ORIGINAL RESEARCH published: 26 January 2022 doi: 10.3389/fevo.2021.825751 Regional Patterns of Late Medieval and Early Modern European Building Activity Revealed by Felling Dates Edited by: Martin De Luis, University of Zaragoza, Spain Reviewed by: Katarina Čufar, University of Ljubljana, Slovenia Chris J. Caseldine, University of Exeter, United Kingdom *Correspondence: Fredrik Charpentier Ljungqvist fredrik.c.l@historia.su.se † These authors have contributed equally to this work Specialty section: This article was submitted to Paleoecology, a section of the journal Frontiers in Ecology and Evolution Received: 30 November 2021 Accepted: 31 December 2021 Published: 26 January 2022 Citation: Ljungqvist FC, Seim A, Tegel W, Krusic PJ, Baittinger C, Belingard C, Bernabei M, Bonde N, Borghaerts P, Couturier Y, Crone A, van Daalen S, Daly A, Doeve P, Domínguez-Delmás M, Edouard J-L, Frank T, Ginzler C, Grabner M, Gschwind FM, Haneca K, Hansson A, Herzig F, Heussner K-U, Hofmann J, Houbrechts D, Kaczka RJ, Kolář T, Kontic R, Kyncl T, Labbas V, Lagerås P, Le Digol Y, Le Roy M, Leuschner HH, Linderson H, Ludlow F, Marais A, Mills CM, Neyses-Eiden M, Nicolussi K, Perrault C, Pfeifer K, Rybníček M, Rzepecki A, Schmidhalter M, Seifert M, Shindo L, Spyt B, Susperregi J, Svarva HL, Thun T, Walder F, Ważny T, Werthe E, Westphal T, Wilson R and Büntgen U (2022) Regional Patterns of Late Medieval and Early Modern European Building Activity Revealed by Felling Dates. Front. Ecol. Evol. 9:825751. doi: 10.3389/fevo.2021.825751 Fredrik Charpentier Ljungqvist 1,2,3* † , Andrea Seim 4,5† , Willy Tegel 4,6 , Paul J. Krusic 7,8 , Claudia Baittinger 9 , Christelle Belingard 10 , Mauro Bernabei 11 , Niels Bonde 9 , Paul Borghaerts 12 , Yann Couturier 13 , Anne Crone 14 , Sjoerd van Daalen 15 , Aoife Daly 16 , Petra Doeve 17 , Marta Domínguez-Delmás 18 , Jean-Louis Edouard 19 , Thomas Frank 20 , Christian Ginzler 21 , Michael Grabner 22 , Friederike M. Gschwind 23 , Kristof Haneca 24 , Anton Hansson 25 , Franz Herzig 26 , Karl-Uwe Heussner 27 , Jutta Hofmann 28 , David Houbrechts 29 , Ryszard J. Kaczka 30 , Tomáš Kolář 31,32 , Raymond Kontic 33 , Tomáš Kyncl 34 , Vincent Labbas 35 , Per Lagerås 36 , Yannick Le Digol 13 , Melaine Le Roy 37 , Hanns Hubert Leuschner 38 , Hans Linderson 25 , Francis Ludlow 39,40 , Axel Marais 13 , Coralie M. Mills 41,42 , Mechthild Neyses-Eiden 43 , Kurt Nicolussi 44 , Christophe Perrault 45 , Klaus Pfeifer 46 , Michal Rybníček 31,32 , Andreas Rzepecki 43 , Martin Schmidhalter 47 , Mathias Seifert 48 , Lisa Shindo 49 , Barbara Spyt 50 , Josué Susperregi 51 , Helene Løvstrand Svarva 52 , Terje Thun 52 , Felix Walder 53 , Tomasz Ważny 54 , Elise Werthe 13 , Thorsten Westphal 20 , Rob Wilson 41 and Ulf Büntgen 7,21,32,55 1 Department of History, Stockholm University, Stockholm, Sweden, 2 Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden, 3 Swedish Collegium for Advanced Study, Uppsala, Sweden, 4 Chair of Forest Growth and Dendroecology, Institute of Forest Sciences, University of Freiburg, Freiburg, Germany, 5 Department of Botany, University of Innsbruck, Innsbruck, Austria, 6 Amt für Archäologie, Kanton Thurgau, Frauenfeld, Switzerland, 7 Department of Geography, University of Cambridge, Cambridge, United Kingdom, 8 Department of Physical Geography, Stockholm University, Stockholm, Sweden, 9 National Museum of Denmark, Copenhagen, Denmark, 10 GEOLAB, University of Limoges, Limoges, France, 11 Institute of BioEconomy, National Research Council, Trento, Italy, 12 Borghaerts Houtdatering, Easterein, Netherlands, 13 DendroTech, Betton, France, 14 AOC Archaeology Group, Edinburgh, United Kingdom, 15 Van Daalen Dendrochronologie, Deventer, Netherlands, 16 The Saxo Institute, University of Copenhagen, Copenhagen, Denmark, 17 BAAC Archaeology and Building History, Graaf van Solmsweg, Netherlands, 18 Amsterdam School for Heritage, Memory and Material Culture, University of Amsterdam, Amsterdam, Netherlands, 19 CNRS, CCJ, Aix-Marseille Université, Aix-en-Provence, France, 20 Laboratory of Dendroarchaeology, Department of Prehistoric Archaeology, University of Cologne, Cologne, Germany, 21 Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland, 22 Institute of Wood Technology and Renewable Materials, University of Natural Resources and Life Sciences, Vienna, Austria, 23 Büro für Dendrochronologie und Baudenkmalpflege, Planegg, Germany, 24 Flanders Heritage Agency, Brussels, Belgium, 25 The Laboratory for Wood Anatomy and Dendrochronology, Department of Geology, Lund University, Lund, Sweden, 26 Bavarian State Office for Monument Protection, Thierhaupten, Germany, 27 German Archaeological Institute, Berlin, Germany, 28 Jahrringlabor Hofmann, Nürtingen, Germany, 29 Association du Patrimoine Artistique, Brussels, Belgium, 30 Department of Physical Geography and Geoecology, Faculty of Science, Charles University, Prague, Czechia, 31 Department of Wood Science and Technology, Mendel University in Brno, Brno, Czechia, 32 CzechGlobe Global Change Research Institute CAS, Brno, Czechia, 33 Labor Dendron, Basel, Switzerland, 34 DendroLab Brno, Brno, Czechia, 35 Department of Historical Sciences, Art, Archaeology, Heritage, University of Liège, Liège, Belgium, and Royal Institute for Cultural Heritage (KIK-IRPA), Brussels, Belgium, 36 The Archaeologists, National Historical Museums, Lund, Sweden, 37 Climate Change Impacts and Risks in the Anthropocene (C-CIA), Institute for Environmental Sciences, University of Geneva, Geneva, Switzerland, 38 Department of Palynology and Climate Dynamics, Georg-August-University, Göttingen, Germany, 39 Department of History and Trinity Centre for Environmental Humanities, School of Histories and Humanities, Trinity College Dublin, Dublin, Ireland, 40 Department of History and Harvard University Center for the Environment, Harvard University, Cambridge, MA, United States, 41 School of Earth and Environmental Sciences, University of St Andrews, Fife, United Kingdom, 42 Dendrochronicle, Edinburgh, United Kingdom, 43 Generaldirektion Kulturelles Erbe Rheinland-Pfalz, Direktion Rheinisches Landesmuseum Trier, Trier, Germany, 44 Department of Geography, Universität Innsbruck, Innsbruck, Austria, 45 Centre d’Etudes en Dendrochronologie et de Recherche en Ecologie et Paléo-Ecologie, Besançon, France, 46 Labor für Dendrochronologie, Egg, Austria, 47 Dendrosuisse: Labor für Dendrochronologie, Brig-Glis, Switzerland, 48 Archäologischer Dienst Graubünden, Amt für Kultur, Chur, Switzerland, 49 Cluster of Excellence ROOTS, Kiel University, Kiel, Germany, 50 Faculty of Natural Sciences, University of Silesia in Katowice, Katowice, Poland, 51 Arkeolan Foundation, Irun, Spain, 52 The National Laboratory for Age Determination, NTNU University Museum, Norwegian University of Science Frontiers in Ecology and Evolution | www.frontiersin.org 1 January 2022 | Volume 9 | Article 825751 Ljungqvist et al. Regional Patterns of Building Activity and Technology, Trondheim, Norway, 53 Competence Center for Underwater Archaeology and Dendrochronology, Zurich, Switzerland, 54 Centre for Research and Conservation of Cultural Heritage, Faculty of Fine Arts, Nicolaus Copernicus University, Toruń, Poland, 55 Department of Geography, Masaryk University, Brno, Czechia Although variations in building activity are a useful indicator of societal well-being and demographic development, historical datasets for larger regions and longer periods are still rare. Here, we present 54,045 annually precise dendrochronological felling dates from historical construction timber from across most of Europe between 1250 and 1699 CE to infer variations in building activity. We use geostatistical techniques to compare spatiotemporal dynamics in past European building activity against independent demographic, economic, social and climatic data. We show that the felling dates capture major geographical patterns of demographic trends, especially in regions with dense data coverage. A particularly strong negative association is found between grain prices and the number of felling dates. In addition, a significant positive association is found between the number of felling dates and mining activity. These strong associations, with well-known macro-economic indicators from preindustrial Europe, corroborate the use of felling dates as an independent source for exploring large-scale fluctuations of societal well-being and demographic development. Three prominent examples are the building boom in the Hanseatic League region of northeastern Germany during the 13th century, the onset of the Late Medieval Crisis in much of Europe c. 1300, and the cessation of building activity in large parts of central Europe during armed conflicts such as the Thirty Years’ War (1618–1648 CE). Despite new insights gained from our European-wide felling date inventory, further studies are needed to investigate changes in construction activity of high versus low status buildings, and of urban versus rural buildings, and to compare those results with a variety of historical documentary sources and natural proxy archives. Keywords: archeology, cultural heritage, dendrochronology, dendroarchaeology, felling dates, history, historical demography shipwrecks to estimate commerce (e.g., Wilson, 2011), pollen to reconstruct agricultural