Forest ecosystem development in European nemoreal-boreal forest (NE Poland) over the last 2200 years: Impact of human activity and climate change

Abstract

Long-term ecological studies can provide useful information on forest ecosystem resilience against past climatic change and human caused disturbances. Here, we present a high-resolution 2200-year-long record of forest development in north-eastern Poland, Suwalki region, using paleobotanical proxies (pollen, plant macrofossils, and charcoal). We show that the pollen abundance of deciduous trees was higher than that of coniferous trees, indicating a near pristine state until 900 AD and a semi-natural forest state until 1500 AD. After 1500 AD, the proportion of coniferous tree taxa surpassed that of deciduous trees and have since remained the dominant forest component. The 17th century experienced massive deforestation coupled with a new phase of human colonization in the area that led to the continued and significant decline of deciduous tree cover, for example, Carpinus, Quercus, and Tilia. Cooling associated with the Little Ice Age may have played a role in Picea’s expansion in this area after 1450 AD. Despite significant climatic shifts associated with the warmer Roman Period or Medieval Climate Anomaly and colder Migration Period, as well as a more sustained human impact, Quercus remained a stable forest component until 1500 AD. The stability of Quercus is an important aspect for forest management strategies as future projections suggest warmer conditions and increased frequency of climate extremes will impact forest composition and structure. Our long-term data suggest that forests in the Suwałki region should contain more abundant deciduous tree species, that is, Quercus, whereas conifer cover should be reduced. We also show clear regional differences in the forest development in the Suwałki region, highlighting the importance of local hydrology, geomorphology, and degrees of human activity on the forest composition.

Keywords

climate change tree succession pollen plant macrofossils fire restoration charcoal human impact

Introduction

Anthropogenically induced climate change and the subsequent rise in global mean temperatures are some of the primary drivers responsible for many recent environmental changes documented globally (IPCC, 2014). Information derived from long-term ecological studies can improve our understanding of forest ecosystem resilience against past climatic change, as well as forcasting how tree communities might respond to future climate change (e.g. Boden et al., 2014; Feurdean and Willis, 2008; Stobbe and Gumnior, 2021; Willis and Birks, 2006; Willis et al., 2007). Climatic changes during the Holocene significantly influenced past tree migration routes and their present distribution in Europe (Birks, 1986; Giesecke and Bennett, 2004; Lang, 1994; Reitalu et al., 2013; Stivrins et al., 2017; van der Knaap et al., 2005; Wacnik et al., 2012). Yet human activities, for example, forest industry, disturbance by fire, and grazing, have also significantly influenced forest composition during the last millennia (e.g. Behre, 1988; Bradshaw, 2004; Carter et al., 2018; Feurdean et al., 2017a, 2017b; Ledig, 1992; Marcisz et al., 2017; Stivrins et al., 2015). Comparing long-term environmental records from regions where human activity was relatively low versus relatively high offers an opportunity to evaluate ecosystem resilience against climate variability in Europe.

North-eastern Poland is a key area for investigating tree migration and potential causes for their postglacial disappearance (cf. Gałka et al., 2014). First, north-eastern Poland is influenced by both western oceanic and eastern continental air masses, providing an excellent opportunity to test the influences of broad-scale synoptic processes on forest succession and development, especially forest taxa, for example, Picea abies and Carpinus betulus, that occur close to their modern European northern distribution limits. Second, human activity in this region was relatively low until ca. 1650 AD in comparison to other parts of Europe due to low industrial and settlement development. Despite the presence of the Bogaczewo culture and Prusian tribes (Yatvingian) until the 13th century (Gałka et al., 2014; Marcisz et al., 2020), this region was not massively deforested unlike other areas of Europe such as Denmark (Kolstrup, 2009) or the mountainous areas in Germany (Beug et al., 1999; Knapp et al., 2013). Climate change and local factors such as edaphic conditions and groundwater level were likely the primary drivers of forest development in north-eastern Poland until human intervention in 1650 AD (Gałka et al., 2014, 2017; Marcisz et al., 2020). Over the last two millennia, several large-scale climate anomalies that could have influenced local and regional forest development in north-eastern Europe were recorded, that is, the Roman Warm Period (RWP, 200 BCE–300 AD), Medieval Climate Anomaly (MCA, 600–1300 AD), Recent Global Warming (RGW, after 1850 AD), the Migration Period (MP, 300–600 AD), and Little Ice Age (LIA, 1300–1850 AD) (cf. Büntgen et al., 2011; Edvardsson et al., 2018; Luterbacher et al., 2016). Assessing forest responses to past climatic shifts is important for understanding forest ecosystems response to projected increases in temperatures and droughts, both of which may increase the probability of fire events (EEA Report, 2012). Consequently, modern climate change is likely to shift forest taxa that have been strained to their ecological limits (Lindner et al., 2010; Milad et al., 2011; Tinner et al., 2013; Zajączkowski et al., 2013), making long-term forest development in north-eastern Poland a particularly important topic for sustainable forest management and nature conservation (Bolibok et al., 2016; Milad et al., 2011).

The aim of this study is to: (i) assess the response of local and regional tree species dynamics to climate change; and (ii) determine the role of human activity and fire on forest development. Our novel approach is the first paleobotanical study to combine pollen and macrofossil proxies at high-resolution, with replicate cores over the last 2200 years in the Suwałki region. Previous paleobotanical studies focusing on past vegetation dynamics from the Suwałki region include Lake Hańcza (Lauterbach et al., 2011), Lake Linówek (Gałka et al., 2014), Lake Kojle-Perty (Gałka et al., 2021), Lake Szurpiły (Kupryjanowicz and Fiłoc, 2016), Lake Jaczno (Poraj-Górska et al., 2017), Mechacz Wielki bog (Gałka et al., 2017), and Jaczno bog (Marcisz et al., 2020). Results from these paleoecological studies provide a more detailed record of regional-scale forest development.

Study site

Lake Kojle, a eutrophic lake (17.1 ha), is located in north-eastern Poland in the Suwalski Landscape Park (SLP) at 150 m.a.s.l. (Figure 1). The landscape of the area was formed during the Pomeranian Phase (ca. 16–17 ¹⁰Be/³⁶Cl ka; Rinterknecht et al., 2006) of the Weichselian glaciation (Krzywicki, 2002). The land relief is characterized by numerous morainic and kame hills up to 275 m.a.s.l. The hills are composed of silty clays, glacial sands, and erratic boulders (Ber, 1998, 2006; Krzywicki, 2002). Soils in the region were developed mainly on Quaternary sediments (clay, sands, gravels, thickness up to between 70 and 300 m; Ber, 1998) and Holocene organic deposits (peat, gytja). Cambisols and Arenosols (cf. IUSS Working Group, 2015) predominate in this region. Basal sediments from the edge of Lake Kojle date to approximately 13,730–13,380 cal. yr BP (Gałka et al., 2015b), but the presence of older sediments in the central portion of the lake cannot be excluded. The climate in this region of Poland is humid continental, with a clear influence of both western oceanic and eastern continental air masses. Mean annual precipitation amounts to 650 mm, while mean monthly temperatures in the study area range from 17°C in July to −5°C in January (Lorenc, 2005). The study area has the lowest number of vegetative days (180–190) in lowland Poland. SLP is dominated by boreo-nemoral plant assemblages, with morainic and kame hills and eskers primarily overgrown with coniferous forests dominated by Picea abies and Pinus sylvestris. Carpinus betulus, Quercus robus, and Tilia cordata are the dominant deciduous trees in the area. Alnus glutinosa and Fraxinus excelsior dominate in marshy depressions or in areas fed by springs. The littoral zone of Lake Kojle is inhabited primarily by Phragmites australis, Typha latifolia, and Cladium mariscus, while Chara spp., Potamogeton lucens, and Nymphaea alba occur in the deeper parts of the lake. Surrounding the lake is a peatland dominated with Alnus glutinosa, Frangula alnus, Carex paniculata, Carex elata, Comarum palustre, and Thelypteris palustris. Several moss communities are also present on the peatland, including Climacium dendroides, Sphagnum squarrosum, and Brachythecium spp.

Figure 1.

