Article
Initial Responses in Growth, Production, and
Regeneration following Selection Cuttings in
Hardwood-Dominated Temperate Rainforests
in Chile
Pablo J. Donoso 1, * , Patricio F. Ojeda 1 , Florian Schnabel 2,3,4
1
2
3
4
5
*
and Ralph D. Nyland 5
Facultad de Ciencias Forestales y Recursos Naturales, Universidad Austral de Chile, Valdivia 5090000, Chile;
p.f.ojeda.gonzalez@gmail.com
German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Leipzig 04103, Germany;
florian.schnabel@waldbau.uni-freiburg.de
Systematic Botany and Functional Biodiversity, University of Leipzig, Leipzig 04103, Germany
Chair of Silviculture, Faculty of Environment and Natural Resources, University of Freiburg,
Freiburg 79085, Germany
Distinguished Service Professor Emeritus, SUNY College of Environmental Science and Forestry, Syracuse,
NY 13210, USA; rnyland@syr.edu
Correspondence: pdonoso@uach.cl
Received: 16 March 2020; Accepted: 4 April 2020; Published: 7 April 2020
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 m2 ha−1 . In each stand, we established
four 2000 m2 plots with a residual basal area of ~40 m2 ha−1 , and four with a residual basal area of
~60 m2 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.
Forests 2020, 11, 412; doi:10.3390/f11040412
www.mdpi.com/journal/forests
Forests 2020, 11, 412
Keywords: mid-tolerant tree species;
Valdivian rainforests
2 of 19
uneven-aged silviculture;
hardwood silviculture;
1. Introduction
Foresters across the world have expressed interest in methods for uneven-aged and continuous
cover forestry (CCF) [1–3]. These include a range of silvicultural treatments, which largely fall
into selection systems and irregular shelterwood systems. With selection systems, harvesting and
regeneration take place simultaneously and continuously, and tree sizes and ages are inter-mixed
singly or in groups [4]. While single-tree selection systems have traditionally been most effective
in stands dominated by the more shade-tolerant tree species, group selection systems can provide
some flexibility for managing mid-tolerant species [5], as may single-tree selection regimes that use a
low-density residual [4,6,7], also when managing stands with mid-tolerant species that have a strong
root sprouting capacity [8].
Valdivian temperate rainforests [9] have species with characteristics favorable to selection systems,
and cover an extensive geographical area in Chile (33–45◦ S). Many different forest types develop
in this region due to differences in climate along the latitudinal gradient and associated with the
Coastal and Andean ranges. The Evergreen forest type is most prevalent, covering nearly 4 million
ha. It is dominated by shade-tolerant or mid-tolerant evergreen hardwood species [10–14], although
mid-tolerant ones (e.g., Eucryphia cordifolia Cav., one of the species with the highest basal area in these
forests) are scarce in the regeneration layer and among the smaller tree size classes in forests in advanced
successional stages of development [13,15–17]. Mature and old-growth stands are uneven-aged, with
negative exponential diameter distributions and basal areas as high as 80–100 m2 per hectare ([11,18];
see also Ponce et al. [19], and references therein, for a definition of old-growth forests). The structure
and composition of these forests is the result of recurring small-scale disturbances [20]. The dynamics
of mature and old-growth forests are mostly driven by the gap regeneration (e.g., for mid-tolerant E.
cordifolia and Drymis winteri J.R. et G. Forster; sensu [21]) and the continuous regeneration modes (e.g.,
for shade-tolerant Laureliopsis philippiana (Looser) Schodde, Aextoxicon punctatum R. et Pav., and Persea
lingue (Ruiz & Pav.) Nees [22]).
Selection silviculture is uncommon in Chile, and we know only one field-based study that
examined single-tree selection cutting in Valdivian rainforests [15], in one of the two experiments
that we evaluate here. They documented changes in the stand structure and mature tree species
composition, and concluded that single-tree selection can maintain many old-growth attributes of
these forests. However, they did not analyze tree growth or tree regeneration responses.
Evaluating these forest responses is warranted before recommending widespread use of this
forest management regime. To that end, we evaluated 5–6 year responses after single-tree selection
cuttings at two low-elevation sites in the Coastal range of south-central Chile, where old-growth forests
have traditionally been partially cut in the past [15]. We hypothesized that selection system cutting to
a low residual basal area (LRBA) would result in better residual tree growth and would enable the
regeneration of mid-tolerant tree species, while shade-tolerant ones would dominate the treatment
with a higher residual basal area (HRBA). Our objectives were to: (a) Develop a mid-term evaluation
of regeneration, growth, and production following selection cutting at two sites; and (b) Evaluate the
effect of two levels of residual basal areas on the development of mid-tolerant and shade-tolerant
species. We did not select unharvested stands for evaluation at these sites (control), since our aim is to
provide and discuss new knowledge for forest matrices that are mostly harvested in these landscapes,
although most times without silviculture [23]. Although we acknowledge this limitation in this study,
we provide several citations on untreated old-growth forests in the region as a reference.
Forests 2020, 11, 412
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2. Methods
2.1. Study Area
We selected stands at Llancahue (LL; 300 m a.s.l., 39◦ 50′ 20” S and 73◦ 07′ 18” W) and Los Riscos
(LR; 250 m a.s.l., 40◦ 53′ 07” S and 73◦ 31′ 30” W) (Figure 1). Both sites had been partially harvested in
the past through illegal selective cuttings, leaving average basal areas in the range of 70 to 80 m2 ha−1 .
