Provenance of the conifers

We do not know the exact provenance of the conifers, this means that the risk of contamination by INNS must be treated as very high.
The conifers were sourced from Boutique Christmas Trees. We know that they came from UK-based farms so only terrestrial plants would have been in contact.
50 trees were delivered and left on the deck of the Battersea Barge by the Riverlight development from December until being brought to Tamesis Dock. They were occasionally visited by our staff but the area was closed to the public and isolated from the natural environment.
Given the visual inspection of the trees, the main concern is with non-visible seed. Given the timings and plants of concern, it is unlikely that much if any seed material would remain, if any were present at some point.

Transport and installation

INNS of concern
Name
Final risk
Type
Risk reasoning
Giant Hogweed — heracleum mantegazzianum
Low
Terrestrial plant
Plants live by slower rivers with more protection. Seed material, while transported by water, should have been washed off locally before the trees were cut, or during transportation. Plant matter was not found and would not propagate. Giant hogweed is dangerous and would not be planted near a UK tree farm.
Japanese Knotweed — Fallopia japonica
Low
Terrestrial plant
Not known to spread by water. Not spread by seed and any plant material would have been noticed and removed.
Marine spalsh midge — telmatogon japonicus
Low
Insect
They could live on hard surfaces which are numerous along the Thames. Live in marine environments with high salinity, may survive in brackish areas but less likely.
Zebra mussel — Dreissena polymorpha
Low
Shellfish
Lives in freshwater, will not have been carried by trees, would establish in the river.
Quagga mussel — dreissena rostriformis
Low
Shellfish
Lives in freshwater, will not have been carried by trees, would establish in the river.
Himalayan Balsam — impatiens glandulifera
Medium
Terrestrial plant
Seeds spread by dispersion and are carried through water, the plants live by rivers. Unlikely to have been near the growing conifers. Seed material should have been washed off by rain or rendered inactive in that time. Plant material was not found.
Fungal diseases — pestalotiopsis
Medium
Fungus is known to attack conifers, hard to prevent contamination and may remain dormant. Easy to notice effects and the trees were healthy and clear or fungus before installation.
Veined whelk — rapana venosa
Medium
Shellfish
Versatile in terms of habitat, they could easily live around the installation. However they tend to avoid cooler water especially during winter.
Chinese mitten crab — eriocheir sinensis
Medium
Shellfish
Travel far ~1.5Mm. Live in either salt or brackish to freshwater so are able to easily move along the Thames.
Signal crayfish — pacifastacus leniusculus
Medium
Shellfish
Known to inhabit the Thames, while the area around the installation is not very hospitable to this species the trees may provide a more sheltered habitat that might serve as a temporary home.
Killer Shrimp — dikerogammarus villosus
Medium
Shellfish
They have been found in the UK since 2010 and enter the Thames via ballast water and other means.
Pale galingale — cyperus eragrostis
Negligible
Terrestrial plant
No vector for introduction. Will not establish itself in fast moving, polluted and brackish waters.
Caroilina fanwort — cabomba caroliniana
Negligible
Aquatic plant
No vector for introduction. Will not establish itself in fast moving, polluted and brackish waters.
Rhododendron — rhododendron ponticum
Negligible
Terrestrial plant
No acidic soil suitable for this species is present. Seeds do not survive well in water.
New Zealand Pigmyweed — crassula helmsii
Negligible
Aquatic plant
This aquatic plant will not have been carried by the trees, and should have been obvious and removed if noticed. Requires slow moving water to establish. Seed material could end up further down stream but again this is unlikely: the trees were cut in Winter and away from ponds, they were transported in winter, any seed material if it had been in contact would have been washed off and/or rendered inactive in that time.
Pacific oyster — magallana gigas
Negligible
Shellfish
Lives in saltwater, will not have been carried by trees, may establish in the river but unlikely.
Asian Hornet — vespa mandariniatall
Negligible
Insect
Unlikely to have been around, avoids conifers. Large and obvious so would have been detected before or during shipping.
Water primrose — ludwigia grandiflora
Negligible
Aquatic plant
This aquatic plant will not have been carried by the trees, and should have been obvious and removed if noticed. Requires slow moving water to establish. Seed material could end up further down stream but again this is unlikely: the trees were cut in Winter and away from ponds, they were transported in winter, any seed material if it had been in contact would have been washed off and/or rendered inactive in that time.

Controls and checks

The trees were delivered individually wrapped and unwrapped before installation. They were checked visually for signs of disease and any noticeable foreign material and left in an area of the deck that was barriered to members of the public during the pandemic.
They were not washed or treated as this would very likely damage the trees so they would not survive. The risk of introduction of invasive species was deemed low due to the visual checks and growing conditions of conifers being very different from the riverside environment.
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