Mapping the status of the North American beaver invasion in the Tierra del Fuego archipelago

Abstract

Quantifying the presence and environmental impact of invasive species is the starting point for research on management and nature conservation. North American beavers (Castor canadensis) were introduced to Argentina from Canada in 1946, and the species has been identified as a major agent of environmental change in the Tierra del Fuego archipelago in the Anthropocene. We studied the invasion status (distribution and density) of beavers through analyses of the dam densities in the Tierra del Fuego landscapes. We identified beaver dams with a GIS using visual interpretation of high-resolution aerial imagery from Microsoft Bing, Google Earth and HERE and related them to natural environmental gradients. These factors comprised geographic (vegetation zones and distance to streams), climatic (temperature, precipitation, evapotranspiration and net primary productivity) and topographic (elevation and slope) data. The datasets (dams and factors) were combined, and the data from the different zonation classes were subsequently compared using ANOVAs and Tukey's mean comparison tests. Deviations from the mean density (x mean density-x total mean density) were calculated to visualize the deviations for the studied factors. The datasets were also evaluated using principal component analyses (PCA). Our results showed a total of 206,203 beaver dams (100,951 in Argentina and 105,252 in Chile) in the study area (73,000 km 2). The main island of Tierra del Fuego presented a greater degree of invasion (73.6% of the total study area) than the rest of the archipelago, especially in areas covered by mixed-evergreen and deciduous forests. The studied geographic, climatic and topographic factors showed positive trends (higher beaver preference) with beaver spread, which were all significant (p <0.05) when compared across the landscape. Although beavers are flexible in their habitat use, our empirical records showed that they had marked preferences and were positively influenced by the most productive forests. Here, we describe a scientific panorama that identified the drivers of species invasion based on satellite data and the available ecological datasets. The identification of such drivers could be useful for developing new tools for management and/or control strategies of the beavers in the Tierra del Fuego archipelago.

Landscape Variables Influence over Active Restoration Strategies of Nothofagus Forests Degraded by Invasive Castor canadensis in Tierra del Fuego

“…These forests naturally regenerate from seedlings, which could survive many years in the understory until microclimatic conditions facilitate their height growth. The understory plant diversity is poor and has low cover (<40%), being inhabited by few shrubs (<50 cm height), and several herbs and grasses [4,6,8,23,28,29].…”

“…These areas were selected across a climate gradient from cool and wet to warm and dry conditions (Figure 1A,B [26]. Plots were established in abandoned beaver meadows, where beavers occupied the areas since the 1960s and 1970s, affecting most of the riversides [6].…”

“…Invasive species are the most important drivers of change in natural environments [1,2], modifying ecosystem services, biodiversity and ecological functions [3,4]. Many of these alterations can have permanent legacies, and require active interventions to restore the natural values and services [5][6][7]. One of the most dramatic alterations to southern forest ecosystems of the last century is related to the invasion of North American beavers (Castor canadensis) in the Tierra del Fuego Archipelago [8], which extensively alter riparian forests and have become the most relevant issue of conservation concern in southern Patagonia to maintain the provision Sustainability 2021, 13, 7541 2 of 17 of ecosystem services [9].…”

“…Nothofagus species are the dominant trees in Tierra del Fuego, and are not adapted to beaver-induced changes [6]. This vulnerability is related to changes in the microclimate, invasive understory plants, suppression of native species, loss of riparian forest characteristics, alteration of natural ecological cycles, nutrient loss, and changes in soil properties [4,8,14,[19][20][21][22].…”

“…Argentina and Chile signed an agreement to eradicate invasive species due to the low resilience of Patagonian forests to the impacts generated by beavers [4,6]. In fact, passive restoration of the areas affected was ineffective in the medium-term (up to 20 years), making active strategies necessary for forest restoration [8].…”