These mid-elevation forests correspond to the Evergreen forest type, and specifically to the subtype
dominated by shade-tolerant species and having a few emergent Nothofagus trees [13]. The main
species at each site are listed for Llancahue (Table 1) and Los Riscos (Table 2) and are identified by
different functional groups; shade-tolerant, mid-tolerant, and intolerant of shade. In the Evergreen
forest type, the shade-tolerant species have a good regeneration potential [16]. The mid-tolerant ones
usually occur as medium- and large-sized trees but are scarce in the regeneration layer and among
the smaller tree size classes [13,15–17]. Shade-intolerant species, if present, are usually constrained to
large-sized trees, and their regeneration in canopy gaps is <1% [20].
Table 1. Mean of the regeneration density (per ha values) of seedlings and saplings according to species
and treatment (HRBA and LRBA) in Llancahue (LL) following the cuts (2013) and five years after the
cuts (2018). Table S7 in the Supplementary Materials provides both the mean and standard deviation.
Seedling Density
HRBA
Sapling Density
LRBA
HRBA
LRBA
2013
2018
2013
2018
2018
1505
46
69
1620
1019
23
185
1227
69
0
209
278
116
0
139
255
0
0
0
0
0
0
0
0
0
2361
4352
1250
1528
9421
0
2477
4931
1111
1944
10,463
23
4745
3171
880
1042
9861
69
8426
3032
1181
648
13,356
0
116
46
278
46
486
0
347
208
324
69
948
Species
Shade-intolerant
Nothofagus dombeyi (Mirb.) Oerst.
Weinmannia trichosperma Cav.
Other species *
Sub-total
Mid-tolerant
Caldcluvia paniculata (Cav.) D. Don
Drimys winteri J.R. Forst. & G. Forst.
Eucryphia cordifolia Cav.
Gevuina avellana Molina
Podocarpus salignus D. Don
Sub-total
Shade-tolerant
Aextoxicon punctatum Ruiz et Pav.
Amomyrtus luma (Molina) D. Legrand &
Kausel
Amomyrtus meli (Phil.) D. Legrand & Kausel
Dasyphyllum diacanthoides (Less.) Cabrera
Laureliopsis philippiana (Looser) Schodde
Lomatia dentata (R. et P.) R. Br.
Lomatia ferruginea (Cav.) R. Br.
Myrceugenia planipes (Hook. & Arn.) O. Berg
Persea lingue (Ruiz & Pav.) Nees
Raukaua laetevirens (Gay) Frodin
Rhaphithamnus spinosus (Juss.) Moldenke
Saxegothaea conspicua Lindl.
Other species **
Sub-total
7662
9676
22,014
16,713
232
370
12,083
17,083
16,088
13,611
717
1019
278
486
1574
1389
3218
1898
0
394
1042
23
23
30,069
0
787
1319
1574
4931
2662
255
486
1157
46
139
40,116
995
0
2269
394
8380
486
0
347
2731
0
0
53,704
4005
417
2454
486
7060
833
46
509
2546
69
115
48,866
0
0
486
116
0
116
0
0
116
0
0
1783
0
0
348
0
185
23
0
0
93
0
0
2038
* Aristotelia chilensis (Molina) Stuntz, Embothrium coccineum J.R. Forst. & G. Forst., Ovidia pillopillo (C.Gray) Hohen.
ex. C.F.W.Meissn. ** Luma apiculata (DC.) Burret, Myrceugenia ovata (Phil.) L.E.Navas.
Forests 2020, 11, 412
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Table 2. Mean and standard deviation of the regeneration density (per ha values) of seedlings and
saplings according to species and treatment (HRBA and LRBA) in Los Riscos (LR) following the cuts
(2013) and six years after the cuts (2019). Table S8 in the Supplementary Materials provides both the
mean and standard deviation.
Seedling Density
HRBA
Species
Shade-intolerant
Embothrium coccineum
Weinmannia trichosperma
Sub-total
Mid-tolerant
Caldcluvia paniculata
Eucryphia cordifolia
Gevuina avellana
Sub-total
Shade-tolerant
Aextoxicon punctatum
Amomyrtus luma
Amomyrtus meli
Laureliopsis philippiana
Lomatia ferruginea
Myrceugenia planipes
Persea lingue
Raukaua laetevirens
Rhaphithamnus spinosus
Other species **
Sub-total
Sapling Density
LRBA
HRBA
LRBA
2013
2019
2013
2019
2019
0
0
0
0
23
23
0
0
0
23
0
23
0
0
0
0
0
0
116
3125
1065
4306
162
3588
1806
5556
162
2500
880
3542
93
2963
1227
4283
116
1319
810
2245
93
1667
486
2246
1435
625
2338
463
2245
1644
1481
0
139
6
10,439
5856
5046
4074
880
3032
3009
509
370
370
116
23,262
1134
1551
1690
486
1968
1296
1736
463
69
23
10,416
3009
6088
3796
694
3843
2685
671
648
301
93
21,828
301
579
532
162
648
139
46
23
23
23
2476
162
949
301
185
486
347
69
23
23
0
2545
** Dasyphyllum diacanthoides, Lomatia dentata, Myrceugenia ovata.
Both study sites have a temperate, rainy climate with a Mediterranean influence [24]. At Llancahue,
the annual rainfall is 2300 mm and the average annual temperature is 12.2 ◦ C [25], while at the Purranque
weather station (a city near Los Riscos, but closer to the central valley with less rainfall) annual rainfall
reaches 1550 mm and the average annual temperature is 10.9 ◦ C [26].
