Caucasus – Northern Iran

This region from the eastern coast of the Black Sea to northern Iran does not belong to the actual area of this website but is discussed briefly here as many of its forest types resemble those of the European temperate zone and larger virgin-like forests have remained there. I will describe the most important forest regions very briefly and discuss a few remarkable reserves in a little more in detail.

Locals call the lowland regions “subtropical” but they are better called warm temperate. Average annual temperature is approx. 15°C and annual precipitation 1200–2000 mm ¹. There was a glacial refugium in the lowlands of western Georgia and adjacent areas², consequently many regional endemics can be found in these regions. In similar sites the tree flora is richer than in western Europe but poorer than in eastern North America and especially eastern Asia³.

Close to the Black Sea coast, there are wet carrs (swamps) and alluvial forests with black alder (Alnus glutinosa subsp. barbata), European ash (Fraxinus excelsior) and Caucasian wingnut (Pterocarya fraxinifolia). These forests have been protected particularly in Kolkheti National Park, Georgia.²

Besides the above-mentioned wet forests, the lowlands near the Black Sea were originally covered by species-rich deciduous forests, dominated by Imeretian oak (Quercus robur subsp. imeretina), Strandzha oak (Q. hartwissiana), sessile oak (Q. petraea subsp. iberica), Caucasian zelkova (Zelkova carpinifolia), European hornbeam (Carpinus betulus), sweet chestnut (Castanea sativa) and oriental beech (Fagus orientalis). The undergrowth of this and most other forest types of the western Caucasus typically consists of a dense, mostly evergreen, vegetatively regenerating shrub layer. The most abundant species are pontic rhododendron (Rhododendron ponticum) and cherry laurel (Prunus laurocerasus). The shrub layer is often only about one metre tall but these species can reach over 10 metres in favourable sites. Lowland forests have mostly been cleared for agriculture. In the Soviet period, the lowlands of west Georgia produced almost all the tea and citrus used in the Soviet Union. After the collapse of the Soviet Union, production was no longer profitable, with large areas becoming wasteland. However, Ajameti Nature Reserve protects a substantial part (47 km²) of these forests.²

The diversity starts to decrease with increasing elevation. By the nature, the foothills are dominated by sessile oak, European hornbeam, oriental hornbeam (Carpinus orientalis), oriental beech and sweet chestnut with evergreen shrubby understorey.²

The next zone is dominated by oriental beech alone, with an evergreen shrubby understorey as above. This zone includes the wettest place in the Caucasus and also in the whole former Soviet Union, a biodiversity hotspot¹ protected in Mtirala National Park (158 km²) and adjacent Kintrishi Nature Reserve (139 km²) in the southwestern corner of Georgia.  Annual precipitation exceeds 2500 mm, even reaching 4000 mm ⁴ on some uppermost slopes. The forests have often been called temperate rainforests. Higher elevation forests look quite undisturbed with large and dead trees, although individual trees have been felled prior to their preservation⁵. Besides oriental beech, the other abundant trees are sweet chestnut, European hornbeam and black alder⁴. Here black alder is not restricted to riversides and wetlands but also grows on slopes and ridges. Besides the evergreen shrubby understorey, in places forest floors resembling those of European beech (Fagus sylvatica) forest can also be found, for example with a low thorny blackberry (Rubus) shrub layer, or with almost non-existent undergrowth. Climbers are scarce on oriental beech but more abundant on other trees. The upper slopes are shrouded by fog almost daily⁵. There are hiking trails in the both protected areas.

