Soil conditions and sheltering techniques improve active restoration of degraded Nothofagus pumilio forest in Southern Patagonia

Abstract

Nothofagus pumilio forests in the Southern Patagonia region of Chile are highly degraded because of clearing for human settlements, extensive livestock grazing, and more recently, the impact of coal mining operations. Most of these legacy areas have remained as extensive meadows of non-native grasses and legumes with limited Nothofagus pumilio forest recovery due to dry soil moisture conditions and exposure to high wind and solar radiation. Therefore, active reforestation is needed to reclaim Nothofagus pumilio forests from abandoned grassland or disturbances caused by surface mine operation. In this study, a surface coal mine operation and an abandoned meadow established in the 1950 s needed to be restored back to N. pumilio forest on Riesco Island, in Southern Chilean Patagonia. We compared the establishment success of Nothofagus pumilio seedlings on replicated blocks under two conditions (experimental treatments): (i) four blocks of meadow previously disturbed by livestock grazing, (MS), and (ii) four blocks where a deep layer of the soil profile was removed, mixed, and then replaced simulating recommendations used for reclaiming surface coal mines (RS). To improve Nothofagus pumilio establishment and protection at each block under both soil conditions, seedlings were planted both unprotected and protected from wind and solar radiation using four different types of shelters: shade cloth, irregular log piles, white polypropylene shelters, and woody branches. Soil physical and chemical properties, seedling survival and growth, leaf water potential, and stomatal conductance were measured. Results at the end of the first and fourth growing seasons showed better conditions for seedling growth in the RS treatment. Mean survival rates began to be different following the second growing season with values of 84.7 ± 2.9% in RS and 60.2 ± 3.2% survival in MS treatments, respectively. At the end of the study, the difference between the treatments was even geater with values of 75.4 ± 5.5% and 32.2 ± 7.1%. Soil removal and replacement significantly changed soil physical properties, but values were still adequate for vegetation development. The use of shelters significantly influenced four-year survival rates of seedlings planted on the disturbed MS treatment with 60 ± 8.2% survival in plastic shelters and less than 25.5 ± 6.5% for all other shelters. The effects of the shelters were less clear in the RS treatment. Our study showed that Nothofagus pumilio restoration on abandoned grassland and reclaimed mine sites in Patagonia is a feasible option when soil conditions and planting techniques improve soil water availability, and when seedling are protected against excessive solar radiation and wind.