Location of the study site, Lake Kojle (Gałka, 2014, modified): (a) Eastern part of Europe; (b) Suwalski Landscape Park and sites mentioned in the text: Lake Hańcza (Lauterbach et al., 2011), Lake Linówek (Gałka et al., 2014), Lake Kojle-Perty (Gałka et al., 2015a), Lake Szurpiły (Kupryjanowicz and Fiłoc, 2016), Lake Jaczno (Poraj-Górska et al., 2017), and Jaczno bog (Marcisz et al., 2020); (c) Lake Kojle–Perty.

Material and methods

Fieldwork

Two 300-cm long sediment sequences, Koj I and Koj II, were collected 2 m from open water on the south shore of Lake Kojle, approximately 20 m apart (Figure 1). Coring was accomplished using a Russian peat corer with a 7 cm tube diameter and 100 cm length. Sediments collected contained both peat in the upper-most sediments, and gyttja-rich organic material consistent with lake sediments. Sediments were placed in PVC tubes, wrapped, and taken back to Adam Mickiewicz University for subsampling. In the laboratory, the sediment was unpacked, cleaned, and cut into 1-cm slices.

Laboratory work

Radiocarbon dates

To establish a chronology from both profiles, five samples from Koj I and 11 samples from Koj II were selected to be radiocarbon dated at the Poznań Radiocarbon Laboratory (Table 1). Samples were prepared with the standard acid-alkali-acid (AAA) method, and ¹⁴C was measured using AMS (Goslar et al., 2004). An age–depth model was calculated using OxCal 4.1 (Bronk Ramsey, 2009) and the IntCal20 (Reimer et al., 2020) atmospheric curve was applied for date calibration. A detailed description of the dated materials and method used is explained in Apolinarska et al. (2018).

Table 1.

Material used to radiocarbon dating of the sediments from Lake Kojle (after Apolinarska et al., 2018, changed).

Sediment sequence	Depth (cm)	Material dated	Nr. Lab.	¹⁴C date(¹⁴C BP)	Calibrated age, 95.4%, (BC/AD)
Koj I	42–44	Pinus sylvestris (n), Betula pubescens (bs, f), Picea abies (bs)	Poz-78460	190 ± 30	1649–. . .
	87–88	Picea abies (n)	Poz-72487	350 ± 30	1461–1636
	152–153	Picea abies (n, bs), Betula pubescens (fs)	Poz-78461	360 ± 30	1456–1635
	213–215	Betula pubescens (f, fs), Betula sect. Albae (f), Pinus sylvestris (bs)	Poz-72488	950 ± 30	1128–1462
	293–295	Betula sect. Albae (f, fs), Pinus sylvestris (bs)	Poz-70181	1735 ± 35	245–405
	11.5*	Menyanthes trifoliata (s), Calliergon giganteum (sl)	Poz-129698	170 ± 30	1660–. . .
Koj II	39–40	Menyanthes trifoliata (s), Bryum pseudotriquetrum (sl)	Poz-67835	185 ± 30	1653–. . .
	61–63*	Cladium mariscus (s), Betula pubescens (fs)	Poz-129695	205 ± 30	1643–. . .
	85–86	Picea abies (n)	Poz-67836	335 ± 30	1475–1640
	110.5*	Cladium mariscus (s), Carex sp. (f), Picea abies (n), Betula sp. (f)	Poz-129854	340 ± 30	1474–1638
	125–126	Scheonoplectus lacustris (f)	Poz-64444	320 ± 30	1484–1644
	144–146	Alnus glutinosa (bs), Carex rostrata (f), Pinus sylvestris (bs), Betula sect. Albae (f)	Poz-70161	650 ± 30	1281–1395
	173–174	Schoenoplectus lacustris (f), Cladium mariscus (s), Picea abies (bs), Betula pubescens (f, fs)	Poz-67837	1250 ± 30	674–877
	192–193	Betula pubescens (f, fs), Alnus glutinosa (bs)	Poz-67838	1340 ± 40	618–775
	235–236	Betula pubescens (f, fs)	Poz-67830	1740 ± 30	245–402
	288–289	Betula pubescens (f, fs), Pinus sylvestris (bs)	Poz-70160	2070 ± 30	−169 to 9

Source: New dates are marked by “*.”

Abbreviations of the plant macrofossils: f: fruit; fs: fruit scale; s: seed; bs: bud scale; n: needle; st: stems with leaves.

Pollen and micro-charcoal

Pollen and micro-charcoal were analyzed to reconstruct both the regional vegetation composition and regional fire activity through time. Given that the pollen record offers a more regional picture of vegetation, pollen analysis was conducted at 2 cm resolution from Koj II using 1 cm³ of sediment. Chemical preparation followed the standard method of Berglund and Ralska-Jasiewiczowa (1986). A minimum of 500 terrestrial pollen grains were counted. Pollen percentages were calculated based on the pollen sum, that is, trees and shrubs (AP) and herbs (NAP), excluding wetland (Cyperaceae, Cladium, Carex type, Filicales monolete, Sphagnum, Equisetum, Typha latifolia, Sparganium type, Menyanthes trifoliata, Lythrum salicaria, Comarum palustre, and Rhynospora alba) and aquatic plants (Potamogeton, Nymphaea, Nuphar, Myriophyllum ssp., Utricularia, algae). Plant nomenclature follows Mirek et al. (2002) (Figures 2 and 3). Human activity pollen indicators were distinguished according to Behre (1988), and van der Linden and van Geel (2006): Rumex acetosa/acetosella, Plantago lanceolata, Plantago media, Plantago major, Artemisia, Chenopodiaceae, Urtica, Polygonum aviculare, Centaurea cyanus, Scleranthus, Agrostemma githago, Spergularia-type, Humulus/Cannabis, Fagopyrum, Zae, Triticum-type, Secale cereale, Cerealia undiff. Concurrent to pollen analysis, micro-charcoal (particles <150 μm) were counted on the pollen slides and quantified as a percentage relative to the total terrestial pollen sum. Micro-charcoal percentages were used as an indicator of regional-scale biomass burning (e.g. Whitlock and Larsen, 2001).

Figure 2.

Age–depth models of the sediments from Lake Kojle: core Koj I and core Koj II (changed).

Figure 3.

Tree macrofossils diagram from Koj I, Lake Kojle. Macrofossil data and macro-charcoal data are presented as absolute values.

Plant macrofossils and macro-charcoal

Plant macrofossils and macro-charcoal were analyzed simultaneously to investigate both the local vegetation development and local fire activity within the Lake Kojle watershed. Macro-charcoal analysis has been shown to provide information on past local fire occurrence (Whitlock and Larsen, 2001), although a recent study showed that macro-charcoal smaller than 600 μm has a much more regional (<40 km) signal (Adolf et al., 2018). Koj I and Koj II were sampled for plant macrofossil and macro-charcoal (pieces >1 mm) analysis at contiguous 1-cm intervals using a sediment volume of 12 cm³. The samples were rinsed in warm water on 0.20 mm mesh size sieves. Macrofossils were determined using a Nikon SMZ800 stereoscopic microscope with 10–200× magnification, and a light microscope. Species determination was aided by plant macrofossil keys (e.g. Katz et al., 1965; Tobolski, 2000). Plant macrofossils and macro-charcoal were summarized using absolute numbers (Figures 2 and 3). Plant nomenclature follows Mirek et al. (2002).

Numerical analysis

Pollen and plant macrofossils results from Koj II were visualized using Tilia-Graph software (Grimm, 1992), whereas Koj I used C2 software (Juggins, 2003). Pollen and plant macrofossils assemblage zones were established using constrained cluster analysis (CONISS, Grimm, 1987). Principal component analysis (PCA) was used to quantitatively determine the main changes in vegetation composition using a correlation matrix of the pollen percentage data using the program Past (Hammer et al., 2001).

Results

Chronology and lithology

Basal dates from Koj I and Koj II illustrate rapid accumulation over the past 1650 and 2200 years, respectively (Table 1, Figure 2). Sedimentation rate was unstable at both sampling sites and ranged between 0.1 and 0.31 cm yr⁻¹ (Figure 2). Both Koj I and Koj II cores consisted of calcareous gyttja between depths 300 and 148 cm (ca. 320–1440 AD; Koj I), and 300–127 cm (ca. 230 BC–1470 AD; Koj II), respectively; detritus gyttja between depths 148–104 cm (ca. 1440–1580 AD; Koj I) and 127–109 cm (ca. 1470–1600 AD; Koj II), respectively. Herbaceous peat was present between depths 104–52 cm (ca. 1580–1770 AD) at Koj I, while herbaceous-moss peat was present between depths 52 and 0 cm (ca. 1770–2014 AD Koj I) and 109–0 cm (1600–2014 AD Koj II), respectively (Figures 3 and 4).