Caucasian fir (Abies nordmanniana subsp. nordmanniana), Caucasian spruce (Picea orientalis) and oriental beech form the next altitudinal zone². The forest type resembles the montane European silver fir (Abies alba) – Norway spruce (Picea abies) – European beech (Fagus sylvatica) forest of central and southern Europe. Perhaps the biggest difference is the evergreen shrub layer described above. This zone in its western part includes perhaps the tallest forests of western Eurasia. The tallest reliably measured native European tree is a 62.7-metre Norway spruce in Slovenia⁶. However, there are claims of even taller Caucasian firs from the Russian and Abkhazian Western Caucasus ^{7 8 9 10}. The highest claims are 85 m ⁷ and 78 m ⁸. The latter is an estimate by Vladimir Dinets, calculated from the length of the shade of the tree¹¹, thus certainly very inaccurate; moreover, the entire area in which this tree grew was logged to clear land for the Sochi Olympics in 2014 ¹². The height of 85 m in the Western Caucasus World Heritage site ⁷ is based on an old measurement or estimation from Buynyy Natural Monument, Russia; the details of the measurement are no longer known¹⁰. According to this old data, Caucasian fir in Buynyy ”often” reaches 60–65 m. Besides Buynyy Natural Monument, the tallest Caucasian firs are said to be growing in the central part of the long Kisha Valley in Caucasus Nature Reserve, Russia¹⁰. The Nature Reserve, protected in 1924, is likely one of the grandest protected areas in the world. Its total extent is 2957 km², two thirds of which is forested, mostly with primeval Caucasian fir – oriental beech forest⁹. Caucasian spruce prefers a slightly drier climate and is not present in Caucasus Nature Reserve⁹. Trees of other species are scanty in the fir–beech forest, the most common being sycamore maple (Acer pseudoplatanus) and Norway maple (A. platanoides). The forest is densely stocked, locally reaching 1800 m³/ha ¹³. European ivy (Hedera helix) grows abundantly on tree trunks and forest floor. Along rivers there are black and grey alder (A. incana) stands.

My measurements with a German–Russian group in 2018, using TruPulse 200X laser, resulted in 60.5 m as the maximum height in the Kisha Valley of Caucasus Nature Reserve (photo right) and 59.5 m in Buynyy Natural Monument. We did not know exactly where the very tallest trees grow, and very likely there are slightly taller trees. The average height of these Caucasian fir stands was 45–55 m. Anyway, the data we collected seems to indicate that the claimed extreme heights of Caucasian fir are inaccurate. One possibility to estimate the maximal height potential of Caucasian fir is to compare heights that the species often reaches with the corresponding heights of the well-known species Norway spruce. In the tallest Norway spruce forests, e.g. in Biogradska Gora National Park, Perućica Nature Reserve and also in the Kirnitzsch Valley of Saxony Switzerland National Park (Germany), the species often reaches 50–55 m, according to my measurements. This holds true also for Caucasian fir in the Kisha Valley and Buynyy Natural Monument where the species often reaches 50–55 m, according to our measurements. This could indicate that the maximal height of Caucasian fir could be approximately the same as that of Norway spruce, i.e. around 61–65 m.

Caucasus Nature Reserve forms the main part of the Western Caucasus World Heritage site and is also a UNESCO biosphere reserve. The Reserve is famous particularly for its over 1000 wisents; though they are actually hybrids between lowland wisent (Bison bonasus bonasus), Caucasian wisent (B. bonasus caucasicus) and American bison (B. bison). Hundreds of brown bears (Ursus arctos) and a few reintroduced Persian leopards (Panthera pardus saxicolor) live in Caucasus Nature Reserve, too.⁹ Apart from a few popular hiking routes, visiting the reserve needs a special permit, including the Kisha Valley.

The southwest-north orientated Likhi Range in central Georgia blocks the humid air masses from the Black Sea, so the climate becomes drier². The drier forest types do not have the evergreen shrubby understorey of the western moist region².

In a natural state, east of the Likhi Range the lowlands would be covered by trees like sessile oak, European hornbeam and oriental hornbeam².

The mountain slopes are still moist enough for oriental beech. Together with European hornbeam it still covers large areas on the southern slopes of the eastern Greater Caucasus Range. This zone includes the second oldest protected area in the whole former Soviet Union¹: Georgia’s Lagodekhi Strict Nature Reserve, protected in 1912, with its beautiful pristine² forests. Today its area is 179 km². 30-metre hornbeams are common; their broad crowns form an arching roof above a well-developed deciduous shrub layer. Oriental beech reaches 40 m at most in Lagodekhi Reserve. Abundant moss grows on tree trunks indicating a moist climate. Climbers occur, as well. The slope forests have abundant openings, which are covered by thorny blackberry thickets. Annual precipitation is approx. 1000 mm on the foothills and exceeds 2000 mm on the upper slopes¹⁴. Average annual temperature at low altitudes is approx. 12°C. There are many hiking trails.

The uppermost forest zone in the entire region discussed above consists of broadleaf krummholz dominated particularly by Caucasian downy birch (Betula litwinowii). Other abundant trees include red-bud maple (Acer trautvetteri), European rowan (Sorbus aucuparia) and Caucasian oak (Quercus macranthera).

Further eastwards the climate becomes still drier: from the eastern end of Georgia to the coast of the Caspian Sea, the natural lowland vegetation is steppe but mostly converted to agriculture.

