In the autumn of 2017, Botaniska's scientific curator Henrik Sjöman joined a group of colleagues from the USA (Chicago Botanical Garden, Morton Arboretum, Longwood Garden and Morris Arboretum) on a collecting expedition to Azerbaijan where they cooperated with researchers and botanists from Azerbaijan in collecting intriguing trees considered valuable for cultivation.
Because of its unique situation between the mighty Caucasus in the west and north-west and the Caspian Mountains in the country's south-eastern region, Azerbaijan offers a fantastic diversity of interesting plants that are valuable for cultivation.
Azerbaijan has a very varied climate, which manifestly influences the landscape. In the central regions there are desert-like landscapes while near the Caspian Sea in the south-eastern region of the country, lush subtropical conditions can be found. In this latter region there is extensive cultivation of tea and lemons, among other crops. In the mountains, the climate and weather are of course very varied, depending upon the altitude above sea level. Tall forests of oriental beeches (Fagus orientalis) can be seen in the Caucasus and spectacular forests of Persian ironwood (Parrotia persica) take one's breath away in the Caspian Mountains.
The Caspian Mountains in Azerbaijan are the westernmost part of this mountain range, while the main part lies in northern Iran where one can see summits over 5,500 metres above sea level. In Azerbaijan, the mountaintops are not as high but high enough to find trees and bushes of interest for cultivating in Swedish conditions.
One key species among the trees in these mountains is the above-mentioned Persian ironwood (Parrotia persica) that can develop into a huge tree over 25 metres tall. In the summer-warm parts of the mountains, the species can create almost uniform forests that colour whole valleys pinkish-red and purple in autumn – marvellous to see. Persians ironwoods are becoming an ever more common element in public settings in Sweden, mostly in southern Sweden. When cultivated, the species variation is fairly limited, so a greater genetic material is needed from which to choose, which makes this collection very valuable.
Dendroflora in Azerbaijan
The aim of the expedition was chiefly woody plant material which seems self-evident in a region that includes so many beautiful, valuable trees for cultivating. One of the most interesting trees in the Caspian forests is the chestnut-leaved oak (Quercus castaneifolia), the long, slender, shiny leaves of which give the tree an exclusive appearance at a distance. The tree can develop into great, proud individuals that can attain 50 metres in height with a broad crown. In southern Sweden, the species may be found in exclusive tree collections where it grows to about 25 metres tall. In Azerbaijan and Georgia, the chestnut-leaved oak is used as a hardy street tree since it has high tolerance for warm and dry growing conditions.
Another lovely oak tree from these forests is the Persian or Caucasian oak (Quercus macranthera) that develops into spreading, proud trees that early on in open spaces acquire a broad, fragmented branch structure greatly reminiscent of the Swedish "savings-bank oaks". A fine quality in the Persian oak is the large leaves. They usually take the form of reversed, broadly ovate 10-20 cm long and 8-14 cm wide leaves with 8-10 soft ovate lobes along each side. Another very interesting tree in Azerbaijan, and one that we in western Europe are beginning to appreciate, is the European hop-hornbeam (Ostrya carpinifolia). In western Azerbaijan, it is found in almost uniform forests that turn a beautiful golden-yellow colour in autumn. The European hop-hornbeam has been shown to be a very hardy tree, so the aim is to find a genetic material that is extra valuable for cultivating in Swedish conditions.
Climate smart trees
The aim of studies and collecting expeditions like that to Azerbaijan is for example to study plants in special growing environments to see how they develop and deal with these unique environments. In Azerbaijan, we were interested in studying natural growing environments that sometimes become extremely wet after heavy rains, but that in between rainfalls require plants to adapt to very warm and dry conditions.
For a sustainable handling of storm water in urban environments in which tree plantations are included, it is essential to be able to lead the water from cloudbursts into these plantations in order to reduce the load on the city's storm water network. This implies that the use of trees that can deal with these extreme and very challenging growing conditions, from wet to dry, is very important.
Thus in Azerbaijan, we visited many river valleys that get flooded after heavy rains during the growing season, only to dry out and become really dry until the next rains. One of the species in these river valleys is the Caucasian alder (Alnus subcordata). It is extremely tough and tolerant of these extreme weather conditions – a truly climate smart tree for urban environments. It will be interesting to evaluate these trees in Botaniska, where they will be contributing qualities that are vital for sustainable city development.
Plants from Azerbaijan in Botaniska
We already have a number of intriguing plants in the Garden from the Caucasian Mountains, so far mainly herbs and some sporadic woody plants like the Persian ironwood. We hope soon to be able to plant out in the Garden and Arboretum many of the remarkable trees and bushes from this expedition.