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Article

Chemical Thinning and Fisheye Clip for Managing Light Intensity in the Understory of Forest Restoration

by
André Junqueira Barros
,
Priscilla de Paula Loiola
*,† and
Ricardo Augusto Gorne Viani
Campus Araras, Federal University of São Carlos/UFSCar/CCA—Post Graduate Program in Agriculture and Environment, São Paulo 13600-970, Brazil
*
Author to whom correspondence should be addressed.
†
Current address: Phenology Laboratory, Department of Biodiversity, Biosciences Institute, UNESP—São Paulo State University, Campus Rio Claro, São Paulo 13506-900, Brazil.
Forests 2023, 14(11), 2140; https://doi.org/10.3390/f14112140
Submission received: 12 October 2023 / Accepted: 20 October 2023 / Published: 27 October 2023
(This article belongs to the Special Issue Silviculture Measures Needed to Keep Up with Changes in Forests)
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Abstract

:
Research highlights: Tropical forest restoration can be supported by the production of timber species in their understory. While they may appear at odds, they can be reconciled to promote environmental conservation and services. The lack of information on the management of tropical species causes a technical constraint for timber production in the understory of restoration sites, especially given the light restrictions. This issue could be amended with the development of methods to easily manage and estimate light availability, targeting management practices that balance restoration success and productivity. Materials and Methods: We conducted this study in an area within the Atlantic Forest, Brazil, where we tested the efficiency of chemical thinning to increase light availability in the understory of a five-year-old restoration planting, aiming to increase the growth rates of desirable timber species. Moreover, we tested the viability of using hemispherical photography taken with a smartphone to assess light incidence to assist restoration management practices. We calculated the percentage of photosynthetically active radiation (PAR) using a ceptometer in four different thinning intensities and compared them to the smartphone measures using correlation analysis. Results: Chemical thinning increased light incidence in the understory, with potential impacts on timber species productivity. Light management through PAR and canopy opening were highly correlated overall, especially after three months of management and 60% of thinning intensity. Conclusions: These findings demonstrate the potential for chemical thinning as a management practice to enhance light availability in the understory of tropical forest restoration sites. Additionally, our study highlights the value of using affordable and accessible tools like smartphones and fisheye clips for the indirect assessment of light conditions to promote natural regeneration and guide forest management and timber production in tropical forest restoration.

