iCONic tree trail – Part 4

This is the fourth in a six-part series about how Perthshire Big Tree Country is helping to save internationally threatened species of conifers. Felicity Martin visits the Royal Botanic Garden Edinburgh to discover how collected seeds become tomorrow’s trees and learns how Perthshire’s forests are providing a safe habitat.

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30 June 2014

Propagating threatened trees

Japan 2013 expedition

In 2013 the iCONic project undertook two major plant hunting trips, in January to Chile (see Part 2) and in the autumn to Japan to collect the seeds of threatened conifers for ex-situ cultivation.

The Japanese Douglas-fir was one specific target of the Japan trip, as it is one of the very few temperate conifer species that has not been grown at Royal Botanic Garden Edinburgh since its establishment in 1670. However, collecting it was a major challenge, as Tom Christian, the iCONic project officer, recounts.

“It grows in very remote parts of Japan with a dramatic topography of steep sided river valleys. Most of the forest is heavily protected making it difficult for our Japanese colleagues to obtain for us the necessary permission to collect. In the UK this is a small-growing species, nothing like its famous cousin, the American Douglas fir, but in Japan we were faced with the extraordinary sight of gigantic trees, about 50m (164 ft) tall.

“One of the challenges was that they were so big they took so long to climb. Having spotted two trees from across the gorge, we clambered down, picked our way across the river, and climbed up an incredibly steep, loose slope to their colossal trunks. Our two tree climbers, Will and Kevin, spent nearly half an hour trying to get lines into the lower branches, then as long again pulling themselves up to the tree tops, where the cones grow at the tips of the branches. It took half an hour to gather cones then another half an hour to descend. And in the end only Will’s tree had cones, but it was impossible to tell until reaching the top!”

Processing cones

When I visited Tom at the Royal Botanic Garden Edinburgh, he took me first to the potting shed and pulled out of store a cloth bag containing Japanese Douglas-fir cones. They had been through the hot drying room, to open the cones so the seeds could be extracted. Tipping them out onto a workbench, he described some of the issues they encounter.

“We only collected from one tree so I can’t generalise, but the vast majority of cones have been parasitised, which could be contributing factor to the species’ decline. We found intact at most 60 to 70 seeds, which, depending on how well they germinate, could produce 20 to 50 plants. It’s not much, but still enough to experiment and distribute them to sites where we feel they stand the best chance of success.

“Historically Japanese Douglas-fir has been planted in the south of Britain where it is relatively dry, but having seen where it grows in Japan we think it would prefer the cool, very wet climate of the west of Scotland or parts of Ireland. By scattering plants through a range of sites we will learn an awful lot more about it, and potentially produce much larger trees than have been seen in the UK before.”

Tom also showed me Koyama’s spruce cones. They were fortunate to collect them on the Japan expedition in 2013, because the species is critically endangered. It is estimated that there are fewer than 1,000 mature individuals left in the wild. It occurs in such a small area of mountains that a typhoon in the wrong place could knock out a significant portion of the global population in one go. They did see some regeneration, but also considerable damage from Sika deer.

From seed to sapling

We followed the progress of the Koyama’s spruce to the Royal Botanic Garden Edinburgh’s outdoor seed frame, where its seeds were waiting to germinate. The seeds are planted on a mixture of loam-based compost and coir (coconut fibre), patted down then covered with a light sieving of the same mix. Hen grit is put on the surface to suppress weeds and prevent heavy rain from disturbing the compost.

The two long seed frames were nearly full of seed pots, with those from the 2013 iCONic expeditions to Chile and Japan stretching for several feet. Some of the Chilean seeds, planted in February 2013 had germinated, but for others it could take two winters to break down dormancy in the seed.

Often only some seeds are planted soon after collection and the rest stored for planting in subsequent years or distributed to other botanic gardens. Generally, the larger the seed the shorter its life span. Those of the Japanese umbrella pine are relatively big, about the size of flattened capers, and likely to deteriorate more quickly in storage. So all of the 943 seeds extracted from cones collected in 2013 were sown the same year. If 50% or more germinate, it will create a wonderful problem of where to put them all.

As soon as the seeds have germinated, they are moved into a greenhouse, which is heated overnight to stop the temperature dropping below freezing in the winter months. Each seedling is pricked out into a small pot then repotted into larger pots as it grows.

Using ‘airpots’ helps the plants to develop a really good fibrous root system with no swirling around the base of the pot. The surface of the pot is covered in outward projecting cones, open at the ends. When the roots approach the openings they stop growing outwards and branch further back. The pots, which are manufactured from recycled plastic at nearby Prestonpans, come as a flat pack and can easily be removed without disturbing the plant by unclipping and unrolling.

Once the trees have reached sufficient size to be planted out, they are moved to a netting shade tunnel to adjust to outside conditions. From here they are distributed to their planting sites.

 Forest plantings

One challenging species to grow, the Chilean plum yew, has been planted at Craigvinean Forest near Dunkeld. The female cones are a small plum-like fruit, with a seed surrounded by a sweet fruity flesh that is used locally in Chile to make jam. In the wild, the seed has to pass through the gut of a bird before germinating. In cultivation, temperature and moisture must be manipulated to break that dormancy.

The species is endemic to Chile where its fragmented populations are threatened by hydro-electric schemes, grazing and the conversion of forests to exotic plantations. It is not widely cultivated in Britain and not many mature individuals are known, partly because it is difficult to establish. It cannot tolerate cold drying winds or wet ground.

The iCONic project is experimenting by planting the Chilean plum yew at a variety of sites, and has noticed that it seems to do well if planted among bracken, a species which prefers drier sites but also possibly because it is finding a beneficial mycorrhizal association. It was planted at Craigvinean Forest – one of the first iCONic sites – in 2008, as part of the pilot phase to help establish protocols. Along with the unusual Bornmueller’s fir, it is growing under a stand of Scots pine, which visitors pass on their way to Pine Cone Point.

Craigvinean Forest is part of Tay Forest Park, a series of Forestry Commission Scotland woodlands at the heart of Perthshire. Charlie Taylor, the FCS’s local Forest District Manger, is delighted that the Forest Park is paying a role in the iCONic project.

“The history of experimental planting at Craigvinean goes back to the 18th and 19th centuries when the Dukes of Atholl, planted millions of larch here and at Craig a’ Barns on the opposite side of the River Tay. They saw the potential of the species, newly introduced from Europe, as a commercial timber crop.

“We are glad to be continuing that tradition by providing sites for conifers from more distant parts of the world, and working with the iCONic project to do further plantings in Craigvinean and the wider forest estate in Perthshire, including a grove of monkey puzzles that we will put in next year.

“The forests here at Craigvinean, and at Allean, Drummond Hill and Weem, are providing a sheltered environment where there is the space to create naturalistic groves of threatened species. All these public forests have way-marked walks, so people have the opportunity to see the trees as they develop.”

In next month’s article we will look in more detail at how the iCONic project chooses sites for planting, and we’ll examine the long-term care needed for trees to grow to maturity.