Figure 4.

Combined pollen and plant macrofossil diagram presenting vegetation changes, human activity, and fire activity from Koj II, Lake Kojle. Pollen percentages are shown in black, and exaggerated (x10) in gray. Plant macrofossils (pm) and macro-charcoal data are presented in absolute values.

Pollen, macrofossils and micro-, and macro-charcoal

Koj I

Based on cluster-analysis, seven zones were identified for the macrofossil assemblages of local vegetation development from Koj I (Figure 3). In Koj I-1 (320–820 AD), Betula sect. Albae and Pinus sylvestris macrofossils were dominant. Single macrofossils of Alnus glutinosa were also recorded. Macro-charcoal pieces (>1 mm) were also common throughout this zone (1–2 pieces), except between 600 and 500 AD where macro-charcoal values increased to 4 pieces. In Koj I-2 (820–1180 AD), Betula sect. Albae and Pinus sylvestris macrofossils remained abundant, whereas remains of Betula pubescens increased. Macro-charcoal pieces were constantly present (1–2 pieces). Koj I-3 (1180–1430 AD) was characterized by the appearance of Picea abies macrofossils. Additionally, the only documented presence of Tilia occurred during Koj I-3. Macro-charcoal pieces were consistently found beginning from ~1300 AD to the end of the zone at low values (<2 pieces). In Koj I-4 (1430-1570 AD), the highest number of Alnus glutinosa and Picea abies macrofossils were revealed, while Betula sect. Albae and Pinus sylvestris macrofossils were continuously present during this phase. Macro-charcoal reached the highest values (seven pieces) in the profile. In the first half of Koj I-5 (1570–1680 AD), numerous remains of Betula pubescens fruits and fruits scales, and Pinus sylvestris bud scales were documented, while Picea abies needles and bud scales increased in the second half of this zone. Macro-charcoal pieces were nearly absent during this zone. Koj I-6 (1680–1700 AD) is unique in that it is the only zone where a burnt Alnus glutinosa fruit was found. Macro-charcoal pieces were common during this zone. In Koj I-7 zone (1700–2014 AD), Alnus glutinosa and Betula sect. Albae macrofossils were dominant, and only a single macro-charcoal piece was found. Picea abies bud scales were also recorded.

Koj II

Based on the pollen, plant macrofossils, and micro- and macro-charcoal data from Koj II, seven zones were identified (Figure 4). In Koj II-1 (200 BC–100 AD), Pinus pollen averaged ca. 30% while Picea averaged ca. 5%. Among the deciduous trees, Betula (ca. 30%), Alnus (ca. 13%), and Quercus (up to 10%) had the highest average values. The occurrence of Pinus, Betula and Picea was supported by their macroremains. Human indicator pollen types, as well as micro-charcoal percentages and macro-charcoal pieces (>1 mm) were low in this zone. Koj II-2 (100–500 AD) was characterized by a decrease in Picea pollen percentages (<1%), and an increase in pollen and macroremains of Betula pubescens, Betula sect. Albae, and of Alnus glutinosa macrofossils in the second half of this zone. Increases in human indicators pollen (ca. up to 2%) and macro-charcoal pieces (three pieces) were visible in this zone. However, micro-charcoal percentages remained low. In Koj II-3 (500–950 AD), Pinus pollen (ca. 25%) and macrofossils decreased, while Betula pollen (ca. 40%) and macrofossils increased. In the second half of Koj II-3, micro-charcoal percentages and macro-charcoal pieces increased. In Koj II-4 (950–1500 AD), a gradual increase in Pinus pollen (ca. 35%), and decrease in Betula pollen (from 35% to 25%) were documented. Numerous Pinus and Betula macrofossils were also present in this zone. In this zone, human activity indicators, such as Rumex acetosa/acetosella, Artemisia, Secale, and Cerealia pollen, increased. Micro- and macro-charcoal were both relatively low in this zone. Koj II-5 zone (1500–1630 AD) was characterized by the almost constant presence of Pinus pollen (average ca. 40%), while Betula pollen (from 25% to 15%) and deciduous trees species such as Ulmus, Fraxinus, and Quercus all decreased. Human pollen indicator species increased in this zone (max. 7.5%) while micro and macro-charcoals remained relatively low. Macrofossils of Pinus, Betula were constantly recorded in Koj II-5, whereas those of Picea showed the highest number in the record. In the first half of Koj II-6 (1630–1750 AD), Pinus pollen increased to ca. 60%, but then decreased in the second half to ca. 50%, along with its macrofossils. Parallel to the increase in Pinus pollen percentages, Carpinus pollen decreased from 6.3% to 0%, Alnus pollen percentages decreased to their lowest values (ca. 5%), while Picea pollen percentages reached their highest values (up to 27%), but Picea macroremains were scarce. Poaceae (ca. 15.4%), Secale (ca. 11.7%), and micro-charcoal percentages also reached their highest values in this zone. In zone Koj II-7 (ca. 1850 AD–present), Alnus glutinosa pollen (27.4%) and macrofossils reached their highest values. High values of NAP pollen (up to 23%), Secale (up to 9%), Cerealia (ca. 10%), as well as micro-charcoal percentages were also recorded throughout this zone but at relatively low percentages. Pinus pollen becomes the dominant tree species during last decades when it reaches ca. 80%, however, its macroremains are absent. Picea pollen value reached ca. 10% during last decades.

Numerical analysis

PCA results from Koj II pollen percentage data reflect major vegetation composition changes (Figure 4). The first and second PCA axes explain 44% and 11% of the total variance, respectively, but only the first axis is statistically significant (Figure 5). On PCA axis 1, Quercus and Betula pollen show the highest negative load (−0.29 and −0.27, respectively), while Picea and cultivars pollen have the highest positive load (r = 24, r = 29). This axis demonstrates the major shift in forest composition at 1650 CE associated with human activities. Macro-charcoal groups together with herbaceous communities associated with both grazing and cultivation activities.

Figure 5.

Results from PCA on pollen record at core Koj II.

Discussion

Impact of climate on north-eastern Poland forest development

Below, we discuss the response of individual tree taxa to climate and human activities.

Picea abies

At Lake Kojle, Picea pollen percentages reaches <5% between 2200 and 1500 AD (Figures 4 and 6), and may manifest in the vicinity of the study site (cf. Giesecke and Bennett, 2004; Latałowa and van der Knaap, 2006; Środoń, 1967), although its macrofossils were noted ca. 1400 AD. Based on the relatively low values of Picea pollen at Koj II, it can be assumed that this tree did not play an important role in the surrounding forests in Kojle until LIA (ca. 1300–1850 AD). On a regional scale, the pollen record from Kojle Lake only shows a slight decrease in Picea pollen percentages, whereas at Mechacz Wielki bog, Picea pollen percentages drop from 17.5 at 150 AD to 2.1% at 250 AD (Figure 7). This decline of Picea pollen could be linked to an increase in European summer mean temperature up to 0.5°C (to the period 1960–1991, Luterbacher et al., 2016) that is associated with the Roman Warm Period.

Figure 6.

Selected paleoecological data from Lake Kojle compared to recent climatic anomalies in Central Europe (cold (warm) time intervals highlighted in blue (pink); based on data from Büntgen et al. (2011) and Luterbacher et al. (2016), and human activity. Solar Minima (cold periods): (1) Oort Minimum, (2) Wolf Minimum, (3) Spörer Minimum, (4) Maunder Minimum, (5) Dalton Minimum, (6) Glassberg Minimum. Human activity phase: (1) Bogaczewo Culture, (2) Sudovian, (3) Yatving, (4) location of the villages in post-medieval settlement, (5) location of the new villages in the 17th century, (6) depopulation and agricultural changes during and after World War II.

Figure 7.

Comparison of selected pollen data from Suwalki Landscape Park (Linówek Lake, Gałka et al., 2014) and Romincka Forest Landscape Park (Mechacz Wielki bog, Gałka et al., 2017).