1. Introduction

Tropical forests are among the most biodiverse and ecologically important ecosystems on the planet, and they are essential for carbon sequestration, biodiversity conservation, and economic development [1,2,3]. Unfortunately, tropical forests have been severely degraded and deforested in recent decades due to human activities, at a rate of 5.5 M ha/y from 2010 to 2015 [4]. This has led to a significant loss of biodiversity, habitat fragmentation, and increased carbon emissions. Consequently, millions of hectares need to be restored around the world, which makes forest restoration a necessary and increasingly frequent management goal [1]. While forest restoration and production objectives may appear at odds, there is growing interest in reconciling these goals to achieve multiple benefits, resolving two significant global socio-environmental concerns [1].
Tropical forests are irreplaceable for global biodiversity conservation [5], and there are several techniques available for their restoration, including planting seedlings or direct seeding trees in areas of low resilience [6]. Planting fast-growing trees is among the most common techniques for tropical forest active restoration [7,8], and they are expected to quickly shade the site, suppressing invasive grasses [9]. Fast-growing species, on the other hand, may allow the development or planting of ecologically and commercially valuable shade-tolerant species under their canopy. Despite these important ecological services, fast-growing species are not always short-lived and can stay in the system for longer periods. This can limit light availability in the understory for natural regeneration, stagnate restoration succession, increase fire frequency, and cause other ecological losses [10,11].
Unmanaged restoration sites can be expected to be less productive than managed sites when considering costs, benefits, and ecological services provided by forests undergoing restoration [12]. Sustainable forest management can speed up succession by removing dominant species that could cause the loss of biological diversity and reduce habitat’s quality [13]. To achieve restoration and timber production goals, silvicultural management (e.g., pruning, thinning, artificial regeneration, new rounds of plantation) is widely applied in tropical forests [14] and can provide forest services under changing environmental conditions [15]. Silvicultural practices foster diversity in the structure, complexity, and composition of restoration plantings, often becoming capable of providing additional services. However, in tropical forest restoration sites, the effective management of fast-growing species remains a challenge due to a lack of knowledge on pruning and thinning practices in the field and the actual effects of them on the growth of timber species planted in the understory [16,17].
Thinning and selective logging can change the forest composition, increase light availability in the understory, and promote tree growth and ecosystem functioning [18,19]. Among the most used silvicultural techniques in tropical forests, thinning is the selective removal of competing individuals, species, or groups at focal sites and early stages of stand development [20,21]. Thus, managing or thinning the dominant trees in a restoration site might restrict the growth of non-pioneer trees in the understory, including timber species [22]. Thinning can also allow for the inclusion of new species or productive components in the forest system, such as native timber trees, which can mitigate restoration costs through long-term production [23,24]. As light is a limiting resource in the understory of tropical forests [25], the thinning of dominant species and canopy opening can be essential for the development of restoration at later stages [26].
Thinning in the early stages of the plantation can increase light penetration in the understory, increasing regeneration and resprouting, and enhancing soil temperature and decomposition rates [27]. Removing specific individual trees in a forest plantation can be challenging, given the inherent risks of fallen branches and operational accidents with a chainsaw. Also, mechanical removal frequently affects the surrounding species and might damage the timber focal species planted for production. Alternatively, chemical thinning can be applied to suppress invasive or unwanted trees in forest management [28,29] leading to standing death in most cases. Chemical thinning consists of applying herbicide in a cut made in the main stem [29,30], aiming to remove target trees by standing death [31]. Less impact is created in the understory, and the managed individuals might either resprout or temporarily continue to serve as shelter for the fauna, such as birds, insects, and small mammals, as they fall gradually [32]. It should be considered that the herbicide used to kill the target trees might translocate through the cambium layers and root system, being left to decompose at the restoration site. Therefore, the balanced use of chemical thinning, accounting for its negative effects, is expected to increase the light availability and the survival and growth of small- and medium-sized timber trees in the understory of tropical restoration forests [33].
Additionally, it is essential to develop methods to estimate light availability in the understory and its change along the thinning gradient treatments to inform management practices. Light availability is a critical factor that can limit the growth and survival of focal timber species, besides affecting the establishment of seedlings and influencing the composition and structure of forest restoration sites [34,35]. Therefore, the management of light can be aimed at balancing restoration success as well as timber growth and performance. Canopy opening size can be a proxy measure of light intensity and is usually taken through hemispherical photography [36], but that can be estimated by a fisheye clip coupled to a smartphone [37]. Percent photosynthetically active radiation (PAR) is frequently measured with specific and high-cost equipment, such as ceptometers [38], which poses an obstacle to widespread and practical evaluations of light availability in the understory, both for researchers and practitioners. In this context, we compare the relationship between these two measures of light incidence in the understory one year after management, after one growing season, to test the efficiency of a simple and low-cost technique for assessing light conditions.
Although there is a vast amount of research on the effect of thinning in different ecological components of temperate forests [15,39,40], the use of chemical thinning in tropical forests has few published studies (but see [33]). Thus, we verified whether (1) chemical thinning of dominant and fast-growing trees can create a light gradient in the understory of a tropical forest restoration site and (2) whether assessing light incidence using a smartphone fisheye clip was similar to the ceptometer measures in a chemically thinned stand for one year. We expected that the greater proportion of trees removed by chemical thinning, despite the resprout that was expected, would create a light gradient in the understory that could be captured by both methods of light estimation.

