BSBINews - BSBI Archive - Botanical Society of the British Isles

Notes - Colonisation of the ramparts and walls of Berwick-upon-Tweed 21
native and alien trees and shrubs. The uncommonness
is partly due to the nature of the
bonding of the large, dressed, sandstone
blocks with narrow, well-mortared joints and
the comparative lack of weathering of the
blocks. The stonework of the flankers is
generally built of coarser sandstones and as a
result is more prone to weathering and colonisation
by bryophytes and higher plants. It also
provides better locations than the revetment
for perching birds, and hence the dissemination
of berried plants. In a total length of over
one kilometre, I was able to record only
twenty individual plants of nine species, five
of which are considered alien by Clement and
Foster (1994). The number of individual
plants is in sharp contrast with the total
numbers recorded on the much shorter lengths
of wall around the Parish Churchyard and
those of Coxon Lane Car Park, on the site of
the former Good Templar Hall, both localities
being within 100 metres of the ramparts.
Further, the two sites are quite different from
each other in terms of both species and
frequency of species. For example, Buddleja
davidii (Butterfly-bush) is rare on the churchyard
wall, yet dominant on the car park walls;
Acer pseudoplatanus (Sycamore) is the most
common species on the former, but absent in
the latter location. Similarly, Sycamore was
the most commonly encountered species on
the rampart walls, but I did not see Buddleja.
Rampart walls from King's Mount to Meg's
Mount (20 plants/9 species/5 aliens): Acer
pseudoplatanus 6; Cotoneaster horizontalis
(Wall Cotoneaster) 4; Fraxinus ornus (Manna
Ash) 3; Rosa canina agg. (Dog-rose) 2; Fraxinus
excelsior (Ash), Ribes sanguineum
(Flowering Currant), Rubus fruticosus agg.
(bramble), Sambucus nigra (Elder), Sorbus
intermedia (Swedish Whitebeam) 1,
(excluding the popUlation of young Sycamore
and Elder growing on the grassy parapet,
rather than the northwest revetment of Meg's
Mount).
Cromwellian Parish Churchyard Walls (51
plants/6 species/3 aliens): Acer pseudoplatanus
17; Sambucus nigra 16; Sorbus aria
(Whitebeam) 8; Ulmus glabra (Wych Elm) 7;
Cotoneaster horizontalis 2; Buddleja davidii 1.
Good Templar Hall (Coxon Lane) Car Park
(48 plants17 species/5 aliens): Buddleja
davidii 27; Cotoneaster simonsii (Himalayan
Cotoneaster) (+ inderminate plants) 9;
Cotoneaster horizontalis 7; Rubus fruticosus
2; Fuchsia magellanica (Fuchsia), Leycesteria
formosa (Himalayan Honeysuckle), Sambucus
nigra 1.
Without doubt, the most interesting record in
these three samples is that of Fraxinus ornus,
two individuals of which were seen on the
stonework of the eastern flanker of Windmill
Bastion and one nearby on its parapet. The
seed source is clearly one of two parent trees
planted less than twenty metres away as
shelter for the formal circle of shrub borders
and seats at the western end of The Ditches.
One specimen is a mature standard tree, some
six metres tall and with a trunk girth at breast
height (gbh) of 1.6m; the other is depauperate
and cankered at a height of 1.3m where the
gbh is 0.7m. No juvenile seedlings and
saplings were seen growing beneath the
parents or in adjacent shrub borders. Both
specimens are hermaphrodite plants and were
flowering profusely on 10 th May 2009.
Considerable research has been recently
undertaken by the EU funded project FRAXI­
GEN (2005) into the breeding biology of
populations of the three European Ash
species, Fraxinus excelsior in northern and
central Europe, and F. angustifolia (Narrowleaved
Ash) and F. ornus in central Europe
and the Mediterranean region. Manna Ash is
androdioecious, a rare breeding system, in
which some populations contain individual
trees which bear hermaphrodite flowers and
others which are male only, or staminate.
Other populations are apparently either wholly
hermaphrodite or wholly staminate and,
obviously, only the hermaphrodites set fruit.
The occurrence of staminate flowers in mixed
populations is considered to be an adaptation
to increasing the likelihood of wind pollination
(W allander, 2001), but the true situation
is far from clear . Working on populations in
southern France, a region in which the species