Populus nigra sub sp. betulifolia, the native black poplar, is Britain’s rarest native timber tree, which largely due to human interference is no longer able to regenerate naturally from seedlings due to the absence of water flooded meadows required for germination and seedling establishment . Without co-ordinated management there is a real risk that it could become extinct.
Herefordshire has one of the best populations of these trees, however there are currently only 200 mature trees recorded in the county. Many of these are veteran or ancient trees and a relatively high number are pollards. The majority are the product of vegetative propagation therefore genetic diversity is likely to be compromised. The clonal composition of these trees is not known.
Black poplars are dioecious – that is, there are male and female trees. Female trees are very scarce, as they have been thinned out or cut down historically due to large amounts of fluffy seeds produced which were deemed a nuisance.
All the trees we have now were planted rather than naturally occurring, and are most likely to be the product of vegetative propagation of a limited number of clones.
Actions required to safeguard the future of Populus nigra
- Identify and Record existing BPs in NW Herefordshire
- Care of existing trees – advice and possible tree surgery
- Propagation and planting of new trees
Identification and Recording
Accurate identification of true native black poplars is an essential first step , however this is not straightforward as there are a number of hybrid forms that can be difficult to distinguish from the native tree. We suggest the following steps to ensure accurate identification and recording:
- Existing trees in the parish are identified by someone with training and experience in differentiating the native tree from the various hybrids
- Trees so identified as native BPs are then verified by an expert. We propose to DNA fingerprint 50 trees through the Forest Research clonal identification service to ensure that propagation material (see below) is based on a broad range of clones.
- The details of these trees are then recorded – see Appendix A
The details of the tree are entered on the Woodland Trust’s “Ancient Tree Inventory” website – this will ensure the record is seen and checked by the county verifier for ancient and veteran trees. It will also allow accurate mapping of the tree and uploading of photographs.
The record will also be added to the county database of native black poplars held by Herefordshire Wildlife Trust.
- A local record of the tree is created as a simple computer file which is shared with the Parish Council thus ensuring information is not lost in the long run, and is available to future Tree Wardens or other interested persons – see Appendix B
- A regular check of trees, ideally annually, and updating of the record to include any changes eg lost trees.
Care of existing trees
As many of our older tree are pollards there is a risk of overgrowth and collapse of the tree if not re-pollarded at intervals – there are a number of examples of trees succumbing to this fate. This operation in itself can cause the tree to die if not undertaken by an experienced tree surgeon – again there are examples of trees being badly pollarded e.g. by contractors to power companies, which have died as a result.
The new growth which occurs following successful re-pollarding is the perfect source of material for truncheons.
Mature maiden trees have a propensity to lose a bough in strong winds, which can cause concern if the tree is in a publicly accessible location. In these circumstances, a crown reduction of the tree can preserve the tree and reduce risk of injury. There is a well publicised local example of the above scenario which nearly caused the loss of an historic veteran tree due to ‘Health and Safety’ concerns, fortunately a compromise of crown reduction preserved the tree.
We suggest a simple written management plan for each identified tree to be included in the local record – see Appendix B
Propagation of new trees
Populus nigra is fairly easy to propagate (but see below for siting of new trees), there are two methods which can be successfully used
- Cutting and planting of truncheons – these are six foot lengths of two to four inch diameter young growth, cut and planted in-situ in late winter. Use a crowbar to make a two foot hole, taper the end of the truncheon and knock in with a lump hammer
- Cutting young thin shoots in summer, eighteen to twenty four inches in length and planting in a pot or garden bed to root, for planting out later.
It is essential that truncheons and cuttings are taken from trees which have been identified as above and are on the Herefordshire list of true native black poplars. Ideally cuttings should be taken from local trees to preserve any local genetics. The provenance of new plantings should be recorded, and once established as a viable tree it should be added to the local record. The county record currently includes trees once over ten years of age.
Siting of trees – P. nigra will thrive if planted in optimum conditions, but will probably fail in the wrong situation. An old name for this species is ‘Water Poplar’, which is a good clue. A wet place with a good depth of soil is ideal, a dry place will likely result in a failed tree. They are not a woodland species and will not tolerate shade or being overgrown by other trees.
Current situation in NW Herefordshire
A small group of Tree Wardens and volunteers have been identifying true native black poplars, ensuring they are recorded on the County database, and trialling propagation methods.
To ensure the trees we have identified for propagation are true native trees, we organised a visit by the BSBI National Recorder for Black Poplars who confirmed our identifications.
We now have an identified stock of trees for propagation, including rare female trees.
We plan to get 50 trees DNA fingerprinted as outlined above, to confirm accurate identification and ensure a broad range of clones are propagated.
We have also identified veteran pollards that require re-pollarding to a) preserve them, and b) provide a source of material for future propagation.
As a first step, we intend to propagate trees on twenty farms in the Curl Brook catchment. This work will be carried out by volunteers.
Our vision is to see the planting of 1000 new black poplars across the County of Herefordshire over the next twenty years. This will require oversight and administration by a larger organisation e.g. Herefordshire Wildlife Trust working in collaboration with the Herefordshire Tree Warden Network