2. Materials and Methods

The study was carried out in Araras (SP), Brazil (22°22′57″ S and 47°19′13 W″), in an approximately four-year-old tropical forest restoration planting of about 11.5 ha. The site is in a seasonal tropical climate, with warm and rainy summers (from October to March) and dry and cold winters (from April to September). The average rainfall is 1426 mm. year−1, but 77% of that is concentrated from October to May [41]. The local vegetation type is the Seasonal Semideciduous Forest, a subtype of the Atlantic Forest domain [42], in which, overall, 20%–50% of the canopy trees lose their leaves in the dry season [43].
The restoration planting was established in an area of Ferralsol soil, which was previously used for decades for agriculture with recurrent and intensive fertilization, owing, for that reason, to the overall high soil fertility along the whole extension (Table S1). The restoration consisted, for the first time, of the plantation of ten fast-growing native tree species (Table 1) in January 2014. All species were mixed and randomly distributed in the area in a 3 × 3 m planting spacing (1111 trees. ha−1) with planting density varying among species. Twenty months later (October and November 2015), when fast-growing trees had already covered the soil by their canopies and shaded the ground, 11 slow-growing timber species were planted in the understory, in the interrow of the fast-growing trees, in a 4 × 3 m spacing (833 trees. ha−1, Table 1, Figure S1). All the planted species are commonly used for Atlantic Forest restoration in Brazil [9]. In the two planting periods, seedlings were 30–40 cm in height when planted. During the first years, management of the restoration consisted of controlling invasive grasses using glyphosate and mechanical mowing, as well as using sulfluramide baits for leaf-cutting ant control.
We established 20 continuous plots of 20 m × 30 m (600 m2 each) covering 1.2 ha of the planting (Figure S1). Plots were allocated about 10 m of the forest restoration edge. Each plot had fifty individuals from five to six timber species. We randomly allocated one of four treatments of chemical thinning in each plot. Treatments consisted of the chemical thinning of the fast-growing trees, removing 0% (no thinning), 30%, 60%, and 100% (all trees removed) of the total basal area of these species in each plot.
Canopy was not managed until this experiment began. Within each plot, we tagged and measured the diameter at breast height (DBH) at 1.3 m with a tape measure in all planted fast-growing trees. Then, we calculated the plot basal area to determine the number of trees to be removed in each plot of the 30% and 60% thinning treatments. In these two treatments, we tried to systematically remove trees across space, aiming to make thinning as homogeneous as possible within the plot. Some of the planted fast-growing species were not found and consequently not thinned out in the plots due to low planting density; thus, considering all plots, nine of the ten tree fast-growing species were submitted to chemical thinning (Table 2).
The chemical thinning of fast-growing trees was applied only once, in March 2018, at the end of the rainy season. We girdled the tree trunks with an axe at a height of 1–1.5 m, always below trunk bifurcation, and then immediately after we applied undiluted glyphosate with a wash bottle all around the girdling [44] (Figure S2). Glyphosate spraying is a common strategy used to control invasive species used in 40% of projects that apply herbicides [45]. For trees with multiple stems, we made one application per stem. The resprouting of the thinned trees was evaluated four months after the application. Trees were classified as resprouted or not. We considered trees with new and green branches coming out below or above the portion of the trunk where chemical thinning was completed as resprouted.
We assessed the light levels one month before, three months, and one year (one growing season) after the thinning treatments. Based on the DBH measurements previous to thinning, at the time of the first measure, fast-growing trees had a median diameter of 11.37 cm and the forest restoration site had a mean basal area of 16.27 m2.ha−1. In addition, at that time, most of the fast-growing trees had their canopies touching each other and shading the understory (Figure S2).
To measure the light incidence, we first used a ceptometer (AccuPAR LP80, Decagon Devices, Inc., Meter Environment Group, Pullman, WA, USA), taking 19 PAR measurements systematically distributed per plot, 15 measures above timber trees, and extra 4 in the middle of the plots. Immediately before measuring light incidence within each plot, we made an under full sun external reference measure [46] in the road that was less than 50 m apart from the most distant plot. PAR measurements were made on days with a blue, cloudless sky between 11:30 h and 13:30 h. Two readings were made for every measure, and their mean value was calculated for further analyses. Measures were taken at 1 m height (Figure S3). The percentage of PAR in the understory (% PARUND) was calculated by dividing the PAR under the forest canopy by the PAR reading taken at approximately the same time under full sun and multiplying the result by 100.
The second measure of light was taken through hemispherical photography recorded with a universal fisheye clip attached to a smartphone camera (Apple iPhone, model 8 Plus). The smartphone was fixed to a tripod 1 m above ground, at level, with a north orientation (Figure S3). Images were recorded in the same places and on the days as the PAR measurements, but in the early morning and late afternoon to avoid sun and wind interferences [47,48]. Canopy images were analyzed using the Gap Light Analyzer 2.0 program [49]. We adjusted to the local coordinates and altitude and used the blue band, which allows greater contrast between the forest canopy and the sky [36,50]. The best gray threshold was visually adjusted, comparing the original image with that generated by the program [36].
To test whether thinning increased light intensity, we used linear mixed models for the % PAR and canopy opening, including treatments and time as fixed factors and plots as random factors, to account for repeated measurements. Linear mixed-effects models (LMM) were fitted using the ‘lme4’ package [51]. The significance of each explanatory variable was tested using the ‘Anova’ function in the ‘car’ package [52]. We performed multiple comparisons of light intensity based on LMM using the ‘emmeans’ package [53].
Also, we applied Pearson’s correlation test between the % PARUND and the canopy opening data extracted from the photographs to verify if methods were correlated one growing season after thinning. We performed this analysis overall and split per treatment. Finally, we used the non-parametric Kruskal–Wallis test followed by the Dunn test to evaluate difference in the resprout rates of fast-growing species after thinning. All analyses were performed in R (alpha = 5%) [54].

3. Results

Chemical thinning was a successful method applied in the field, causing the defoliation of most of the trees up to 45 days after thinning (Figure S2). Indeed, some trees had already started resprouting 45 days after thinning (Figure S2). and almost half of the trees (44%) experienced a degree of resprouting 4 months after thinning, with resprouting considerably varying according to species (from 9.67% to 82.47%, Table 2).
Despite the resprouting levels, the thinning treatments caused the standing death of most of the target trees and created a light incidence gradient among their levels, observed both by the ceptometer (% PARUND, p < 0.001) and the fisheye clip (r = 0.76; p < 0.001, Figure 1). However, light level changes associated with the thinning gradient were not as expected; lower levels of thinning did not cause a difference in the light incidence in the forest understory (no difference between 0% and 30% management intensities, by both indices and evaluation times). Thinning was effective in increasing % PARUND and canopy opening in the understory after one year and when >60% of the basal area of fast-growing species was thinned (Figure 1).
We found a strong positive correlation between photosynthetically active radiation and canopy opening percent, one growing season after thinning (Figure 2). PAR and canopy opening levels were not identical during the year post-treatment nor among the treatments of thinning. The two indices were more positively related when the thinning intensity was >60%; however, they were significantly and positively related in all situations analyzed (p < 0.001).