The next changes in the abundance of Picea are between 750 and 900 AD and ca. 1050 at Mechacz Wielki bog (Figure 7, increase from ca. 10% up to 42%) and between 800 and 950 AD and ca. 1050 AD at Jaczno bog (from ca. 5% up to 16%). The increase in Picea pollen abundance at both sites may reflect a decline of 0.5°C in European summer mean temperature (Luterbacher et al., 2016). However, the difference in the abundance of Picea percentages between sites may also be a result from site type. Picea is well-adapted to grow on a peaty ground and wetter habitat, thus its higher abundance at boggy sites (Mechacz and Jaczno) in comparison to Lake Kojle, could be related to its growth closer to these sampling sites (cf. Hájková et al., 2019; Kołaczek et al., 2021).

Picea macrofossils from both Koj I and Koj II reached their highest abundances between ca. 1500 and 1630 AD (Figures 4 and 6), while Picea pollen percentages reached a maximum (27%) later ca. 1650 AD. The discrepancy between the timing in the maximum in Picea abies macrofossils and pollen percentages is likely attributed to the deposition site, which transitioned from a shallow lake to a peat bog in 1580 AD. It cannot be excluded that the local Picea abies population growing at the edge of Lake Kojle wetland disappeared due to an increase in water level depth ca. 1630 AD, as suggested by the coincident decline of deciduous trees macroremains (Alnus glutinosa and Betula pubescens) ca. 1630 AD (Figure 6). An increase in moisture availability in the Suwalki region at that time was documented at Mechacz Wielkie (Gałka et al., 2017) and Jaczno (Marcisz et al., 2020) bogs. However, local deforestation in the surroundings of Kojle Lake cannot be ruled out, considering the high percentages of human indicators and macro-charcoal fragments (Figure 6). Picea pollen percentages also increased at many sites across the Suwałki region, that is, Jaczno bog (Marcisz et al., 2020), Linówek Lake (Gałka et al., 2014), Mechacz Wielki bog (Gałka et al., 2017), and Lake Żabińskie (Wacnik et al., 2016). Regardless, the timing of Picea abies dominance locally and regionally between 1450 and 1650 AD (before massive deforestation) may be associated with climatic cooling during the LIA (Luterbacher et al., 2016) and solar minima occurrence, for example, Spörer Minimum (1450–1550 AD), Maunder Minimum (1645–1717 AD), and Dalton Minimum (1790–1820 AD) (Büntgen et al., 2011) (Figure 6). Picea abies is a boreal species, thus, the cold climatic conditions during the LIA might have increased the ability of spruces to outcompete temperate tree species, that is, Quercus, Tilia, Ulmus, Carpinus (Latałowa and van der Knaap, 2006).

Carpinus betulus

According to Huntley and Birks (1983), Carpinus pollen values >5% indicates its presence in a region, and >10% indicate its abundance in local forest communities. However, studies detailing pollen-vegetation relationships also indicate that Carpinus pollen tends to be slightly overestimated in the pollen record (Mazier et al., 2008). At Lake Kojle, Carpinus betulus pollen percentages average 5% demonstrating that the species has been a minor component of the forest canopy over the past 2200 years. After 1650 AD, local Carpinus betulus percentages abruptly decreased (<0.5%), which corresponds to the regional decline of Carpinus betulus associated with human impact (Gałka et al., 2014, 2017; Kupryjanowicz, 2007; Marcisz et al., 2020; Wacnik et al., 2016). However, prior to 1650 AD, regional sites also document the sensitivity of the species to past climate variability. Although pollen percentages of Carpinus betulus increase only slightly at Lake Kolje, its proportion increases significantly (up to 20%) between 450 and 730 AD during the Migration Period, and again at 1450 and 1630 AD during the LIA at Mechacz Wielki bog (Gałka et al., 2017), and between 1450 and 1650 AD near Lake Linówek (Gałka et al., 2014) (Figure 7). C. betulus also reached its highest values (up to 10%) between 600 and 850 AD and 1550 and 1600 AD at Jaczno bog (Marcisz et al., 2020). All these time intervals are characterized by wetter conditions in the region (Büntgen et al., 2011; Edvardsson et al., 2018; Gałka et al., 2017; Marcisz et al., 2020). Wacnik et al. (2016) also recorded increases in Carpinus pollen between ca. 1200 and 1650 AD at Lake Żabińskie, and correlates this to cooler and wetter climatic conditions. Thus, based on the regional evidence, we suggest that episodes of Carpinus expansion into north-eastern Poland were driven by cooler and wetter conditions. However, this contradicts its recent ecological and reproductive requirements, that is, higher summer temperatures and a longer growing season (Huntley and Birks, 1983). The lack of a clear visual correlation between abrupt climate change and increases in Carpinus betulus prior to 1650 AD at Lake Kolje is surprising, because our study site is located at the species eastern-most distribution limit, similar to other regional sites such as Mechacz Wielki bog, Jaczno bog, Linówek Lake. Carpinus tolerates moderately continental climates (Ralska-Jasiewiczowa et al., 2004), prefers slightly humid air conditions and soils, and does not tolerate dry, shallow soils (Faliński and Pawlaczyk, 1993). We therefore suggest that the continental climate, coupled with moist soil conditions at our study site, resulted in stable Carpinus betulus populations. While Ralska-Jasiewiczowa et al. (2004) suggest that the local edaphic and climatic conditions influenced Carpinus migration through time, the authors also suggest that humans influenced the species range dynamics. This is supported by Lamentowicz et al. (2015), who documented anthropogenic impact on Carpinus succession in northern Poland over the last 3000 years at Bagno Kusowo bog (north-central Poland). In addition, palynological studies conducted near the archeological sites (Giecz, Gniezno, Ostrów Lednicki) located in central-western Poland revealed that Carpinus succession (up to 20%) during Early Medieval Period (up to 20%) was linked to human settlement phases (Makohonienko, 2000; Tobolski, 1990). Thus, the influence of climate, human activity, and local edaphic conditions on Carpinus succession prior to 1650 AD should also be taken into consideration in the Polish Suwałki region (see human impact).

Alnus

From 200 BC onward at Lake Kojle, Alnus percentages vary slightly, generally reaching ca. 10% and abruptly decreasing below 5% ca. 1630 AD (Figure 5). In the Baltic countries and Scandinavia, Alnus pollen percentages dramatically decreased (>25%) during the MCA (ca. 800–1200 AD), correlating with human activity, climate, and/or pathogen outbreaks (cf. Gałka et al., 2021; Saarse et al., 2010; Sarmaja-Korjonen, 2003; Stivrins et al., 2017). Across the Suwałki region, the temporary decline in Alnus at Lake Szurpiły (located 5 km from Lake Kojle) ca. 900 AD is explained by human impact, for example, alder wood could have been used for construction, or as smoking material for fish and meat by the Yatvingian society living next to the lake (Kupryjanowicz and Fiłoc, 2016). In addition, a significant decrease in Alnus pollen (from 10% to 1%) was recorded at both Mechacz Wielki bog between 900 and 1050 AD (Figure 7, Gałka et al., 2017) and at Jaczno bog between 980 and 1050 CE (Marcisz et al., 2020). However, there is no apparent decline in Alnus pollen at Lake Kojle during the MCA. Nevertheless, we acknowledge that Alnus populations may have declined, as reflected by the lack of its plant macrofossils at Koj II (Figure 3), and a partial reduction at Koj I (Figure 4). These results agree with Gałka et al. (2014), who also established no dramatic decrease in Alnus at Lake Linówek. The distinctive differences in Alnus pollen across the Suwałki region as well as in some parts of Baltic countries (cf. Gałka et al., 2021) may reflect changes in forest development at the local scale as a result of local hydrological and geomorphological conditions, such as the presence of fens, springs on the slops, depressions, and river valleys. For example, the Mechacz Wielki bog is a peatlands complex (146 ha) that is highly dependent upon groundwater levels. Thus, Alnus populations at Mechacz Wielki bog and its surroundings might have been more susceptible to droughts encountered during the MCA (Edvardsson et al., 2018; Gałka et al., 2017; Marcisz et al., 2020). Conversely, Alnus populations around Lakes Kojle or Linówek have better access to the groundwater, which may have made Alnus forests more resistant to fluctuating groundwater levels experienced during the MCA, and potentially explaining why these two sites do not reflect the regional trend in declining Alnus during the MCA. However, further research into how local hydrology and geomorphology affect Alnus populations is necessary to determine whether this hypothesis is null.

