Archive for the ‘Tree Team and Propagation’ Category

Tree of the month: May 2016

Friday, April 29th, 2016

What is tree of the month?
Abies delavayi

Abies delavayi - female cone

Why is it tree of the month?
Delavay’s fir, named for the French missionary P.J.M. Delavay who collected plants in China in the late 1800s, is a species found at high elevations in southwest China and neighbouring regions. One of a number of Abies species that have blue cones, they are particularly noticeable just now. Abies species tend to produce cones towards the top of the tree and not all do so when young, but one of our plants, planted in 2002 has been doing so for the last few years. What is more, many of the are on low branches making them ideal for a closer look, or the odd photograph!

Dendrologist Dan Crowley admiring Abies delavayi

Where can I find it?
This particular specimen (17.0253) is found between Mitchell Drive and Main Drive, close to the boundary with the Downs. Another, from the same seed source, grows along Broad Drive, though doesn’t form cones so reliably.

Abies delavayi - whole tree

Dan Crowley, Dendrologist

Tree of the month: April 2016

Friday, April 1st, 2016

What is tree of the month?
Acer hyrcanum

Why is it tree of the month?
Described in the Hillier Manual of Trees and Shrubs as a small tree. Our specimens in Silk Wood are slightly larger than this. As early plantings in this part of the arboretum, our two largest trees have stood the test of time and continue to look the part. They flower wonderfully in April and are not far off just now! Emerging just before or with the leaves, the entire crown is adorned with the goodness of spring. A beautiful sight!

The species is native to the Balkan peninsula, the Caucasus and parts of Western Asia. Like many species from this part of the world, it is quite happy at Westonbirt! It is closely related to the more commonly seen sycamore, Acer pseudoplatanus, but is far more showy in spring. It is believed to have been in cultivation since 1865.

Where can I find it?
Our two largest trees are in Silk Wood and can’t be missed along Willesley Drive and Broad Drive. Close relatives of the species can be found throughout the site, as part of the Plant Heritage National Collection of Acer.

Dan Crowley, Dendrologist

Tree of the month: March 2016

Tuesday, March 1st, 2016

What is tree of the month?
Quercus canariensis (Algerian Oak)

Why is it tree of the month?
Described by W.J Bean as ‘one of the handsomest of all oaks’, Quercus canariensis stands out in a crowd, and particularly at this time of the year. Being semi-evergreen it retains its leaves through winter, sometimes even up until fresh ones emerge in spring.

Though specific epithets often give an indication of origin, this is not the case with Quercus canariensis, as it is native to North Africa and the Iberian peninsula, and not the Canary Islands! In cultivation in Britain since at least 1845, our oldest specimen is one of the original plantings along Broad Drive, dating from around 1875. It grows in what was known as the European Oak Collection, alongside a number of other Quercus from this part of the world.

Variable in appearance the wild, our largest trees are considered to be the ‘English form’. That is to say they are of the typical appearance of trees encountered in cultivation in this country, which (as with many species grown in gardens) is not representative of the species in the wild. Younger trees in the collection are from known wild origin in Spain – observe the differences for yourselves!!

Where can I find it?
The largest example in Silk Wood is along Broad Drive (see above, it is also part of the TreeQuests app so you may encounter it if you take a trail using that!) and in the Old Arboretum is close to the north end of Holford Ride and Loop Walk. Younger, wild origin examples can be seen close to Waste Gate, in 2050 Glade. You can find them all on the interactive map.

Dan Crowley, Dendrologist

Tree of the month: February 2016

Tuesday, February 2nd, 2016

Picea brachytyla

What is tree of the month?

Picea brachytyla – Sargent spruce.

Why is it tree of the month?

Hailing from the high mountains of Asia, Sargent spruce is among the most attractive members of the genus. The two bright white, coalescing stomatal bands on the undersides of the needles are a stand out character. Named after Charles Sprague Sargent, former director of the Arnold Arboretum, Massachusetts, USA, it was first introduced by the Gloucestershire born Ernest Wilson. Relatively common in botanic gardens, the species is listed as Vulnerable on the IUCN red list.

Where can I find it?

Fine, large specimens can be seen on Morley Ride in the Old Arboretum and in Sand Earth, Silk Wood. Younger examples can be found close to Loop Walk in the Old Arboretum and along Willesley Drive (var. complanata) in Silk Wood.

Dan Crowley, Dendrologist

Baby giant

Tuesday, February 2nd, 2016

One of the first plantings of 2016, this young Giant Redwood (Sequoiadendron giganteum) was planted on the downs area of Westonbirt. It is the first Giant Redwood of Westonbirt origin to be successfully germinated and grown on site.

Cairn Hurst with a Giant Redwood.