4. Discussion

Although there is a vast amount of research on the effects of traditional mechanized thinning, the chemical thinning effects on the structure of tropical forests under restoration have few published studies. In the only study available, thinning was effective at causing the mortality of most target pioneer trees [33]. Considering that passive restoration of the tree community composition is slow in tropical forests, where at least one century might be needed to achieve stability [55,56], secondary succession can be decreased or even halted in some species mixtures [57]. This slowing of succession trends, therefore, affects the role of these natural and managed forests in conserving ecological functionalities [12]. In our case, chemical thinning was useful and effective for tropical trees, creating a light gradient in the understory of restoration plantations, which can be used to hasten successional pathways, potentially increasing the biological value and capacity of providing ecosystem services in older forests [22,58].
Many fast-growing and shade tree species used in tropical restoration plantings, including most of the ones in this study, are also deciduous or semi-deciduous, resulting in greater canopy opening in the dry season and, consequently, a greater amount of light reaching the understory of forest restoration plantings [9]. In our results, an increase in the percentage of light incidence was observed three months after management in all treatments, including the no-thinning treatment. This result was likely caused by the seasonal leaf fall of the fast-growing trees in the dry season. This natural and cyclic light gradient provides canopy openings, which also foster evergreen species growth [59]; however, this cyclic availability of light comes in the slow-productivity season for the whole community (winter or dry season). Timber species, which grow slowly, mainly during the wet season, when temperature and precipitation increase, should therefore benefit, in the wet season, from the removal of target fast-growing species. Management can accelerate their growth, production, and the entire restoration process while also increasing the recruitment of late-successional species in secondary forests [12]. Thus, chemical thinning serves as an important technique for managing light levels in tropical forest plantings.
Most of the selective logging in tropical forests shows little immediate effect on the number of species and species abundance distributions since they usually focus on basal areas [12,21]. Currently, thinning and logging techniques based on species and their functional traits and silvics might lead to differences in the amount of light that is increased in the understory as well as on the composition of the sites. For example, the dominance of pioneer species with a relatively low maximum height and softwood density would undermine the role of carbon storage, while increasing these attributes could increase the potential of tropical forests to mitigate climate change [1]. Shade-tolerant or rare species might not respond well or increase their growth after thinning, being suppressed by fast-growing species [60]. Therefore, we argue for the importance of further investigations into forest management that would be necessary to accelerate the recovery process of secondary forests and forests under restoration. For instance, this could involve the stagged removal of pioneer or mid-successional species (more than once in time) to avoid competition with late-successional and/or timber species. With this goal, we argue about the important role chemical thinning may play to create a light gradient in tropical forests under regeneration, focused on altering species composition and ecosystem functioning in the future, using a species-based decision to manage the trees.
Even at low harvesting intensities (e.g., <5 trees extracted per hectare), forests under conventional logging lose ecosystem services due to soil damage coupled with increased invasive species occurrence [14]. On the other hand, thinning at low intensities was shown to maintain species diversity and support species functional composition [12]. In these circumstances, the abundance of pioneers was substantially reduced, and the growth of late successional species was enhanced [21]. In our case, in a young forest restoration site, only greater intensities of thinning effectively resulted in differences in light levels (>60% of the overall basal area removed). With increased thinning intensity, however, the recruitment and growth of pioneer species may also increase [21], and invasive or undesirable species may establish in response to elevated light levels [45]. Consequently, it is important to determine other ecological responses to chemical thinning in different intensities, considering the environmental conditions and the goals of the restoration plans in tropical forests, such as increasing the diversity of natural regeneration [21,22]. Further studies could also expand the evaluation of chemical thinning effects in other components of the community along trophic levels and time, aiming to promote biodiversity and ecosystem services, including timber production [61].
Although studies have shown that the analysis of hemispherical photography is more efficient in terms of time, cost, and accuracy of the measure than the use of a ceptometer [46,62], similar performances with positive correlations were previously found between the two methods [63]. There are few references on the use of smartphones with a fisheye clip to take hemispherical photography, and we highlight the feasibility of this method to estimate light intensity. The fisheye clip is a low-cost tool that could successfully capture light levels after one growing season, replacing expensive equipment [64]. They are also reliable when compared with images from professional cameras [37,65], and smartphones are widely available globally. We advocate for increased use of smart phone fisheye clips for estimating light availability in the understory of natural or planted forests.