production (e.g., Izdebski et al., 2016), glacier microfossil records to estimate changes in land use (Brugger et al., 2021), ancient DNA to reconstruct migration patterns (e.g., Margaryan et al., 2020), and anthropometric estimates of the biological standard of living from skeletonbased stature measurements (e.g., Kopke and Baten, 2005). These disparate types of data have the potential to detect and analyze patterns of prosperity and hardship in human history (Fischer, 1996), whereas the heterogeneous character of most documentary sources limits their suitability for such studies (see, e.g., Turchin and Nefedov, 2009). Inferring variations in building activity from annually resolved and absolutely dated felling dates can reveal information about large-scale societal changes. The very large amount of available data in combination with their exact dating to a calendar year makes felling dates unique among non-documentary sources of human activity. Felling dates have hitherto mainly been used to infer large-scale demographic and societal changes only for those periods and regions lacking written sources from which to reconstruct demographic trends, e.g., among the Ancestral Puebloans in the southwestern United States (pioneered by INTRODUCTION Variations in building activity reflect changing demographic, economic, and social conditions (e.g., Barras, 2009; Aksözen et al., 2017a,b) and, potentially, provide a broad overview of societal well-being over space and time. However, prior to the modern period building activity rates are poorly documented in Europe, precluding the use of written sources for their assessment. An alternative source for estimating building activity rates are large datasets of dendrochronologically obtained felling dates of historical construction timbers. Such data, derived from the efforts of many to date individual constructions in archeological research and cultural heritage work, when collated into an aggregate dataset, can be highly useful for exploring large-scale changes in building activity (e.g., Ljungqvist et al., 2018). Recent historical scholarship has increasingly employed data from the natural sciences and archeology to understand macro scale changes not readily detectable or quantifiable using documentary sources or traditional archeological materials. Such studies include pollution data from ice-cores as a proxy for mining activity (e.g., McConnell et al., 2019), numbers of Frontiers in Ecology and Evolution | www.frontiersin.org 2 January 2022 | Volume 9 | Article 825751 Ljungqvist et al. Regional Patterns of Building Activity last measured tree ring is the terminal ring (so-called waney edge) were used. The determination of the exact year of tree felling is termed waney edge dating (Bannister, 1962). The majority of felling dates were derived from timbers in different parts of buildings such as roof trusses, ceiling joints, basement pillars, etc. A small number of felling dates were obtained from archeological materials (Figure 2). The tree species used for constructions can vary greatly from region to region. For exterior/exposed applications like bridges and hydraulic engineering, oak (Quercus spp.) and fir (Abies alba Mill.) were used almost exclusively. Conifer species such as fir, spruce (Picea abies L.), pine (Pinus sylvestris L.) and larch (Larix decidua Mill.) were preferred for half-timbering and roof trusses (Tegel et al., 2010). However, the species’ natural distribution also played a decisive role in dictating the application. In the western Euro-Atlantic region, where oak woodlands predominated, this was the species used for construction purposes. In northern Europe, pine was the preferred species for construction timber (e.g., Mills et al., 2017), whereas fir and spruce were mostly used in central Europe (Grabner et al., 2018; Kolář et al., 2021). The natural distribution of larch is limited to the high altitudes of the Alps and parts of the Tatra Mountains (Büntgen et al., 2009), where this species was preferred as construction timber. Douglass, 1921, 1929, 1941; more recently, see Bocinsky et al., 2016; Robinson et al., 2021). In Europe, there are limited examples in archeological and historical research of using felling dates for reconstructing building activity changes at large spatial scales, but several smallscale studies have provided valuable insights into demographic declines or the timing of societal crises (Baillie, 1982, 1995, 1999; Mallory and Baillie, 1988; Schweingruber, 1988; Wrobel and Eckstein, 1993; Nicolussi, 2002; Eckstein, 2007), and also into past settlement and demographic dynamics in the Swiss Alps (Büntgen et al., 2006), the northwestern Carpathian arc (Büntgen et al., 2013), the north-eastern France (Tegel et al., 2016), in Sweden (Bartholin, 1989, 1990; Lagerås et al., 2016), in parts of Norway (Thun and Svarva, 2018), in eastern Austria (Grabner et al., 2018), and Ireland (Brown and Baillie, 2012; Campbell and Ludlow, 2020). Using 49,640 precisely dated felling dates, between 1250 and 1699 CE, Ljungqvist et al. (2018) identified variations in European building activity, and attempted to quantify the major drivers behind those variations. They found (a) building activity decreased during periods with multiple or severe plague outbreaks, (b) building activity was significantly lower when grain prices were high, (c) first evidence of the Late Medieval Crisis as early as c. 1300 CE and lasting until c. 1415 CE, and (d) building activity decreased abruptly by about 36 percent of prior levels during the Thirty Years’ War (1618–1648 CE). In sum, Ljungqvist et al. (2018) demonstrated how sudden declines in building activity are sensitive indicators of the onset of a crisis. However, the spatial aspects of the timing, duration, and amplitude of decreased building activity associated with the Late Medieval Crisis and the Thirty Years’ War (1618–1648) were not investigated. To date, no study has attempted to use dendrochronological felling dates from historical construction timbers to investigate the spatial dynamics of past European-scale building activity. This article aims to fill that gap by assessing regional patterns of construction activity during the 1250–1699 CE period in relation to regional demographic, economic, and social conditions. To do so we apply geostatistical analysis to explore regional differences in the number of felling dates to infer the timing, duration, and intensity of periods of crisis and prosperity at different spatial and temporal scales. This study thereby constitutes a considerable extension in scope, and aim, and geographical coverage, compared to Ljungqvist et al. (2018). Other Datasets Used for Comparisons Inferred building activity levels were compared with different independent indicators of periods of “crisis” and “prosperity” representative of large spatial scales. The indicators of past economic, societal, and demographic conditions include: (a) atmospheric lead emissions data, an indicator of mining activity (in particular silver production); (b) church construction, an indicator of societies’ available economic surplus as well as demographic trends; (c) grain price data, reflecting the availability of the most important food source and general economic well-being; (d) wine prices, indicating economic conditions and general purchasing power; and (e) consumer price indices, also indicating general purchasing power and thus economic well-being. In addition, we compare building activity levels with reconstructed growing season temperature, soil moisture levels and a reconstruction of southwestern German groundwater levels. Changes in the amount of atmospheric lead in high-resolution Arctic and alpine ice-cores have been linked to the mining and smelting of raw ores, especially silver, in Europe. Such records have proved to be an indicator of prosperity and crisis (i.e., in times of prosperity, pollution levels were high) over the past two millennia (Hong et al., 1994; Rosman et al., 1997; More et al., 2017; Loveluck et al., 2018; McConnell et al., 2018, 2019; Carvalho and Schulte, 2021). We employ the lead pollution series of McConnell et al. (2019) as proxies for mining activity in western Europe and central Europe. To a large extent, church building in medieval and early modern times reflected a society’s surplus, although it can be argued the Catholic Church, as an institution and major financial power, was much more resilient to crises that would otherwise affect secular constructions. We employ an independent timeseries of urban church building in western Europe, measured in MATERIALS AND METHODS Felling Dates We collected 54,045 georeferenced felling dates for the period 1250–1699 from western and central Europe, north of ∼42◦ N (Figure 1A). This collection is the result of a European-wide collaborative network that includes data from laboratories in Austria, Belgium, Czechia, Denmark, France, Germany, Ireland, Italy, Netherlands, Norway, Poland, Slovakia, Spain, Sweden, Switzerland, and United Kingdom (Table 1). The same criteria as in Ljungqvist et al. (2018) were applied and only data where the Frontiers in Ecology and Evolution | www.frontiersin.org 3 January 2022 | Volume 9 | Article 825751 Ljungqvist et al. Regional Patterns of Building