Reconstruction of vegetation and climate of the past of the central Caucasus for materials from the Tarskoe swamp

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1. Introduction

In the North Caucasus, very few Holocene natural archives have been studied, and we can’t reconstruct vegetation history or assess the long-term influence of agriculture and pastoralism on mountain ecosystems.

The Tarskoe swamp is one of the most promising sites. It had been studied twice before 2019. The first study did not provide dating for the core (Neishtadt, 1955; 1957); at the second, the core did not contain the upper sediments, they might have been removed during peat harvesting (Knyazev et al., 1992). The new drilling in 2019 fixed these problems.

The Tarskoe swamp is one of the largest peat bogs in the mid of North Caucasus, it occupies about 20 ha in the basin between the Lesisty and Pastbishchny ranges (42°57’46”N, 44°43’32”E; 806 m a.s.l.). The climate is temperate continental with warm and very humid summer and medium cold, snowy winter. The swamp is located to the low-mountain belt of broad-leaved forests dominated by Fagus orientalis Lipsky and Carpinus betulus L. with Quercus robur L., and an admixture of Corylus avellana L., Ulmus glabra Huds. and Pyrus caucasica Fed. Swamp vegetation is formed by Carex sp. and Phragmites australis (Cav.) Trin. ex. Stend with Matteuccia struthiopteris L. and Sphagnum sp., with thickets of Alnus glutinosa L. in some places. The swamp was drained for pasture and haymaking in the mid-20th century. Traces of drains are still visible. The new drilling was made between them in an undisturbed area.

2. Materials and methods

2.1. Sediment description

A 327 cm core was collected using a Russian corer with a 5 cm diameter, the Tarskoe core consists of 7 sections, 50 cm long each. The lithology of the core:

0 – 276 cm: moss-herbs peat (Sphagnum, Bryidae, Carex, Eriophorum) with interlayer of total sphagnum peat from 140 cm to 153 cm.

276 – 290 cm: herbaceous decomposed peat

290 – 300 cm: clay with herbaceous detritus

300 – 315 cm: total sedge decomposed peat rich in mineral matter

315 – 327 cm: clay

2.2. Dating

The chronology is based on twelve ¹⁴C dates (Table). No suitable terrestrial remains were found, so the main material was bulk. We use Bchron package in the R for the age model (Haslett and Parnell, 2008; R: The R Project for Statistical Computing). The average sedimentation rate is 12 years/cm.

 

Table. Dating of the Tarskoe swamp.

N	Depth (cm) mean	Lab No. Ki	Age BP	Median Probability	Age BP 2σ
1	25	19688	1320 +/- 30		653-707
2	50	19689	1920 +/- 40	1835	1730 - 1939
3	75	19690	1880 +/- 80	1795	1687 - 1993
4	100	19691	2160 +/- 70	2152	1992 - 2335
5	125	19692	2329 +/- 40	2346	2302 - 2469
6	150	19693	2340 +/- 40	2356	2305 - 2491
7	175	19694	2750 +/- 50	2844	2759 - 2954
8	200	19695	2930 +/- 40	3081	2960 - 3183
9	225	19696	2980 +/- 40	3155	3003 - 3252
10	250	19697	2730 +/- 50	2827	2753 - 2939
11	275	19698	3490 +/- 50	3761	3631 - 3896
12	300	19699	4010 +/- 80	4492	4243 - 4656

 

2.3. Microcharcoal analysis

Microcharcoal analysis was made on pollen slides for the 78 samples of 6 ml volume, each sample containing one tablet of Lycopodium at 15853 spores. The diagram of the concentration of microcharcoal was made in the Tilia-Tilia Graph (Grimm, 2004) (Fig.).

 

Fig. Pollen and microcharcoal diagram of the Tarskoe swamp.

 

3. Results

The objectives of the study determined subsampling from the core: sediments of the Bronze Age and of the turn of the Eras were studied in detail (each cm); the rest of the profile was subsampled with an interval of 10 cm. We counted ca. 500 terrestrial pollen in each of 78 samples and identified 185 palynological taxa. The bottom sample had an unrepresentative amount of pollen. Only terrestrial pollen (AP + NAP) were used for the main percentage calculations. For the Cyperaceae, aquatics, spores of mosses or pteridophytes percentage were calculated from the total sum. Local pollen zones (LPZs) were singled out by cluster analysis. The AP/NAP ratio indicates the predominance of forest vegetation. But large proportion of NAP (up to 65%) at the base of the sequence is more typical of semi-open landscapes.

LPZ1 (4.6-4.4 cal. ka BP) reflects the beginning of swamping; deciduous forests alternated with meadow there (Fig.). The predominance of Pinus pollen (up to 27%) is associated with an openness increase and long-distance wind transport, rather than with real participation in the local forest. The composition of the forests was formed by Fagus, with Carpinus, Corylus, Tilia, a small amount of Acer and Prunus, in some places with wild Vitis. Vast open spaces are identified by the abundance of Asterаceae, Cichоriaceae and Poaceae, many Caryophyllаceae, Apiaceae, Scabiosa, Centaurea jacea. Hippоphae rhamnoides L. are associated with forest edges. Weak human impact is suggested by the presence of Arctium and Cardus.