With a success rate of around 25% for seed collected from Redwoods in their native habitat of California, getting home-grown seed to germinate was never going to be an easy task. Keen to give it a go anyway in late autumn 2013 I gathered a handful of cones from the Old Arboretum and decided the best approach would be to replicate conditions found in the wild.

Looking to mimic a forest fire (Giant Redwoods in the wild are protected from fire by their thick insulating bark) I gathered a small pile of redwood twigs to which I set fire. I then placed several cones and some loose seed on a sheet of perforated tinfoil and held it over the fire for a couple of minutes, taking care not to turn the seed to charcoal!

The smoke, as well as heat from the fire, is thought to play a part in breaking seed dormancy. Both loose seed and seeds from the cones were collected and placed in a container in the fridge for a month, a process known as cold stratification; whereby winter conditions are replicated in order to break seed dormancy.

After the month had passed I met with Westonbirt’s propagator Penny Jones to pot up the seed and give them the best possible start in life. We filled two pots with seed compost and scattered the seed evenly on the surface. A fine covering of washed grit was added to help reduce moisture loss while letting the soil breathe. We watered both pots, moved them to the greenhouse and crossed our fingers in the hope that in a couple of months a few young Redwoods would appear.

A couple of months later only one seedling had germinated. One seedling from some two or three hundred seeds! During the following two years Penny expertly looked after the little tree, potting it up a few times and moving it from the greenhouse to the polytunnel to the shade house, where it slowly acclimatized to the weather outdoors and grew at an astonishing rate.

On Tuesday 12 January 2016 Ken Waite and I planted the young Redwood on the downs area near the Welcome Building. It has grown over two feet in two years; hopefully it will grow at the same rate for many years to come and become a welcoming figure for everyone visiting Westonbirt.

Cairn Hurst, Arborist, Westonbirt Tree Team

Arborist Cairn Hurst successfully germinated Giant Redwood seed by replicating the forest fire conditions of their…

Posted by Westonbirt Arboretum on Tuesday, 2 February 2016

The end of a big black pine…

Wednesday, January 27th, 2016

You may notice some temporary traffic lights outside the arboretum today and tomorrow (27 and 28 January 2016).

We have arranged for this traffic management to be put in place as we need to work above part of the A433 road that runs along our boundary.

The work at height in question is the removal of a black pine (Pinus nigra), specimen number 02-0226 to be specific.

We have been monitoring this particular tree for several reasons and over many years, as part of our tree safety management programme.

The tree is within zone one, which is an area with a high ‘target value’, such as places with high public use, paths and rides, adjacent to buildings, visitor centres, car parks, or as in this case near a public road.

The decision to remove any tree is one that is never taken lightly, and an assessment of risk is always based on the following:

  • The identification of hazards that pose a significant risk – defects or factors that could result in failure and have the potential to cause harm
  • Quantifying the risk associated with the hazards identified should be estimated by considering the following factors:
    • The probability of tree failure depending on the severity of the hazards identified;
    • The likely consequence of tree failure, which will depend largely on the dimensions of the overall tree or the particular limbs identified as hazards;
    • The occupancy of the site or level of use – proximity and business of paths etc.

This is an old black pine that has graced the Old Arboretum opposite the school gates since it was planted by the Holford family.

However, it is now in poor condition with some physical defects:

  • It has a major lean and over-hangs a main road;
  • There are early signs of root plate instability;
  • It is multi-stemmed and has been supported with cable bracing in the past which requires frequent inspection.

Due to this combination of factors, we have judged that it has now reached the end of the line and needs to be removed.

We are fortunate enough to have a highly skilled team of arborists at Westonbirt who are undertaking this tree work in a safe and efficient manner.

On a positive note and as always, this very same team will look to plant a young specimen when the ground settles here in due course.

Mark Ballard, Curator

Tree of the month: January 2016

Tuesday, January 12th, 2016

Oriental planeWhat is tree of the month?
Platanus orientalis (oriental plane)

Why is it tree of the month?
A parent of the often seen London plane, Platanus x hispanica (the other being Platanus occidentalis), the oriental plane is attractive in leaf and equally so without, with its patchwork bark exposed and fruit dangling from the branches. Attaining large proportions, it has more of a weeping habit than the hybrid and plants will layer, given the opportunity. In cultivation since the sixteenth century, it is native to southeastern Europe and western Asia.

Where can I find it?
Significant specimens can be found in the Old Arboretum on Mitchell Drive and Main Drive. Another characterful example can be found in Silk Wood on Willesley Drive close to the junction with Green Lane. Younger plants are also dotted around the collection, including known wild origin specimens from Cyprus, Lebanon and Turkey.

Dan Crowley, Dendrologist

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