Figure 1. Location of the study sites and the position of the high residual basal area (HRBA, n = 8) and
low residual basal area (LRBA, n = 8) plots at the two sites.
Forests 2020, 11, 412
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Llancahue lies between 50 and 410 m a.s.l. [27], and soils are moderately deep with a clay texture,
originating from ancient volcanic ashes deposited in the metamorphic complex of the Coastal range [28].
Llancahue has mostly old-growth forests with different degrees of past harvesting, generally classed
as being only minor disturbances. They are dominated by the shade-tolerants A. punctatum and L.
philippiana, and the mid-tolerants E. cordifolia and D. winteri.
Los Riscos is located in a transition between the Intermediate Depression and the Coastal range,
with a strongly undulating topography that varies between 220 and 310 m a.s.l. [29]. Soils are
moderately deep and originated from Holocene volcanic ash [28]. The old-growth forest of Los Riscos
is dominated by the same species as those at Llancahue (A. punctatum, L. philippiana, and E. cordifolia),
but D. winteri is nearly absent and P. lingue is common.
2.2. Experimental Design
At each site, eight plots (50 m × 40 m; 2000 m2 ) were located in old-growth forests that had partial
cuts in the past and reverse-J diameter distributions (e.g., [15]), and the locations were selected to
ensure that the initial starting conditions for the experiment were as similar as possible using visual
criteria. Two treatments (described later) were then randomly allocated to the eight plots so that each
treatment had four plots at each site. We marked all the trees at breast height and measured ones with
a diameter at breast height (dbh, at 1.3 m) ≥ 5 cm, recording: diameter, tree species according to shade
tolerance (shade-tolerant; mid-tolerant; intolerant), and the crown position (emergent, higher and
lower canopy, higher and lower reserve, or subcanopy) before the selection cuttings. For a random
subsample stratified by the broad diameter classes of trees per plot, we also measured the total height
(h) with an ultrasound VERTEX III hypsometer (Haglof Inc., Madison, Mississippi, USA) to develop
height-diameter functions to use in estimating heights for all trees. We measured 320 trees in Llancahue
and 399 trees in Los Riscos (Tables S1 and S2 in the Supplementary Materials).
The two selection cutting treatments used in the experiment were specified using the BDq approach
described by Guldin [30]. The two treatments differed in terms of their residual basal area (B): one was
60 m2 ha−1 (high-HRBA) and the other was 42 m2 ha−1 (low-LRBA; Table 3). Both treatments used a
maximum diameter (D) of 80 cm and a q factor of 1.3. However, since these forests have many trees
>80 cm [11], for this first selection cut we left 10–13 m2 per ha of these large trees (20% or 25% of the
total residual basal area with HRBA and LRBA, respectively), and that basal area was included in B. To
implement the selection cutting we followed procedures provided by Nyland [4], and constructed
a marking guide that compared the target structure with the actual diameter distribution in each
stand. We merged on average four 5-cm diameter classes to deliver a marking guide that included one
prescription for each broad range of diameters (e.g., cut one of two trees, cut one of four trees, etc.).
The selection criteria used in the cuttings was to leave the best possible quality trees (i.e., quality 1
trees—those with straight boles, well-developed crowns, and no apparent health problems), within the
limitations of the residual basal areas imposed in the experimental design. Harvesting was conducted
with oxen and closely supervised. As a result, Bacardit [31] determined that damage to the residual
trees was marginal in Llancahue, and we estimate that it was similar in Los Riscos. The selection
cuttings were conducted during spring-summer of 2012–2013. The harvesting intensities across plots
ranged from 25% to 35% of the initial basal area, the latter representing the maximum harvest allowed
by the Chilean law for this silvicultural system (Table 3). Therefore, the value chosen for the low basal
area is a result of both legal constraints and a conservative estimate in these forests where Chusquea quila
Kunth represents a potential hazard for regeneration when too much light is available (which could be
the case with lower basal areas; Donoso and Nyland [16], and references therein). In addition, residual
basal areas of 60 to 70 percent of the original have been used in regions with decades of selection
silviculture [4,32]. The high basal area value was selected since it represents close to two-thirds of the
maximum basal area in these forests (see above), e.g., similar to the harvesting intensities elsewhere in
hardwood forests subjected to selection cutting [33]. We re-measured these plots after the fifth (LL) and
sixth (LR) growing seasons, including ingrowth to the lower diameter class and trees that died. Then,
Forests 2020, 11, 412
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we assessed the tree growth and regeneration, with a special focus on functional groups according to
shade tolerances based on information from Donoso [14,22] and Gutiérrez et al. [34].
Table 3. Numbers of trees and basal area in all plots selected for the study before and after the selection
cuttings. LRBA: Low residual basal area; HRBA: high residual basal area. Notice that original values
were lower in the LRBA plots.
