plant exploration

Searching

Betula litwinowii often grows as a multi-stemmed tree in woodland in Georgia

All photographs by Paul Bartlett Paul by All photographs for birches ver the last couple of Birches of northeast Some National Plant years I have been lucky Arunachal Pradesh Collection holders O enough to travel into some In October 2010, I took part in a beautiful and remote areas of the plant study expedition under the travel widely to study world to study birch trees in their leadership of Keith Rushforth to the wild plants. Paul native environment. northeast corner of Arunachal artlett The landscapes of northeast India Pradesh in India, close to the border B describes and Georgia may be very different, with Burma. This part of the state recent trips to but they both support several has long been a disputed territory species of Betula – species that are between China and India so India and Georgia largely unknown to the majority westerners have frequently been to find Betula. of gardeners. barred from entering, with only the

112 June 2013 PlantsmanThe occasional group getting access to the forests of this land. For this reason the flora of the region is largely undisturbed and unstudied. My interest was in the Betula and Alnus of the area. I wanted to study them in the wild and see which species existed through the various layers of forest, and observe their relationships with other plants. I was grateful to receive an RHS bursary to help with the costs of this expedition. We observed four species of birch in the Mishmi Hills of Anjaw district – namely Betula alnoides, B. ashburneri B. cylindrostachya and B. utilis. We also found birches that appeared to be a hybrid of B. ashburneri and B. utilis, Betula alnoides and B. cylindrostachya occur at the lowest altitude, present as occasional trees or in groups of no more than four or five, from 900 to 2,500m. Seedlings grow on open ground at roadsides and landslip sites, generally on sloping ground facing south or west. In the cloud forest both species grow to 20m with a trunk diameter of 40–75cm. Both have smooth, glossy, whitish- The Mishmi Hills of Arunachal Pradesh are home to four species of birch with one reaching 3,700m grey to creamy-brown bark, but the long, thick, closely spaced lenticels vein-end teeth and the twigs being on the rotten trunks of fallen trees give the bark a rough appearance. very hairy. Higher up, the big trees The bark of mature B. utilis in this The outer bark peels in thin tatters were mostly B. alnoides because they area is dark reddish-brown to purple, at the base, but is quite tight and were autumn-flowering, whereas and smooth and free-peeling in large non-peeling through most of the B. cylindrostachya is spring-flowering sheets. At the base, the outer bark is tree. At the base of mature trees the – the best way of differentiating thicker and cracks away in chunks bark is heavily cracked and plated, these two species. Both produce a while still retaining the colour and with fewer lenticels. In crowded distinctive smell of wintergreen texture of the higher bark. Like conditions branching starts at about when the bark or shoots is wounded. B. alnoides lower down, B. utilis in the two-thirds height, giving a light and Betula utilis occupies the 2,200– forest branches at two-thirds height, open crown. Younger trees to 10m 3,000m zone and there is some producing a thin, open crown. in open arable areas form broader overlap with B. alnoides in the cloud Younger trees at the upper limit of spreading crowns with major branch forest. Higher up, in the temperate temperate forest (2,900m) have junctions happening lower down. forest, B. utilis is the only birch. Here many lower branches and a much It seemed that B. cylindrostachya it stands among Abies, Alnus, Pinus, broader shape, though are still quite was less common, but it is difficult to Quercus and Tsuga. It is an attractive delicate. Higher up, where the forest separate from B. alnoides using trunk tree, the only one in this area with peters out, B. utilis rarely gets to morphology alone. The saplings at such a smooth, colourful trunk, more than 10m and the bark is paler, low altitude on roadsides were reaching a height of 15–20m as it showing more silver among the dark probably B. cylindrostachya, judging competes for light. We found reds and browns. This increase in by the number of leaf teeth between seedlings on disturbed ground and betulin, which gives the white ➤