In LPZ2 (4.4-3.2 cal. ka BP), the decreasing Pinus and increasing Fagus (30-52%) mark this phase as start of reforestation. The value of Tilia falls, but Carpinus, Alnus, Ulmus, Quercus, Betula and Fraxinus excelsior L. rise; Prunus, Pterocarya, and Juglans are occasionally found. A lot of open and edge forest areas are identified by the Hippоphae and Spiraea, even Daphne indicates lightening of the forest. Artemisia increases; Poaceae, Chenopodioideae are constantly present; Cichоriaceae, Rosaceae, and Apiaceae have several peaks. An increase in pastoral pressure is suggested by Plantago lanceolata (max), Rumex acetosa, Urtica and Cаnnabis; Cerealia pollen appears frequently.

Starting from LPZ3 (3.2-2.6 cal. ka BP), the stage of the minerotrophic swamp ends and Sphagnum mosses appear, it becomes more favorable for Alnus along the swamp periphery. The forest becomes more closed: Fagus reaches 57%, Carpinus 15%, Ulmus, Corylus and Vitis increase, but Quercus decreases; Picea, Prunus, Pterocarya, Juglans, Castanea are common. The NAP composition has the same dominants, but the diversity decreases. The anthropogenic markers are Plantago lanceolata, Urtica, Brassicаceae, singly Cerealia.

In LPZ4 (2.6-2.1 cal. ka BP), Fagus predominates (37-52%), Alnus reaches 30%, especially in Sphagnum interlayer, but Carpinus gradually decreases, dark conifers disappear, and the diversity of broad-leaved trees declines. The NAP composition shows insignificant changes, only Artemisia and Thalictrum increase. Plantago media, P. lanceolata-type, and Urtica, infrequent Cerealia, Brassicаceae, Аrctium and Rumex acetosa are associated with humans.

LPZ5 (2.1-1.8 cal. ka BP) reflects the initial gradual increase in open areas. Fagus and Carpinus decrease, but shares of Pinus, Betula, dark coniferous, shrubs, and lianes rise. The Poaceae and diversity of meadow grasses increase; the Secale curve appears.

In LPZ6 (1.8 cal. ka BP – present), forest area continues decreasing or becomes sparser. Fagus noticeably reduces up to 15%, and then Alnus to 18%, with a slight rise in Carpinus, Corylus, and Quеrcus. Besides, value of distant pollen (Pinus, Picea, and Abies) increases. Open areas increase, as demonstrated by Poaceae (max), Cichоriaceae and Asteraceae. The pasture indicators include Plantago lanceolata, Rumex acetosa, and Cardus; and the agricultural ones - Cerealia and Secale.

The maximum concentration of microcharcoal in the section is noted in LPZ2(1500 units), the next highest value is observed in LPZ6 a little more than 1000 units. LPZ3 and LPZ4 has a very low concentration of microcharcoal.

4. Discussion and сonclusions

At the beginning of the formation of the swamp about 4.6 cal. ka BP, the landscape of the foothills of the central part of the North Caucasus was semiopen, with a large proportion of meadows than today, perhaps this kind of landscape was under the influence of previous human activity, precisely of agriculture Maikop culture in the Bronze Age. This short-term episode is gradually replaced by broad-leaved forests, with a predominance of beech. Among the local transformations the replacement of Cyperaceae to Alnus and the appearance of Sphagnum, indicates a change in the type of water supply of the swamp. The greatest value of microchrcoal is most likely associated with anthropogenic activity, and is almost always synchronous with the appearance of cultivated cereals pollen. The first peak of microcharcoal (LPZ2) is associated with an increase in diversity among a group of human-related grasses and appearance of cultivated cereals pollen about 4.3 cal. ka BP; the second peak (LPZ6) realeted with the increases of quantity of weeds and significantly increases the proportion of cultivated cereals pollen.

Acknowledgments

Radiocarbon dating of sediments by the Russian Science Foundation, grant No. 19-18-00406, pollen analysis by the Russian Foundation for Basic Research, grant No. 20-35-90014.

Conflict of interest

The authors declare no conflict of interest.

Об авторах

E. D. Yuzhanina

Tyumen Scientific Centre of the Siberian Branch of the Russian Academy of Sciences

Автор, ответственный за переписку.
Email: el.yuzh@gmail.com
Россия, 86, Malygin St., Tyumen, 625026

N. E. Ryabogina

Tyumen Scientific Centre of the Siberian Branch of the Russian Academy of Sciences

Email: el.yuzh@gmail.com
Россия, 86, Malygin St., Tyumen, 625026

A. V. Borisov

Institute of Physicochemical and Biological Problems of Soil Science of the Pushchino Scientific Centre for Biological Research of the Russian Academy of Sciences

Email: el.yuzh@gmail.com
Россия, 2, Institutskaya St., Pushchino, 142290

I. A. Idrisov

Institute of Geology of the Dagestan Scientific Centre of the Russian Academy of Sciences

Email: el.yuzh@gmail.com
Россия, 45, M. Gadzhiev St., Makhachkala, 367032

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