The role of human activity and fire on tree succession in the Suwałki region of north-eastern Poland

Humans impacted local tree development in distinct phases over the past 2200 years: Phase 1 ca. 100–200 AD; Phase 2 ca. 450 AD; Phase 3 ca. 850–900 AD; Phase 4 ca. 1500 AD; Phase 5 ca. 1630 AD; and Phase 6 ca. modern (Figure 6). The first phase is visible as a relatively weak anthropogenic signal, that is, the presence of pollen of cultivars (Secale and Cerealia) and pastures (Plantago lanceolata and Rumex acetosa/acetosella) and low amounts of micro- and macro-charcoal that can be linked to the Bogaczewo Culture (Figure 6; Brzozowski and Siemaszko, 2005). Humans may have used low-severity fires between 100 and 200 AD. However, fire activity also increased across north-east Poland at the onset of the Roman Warm Period when conditions became warmer (Luterbacher et al., 2016) and drier in the CE Europe (Büntgen et al., 2011; Edvardsson et al., 2018; Marcisz et al., 2017), suggesting that climatic conditions alone or superimposed on human ignitions could have facilitated fires during Phase 1.

Pinus sylvestris experienced a decrease in abundance during Phase 2, ca. 500 AD (Figure 6). This, coupled with the presence of microcharcoal, may indicate human-induced fire activity related to the Yatvingian tribal center occupied in the modern village of Szwajcaria, ca. 20 km from Kojle (Szkiruć, 1986). Fire activity also increased at Mechacz Wielki bog between 400 and 600 AD (Marcisz et al., 2017), suggesting a regional human-induced signal. Immediately following a peak in macro-charcoal at 450 AD, Betula pollen and plant macrofossils significantly increased at Lake Kojle and remained relatively high until ca. 850 AD. This suggests that Betula, an early successional tree, became one of the main local forest components at Lake Kojle after this period of enhanced fire activity. Human impact during Phase 2 appears to have affected other forest taxa. For example, despite Pinus sylvestris being a rapid post-fire colonizer (cf. Feurdean et al., 2017a), repeated fires may have led to its long-term low abundance (500 years) (Figure 5). In addition, Picea abies, which was a relatively minor forest component during Phase 2, slowly recovered from fire to pre-200 AD abundances. There are contradictory conclusions regarding Picea’s behavior to fire (cf. Brown and Giesecke, 2014; Carcaillet et al., 2007; Carter et al., 2018; Feurdean et al., 2017b; Ohlson et al., 2011; Reitalu et al., 2013). Our results (Figure 5) agree with other studies from the boreo-nemoral region, showing a positive response of Picea abies to enhanced late-Holocene fire activity (Brown and Giesecke, 2014; Feurdean et al., 2017b).

Human indicator species, mainly Secale, Cerealia, and Artemisia, as well as micro-macro-charcoal, increased markedly during the Phase 3, ca. 900 AD (Figures 4 and 5), which coincides with settlement activity among the Prussian tribe and the Jatvingians group. For example, the closest settlement (fortified settlement at Góra Zamkowa) to our site is approximately 5 km from Lake Kojle, which was a major Jatvingians settlement complex that lasted until the second half of the 13th century (Engel and Sobczak, 2012). The decrease in deciduous tree cover, such as Betula, Tilia, Fraxinus, and Ulmus, can therefore be attributed to deforestation during Phase 3, as soil types within these forested communities are usually more fertile and suitable for agriculture (Roberts et al., 2018). Similar ecological responses were recorded across the Suwałki region (Gałka et al., 2014; Kupryjanowicz and Fiłoc, 2016; Marcisz et al., 2020), suggesting that the regional forest ecosystem may have been modified by either the Prussian tribe or the Jatvingians group.

The increase of Cerealia pollen and the first Centaurea cyanus pollen during Phase 4, occurring between 1450 and 1500 AD, likely reflect the presence of permanent field systems (Vuorela, 1986). Permanent settlements were typically located in wooded areas due to work felling timber, producing tar, charcoal, and beekeeping (Szkiruć, 1986). These activities likely led to the reduction in Betula, Quercus, and Fraxinus population size during Phase 4 at Lake Kolije and of Betula at Linówek Lake and Mechacz Wielki bog (Figure 7). By this time, many western European countries had been heavily deforestedy during the Middle Ages (800–1500 AD), making the forests in eastern Poland a vital and important source of timber for ship building, paintings, and sculptures from the 15th century onward (Haneca et al., 2005; Ważny, 2005). In addition, land conversion from forest to arable fields in the Suwałki region substantially increased the demand of cereals, both locally and regionally, as an export to Western Europe (Dziewanowski-Stefańczyk, 2010; Topolski, 1999).

The 17th century (Phase 5) was a key period for forest development as a new phase of colonization and villages occurred in the vicinity of Lake Kojle. Specifically, the 17th century saw the rise of the Wolka Blaskowa (Blaskowizna) culture, as well as the construction of two mills (1603) AD and several villages (1642 CE; Hancza, Smolniki, Jaczno, Kojle) near the study site (Szkiruć, 1986). This time period also coincides with the colonization by Lithuanian princes, then by the Camaldolese (Benedictine) monastery (located in 1668 AD near Jezioro Wigry), which was succeeded by the arrival of settlers (Old Belivers, Eastern Orthodox Christians) from Russia in the Suwałki region (Matusiewicz et al., 2005; Szkiruć, 1986). Micro-charcoal percentage values were at their highest during this period (Figure 6), suggesting that some forms of fire management may have been involved, that is, for deforestation, field clearance. This new phase of colonization resulted in the continued removal of both deciduous trees, for example, Carpinus, Quercus, Tilia, and Betula, as well as conifer trees, for example, Pinus. However, of all deciduous taxa, Quercus experienced the largest reduction beginning in the 17th century (Figure 6). Prior-to the 17th century, Quercus (likely Q. robur) was an important secondary canopy species across the region (Gałka et al., 2014, 2015a, 2017; Kupryjanowicz, 2007; Kupryjanowicz and Fiłoc, 2016; Marcisz et al., 2020; Szal et al., 2014; Wacnik et al., 2012, 2016), comprising an average of 10% of the total tree pollen sum at Lake Kojle. Due to its wide tolerance of soil moisture and fertility requirements (Milecka et al., 2004), Quercus was common in various habitats, even within coniferous forests. Although climate is generally considered to be the primary factor in determining the distribution of Quercus over the last millenia (assuming limited human impact in CE Europe; Milecka et al., 2004), we did not observe significant changes in the proportion of Quercus in relation to the various climatic changes prior to the 17th century. A similar decline in deciduous tree cover was also recorded at Lake Linówek (Gałka et al., 2014), Lake Szurpiły (Kupryjanowicz and Fiłoc, 2016), Jaczno bog (Marcisz et al., 2020), and Mechacz Wielki bog (Gałka et al., 2017) during the 17th century, further indicating regional-scale deforestation.

Between 1850 and 1900 AD, Alnus pollen and macrofossils both increased dramatically as Alnus glutinosa expanded into already developed peatlands around Lake Kojle, most likely a result of lower lake levels or terrestrialization. However, the increase in Alnus was not temporally heterogeneous at Lake Kojle at both sampling sites. Specifically, the temporal differences may be related to the spatial variability of alder habitats across the surface of the fen. Regardless, there is no apparent increase in Alnus regionally between 1850 and 1900 AD (Gałka et al., 2014, 2017; Marcisz et al., 2020; Poraj-Górska et al., 2017). In addition, the lack of local fire may have favored the local expansion of Alnus on the peatland and around the lake. A significant decrease in Betula pollen from 1850 AD to the present was also documented. This agrees with pollen data from Lake Linówek (Gałka et al., 2014), but disagrees with pollen data at both Lake Szurpiły (Kupryjanowicz and Fiłoc, 2016) and Lake Jaczno (Poraj-Górska et al., 2017). The contradictory results are either a more localized response of Betula spreading as a pioneer species on the abandoned fields around Lake Szurpiły and Lake Jaczno, or a result of different depositional environments, that is, localized pollen deposition on peatlands (at our study site and Lake Linówek) and regional pollen rain in lacustrine habitats (Lake Szurpiły and Lake Jaczno). However, the decrease in Betula at Kojle Lake II may also be related to fire, as micro-charcoal peaks during the second half of XXth took place (Figure 6).