5. Conclusions

We conclude that chemical thinning leads to increased light incidence and might be a path for sustainable tropical forest restoration, ensuring timber production without reducing the inherent value of the environment [33]. However, shade tree species used in tropical forest restoration plantings vary in their growth, canopy size, perennity, foliage density, and light interception [9]; thus, species composition and plantation age are important factors to consider when defining thinning intensities with the goal of increasing lights in the understory. Further studies should address this question, as well as how understory trees respond to their higher light availability. Silvicultural activities, such as thinning, regeneration harvests, and artificial regeneration or restoration plantings, can provide a variety of forest services under changing environmental conditions. Since light is a limiting resource for plant development in the understory of tropical forests [25], thinning and light availability in this stratum are essential to maintaining growth rates of desirable species and the productivity levels of the site at later stages of the forest succession [26], therefore contributing to the global high demand for tropical forest restoration [61,66]. In addition, canopy opening around 60% of intensity increased light availability in the understory, which was also shown to benefit soil carbon stocks and nutrients, thus supporting the recommendation for optimal thinning activity [27]. The methods here analyzed can be used to assist decision-making in a wide variety of contexts in forest science, such as promoting natural forest regeneration, forest management and restoration, timber production, and functioning in tropical forests.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/f14112140/s1. Table S1. Soil chemical attributes of each plot in the study site, Araras (SP), Southeastern Brazil. Figure S1. Scheme of the distribution of fast-growing and timber trees in an example plot of 20 × 30 m, in the study site (A) and the distribution of the 20 plots in the study site (B). Figure S2. The forest restoration site in different moments: its edge in December 2017, prior to fast-growing trees thinning and when the plantation was 4 years old (A); chemical thinning with glyphosate in March 2018 (B); about 45 days after thinning, in May 2018, in a 100% plot, note that most of the trees are defoliated and some trunks have fallen (C); and resprouting of a Guazuma ulmifolia tree, about 45 days after thinning. Figure S3. Light measurements in the forest restoration understory, with the ceptometer in July 2018, three months after thinning (note that the timber species under the ceptometer is in the interrow of the fast-growing trees) (A); and one take of hemispherical photography—with a fisheye clip attached to a smartphone—for canopy opening measurement, also three months after thinning (B).

Author Contributions

A.J.B. and R.A.G.V. conceptualized the study, A.J.B. collected the data, and P.d.P.L. analyzed the data. All authors wrote the original draft and P.d.P.L. edited the final manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—Finance Code 001, granted to A.J. Barros, and processes no. PNPD-086/2013 and 88887.583146/2020-00, granted to PPL. We thank the São Paulo Research Foundation (FAPESP), for grant #2013/50718-5.

Data Availability Statement

Data is publicly available at Zenodo, under the https://doi.org/10.5281/zenodo.10044387 (accessed on 10 September 2023).

