Compilation of Publications

This study consisted of a search for scientific articles focused on dendrochronological research in Mexico from 2000 to 2023. The search was conducted in Scopus, Web of Science, Redalyc, and Scielo. The search included keywords in both Spanish and English, such as “dendrochronology”, “tree rings” and “Mexico” used to retrieve titles, abstracts, and keywords of publications. In addition, these terms were combined with the words “dendroclimatology”, “dendropyrology”, “dendrochemistry”, “dendrovulcanology”, “dendrogeomorphology”, “dendroarchaeology”, “dendroecology”, and “dendrohydrology” to identify all dendrochronological subfield. The databases and keywords used for article searching could have underestimated some available information; however, the data reported represent the state of dendrochronological publications currently available in Mexico.

Data Analysis

The articles found in Scopus were used as a reference, and duplicates from other databases were removed. This bibliometric review excluded review articles, articles in non-indexed journals, technical reports, theses, and conference proceedings. A total of 229 articles were identified and classified according to the following parameters: year of publication, influential authors, publishing journals, study area (state and GPS coordinates), tree species, subfield of study (dendroclimatology, dendrochemistry, dendrogeomorphology, etc.), influential institutions, and co-occurrence analysis of keywords used by the authors. The analysis of co-occurrence was useful for understanding the relationship between words and groups and by topic and meaning. A total of 25 keywords with a frequency of ≥5 were selected from a total of 535. Collaboration networks were analyzed using VOSviewer version 1.6.20 (^{van Eck & Waltman, 2023}) to identify the leading authors, institutions, and even countries involved in dendrochronological research in Mexico. Additionally, co-occurrence analysis was conducted based on the VOS clustering algorithm to determine relationships between keywords (^{Kirby, 2023}). VOSviewer is a robust tool that uses clustering algorithms based on the strength of connections between elements to build networks (^{Effendi et al., 2021}). This analysis provided insights into the most frequently addressed topics in publications, the research fields developed, and potential research gaps to be explored in future dendrochronological studies.

Trends in Dendrochronological Research

A total of 229 articles (Appendix 1) related to dendrochronological research in Mexico were identified for the 2000-2023 period. Figure 1 shows that fewer than 10 publications were identified before 2000, most of the authors were researchers from the United States of America (USA). Between 2000 and 2023, the number of publications exhibited an exponential trend (R² = 0.837), with an average of 9.5 articles per year. The trend became significant from 2013 to 2023, because 83 % of the total was published in this period (12.6 articles per year) with 21 articles in the years 2022 and 2023, and 17 and 20 articles in 2018 and 2020, respectively (Figure 1. In contrast, prior to 2010 (2000-2010), an average of four articles were published annually, with 2001 having the lowest output (one article, Figure 1).

Figure 1 Dendrochronological research articles developed in Mexico, published (dark bars) and accumulated (red line) by year. Period 2000-2023. 

In addition to research articles published in Journal Citation Reports, there are a considerable number of publications in Mexican journals that are not indexed, as well as research essays, bachelor theses (approximately 130), dissertations (20), technical reports (20), review articles (4) and electronic reports. Despite the volume of these dendrochronological publications, this study only included indexed articles, specifically from Scopus and Web of Science, because these databases are regarded as key sources for bibliometric analyses (^{Pranckuté, 2021}).

The increase in studies is driven by the growing interest in dendrochronological research. As a result, research and educational institutions in Mexico are offering both traditional and intensive courses in dendrochronology, with applications across various scientific fields. These institutions include the Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias (INIFAP), Universidad Nacional Autónoma de México (UNAM), Universidad Juárez del Estado de Durango (UJED), Colegio de Postgraduados, Universidad Autónoma de Nuevo León (UANL) and Universidad Autónoma de Tamaulipas (UAT). Additionally, the expanding collaboration and interaction with researchers from foreign educational institutions, such as the University of Arizona, Northern Arizona University, the University of Arkansas, the University of California, and Ithaca University, have enriched the scope of dendrochronological research and contributed to the training of undergraduate and graduate students. This has also increased the participation of scientists in dendrochronology. This training extends beyond dendroclimatology to several subfields, including dendrogeomorphology, dendrochemistry, and dendrovolcanology.

Distribution of Dendrochronological Publications

The bibliometric analysis produced a map showing the distribution of publications by federal entity, representing the sites where dendrochronological studies were conducted, and samples were collected. Sometimes, samples were collected from multiple sites, species, and even countries (^{Stahle et al., 2016}).