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Most Betula utilis (left) in the Mishmi Hills have reddish brown, shiny bark.Betula alnoides (right) is an autumn-flowering species with prominent lenticels colour, is probably due to higher tatters. The most obvious difference – grey-brown, but matt and rough light levels. At this altitude is in the mature fruiting catkins. with only round lenticels. There was (3,000m), B. utilis can be found in These are held on very short a complete absence of elongated groves and closer groupings. peduncles, either horizontal or lenticels and the bark hardly peeled The highest altitude birch in the upright, whereas on B. utilis they at all. The trees were 6–8m high, but Mishmi Hills is B. ashburneri, found hang pendent on longer peduncles. quite broad and spreading, sometimes at 3,000–3,700m. This was an On the slopes above temperate with several stems, but not truly multi­ exciting discovery for us, as it was forest B. ashburneri is common, often stemmed. The leaves resembled only previously known to exist in forming dense thickets or copses those of B. utilis, but were more hairy Tibet, Yunnan and Sichuan. This alongside Abies, Acer, Rhododendron, on the underside. The twigs were suggests that it will be recognized Salix, Sorbus and Vaccinium. slightly rough and very hairy, again across more of the Himalaya in the Generally it occupies boulder slopes much more hairy than those of future. In the past it has probably or riverside sites. Even at these B. utilis. There were 10–14 leaf veins been recorded erroneously as a altitudes the litter layer is deep and and the leaf margins were turned stunted form of B. utilis. there is plenty of moisture. Material down, making the teeth more visible Betula ashburneri here is generally from these trees has been analysed from the side than the top – again, a gnarled, twisted, multi-stemmed by Richard Buggs and Nian Wang of different to B. utilis. The ripe fruits shrub to 3m. Its shape is evidence of Queen Mary, University of London, were pendent and the fruit scales exposure and the amount of snow its who confirmed it as diploid (2n=28), were similar to those of B. utilis, but branches have to bear in the whereas B. utilis is tetraploid (4n=56). the male catkins were smoother than monsoon season. At the lowest end The most interesting discovery in those of B. utilis. We only found a of its range it can be quite upright, this area was populations of small few trees, and only in a small corridor with fewer stems and a height to 5m. trees in two valleys at about 2,900m. between B. utilis and B. ashburneri. The bark on high-altitude B. ashb­ In both cases this was the cross-over It is unlikely that they are a separate urneri is grey-brown with a metallic zone between temperate-forest species. Therefore, we could only sheen. It is rougher than B. utilis with B. utilis and alpine B. ashburneri. What conclude that we had come across short lenticels and peels in thin we noticed first was the unusual bark a zone of natural hybrids.

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Betula unique to the Caucasus region – the reason for my visit. The exped­ ition was supported financially by the RHS Blaxall Valentine Fund, the Stanley Smith (UK) Horticultural Trust, Plant Heritage Devon Group, the Percy Sladen Memorial Fund, and the Royal Forestry Society Randle Travel Fund. Most published research on these trees has been carried out by Russian and Georgian botanists. It is not widely available in English so our knowledge is limited to plants growing in UK botanic gardens and a few translations by Russian botanist Dr AK Skvortsov. Manana Khutsishvili, head of the herbarium at Tbilisi Botanic Garden, kindly agreed to act as my guide and translator. She also organized a driver and vehicle, and arranged Betula ashburneri is a high altitude species, often forming a gnarled shrub with twisted trunks accommodation and local guides. This made the idea of roaming over Uses in cultivation habit it could be an intriguing foil for the whole country in search of a few The dark reddish brown bark of other plants, and the autumn leaf birches a more practical one. B. utilis from Arunachal Pradesh colour is an attractive yellow. In In the herbarium at Tbilisi I found would make an excellent feature in a Arunachal Pradesh it did not grow that B. litwinowii is very variable, garden. There are already trees of a beyond 5m in height and was usually hinting at widespread hybridization. similar colour in cultivation from much smaller. It would be Also, from herbarium specimens it Sinclair & Long’s collections in interesting to see how its size would is almost indistinguishable from Bhutan, such as B. utilis ‘Bhutan be affected by our milder climate. I B. raddeana, another Georgian species. Sienna’. But the Arunachal Pradesh expect it to be fully hardy. Betula medwedewii also showed a trees are a darker colour so an great deal of variation. We set off introduction from here would be Birches of the Caucasus into the hills with a slightly confused worthwhile. mountains of Georgia picture of Betula in Georgia. Both B. alnoides and B. cylindrostachya In September 2012 I set off on an We first travelled to the region of are from warmer, subtropical forest. expedition to the ex-Soviet country Samegrelo-Zemo Svaneti in the They are less suitable for northern of Georgia in the Caucasus northwest. We were searching for Europe and, although some have mountains. Georgia lies at a B. megrelica, a very rare shrubby birch grown well in sheltered areas, most botanical and cultural crossroads that is only known from one plant, current introductions are not reliably between Russia in the north and and seedlings raised from it, that hardy. The trees we saw were at Persia in the south, with Europe and grew at Moscow Botanic Garden. It quite low elevations, so it is unlikely the Black Sea to the west and the was collected on Mount Migaria and their new growth would ripen Caspian Sea and Asia to the east. It may just be a variant of B. medwedewii. enough in our poor summers to is a mountainous, heavily forested For several days we searched the hills survive the winter. land with a great diversity of plant around Mount Migaria. This Betula ashburneri, on the other life, thanks mainly to its avoidance of involved 4-hour ascents of rough hand, would make an interesting the great ice ages of the past. Its mountain tracks in a six-wheel addition to even the smallest garden. geographical position has resulted in Russian truck, followed by more With its quirky, multi-stemmed the preservation of several species of enjoyable hiking through the tree ➤