N (Trees Per ha)
Basal Area (m2 ha−1 )
Volume (m3 ha−1 )
Site
Plot
Treatment
2012 (Before)
2013 (After)
2012 (Before)
2013 (After)
2012 (Before)
2013 (After)
LL
P1
P3
P5
P7
LRBA
LRBA
LRBA
LRBA
1360
1640
1241
1619
1331
1532
1136
1426
49.7
68.3
62.9
73.3
41.3
41.4
38.7
43.4
369.7
542.8
550.5
563.3
278.3
371.12
327.6
342.7
1465 ± 196
1356 ± 168
63.6 ± 10.2
41.2 ± 1.9
506.6 ± 91.6
329.9 ± 38.9
1681
1526
1411
1966
1244
1277
924
1665
64.4
50.7
88.0
58.3
39.9
42.4
42.7
44.9
448.7
348.6
659.3
397.0
273.0
291.6
301.6
295.3
1646 ± 240
1277 ± 303
65.4 ± 16.1
42.0 ± 2.0
463.4 ± 136.8
290.4 ± 12.3
2085
1355
1608
1519
2016
1263
1568
1448
75.6
97.5
58.9
81.2
59.4
59.9
53.0
60.6
595.9
735.0
445.4
653.0
508.5
477.1
401.9
511.6
1641 ± 313
1574 ± 320
78.3 ± 15.9
58.2 ± 3.5
607.3 ± 122.1
474.8 ± 51
1688
1804
1556
1332
1045
1378
1158
1011
84.1
86.3
97.0
97.0
62.2
58.6
61.0
61.6
593.2
627.6
691.3
634.1
435.0
435.5
432.0
399.5
1595 ± 203
1148 ± 166
91.1 ± 6.9
60.9 ± 1.6
636.6 ± 40.7
425.5 ± 17.4
Mean ± standard deviation
LR
P2
P3
P4
P7
LRBA
LRBA
LRBA
LRBA
Mean ± standard deviation
LL
P2
P4
P6
P8
HRBA
HRBA
HRBA
HRBA
Mean ± standard deviation
LR
P1
P5
P6
P8
HRBA
HRBA
HRBA
HRBA
Mean ± standard deviation
2.3. Estimation of Stand Variables
With the diameter from each plot, we calculated the basal area (G) and estimated the height (h)
for each tree. The height functions dependent on the measured diameters were adjusted following the
Stage’s model ([35]; Equation S1 in the Supplementary Materials). We also fit the volume (V) equations
for each individual species (Table S3 in the Supplementary Materials). With this information, we
determined the stand-level (ha) values for the tree density (N, number of trees), basal area, ingrowth
(trees entering the minimum 5 cm diameter during the measured period (last five or six years)),
mortality (trees that died during the measured period), and volume post-treatment (2013) and at 5–6
years after treatment (2018–2019). By these means, we calculated the periodic annual increment (pai;
value in t1 —value in t0 divided by the number of years) in tree diameter, stand basal area, and volume,
where the latter two variables included ingrowth and mortality.
Regeneration was sampled by systematically establishing 27 circular subplots of 4 m2 at a distance
of 5 m in three parallel transects in each plot. Seedling regeneration was counted by height class
(5–<50 cm, 50–<100 cm, 100–<200 cm) and species on three occasions: pre-treatment (dormant season
2012), post-treatment (after growing season 2012–2013), and after 5–6 years. Saplings (trees ≥200 cm in
height and <5 cm in d) were measured only at 5–6 years after the cuts.
2.4. Statistical Analyses
For individual trees, we analyzed the growth response of the diameter by functional group (all
trees, mid-tolerant species, and shade-tolerant species), using linear mixed models (LMM), following
the framework of Zuur et al. [36]. In these, the log of pai in diameter (cm year−1 ) was used as the
response variable. The log(d) and diameter class (5–≤20 cm, 20–≤50 cm, 50–80 cm, >80 cm) in 2013,
site (LL or LR), and treatment (HRBA or LRBA) were fixed effects, and significant interactions were
Forests 2020, 11, 412
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included as fixed effects. The nested plots within the sites were identified as a random effect to
represent the nested data structure (see Table S4 in the Supplementary Materials).
For the stand-level data, a generalized linear model was conducted for ingrowth (n ha−1 ) and a
linear model for pai in the basal area (m2 ha−1 year−1 ) and volume (m3 ha−1 year−1 ), where the treatment
(HRBA, LRBA) and site (LL, LR) were independent variables (see Table S6 in the Supplementary
Materials). Mortality was nominal in these experiments (from 0.53 to 1.18 m2 ha−1 for the entire period,
in trees that averaged from 11 to 21 cm in dbh).
For tree regeneration, we made pairwise comparisons between the two sites for all seedlings and
seedlings by functional group. We also analyzed the tree regeneration density for each functional group
(shade-intolerant, mid-tolerant, and shade-tolerant species) with generalized linear mixed models.
In these models, the response was the regeneration density, the probability density function followed a
Poisson distribution (n ha−1 ), while the year (pre-treatment, post treatment, or 5–6 years later), height
class (5–<50, 50–<100, and 100–<200 cm), site (LL and LR), and treatment (HRBA and LRBA), as
well as significant interactions, were fixed. The nested subplots within the plot and the sites were
identified as random effects to account for the hierarchical structure of the data (see Table S5 in the
Supplementary Materials).
We used the Tukey HSD post-hoc test with the emmeans package of R to compare differences
between levels with significant variables and interactions. Comparisons were conducted according
to treatment (low and high residual basal areas) and site (Llancahue and Los Riscos) for the periodic
annual increment (pai) in diameter growth, by classes, and for the regeneration density, by years of
measurement and height classes.
