The Twelve Mile Creek Headwater Forests (the Fonthill Sandhill Valleys, Short Hills Provincial Park, Decew Gorge, North Pelham Valley, Effingham Forest, and St. John's Valley) are situated near the mouth of the Short Hills Valley to the north and west of the cities of Thorold and St. Catharines. Most of the valley is covered by glacial debris from the Fonthill Kame, and is highly dissected by Twelve Mile Creek and its tributaries, creating a complex series of uplands, ridges, and valleys (some up to 30 m deep). The upper valley slopes support beech forests, while the lower slopes are dominated by Sugar Maple with scattered Tulip Trees, and mixed forests of Eastern Hemlock, Sugar Maple and American Beech. The bottomlands have open seeps with Skunk Cabbage, meadow marshes, thicket swamps of Spicebush and alders, and forests of walnut, Red and Sugar maples, Yellow Birch and White Pine.
In addition to birds, the headwater forests support a rich assemblage of flora and fauna. Detailed botanical surveys within each of the forest blocks have recorded between 400 and 500 vascular plant species, and 9 to 15 species of nationally and/or provincially rare plants. The provincially Vulnerable Southern Flying Squirrel has also been recorded in the North Pelham Valley.
The Twelve Mile Creek Headwater Forests have supported a significant population of Hooded Warbler since their discovery at the site in 1993. Hooded Warblers have been identified as a nationally Threatened Species by COSEWIC. Over the past few years, the estimated number of Hooded Warblers within the headwater forests has ranged from 4 to 8 pairs. This represents between 1.9% and 5.5% of the estimated Canadian Hooded Warbler population. In 1998, a total of 5 territorial males were recorded in the Fonthill Sandhill Valley portion of the complex.
In addition to a significant breeding population of Hooded Warblers, the headwater forests also support a pair of Louisiana Waterthrush (nationally vulnerable) and a rich assemblage of species that are largely restricted to eastern temperate forests. These species include: Red-shouldered Hawk (nationally vulnerable), American Woodcock, Eastern Screech-Owl, Ruby-throated Hummingbird, Red-bellied Woodpecker, Tufted Titmouse, Eastern Wood-Pewee, Carolina Wren, Wood Thrush, Yellow-throated Vireo, Blue-winged Warbler, Pine Warbler, Cerulean Warbler (nationally vulnerable), Scarlet Tanager, Eastern Towhee, and Field Sparrow.
The primary threats affecting the Twelve Mile Creek Headwater Forests are poorly managed logging, housing development, erosion and habitat loss associated with heavy use of ridge trails by motorbikes and all-terrain vehicles, and invasion by non-native species (Garlic Mustard). In some areas Garlic Mustard completely dominates other herbaceous species.
Portions of the Twelve Mile Creek Headwater Forests are ostensibly conserved, such as the St. John's Valley, which is mostly owned by the Niagara Peninsula Conservation Authority, and the Short Hills Provincial Park, which is owned by the Ontario Ministry of Natural Resources. Areas that remain in private ownership are vulnerable to land use patterns that may have a negative effect on the birds (poorly managed logging) or land use change such as conversion to agriculture or the development of residential estates. The Fonthill Sandhill Valley, in particular, is vulnerable to logging, urban expansion, and erosion from vehicles.IBA Criteria Habitats Land Uses Potential or Ongoing Threats Conservation Status