General Impact
Castor canadensis (beavers) are known as "ecosystem engineers" for their ability to alter the physical and chemical nature of water bodies and their adjacent terrestrial systems in both their native and introduced range (Nummi, 2006). Two recent studies have investigated the impacts of beavers on ecosystems in their introduced range in southern South America. Beavers have been found to cause significant reduction in forest cover up to 30m from water effectively removing riparian forest. In their introduced range of South America Beavers modify the original ecosystem from closed Nothofagus forest to a grass- and sedge-dominated meadow. Nothofagus forest and seedlings are suppressed by beavers but herbaceous plants have been shown to increase in number and diversity. Unfortunately most of the increase in herbaceous plant diversity is due to invasion of the areas by non-native species (Anderson et al. 2006). Deforestation caused by C. canadensis also has the immediate effect of increased erosion due to exposed slopes (Lizzaralde et al, 2004). Forests may not completely regenerate in meadows for more than 20 years after removal of beavers due to flooding and sediments completely covering the forest floor which impedes seedling germination and establishment (Martinez Pastur et al, 2006). Anderson and Rosemand (2006) investigated the effect of beavers on the aquatic ecosystem and found that ponds created by beavers had increased productivity but at the expense of significantly reduced macroinvertebrate diversity. Via physical, chemical and geomorphological alterations, beavers modify the structure and function of entire biotic communities and ecosystems. Lizarralde et al (2004) found that beaver colonized sites in the Tierra del Fuego Archipelago, Argentina had submerged vegetation and algae indicative of high nitrogen concentrations. Wood debris from fallen trees causes an accumulation of organic material that modifies the biochemical composition of waters, sediments, soils and adjacent riparian areas. These alterations make beaver-altered sites more suitable for introduced fish species (Salmo trusttafario, Salvelinus fontinalis and Onchorrychus mybis) and sustained invertebrate communities typidcal of slow-water habitats (Lizzaralde et al, 2004). Beavers dam the river in which their lodge occurs, and sometimes the dam breaks causing extensive flooding. Dams act as barriers to migration in the stream and also form areas of impounded water behind them, increasing water temperature (Alexander, 1998). Beavers are also known for their ability to rapidly clear a forested area, and also cause flooding to roads by plugging highway culverts (Jensen et al. 2001).
Location Specific Impacts:Tierra del Fuego (Argentina) (Argentina) 
Economic/Livelihoods: Beavers impact on forestry activities as the beaver dams kill trees in adjacent areas.
Ecosystem change: The beaver, in building its dams, destroys trees by ringing them and inundates Nothofagus forests (Jaksic et al., 2002).
Herbivory: Beavers feed on leaves and bark.
Interaction with other invasive species: Beavers impact on forestry business because the beaver dams kill trees in adjacent areas, allowing exotic plants to invade meadows.
Modification of nutrient regime: The beaver alters the nutrient dynamics of Nothofagus forests in Tierra del Fuego (Jaksic et al., 2002). Tierra del Fuego (Chile) (Chile)
Economic/Livelihoods: Beavers impact on forestry business because the beaver dams kill trees in adjacent areas.
Ecosystem change: The beaver, in building its dams, destroys trees by ringing them and inundates Nothofagus forests (Jaksic et al., 2002).
Herbivory: Beavers feed on leaves and bark. In Chilean Tierra del Fuego, beavers are damaging over 5,400haof native southern beech (Nothofagus pumilio) by constructing dams and by direct consumption (Jaksic et al., 2002).
Interaction with other invasive species: Beavers impact on forestry activities as the beaver dams kill trees in adjacent areas. It also allows exotic plants to invade meadows.
Modification of nutrient regime: The beaver alters the nutrient dynamics of Nothofagus forests in Tierra del Fuego (Jaksic et al., 2002). Anttola (Finland)
Economic/Livelihoods: Beavers can cause damage to commercial forestry.
Modification of hydrology: Beavers cause forests to flood by their damming activity. Pieksamaki (Finland)
Economic/Livelihoods: Beavers can cause damage to commercial forestry.
Modification of hydrology: Beavers cause forests to flood by their damming activity.
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