Charcoal morphologies and morphometrics of a Eurasian grass-dominated system for robust interpretation of past fuel and fire types

This data publication provides data from burning experiments performed at the Department of Physical Geography, Goethe Univeristy, Frankfurt am Main (Germany). We burned plant specimens from seven graminoid, fifteen forb, and one shrub species from the steppe area in the Dobrogea, Black Sea, Romania, and Konoplyanka, Trans-Urals, Russia. The experiments were conducted to determine the effect of increasing temperatures on the charcoal mass, morphometric characteristics, and morphologies of charred plant material. For this we dried these plants in a desiccator (40°C) for 24 h. Subsequently, following the protocol of Feurdean (2021), we roasted the plant material in a muffle furnace at five district temperature settings: 250, 300, 350, 400, and 450°C. For each temperature subset, remains of individual plant species from the entire plant or as selected plant parts (Table 1), were placed in ceramic crucibles, weighed, then placed into the cold muffle oven covered with a lid to limit oxygen availability and avoid mixing the charred particles. The temperature was gradually raised for one hour, after which it was held constant for a duration of two hours. Crucibles with charred plants were cooled in a desiccator, then weighed to calculate the charred to pre-burning mass ratio. A small part of the charred mass was gently disaggregated with a mortar and pestle to mimic the natural breakage that charcoal particles experience over time through sedimentation processes. The charred and disaggregated sample was then washed through a 125 μm sieve to remove smaller fragments. Photographs of charcoal particles were manually taken at 4X magnification with a digital camera (KERN ODC 241 tablet camera. The charcoal particles and morphometric measurements, including the major (L) and minor (W) axes surface area (A), and perimeter (P) for individual charred particles larger than 150 μm, were automatically determined from these photographs using the algorithm of Feurdean (2021). Subsequently, we calculated the aspect (L/W; W/L) and A/P ratios). These metrics were applied on more than 150 charcoal particles (range between 41 and 508), per sample; the lower number of measurements generally corresponds to samples burnt at high temperatures, where particles were more susceptible to breakage or partial ashing.

本数据集收录了德国美因河畔法兰克福歌德大学（Goethe University）物理地理系开展的燃烧实验数据。我们选取了来自罗马尼亚黑海沿岸多布罗加（Dobrogea）草原地带以及俄罗斯外乌拉尔科诺普良卡（Konoplyanka）草原地带的植物标本开展燃烧实验，涉及7种禾草类（graminoid）植物、15种非禾本科草本（forb）植物及1种灌木。本实验旨在探究升温温度对炭化植物材料的炭质量、形态计量特征及形貌的影响。

实验前，我们将所有植物样品置于干燥器（desiccator）中，于40°C下干燥24小时。随后参照Feurdean（2021）的实验方案，使用马弗炉（muffle furnace）在5个梯度温度条件下对植物材料进行焙烧：250、300、350、400及450°C。对于每个温度组别，将单个植物物种的全株或选定植物部位的残余物（见表1）置于陶瓷坩埚（ceramic crucibles）中称重，随后放入加盖的冷马弗炉内，以限制氧气供应并避免炭化颗粒相互混杂。

实验炉以1小时的时间逐步升温至设定温度，并在此温度下恒温保持2小时。待炭化完成后，将装有炭化植物样品的坩埚置于干燥器中冷却，随后再次称重以计算炭化前后的质量比值。取少量炭化样品使用研钵和研杵（mortar and pestle）轻轻研磨，以模拟炭颗粒在沉积过程中随时间发生的自然破碎作用。将经研磨分散后的炭化样品通过125 μm孔径的筛子冲洗，以去除更小的碎屑。

使用数码相机（KERN ODC 241平板相机）以4倍放大倍率手动拍摄炭颗粒照片。针对尺寸大于150 μm的单个炭颗粒，采用Feurdean（2021）提出的算法，从照片中自动提取其形态计量参数，包括长轴（L）、短轴（W）、表面积（A）及周长（P）。随后计算长宽比（L/W；W/L）及表面积/周长比（A/P）。

每个样品的测量指标均基于超过150个炭颗粒（数量范围为41至508）；较低的测量颗粒数通常对应高温燃烧后的样品，此类样品的颗粒更易发生破碎或部分灰化。