The Indian River Valley is an area that has been restructured by placer mining operations that have been occurring here for more than 30 years. Most of the placer mining in this area occurred prior to 1998. The original peat wetland surface has been transformed into a new habitat composed of dense successional vegetation with a vastly increased water surface. The objectives of this baseline study were to document the wildlife, especially avian communities, found in these abandoned areas and compare them with the original wetlands that remain intact and are contiguous to these areas.
The field study occurred from May to July 2014 and consisted of three sessions of 60 point count surveys for monitoring land birds (30 in post-mined areas and 30 in unmined areas), stand watch surveys over the ponds for monitoring waterfowl, point count surveys for monitoring the common nighthawk, roadside surveys and stand watches for diurnal raptors and a collection of incidental sightings of birds and mammals.
A total of 92 bird species, breeders and non-breeders were detected within all the different surveys. Seventy-nine species were found in post-mined areas and 65 in unmined areas. The point count surveys allowed us to monitor 52 species in total, with 42 species in post-mined areas and 41 in unmined areas. Half of the bird species are similar on both areas.
It appears also that species are more abundant in post-mined areas and are more evenly distributed. Post-mined areas seem suitable for more generalist species, species that use various habitats. Conversely, there are more specialist species on unmined areas. Statistical analysis (canonical correspondence analysis) showed that habitat variables, such as the presence of dense deciduous trees, marsh, water and shrubs, have an effect on the distribution and abundance of bird species.
Both unmined and post-mined areas host a great number of species of conservation concern. Twenty-five species were detected during the breeding surveys, 18 in post-mined areas and 20 in unmined areas (with 13 species overlap). Post-mined areas appear to be suitable for highly threatened birds such as the common nighthawk, bank swallow, rusty blackbird and American kestrel.
Mining activity has increased the number of ponds and water surface available for waterfowl populations. After studying old aerial photos before mining activity, we saw that water surface in the studied areas went from 5.8% of the general habitat to 20% today. A breeding survey was conducted over 53 post-mined ponds and 12 unmined ponds during five sessions from May to July 2014.
Species richness of waterfowl is considered as a valuable indicator of the quality of wetlands and can represent the wetland productivity. A total of 21 species were observed. Twelve breeding species were detected and 12 seen with broods in post-mined areas. On unmined ponds, 10 breeding species were observed and five seen with broods.
Waterfowl and allied species populations are enhanced by the large number and diversity of ponds available in post-mined areas. Post-mined ponds provide habitat for breeding, foraging, staging and molting thanks to the great variety of sizes and shapes of these ponds. Species of conservation concern, such as the horned grebe, are also occurring and breeding in these man-made ponds.
The study focused on road accessible ponds. The ponds in unmined areas were smaller and less frequent; therefore we were able to monitor only a few unmined ponds. Natural wetlands are sparse and very difficult to access. Due to the difference of sampling effort, it wasn’t possible to compare accurately the bird densities between these two areas. Nevertheless, sorting the ponds by size classes, we were able to compare the two first classes (smaller ponds) between unmined and post-mined ponds. The number of breeding pairs, species and birds was the same between the two areas, except for a higher number of broods on unmined ponds.
Five species of diurnal raptors (birds of prey that hunt in the day) were detected on both areas, including the American kestrel, northern harrier and bald eagle, but these species are more likely to nest in unmined areas and use post-mined areas for hunting.
No specific protocol was set up for monitoring mammals, but all random sightings were noted. Mammals such as beaver, moose and snowshoe hare were particularly abundant within the study area and especially in post-mined areas, due to the successional vegetation such as willow, alder and aquatic vegetation. The Indian River Valley is an important foraging habitat for black bears that find the different food resources that they need from spring to winter. They were abundant as well. Other mammals were observed occasionally such as caribou, lynx, porcupine and grey wolf.
Spontaneous re-vegetation of 30-year-old mined areas on the Indian River Valley seems successful although no formal reclamation measures were applied. Indeed, the mining activity occurred in these areas prior to 1998 when no land restoration measures such as contouring and spreading soils was required. Thanks to several suitable conditions such as the high water table, low valley gradient, abundant moisture and deep black muck organic soil, a new habitat has developed. The mosaic of created habitats provides an excellent environment for food, nesting and shelter to a wide diversity of bird species.
A number of techniques can be used to promote wildlife and re-vegetation. Basically, there are three main approaches:
Technical reclamation, which is still the dominant practice, consists of covering the sites with fertile topsoil, sowing grass-herb mixtures, and/or planting trees. Artificial reseeding is not common in the Yukon due to the risk of the introduction of invasive species of plants.
Spontaneous succession, referring to a complete absence of human intervention, has occurred in the Indian River Valley. Spontaneous succession is advocated especially if environmental site conditions are not very extreme and there are no expected negative influences on the surroundings, such as landslides, erosion, contamination of water or soil, or negative aesthetic perception (Pratt and Hobbs, 2008).
Directed succession, which involves actively influencing natural processes leading towards habitats of high conservation value by such activities as support for conservation-desired plants.
To conclude, this baseline study opens the door to what could be a larger study on post-mining restoration successes in the Yukon. Improvements for further investigations and a larger scale study would include a greater sampling effort, a longer term study, a better focus on the vegetation and consideration of different factors and species groups. For example, in order to enhance the value of the man-made ponds and increase the efficacy of mining areas reclamation, it would be interesting to have a better understanding of the features that attract waterfowl populations (e.g. invertebrate abundance and diversity, water quality, temperature and depth). All these study improvements would require additional consulting with interested stakeholders in the territory and additional funding.
*Anne Chevreux is a wildlife biologist. Her study – A survey of avian communities in post-mined and unmined wetlands in the Klondike gold fields, Yukon, Canada – was originally prepared for Schmidt Mining Corp. She may be reached via email firstname.lastname@example.org, phone 867-335-6509 or Skype annemichon.