In Mexico, dendrochronological studies have been carried out in 25 states. Figure 2 indicates that Durango has the highest number of publications (44), followed by Puebla (33), Chihuahua (22), and Estado de México (22). Most of these studies have been conducted in the Sierra Madre Occidental, Sierra Madre Oriental, and the Trans-Mexican Volcanic Belt-physiographic provinces characterized by temperate coniferous forests (^{Instituto Nacional de Estadística y Geografía [INEGI], 2021}). However, some studies have been conducted in tropical ecosystems, such as Yucatán (Figure 2), where 52 species were explored to assess their dendrochronological potential (^{Roig et al., 2005}). This information is essential for analyzing biomass production, ecological aspects, and the influence of human-induced environmental changes. In contrast, states such as Sinaloa, Tabasco, Campeche, Quintana Roo, Aguascalientes, Nayarit, and Guerrero have no published studies (Figure 2), despite the existence of some dendrochronological series. This highlights the urgent need to conduct research with local species in these regions.

Figure 2 Distribution of sampling sites for dendrochronological research publications in Mexico. 

Tree Species Studied in Dendrochronological Research

Dendrochronological publications in Mexico have analyzed a total of 76 tree species. Figure 3 shows that the most extensively studied species are Pinus hartwegii Lindl. (47 publications), Pseudotsuga menziesii (Mirb.) Franco (33 publications), Abies religiosa (Kunth) Schltdl. & Cham. (26 publications), Taxodium mucronatum Ten. (18 publications), Pinus cembroides Zucc. (15 publications), and Pinus leiophylla Schiede ex Schltdl. & Cham. (15 publications). The remaining species have been studied in fewer than 13 publications. In addition, seven studies did not specify the species analyzed, and 30 species were each studied in only one publication (Figure 3). Of the 229 studies conducted in Mexico, 160 (70 % of the articles) focused on just five species, predominantly conifers. This highlights the need to include other coniferous and broadleaf species found in both temperate and tropical environments (^{Marcelo-Peña et al., 2020}; ^{Quesada-Román et al., 2022}; ^{Roig et al., 2005}).

Figure 3 Number of dendrochronological studies conducted in Mexico, grouped by species analyzed (2000-2023) 

Dendrochronological studies in Mexico have analyzed various species, often integrating data from multiple species to strengthen the common climatic signal in reconstructions. This approach enhances the robustness of climatic interpretations, particularly in studies addressing broad spatiotemporal scales, such as the North American and Mexican Drought Atlas (^{Cook et al., 2016}; ^{Stahle et al., 2016}). Some studies have explored the dendrochronological potential of species like Pinus hartwegii, Pinus leiophylla, Pinus ayacahuite, Abies religiosa, and Juniperus monticola Martínez. These studies have investigated the impact and frequency of disturbances, such as debris flows, lahars, and pollution (^{De la Peña et al., 2024}; ^{Franco Ramos et al., 2018}; ^{Villanueva-Díaz et al., 2016}).

Collaborations between authors and institutions

The collaboration network analysis, using the VOS clustering algorithm from the VOSviewer 1.6.20 software, highlighted the interactions between authors and institutions and their influence in the field of research. From this analysis, only the top 25 authors (Figure 4) and 20 institutions (Figure 5) publishing articles focused on dendrochronology were selected. Figure 4 shows that the authors' network consists of five groups, represented by J. Villanueva-Díaz (group 1, blue), J. Cerano-Paredes (group 2, red), A. Gómez-Guerrero (group 3, yellow), D. Stahle (group 4, green), and O. Franco-Ramos (group 5, purple). The key researcher among these five groups is J. Villanueva-Díaz, who has published 87 articles on dendrochronology in Mexico. Two other notable researchers, based on the number of publications, are J. Cerano-Paredes (40 publications) and M. Pompa-García (29 publications). The institutional affiliations of these three authors are located in northern Mexico (Durango), which explains why most dendrochronological studies are conducted in the central-northern region of Mexico (Figure 2). This finding agrees with a similar study conducted by ^{Acosta-Hernández et al. (2017)}. However, it is important to highlight the influence of foreign researchers (Figure 4, group 4, green), who emphasize the significance of dendroclimatic studies in analyzing the historical variability of precipitation in Mexico and the southwestern United States. They also focus on understanding how this variability is affected by large-scale atmospheric circulation modes and the response functions of various species. For example, ^{Therrell et al. (2002)} found that tree growth rings in northern Mexico are more sensitive to winter-to-early-summer seasonal precipitation. In contrast, in southern Mexico, they are more sensitive to seasonal rainfall from April to June. This information agrees with studies by ^{Cleaveland et al. (2003)} and ^{Díaz et al. (2001)}.

