Initial Responses in Growth, Production, and Regeneration following Selection Cuttings in Hardwood-Dominated Temperate Rainforests in Chile

Abstract

Hardwood-dominated forests in south-central Chile have shade-tolerant and mid-tolerant tree species capable of regenerating and growing well in partial shade. To test the potential for using an uneven-aged silviculture in these forests, we established single-tree selection treatments at two mid-elevation sites within the Evergreen forest type in the Coastal range (Llancahue and Los Riscos, 40-42 • S Lat). They had an average initial basal area of 70-80 m 2 ha −1 . In each stand, we established four 2000 m 2 plots with a residual basal area of~40 m 2 ha −1 , and four with a residual basal area of 60 m 2 ha −1 . We planned for a maximum residual diameter of 80 cm, but needed to leave 20%-25% of the residual basal area in larger trees due to their great abundance in these old-growth forests. We re-measured these plots 5-6 years after the cuttings. We used mixed-effects models to evaluate the periodic annual increment (pai) in diameter and the abundance of tree regeneration, and linear models to evaluate ingrowth and changes in the basal area and volume. At Llancahue, the diameter pai of individual trees was significantly greater in the treatment with lower residual densities, especially for mid-tolerant species in lower diameter classes (5-20 cm). At both sites, the pai in the stand basal area and volume was greater in the more heavily stocked treatment, but differences were significant only at Llancahue. Regeneration was dominated by shade-tolerant species at both sites but was more abundant and more diverse at Llancahue. Taller tree regeneration (50-<200 cm) significantly increased after the cuttings at both sites, while small regeneration (5-<50 cm) overall remained at pre-cut levels. This pattern was similar for mid-and shade-tolerant species. However, we found no differences in regeneration responses between the lower and higher levels of the residual basal area. Sapling densities did not differ at both sites for shade-tolerant species, but for mid-tolerant species these were more abundant at Los Riscos. While both sites had many similar trends after implementing selection cuts (a greater individual growth in the treatment with lower basal areas but a higher stand-level growth in the treatment with a high basal area, more abundant regeneration of shade-tolerant species, etc.), they illustrate a differential potential for implementing uneven-aged silviculture, especially due to site-species interactions. These results are a first step towards evaluating the prospects for selection cuttings in these experiments and elsewhere in Valdivian temperate rainforests.

Present and prospects for multi-aged silviculture in Chilean temperate forests: Targeting secondary forests in transition and partially harvested old-growth forests

“…We chose to assess changes through the OGI and found that it increased in the secondary and mature forests subjected to variable-density thinning and irregular shelterwood, respectively, but declined in the older forest subjected to single-tree selection cutting. While this might be expected, especially since the selection cut defined a maximum residual diameter (Donoso et al, 2020b), these results illustrate that restoring old-growth attributes through ecological silviculture should aim to attain a percentage of the OGI (e.g., ≈70%; Ponce et al, 2019). It also might reconsider the variables included to calculate this index, such as coarse woody debris (see also Acker et al, 1998).…”

“…In a mature N. dombeyi-dominated forest, we evaluated an irregular shelterwood cutting (sensu Raymond and Bédard, 2017). In a partially harvested old-growth forest, we evaluated a single-tree selection cut (Donoso et al, 2020b). Harvests in these forests provided mostly firewood that allowed profitable operations (personal observation Donoso et al, 2014).…”

Mid-term results and prospects for irregular shelterwood systems in hardwood-dominated temperate rainforests in Chile

“…We recorded species, dbh, tree form and health (each in three categories), and the crown position (dominant, codominant, intermediate, suppressed/ submerged) following the forest inventory protocols of Prodan et al (1997). In addition, we measured the top height of a stratified subsample by tree diameter classes (Table 2) per plot with a VERTEX IV ultrasonic hypsometer (Haglof Inc., Madison, Mississippi, USA) to fit height-diameter functions, and estimate heights and volumes of all trees (according to the functions given in Drake et al (2003) for Hueicolla and in Donoso et al (2020a) for Llancahue). We measured 88 trees in Hueicolla and 134 trees in Llancahue from the new cohort (residual trees from the shelterwood cuttings were not included).…”

“…With the dbh of each tree per plot, we calculated the basal area (G) and estimated the height (h) and volume (V) of each tree according to species (Drake et al 2003;Donoso et al 2020a). With this information, we determined stand level (per ha) values for tree density (N, number of trees), basal area, and volume after treatment (Hueicolla: 1982, Llancahue: 2009 and for the last measurement (2021 to 2022).…”

Silviculture of South American temperate native forests

“…We planned for a maximum residual diameter of 80 cm but needed to leave 20-25% of the residual basal area in larger trees due to their great abundance in these old-growth forests. Plots were re-measured 5-6 years after the cuttings (Donoso et al 2020a). At Llancahue, the PAI in diameter of individual trees was significantly greater in the treatment with lower residual densities, especially for mid-tolerant species in lower diameter classes (5-20 cm).…”