All statistical analyses were performed in R [37] using the nlme package for the LMMs [38] and a
significance level of α = 0.05. The random and fixed effect structure was determined via using the
restricted maximum likelihood (REML) and maximum likelihood estimation, respectively. The final
model results are based on the REML estimation.
3. Results
3.1. Diameter Growth
The periodic annual increment (pai) in diameter was significantly higher for mid-tolerant species
in the LRBA plots compared to the HRBA plots at Llancahue for the lower diameter classes (<20 cm)
and the highest diameter classes (>80 cm) (Figure 2). At Los Riscos, there were no significant differences
for any combination of functional group and diameter class (Figure 2).
Forests 2020, 11, 412
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Figure 2. Mean (bars) and standard deviation (whiskers) in pai in d (cm year−1 ) according to treatment
−
(HRBA, LRBA), site (LL, LR), DBH CLASS (<20 cm; 20–50 cm; 50–80 cm; >80 cm), and functional group.
–
Different letters between bars of the same DBH class –show significant
differences (value of p < 0.05).
3.2. Ingrowth
Ingrowth (Figure 3), as measured by trees reaching or surpassing the threshold minimum diameter
of 5 cm during the post-cutting period, was significantly higher in the LRBA treatment at Llancahue
for all tree species together. At Los Riscos, the HRBA treatment showed more ingrowth, but this was
not significantly different from the LRBA plots. We did not statistically compare ingrowth between
shade- and mid-tolerant species, but at Llancahue the values were greater for the former, while at
Los Riscos they were similar. Furthermore, there was a very dynamic change in density across most
diameter classes in all treatment/site combinations (Figure S1 in the Supplementary Materials).
Forests 2020, 11, 412
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Figure 3. Ingrowth according to functional group by site (LL or LR) and treatment (HRBA or LRBA).
Different letters between the same site show significant differences (p-value < 0.05). Boxes represent the
interquartile range (IQR, Q3 minus Q1), including the median of the data, and whiskers include the
remaining data.
3.3. Growth in Basal Area and Volume
At Llancahue and Los Riscos, the pai in both the stand basal area and volume were greater
in the HRBA plots (a median of 0.7–1.0 vs. 0.4–0.6 m2 ha−1 year−1 in the basal area, and 5–7 vs.
4–5 m3 ha−1 year−1 ), but these differences were only significant at Llancahue. For equivalent residual
−
−
–
–
–
–
basal area classes, Llancahue had a higher pai than Los Riscos (Figure 4).
−
−
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Figure 4. Pai for the net basal area and volume according to treatment (HRBA, LRBA) and site (LL, LR).
Different letters between the same site show significant differences (p-value < 0.05). Boxes represent the
interquartile range (IQR, Q3 minus Q1), including the median of the data, and whiskers include the
remaining data.
3.4. Regeneration
First, we compared tree regeneration throughout the periods of evaluation (Figure 5). This was
dominated by shade-tolerant species at both sites, before and after the cuts (Figure 5). Initial conditions
(before the cuts, 2012) showed high tree regeneration densities at both sites (20,000–40,000 seedlings
per ha; Figure 5). After the cuts, tree regeneration was more abundant and richer at Llancahue, where
–
it included 24 tree species, while Los Riscos had 17 tree species (Figure 5; Tables 1 and 2).
Tree regeneration had significant differences before and after the cuts, and along the post-cut
measured period at both sites (Figure 5). At Llancahue, the tree regeneration density was higher after
harvesting for the LRBA treatment, and five years after the cuts it did not differ significantly from the
post-cut values for all species pooled, nor for the shade tolerance group. The tree regeneration density
for the HRBA treatment did not differ significantly across the years. In contrast, at Los Riscos, for both
treatments the tree regeneration density was higher before the cuts in both residual density levels for
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all species pooled and for shade-tolerant species, but six years after harvest it increased to numbers not
significantly different from the pre-harvest levels (Figure 5).
Figure 5. Mean (bars) and standard deviation (whiskers) in the density of all seedlings (n ha−1 ) by
−
functional group according to year, treatment, and site. The different letters between bars of the same
color show significant differences between the years (value of p < 0.05).
The tree regeneration density of mid-tolerant (Figure 6) and shade-tolerant species (Figure 7)
showed significant differences throughout measurements for every single height class at both sites.
With regards to mid-tolerant species, at Llancahue regeneration behaved differently according to height
classes. For the HRBA treatment, the lower regeneration height class (5–<50–cm) had a significant
increase after the cuts, but it declined significantly to pre-cut levels five years after. For the LRBA
treatment, numbers significantly increased after the cut and remained similar during the evaluation
period. Regeneration had similar responses in the intermediate and taller height classes (50–<100 cm
– both treatments, basically with significant increases at the end of the evaluation
and–100–<200 cm) for
period. At Los Riscos, both the HRBA and the LRBA treatments showed very similar results throughout
the evaluation period. Tree regeneration in the lower height class did not significantly differ between
the pre- and post-cut conditions, but it significantly declined six years after the cut. The intermediate
and taller height classes showed similar trends, with significant reductions in the tree density after the
cuts and with significant increases five years after, meaning a recovery to pre-cut densities.
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Figure 6. Mean (bars) and standard deviation (whiskers) in the density of seedlings
(n ha−1 ) for
−
mid-tolerant species according to height classes
(5–<50
cm; 100–200 cm), year, treatment,
–
– cm; 50–<100
–
and site. Different letters between bars of the same color show significant differences between
measurement years (p-value < 0.05).
