Archive for the ‘Tree Team and Propagation’ Category

Tree of the month: December 2015

Tuesday, November 24th, 2015

Abies numidica
Abies numidica foliage
What is tree of the month?
Abies numidica (Algerian fir)

Why is it tree of the month?
Critically Endangered in the wild, Abies numidica is one of the world’s rarest true firs. It only grows wild in Algeria, where threats to its natural habitat include fire, grazing and wood use for fuel. Also rare in cultivation, its form and foliage are quite distinctive when you get to know it – seek it out!

Where can I find it?
A fine specimen grows just off Holford Ride close to Loop Walk in the Old Arboretum. Another sizeable tree is on Mitchell Drive, close to the junction with Loop Walk. See the interactive map for more detail!

Dan Crowley, Dendrologist

Tree of the month: November 2015

Monday, November 2nd, 2015

Nikko maple

What is tree of the month?
Acer nikoense – Nikko maple

Why is it tree of the month?
For late autumn colour, when this species performs, it performs very well. A trifoliolate leaved maple from Japan, closely related to Acer griseum, which can also be stunning well into November.

Where can I find it?
Good examples can be found on Main Drive and in Acer Glade in the Old Arboretum. We will be adding plants from wild collected seed in the next few years.

Dan Crowley, Dendrologist

Chalara confirmed at Westonbirt

Monday, October 19th, 2015

Chalara dieback of ash, commonly known as ash dieback, caused by the Hymenoscyphus fraxineus fungus, has been confirmed at Westonbirt, The National Arboretum, this autumn. The disease was first spotted in Gloucestershire earlier this year, and so it was no surprise to find it in the arboretum.

Mark Ballard, Curator at Westonbirt, tells us more…

The risk of pests and disease is the same with any collection of trees, big or small, and after Chalara has been found to be present in woodland in and around Gloucestershire this year, we were awaiting the inevitable.

Our team first spotted ash trees with possible symptoms during our routine health and safety tree inspections, which was then confirmed to be Chalara by laboratory sample analysis very recently.

The symptoms themselves only became apparent this year and we believe the infection to be very recent. The affected ash trees at present are all in Silk Wood; they are mostly native common ash (Fraxinus excelsior), and are situated within areas of deciduous woodland.

However, through this, Westonbirt is playing a key role in supporting research into Chalara-tolerant or resistant ash trees through surveys and laboratory samples, which you can read more about below.

What are our plans for the future? We don’t expect this will have a major impact on the Westonbirt landscape. The ash trees are within deciduous woodland, and the change should be very gradual. We expect there to be lots of natural regeneration, but we will continue to assess the affected areas as time goes on.

1. How did the disease get here?
It most probably arrived in the form of spores of the fungus blown by the wind from other infection sites.

2. Who found it?
Arboretum staff first spotted ash trees with symptoms during routine inspections, and the disease was confirmed by laboratory analysis of samples.

3. How long has it been here?
Despite continual surveying at Westonbirt, symptoms only became apparent this year and it is believed that the infection is very recent.

4. Has it been found at Westonbirt before?
No, this is the first time it has been observed anywhere in the arboretum.

5. Where are the affected ash trees?
At the moment the affected ash trees have all been found in areas of Silk Wood.

6. How much ash woodland is there at Westonbirt?
Out of the 240 hectares that Westonbirt covers, there are about 50 hectares (123 acres) of mixed deciduous woodland in which ash trees are prominent.

7. Are the affected trees young or old, planted or regenerated?
The affected trees are native common ash (Fraxinus excelsior) in areas of mixed deciduous woodland within the arboretum, and most are younger, naturally regenerated (self-seeded) trees. However, one Manna ash cultivar (Fraxinus ornus ‘Savar’) has also tested positive for Chalara. We will continue to closely monitor other specimen ash trees, and send further samples for analysis as and when appropriate.

8. What are you doing about it?
Westonbirt is playing a key role in research into Chalara-tolerant or resistant ash trees. We expected that the disease would affect the arboretum eventually, so we surveyed and documented the health of all our ash trees in 2013, before Chalara affected them.

We have 27 species of ash tree, and a total of 45 taxa (species, sub-species, varieties and cultivars). We are in a strong position to monitor how each one reacts to the disease, which in turn will help us to formulate advice for woodland owners.