June 2013 115 plant exploration line and across mountain ridges. well, but very little is known about it. We did not find B. megrelica All B. raddeana here were multi- but did locate a small population stemmed with a height of 5–10m. of B. medwedewii on the slopes of Their bark was dark and rough on Mount Jvari at 1,500–1,700m. These young stems, turning orange, pink shrubs were multi-stemmed and 0.5– and white on older stems. 1.2m high. Found on open hillside After returning to Tbilisi we trav­ with sporadic Fagus orientalis, Picea elled southwest to the Adjara region orientalis, Sorbus graeca and Rhodo­ on the Black Sea coast. Based in dendron luteum, the shrubs showed Batumi, we travelled inland to Mount much evidence of grazing damage by Tbeti on the border with Turkey. In goats. This birch is very slow-growing, the company of local guide, David so grazing of apical growth removes Kharazishvili of Batumi Botanic the plants ability to flower and Garden, we found B. medwedewii at produce seed. This has obvious about 2,100m on open hillside with implications for the survival of this the same companion species we saw species in Samegrelo, where it must in Samegrelo. Here the shrub was be considered endangered. growing with more vigour and The other birch I found in Same­ appeared undamaged by grazing. grelo was B. litwinowii, but identific­ They were all multi-stemmed with a ation was difficult. It is thought by height of 2–2.5m. Our local guides some to be a variety of B. pubescens. confirmed that they had not seen Although some trees are this, Betula litwinowii often clings dramatically to trees bigger than this, so it would others were intermediate­ between steep mountainsides in Georgia appear to be their mature height in B. pubescens and B. pendula, which that location. They were attractive were difficult to distinguish from it. shrubs, full of upright fruiting Our next area of study was in the catkins and their leaves just starting High Caucasus mountains around to show their yellow autumn colour. the town of Stepantsminda, in north However, they were limited to one Georgia on the border with Russia. small area of mountainside in our The mountains reach 5,000m and study area. Our guides in Adjara are snow-clad throughout the year, stressed that B. medwedewii is rare, with glaciers hanging off the upper even in that district. slopes. Here we found woodlands of From Adjara we travelled inland to crooked, multi-stemmed B. litwinowii Bakuriani, a popular winter ski area. clinging to the mountainsides. At the The mountains here are barer than top of their range, at about 2,150m, on the coast, indicating a cooler the trees are no more than head climate. We found small groups of height, but lower down, at 1,900m, B. litwinowii above the tree-line, at they are much larger. The multi- 2,100–2,300m, and one area of stemmed habit at high elevations crook-stem forest. But we did not seems to be caused by the climate. find any B. raddeana here. These woodlands were fascinating I managed to collect seed from to wander through; full of twisted, B. litwinowii in many different areas. gnarled, white stems, covered with Once I have germinated the seed I moss and lichen. shall be passing cambium tissue to In this area I also found one pop­ Richard Buggs to carry out DNA ulation of B. raddeana growing on a and flow cytometry analysis. This wooded scree slope at 1,655m. This will determine ploidy levels and give Although intermediate in morphology between species is known from other B. pendula and B. pubescens, Betula litwinowii an indication of species relationships countries in the Caucasus region as can have striking white stems and levels of hybridization in the

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The bark of Betula raddeana (left) can take on orange, pink or white colours. Above the tree-line on Mount Tbeti in Georgia,Betula medwedewii (right) is shrubby wild. The same tests will be carried stemmed appearance, metallic qualities. The various provenances out with material from B. medwedewii yellow-brown bark, neat leaves and need to be grown on and analysed to and B. raddeana. We shall then have a upright fruiting catkins. Grafted see if there is hybridization. Some of much better understanding of the plants, usually onto B. pubescens, will the trees I studied were graceful and Betula of Georgia. Seedlings of become large shrubs. Plants raised delicate; qualities that are attractive Georgian birch will also be distrib­ from cuttings or seed will retain the in any garden. uted to other gardens in the UK. characteristic small size. Betula raddeana seems to be a Conclusion Uses in cultivation variable species and almost certainly Studying birches in so many wild Betula medwedewii and B. raddeana hybridizes with B. litwinowii in the locations, each with its own are occasionally available in the wild. There is a limited amount in combination of climate and geology, nursery trade. Trees of B. medwedewii cultivation so it is worth introducing has taught me a great deal about the in the National Plant Collection other provenances with different role of these trees in mountain (NPC) at Stone Lane Gardens are qualities. The trees I saw near landscapes. I have been able to see twice the height of those in the wild Stepantsminda had good white stems which plants they cohabit with and populations I studied, so it would when mature. It will be interesting the extremes of weather and terrain appear that the UK climate is kinder to observe these trees as they grow in that they cope with. to them. Betula medwedewii makes an our NPC. Will they grow as multi- In particular, it has been extremely unusual shrub, with its quirky, multi- stemmed trees or will they react to useful to observe the environmental our moderate climate by growing conditions in which B. medwedewii further information taller and straighter? And here we can thrive, and how precarious the Stone Lane Gardens is home to see one of the strengths of NPCs: a existence of this rare birch is. extensive plantings of wild-collected source of material of plants from the Betula and Alnus. Many unusual wild that might be suitable for Paul Bartlett is Garden Manager species and cultivars are available commercial production in the UK. at Stone Lane Gardens, Devon, from the nursery. Tel 01647 231311 where National Plant Collections www.stonelanegardens.com Betula litwinowii needs more study before we can assess its commercial of Betula and Alnus are held.

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