For shade-tolerant species, at Llancahue tree regeneration in the HRBA treatment significantly
–
–
– (100–<200 cm) when comparing
increased (5–<50
cm), declined (50–<100
cm), or remained unchanged
pre-cut and post-cut conditions. Five years after the cut, tree regeneration significantly declined to
pre-cut levels in the case of the lower height class, and reached significantly greater densities in the
intermediate and taller height classes. For the LRBA treatment, regeneration densities significantly
increased following the cut in the case of the lower height class, and remained unchanged in the
intermediate and taller height classes; and five years after the cut the lower height class did not show
any further significant change in regeneration density, but the intermediate and taller height classes
had significant increases in comparison with the post-cut densities.
At Los Riscos (Figure 7), the behavior of the tree regeneration of shade-tolerant species was the
same for each height class and residual basal area treatment. Tree regeneration significantly declined
following the cut, and from there significantly increased six years after the cut to densities similar to
those in the pre-cut conditions.
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Figure 7. Mean (bars) and standard deviation (whiskers) in the density of seedlings
(n ha−1 ) for
−
shade-tolerant species according to height –classes (5–<50
cm; 50–<100
cm; 100–200 cm), year, treatment
–
–
and site. Different letters between bars of the same color show significant differences between
measurement years (p-value < 0.05).
4. Discussion
4.1. General Response Patterns Following Selection Cuttings in Valdivian Rainforests
Privately-owned old-growth or late-successional uneven-aged forests are usually harvested, but
they tend to be high-graded, since, beyond theory (e.g., [12,23]), no management prescriptions or
options have been tested for them. We evaluated the first trials in the temperate rainforest of Chile
(specifically in the Evergreen forest type), aimed at converting unmanaged uneven-aged forests (actually
forests with unplanned partial cuts in the past) into selection forests. We implemented the same
experiments and protocols at two study sites, based on the facts that these were at similar elevations,
were dominated by similar species, and had similar original basal areas before being harvested to the
LRBA (lower pre-cut basal areas) or to the HRBA (higher pre-cut basal areas) treatments. Harvesting
intensities had to be constrained to legal requirements (not cutting more than 35% of the basal area).
To reach the target basal area thresholds (expected residual basal areas), these cuts left appreciable
numbers of old and senescent trees larger than the preferred residual maximum diameter (80 cm),
as well as some poor quality trees among the immature classes. Even so, 56% and 55% of the trees
in the high residual basal area treatments (HRBA) at Llancahue and Los Riscos, and 65% and 62%
in the low residual basal area (LRBA) treatments, were of the quality class 1 at the time of the last
measurement (data not shown). Overall, these experiments allowed robust comparisons between two
levels of residual basal areas in stands with similar pre-cut and post-cut characteristics. However,
minor differences in the climate and species composition may reflect site differences that might explain
some of the differential results observed at the two sites.
Evergreen forests in south-central Chile are usually dominated by one mid-tolerant species
especially dominating the basal area (E. cordifolia) and two shade-tolerant canopy species dominating
the tree densities (L. philippiana and A. punctatum) [12,16,18]. This was also the case in Llancahue
and Los Riscos, but in Llancahue D. winteri was the fourth most important tree species, while in Los
Riscos P. lingue was the fourth most important (measured by their relative importance values). While
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D. winteri is well adapted to soils with high moisture throughout the year [22,39], P. lingue is well
adapted to dryer conditions, especially during the summer months [22]. Earlier, Donoso [18] reported
Llancahue as a better site for Evergreen forests than ones with dryer conditions or shallower soils.
Based on these evidences, and the differential rainfall at the two sites, differences that we observed in
the current research suggest that Llancahue is a relatively better site than Los Riscos.
General responses to selection cuttings were similar between the two sites. Mid-tolerant tree
species tended to have greater diameter growth rates in the lower residual basal area than in the higher
residual basal area treatment (differences were significant in some diameter classes in Llancahue), and
seemed very similar for shade-tolerant species in treatments with low and high residual basal areas.
Growth in basal area and volume was greater in the treatment with a high residual basal area. Tree
regeneration increased during the 5/6 years that followed the selection cuttings, especially for the
shade-tolerant species and the taller regeneration classes (from 50 to <200 cm). Sapling densities were
similar for shade-tolerant species at both sites and basal area densities.
In spite of many common trends at both sites, Llancahue had greater stand-level growth rates
(basal area and volume) and greater regeneration densities than Los Riscos, except for saplings for
mid-tolerant species, where densities were greater at Los Riscos (see discussion below).
4.2. Growth in Stand Variables: Comparisons and Expectations
Growth rates in the basal area at both sites ranged (median) between 0.4 and 0.7 m2 ha−1 year−1 in
the LRBA treatment, and between 0.6 and 1.0 m2 ha−1 year−1 in the treatment with HRBA. However, the
basal area growth for these research sites was lower than the 1.4 m2 ha−1 year−1 simulated by Donoso [12]
and Schütz et al. [2] for selection forests on relatively good sites (e.g., in the Intermediate Depression or
low elevations of the Coastal range; [18]). Basal area growth for these hardwood-dominated research
sites can be compared with that compiled by Forget et al. [33] for northern hardwoods in North
America, who reported a range from 0.18 to 0.42 m2 ha−1 year−1 in Quebec (Canada), and from 0.38 to
0.75 m2 ha−1 year in Northeastern USA, for stands with residual basal areas between 11 and 27 m2 ha−1 .