Conclusive remarks and implications for forest management in the Suwałki region

The pollen records at Lake Kolja, together with others from the Suwałki region, suggest that Pinus sylvestris and Picea abies have become dominant forest canopy taxa in north-east Poland during the second half of XX^th century because of the preference for fast-growing conifers by the wood industry (Boden et al., 2014). However, a recent change in the restoration initiatives of Poland’s State Forest policy include increasing the share of deciduous trees to levels seen centuries ago. Restoration efforts have already been conducted in southern Poland, where monocultural forests of Picea abies and Pinus sylvestris have been replaced by more natural Abies alba and Fagus sylvatica forests. While island plantings of deciduous trees have also been carried out in other regions of northern Poland, for example, the Tuchola Forest and Noteć Forest region (personal observ.), the primary restoration method at present is a natural approach of gradually letting forests return to their former tree composition (Barzdajn, 2006; Jaworski and Pach, 2014; Masternak et al., 2015).

Our research illustrates that deciduous tree taxa, such as Betula and Alnus as well as Quercus, Carpinus, Tilia, Fraxinus, and Ulmus, were important forest taxa prior to intensive human landscape modifications, beginning ~1650 AD. While Poland’s State Forest policy is to increase the proportion of deciduous trees to baseline levels (pre-human impact period), we suggest future climate change also be taken into consideration in the new forest policy restoration initiatives (cf. Stobbe and Gumnior, 2021). Based on our results, we suggest that Quercus (most likely Q. robur) may be a more suitable deciduous taxon to reintroduce to the region (cf. Andrzejczyk and Brzeziecki, 2018) as it has been shown to be tolerant of warm conditions in the past (during the Roman and MCA), thus analogous to potential future climatic conditions in the region. The stability of Quercus is an important aspect, particularly under predicted climate changes scenarios (Jacob et al., 2014) and changes in forest ecosystems in Europe (Boden et al., 2014; Feurdean et al., 2017a; Lindner et al., 2014; Stobbe and Gumnior, 2021). Although our results show that past climatic changes of the last 2200 years provoked a response from most tree species, human activity (e.g. deforestation and local fires) superimposed—and even surpassed—the effect of climatic changes during the most recent times, in particular from 1600 AD to the present. Unique periods of sustained human activity were identified between 100–200 AD, 450 AD, 850–900 AD, 1500 AD, 1630 AD, and 1760 AD, with the most intensive activity occurring post-1500 AD. Additional high-resolution multiproxy research from the region is necessary to better distinguish and understand the role of natural factors and human activities, which have impacted forest ecosystems in the past.

Footnotes

Acknowledgements

We thank Marcin Sznel for his help during core sampling, Vachel Carter for reading early versions of the manscript, and Anne V. Nguyen for linguistic corrections.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Research was funded by the National Science Centre, grant No. DEC-2013/09/B/ST10/01589 (PI: Mariusz Gałka).

ORCID iDs

Mariusz Gałka

Milena Obremska

References

Adolf

Wunderle

Colombaroli

, et al. (2018) The sedimentary and remote-sensing reflection of biomass burning in Europe. Global Ecology and Biogeography 27: 199–212.

Andrzejczyk

Brzeziecki

(2018) Wpływ grabu (Carpinus betulus L.) na wzrost i przeżywalność dębu (Quercus robur L.) w fazie młodnika. Effect of hornbeam (Carpinus betulus L.) on growth and survival of pedunculate oak (Quercus robur L.) during the thicket stage. Sylwan 162: 989–997.

Apolinarska

Obremska

Aunina

, et al. (2018) Response of the aquatic plants and mollusc communities in Lake Kojle (Central Europe) to climatic changes between 250 BCE and 1550 CE. Aquatic Botany 148: 35–45.

Barzdajn

(2006) Restytucja jodły pospolitej w Sudetach. Dotychczasowe osiągnięcia. Studia i Materiały CEPL 11: 69–84.

Behre

K-E

(1988) The role of man in European vegetation history. In: Huntley

Webb

(eds) Vegetation History. Dordrecht: Kluwer, pp.633–672.

Ber

(1998) Glaciotectonic of the Suwałki-Augustów Lakeland in connection to neotectonic movements and tectonic structures of the crystalline basement (NE Poland). Przegląd Geologiczny 47: 831–839.

Ber

(2006) Pleistocene interglacials and glaciations of northeastern Poland compared to neighbouring areas. Quaternary International 149(1): 12–23.

Berglund

Ralska-Jasiewiczowa

(1986) Pollen analysis and pollen diagrams. In: Berglund

(ed.) Handbook of Holocene Palaeoecology and Palaeohydrology. Chichester–Toronto: Wiley & Sons Ltd, pp.455–484.

Beug

H-J

Henrion

Schmuser

(1999) Landschaftsgeschichte im Hochharz. Die Entwicklung der Walder und Moore seit dem Ende der letzten Eiszeit. Goslar: Gessellschaft zur Forderung des Nationalparks Harz e.V.

10.

Birks

HJB

(1986) Late-Quaternary biotic changes in terrestrial and lacustrine environments, with particular reference to north-west Europe. In: Berglund

(ed.) Handbook of Holocene Palaeoecology and Palaeohydrology. Chichester: Wiley & Sons Ltd, pp.3–65.

11.

Boden

Kahle

H-P

Wilpert

, et al. (2014) Resilience of Norway spruce (Picea abies (L.) Karst) growth to changing climatic conditions in southwest Germany. Forest Ecology and Management 315: 12–21.

12.

Bolibok

Zajączkowski

Dobrowolska

, et al. (2016) Potencjalny zasięg klimatyczny jodły (Abies alba Mill.) w Polsce. Sylwan 160: 519–528.

13.

Bradshaw

RHW

(2004) Past anthropogenic influence on European forests and some possible genetic consequences. Forest Ecology and Management 197: 203–212.

14.

Bronk Ramsey

(2009) Bayesian analysis of radiocarbon dates. Radiocarbon 51: 337–360.

15.

Brown

Giesecke

(2014) Holocene fire disturbance in the boreal forest of central Sweden. Boreas 43: 639–651.

16.

Brzozowski

Siemaszko

(2005) Najstarsze dzieje okolic Suwałk (The earliest history of the Suwalki area, in Polish). In: Kopciała

(ed) Suwałki miasto nad Czarna Hancza. Wydawnictwo Hancza, Suwałki, pp 67–87.

17.

Büntgen

Tegel

Nicolussi

, et al. (2011) 2500 years of European climate variability and human susceptibility. Science 331: 578–582.

18.

Carcaillet

Bergman

Delorme

, et al. (2007) Long-term fire frequency not linked to prehistoric occupations in northern Swedish boreal forest. Ecology 88: 465–477.

19.

Carter

Moravcová

Chiverrell

, et al. (2018) Holocene-scale fire dynamics of central European temperate spruce-beech forests. Quaternary Science Reviews 191: 15–30.

20.

Dziewanowski-Stefańczyk

(2010) Handel zagraniczny jako czynnik wzrostu gospodarczego w XVI-XVII wieku. In: Kaliński

(ed.) Polskie osiągnięcia gospodarcze. Warszawa: Wydawnictwa Akademickie i Profesjonalne, pp.39–73.

21.

Edvardsson

Stančikaitė

Miras

, et al. (2018) Late-Holocene vegetation dynamics in response to a changing climate and anthropogenic influences – Insights from stratigraphic records and subfossil trees from southeast Lithuania. Quaternary Science Reviews 185: 91–101.

22.

EEA Report (2012) European Environment Agency: Climate Change, Impacts and Vulnerability in Europe as Indicator- Based Report 12. Copenhagen: European Environment Agency, p. 300.

23.

Engel

Sobczak

(2012) Gród jećwieskiego wodza Szjurpy (Sjurpy) i jego system obronny. In: Rant-Tanajewska

Świerubska

Dziubiak

, et al. (eds) 09596836221088249V lat Suwalskiego Parku Krajobrazowego. Jeleniewo: Suwalski Park Krajobrazowy. pp.27–36.

24.

Faliński

Pawlaczyk

(eds) (1993) Zarys ekologii. In: Bugała

(ed.) Grab zwyczajny Carpinus betulus L. Nasze Drzewa Leśne 9, 147–263. Sorus, Poznań - Kórnik.