Figure 4 Visualization map of collaboration networks among the top 25 authors based on the number of publications. The size of the nodes (circles) and the thickness of the lines are proportional to the number of publications by the authors and the collaborations among them. 

Figure 5 Visualization map of collaboration networks between institutions according to the number of publications. The map shows the size of the nodes; the connection between these represents the network of collaboration between institutions. The thickness of the lines is proportional to the number of publications and collaborations accumulated. 

The collaboration network analysis among the top 20 institutions highlights the degree of communication and collaboration between them, grouped into five groups (yellow, green, red, blue, and purple), as shown in Figure 5. These groups are represented by INIFAP, UNAM, UJED, the University of Arkansas, Colegio de Postgraduados, and the University of California. INIFAP shows strong connections, maintaining significant scientific collaboration with other groups, including two groups of foreign institutions (Figure 5). INIFAP has contributed to 104 articles, while UNAM has contributed to 75 articles; these two institutions have been the most prominent contributors to the development of dendrochronological research in Mexico and maintain strong scientific collaborations. On the other hand, group 3 (Figure 5, red) appears isolated from the other groups, indicating minimal connections between them. Institutions in southern Mexico are not among the top 20, partly because dendrochronological studies in tropical environments are scarce (Figure 2) (^{Roig et al., 2005}). This contrasts with the dendrochronological research conducted in tropical ecosystems (^{Quesada-Román et al., 2022}; ^{Tomazello Fo et al., 2009}).

Keyword Analysis

The keyword analysis is presented in Figure 6, which shows groups differentiated by colors (green, purple, blue, yellow, and red). A shorter distance between nodes indicates a stronger relationship between keywords. For example, there is a close association between the terms “dendrochronology” with “El Niño-Southern Oscillation (ENSO)”, “climate” and “climate variation”. The most frequent keywords are represented in larger nodes (circles), for example; “dendrochronology’, “ENSO’, “tree rings” and “drought”. Group 1 (red) is made up of seven keywords; “climate change”, “dendroclimatology”, “dendroecology”, “drought stress”, “early wood’, “tree rings” and “late wood”. Group 2 (green) is made up of five words; “dendrochronology”, “climate”, “fire history”, “fire regime” and “Pacific Decadal Oscillation”. Group 3 (blue) is made up of five words; “ENSO”, “drought’’, “climate reconstruction”, “precipitation reconstruction”, and “tree-ring chronology”. Groups 4 and 5 are made up of four words each. It is important to note, that in four of the five groups, the climatic phenomena are highlighted (example; drought, stress, climate change, climate variability, climate reconstruction, precipitation, temperature), while, in the remaining group, the use and analysis of tree rings to evaluate geomorphological processes are highlighted. We also identified that the keywords and their frequencies have changed over time, the keywords “dendrochronology”, ‘ENSO”, “tree rings”, “drought” and “dendroecology” are the five most frequent keywords during 2000-2023 (Figure 6), which demonstrates concern for climate issues, the evaluation of droughts and their effects of global circulation phenomena on tree rings. This coincides with other studies where it has been reported that dendroclimatic studies have been the most addressed in Mexico (^{Acosta-Hernández et al., 2017}; ^{Sánchez-Calderón et al., 2022}). In recent years (2016-2023), the keyword ‘dendrogeomorphology’ has gained prominence, indicating the growing relevance of studies under this approach despite its recent implementation in Mexico. The first study of this type was published 15 years ago, identifying and describing alterations in tree growth rings caused by lahar events (^{Bollschweiler et al., 2010}). However, it was not until 2016 that dendrogeomorphological studies increased (Figure 8), focusing on evaluating and analyzing various types of mass movement processes (^{Figueroa-García et al., 2021}; ^{Franco-Ramos et al., 2019}). Regarding less-cited keywords, it seems that some applications of dendrochronology in Mexico-such as dendrovolcanology, dendroarchaeology, and dendrochemistry-have been underexplored (^{Cui et al., 2022}).

