Allegheny Mountain dusky salamander COSEWIC assessment and status report: chapter 10

Limiting factors and Threats

Limiting factors and threats facing both Canadian populations are likely to be similar to each other and to D. ochrophaeus elsewhere. Human activities that could modify the habitat of this species, especially anything that can affect the quality, abundance, or temperature of ground and surface water or damage forest habitat, would likely be detrimental to the survival of these populations. The major limiting factors for this species, in order of decreasing importance, are factors affecting underground water reserves, microhabitat features, and movement. Furthermore, because of their minute ranges, both populations are highly susceptible to stochastic environmental events.

Underground water reserves feed seeps and springs inhabited by D. ochrophaeus, and are essential in providing brooding, feeding, and overwintering habitat in both Quebec and Ontario. In Covey Hill, the nature of the rock and the presence of a large peat marsh at the top of the hill serves as an important reservoir that feeds the water table (Barrington et al. 1993). Water extraction for residential developments or campgrounds, resorts, golf courses, and large industries would decrease the amount of water available to sustain the salamander's habitat, and would likely have detrimental impacts (Barrington et al. 1993; Jutras 2003; Desroches and Rodrigue 2004). Project ideas for groundwater exploitation for both commercial and industrial use are being proposed on a regular basis. Recently, a project to pump and exploit spring water was proposed in the Franklin Area of Quebec near Covey Hill, but the proposal was withdrawn after opposition by the local community (Bonin 2001). The situation is potentially serious, as current laws do not make it possible to protect natural habitat from the effects of such exploitations. The situation is further complicated, as ground water is shared across the border with the United States. The current quantity of groundwater used in the Covey Hill area by agricultural and private residences does not constitute a threat to groundwater levels (Alvo and Bonin 2003). A campsite facility and surrounding orchards likely use a considerable amount of water but are fortunately at a lower altitude than where the salamanders are found. Further development on the higher part of the hill, however, or any destruction of the peat marsh, would likely change groundwater levels. Even if residential use of water supply is moderate, a large development such as a golf course could have a significant impact (Alvo and Bonin 2003).

The Niagara population faces a similar situation where current groundwater levels are adequate for salamander survival but any further major developments along adjacent lands could cause changes to the hydrologic cycle. Such changes may increase or decrease peak flows and discharge volumes from tableland areas. Any change in water flow is potentially detrimental to the Niagara population.

Both populations also have the potential to be contaminated by polluted runoff waters. At Covey Hill, the population is at a higher elevation than much of the farmland and development which may prevent contamination to some extent. Agricultural land and adjacent golf courses have the potential to contaminate groundwater sources with high levels of pesticides and fertilizers. In Niagara, runoff is more likely to flow from nearby industrial and urban areas into the gorge waterway. This is a major concern for the Niagara population, as storm discharge may contaminate water with an array of chemicals, heavy metals, oil, and other pollutants. Kucken et al. (1994) found that acidification and metal stream contamination caused a 50% reduction in populations of D. ochrophaeus compared to in reference sites. Orser and Shure (1972) found that salamander populations of the closely related D. fuscus were significantly affected by runoff and soil erosion resulting from urbanization in spring-fed streams near Atlanta, Georgia. Also in Ontario, levels of TDS (total dissolved solids) may be a limiting factor for D. ochrophaeus, as individuals are found only in a seepage area that has very high TDS (total dissolved solids) and conductivity. This is distinctive among other streams and seepage areas in the gorge which have much lower TDS and conductivity (R. Tervo unpubl. data).

Deforestation for agricultural or urban development may also have large impacts on D. ochrophaeus populations. Forests act as important water reservoirs, and when they are lost their absence can result in a much more variable flow of water in nearby streams (Bormann and Likens 1979; Likens 1985). Logging can alter the physico-chemical properties of the water (Martin et al. 1984; Likens 1985). In a western Oregon study that examined occurrence and abundance of four species of aquatic amphibians in unlogged streams and streams that had been logged 14 - 40 years prior, species richness, density and biomass were highest in streams in unlogged forests (Corn and Bury 1989). Another study on the effects of clearcutting by Knapp et al. (2003) found that sites with canopy removal had significantly fewer salamanders than the uncut control. The study also found that gravid female D. ochrophaeus weighed less in cut treatments. This difference may be significant as body weight is directly correlated with number of eggs produced, and lower weight may indicate the females were in poorer physiological condition. Deforestation can lead to soil erosion, increased sedimentation in streams, changes in light intensity, and modification or loss of habitat. Such changes are likely to affect intermittent streams which form the principal habitat of this species, and which are not protected from forest harvesting practices (Alvo and Bonin 2003; Jutras 2003; Knapp et al. 2003). Sedimentation in streams following logging may block overwintering and nesting cavities of this species (Alvo and Bonin 2003). Microhabitat features that are important for plethodontid salamanders are burrows, cover objects, substrate type and vegetation type (Southerland 1986). Alteration of these natural features by residential construction, agriculture, or other human practices could limit population size. Decreased leaf litter production and an increase in temperature, through greater sun exposure, can lead to drier conditions whereby salamanders forage less effectively. Invertebrate prey may also decrease. While deforestation is likely to be a greater threat to the Quebec population, any tree removal surrounding the Niagara population could also have a negative impact.

Movements of individuals are important for interspecific interactions and to maintain metapopulation dynamics. Although the movements of this species are poorly known, landscape barriers (e.g. roads, cultivated fields, deforestation) could compromise the population through further fragmentation. The extent to which this species moves at different times of year should be studied in the Canadian range, given that movement seems to vary considerably in different contexts.

Other potential threats may include all terrain vehicle use, collecting, or human recreation in or near salamander habitat (Jutras 2003). In more permanent stream habitats, introduction of predatory fish could impact salamander populations (Bonin 2001; Jutras 2003). Although Desmognathusochrophaeus and D. fuscus have altogether only ever been found in two sites in the Niagara Gorge, habitat destruction and changes in groundwater flow have already created unsuitable habitat in areas of the gorge between the sites. Also, as the Niagara population is only found in a single cascade channel, it is also likely to be vulnerable to natural catastrophes. Rock falls and mudslides occur frequently in the Niagara Gorge (R. Tervo pers. comm.), and have the potential to wipe out the necessary seepage habitat of this population. Distribution in both Quebec and Ontario is so limited that any further degradation or loss of habitat is likely to compromise the long-term survival of this salamander in Canada.

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