25.

Feurdean

Florescu

Vannière

, et al. (2017a) Fire has been an important driver of forest dynamics in the Carpathian Mountains during the Holocene. Forest Ecology and Management 389: 15–26.

26.

Feurdean

Veski

Florescu

, et al. (2017b) Broadleaf deciduous forest counterbalanced the direct effect of climate on Holocene fire regime in hemiboreal/boreal region (NE Europe). Quaternary Science Reviews 169: 378–390.

27.

Feurdean

Willis

(2008) Long-term variability of Abies albain NW Romania: Implications for its conservation management. Diversity and Distributions 14: 1004–1017.

28.

Gałka

(2014) Pattern of plant succession from eutrophic lake to ombrotrophic bog in NE Poland over the last 9400 years based on high-resolution macrofossil analysis. Annales Botanici Fennici 51: 1–21.

29.

Gałka

Miotk-Szpiganowicz

Marczewska

, et al. (2015a) Palaeoenvironmental changes in Central Europe (NE Poland) during the last 6200 years reconstructed from a high-resolution multi-proxy peat archive. The Holocene 25: 421–434.

30.

Gałka

Tobolski

Bubak

(2015b) Late glacial and early Holocene lake level fluctuations in NE Poland tracked by macro-fossil, pollen and diatom records. Quaternary International 388: 23–38.

31.

Gałka

Feurdean

Sim

, et al. (2021) A multi-proxy long-term ecological investigation into the development of a late Holocene calcareous spring-fed fen ecosystem (Raganu Mire) and boreal forest at the SE Baltic coast (Latvia). Ecological Indicators 126: 107673.

32.

Gałka

Tobolski

Lamentowicz , et al. (2017) Unveiling exceptional Baltic bog ecohydrology, autogenic succession and climate change during the last 2000 years in CE Europe using replicate cores, multi-proxy data and functional traits of testate amoebae. Quaternary Science Reviews 156: 90–106.

33.

Gałka

Tobolski

Zawisza

, et al. (2014) Postglacial history of vegetation, human activity and lake-level changes at Jezioro Linówek in northeast Poland, based on multi-proxy data. Vegetation History and Archaeobotany 23: 123–152.

34.

Giesecke

Bennett

(2004) The Holocene spread of Picea abies (L.) Karst. in Fennoscandia and adjacent areas. Journal of Biogeography 31: 1523–1548.

35.

Goslar

Czernik

Goslar

(2004) Low-energy 14C AMS in Poznan radiocarbon Laboratory, Poland. Nuclear Instruments and Methods in Physics Research B 223–224: 5–11.

36.

Grimm

(1987) CONISS: A FORTRAN 77 program for stratigraphically constrained cluster analysis by the method of incremental sum of squares. Computational Geosciences 13(1): 13–35.

37.

Grimm

(1992) TILIA/TILIA Graph. Version 1.2. Springfield, IL: Illinois State Museum.

38.

Hájková

Jamrichová

Wiezik

, et al. (2019) Spruce representation in zonal woodlands may be overestimated when using pollen spectra from peatlands. Review of Palaeobotany and Palynology 271: 104104.

39.

Hammer Harper

DAT

Ryan

(2001) Past: Paleontological statistics software package for education and data analysis. Palaeontologia Electronica 4: art. 4: 9pp.

40.

Haneca

Wazny

Van Acker

, et al. (2005) Provenancing Baltic timber from art historical objects success and limitations. Journal of Archaeological Science 32: 261–271.

41.

Huntley

Birks

HJB

(1983) An Atlas of Past and Present Pollen Maps for Europe: 0- 13000 Years Ago. Cambridge, London: Cambridge University Press.

42.

IPCC (2014) Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. In: Pachauri

Meyer

(eds) Core Writing Team. Geneva, Switzerland: IPCC. p. 151.

43.

IUSS Working Group (2015) World Reference Base for Soil Resources 2014, Update 2015 International Soil Classification System for Naming Soils and Creating Legends for Soil Maps. Rome: FAO.

44.

Jacob

Petersen

Eggert

, et al. (2014) EURO-CORDEX: New high-resolution climate change projections for European impact research. Regional Environmental Change 14: 563–578.

45.

Jaworski

Pach

(2014) Stan wielogatunkowego lasu naturalnego (Abies, Fagus, Picea) regla dolnego w rezerwacie Oszast na tle stanu monokultur świerkowych w Beskidzie Żywieckim i Beskidzie Śląskim. A comparison of lower montane natural forest (Abies, Fagus, Picea) in Oszast Reserve and spruce monocultures in the Żywiecki Beskid and Śląski Beskid. Forest Research Papers 75: 13–23.

46.

Juggins

(2003) C2 User Guide. Software for Ecological and Palaeoecological Data Analysis and Visualisation. Newcastle upon Tyne, UK: University of Newcastle.

47.

Katz

Kipiani

(1965) Atlas opredelitel’ plodov i semyan vstretchayushchikhsya v chetvertinnykh otuocheniyakh SSSR. Nauka, Moskva (in Russian), Publishing House, p.378.

48.

Knapp

Robin

Kirleis

, et al. (2013) Woodland history in the upper Harz Mountains revealed by kiln site, soil sediment and peat charcoal analyses. Quaternary International 289: 88–100.

49.

Kolstrup

(2009) Vegetational and environmental history during the Holocene in the Esbjerg area, west Jutland, Denmark. Vegetation History and Archaeobotany 18: 351–369.

50.

Kołaczek

Buczek

Margielewski

, et al. (2021) Development and degradation of a submontane forest in the Beskid Wyspowy Mountains (Polish Western Carpathians) during the Holocene. The Holocene 31(11-12): 1716–1732.

51.

Krzywicki

(2002) The maximum ice sheet limit of the Vistulian Glaciation in north-eastern Poland and neighbouring areas. Geological Quarterly 46: 165–188.

52.

Kupryjanowicz

(2007) Postglacial development of vegetation in the vicinity of the Wigry Lake. Geochronometria 27: 53–66.

53.

Kupryjanowicz

Fiłoc

(2016) Palynological studies in the Yatving territory. In: Bitner-Wróblewska

Brzeziński

Kasprzycka

(eds) Yatving Archaeology. Past Research, New Perpectives. Warszawa: Państwowe Muzeum Archeologiczne w Warszawie, pp.133–157.

54.

Lamentowicz

Gałka

Lamentowicz

, et al. (2015) Reconstructing climate change and ombrotrophic bog development during the last 4000 years in northern Poland using biotic proxies, stable isotopes and trait-based approach. Palaeogeography Palaeoclimatology Palaeoecology 418: 261–277.

55.

Lang

(1994) Quartäre Vegetationsgeschichte Europas. Jena: Fischer.

56.

Latałowa

van der Knaap

(2006) Late Quaternary expansion of Norway spruce Picea abies (L.) karst. In Europe according to pollen data. Quaternary Science Reviews 25: 2780–2805.

57.

Lauterbach

Brauer

Andersen

, et al. (2011) Multi-proxy evidence for early to mid-Holocene environmental and climatic changes in northeastern Poland. Boreas 40: 57–72.

58.

Ledig

(1992) Human impacts on genetic diversity in forest ecosystems. Oikos 63: 87–108.

59.

Lindner

Fitzgerald

Zimmermann

, et al. (2014) Climate change and European forests: What do we know, what are the uncertainties, and what are the implications for forest management? Journal of Environmental Management 146: 69–83.

60.

Lindner

Maroschek

Netherer

, et al. (2010) Climate change impacts, adaptive capacity, and vulnerability of European forest ecosystems. Forest Ecology and Management 259: 698–709.

61.

Lorenc

(2005) Atlas klimatu Polski. Instytut Meteorologii i Gospodarki Wodnej. Warszawa, p. 116.

62.

Luterbacher

Werner

Smerdon

, et al. (2016) European summer temperatures since Roman times. Environmental Research Letters 11(2): 1.

63.

Makohonienko

(2000) Przyrodnicza historia Gniezna. Homini: Poznań-Bydgoszcz.

64.

Marcisz

Gałka

Pietrala

, et al. (2017) Fire activity and hydrological dynamics in the past 5700 years reconstructed from Sphagnum peatlands along the oceanic–continental climatic gradient in northern Poland. Quaternary Science Reviews 177: 145–157.