Activity FIGURE 1 | (A) The geographical distribution of all 54,045 tree felling dates 1250–1699 CE from archeological and historical construction timber displayed using the Lambert conformal conic projection in ArcGIS and displayed with contemporary political boundaries. (B) Number of felling dates per year for each regional dataset [color-coded as in (A)] over the period 1250–1699 CE. The black line shows the significant regime shifts in the number of felling dates using the full dataset. millions of cubic meters per 20-year period, compiled from data of extant church structures (Buringh et al., 2020). The spatial coverage of this time-series is restricted to present-day Italy, France, Switzerland, Germany, the Low Countries, and Great Britain, and it only extends to 1500 CE. Grain-based foods were by far the most important food source in medieval and early modern Europe (Rahlf, 1996; Frontiers in Ecology and Evolution | www.frontiersin.org Bateman, 2015). During medieval and early modern times, the price of grain had a determining effect on the entire economy and the general standard of living (Allen, 2000, 2001). To compare building activity history with the price of grain we used the 300year detrended European grain price average as published by Ljungqvist et al. (2022). This grain price record consists of 56 series from cities across most of central and western Europe, 4 January 2022 | Volume 9 | Article 825751 Ljungqvist et al. Regional Patterns of Building Activity TABLE 1 | List of data contributors of the felling dates, contribution size, the geographical origin of their samples, and key references to the contributed data. Country or region Data contributor(s) Austria Michael Grabner; Kurt Nicolussi; Klaus Pfeifer Number 4654 3 Key references Nicolussi, 2002; Buchinger and Grabner, 2017; Karanitsch-Ackerl et al., 2017; Grabner et al., 2018 Basque Country, Spain Josué Susperregi Belgium Kristof Haneca; David Houbrechts; Willy Tegel 455 Czechia Tomáš Kyncl; Tomáš Kolář; Michal Rybníček 7695 Kolář et al., 2012, 2021, 2022 Denmark Claudia Baittinger; Niels Bonde; Aoife Daly 298 Daly, 2007 France Yann Couturier; Yannick Le Digol; Jean-Louis Edouard; Thomas Frank; David Houbrechts; Vincent Labbas; Axel Marais; Elise Werthe; Melaine Le Roy; Christophe Perrault; Lisa Shindo; Willy Tegel 2346 Edouard, 2010; Tegel et al., 2010; Meirion-Jones and Grandchamp, 2013; Davy and Foisneau, 2014; Durandière et al., 2015; Biguet and Letellier-d’Espinose, 2016; Le Roy et al., 2017; Shindo et al., 2018 Germany Thomas Frank; Friederike M. Gschwind; Franz Herzig; Karl-Uwe Heussner; Jutta Hofmann; Hanns H. Leuschner; Mechthild Neyses-Eiden; Klaus Pfeifer; Andreas Rzepecki; Willy Tegel; Thorsten Westphal 19894 Hollstein, 1980; Becker, 1991; Kelly et al., 2002; Westphal, 2002, 2003 Ireland Francis Ludlow Italy Mauro Bernabei; Kurt Nicolussi 392 Bernabei et al., 2016, 2017, 2021; Nicolussi, 2002 Netherlands Paul Borghaerts; Sjoerd van Daalen; Petra Doeve; Marta Domínguez-Delmás; Esther Jansma 1485 houtdatering.nl; https://doi.org/10.34894/ZWBVSW 40 Susperregi, 2007; Susperregi et al., 2017 Haneca et al., 2009, 2020; Haneca and van Daalen, 2017; Van Eenhooge et al., 2018 Baillie, 1982, 1995, 1999, 2006; Brown and Baillie, 2012; Campbell and Ludlow, 2020 Norway Thomas S. Bartholin; Helene Løvstrand Svarva; Terje Thun 1537 Thun, 2009; Thun and Svarva, 2018 Poland Ryszard J. Kaczka; Tomasz Ważny 1496 Ważny, 1990, 2001; Konieczny, 2009, 2010, 2011, 2012; Ruszczyk and Konieczny, 2012; Klajmon, 2013; Spyt et al., 2016 Slovakia Tomáš Kolář; Tomáš Kyncl; Michal Rybníček 811 Prokop et al., 2016 Sweden Anton Hansson; Per Lagerås; Hans Linderson; Andrea Seim 1591 Meissner et al., 2012; Seim et al., 2015; Lagerås et al., 2016 Switzerland Raymond Kontic; Martin Schmidhalter; Mathias Seifert; Willy Tegel; Felix Walder 9008 Seifert, 2018 United Kingdom Vernacular Architecture*; Anne Crone; Coralie Mills; Robert Wilson 2340 Alcock, 1987, 1993, 1998; Miles, 1997; Meeson, 2012 *Digitized from data published in Vernacular Architecture originating from numerous investigators. FIGURE 2 | Examples of type of buildings and material used to derive the felling dates from. Top: Half-timbered building in Sonterswil (Thurgau, Switzerland) from the 17th century. Tower of the town wall from Ribeauvillé (Alsace, France) from the 16th century. Log houses in the Lötschental Valley (Valais, Switzerland) from the 18th century. Below: Roof truss of the Chapelle Saint-Denis in Marmoutier (Alsace, France) from the 16th century. Roof truss from the church in Forshem, southwestern Sweden, with a nave from the 12th century and a chancel from the 13th century. Cross section of an oak beam from the Cathedral of Reims (France) from the 13th century. Frontiers in Ecology and Evolution | www.frontiersin.org 5 January 2022 | Volume 9 | Article 825751 Ljungqvist et al. Regional Patterns of Building Activity in a way that made the most historical sense, acknowledging that any such clustering is to a degree subjective. The seven regions are: (1) the British Isles; (2) the Nordic countries, including Schleswig-Holstein, present-day Germany; (3) France, excluding Alsace, and Basque Country (Spain); (4) the Benelux countries, Belgium, the Netherlands, and Luxembourg; (5) central Europe (north), consisting of Germany, excluding BadenWürttemberg, Bavaria and Schleswig-Holstein, and Poland; (6) central Europe (south), consisting of Alsace, Austria, BadenWürttemberg, Bavaria, Czechia, Slovakia, and South Tyrol (Italy); and (7) Switzerland. The groups are based on natural, geographical, cultural, historical, ecological, social and economic features which, over the period of investigation or at least over longer historical periods, shared close economic relations and cultural unity. Long-term trends toward fewer available dates in the felling dataset are partly related to a general decrease in the preservation of constructions back in time. This time-dependent constraint must be removed to provide a meaningful construction history. As in Ljungqvist et al. (2018), we thus removed the longterm trends by calculating the ratios between the raw values and 300-year cubic smoothing splines (Cook and Peters, 1981). After removing the long-term trend, the felling date data were transformed to standard normal deviates with a mean of zero and a standard deviation of one. For correlation statistics all datasets are, when not using the annual values, smoothed using 10-year splines as well as 10-year, non-overlapping, box-car filters. Throughout this study, we use the p < 0.05 significance level for both the Pearson correlation (r) and Spearman rank correlation (rs ) coefficients. The fewer available degrees of freedom were taken into consideration when using 10-year smoothed series. For detecting the timing of significant regime shifts, i.e., trends toward increasing or decreasing numbers, we employ the Rodionov (2004) sequential algorithm, as updated by Rodionov (2006) to accommodate autocorrelation, and consider only years with regime shifts significant at the p < 0.05 level. The software is a macrobased implementation for Microsoft Excel (called Regime test shift v6-2). Shifts in the time-series were computed on the mean felling date numbers using the default cut-off length of 20 years and omitting the last 10 years at each end of the time-series. Heat maps for consecutive 50-year periods between 1250 and 1699, and for periods of 31 years around the Late Medieval Crisis and the Thirty Years’ War, were generated using the software ArcGIS 10.6. Here, the kernel density function in the Spatial Analyst toolbox was applied on the recorded felling date location (i.e., point data) for the above-mentioned periods (DiBiase et al., 2006). We used a search radius of 60 km to estimate the spatial concentrations of the felling dates within the individual periods. The Kernel density maps were reclassified for final comparison. To evaluate the regional impact of the Late Medieval Crisis and the Thirty Years’ War, we calculated the absolute differences in the number of felling dates between the 31-year periods by using the Raster Calculator in the Map Algebra toolbox (Spatial Analyst Tools) in ArcGIS 10.6. Again, the resulting maps were standardized (i.e., reclassified) to make standardized to z-scores relative to the 1546–1650 period. These data include 25 price series of wheat, 14 of rye, 10 of barley, and of 7 oats. This new price compilation is much more comprehensive than the European grain price average of 19 series from Esper et al. (2017) used in Ljungqvist et al. (2018), and represents a much larger spatial domain. We also calculated an average of multiple wine price series from across Europe (Allen and Unger, 2019), as wine was an important market commodity in much of Europe, and its price level is indicative of the economic conditions on a broad scale (Chilosi and Federico, 2021). Recognizing that other living costs besides grain and wine affected the population’s purchasing power, and thus economic well-being, we use annual consumer price indices for London (1264–1699), Strasbourg (1386–1699), Krakow (1409–1699) (Allen, 2001), and Stockholm (1290–1699, Edvinsson and Söderberg, 2010) to estimate changes over time in consumer price indices. These indices are