Figure 6 Visualization map of co-occurrence of the 25 main keywords used by the authors. The colors represent different groups and the lines are the connection between keywords. 

Figure 7 Proportion of publications by dendrochronological subfield in Mexico from 2000-2023. 

Figure 8 Number of studies in the subfields of dendrochronology by year of publication. 

Subfields Studied in Dendrochronology

The publications were classified according to the studied subfields of dendrochronology. Figures 7 and 8 show the nine main subfields/thematic groups. Most of the studies have been developed with a dendroclimatic approach (119 publications, 52 %); in this aspect, the first article was published by ^{Díaz et al. (2001)}, who reconstructed the precipitation from September to July in Baja California Sur for the period 1862-1996. The years 2022 and 2023 had the highest number of publications on this topic (10 publications per year), followed by 2018 and 2015 (nine publications per year). These focused mainly on precipitation reconstructions, drought identification, influence of climatic variables on forest growth, and response function analysis (^{Carlón-Allende et al., 2021}; ^{Villanueva-Diaz et al., 2007}), as well as the development of the Drought Atlas for Mexico, which was based on a network of 252 tree-ring chronologies (^{Stahle et al., 2016}). Dendroecological studies have also had significant contribution (29 publications, 13 %; Figures 7 and 8), mainly from 2016, where the implications of climate change on the ecological functions of trees, spatio-temporal identification of past forest disturbances (^{Pompa-García et al., 2023}) and the dynamics of the long-term trend of forests (^{Correa et al., 2021}) are addressed. Another subfield with relevant development in Mexico is dendropirology with 24 publications representing 10 % of the total (Figures 7 and 8), in which spatio-temporal reconstruction of fire regimes and frequency (^{Zúñiga-Vásquez et al., 2023}) and climatic influence on fire occurrence (^{Yocom et al., 2014}) have been performed, being this development more constant from 2019 (Figure 8).

Regarding studies with a dendrogeomorphological approach, 18 publications (8 %) have been published, particularly since 2016 (Figure 8). These studies have focused on the evaluation of mass removal processes such as lahars, debris flows, soil erosion and rotational movements (^{Figueroa-García et al., 2021}; ^{Franco-Ramos et al., 2023}; ^{Šilhán et al., 2024}; ^{Stoffel et al., 2011}). Some studies were also conducted in less explored fields such as dendrochemistry (16 publications), dendrohydrology (eight publications), dendrovulcanology (six publications), dendroarchaeology (three publications) and exploratory studies (six publications, Figures 7 and 8). These subfields of dendrochronology could be considered windows of opportunity to assess the natural and anthropogenic impact of land use changes in recent centuries. In addition, there is a lack of exploratory studies that represent an extensive field for identifying the dendrochronological potential of little studied genera such as Quercus or broadleaf species from tropical environments.

Most influential journals in dendrochronology research in Mexico

Figure 9 shows the 103 national and international journals, where the 229 articles studying dendrochronology in Mexico were published. According to Table 1, 30 % of the articles are concentrated in six journals: 7 % were published in the journal Forests (15 articles), 6 % in Madera y Bosques (14 articles), 5 % in Trees-Structure and Function (11 articles), 4 % in Revista Chapingo Serie Ciencias Forestales y del Ambiente (10 articles), 4 % in Dendrochronologia (nine articles) and 4 % in Tree-Ring Research (nine articles), which shows that foreign journals are preferred by researchers. Of the total number of articles, 53 % were published in 20 journals (Table 1), while 47 % were published in the rest (83 journals, Figure 9).

Figure 9 Number of articles on dendrochronology in Mexico, grouped according to the journal of publication in the period 2000-2023. 

Mexican journals published 26 % (57 articles) of dendrochronological research, with notable contributions from Madera y Bosques (14 articles), Revista Chapingo Serie Ciencias Forestales y del Ambiente (10 articles), Investigaciones Geográficas (seven articles) and Agrociencia (five articles). These have been preferred by researchers for more than a decade, as reported by ^{Acosta-Hernández et al. (2017)} eight years ago in a review study. Most articles published in leading journals (Table 1) have a dendroclimatic focus (^{Carlón Allende et al., 2018}; ^{Herrera-Soto et al., 2018}; ^{Villanueva-Díaz et al., 2020}).