WORCESTERSHIRE BLACK POPLAR SURVEY 2002
Paul Mousley
Introduction
In early 2002 I was commissioned by the Worcestershire Wildlife
Trust to conduct a survey of native Black Poplar trees Populus
nigra var betulifolia in Worcestershire. This survey was to build
upon the work previously carried out by the Environment Agency
and the Worcestershire Flora Project in order to gain a better
picture of the status of the species in our county.
The Black Poplar is one of Britain's rarest and most endangered
trees. We are lucky that in Worcestershire to have one of the
densest populations in the country. However, there is estimated
to be no more than around 1000 in Worcestershire, and only 7000
nationally.
Despite being recognised as a Red Data Book (RDB) endangered
species and it's inclusion in the Biodiversity Action Plan (BAP),
comparatively little is known about the species compared to other
more common trees such as Oak Quercus spp. and Ash Fraxinus
excelsior. More research is clearly urgently needed in order to
establish a knowledge base for the species.
In a more local perspective the various species lists and surveys
that have previously been carried out show a number of different
estimates of the numbers and distribution, etc. across the county.
This situation needs to be clarified in order for any serious
conservation strategies to be considered.
It is evident that conservation of the species needs to begin and
be focussed in the right direction, and this direction needs to
be established.
The objectives of the survey were as follows:
1 To confirm that current recorded black poplars are still valid
2 To find any new trees that may be waiting to be discovered
3 To gain information about the current status of the population
4 To establish a comprehensive database as a working record of
the black poplar in Worcestershire
5 To use the knowledge gained from the survey to make
recommendations for future management of the population
Methodology
In order to meet the objectives above, a survey of the currently
known trees was undertaken and the information gathered entered
into a database. The trees were located and the following
measurements/observations taken: an eight figure grid reference
of their location; height; girth (Diameter at breast height (DBH)
(1.4m)); sex; health class (Healthy, Fair, Poor or Dead); age
class (Immature, Mature or Over-mature/Senescent); management
regime; and adjacent land use. In addition, a sketch was made of
each tree and a small scale sketch map was drawn to pin-point its
location in the landscape so that it could be easily found in the
future.
This data was then used to establish information about the
population and its needs. This can then be used to establish
recommendations for the management of the species in the future.
Results and conclusions
The survey is only approximately one quarter complete (the
southern part of Worcestershire), however, there are some
interesting preliminary observations and conclusions which can be
made.
Only 29 (10%) of the trees surveyed were present in the
Environment Agency list and 63 (22.5%) were present on the Flora
Group list. This confirms that the survey is indeed a vital part
of the conservation of the trees and is a very positive sign that
there may be more individuals in the county than was anticipated.
Due to the difficulty in accurately establishing the gender of
many individuals the data is incomplete, however, it is known
that of the 279 trees surveyed; 58 are male and only 5 female.
This obviously raises series questions as to the ability of the
species to retain genetic diversity via inter-breeding. It should
also be noted that thus far, to our knowledge the male and female
trees are extremely spatially separated, which will inevitably
compound the problem.
The trees surveyed range in height from 0.5m to 45m with an
average height of 16.59m and the diameter ranged from 0.02m to 6m
with an average diameter of 2.91 metres.
In terms of age the great majority of the trees surveyed (76%)
were mature individuals, with very few (14.7%) young trees
available to follow these as they fall into senescence, an area
which clearly needs to be addressed when conservation is
considered. Young trees were found to have been planted as stakes
cut from their older neighbours, and were only found on
Castlemorton Common, leaving the rest of the county in
significant need.
Pollarded black poplars round a pond on Castlemorton Common.
Photo G H Green
The majority of trees (82%) were found to be in good health,
which is extremely encouraging as it indicates that the
population is in a relatively stable and viable condition at the
moment, and there is time for conservation efforts to be planned
and put into place.
A total of 56 (20%) of the trees surveyed were hollow, which is
encouraging as the evidence seems to suggest that black poplars
are less hardy than, say, the crack willow Salix fragilis and
tends to fragment and decline when it becomes hollow.
The frequency of management ranged from less than one year to 65
years, with an average of nine years. Around 40% of the trees
surveyed are under current management. The continued management,
particularly of the pollarded trees is an important factor when
considering the conservation of the population and efforts should
be made to increase the numbers that are being managed. It has
been observed that the excessive weight of the large bows on
neglected poplars compounds their tendency to fragment under
stress.
As most of the individuals are found in a rural setting, the
majority are found in close association with hedges and fields.
It is broadly accepted that the black poplar is a water loving
tree and this is supported by the fact that nearly 64% of those
surveyed were found in close association with water courses,
ponds and ditches.
The following species are commonly found in association with the
Black Poplar: Ash, Beech, Birch, Black Poplar, Elder, Field
maple, Hawthorn, Hazel, Holly, Oak, Pear, Sycamore, Willow.
The distribution of the population tends to be concentrated into
large groups of individuals, with comparatively few lone trees in
the landscape (see distribution map). There seems to be a denser
population towards the SW of the county, which thins out towards
the west. Similarly, the population appears to be denser in the
south. This trend is only a preliminary conclusion, however, and
will be given greater resolution as the survey continues. The
largest concentration found thus far is on Castlemorton Common,
which has large numbers of individuals (nearly 160) along its
many streams and around its many ponds. This site is also the
only area where significant planting of stakes takes place in the
county and as such there is a range of ages and sizes of trees.
The map also illustrates that records of the trees are scattered
throughout the county, and it seems likely that as the survey
progresses more trees will be discovered and recorded.
Continuing Action:
The survey is only approximately one quarter complete and is a
very important aspect in the management of the Black Poplar and
our countryside. I am unfortunately unable to continue with the
survey, so a willing volunteer would be greatly appreciated. You
don't have to be an expert, as full training will be provided;
however, some background knowledge is obviously an advantage. If
you think that you could be that person we would be grateful if
you would contact Steve Bloomfield at the Worcestershire Wildlife
Trust on: 01905 754919.
Map showing distribution of black poplars included in the data-base
prepared for this survey including trees contained in the
Worcestershire Flora Project and Environment Agency databases.
Only those trees in roughly the south half of the county were
checked in the field during the currently reported survey. Map
prepared by Bert Reid.
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