Acknowledgments

We thank the LASPEF-UFSCar team for helping with data sampling, and the Santo Antônio Farm, for allowing the experiment and supporting field operations.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Chazdon, R.L.; Brancalion, P.H.S.; Lamb, D.; Laestadius, L.; Calmon, M.; Kumar, C. A policy-driven knowledge agenda for global forest and landscape restoration. Conserv. Lett. 2017, 10, 125–132. [Google Scholar] [CrossRef]
  2. Guariguata, M.R.; Balvanera, P. Tropical forest service flows: Improving our understanding of the biophysical dimension of ecosystem services. For. Ecol. Manag. 2009, 258, 1825–1829. [Google Scholar] [CrossRef]
  3. Kapos, V. Seeing the forest through the trees. Science 2017, 355, 347–349. [Google Scholar] [CrossRef]
  4. Keenan, R.J.; Reams, G.A.; Achard, F.; Freitas, J.V.; Grainger, A.; Lindquist, E. Dynamics of global forest area: Results from the FAO Global Forest Resources Assessment 2015. For. Ecol. Manag. 2015, 352, 9–20. [Google Scholar] [CrossRef]
  5. Gibson LLee, T.M.; Koh, L.P.; Brook, M.W.; Gardner, T.A.; Barlow, J.; Peres, C.A.; Bradshaw, C.J.A.; Laurence, W.F.; Lovejoy, T.E.; Sodhi, N.S. Primary forests are irreplaceable for sustaining tropical biodiversity. Nature 2011, 478, 378–381. [Google Scholar] [CrossRef] [PubMed]
  6. Palma, A.C.; Laurance, S.G.W. A review of the use of direct seeding and seedling plantings in restoration: What do we know and where should we go? Appl. Veg. Sci. 2015, 18, 561–568. [Google Scholar] [CrossRef]
  7. Elliot, S.; Tucker, N.I.J.; Shannon, D.P.; Tiansawat, P. The framework species method: Harnessing natural regeneration to restore tropical forest ecosystems. Phil. Trans. Roy. Soc. B 2022, 378, 20210073. [Google Scholar] [CrossRef]
  8. Rodrigues, R.R.; Lima, R.A.F.; Gandolfi, S.; Nave, A.G. On the conservation of high diversity forests 30 years of experience in the Brazilian Atlantic Forest. Biol. Conserv. 2009, 142, 1242–1251. [Google Scholar] [CrossRef]
  9. Almeida, C.; Viani, R.A.G. Selection of shade trees in forest restoration plantings should be based on crown tree architecture alone. Rest Ecol. 2019, 27, 832–839. [Google Scholar] [CrossRef]
  10. Dwyer, J.M.; Fensham, R.; Buckley, Y.M. Restoration thinning accelerates structural development and carbon sequestration in an endangered Australian ecosystem. J. Appl. Ecol. 2010, 47, 681–691. [Google Scholar] [CrossRef]
  11. Vargas RAllen, E.B.; Allen, M.F. Effects of vegetation thinning on above- and belowground carbon in a seasonally dry tropical forest in Mexico. Biotropica 2009, 42, 302–311. [Google Scholar] [CrossRef]
  12. Ding, Y.; Zang, R. Effects of thinning on the demography and functional community structure of a secondary tropical lowland rain forest. J. Environ. Manag. 2021, 279, 111805. [Google Scholar] [CrossRef] [PubMed]
  13. Dey, D.C.; Kabrick, J.M.; Schweitzer, C.J. Silviculture to restore Oak savannas and woodlands. J. For. 2016, 115, 202–211. [Google Scholar] [CrossRef]
  14. Putz, F.E.; Sist, P.; Fredericksen, T.; Dyktra, D. Reduced impact logging: Challenges and opportunities. For. Ecol. Manag. 2008, 256, 1427–1433. [Google Scholar] [CrossRef]
  15. Ameray, A.; Bergeron, Y.; Valeria, O.; Girona, M.M.; Cavard, X. Forest carbon management: A review of silvicultural practices and management strategies across boreal, temperate and tropical forests. Curr. For. Rep. 2021, 7, 245–266. [Google Scholar] [CrossRef]
  16. Holl, K.D.; Reid, J.L.; Chaves-Fallas, J.M.; Oviedo-Brenes, F.; Zahawi, R.A. Local tropical forest restoration strategies affect tree recruitment more strongly than does landscape forest cover. J. App. Ecol. 2017, 54, 1091–1099. [Google Scholar] [CrossRef]
  17. Lohbeck, M.; Poorter, L.; Marínez-Ramos, M.; Rodriguez-Velásquez, J.; van Breugel, M.; Bongers, F. Changing drivers of species dominance during tropical forest succession. Func. Ecol. 2013, 28, 1052–1058. [Google Scholar] [CrossRef]
  18. Haughian, S. Short-term effects of alternative thinning treatments on the richness, abundance and composition of epixylic bryophytes, lichens, and vascular plants in conifer plantations at microhabitat and stand scales. For. Ecol. Manag. 2018, 415, 106–117. [Google Scholar] [CrossRef]
  19. Lin, N.; Deng, N.; Lu, D.; Xie, H.; Feng, M.; Chen, S. Short-term effects of thinning on tree growth and soil nutrients in the Middle-aged Chinese Fir (Cunninghamia lanceolata (Lamb.) Hook.) Plantations. Forests 2023, 14, 74. [Google Scholar] [CrossRef]
  20. Peñas-Claros, M.; Fredericksen, T.S.; Alarcón, A.; Blate, G.M.; Choque, U.; Leaño, C.; Licona, J.C.; Mostacedo, B.; Pariona, W.; Villegas, Z.; et al. Beyond reduced-impact logging: Silvicultural treatments to increase growth rates of tropical trees. For. Ecol. Manag. 2008, 256, 1458–1467. [Google Scholar] [CrossRef]