In addition, a significant amount of scion material (detached shoots or twigs containing buds) from our ash trees has been grafted on to rootstocks, and these will be planted out in eastern England, where the disease is most prevalent. This will aid the on-going research into tolerant or resistant ash trees. The Royal Botanic Gardens at Kew, Edinburgh and Wakehurst have also provided scion material for this project.

9. Is the disease harmful to humans or animals?
No, there is no risk to people or animals.

10. Will you be restricting public access to stop the spread of the disease? What should the public do?
No, we will not be requiring restrictions on access to the arboretum in general, or to woodland areas, but we do encourage visitors to all woodland to help limit the spread of disease by taking some simple biosecurity measures. These include not taking plant material away from affected sites, brushing soil and plant material off their footwear, clothes, wheels and dogs etc before they leave areas with infected trees, and washing these items at home before visiting another park, garden or woodland.

11. What biosecurity precautions are taken at Westonbirt to prevent the spread of Chalara or other plant diseases?
We have regular plant health training days, and the health of our trees is checked regularly. Our working vehicles, machinery and equipment are not taken off site, and contractors who come on to our site must comply with regulations for clean vehicles and equipment. We also have a quarantine facility for screening potentially infected material arriving here.

12. Is this likely to impact on the new Treetop Walkway?
No, the new Treetop Walkway is situated in an area of the arboretum which is away from ash woodland, and is next to only a few single ash trees. Any ash trees in the vicinity will continue to be closely monitored and managed, as with all nearby trees.

13. What does the future hold? Will Westonbirt lose all its ash trees?
It remains to be seen how the disease will progress. We know that older, larger and well established trees can survive exposure to the disease for some time, especially those standing in open, drier locations. We expect that the different species and sub-species represented at Westonbirt will vary in their reactions to the disease. So the overall impact should be gradual, and differ from area to area over time.

It is our intention to allow other species of deciduous trees to naturally form a mixed stand without replanting, in line with our tree management objectives. However, if a closed stand does not form, we will consider regenerating the woodland by planting alternative species in line with relevant guidance and best practice.

14. Are there any treatments or cures available for Chalara ash dieback?
There is no cure, but some chemical treatments are being investigated for their potential to protect high-value individual trees or groups of trees. However, any treatment would have to be perpetually repeated, because the fungus will remain in the area and continue to re-infect trees.

Our Forest Research agency and other research institutions are working to identify the genetic factors which enable some ash trees to survive exposure to the disease, so that we can breed Chalara-tolerant or resistant ash trees for the future.

15. Aren’t dead and dying ash trees unsafe for people?
We regularly check on the safety of our trees, especially those which border paths, buildings and other areas which people use, and prune or remove any which are becoming unsafe.

16. Why don’t you just fell/remove all the dead and dying trees?
Provided they are not becoming unsafe, we want to keep the ash trees for as long as possible to study their reaction to the disease. This is because our collection of ash species and varieties from around the world is a valuable resource for research into the disease.

In addition, all trees are important for wildlife, for example as sources of food for insects and lookout perches for birds of prey, and they continue to play an important role in a diverse landscape.

Mark Ballard, Curator

Tree of the month: October 2015

Thursday, September 24th, 2015

Carya cordiformis

What is tree of the month?
Carya cordiformis – bitternut

Why is it tree of the month?
The hickories are renowned for their autumn colour and C. cordiformis is always a hit. Attaining a considerable size and turning a beautiful yellow, it is well worth growing where space allows. It is also one of the easiest of the genus to identify, with its narrow leaflets, small, ribbed fruit and sulphur yellow buds.

Where can I find it?
The UK champion (for height) can be found not far from Mitchell Drive in the Old Arboretum (G26 on your seasonal trail map), growing alongside other fine members of the genus. Similarly, our finest specimen in Silk Wood (see photo) can be found in what was once the Hickory Collection, at the south end of Broad Drive. Along with these, specimens from last years successful seed collecting expedition to the USA will be making their way into the collection this autumn.

Dan Crowley, Dendrologist

Tree of the month: September 2015

Friday, August 28th, 2015

Heptacodium miconioides
What is tree of the month?
Heptacodium miconioides

Why is it tree of the month?
This large shrub (or small tree!) native to China flowers in September. The white flowers are attractive among the green foliage and a most pleasant sight among the early colourers in the annual autumn show.

Where can I find it?
Notable specimens can be found in Colour Circle in the Old Arboretum and in Maple Loop in Silk Wood.

