the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 11 Nov 2025
Mapping and spatial distribution of relict charcoal hearths across Poland
Abstract. This study presents the first national-scale spatial inventory of relict charcoal hearths (RCHs) in Poland, based on high-resolution LiDAR data and digital terrain analysis. Using a combination of manual interpretation, GIS-based feature extraction, and K-prototypes clustering, we identified and classified 634,815 RCHs across forested regions of the country. Each feature was georeferenced and categorized by size, morphological characteristics, slope position, and environmental context, including current and potential vegetation and soil types. Spatial analyses revealed significant regional differences in hearth density, with the highest concentrations found in western and south-central Poland, particularly in the Lower Silesian, Stobrawa, and Świętokrzyskie forests. Cluster analysis distinguished three major types of RCHs, differing in their environmental settings and spatial organization: (1) lowland pine-dominated clusters on gentle terrain, (2) isolated features on steep slopes in mixed forests, and (3) high-density hearth groups in elevated areas. Although large portions of the country appear devoid of RCHs, we argue that this reflects limitations in preservation and detection – due to long-term agricultural activity in lowlands and erosion in mountainous areas – rather than an actual absence of charcoal production. The resulting ReCHAR database offers a unique, open-access tool for interdisciplinary research on forest history, human-environment interactions, and early industrial landscapes. Its modular design supports further expansion, including links to historical settlements and industries reliant on charcoal, such as metallurgy, glassmaking, and tar or potash production.
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Status: open (until 30 Dec 2025)
- RC1: 'Comment on essd-2025-421', Anonymous Referee #1, 16 Nov 2025 reply
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RC2: 'Comment on essd-2025-421', Anonymous Referee #2, 02 Dec 2025
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General Comments
This manuscript presents the first national-scale spatial inventory of relict charcoal hearths (RCHs) in Poland, based on high-resolution LiDAR data and digital terrain analysis. By integrating manual interpretation, GIS-based feature extraction, and K-prototypes clustering, the authors identify and classify 634,815 RCHs across the country’s forested regions. The resulting open-access ReCHAR database is an important outcome of the study, and it is thoughtfully designed to support future expansion and integration with additional spatial datasets.
I found the paper highly interesting and well structured, with clearly organized sections and a clear, readable narrative. One of its major strengths lies in the national-scale perspective: an approach that goes beyond the regional scope typically adopted in similar studies from other European countries. The decision to make the dataset publicly accessible and expandable further enhances its value. This kind of work is undoubtedly necessary, aligning well with recent European initiatives dedicated to the study of historical charcoal production sites (see e.g. https://www.cost.eu/actions/CA22155/).
Specific comments
A key limitation, however, concerns the absence of chronological considerations as variable in the spatial analysis. All identified RCHs are implicitly treated as contemporaneous, although existing research (e.g., Rutkiewicz et al., 2021) demonstrates that this is unlikely. This assumption affects the reliability of the spatial and typological analyses that the paper aims to develop. Regional differences and variability in charcoal production practices cannot be analysed on morphological and environmental variables solely: the results risk being misleading without chronological differentiation.
In the conclusions, the authors themselves mention plans to incorporate additional data sources (e.g., toponymy, structures related with charcoal production), and I strongly encourage integrating a diachronic dimension (at least in selected sample areas). Stratigraphic investigations of RCHs, anthracological analyses, radiocarbon dating, and studies of the history of sampled forest environments would significantly strengthen interpretations and provide more reliable insights into the long-term dynamics of charcoal production and its environmental impacts.Despite this limitation, the study offers significant potential and, in my view, is suitable for publication after minor revisions (few technical correction). Specifically, I recommend the following:
1) Bibliography
- Several references cited in the text appear missing from the bibliography (e.g., Buras et al., 2015; Miechówka and Drewnik, 2018; Fokt, 2012).
- Some inconsistencies in formatting should be corrected (e.g., capitalisation issues in lines 557 and 635; missing spaces between the date and the publisher/location, as in line 498).