Nyland [4] estimated that northern hardwoods of the USA having a mid-cycle stocking of about 20.6
m2 ha would have a basal area growth of 0.67 m2 ha−1 year−1 . Thus, overall the basal area growths
reported for these Chilean forests are comparable, considering that: (a) the experimental sites are in an
early transformation into selection forests, and their growth will likely increase with an increase of
stocking of more vigorous and higher quality trees; and (b) the first five years in a cutting cycle likely
represent growth rates lower than the mean growth throughout an entire cutting cycle [4,33]. Thus, we
must wait for future re-measurements to see if growth rates eventually reach that level.
Ultimately, the post-cutting growth and production will determine when stands with different
residual basal areas have a sufficient added volume for a minimum operable cut, and will determine
the cutting cycle length [6]. Initially, we projected waiting until the basal area reaches 55 m2 ha−1 before
the next cuts for the LRBA treatment, and 70 m2 ha−1 for the HRBA treatment. That should provide
an adequate volume for an operable cut at an acceptable time. With the growth rates reported here,
the cutting cycles would be 25 and 17 years, respectively. However, if growth rates in these stands
reach 1.0 m2 ha−1 year−1 , i.e., intermediate values between the reported values in this study and those
estimated by Donoso [12], cutting cycles would shorten to 15 and 10 years for the LRBA and HRBA
conditions. Future evaluations of these stands will allow us to better determine appropriate cutting
cycles. However, the current data indicate that the 5-year cutting cycle coupled with 35% harvesting of
the basal area, as allowed in Chilean law, is unsustainable [23].
4.3. Does a Lower Residual Basal Area Promote Mid-Tolerant Species?
This question has been of interest from the onset of the experiment, and was central to our working
hypothesis. Overall, during the initial 5–6 years following selection cuttings, treatment with lower
residual basal areas have shown a tendency for better diameter growth and better regeneration of both
the mid-tolerant and shade-tolerant species.
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Our data show a greater diversity of mid-tolerant species at Llancahue than at Los Riscos, with
the former site having three long-lived species in this category (E. cordifolia, D. winteri, and the conifer
(Podocarpaceae) Podocarpus saligna D. Don). At Los Riscos, only E. cordifolia is a canopy species (C.
paniculata (Cav.) D. Don and Gevuina avellana Molina are small-sized mid-tolerant tree species [22]).
The post-cutting diameter growth for these species at both Llancahue and Los Riscos seemed greater
(0.2–0.4 cm, Figure 2) than that reported for old-growth Valdivian forests (<0.2 cm; [12]), suggesting an
improvement in diameter growth due to the selection cuts. However, only at Llancahue did the lower
level of the residual basal area significantly improve the diameter increment for these mid-tolerant
species, but only for trees in the smallest and largest diameter classes. These results are consistent with
previous ones for northern hardwoods in North America. There, selection cutting resulted in better
growth across all diameter classes, the highest rates for the trees with mid-range diameters, and better
growth for lower residual basal areas ([40], and references therein).
The data also show favorable results for regeneration. The densities of mid-tolerant species ranged
from 9.5 to 13.4 thousand seedlings per ha in Llancahue, and 3.5 to 5.5 thousand in Los Riscos. That is
much higher than the <2 thousand per ha reported by Donoso and Nyland (2005) [16] for these species
in unmanaged Coastal old-growth forests. Regeneration in general increased after harvesting for both
shade-tolerant and mid-tolerant species, and especially for mid-tolerant species in the intermediate
and taller height classes. This suggests a growth response for this group, plus recruitment from the
smaller regeneration class. The data also indicate the additions of new seedlings to ensure the stocking
of advance regeneration for the future. The fact that regeneration responses did not differ between
residual basal area treatments suggests that the canopy still had unclosed gaps and an enhanced
understory brightness through the 5–6 year post-harvest period.
Sapling densities nearly doubled those reported by Donoso and Nyland [16] for better sites in the
unmanaged old-growth forests in the Coastal range. As with seedlings of intermediate and tall height
classes, these increasing sapling densities reflect recruitment from taller regeneration classes, triggered
by an improved growth of advance regeneration released by the selection cutting [41]. Mid-tolerant E.
cordifolia ranked first in sapling density at Los Riscos, but more moderately so at Llancahue. The fact
that E. cordifolia occurred at a much lower sapling density at Llancahue compared to Los Riscos may
indicate the negative effect of browsing by cows and oxen from neighboring ownerships, especially
upon this highly palatable species [42]. In addition to expecting an increased regeneration and growth
of mid-tolerant species (e.g., E. cordifolia) in lower residual basal areas, saplings’ vigor and tolerance to
browsing (measured as plant fitness and recovery after browsing) should also be enhanced by selection
cutting [43]. The four-fold larger numbers of E. cordifolia sapling in the LRBA treatment compared to
the HRBA treatment in Llancahue may signal this.