highly correlated to changes in real wages (Allen, 2000) and thereby provide an indication of relative societal wealth among ordinary people (De Pleijt and van Zanden, 2016). Despite considerable uncertainties in calculating the annual consumer price indices, we maintain that these indices still capture the economic feasibility to construct new buildings or to undertake major repair of existing ones. To represent growing season temperature, we used the June– August temperature reconstruction by Luterbacher et al. (2016), as updated by Ljungqvist et al. (2019), resolved on a 5◦ × 5◦ grid across Europe. From these data we extracted the gridcells covering 60◦ N–40◦ N by 10◦ W–30◦ E. For relative soil moisture availability, we use data from the Old World Drought Atlas (OWDA; Cook et al., 2015). The OWDA is a tree-ringbased reconstruction of annually resolved June–August (JJA) self-calibrating Palmer Drought Severity Index (scPDSI) values (Palmer, 1965; van der Schrier et al., 2011, 2013) resolved on a 0.5◦ × 0.5◦ grid across Europe. For obvious reasons, the spatial and temporal extent of both reconstructions is limited by the distribution and length of the tree-ring chronologies available for reconstruction. Consequently, for portions of Europe as one goes further back in time, the quality of the reconstructions decreases (Cook et al., 2015). For further comparison, we used an annually resolved groundwater level (GWL) reconstruction for the Upper Rhine Valley (Germany and France) derived from tree-ring width data (Tegel et al., 2020). This reconstruction is entirely independent from the tree-ring data used to produce the OWDA. The GWL reconstruction is a proxy for long and short-term hydroclimate variations over western and central Europe, which has been linked to the multi-decadal North Atlantic climate variability (Tegel et al., 2020). Regional Grouping of the Felling Dates and (Geo)statistical Analyses Applying quantitative spatial and geostatistical analyses to the felling date data (such as grouping analysis) in ArcMap 10.6 (program package of ArcGIS; ESRI, 2017), produced no distinct regional groups or clusters. Hence, we manually grouped the data, over the period 1250–1699 CE, into seven separate regions Frontiers in Ecology and Evolution | www.frontiersin.org 6 January 2022 | Volume 9 | Article 825751 Ljungqvist et al. Regional Patterns of Building Activity them comparable. Regarding the Thirty Years’ War, only the regions with a population loss of at least 33% (Eickhoff et al., 2012, p. 26) were georeferenced and digitized by us for this purpose. RESULTS Patterns of Spatio-Temporal Change in Building Activity The felling dates show a clear decline just prior to c. 1300 followed by a second decline c. 1340 (Figure 1B). Step-wise increases in building activity subsequently occurred during the late 14th century and throughout the 15th century. This feature is not merely a consequence of increasing data coverage over time, as it is also clearly apparent in the detrended data. Only toward the end of the 15th century did building activity levels become comparable to those of the 13th century. A peak in building activity can be observed in the mid-16th century, followed by a rather pronounced decline. The sharpest, and most distinct decline in building activity coincides with the Thirty Years’ War (1618–1648). By the end of the 17th century building activity reached levels comparable to those of the 13th and mid-16th centuries. Considerable regional-scale variations in building activity were found. These variations are expressed in the relatively low correlation coefficients between the seven regions (see Figure 3 and Table 2). Exceptions are the strong correlation between the regions central Europe (south) and the British Isles, and between central Europe (south) and central Europe (north). The biggest differences between the regional-scale datasets relate to the timing and duration of the Late Medieval Crisis and the effect of the Thirty Years’ War (1618–1648). On the whole, times of high and low building activity are far from synchronized across regions even though some general patterns can be identified (Table 3). Moreover, the building activity history for the Nordic countries looks rather different from that of the regions on the continent. This may, partly, be related to the lower number of felling dates available for the Nordic countries. Clear spatial patterns in the form of changing hot-spots of building activity can be observed for the 50-year periods ranging from 1250–1299 to 1650–1699 (Figure 4). However, as the maps in Figure 4 contain absolute values, with their increasing trends over time, the periods of relative increase and decrease activity are arguably better captured in Figure 3. What is notable is that the different sub-regions, to a large extent, show different and even opposing trends for certain periods. For example, in the British Isles, in central Europe (north) and Switzerland, building activity increases around the 1530s. At the same time in France building activity begins to decline. In general, the different sub-regions show rather similar long-term trends, albeit with different start and end years containing periods of high and low building activity. FIGURE 3 | The felling date data 300-year filtered and standardized to z-score values over the entire 1250–1699 CE period for the regional subsets as well as for the full dataset. The red lines show the significant regime shifts in the number of felling dates, using a 30-year cut-off length. the number of felling dates between 1250–1299 and 1300–1349 is 37%, whereas the declines between 1300–1349 and 1350–1399 are insignificant an 1%. Between 1350–1399 and 1400–1449 building activity recovers by 28% (Table 4). On a 31-year The Late Medieval Crisis The decreasing building activity during the Late Medieval Crisis occurs well before the Black Death (1346–1353). The decline in Frontiers in Ecology and Evolution | www.frontiersin.org 7 January 2022 | Volume 9 | Article 825751 Ljungqvist et al. Regional Patterns of Building Activity TABLE 2 | Annual correlation between the 300-year filtered and standardized regional subsets of felling dates. British Isles Nordic British Isles France Benelux C. Europe (N.) C. Europe (S.) Switzerland — 0.09 (0.20) 0.14 (0.20) 0.40 (0.66) –0.09 (–0.13) 0.35 (0.44) 0.48 (0.73) Nordic 0.09 (0.20) — 0.01 (–0.02) 0.21 (0.38) 0.27 (0.41) 0.36 (0.52) 0.22 (0.36) France 0.14 (0.20) 0.01 (–0.02) — 0.23 (0.39) 0.16 (0.23) 0.19 (0.31) 0.19 (0.39) Benelux 0.40 (0.66) 0.21 (0.38) 0.23 (0.39) — 0.13 (0.23) 0.34 (0.31) 0.42 (0.39) C. Europe (N) –0.09 (–0.13) 0.27 (0.41) 0.16 (0.23) 0.13 (0.23) — 0.32 (0.38) 0.05 (0.10) C. Europe (S) 0.35 (0.44) 0.36 (0.52) 0.19 (0.31) 0.34 (0.31) 0.32 (0.38) — 0.55 (0.68) Switzerland 0.48 (0.73) 0.22 (0.36) 0.19 (0.39) 0.42 (0.39) 0.05 (0.10) 0.55 (0.68) — Values within parenthesis refer to correlations of 10-year low-pass filtered values. Values significant at the p < 0.05 level, using a two-tailed significance test, are highlighted in bold. TABLE 3 | List, in chronological order, of significant regime shifts in the unfiltered regional subsets of felling dates as well as in the full dataset. Region Unfiltered Entire dataset 1297↓ 1405↑ 1444↑ 1482↑ 1537↑ Benelux 1291↓ 1447↑ 1524↑ 1565↓ 1670↓ 1564↓ 1618↓ British Isles 1397↑ 1428↑ 1533↑ 1626↓ 1675↓ C. Europe (N) 1297↓ 1332↓ 1489↑ 1537↑ 1621↓ C. Europe (S) 1405↑ 1444↑ 1544↑ 1647↑ 1677↑ 1617↓ 1648↑ 1668↑ France 1293↓ 1556↑ Nordic countries 1350↓ 1546↑ 1482↑ 1537↓ 1586↓ 1583↑ 1674↓ Switzerland 1354↑ 1411↑ 1484↑ 1536↑ Region 1583↓ 1617↓ 1648↑ 1664↑ 1683↑ 1658↑ Unfiltered and 10-year spline low-pass filtered Entire dataset 1293↓ 1340↓ 1389↑ 1420↑ 1445↑ 1470↑ 1492↑ 1536↑ 1565↓ Benelux 1292↓ 1444↑ 1462↑ 1483↓ 1508↑ 1524↑ 1566↓ 1587↑ 1669↓ British Isles 1306↑ 1385↑ 1424↑ 1443↑ 1479↓ 1533↑ 1570↑ 1594↓ C. Europe (N) 1267↓ 1297↓ 1307↓ 1332↓ 1488↑ 1537↑ 1619↓ 1645↑ C. Europe (S) 1306↑ 1387↑ 1419↑ 1444↑ 1470↑ 1521↓ 1546↑ France 1271↓ 1294↓ 1396↑ 1412↓ 1456↑ 1480↑ 1537↓ Nordic countries 1297↓ 1348↓ 1545↑ 1577↑ 1634↑ 1653↓ 1663↑ Switzerland 1307↑ 1354↑ 1365↓ 1401↑ 1470↑ 1489↑ 1535↑ Region 1618↓ 1647↑ 1626↓ 1638↓ 1674↓ 1659↑ 1680↑ 1569↓ 1602↑ 1617↓ 1585↓ 1661↑ 1680↑ 1575↓ 1606↓ 1633↑ 1649↑ 1663↑ 1680↑ 1666↑ 1679↑ 1659↑ 300-year filtered and standardized Entire dataset 1297↓ 1444↑ 1617↓ 1659↑ 1683↑ Benelux 1291↓ 1413↓ 1447↑ 1483↓ 1524↑ 1568↑ British Isles 1305↑ 1346↓ 1444↑ C. Europe (N) 1304↓ 1360↑ 1555↑ 1607↓ 1648↑ 1683↑ C. Europe (S) 1270↓ 1306↑ 1339↓ 1420↑ 1449↑ 1523↓ France 1304↓ 1459↑ 1537↓ 1676↑ Nordic countries 1350↓ 1392↑ 1462↓ 1583↑ Switzerland 1443↓ 1443↑ 1617↓ Region 1617↓ 1669↑ 300-year filtered and standardized and 10-year spline low-pass filtered Entire dataset 1295↓ 1340↓ 1383↑ 1445↑ 1487↑ 1520↓ 1536↑ 1617↓ 1647↑ 1664↑ 1683↑ Benelux 1275↑ 1291↓ 1343↑ 1370↓ 1403↓ 1444↑ 1482↓ 1523↑ 1567↓ 1642↑ 1669↓ British Isles 1268↓ 1306↑ 1339↓ 1426↑ 1456↓ 1536↑ 1636↓ C. Europe (N) 1278↑ 1299↓ 1332↓ 1360↑ 1381↑ 1428↓ 1489↑ 1520↓ 1537↑ 1578↓ 1608↓ 1625↓ C. Europe (S) 1270↓ 1294↑ 1339↓ 1372↑ 1420↑ 1445↑ 1498↓ 1569↓ 1618↓ 1664↑ France 1271↓ 1294↓ 1324↑ 1396↑ 1412↓ 1456↑ 1480↑ 1537↓ 1586↓ 1614↑ 1660↑ 1681↑ Nordic countries 1348↓ 1381↑ 1462↓ 1577↑ 1653↓ Switzerland 1291↓ 1308↑ 1365↓ 1404↑ 1432↓ 1484↑ 1536↑ 1575↓ 1617↓ 