Archive for the ‘Tree Team and Propagation’ Category

Tree of the Month: August 2016

Thursday, July 28th, 2016
...with Dendrologist Dan Crowley.

…with Dendrologist Dan Crowley.

What is tree of the month?
Sorbus ‘John Mitchell’

Why is it tree of the month?
Notable for its huge round leaves, this whitebeam, Sorbus ‘John Mitchell’ is a not uncommon sight in cultivation and has its origins here at Westonbirt. It was long considered to be a selection of Sorbus thibetica but is in fact something quite different. One of its parents is likely to be a round-leaved form of our native Sorbus aria and the other is as yet unknown, though is likely of Asian origin. The hybrid first arose here (precise date unknown!) and was named for the first curator of Westonbirt, William John Mitchell.

Where can I find it?
We currently have two trees in the collection (we are keen to grow more!). Our largest stands close to Mitchell Drive (G25 on the map) and a smaller but equally beautiful tree is located close to another of our famous trees, the Holford pines (Pinus x holfordiana), near Holford Ride (E24).

Dan Crowley, Dendrologist

Tree of the month: July 2016

Monday, July 4th, 2016

What is tree of the month?
Stewartia monadelpha

Dan Crowley
Why is it tree of the month?
Stewartia is a member of the tea family, Theaceae, as suggested by the solitary white flowers that appear in summer. S. monadelpha has the smallest flowers in the genus and these are borne in some profusion on branches throughout the crown. The flowers have conspicuous bracteoles which are a useful aid to identification and the tree is also notable for its reddish bark which peels.

Stewartia monadelpha
The genus was named after John Stuart, Earl of Bute (1713-92), though Linnaeus was misled into spelling the generic name ‘Stewartia’ rather than ’Stuartia’ which led to some confusion around which should be used. Though there was widespread use of ‘Stuartia’ in the 19th century, the accepted spelling is Stewartia, as found in modern botanical texts.

Stewartia monadelpha
Where can I find it?
Currently we have just two trees here at Westonbirt. These are both on Circular Drive in the Old Arboretum and enjoying the acidic conditions they are afforded in this area.

Dan Crowley, Dendrologist

Tree of the month: June 2016

Tuesday, May 31st, 2016

Dan Crowley, Westonbirt's dendrologist
What is tree of the month?
Aesculus indica (Indian horse chestnut)

Indian chestnut - whole tree
Why is it tree of the month?
The Indian horse chestnut is notable for both its bronze new foliage (see the whole tree photo!) and flowers in panicles that provide an arboreal highlight as we move in to the summer months. The leaves turn a glossy green and the showy flowers usually appear in June to July and look as though they won’t too far away this year! In maturity the bark peels in long strips.

Indian horse chestnut - leaves and flower headsIndian horse chestnut - bark
The species is native of the north west Himalaya and was introduced in 1851. It is seen far less frequently in the UK than its European relative, Aesculus hippocastanum, and its later flowering time than this species is an added attraction.

Where can I find it?
Our largest example can be found on Loop Walk in the Old Arboretum and an equally interesting example of multi-stemmed habit is found close to the relatively new path which links Mitchell Drive and Main Drive in the Old Arboretum.

Dan Crowley, Dendrologist

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