Dan Crowley, Dendrologist

Tree of the month: August 2015

Thursday, July 30th, 2015

Hybrid wingnut
What is tree of the month?
Pterocarya x rehderiana (hybrid wingnut)

Why is it tree of the month?
This vigorous grower named after the great Taxonomist Alfred Rehder (1863-1949) is a hybrid between the Caucasian (P. fraxinifolia) and Chinese wingnuts (P. stenoptera). The fruit, hanging in racemes, is particularly showy at this time of year.

Where can I find it?
Our specimen at Pool Gate is quite probably one of the original hybrids, with offspring from this growing strong on Sir Georges Walk.

Dan Crowley, Dendrologist

Old plants, new tricks

Monday, July 20th, 2015

Westonbirt Arboretum’s Tree Team is working with The Duchy College to grow new plants from some of the collection’s oldest and rarest rhododendrons.

Last month Westonbirt welcomed a special delivery of 19 young rhododendrons, from four different taxa, ‘micro-propagated’ and grown for the last four years at The Duchy College’s specialist facilities in Cornwall.

Micro-propagation is a method of vegetative plant production undertaken in laboratory-like, sterilised conditions using petri-dishes and Agar gel. Tiny cells taken from the rhododendrons’ flower buds one to three months before expected flowering were used to grow roots and shoots. One great advantage is that a vast number of plants can be raised from a single fragment of plant material.

The technique means that the team can grow new plants from rare hybrids introduced over a century ago by Westonbirt’s founder Robert Holford and his son, Sir George Holford. The Holfords used selective breeding and seeds collected by famous Victorian plant hunters to create the hybrid varieties, some of which are exclusive to Westonbirt’s collection.

The team at Westonbirt is used to creating and caring for young trees and shrubs at its propagation facilities. 1,511 specimens are housed in the glasshouses, polytunnels, shade house and standing down area at any one time and can remain there from two to five years before being planted out into the collection.

Usually, specimens are either grown from seed collected in the wild (such as on the recent collecting trips to the USA and South Korea), or from techniques such as air-layering. Air layering is when small areas of the branch are wrapped with moss and rooting hormones and sealed in black plastic, convincing the plant that it is underground. The roots are then left to grow on the plant until they are strong enough to be potted. Micro-propagation is a technique generally reserved for very old, more difficult, or less vigorously growing plants.

Westonbirt had its collection of rhododendrons professionally surveyed in 2007. Many were identified then as important Victorian hybrids, and so the programme of getting these rare plants propagated began.

“The rhododendrons we are reproducing are very exciting from an historical point of view; they represent one of the most significant periods of horticultural development at Westonbirt,” said Penny Jones, Propagator.

The young rhododendrons will stay in Westonbirt’s propagation unit for around four years until they are ready to be planted out in the collection.

Tree of the month: July 2015

Friday, July 3rd, 2015

Tilia oliveri, image credit Edward Parker

What is the tree of the month?
Tilia oliveri (Oliver’s lime)

Why is it tree of the month?
The beautiful foliage with a pale underside, along with the large flower bract make this species quite distinctive. Soon to flower, this is most definitely a seasonal highlight.

Where can I find it?
The champion grows on Specimen Avenue, whilst there are other mature trees in Acer Glade and on Holford Ride.

Dan Crowley, Dendrologist

Tree of the month: June 2015

Tuesday, June 2nd, 2015

Styrax japonicus snowbell tree credit Gina Mills
What is tree of the month?
Styrax japonicus, also known as the snowbell tree.

Why is it tree of the month?
An ornamental beauty, the white, bell shaped flowers which hang beneath the branches are not to be missed.

Where can I see it?
Specimens of varying ages grow in both the Old Arboretum and Silk Wood. One close to Savill Glade always catches the eye from Main Drive, where it grows alongside the also lovely S. obassia.

Dan Crowley, Dendrologist

Tree of the month: May 2015

Thursday, April 23rd, 2015

Acer amamiense

What is tree of the month?
Acer amamiense

Why is it tree of the month?
The new foliage flushes beautiful shades of purple. It really is a treat. The new growth is also rather hairy!

Where can I see it?
We have six plants. Three in 2050 glade, two around Savill Glade and one at the south end of Palmer Ride.

Dan Crowley, Dendrologist

> Find the locations of these plants using the Interactive Map