  21. Swinfield, T.; Afriandi, R.; Antoni, F.; Harrison, R.D. Accelerating tropical forest restoration through the selective removal of pioneer species. For. Ecol. Manag. 2016, 381, 209–216. [Google Scholar] [CrossRef]
  22. Oliveira, C.D.C.; Durigan, G.; Putz, F.E. Thinning temporarily stimulates tree regeneration in a restored tropical forest. Ecol. Eng. 2021, 171, 106390. [Google Scholar] [CrossRef]
  23. Aronson, J.; Durigan, G.; Brancalion, P.H.S. Conceitos e Definições Correlatos à Ciência e à Prática da Restauração Ecológica; IF Série Registros: São Paulo, Brazil, 2011; 38p. [Google Scholar]
  24. Brancalion, P.H.S.; Viani, R.A.G.; Strassburg, B.B.N.; Rodrigues, R.R. Finding the money for tropical forest restoration. Unasylva 2012, 239, 41–50. [Google Scholar]
  25. Wright, S.J.; Kitajima, K.; Kraft, N.J.B.; Reich, P.B.; Wright, I.J.; Bunker, D.E.; Condit, R.; Dalling, J.W.; Davies, S.J.; Díaz, S.; et al. Functional traits and the growth–mortality trade-off in tropical trees. Ecology 2010, 91, 3664–3674. [Google Scholar] [CrossRef] [PubMed]
  26. Engelbrecht, B.M.J.; Herz, H.M. Evaluation of different methods to estimate understory light conditions in tropical forests. J. Trop. Ecol. 2001, 17, 207–224. Available online: http://www.jstor.org/stable/3068642 (accessed on 10 September 2023). [CrossRef]
  27. Zhang, X.; Chen, L.; Wang, Y.; Jiang, P.; Hu, Y.; Ouyang, S.; Wu, H.; Lei, P.; Kuzyakov, Y.; Xiang, W. Plantations thinning: A meta-analysis of consequences for soil properties and microbial functions. Sci. Total Envioron. 2023, 15, 162894. [Google Scholar] [CrossRef] [PubMed]
  28. Mcivor, I.; van den Dijssel, M. Killing Old Popular Trees Using Chemicals. Plant and Food Research Gen. Tech. Rep. The New Zeland Institute Palmerston North. 2017. Available online: http://www.poplarandwillow.org.nz/documents/killing-old-poplar-trees-using-chemicals.pdf (accessed on 16 December 2021).
  29. Tubby, K.V.; Willoughby, I.H.; Forster, J. The efficacy of chemical thinning treatments on Pinus sylvestris and Larix kaempferi and subsequent incidence and potential impact of Heterobasidion annosum infection in standing trees. Int. J. For. Res. 2017, 90, 728–736. [Google Scholar] [CrossRef]
  30. Oliveira, C.D.C.; Melo, A.C.G.; Durigan, G. Thinning enhances success of enrichment planting with selected tree species under a pure stand of Leucaena leucocephala. Rest Ecol. 2023, e13985. [Google Scholar] [CrossRef]
  31. Willoughby, I.H.; Stokes, V.J.; Connolly, T. Using Ecoplugs containing glyphosate can be effective method of killing standing trees. Int. J. For. Res. 2017, 90, 719–727. [Google Scholar] [CrossRef]
  32. Mendes, J.C.T.; Seixas, F. Impacts of logging on the structure of the native understory vegetation in an area of legal reserve. Sci. For. 2017, 45, 685–695. [Google Scholar] [CrossRef]
  33. Gourlet-Fleury, S.; Mortier, F.; Fayolle, A.; Baya, F.; Quédraogo, D.; Bénédet, F.; Picard, N. Tropical forest recovery from logging: A 24-year silvicultural experiment from Central Africa. Phil. Trans. Roy. Soc. B 2013, 368, 20120302. [Google Scholar] [CrossRef] [PubMed]
  34. Bazzaz, F.A. The physiological ecology of plant succession. Ann. Rev. Ecol. Syst. 1979, 10, 351–371. [Google Scholar] [CrossRef]
  35. Swaine, M.D.; Whitmore, T.C. On the definition of ecological species groups in tropical rain forests. Vegetatio 1988, 75, 81–86. [Google Scholar] [CrossRef]
  36. Monte, M.A.; Reis, M.D.G.F.; Reis, G.G.; Leite, H.G.; Stocks, J.J. Métodos indiretos de estimação da cobertura de dossel em povoamentos de clone de eucalipto. Pesqui. Agropecu. Bras. 2007, 42, 769–775. [Google Scholar] [CrossRef]
  37. Bianchi, S.; Cahalan, C.; Hale, S.; Gibbons, J.M. Rapid assessment of forest canopy and light regime using smartphone hemispherical photography. Ecol. Evol. 2017, 7, 10556–10566. [Google Scholar] [CrossRef]
  38. Francone, C.; Pagani, V.; Foi, M.; Cappelli, G.; Confalonieri, R. Comparison of leaf area index estimates by ceptometer and PocketLAI smart app in canopies with different structures. Field Crops Res. 2014, 155, 38–40. [Google Scholar] [CrossRef]
  39. Duguid, M.C.; Ashton, M.S. A meta-analysis of the effect of forest management for timber on understory of plant species diversity in temperate forests. For. Ecol. Manag. 2013, 303, 81–90. [Google Scholar] [CrossRef]
  40. Nave, L.E.; Vance, E.D.; Swanston, C.W.; Curtis, P.S. Harvest impacts on soil carbono storage in temperate forests. For. Ecol. Manag. 2010, 259, 857–866. [Google Scholar] [CrossRef]
  41. CCA/UFSCar. Climatological Data. 2015. Available online: https://www.cca.ufscar.br/ptbr/servicos/dados-climatologicos (accessed on 16 December 2021).
  42. Oliveira-Filho, A.T.; Fontes, M.A. Patterns of floristic differentiation among Atlantic Forests in Southeastern Brazil and the influence of climate. Biotropica 2000, 32, 793–810. [Google Scholar] [CrossRef]