1634↑ 1660↑ 1646↑ 1678↑ A downward arrow marks a year with a shift toward a decreasing number of felling dates and an upward arrow a year with a shift toward an increasing number of felling dates. Frontiers in Ecology and Evolution | www.frontiersin.org 8 January 2022 | Volume 9 | Article 825751 Ljungqvist et al. Regional Patterns of Building Activity FIGURE 4 | Heat-maps of the number of felling dates for each 50-year period covered by our dataset. The maps are shown with contemporary political boundaries. TABLE 4 | Summary statistics for the felling dates for the 31-year periods around the time of the Late Medieval Crisis including the number (n) mean (x̄), median (x̃), and standard deviation (SD). Region Entire dataset 1286–1316 1317–1347 1348–1378 1379–1409 n x̄ x̃ SD n x̄ x̃ SD n x̄ x̃ SD n x̄ x̃ SD 2174 70 73 20.22 1797 58 56 13.19 1572 51 51 13.22 2015 65 65 14.58 Benelux 61 2 1 2.34 51 2 1 1.74 51 2 1 1.36 59 2 2 1.62 British Isles 45 1 1 1.15 68 2 2 1.68 62 2 2 1.55 96 3 3 1.64 C. Europe (N) 1292 42 41 19 666 21 21 9.11 589 19 18 6.97 700 23 22 9.29 C. Europe (S) 278 9 7 5.00 419 14 11 8.16 333 11 9 6.37 540 17 18 6.52 France 77 2 1 3.37 60 2 2 1.73 55 2 1 2.03 101 3 2 3.00 Nordic countries 1796 6 5 4.96 158 5 4 4.96 44 1 1 1.43 122 4 2 4.94 Switzerland 242 8 6 6.57 375 12 10 5.92 438 14 14 9.71 407 13 12 6.25 of felling dates between 1286–1316 and 1348–1378 is 28%. The 28% increase between 1348–1378 and 1379–1409, brings building activity levels to nearly the same levels as between 1286–1316 (Table 4). time-scale, the decrease between 1286–1316 and 1317–1347 is 18% whereas between 1317–1347 and 1348–1378, following the establishment and spread of the plague, the decrease is only 12% (Figure 5). In total, the decrease in the number Frontiers in Ecology and Evolution | www.frontiersin.org 9 January 2022 | Volume 9 | Article 825751 Ljungqvist et al. Regional Patterns of Building Activity FIGURE 5 | Changes in the number of felling dates for four 31-year periods around the time of the Late Medieval Crisis. (A) Between 1286–1316 and 1317–1347, (B) Between 1317–1347 and 1348–1378, (C) Between 1348–1378 and 1379–1409. The maps are shown with contemporary political boundaries. and 1649–1679 (Table 5). However, the impact of the Thirty Years’ War is very unevenly distributed across Europe, and largely limited to the parts of central Europe directly affected by the conflict. The decrease in the number of felling dates was largest in central Europe (north) (43%) compared to 24% in central Europe (south). However, in central Europe (south) the recovery of building activity first starts in the 1660s. Switzerland also experienced a decrease in the number of felling dates by 16% during the Thirty Years’ War, but this decrease is mainly limited to the c. 1618–1634 period (Table 5). Swiss building activity levels were again close to the long-term average during the latter portion of the Thirty Years’ War, with successive years of unusually high construction levels. Considering the spatial pattern in more detail, the strongest decrease during the Thirty Years’ War occurred in central Germany and portions of eastern Germany (Figure 6). In regions affected by the Thirty Years’ War, and having an estimated population loss of less than 33%, the decrease in number of felling dates was 31.84% between 1587–1617 and 1618–1648. In contrast, the decrease in number of felling dates was 41.4% in war-affected regions with an estimated population loss between 33 and 66%. Finally, in regions with a population loss exceeding 66%, the decrease in number of felling dates was as high as 68.3% (Figure 6). These differences are statistically significant at a p ≤ 0.01 level. Thus, it is clearly evident that there is a strong correspondence between the magnitude of population loss and the magnitude of decreased building activity, demonstrating the ability of the felling dates to capture not only the timing, but also the extent, of larger demographic changes. The magnitude and timing of the decrease in building activity during the Late Medieval Crisis is, however, highly variable between regions (Figure 5). The strongest decrease, pre-dating the Black Death, is seen in northeastern Germany and in France. In central Europe (south) this decrease is smaller and first occurs following the arrival of the plague. Considering the timing of significant regime shifts in the 300-year detrended and 10-year low-pass filtered building activity data of the entire dataset, the late medieval decrease in felling dates first appears in c. 1295 and then intensifies c. 1340. The recovery occurs in three phases c. 1383, 1445, and 1487. In more detail, several regions either show periods of declining building activity or an increasing building activity prior to the Black Death (Figure 5 and Table 3). The Nordic countries, dominated by data from Sweden, stand out for their lack of any significant evidence of decreasing numbers of felling dates prior to 1348 and the Black Death (Figure 3). The recovery from the Late Medieval Crisis shows a similar heterogeneous pattern between regions. Both central Europe (south) and central Europe (north), France and Switzerland show increases in the second half of the 14th century followed by new decreases in the first half of the 15th century (Figure 3). Looking at the heat-maps of building activity, the expansion of building activities continues from the 13th century into and throughout the 14th century in Austria, Czechia, and Switzerland. In these southern regions the evidence, as derived from felling date data, for any crisis is not clear. Other regions contain too few felling dates for the period to arrive at any more definitive conclusions (Figure 4). The Thirty Years’ War (1618–1648) A distinct decrease in building activity is recorded during the Thirty Years’ War (1618–1648) (Figure 6). The number of felling dates is reduced by 22% between 1587–1617 and 1618–1648, followed by a subsequent increase of 41% between 1618–1648 Frontiers in Ecology and Evolution | www.frontiersin.org Periods of High Building Activity Despite small regional variations, common periods of high building activity are detected c. 1250–1295, c. 1445–1520, for 10 January 2022 | Volume 9 | Article 825751 Ljungqvist et al. Regional Patterns of Building Activity FIGURE 6 | Changes in the number of felling dates for three 31-year periods of the time of the Thirty Years’ War (1618–1648) to the period 1587–1617 and to the period 1649–1679 CE. The maps are shown with contemporary political boundaries. Regions with a population loss of 66% and above, of 33–66%, and below 33% are shown on the map. TABLE 5 | Summary statistics for the felling dates for the 31-year periods around the Thirty Years’ War (1618–1648) including the number (n) mean (x̄), median (x̃) and standard deviation (SD). Region 1587–1617 1618–1648 1649–1679 n x̄ x̃ SD n x̄ x̃ SD n x̄ x̃ SD Entire dataset 5508 178 173 28.03 4293 138 138 26.50 6061 196 188 37.46 Benelux 222 7 8 3.09 218 7 8 3.83 176 6 5 3.66 British Isles 321 10 11 3.45 205 7 7 3.41 150 5 4 2.88 C. Europe (N) 1282 41 43 10.71 734 24 21 10.90 1561 50 48 14.11 C. Europe (S) 2099 68 69 18.84 1600 52 50 16.08 2531 82 78 25.04 France 109 4 3 2.91 123 4 4 1.97 147 5 4 2.87 Nordic countries 452 15 12 10.75 550 18 17 8.95 480 15 12 10.83 Switzerland 1033 32 31 11.41 864 28 26 12.26 1029 33 32 9.95 Switzerland. Finally, the building activity boom in the second half of the 17th century, following the Thirty Years’ War, is most evident in central Europe (both north and south) and France (Table 3). a few decades in the mid-16th century, and in the second half of the 17th century (Figures 3, 4). Pre-Late Medieval Crisis construction peaks are absent from Switzerland and the Nordic countries, while occurring earlier in the British Isles, France, central Europe (south), the Benelux countries, and central Europe (north). Regarding the late-15th century period of high building activity levels, this building boom is most evident in the Benelux countries, central Europe (both north and south), and in France where it occurs slightly later. It is absent in the British Isles, Switzerland, and the Nordic countries. The mid-16th century period of high building activity is only distinctive in the Benelux countries, central Europe (north), and Frontiers in Ecology and Evolution | www.frontiersin.org Building Activity, Grain Price Level, Economic Well-Being, and Climatic Change A significant negative correlation, r = –0.29 (rs = –0.29) using annual data and r = –0.55 (rs = –0.59) at decadal time-scales, is found between European building activity levels and the average 11 January 2022 | Volume 9 | Article 825751 Ljungqvist et al. Regional Patterns of Building Activity TABLE 6 | Correlation between 300-year filtered and standardized subsets for comparison with the entire felling date dataset. Correlated variables None Pearson r value Spearman’s rs value Data series smoothing Data series smoothing 10-year spline 10-year box-car None 10-year spline 10-year box-car Lead pollution (western Europe) 0.22 0.39 0.45 0.26 0.43 0.48 Lead pollution (eastern Europe) 0.12 0.21 0.27 0.18 0.28 0.24 Grain price average –0.27 –0.52 –0.55 –0.29 –0.56 –0.59 Wine price average –0.20 −0.30 –0.31 –0.22 −0.24 −0.23 CPI London –0.11 −0.18 −0.20 –0.18 −0.28 –0.31 CPI Strasbourg –0.22 −0.36 –0.41 –0.21 −0.31 −0.34 CPI Krakow –0.30 –0.44 –0.50 –0.21 −0.31 –0.40 CPI Stockholm −0.03 −0.01 0.08 0.08 −0.21 −0.11 Church construction JJA temperature Drought index SW. Germany groundwater – – −0.05 −0.14 – – −0.17 0.03 –0.14 0.38 –0.11 −0.17 0.34 −0.01 0.13 −0.01 −0.02 0.14 −0.24 –0.30 –0.16 −0.26 –0.31 −0.17 Values significant at the p < 0.05 level, using a two-tailed significance test, are highlighted in bold. European grain price level (Table 6). This significant negative grain price–building activity association strongly suggests less construction activity occurred when grain prices were high and vice versa. No other indicator of economic or social well-being shows such a strong relationship with building activity as grain prices. For example, the correlations between European building activity levels and average European wine prices are much weaker and only partly significant with r = –0.20 (rs = –0.22) at annual and r = –0.29 (rs = –0.23) at decadal time-scales (Table 6). Common regime shifts are also detected in the grain prices and the felling date numbers, whereas such a similarity is lacking in the wine price data. A positive correlation is also found between European building activity and lead pollution originating from mining in western Europe at both annual time-scales (r = 0.22 and rs = 0.26) and decadal times-scales (r = 0.45 and rs = 0.48) (Table 6). The lead pollution record originating from eastern Europe shows a much weaker positive relationship with building activity levels and is only statistically significant at annual resolution. Decreasing values of lead pollution from western Europe c. 1308 suggests the onset of the Late Medieval Crisis started about a decade later than that indicated by the felling dates (Table 7). A further decrease in lead pollution occurs in 1360, as opposed to the 1340 downturn in the felling dates (Figure 7). The stepwise recovery from this crisis mostly coincides in timing with a recovery in European building activity. Shifts toward decreased lead pollution, originating from western Europe, are seen in 1569 and 1589, signaling the start of the so-called Crisis of the Seventeenth Century (Hobsbawm, 1954; Parker, 2013). Unlike the felling date data, the Thirty Years’ War (1618–1648) is not defined by significant regime shifts in lead pollution. The lead pollution record for eastern Europe shows only five regime shifts, suggesting a later onset and longer duration of the Late Medieval Crisis (Figure 7). A significant negative relationship is found between annual consumer price indices from Krakow and Strasbourg, and Frontiers in Ecology and Evolution | www.frontiersin.org European building activity levels; r = –0.30 and r = –0.22, respectively for annual data; and r = –0.50 and r = –0.44, respectively, for 10-year box-car filtered data (Table 6). Interestingly, the Pearson correlations are higher than the Spearman’s implying a rather linear relationship between the two indices (Table 6). The relationship with the London annual consumer price index is considerably weaker and of a more nonlinear nature. Correlations with the Stockholm annual consumer price index, despite being the second longest index considered, are weak and insignificant. It should be noted that the Stockholm index also does not show much agreement with the other three consumer price indices. Finally, a positive correlation (r = 0.38, rs = 0.34) is found between church construction rates and European building activity level. Weak, but in some cases significant, are the associations between climate reconstructions and European building activity levels. The strongest negative correlations are obtained using the tree-ring-width-based southwestern Germany GWL reconstruction (r = –0.14 for annual data, and r = –0.30 for 10year box-car filtered data). Thus, periods of low GWL s appear to correspond to periods of higher building activity and vice versa. On the other hand, no significant correlations can be found between building activity levels and the tree-ring based drought (scPDSI) reconstruction. The relationship between building activity and reconstructed June–August temperature is negative but does not reach statistical significance. We also analyzed the presence of regime shifts in the climate reconstructions and found little agreement with the regime shifts in building activity. DISCUSSION Felling Dates as a Historic Source Material The results of this study demonstrate that felling dates contain genuine information about variations in past societal well-being 12 January 2022 | Volume 9 | Article 825751 Ljungqvist et al. Regional Patterns of Building Activity TABLE 7 | List of significant regime shifts in the in 300-year filtered and standardized subsets for comparison with the regime shifts in the felling date dataset. Variable Entire felling date dataset 1295↓ 1340↓ 1383↑ 1445↑ 1487↑ 1520↓ 1536↑ 1617↓ 1647↑ 1664↑ 1683↑ Lead pollution (western Europe) 1293↑ 1308↓ 1360↓ 1387↑ 1415↑ 1445↑ 1484↑ 1540↑ 1569↓ 1589↓ 1651↓ Lead pollution (eastern Europe) 1328↓ 1359↓ 1495↑ 1535↑ 1559↓ Grain price average 1443↓ 1526↑ 1551↑ 1569↑ 1587↑ 1621↑ 1639↓ 1654↓ Wine price average 1382↑ 1400↑ 1427↓ 1499↓ 1527↑ 1551↑ 1576↑ 1588↑ 1628↑ 1658↓ CPI London 1307↑ 1325↓ 1377↓ 1442↓ 1464↓ 1553↑ 1572↑ 1593↑ 1611↑ 1630↑ CPI Strasbourg 1448↓ 1543↑ 1569↑ 1622↑ 1644↓ 1674↑ CPI Krakow 1506↓ 1533↑ 1551↑ 1588↑ 1636↑ 1662↓ CPI Stockholm 1528↓ 1580↓ 1604↓ 1627↑ 1646↑ 1679↓ JJA temperature 1304↑ 1328↓ 1354↑ 1426↓ 1450↓ 1472↑ 1567↓ 1588↓ 1610↑ 1636↑ Drought index 1298↓ 1336↑ 1392↓ 1484↑ 1610↓ 1639↑ SW. Germany groundwater 1313↑ 1340↑ 1370↓ 1444↓ 1491↓ 1523↑ 1558↑ 1594↓ 1644 1671↑ 1677↓ 1671↓ Regime shifts detected using the 10-year spline filtered data. A downward arrow marks a year with a shift toward a decreasing number of felling dates and an upward arrow a year with a shift toward increasing values. mining district experienced lesser stagnation than most other regions subsequent to the Black Death. The high building activity level in the 16th century in this region coincides with a phase mining industry growth in central Europe as well as elsewhere (Bohdálková et al., 2018). To some extent, the choice of detrending and filter length influences our results, especially in the detection of statistically significant regime shifts (Table 3). We noted a difference in the number and timing (year) of regime shifts depending on whether the data have been 300-year spline detrended as well as 10year smoothed. For example, considerably fewer regime shifts were obtained using data without 10-year smoothing, suggesting that for investigation of decadal regime shifts, filters of short lengths are useful. As expected, a strong agreement (r = 0.83) in the annual felling dates, and in the timing of regime shifts, is found between the slightly different datasets used by Ljungqvist et al. (2018) and the one presented here. The new felling date dataset is slightly larger but only contains data that are georeferenced. In comparison to Ljungqvist et al. (2018), this new dataset reveals lower levels of building activity around c. 1400 CE, c. 1500 CE, and a somewhat less pronounced decline in activity during the Thirty Years’ War. The latter difference can be explained by the larger geographical coverage that includes more regions unaffected by the war. However, the lower rates in construction during the fourteenth and 15th century presented here cannot be readily explained and are unrelated to the inclusion of new data from any particular region. The most important difference is arguably a more stepwise, and slightly later, recovery in building activity following the Late Medieval Crisis. Another noteworthy feature is an earlier onset of the “Crisis of the Seventeenth Century” (Hobsbawm, 1954; Parker, 2013), also evident in the recent felling-date-based study for Czechia by Kolář et al. (2022). at regional and macro-historical scales. The ability to capture the Late Medieval Crisis (Figure 5), the mid-16th century population boom (Clark, 1977; McEvedy and Jones, 1978; Turchin and Nefedov, 2009), the Thirty Year’s War (Figure 5), and the demographic increase in the latter 17th century (Biraben, 1979; Bardet and Dupâquier, 1997; Bulst and Pfister, 1997) demonstrates the usefulness of the felling dates as a historical source material. In particular, the ability of the felling dates to capture relative population losses in regions affected by the Thirty Years’ War confirms their skill as a demographic proxy (Figure 6). No notable population decreases were found in regions known to have been little impacted by the war such as the Netherlands (Parker, 2006; De Pleijt and van Zanden, 2016). However, large numbers of felling dates are needed for establishing statistically significant changes, particularly on smaller spatial scales. Thus, using the felling dates on their own appears to have its limitations, rendering them most useful within a source pluralistic framework (e.g., Myrdal, 2012). Admittedly, the regional trends in building activity observed here depend heavily on the regional groupings used in this study. The merits of the groupings employed in this study can be debated, and alternatives offered, but datadriven approaches proved unable to