Searching for Birches

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 ➤ June 2013 113 plant exploration 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. 114 June 2013 PlantsmanThe Betula unique to the Caucasus region – the reason for my visit. The expedition 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.

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