物则在所有区段的全长度范围内测量。

### 研究背景
1982年春季，作为新墨西哥州南部霍罗尼玛长期生态研究站（Jornada Long-Term Ecological Research site）建立工作的一部分，研究人员对1500公顷内流流域中的135公顷区域实施了家畜放牧封禁。在此之前的100年里，该流域与霍罗尼玛盆地的其余区域均遭受了中度至重度放牧。伴随放牧活动，植被发生了显著变化：原本几乎连续覆盖的C4多年生草本荒漠草原，逐渐演变为以荒漠灌丛为优势群落的镶嵌景观，其中仅残存零星原生草原斑块（Buffington与Herbel，1965）。
该封禁区域位于一座陡峭孤立山峰山麓的东北向坡地上，涵盖从山麓到盆地底部的多种地貌单元，这为研究植被对景观特征的响应以及放牧解除后的植被恢复提供了研究契机。