Cover of Woody and Herbaceous Functional Groups in Burned and Unburned Plots, Mojave Desert, 2009-2013

Arid ecosystems are often vulnerable to transformation to invasive-dominated states following fire, but data on persistence of these states are sparse. The grass/fire cycle is a feedback process between invasive annual grasses and fire frequency that often leads to the formation of alternative vegetation states dominated by the invasive grasses. However, other components of fire regimes, such as burn severity, also have the potential to produce long-term vegetation transformations. Our goal was to evaluate the influence of both fire frequency and burn severity on the transformation of woody-dominated communities to communities dominated by invasive grasses in major elevation zones of the Mojave Desert of western North America.

We used a chronosequence design to collect data on herbaceous and woody cover at 229 unburned reference plots and 578 plots that burned between 1972 and 2010. We stratified the plots by elevation zone (low, mid, high), fire frequency (1 to 3 times), and years postfire (YPF; 1 - 5, 6 - 10, 11 - 20, and 21 - 40 YPF). Burn severity for each plot was estimated by the difference normalized burn ratio (dNBR). A Geographic Positioning System (GPS) was used to match the plots as closely as possible with the corner of a dNBR pixel. Each plot was 0.1 ha (32 m x 32 m) and contained three randomly positioned 25-m transects. Point intercept sampling was conducted at 0.5 m intervals along each transect (N = 50 points per transect, 150 points per plot). All plants intercepted by a wooden rod (1mm diameter) were recorded to species at each point. Species cover in each plot was estimated as the sum of point intercepts for each species divided by 150.

These data support the following publication:
Klinger, R. and Brooks, M., 2017. Alternative pathways to landscape transformation: invasive grasses, burn severity and fire frequency in arid ecosystems. Journal of Ecology, 105(6), pp.1521-1533.

干旱生态系统在火灾后往往极易向入侵物种主导的群落状态转变，但这类群落状态的持续性相关数据仍十分匮乏。草-火循环（grass/fire cycle）是入侵性一年生草本与火灾频率之间的反馈过程，往往会形成以入侵草本为主的替代性植被状态。然而，火况（fire regimes）的其他组成部分，比如火烧烈度（burn severity），同样可能引发长期的植被转变。本研究旨在评估火灾频率与火烧烈度对北美西部莫哈韦沙漠主要海拔带内木本植物主导群落向入侵草本主导群落转变的影响。
我们采用时间序列（chronosequence）设计，在229个未受干扰的对照样地与578个1972年至2010年间发生过火的样地中，采集草本与木本盖度数据。我们按海拔带（低、中、高）、火灾频率（1~3次）以及火后年限（years postfire，简称YPF；1~5年、6~10年、11~20年及21~40年）对样地进行分层。每个样地的火烧烈度通过差值归一化燃烧比（difference normalized burn ratio，dNBR）进行估算。我们采用全球定位系统（Geographic Positioning System，GPS）将样地尽可能匹配至dNBR像素的角点位置。每个样地面积为0.1公顷（32米×32米），内设3条随机布设的25米样线。沿每条样线以0.5米的间隔设置点截采样法（point intercept sampling）采样点（每条样线设50个采样点，每个样地共150个采样点）。在每个采样点，使用直径1毫米的木质杆进行截获，记录所有被杆截获的植物的物种信息。每个样地的物种盖度通过该物种的点截采样次数总和除以150进行估算。
本数据集支持以下已发表成果：Klinger, R. 和 Brooks, M., 2017. 《景观转变的替代路径：干旱生态系统中的入侵草本、火烧烈度与火灾频率》，《Journal of Ecology》，105(6), pp.1521-1533.