2) Line 82
- “Massive” should be capitalised after the period.
3) Lines 167–168
- Remove the parentheses after “Lasota et al., 2018”.
- Remove the repeated “et al., 2018” before “Miechówka and Drewnik, 2018)”.Citation: https://doi.org/10.5194/essd-2025-421-RC2
Data sets
ReCHAR database - spatial distribution of relict charcoal hearths across Poland M. Słowiński et al. https://doi.org/10.5281/zenodo.15630690
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- 1
Slowinski et al. present the first national-scale spatial inventory of relict charcoal hearths (RCHs) in Poland. This study is also the first of its kind in Europe and possibly the world. The authors state that, to their knowledge, there is currently no equivalent dataset of this scale or resolution available elsewhere in Europe or worldwide (line 200). To my knowledge, this is absolutely correct, thus setting a new benchmark for this research.
The authors are to be highly congratulated for mapping the entire area of Poland, which allowed them to identify and classify 634,815 RCHs in the country's forested regions using a combination of manual interpretation, GIS-based feature extraction and K-prototype clustering. Although the number of RCH sites sounds enormous, it simply represents the 'new reality' that must be acknowledged when assessing the legacy of past land use on soils and landforms, as comparable RCH numbers have been found in other European and US regions in recent years. This is becoming increasingly significant as RCHs are just one type of land-use legacy landform (LULL), alongside relicts of transportation, mining and agriculture, which also have long-lasting effects on modern ecosystems. This study should therefore be considered the first step in building transnational inventories of RCHs and other LULLs.
The study takes a sensible approach to creating such an international inventory, with the aim of developing an open-access, community-driven research platform that supports the documentation, analysis and exchange of data relating to anthropogenic forest disturbances and the spatial history of the landscape. The authors are encouraged to take the next step and apply for an EU project involving researchers from other European countries, with the aim of realising their vision of creating and further improving a functional RCH data platform in Europe.
While I am convinced of the novelty of the study and the published dataset, there are some minor improvements that could be made to increase the visibility of the paper and its appeal to an international readership.
• Line 48 ff: To address the internal readership, it would be worth mentioning that this was also of great importance in the USA. Studies have especially been published in New England (e.g. https://doi.org/10.1016/j.apgeog.2023.103121). Some of these studies present state-wide inventories comparable to those presented in the paper: https://doi.org/10.1002/arp.1889, https://doi.org/10.1016/j.catena.2023.107426.
• Randomly, some references cited in the text are missing, e.g. Schneider et al. (2019, 2022) and Buras et al. (2015) in line 90 ff. Please check the entire text to ensure a correct and full list of references.
• Line 112 ff: Perhaps this phrasing is slightly misleading because the 'preservation' is not only an effect of modern agriculture; RCHs were originally often situated in marginal landscapes with less productive soils, favouring forest use over crop production.
• Line 189 ff: Please specify 'visually recognised'! Was identification carried out by different people, with manual picking and double-checking? Have you experienced any deviation between operators, especially with regard to false positives?
• Figure 2 and related data set: Why did you choose 25 km² and not 1 km²? There is already a wide variety of units used in the literature. To establish a consistent dataset on a European scale, a density unit of RCH per 1 sq m would be easier to handle and could be processed more easily in future projects. It would be good to provide the density data accordingly. Perhaps it is somewhere in the supplementary material that the reader cannot see.
• Line 273 ff: It is an interesting interpretation that the depressions should have been used for tar collection. Do you have physical proof from the RCH excavations, i.e. remains of tar in these depressions or on the RCH platforms? This interpretation could indeed explain the differences between RCH types with circular ditches and those with separated pits around a charcoal hearth. However, producing tar and charcoal simultaneously seems an unusual operation, and tar production sites have different architecture. The Fokt (2012) paper cited is not in the reference list. Therefore, it is not possible to investigate this further.
In summary, this is a great compilation of data and is well worth publishing after minor revisions have been made in light of the comments given.