4.4. Prospects for Uneven-Aged Management in Valdivian Temperate Rainforests
Donoso [12] evaluated the ecological bases to sustain uneven-aged silviculture, arguing that
long-term success depended on the uneven-agedness of the forests, a reverse-J or rotated-S diameter
structure, and the dominance of shade-tolerant tree species. Consistent with this, when Schnabel et
al. [15] examined the short-term effects of single-tree selection cutting on stand structure and tree
species in the Llancahue experiment, they determined that the cut left a balanced structure with a
reverse-J diameter distribution, resulted in continuous forest cover, and left sufficient small-sized
trees. That suggests a potential for sustainable management by returning periodically to recreate the
desired residual conditions. Furthermore, the selection cutting did not lead to significant changes
in tree species richness and diversity compared to old-growth forests, but it did significantly reduce
the diameter and height complexity, especially by removing an important number of large-sized
trees (dbh 50 cm+, height 23 m+) [15]. Considering that we followed the same protocols at Los
Riscos, we believe that these results also occurred at this site. Thus, while improving the quality
and vigor of the residual stand and working toward a balanced diameter distribution are crucial
for timber production objectives, they must be reconciled with the need to maintain key structural
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attributes of ecologic importance, such as ensuring an appropriate diameter and height diversity. Such
modifications could be combined with setting aside groups of habitat trees within a landscape of stands
managed via selection silviculture [15,44]. With those kinds of adjustments, findings from the current
investigation of regeneration and growth responses suggest that selection cutting can adequately
accommodate the concerns of Donoso [12], and serve as a useful alternative for managing Valdivian
hardwood-dominated forests.
The continued monitoring of the experimental treatment, coupled with findings from other studies
in Andean forests, should provide additional information about these combined effects of uneven-aged
silviculture in South American temperate forests. For example, at a broader scale, the Evergreen forests
in the Andean range are considered to occupy better sites than those in the Coastal range [17,45], so better
growth rates could be expected in these forests. Furthermore, while the forest harvesting intensities in
this study are in line with the Chilean law and with general recommendations, the monitoring of these
experiments and of future experiments with different residual basal areas or harvesting intensities
must signal which densities may trigger greater growth rates in more commercially valuable species,
while also maintaining high degrees of diversity and complexity. These experiments should also
evaluate alternative cutting cycle lengths. Additionally, new experiments should evaluate different
residual structures and maximum diameters. Considering all these variables, and the fact that selection
silviculture, rather than just unplanned partial cuttings, is just beginning to be practiced by some
landowners, there is lots of room to continue studying the prospects for uneven-aged silviculture in
these southern hemisphere hardwood-dominated temperate forests.
5. Conclusions
Prospects for the implementation of uneven-aged silviculture in hardwood-dominated Evergreen
forests in Chile seem optimistic. We evaluated responses to selection cuts in two forests within the
lower elevations of the Coastal range, where site productivity is considered lower than in the Andes.
Since this was the first entry to these forests, we had to leave an unusually high amount of overmature
trees, beyond the expected diameter for maturity. Still, the results indicated positive responses in
tree regeneration and growth, although with some differences between the two sites. For example,
basal area growths were similar to those found in hardwood-dominated forests in North America,
where uneven-aged management is common. Further evaluations of the present experiments, plus the
implementation of new studies or operational cuts with selection silviculture (hopefully at some stage
with truly balanced diameter structures), will eventually illustrate the potential of this silvicultural
approach for the South American temperate rainforests.
Supplementary Materials: The following are available online at http://www.mdpi.com/1999-4907/11/4/412/s1,
Figure S1: Diameter distribution after harvest and 5/6 years later, according to site and treatment: a) Low residual
basal area Llancahue; b) High residual basal area Llancahue; c) Low residual basal area Los Riscos; d) High residual
basal area Los Riscos, Table S1: Parameters and measures of goodness of fit and prediction of height-diameter
functions in Llancahue (LL). n: number of samples, Table S2: Parameters and measures of goodness of fit and
prediction of height-diameter functions in Llancahue (LL). n: number of samples, Table S3: Total stem volume
functions used in the study, Table S4: Mixed-effect models for the effect of site and treatment on the diameter
increment, Table S5: Mixed-effect models for the effect of year, height class, site, and treatment on the regeneration
density, Table S6: Effect of site and treatment in the generalized linear model (ingrowth) and the linear model (Pai
in basal area and volume), Table S7: Mean and standard deviation of the regeneration density (per ha values) of
seedlings and saplings according to species and treatment (HRBA and LRBA) in Llancahue (LL), Table S8: Mean
and standard deviation of the regeneration density (per ha values) of seedlings and saplings according to species
and treatment (HRBA and LRBA) in Los Riscos (LR).
Author Contributions: Conceptualization, P.J.D.; methodology, P.J.D.; formal analysis, P.J.D., P.F.O., and F.S.;
investigation, P.J.D.; resources, P.J.D.; data curation, P.J.D., P.F.O., and F.S.; writing—original draft preparation,
P.J.D., and P.F.O.; writing—review and editing, P.J.D., and R.D.N.; visualization, P.J.D.; supervision, P.J.D.; project
administration, P.J.D.; funding acquisition, P.J.D. All authors have read and agreed to the published version of
the manuscript.
Funding: Pablo J. Donoso thanks project FIBN-CONAF 034/2011 that provided the financial support to establish
this experiment. Florian Schnabel acknowledges funding by the International Research Training Group TreeDì
funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Fundation)-319936945/GRK2324.
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Acknowledgments: Pablo J. Donoso and Patricio F. Ojeda thank Forestal Anchile Ltda. that harvested the
experiment at Los Riscos, and provided lodging support for the final measurement.
Conflicts of Interest: The authors declare no conflict of interest.
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