65.

Marcisz

Kołaczek

Gałka

, et al. (2020) Exceptional hydrological stability of a Sphagnum-dominated peatland over the late Holocene. Quaternary Science Reviews 231: 106180.

66.

Masternak

Niebrzydowska

Głębocka

(2015) Zmienność genetyczna jodły pospolitej (Abies alba Mill.) zachowanej na terenie Nadleśnictwa Katowice. Genetic variation of silver fir (Abies alba Mill.) preserved in the Katowice Forest District. Forest Research Papers 76: 315–321.

67.

Matusiewicz

Rodziwonowicz

Skłodowski

(2005) Historia Suwałk do 1945 roku. In: Kopciała

(ed.) Suwałki miasto nad Czarną Hańczą. Suwałki: Wydawnictwo Hańcza, pp.89–472.

68.

Mazier

Brostöm

Gaillard

, et al. (2008) Pollen productivity estimates and relevant source area of pollen for selected plant taxa in a pasture woodland landscape of the Jura Mountains (Switzerland). Vegetation History and Archaeobotany 17: 479–495.

69.

Milad

Schaich

Bürgi

, et al. (2011) Climate change and nature conservation in Central European forests: A review of consequences, concepts and challenges. Forest Ecology and Management 261: 829–843.

70.

Milecka

Kupryjanowicz

Makohonienko

, et al. (2004) Quercus L. - Oak. In: Ralska-Jasiewiczowa

Latałowa

Wasylikowa

, et al. (eds) Late Glacial and Holocene History of Vegetation in Poland Based on Isopollen Maps. Kraków: W. Szafer Institute of Botany, Polish Academy of Sciences, pp.189–199.

71.

Mirek

Piękoś-Mirkowa

Zając

, et al. (2002) Flowering Plants and Pteridophytes of Poland. A Checklist. Kraków: W. Szafer Institute of Botany, Polish Academy of Sciences.

72.

Ohlson

Brown

Birks

HJB

, et al. (2011) Invasion of Norway spruce diversifies the fire regime in boreal European forests. Journal of Ecology 99: 403.

73.

Poraj-Górska

Żarczyński

Ahrens

, et al. (2017) Impact of historical land use changes on lacustrine sedimentation recorded in varved sediments of Lake Jaczno, northeastern Poland. CATENA 153: 182–193.

74.

Ralska-Jasiewiczowa

Miotk-Szpiganowicz

Zachowicz

, et al. (2004) Carpinus betulus L. - Hornbeam. In: Ralska-Jasiewiczowa

Latałowa

Wasylikowa

, et al. (eds) Late Glacial and Holocene History of Vegetation in Poland Based on Isopollen Maps. Kraków: W. Szafer Institute of Botany, Polish Academy of Sciences. pp.69–78.

75.

Reimer

Austin

WEN

Bard

, et al. (2020) The Intcal20 Northern Hemisphere radiocarbon age calibration curve (0–55 cal kBP). Radiocarbon 62(4): 725–757.

76.

Reitalu

Seppä

Sugita

, et al. (2013) Long-term drivers of forest composition in a boreonemoral region: The relative importance of climate and human impact. Journal of Biogeography 40: 1524–1534.

77.

Rinterknecht

Clark

Raisbeck

, et al. (2006) The last deglaciation of the southeastern sector of the Scandinavian Ice Sheet. Science 311: 1449–1452.

78.

Roberts

Fyfe

Woodbridge

, et al. (2018) Europe’s lost forests: a pollen-based synthesis for the last 11,000 years. Scientific Reports 8: 716.

79.

Saarse

Niinemets

Poska

, et al. (2010) Is there a relationship between crop farming and the Alnus decline in the eastern Baltic region? Vegetation History and Archaeobotany 19(1): 17–28.

80.

Sarmaja-Korjonen

(2003) Contemporaneous Alnus decline and the beginning of Iron Age cultivation in pollen stratigraphies from southern Finland. Vegetation History and Archaeobotany 12: 49–59.

81.

Środoń

(1967) Świerk pospolity w czwartorzędzie Polski (The common spruce in the Quaternary of Poland). Acta Palaeobotanica 8: 3–59.

82.

Stivrins

Brown

Reitalu

, et al. (2015) Landscape change in central Latvia since the Iron Age: Multi-proxy analysis of the vegetation impact of conflict, colonization and economic expansion during the last 2000 years. Vegetation History and Archaeobotany 24: 377–391.

83.

Stivrins

Buchan

Disbrey

, et al. (2017) Widespread, episodic decline of alder (Alnus) during the medieval period in the boreal forest of Europe. Journal of Quaternary Science 32: 903–907.

84.

Stobbe

Gumnior

(2021) Palaeoecology as a tool for the future management of forest ecosystems in Hesse (Central Germany): Beech (Fagus sylvatica L.) versus lime (Tilia cordata Mill). Forests 12(7): 924.

85.

Szal

Kupryjanowicz

Wyczółkowski

(2014) Late Holocene changes in vegetation of the Mrągowo Lakeland (NE Poland) as registered in the pollen record from Lake Salęt. Studia Quaternaria 31: 51–60.

86.

Szkiruć

(1986) Suwalski Park Krajobrazowy. Warszawa: Ludowa Spółdzielnia Wydawnicza.

87.

Tinner

Colombaroli

Heiri

, et al. (2013) The past ecology of Abies alba provides new perspectives on future responses of silver fir forests to global warming. Ecological Monographs 83: 419–439.

88.

Tobolski

(1990) Paläoökologische Untersuchungen des Siedlungsgebietes im Lednica Landschaftspark (Nordwestpolen). Offa 47: 109–131.

89.

Tobolski

(2000) Przewodnik do oznaczania torfów i osadów jeziornych. Warszawa: Wydawnictwo Naukowe PWN.

90.

Topolski

(1999) Polska w czasach nowożytnych. Od środkowoeuropejskiej potęgi do utraty niepodległości (1501-1795). Poznań: Wydawnictwo Naukowe UAM.

91.

van der Knaap

van Leeuwen

JFN

Finsinger

, et al. (2005) Migration and population expansion of Abies, Fagus, Picea, and Quercus since 15000 years in and across the Alps, based on pollen-percentage threshold values. Quaternary Science Reviews 24: 645–680.

92.

van der Linden

van Geel

(2006) Late Holocene climate change and human impact recorded in a south Swedish ombrotrophic peat bog. Palaeogeography Palaeoclimatology Palaeoecology 240: 649–667.

93.

Vuorela

(1986) Palynological and historical evidence of slash- and burn cultivation in South Finland. In: Behre

K-E

(ed.) Anthropogenic Indicators in Pollen Diagrams. A. A. Balkema, Rotterdam, pp.53–64.

94.

Wacnik

Goslar

Czernik

(2012) Vegetation changes caused by agricultural societies in the Great Mazurian Lake District. Acta Palaeobotanica 52: 59–104.

95.

Wacnik

Tylmann

Bonk

, et al. (2016) Determining the responses of vegetation to natural processes and human impacts in north-eastern Poland during the last millennium: Combined pollen, geochemical and historical data. Vegetation History and Archaeobotany 25: 479–498.

96.

Ważny

(2005) The origin, assortments and transport of Baltic Timber. In: Van de Velde

Beeckman

Van der Acker

, et al. (eds) Constructing Wooden Images. Brussels: Brussels University Press, pp.115–126.

97.

Whitlock

Larsen

(2001) Charcoal as a fire proxy. In: Smol

Birks

HJB

Last

(eds) Tracking Environmental Change Using Lake Sediments. Dordrecht: Springer, pp.75–97.

98.

Willis

Araújo

Bennett

, et al. (2007) How can a knowledge of the past help to conserve the future? Biodiversity conservation and the relevance of long-term ecological studies. Philosophical Transactions of the Royal Society B: Biological Sciences 362: 175–187.

99.

Willis

Birks

(2006) What is natural? The need for a long-term perspective in biodiversity conservation. Science 314: 1261–1265.

100.

Zajączkowski

Brzeziecki

Perzanowski

, et al. (2013) Wpływ potencjalnych zmian klimatycznych na zdolność konkurencyjną głównych gatunków drzew w Polsce. Impact of potential climate changes on competitive ability of main forest tree species in Poland. Sylwan 157: 253–261.