This Week:
What’s not to like – clear skies, just an occasional puffy white cloud, no airplanes, the sounds of gentle breezes in the trees and everywhere the chatter of birds feeding their young … but my goodness the poor Common needs rain.
Sightings this week include large red damselflies fledgling wrens and great spotted woodpeckers.
Superb capture through the lens of Andrew Wilson shows a hungry great spotted woodpecker chick being fed by a no doubt very tired parent.
Poplars and willows are in the same family: Salicaceae. Like willow, they are fast growing trees that thrive in damp soils. Poplars are usually dioecious – male and female flowers are found on separate trees. They are wind-pollinated and the white ‘fluff’ you see are the seeds of the female trees. Pollen is produced on the male trees much earlier in the season. Poplars tend to hybridise easily and often grow larger than their parent trees. There are at least thirty species of poplar native to the northern hemisphere. On Barnes Common, there are good examples of four poplars in various conditions:
Black Poplar (Populus nigra) is one of our most endangered native trees. There are estimated to be just 7,000 native black poplars, of which only 600 are female.[1] Native to South-East and Central England, poplars seed well. However, for seedlings to germinate and survive, they need clear damp soil which does not flood or dry out. Changes in farming and river management practices over the past 150 years few trees have impacted on suitable open habitats. Growing relatively easily from cuttings, farmers would put in a ‘truncheon’ (long cutting) where a tree was wanted. Using cuttings in this way created more trees but less genetic diversity and many of the trees today are clones. Fifteen years ago, FoBC planted four (male) saplings from the Royal Parks. One continues to flourish today. The 25% take rate shows how important it is not only to have moist soil but also good light. Black poplars are important hosts for phytophagous insects, with one study recording 189 different species.[2]
DNA testing of some of the trees along the Thames towpath locally has shown a considerable degree of genetic diversity, as well as some female trees. Here on the Common, we have two mature black poplars (most likely planted after the railway was built). One is in near terminal condition near Queen’s Ride and one needing ‘haloing’ (work to reduce competition to its crown from surrounding trees) immediately south-west of the station. Both are scheduled for DNA testing.
FoBC is involved in an important project to propagate from these genetically diverse, local trees. In February 2019, Phase I involved taking eighty cuttings from eight different clones, with excellent results: seven of the clones had an 80 – 100% take rate, with one achieving 70%, which is encouraging. In February 2020, Phase II saw a second set of cuttings taken from a further twelve clones growing locally. The Phase I established ‘whips’ were lifted to a nursery created by conservation staff and volunteers, where it is hoped they will continue to thrive over the next year or two. This is a significant programme with the potential to increase the genetic diversity of this endangered tree and for lessons to be learned along the way.
Lombardy Poplar (P nigra ‘Italica’) was brought from Turin to Essex in 1758. Cuttings were soon growing fast in all parts of the British Isles. It was often planted in avenues, perhaps as a reminder of the ‘Grand Tour’ taken by so many landowners to Italy.
The traditional tall, narrow, tapering tree is male. The female ‘Gigantea’ is less common, with bigger branches which fan out to a broad top.
There are examples of the male tree scattered around the Common (as well as just off it) with a good example at the edge of van Buren’s Meadow and others on Station Road, at Vine Road Rec and on railway property at Vine Road.
All will have been planted.
Grey Poplar (P. x canescens) is now generally accepted to be a hybrid of white poplar P.alba and aspen (P.tremula). It is very similar to white poplar and bark can be difficult to distinguish. The bark near the base of older trees can become deeply rutted – even an impressive dinosaur-like plate.
The leaves have similar white down when first bursting, giving grey poplar a silver-white sheen in Spring, turning to grey-green by high Summer. White poplar leaves are more triangular and tooth-edged whilst Grey Poplar leaves are rounder with deeper cut lobes.
Grey poplars can grow close to 40m tall, almost twice the size of white poplar or aspen. It does not take much breeze for the grey poplars to make their quivering sound and they can howl well in a gale. There are grey poplars growing in woods opposite Woodlands Road which can flood seasonally. There are no white poplars on Barnes Common.
Hybrid Black Poplar (P. x canadensis) is a cross between P. nigra and the North American Eastern Cottonwood, P. deltoides. There are many variations of this hybrid growing in and around Barnes (some planted 150 years ago). Many of the largest trees are suffering decay and where these are of safety concern, such as near the Towpath, they have had to be cut back if not cut down. The size of the bracket fungi growing near the base of these trees is indicative of the spread of rot within the trunk. We have in the past decade lost three on the Common, the most recent during the winter of 2019/20. There is one currently left as standing dead-wood and one in decay near van Buren’s Meadow (see photo), but the splendid specimen just south of the station survives. However, this tree, overshadowing two busy footpaths, must be watched carefully. The upper limbs were pollarded some years ago and the regrowth is now reaching critical weight so will need re-pollarding if branches are not to fall.
Pollarding: there is a lesson in this for all large trees – in gardens as well as parks: pollarding not only reduces a tree’s size, the weight on branches and lets in more light, but it can also extend a tree’s life as the roots survive longer than branches exposed to the air. Trees which might only last a few hundred years can live to a thousand or more. However, each branch cut will give rise to several new shoots – so effectively the cut area has to support the growth of maybe five or six young trees – and after several years the strength of the knuckle will not be able to bear the weight and the stresses of high winds. Therefore, once this intervention is started, trees are likely to need further attention every few years.
Mythology: In Greek mythology, following Phaetons’ fatal attempt to drive Apollo’s chariot, his sisters made such a fuss mourning him that the gods turned them into black poplars. Closer to home, the fallen red catkins of P nigra have been called ‘devil’s fingers’ and should never be picked up. A crown of aspen was thought to give protection for those visiting the underworld and such crowns have been found in excavations at ancient burial sites.
Uses: Black poplar was often used for floorboards, as it is relatively fire resistant; and for base boards for carts as it is strong and springy. It is a strong, light wood used historically for shields and more recently artificial limbs. Many black poplars were pollarded, with staves used for roofing, bean poles, pegs and basket making. The bark was used in tanning. The slow-burning properties makes the wood suitable for matches as well as for veneers, and for making ‘rough’ boxes such as wine crates or wooden fruit baskets. Hybrid poplars have been tested in biomass projects, using short rotation coppicing, due to their rapid growth rates.
Next week: Conifers
M Hildesley 1st June 2020
Images: M Hildesley
Great Spotted Woodpecker Image: A W Wilson
[2] Kennedy, C.E.J. & Southwood, T.R.E. (1984) The number of species of insects associated with British Trees: a re-analysis.