Wednesday, 16 September 2015

Plantations : woods, forests or something else?

Stand of trees at New Fen - geograph.org.uk - 636879
Poplars at Lakenheath
CC-BY-SA 2.0   © Copyright Alison Rawson and licensed for reuse under this Creative Commons Licence.
One type of woodland area I have alluded to a couple of times in the past are plantations (see here and here). I've always been frustrated at not having found good illustrations, but in the past couple of weeks I've noted a few which either already have good open images available or I've been able to snap a picture myself.

Plantations run the gamut from small areas to fully-fledged forests. In general what connects them is that the trees are planted in orderly rows, and the plantation has an expected lifetime, after which the trees will be harvested or replanted. Photographs enable some of the variety to be shown. In turn this should highlight the sorts of information we might want to capture by OpenStreetMap tags.

Three Plantations

Ratby Burroughs

Planted trees at Ratby Burroughs
CC-BY-SA 2.0   © Copyright SK53 and licensed for reuse under this Creative Commons Licence.
The first plantation I came across was a relatively newly planted extension to Burroughs Wood which is a Woodland Trust reserve.and part of the National Forest. These plantings are designed to add additional woodland cover quickly, and are certainly fairly common on Woodland Trust sites. There's always a bit of controversy about how necessary such plantings might be. Apparently deer populations in Leicestershire are sufficiently high as to cause real concern about natural regeneration of woodlands. However, a deer-proof fence on land adjacent to an existing wood might allow the wood to extend itself naturally.

As can be seen the trees are perhaps 10-15 years old, and are reasonably well established. I think it is unfortunate that they were planted in straight rows. Many of the oaks had dead branches suggesting that the trees need thinning, or perhaps some will die (self-thinning) and then the obvious grid will be lost. Perhaps because the trees were somewhat stressed they were absolutely wonderful for finding plant galls.

This type of planting is common in other situations: in country parks; on post-industrial sites as part of remediation schemes; as screens for factories, business parks, busy roads (or even on nature reserves); and on newer parkland golf courses. Newer plantings can often to spotted on aerial photos before the canopy closes over because they show up as closely packed green (or, in Autumn, yellow-orange) dots.

Hope Valley, Derbyshire

Small plantation of Poplars at moribund waterworks.
Hope Valley, The Peak District
CC-BY-SA 2.0   © Copyright SK53 and licensed for reuse under this Creative Commons Licence.


The second I came across was rather anomalous in several ways.

It was next to a stream, Peakshole Water, in the Peak District National Park. Although the actual altitude was quite low, this is an upland area, with high rainfall. Woodlands tend to be dominated by Ash or Sycamore in the immediate vicinity.

Black Poplars, Populus nigra (or their hybrids, Populus x canadensis) are certainly not a tree species one expects to encounter: although I did see a few Aspens (Populus tremula) which looked far more in place a little further along towards Hope. Poplars tend to quite short-lived, and these trees have the look of senescence to them. Given that the trees look very similar I would imagine they are all clones of a single stock.

It is now possible to use  the National Library of Scotland's collection of out-of-copyright 6 inch maps for England and Wales to work out when these trees were planted. They seem to be planted entirely within an area which is marked as a waterworks (filter bed) on the older maps, but they do not appear on the map surveyed in 1938. Presumably they were planted post-WWII. It is difficult to surmise for what purpose. The original plantation would have consisted of less than 50 trees, and it's not a particularly congenial location. Perhaps this was an early environmental remediation strategy.

Lakenheath Fen


Poplar plantation at Lakenheath RSPB Reserve, Suffolk
CC-BY-SA 2.0   © Copyright Hugh Venables and licensed for reuse under this Creative Commons Licence.

The last group of plantations were ones I saw from the train from Ely to Thetford. These are rather well-known. Originally planted to provide wood for making match-sticks they are now part of a major nature reserve run by the RSPB at Lakenheath Fen. I had no idea that the train ran so far from the village of Lakenheath, or that the station was on the doorstep of the RSBP reserve (so scope for a later visit next time I'm in Cambridge). Once the plantations came into view they were very obviously different from other woodlands seen from the train.

