1. Underplanting Nothofagus for restoration purposes in Chile
Pablo J. Donoso1 and Daniel P. Soto2
1 2
Introduction
Nothofagus species are among the main pioneer trees in Chile, have a rapid growth and high timber value. In south-central Chile (37-41°S) N. dombeyi (intolerant to shade) and N. alpina (mid tolerant to shade) used to be emergent trees in highly productive Andean forests (up to 120 m2 of basal area per hectare; fig. 1). Thousands of these forests have been severely high-graded, and dense understory thickets of bamboo species (Chusquea sp.) have developed. Hence, arrested succession severely reduces the provision of ecosystem services. Following understory competition control, we have experimented underplanting of N. dombeyi and N. alpina in these high-graded forests. We report some of these results and discuss potential operational applications of these, and potentially other, Nothofagus species for restoration purposes in high-graded forests in south-central Chile.
Methods
Sites. Annual precipitation is ~3,500 mm and average temperature ~10°C. Andisols (Acrudoxic Hapludand) are mesic, mixed and coarse. High-graded forests had average canopy openness of up to 40% (fig. 2) and were planted with one-year old seedlings (fig. 3). Original forests are dominated by Nothofagus and have several canopy tree species (e.g., Laureliopsis philippiana, Saxegothaea conspicua, Dassiphyllum diacanthoides, Weinmannia trichosperma). Forest dynamics is dominated by frequent large-scale disturbances.
Study 1 (fig. 4). Six-year results of plantations in m2 gaps at m a.s.l. following manual control of understory competition (fig. 4).
Study 2 (fig.) Two-year results of plantations in partially opened forests following soil scarification with bulldozer (900-1,000 m a.s.l.).
Figure 1. Emergent N. dombeyi 50 m in height and 200 cm in diameter.
Results
Study 1
Figure 4. Site preparation in a 700 m2 gap in an Andean high-graded forest..
Figure 5. Box plots of growth , by species, after six years .
Figure 6. Growth of each species as a function of light at age six..
Figure 3. Seedlings 30 cm in height, 16 cm in root depth and 4 mm in root collar diameter.
Figure 2. Relationship of gap size (from study 1), canopy openness and light availability.
Figure 7. Seven-year old N. dombeyi and N. alpina trees in ~700 m2 gaps. Forest succession is proceeding, with natural regeneration of W. trichosperma (right picture) and other tree species, but some early release cuts may be necessary.
Study 2
Figure 8. Scarified soils and a three-year old N. alpina sapling.
Table 1. General characteristics of the sampled seedlings after two seasons since outplanting.
Main ideas and prospects
Nothofagus dombeyi is more sensitive to shade but has a greater ecological plasticity than N. alpina, which must be considered when underplanting in these variable degraded forests
Soils scarfication with heavy machinery is efficient and mimics Andean large-scale and intensive disturbances, but compaction must be reduced especially for N. alpina.
Nothofagus dombeyi and N. alpina have a high survival and good (but highly variable) growth when underplanted in high-graded forests following understory control. They facilitate natural regeneration, greater diversity and forest succession.
Since life history traits of Nothofagus species and forest dynamics through the Andes of south-central Chile are similar, underplanting of highly valuable Nothofagus species (also N. obliqua and N. glauca) is promising to rehabilitate degraded forests and engage landowners.
Costs/benefit analyses should be carefully estimated to promote subsidies for restoration according to site conditions, and should prove efficient to trigger restoration in Chile.
References
Donoso C, Deus R, Cockbaine JC, Castillo H Variaciones estructurales del tipo forestal Coihue-Raulı-epa. Bosque 7:17–35.
Donoso PJ, DP Soto, C Fuentes Differential growth rates through the seedling and sapling stages of two Nothofagus species underplanted at low-light environments in an Andean high-graded forest. New Forests 46(5-6):
Soto DP, PJ Donoso, CE Salas, KJ Puettmann Light availability and soil compaction influence the growth of underplanted Nothofagus following partial shelterwood harvest and soil scarification. Can. J. For. Res. 45: 998–1005.
Figure 9. Observed values and fitted models for the relative growth response of N. dombeyi and N. alpina in response to light availability, separated by soil compaction (comp.) levels. Shaded areas are 95% confidence intervals. Soil compaction is more detrimental to N. alpina, and its effect starts with lower light levels than N. dombeyi.