Gaer House Woods

Site of Special Scientific Interest · 51.9078, -2.9199

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Gwent County

Habitats

Fast flowing river and stream

Description

Description The largest area of ancient semi-natural alder Alnus glutinosa woodland of this type in the county, situated alongside tributary streams of the River Monnow. Other abundant canopy species include ash Fraxinus excelsior and elm Ulmus glabra. Understorey species include hawthorn Crataegus monogyna, holly Ilex aquifolium, goat-willow Salix caprea and hazel Corylus avellana which is co-dominant with alder in some areas. The ground flora is characteristic of this plateau type alder woodland with meadow-sweet Filipendula ulmaria, opposite-leaved golden saxifrage Chrysosplenium oppositifolium and wood-sorrel Oxalis acetosella.

Species mentioned

English name
search for this in other sites		 Latin name
search with Google		 IUCN / Red List Type Family
opposite-leaved golden- saxifrage Chrysosplenium oppositifolium LC herb saxifragaceae
meadow sweet Filipendula ulmaria LC herb rosaceae
wood sorrel Oxalis acetosella LC herb oxalidaceae
hawthorn Crataegus monogyna LC shrub rosaceae
alder Alnus glutinosa LC tree salicaceae
hazel Corylus avellana LC tree corylaceae
ash Fraxinus excelsior LC tree oleaceae
holly Ilex aquifolium LC tree aquifoliaceae
wych elm Ulmus glabra LC tree ulmaceae
goat willow Salix caprea LC tree shrub salicaceae

Insects to look out for

These moths, butterflies and beetles are known to feed on plants recorded at this site, and carry a notable UK conservation status — but a host-plant being present doesn't mean the insect has actually been recorded here. Treat this as "worth watching for," not a confirmed sighting.

SpeciesStatusVia host-plant
Figure of eight
Diloba caeruleocephala		 Endangered Crataegus spp.
The lappet
Gastropacha quercifolia		 Endangered Crataegus monogyna, Salix spp.
Scarce vapourer
Orgyia recens		 Endangered Alnus glutinosa, Corylus avellana, Crataegus spp., Filipendula ulmaria, Salix spp., Ulmus spp.
White-letter hairstreak
Satyrium w-album		 Endangered Ulmus glabra, Ulmus spp.
Mouse moth
Amphipyra tragopoginis		 Vulnerable Crataegus spp., Salix caprea
The sprawler
Asteroscopus sphinx		 Vulnerable Corylus avellana, Crataegus spp., Fraxinus excelsior, Salix spp., Ulmus spp.
Broom moth
Ceramica pisi		 Vulnerable Ulmus spp.
Scarce chocolate-tip
Clostera anachoreta		 Vulnerable Salix spp.
Mottled umber
Erannis defoliaria		 Vulnerable Corylus avellana, Crataegus spp., Salix spp., Ulmus spp.
Satyr pug
Eupithecia satyrata		 Vulnerable Filipendula ulmaria, Salix spp.
The lackey
Malacosoma neustria		 Vulnerable Corylus avellana, Crataegus monogyna, Salix spp., Ulmus spp.
Pale brindled
Phigalia pilosaria		 Vulnerable Alnus glutinosa, Corylus avellana, Crataegus monogyna, Fraxinus excelsior, Salix caprea, Ulmus glabra
Early moth
Theria primaria		 Vulnerable Crataegus monogyna
Pale eggar
Trichiura crataegi		 Vulnerable Corylus avellana, Crataegus monogyna, Salix spp.
Flounced chestnut
Agrochola helvola		 Near Threatened Crataegus monogyna, Salix spp., Ulmus spp.
Beaded chestnut
Agrochola lychnidis		 Near Threatened Crataegus monogyna, Salix spp.
Grey chi
Antitype chi		 Near Threatened Crataegus monogyna, Salix caprea
Purple emperor
Apatura iris		 Near Threatened Salix caprea
Minor shoulder-knot
Brachylomia viminalis		 Near Threatened Salix caprea
Dusky-lemon sallow
Cirrhia gilvago		 Near Threatened Ulmus glabra
The sallow
Cirrhia icteritia		 Near Threatened Salix spp., Ulmus glabra
Dingy mocha
Cyclophora pendularia		 Near Threatened Alnus glutinosa, Salix caprea
Kentish glory
Endromis versicolora		 Near Threatened Alnus glutinosa
Large thorn
Ennomos autumnaria		 Near Threatened Alnus glutinosa, Corylus avellana, Crataegus spp., Salix spp., Ulmus spp.
Dusky thorn
Ennomos fuscantaria		 Near Threatened Fraxinus excelsior
Grey pug
Eupithecia subfuscata		 Near Threatened Crataegus monogyna, Salix spp.
Double dart
Graphiphora augur		 Near Threatened Crataegus spp., Salix spp., Ulmus spp.

Host-plant data: Cook et al. (2025), Traits data for the butterflies and macro-moths of Great Britain and Ireland, 2024, UK Centre for Ecology & Hydrology / Butterfly Conservation; and Padovani et al. (2020), Database of Insects and their Food Plants (DBIF), UK Centre for Ecology & Hydrology (both Open Government Licence). Contains data supplied by UK Centre for Ecology & Hydrology.

Plant communities

A14 — Fast flowing river and stream

Myriophyllum alterniflorum community

Isolepis fluitans, Juncus bulbosus, Fontinalis antipyretica, Lobelia dortmanna, Equisetum fluviatile, Myriophyllum alterniflorum, Lemna minor, Callitriche stagnalis, Littorella uniflora, Potamogeton filiformis, Potamogeton gramineus, Potamogeton natans, Ranunculus peltatus, Chara spp., Nitella hyalina

A17 — Chalk river and stream, Fast flowing river and stream

Ranunculus penicillatus ssp. pseudofluitans community

Berula erecta, Nasturtium officinale, Elodea canadensis, Lemna minor, Callitriche stagnalis, Veronica beccabunga, Polygonum amphibium, Polygonum hydropiper, Potamogeton crispus, Potamogeton pectinatus, Ranunculus penicillatus ssp. pseudofluitans

A18 — Fast flowing river and stream

Ranunculus fluitans community

Fontinalis antipyretica, Fontinalis squamosa var. curnowii, Myriophyllum alterniflorum, Myriophyllum spicatum, Elodea canadensis, Mentha aquatica, Lemna gibba, Lemna minor, Potamogeton perfoliatus, Ranunculus fluitans, Glyceria fluitans, Phalaris arundinacea

A9 — Fast flowing river and stream, Marginal and inundation, Pond ditch and canal, Sluggish river and stream

Potamogeton natans community

Schoenoplectus lacustris, Juncus bulbosus, Sparganium angustifolium, Sparganium erectum, Sparganium minimum, Alisma plantago-aquatica, Lobelia dortmanna, Equisetum fluviatile, Myriophyllum alterniflorum, Elodea canadensis, Lemna minor, Lemna trisulca, Nymphaea alba, Callitriche platycarpa, Callitriche stagnalis, Littorella uniflora, Potamogeton natans, Ranunculus trichophyllus, Glyceria fluitans, Chara subspinosa