The plantations are of a hybrid Black Poplar cultivar. Poplars, like other trees in the Salicaceae, the Willow family, do not grow heartwood. This means that they can grow very rapidly, but equally are short-lived and less robust than trees with the additional structural rigidity gained from heartwood. In this case they were planted by the firm Bryant & May with a view to making matchsticks (someone noted on the walk at the Weingartnermoor that I seemed obsessed with uses of particular trees)

Typical Poplar plantations are planted with the cultivar favoured at the time of planting; a cultivar which may no longer be available by the time the trees mature. There is widespread research aimed at producing new varieties, at least in part supported by the FAO's International Poplar Commission. Such plantations can be found all over Europe, in the northern parts of the Indian sub-continent, and no doubt elsewhere. In many parts of Europe they can be easily recognised in winter, not just because the trees are obviously in rows, but usually because one or more are hosts to Mistletoe (Viscum album).

At Lakenheath, they are known for supporting the only regular breeding site of the Golden Oriole (Oriolus oriolus) in Britain. Anyone wanting to know more about the reserve and it's history should consult a recent article in British Wildlife magazine (although this has little to say about the poplars).

Elsewhere


The Slate. - geograph.org.uk - 452589
Forestry Plantations around The Slate and Killypole, Kintyre, Argyll
Steve Partridge CC-BY-SA-2.0, via Wikimedia Commons
In Britain by far and away the largest area covered by plantations are forests of conifers. These have been planted all over the country since the creation of the Forestry Commission, but are commonest on former moorlands and rough grazing in the uplands. As I've said before these form the archetypal images of forests in the UK.

Eucalipto Galicia
Eucalyptus plantation near Viveiro, Galicia
Source: Martin253 via Wikimedia Commons, Public Domain
Forestry plantations are no doubt common elsewhere in Europe, although in many places they will be part of an integrated approach to forest management which is rather different from that seen in Britain and Ireland. However, in Spain during the Franco era there were considerable efforts to plant fast growing trees as plantations: notably of various Eucalyptus species, with perhaps the commonest species being E. globulus.
Oilpalm malaysia
Malaysian Palm Oil Plantation
Source: Wikimedia
Several types of trees are notable for being planted extensively in the tropics: for example, Rubber for its sap, Teak for timber, and Coconut Palms for oil.

The current tagging for orchards does allow for Palm plantations to be tagged as orchards, although they don't look very like typical orchards. At least around Lumut in Malaysia these appear quite characteristic in aerial photos. (As an aside, using landuse=orchard for Dehesa wood pasture seems going too far).

Conclusions

Plantations exist throughout the globe.and are a significant part of the world's woodlands. Many plantations are of economic importance, and most probably have an adverse effect on both local and global biodiversity. Furthermore they often differ in many ways from conventional ideas of woodland: forest plantations in Britain are often impenetrable for walkers, the ground layer is often absent.

I therefore think there are a wide range of reasons why we might want to be able to distinguish them from other woodlands on OpenStreetMap. To date I have marked a very small number using plantation=yes, but this is very much a placeholder tag and I'm open to other suggestions. At one end of the spectrum orchards and olive groves can be regarded as particular types of plantations. To an extent there is a continuum between traditional orchards and many large scale woodland plantation. In addition there are issues as to appropriate tagging when trees are planted for crop products other than timber and wood.

I also believe that we should keep a distinction between a plantation and newly (or obviously) planted woodland (just as we will retain a distinction between an orchard and a plantation). I think the key criteria for identifying a plantation are:
  • Monoculture (or nearly so). Trees are all of a single species. In some cases a mix of species may be planted around the edge of the plantation (for instance in modern forestry practice in Britain)
  • Single Age Class. Trees are obviously of a similar size (and therefore age). Evidence of sapling growth will be minimal.
  • Planted in Rows. As most plantations either have a commercial objective, or are planted in such a way to minimise costs, they tend to be planted in long rows. This not only assists the process of planting, but also harvesting.
  • Short to Medium term lifecycle. The trees of the plantation are expected to be harvested within 20-50 years (less if for Christmas Trees). If the plantation is producing a crop (as in Oil Palm plantations), the trees will be replaced in the same time-frame.
This definition therefore tends to exclude areas of woodland planted to enhance amenity or for environmental remediation. In these cases I have from time to time used planted=yes to identify such woodlands. In practice it would be nice to have a planted_date key as well.

If you are interested in developing on these ideas I suggest using the OSM tagging mailing list for further discussion.


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