deterministically identify statistically defendable and historically consistent alternatives (see Section “Other Datasets Used for Comparisons”). Future studies are needed to possibly disentangle and quantify construction phases at sub-regional to regional scales. We note, for example, the central Europe (north) region is heavily dependent on felling dates from cities along the German Baltic Sea coast (Figure 1A). Thus, the high building activity levels in medieval times derived from these data follow the expansion phases of the Hanseatic League during the 13th century (Jahnke, 2013). High levels of building activity, related to mining activity, in the Ore Mountain Range in German Saxony and Czech Bohemia is particularly evident in the periods 1250–1299, 1350–1399, and 1500–1599. While the first period represents the peak of medieval mining activity, the high level of building activity during the second period suggests this Frontiers in Ecology and Evolution | www.frontiersin.org Biases in the Collected Material Our felling date dataset contains inevitable geographical biases (Figure 1A), and smaller temporal ones (Figure 1B). It is also biased toward artisan and bourgeois houses in urban settings and ecclesiastical buildings. This implies that construction activities 13 January 2022 | Volume 9 | Article 825751 Ljungqvist et al. Regional Patterns of Building Activity of recycled building timbers distributed over time. The latter is difficult to directly address without more detailed construction and renovation histories for each building. However, we find it reasonable to presume that the proportion of freshly cut to recycled building timber remains approximately the same during both low and high periods of building activity. As noted in Bannister (1962), a clustering of dates, when sufficient in number, helps to distinguish between renovation work and original construction. Thus, large groups of felling dates clustered within a few years of each other suggest new constructions. For studies such as this, the amount of data available from any particular region and sub-region is largely related to the length of time during which tree-ring dating has been implemented to study historic buildings and to the continuity of those studies. In the southwestern part of Europe, for example, dendrochronological studies on historic buildings are almost absent in Portugal, and while they started in the 1980s for Spain (Richter, 1986; Richter and Eckstein, 1986), little has been published in spite of the abundance of built heritage (RodriguezTrobajo, 2008; Domínguez-Delmás et al., 2015, 2017, 2018). An exception is the Basque Country region in the northeast, where dendrochronological techniques are regularly applied in historic buildings since the late 1990s (Susperregi, 2007; Susperregi et al., 2017). Similarly, the southeastern part of central Europe poses a particular problem. For example, Slovenia has little historical tree-ring material prior to c. 1500 CE (Čufar et al., 2008, 2014a,b). A large proportion of medieval structures in Slovenia were destroyed during Ottoman attacks in the 15th and 16th centuries and during the subsequent Ottoman–Habsburg Wars (1526–1791 CE) (Murphey, 1999; Dávid and Fodor, 2000) as well as the huge earthquake in 1511 CE (Ribarič, 1979; Čufar et al., 2014b). The situation in Slovenia is, in a certain way, similar to that in Hungary. We have, thus, not been able to include these regions of southeastern Europe. By contrast, though many felling date data exist in Sweden (Bartholin, 1990), only a fraction are accessible in digital form, and only for parts of the country (Meissner et al., 2012; Lagerås et al., 2016). Compared to most other parts of the British Isles, limited data is available from Scotland (Crone and Mills, 2003; Mills et al., 2017). The timber-framed building tradition, which was so ubiquitous on the Continent and in England and Wales, did not develop to the same extent in Scotland, especially in the countryside (Stell, 2010). The medieval housing stock that survives is primarily high status, the tower houses, mansions, churches and castles of the ruling and ecclesiastical elite, and of these very few retain their original timbers. Of the 45 Scottish buildings with felling dates only seven pre-date 1500. By the 16th century Scottish builders were almost entirely reliant on oak and pine imports from Scandinavia and the Baltic Countries (Crone and Mills, 2012). FIGURE 7 | Figure showing the new entire felling date dataset, and the one Ljungqvist et al. (2018) for comparison, together with other datasets indicating general societal well-being and prevailing climate conditions. All data is standardized to z-score values over the entire period and 300-year filtered values. The red lines show the significant regime shifts in the number of felling dates, using a 30-year cut-off length. Comparison With Other Indicators of Societal Well-Being in areas where forestry systems such as coppice or coppice-withstandards were in place are not well reflected in our dataset. Other biases may exist as well, particularly the unknown quantity Frontiers in Ecology and Evolution | www.frontiersin.org The strongest association between European building activity rates and metrics of societal well-being is found with the 14 January 2022 | Volume 9 | Article 825751 Ljungqvist et al. Regional Patterns of Building Activity (Ljungqvist et al., 2022) while this study has revealed a strong positive association between grain price and building activity. However, significant (negative) correlations between building activity and groundwater supply are found for the Upper Rhine Valley watershed (Table 6). The groundwater reconstruction is located in the approximate center of our felling data coverage. The observed association with building activity strongly suggests that drier conditions coincided with higher building activity and vice versa. The likely causal mechanism here is a groundwater connection with grain production (for details, see Ljungqvist et al., 2022). In addition, periods of low building activity correspond to the first two maximum glacier advances during the Little Ice Age in the Alps. The Great Aletsch and Gorner glaciers peaked at c. 1300–1370 CE and 1600–1670 CE (Holzhauser et al., 2005; Holzhauser, 2010). Le Roy et al. (2015) show that Mer de Glace glacier was advancing during the late 13th century and reached very high levels as early as 1280s–1290s, before peaking in the c. 1350s, which is paralleled by late medieval drop in the number of felling dates. grain price average for Europe (see section “Building Activity, Grain Price Level, Economic Well-Being, and Climatic Change”). Grain was the main (>70%) calorie source for most of the population (Allen, 2000; Collet and Schuh, 2018), despite some minor regional variation as per the notable focus on dairying in Gaelic Ireland (Campbell and Ludlow, 2020). Considering this, and the fact that grain price levels reflected the interplay of supply and demand (Persson, 1999), it is reasonable to use grain price levels as an indicator for both the availability of food, and the average standard of living (Campbell, 2016). It is known that grain price levels considerably affected real wage levels (Allen, 2001) as well as the longterm demographic development in the medieval and early modern periods (Turchin and Nefedov, 2009; Alfani and Ó Gráda, 2017). Thus, when grain price levels were low the general standard of living was higher, demographic growth was stronger, and there was both a need for new buildings and the resources to fund their construction. Wine price level data show a much weaker, but apparently more linear, association with European building activity than grain prices. This can be explained in two ways. First, there are fewer wine price series than grain price series available for comparison, and their spatial distribution is much more limited (Allen and Unger, 2019). Second, wine was a far less essential commodity than grain, and its price thus reflected general societal well-being to a lesser extent. The strong positive association between European building activity and lead pollution originating in western Europe, compared to pollution originating from eastern Europe, can presumably be explained by the dominance of felling dates from western and central Europe in our dataset. The many synchronized regime shifts, shared by both European building activity and western European lead pollution levels, suggest that the two datasets, when combined in this manner, may be a defensible measure of large-scale development and relative prosperity. Some of the reconstructed annual consumer price indices also show strong (negative) associations with reconstructed European building activity levels. However, it is important to emphasize that the reconstructed annual consumer price indices are not independent from the grain price data (see, e.g., Allen, 2001). The Krakow annual consumer price index shows the strongest correlation, followed by the Strasbourg index. This is hardly surprising considering both cities are located in the central European region, the region with the largest number of felling date data. A positive, but insignificant, relationship is also found between the independent church construction