Abstract
North American beavers (Castor canadensis) are responsible for the major changes in the Tierra del Fuego Archipelago, altering riparian forests for the long-term. Passive restoration of the areas affected was ineffective in the medium-term (up to 20 years), being necessary active strategies. Plantations in abandoned ponds were made with Nothofagus pumilio and N. antarctica tree species across Tierra del Fuego island (Argentina). In the first experiment, we analysed the influence of biotic and abiotic factors in three micro-habitats in the impacted areas: front and tail of ponds, and cut not-flooded forest areas. Five-years-old N. pumilio seedlings had 39% survival in front, 21% in tails, and 46% in cut areas at year-3 of the restoration experiments, being negatively influenced by plant cover and soil moisture. Lower growth was recorded during year-1 (0.7–0.9 cm yr−1), but increased on time (1.9 cm yr−1 front, 1.6 cm yr−1 tail, 4.3 cm yr−1 cut areas). A second experiment explores the alternative to substitute the tree species to face the harder conditions of the impact and climate change. For this, we conducted a new plantation at four locations across the main bioclimatic zones, where 10–40 cm N. antarctica plants attained 17% survival in meadows (front and tail) and 30% in cut areas, being higher with larger than smaller plants (25% vs. 18%), and where they are mainly influenced by rainfall (4% in sites <400 mm yr−1 and 41% in >400 mm yr−1). The main damage was detected in the above-ground biomass due to dryness, but root survival allowed the emergence of new shoots in the following growing season. It is necessary to monitor different Nothofagus species across natural environments in the landscape to determine the feasibility and effectiveness of different strategies in restoration plans, considering the selection of climate-resilient tree species.
Highlights
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
Remnant BA was lowest in the old beaver dams (FRO and TAI) where flooding impacted tree survival, compared to those areas just foraged (CUT), representing 1.3%, 4.9%
We explore two approaches: (i) maintain the dominant forest species (N. pumilio) through plantations and removing the understory competition, where the hypothesis is that the main trade-offs are the lack of regeneration recruitment and the negative influence of grasses, and (ii) change the dominant forest species (N. antarctica) through plantations without understory removal to decrease the costs, where the hypothesis is that the main trade-offs are lack of physiological adaptations of N. pumilio to the new environmental conditions
Summary
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]. Sustainability 2021, 13, 7541 of ecosystem services [9]. Beavers generate extensive impacts on the environmental conditions of streams and riparian zones [10], including: (i) flooding areas that removed tree canopy cover and accumulates sediments that leads to changes in soil properties, and (ii) areas where trees are harvested (30–60 m from beaver ponds) [4,11,12,13,14]
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