However, further south between the southern coast of the Caspian Sea and the Alborz Mountains, there is another moist forest region. As in western Georgia, there was a glacial refugium in the lowlands of northern Iran². The whole region has 65–90 tree species depending on the source, and the definition of tree^{15 16 17}. The forests of northern Iran and western Georgia have a number of common features², but western Georgia’s dense evergreen shrubby understorey is missing, a result of drier summers. Lianas are prominent in Northern Iran. Thickets of thorny shrubs grow in openings.

Most of the flat country along the mild coast of the Caspian Sea has been cleared for cultivation with only small patches of the original forest remaining. The trees are mainly deciduous, but evergreen European box (Buxus sempervirens) constitutes a main part of the forest. Major deciduous species include chestnut-leaved oak (Quercus castaneifolia), velvet maple (Acer velutinum), Caucasian alder (Alnus subcordata), Caucasian wingnut, Caspian locust (Gleditsia caspica), Persian silk tree (Albizia julibrissin) and date-plum (Diospyros lotus) ^{16 18}.

In 2005, there were still at least 1000 km² of untouched primary forests on the moist northern slopes of the Alborz Mountains¹⁵. Precipitation is fairly high, over 2000 mm/year in the west decreasing towards the east¹⁶. The most important trees on the lower slopes are chestnut-leaved oak, European hornbeam and Persian ironwood (Parrotia persica). The next zone is often shrouded by fog and dominated by oriental beech. Unlike in the Caucasus region, the uppermost zone (to the tree line at 2500–3000 m) is drier, annual precipitation being only 400–600 mm with a 4 month dry period; it is dominated by low Caucasian oak and oriental hornbeam. Traditionally cattle graze the cool, dry upper ridges in spring and summer, and are taken down to the coast for autumn and winter; consequently, the forests in the moist and often steep-sloped oriental beech zone are those best preserved.¹⁶ World Heritage site “Hyrcanian Forests” was established in northern Iran in 2019, consisting of 15 forest areas totalling 1295 km^{2 19}. Hirkan National Park (404 km²) at the southeastern corner of Azerbaijan belongs to the same forest region, too.

The dry southern slopes of the Alborz Mountains were originally covered by Persian juniper (Juniperus excelsa subsp. polycarpos) woodland but it has mostly been cleared¹⁸.

KR

References:

1. Krever, V. et al. (eds.) 2001: Biodiversity of the Caucasus Ecoregion. An Analysis of Biodiversity and Current Threats and Initial Investment Portfolio. WWF.
2. Nakhutsrishvili, G. (2013): The Vegetation of Georgia (South Caucasus). Springer.
3. http://www.ents-bbs.org/viewtopic.php?f=144&t=6804
4. Memiadze, N. et al. (2013): Flora of Mtirala National Park. International Caucasian Forestry Symposium.
5. Mtirala National Park administration, pers. comm. (2014)
6. https://www.monumentaltrees.com/en/
7. IUCN (1999): World Heritage Nomination – IUCN Technical Evaluation: Western Caucasus (Russian Federation).
8. https://www.conifers.org/
9. Pers. comm.
10. Caucasus Nature Reserve, e-mail (2018).
11. Dinets, W., e-mail (2011).
12. Dinets, W., e-mail (2018).
13. http://www.zapoved.net
14. http://enrin.grida.no/htmls/georgia/soegeor/english/biodiv/reserves/lagodekh.htm
15. Knapp. H. D. (2005): Die globale Bedeutung der Kaspischen Wälder. In Nosrati, K et al. (eds.): Schutz der Biologischen Vielfalt und integriertes Management der Kaspischen Wälder (Nordiran). Bundesamt für Naturschutz.
16. Sagheb Talebi, K., Sajedi, T. & Pourhashemi, M. (2014): Forests of Iran. Springer.
17. Seifollahian, M., Rastaghi, M. E. & Hedayati, M.-A. (2005): Die Bedeutung der Pflanzenarten der Kaspischen Wälder. In Nosrati, K et al. (eds.): Schutz der Biologischen Vielfalt und integriertes Management der Kaspischen Wälder (Nordiran). Bundesamt für Naturschutz.
18. Bobek, H. (1951): Die natürlichen Wälder und Gehölzfluren Irāns. Geographisches Institut Universität Bonn.
19. http://whc.unesco.org/en/list/1584