series and reconstructed European building activity levels. However, the short period of overlap (1250–1500 CE), and the fact that the church construction series is only available at 20-year timesteps, means that the degrees of freedom are too few to compute statistical significance. The correlations between European building activity and past temperature and drought are mostly negative and insignificant. The weak relationship between temperature and building activity is surprising considering that temperature has been shown to have a strong negative association with grain prices Frontiers in Ecology and Evolution | www.frontiersin.org Prospects for Future Research This study has made evident that the sparse coverage of felling dates in many regions limits robust identification and comparison of spatial patterns to certain portions of Europe. Thus, efforts to collect felling dates from currently sparsely covered regions should be encouraged when it is possible; we acknowledge that not every region has old buildings preserved. This problem could, in theory, be partly mitigated by including all available felling dates, meaning even those without waney edge felling dates, but for which estimated felling dates are available (e.g., when samples contain sapwood rings). We have refrained from doing so for mainly two reasons: (1) The spatial coverage would not be dramatically increased. (2) A degree of annual precision would be lost due to the “smoothing” effect created by introducing dating uncertainties (Bocinsky et al., 2016). Future studies could address changes in the relative building activity rates of different types of constructions e.g., high status and low status buildings, to investigate social stratification, and their (financial) resilience to sudden social or demographic disruptions. For example, Haneca et al. (2020) demonstrated that the Catholic Church as an institution and financial power was much more resilient to social crises (e.g., recurrent plague outbreaks) compared to the general population. Likewise, it would be interesting to assess urban and rural building activity separately to study the inter-linkage between urban and rural economic and demographic development over time and space. Furthermore, it would be of interest to investigate the changes in the composition of tree species used for construction over time. The use of less preferred tree species would indicate changes in forest species composition, advancing deforestation and resulting in a lack local construction timber. Similarly, changes in the age of the trees used for construction activities could be informative with regard to resource availability (e.g., Baillie, 1982, 1995; Eckstein, 2007). Answering these types of questions, however, would require the collection of more 15 January 2022 | Volume 9 | Article 825751 Ljungqvist et al. Regional Patterns of Building Activity extensive contextual data from each construction, a serious challenge on its own. Finally, the strikingly strong agreement found in this study between reconstructed building activity history from felling dates and grain prices merits further investigations. Felling dates could be compared with grain prices on regional scales where the grain prices are identified through hierarchical cluster analysis to strongly co-vary. Future studies could strive to compare the association between the number of felling dates and plague outbreaks on local to regional scales [as done for Ireland by Mallory and Baillie (1988) and Baillie (2006), and for Czechia by Kolář et al. (2022)]. Ljungqvist et al. (2018) found that the number of plague outbreaks, at an aggregated scale, showed an even stronger association with the number of felling dates than grain prices. However, this required improved plague data at finer spatial scales. Extant plague datasets contain too many geographical biases, for most parts of Europe, to allow for meaningful regional studies of plague–building activity associations (e.g., Roosen and Curtis, 2018). Furthermore, comparing the number of felling dates with the number of major armed conflicts, or their intensity, on local to regional scales would be of interest, for example for Czechia (Kolář et al., 2022). This would be challenging as the quantification of the number of armed conflicts is prone to bias (see van Bavel et al., 2019; Ljungqvist et al., 2021) and available war datasets do not properly capture the societal costs of the conflicts of interest. DATA AVAILABILITY STATEMENT The data analyzed in this study is subject to the following licenses/restrictions: Private data. Requests to access these datasets should be directed to FCL, fredrik.c.l@historia.su.se. AUTHOR CONTRIBUTIONS FCL and AS designed the study, set up the experiments, and wrote the manuscript together with WT, PJK, and UB. All remaining authors contributed with felling date data and with additions to, and edits of, the text. All the authors reviewed the final manuscript. FUNDING FCL and AS were supported by the Swedish Research Council (Vetenskapsrådet, grant no. 2018-01272). FCL conducted the work with this article as a Pro Futura Scientia XIII Fellow funded by the Swedish Collegium for Advanced Study through Riksbankens Jubileumsfond. WT was supported by the German Research Foundation (DFG, TE 613/3-1). AD received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 677152). AH was supported by Riksbankens Jubileumsfond (grant no. IN20-0026). MD-D was funded by the Dutch Research Council (Nederlandse organisatie voor Wetenschappelijk Onderzoek, grant no. 016.Veni.195.502). TK, MR, and UB were supported the SustES project – “Adaptation strategies for sustainable ecosystem services and food security under adverse environmental conditions” (CZ.02.1.01/0.0/0.0/16_019/0000797). LS was supported by Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – EXC 2150 ROOTS – 390870439. FL was supported by a European Research Council (ERC) Synergy Grant (4-OCEANS; grant agreement no. 951649) under the European Union’s Horizon 2020 research and innovation programme. CONCLUSION This article has demonstrated that large datasets of dendrochronologically dated felling dates from historical construction timbers can serve as useful source material for exploring the spatial dimensions of construction rates. The broader spatio-temporal patterns of building activity rates in western and central Europe were investigated employing 54,045 georeferenced waney edge felling dates spanning the 1250–1699 CE period. Using geostatistical and statistical techniques, we investigated the spatial-temporal dynamics of reconstructed building activity, as inferred from the felling dates, in relation to various measures of demographic, economic, climate, and social conditions. We compared regional similarities and differences in the timing, duration, and magnitude of periods of “crisis” and “prosperity” at different spatial and temporal scales as reflected by changes in building activity. Our conclusions are: (a) in regions with adequate data coverage, felling dates capture major demographic trends, (b) there is a strong negative association between the number of felling dates and grain prices, (c) there is a moderately strong positive association between the number of felling dates and mining activity, and (d) there are more regime shifts detected in regions with dense felling date coverage. Finally, we can demonstrate that quantitative research based on felling dates reflecting building activity offers an important tool to test hypotheses, and better explain causal relationships in demographic developments. Frontiers in Ecology and Evolution | www.frontiersin.org ACKNOWLEDGMENTS We thank Barbara Leuschner, Dendrochronologisches Labor Göttingen, for making felling date data from northern and central Germany available for the study. We thank Esther Jansma for constructive comments on an earlier version of this article, for contributing with felling dates data from the Netherlands, and for making them publicly available at https: //doi.org/10.34894/ZWBVSW. We thank Mike Baillie and David Brown for access to Irish felling dates data, and David Brown, Brendan Maione-Downing, and Brianán Nolan for assisting their compilation, as kindly supported by the Initiative for the Science of the Human Past at Harvard University. Finally, we would like to thank the British scholars that have published their felling dates and associated metadata in the journal Vernacular Architecture, including in particular Nat W. 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Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher. Copyright © 2022 Ljungqvist, Seim, Tegel, Krusic, Baittinger, Belingard, Bernabei, Bonde, Borghaerts, Couturier, Crone, van Daalen, Daly, Doeve, Domínguez-Delmás, Edouard, Frank, Ginzler, Grabner, Gschwind, Haneca, Hansson, Herzig, Heussner, Hofmann, Houbrechts, Kaczka, Kolář, Kontic, Kyncl, Labbas, Lagerås, Le Digol, Le Roy, Leuschner, Linderson, Ludlow, Marais, Mills, Neyses-Eiden, Nicolussi, Perrault, Pfeifer, Rybníček, Rzepecki, Schmidhalter, Seifert, Shindo, Spyt, Susperregi, Svarva, Thun, Walder, Ważny, Werthe, Westphal, Wilson and Büntgen. This is an openaccess article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. 20 January 2022 | Volume 9 | Article 825751