  43. IBGE. Manual Técnico da Vegetação Brasileira, Instituto Brasileiro de Geografia e Estatística—IBGE. 2012. Available online: https://biblioteca.ibge.gov.br/index.php/biblioteca-catalogo?view=detalhes&id=263011 (accessed on 10 September 2023).
  44. Onofre, F.F. Restauração da Mata Atlântica em Antigas Unidades de Produção Florestal com Eucalyptus Saligna (Smith). no Parque das Neblinas. Master’s Thesis, University of São Paulo, Bertioga, SP, Brazil, 2009. [Google Scholar]
  45. Weidlich, E.V.A.; Flórido, F.G.; Sorrini, T.S.; Brancalion, P.H.S. Controlling invasive plant species in ecological restoration: A global review. J. Appl. Ecol. 2020, 57, 1806–1817. [Google Scholar] [CrossRef]
  46. Hakamada, R.; Giunti-Neto, C.; Lemos, C.C.Z.; Silva, S.R.; Otto, M.S.G.; Hall, K.B.; Stape, J.L. Validation of an efficient visual method for estimating leaf area index in clonal Eucalyptus plantations. For. Sci. 2016, 78, 275–281. [Google Scholar] [CrossRef]
  47. Dias, D.M.; Pagotto, M.A.; Pereira, T.C.; Ribeiro, A.S. Estrutura arbórea e sazonalidade da cobertura do dossel em vegetação florestada e aberta no Parque Nacional Serra de Itabaiana, Sergipe, Brasil. Sci. Flo. 2017, 27, 719–729. [Google Scholar] [CrossRef]
  48. Garcia, L.C.; Rezende, M.Q.; Pimenta, M.A.; Machado, R.M.; Lemos-Filho, J.P. Heterogeneidade do dossel e quantidade de luz no recrutamento do sub-bosque de uma mata ciliar no Alto São Francisco, Minas Gerais: Análise através de fotos hemisféricas. Rev. Bras. Biociências 2007, 5, 99–101. [Google Scholar]
  49. Frazer, G.W.; Canham, C.D.; Lertzman, K.P. Gap Light Analyzer (GLA): Imaging software to extract canopy structure and gap light transmission indices from true-colour fisheye photographs. In User’s Manual and Program Documentation, Version 2.0; Simon Fraser University: Burnaby, BC, Canada; Institute of Ecosystem Studies: Millbrook, NY, USA, 1999. [Google Scholar]
  50. Schiavo, B.N.V. Métodos para Estimativa do Índice de área Foliar em um Fragmento de Floresta Ombrófila Mista Montana no Estado do Paraná. Master’s Thesis, Federal University of Paraná, Curitiba, PR, Brazil, 2016; 122p. [Google Scholar]
  51. Bates, D.; Mächler, M.; Bolker, B.M.; Walker, S.C. Fitting linear mixed-effects models using lme4. J. Stats. Soft. 2015, 67, 1–48. [Google Scholar] [CrossRef]
  52. Fox, J.; Weisberg, S. An R Companion to Applied Regression, 3rd ed.; Sage: Thousand Oaks, CA, USA, 2019; Available online: https://socialsciences.mcmaster.ca/jfox/Books/Companion/ (accessed on 10 September 2023).
  53. Lenth, R. Emmeans: Estimated Marginal Means, Aka Least-Squares Means. R Package Version 1.8.6. 2023. Available online: https://CRAN.R-project.org/package=emmeans (accessed on 10 September 2023).
  54. R Core Team. R: A Language and Environment for Statistical Computing; R Foundation for Statistical Computing: Vienna, Austria, 2023; Available online: www.R-project.org/ (accessed on 10 September 2023).
  55. Hu, J.; Herbohn, J.; Chazdon, R.; Baynes, J.; Wills, J.; Meadows, J.; Sohel, M.S. Recovery of species composition over 46 years in a logged Australian tropical forest following different intensity silvicultural treatments. For. Ecol. Manag. 2018, 409, 660–666. [Google Scholar] [CrossRef]
  56. Rozendaal, D.M.A.; Bongers, F.; Aide, T.M.; Alvarez-Dávila, E.; Poorter, L. Biodiversity recovery of Neotropical secondary forests. Sci. Adv. 2019, 5, eaau3114. [Google Scholar] [CrossRef]
  57. Mesquita, R.C.G.; Ickes, K.; Ganade, G.; Williamson, G.B. Alternative successional pathways in the Amazon Basin. J. Ecol. 2001, 89, 528–537. [Google Scholar] [CrossRef]
  58. Cerullo, G.R.; Edwards, D.P. Actively restoring resilience in selectively logged tropical forests. J. App. Ecol. 2019, 56, 107–118. [Google Scholar] [CrossRef]
  59. Gandolfi, S.; Joly, C.A.; Leitão-Filho, H.F. “Gaps of deciduousness”: Cyclical gaps in tropical forests. Sci. Agric. 2009, 66, 280–284. [Google Scholar] [CrossRef]
  60. McKinney, M.L.; Lockwood, J.L. Biotic homogenization: A few winners replacing many losers in the next mass extinction. Trends Ecol. Evol. 1999, 14, 450–453. [Google Scholar] [CrossRef]
  61. Holl, K.D. Restoring tropical forests from the bottom-up. Science 2017, 355, 455–456. [Google Scholar] [CrossRef]
  62. Jonckheere, I.; Fleck, S.; Nackaerts, K.; Muys, B.; Coppin, P.; Weiss, M.; Baret, F. Review of methods for in situ leaf area index determinations: Part I. Theories, sensors and hemispherical photography. Agric. For. Meteorol. 2004, 121, 19–35. [Google Scholar] [CrossRef]
  63. Chianucci, F.; Cutini, A. Estimation of canopy properties in deciduous forests with digital hemispherical and cover photography. Agric. For. Meteo. 2013, 168, 130–139. [Google Scholar] [CrossRef]
  64. Orlando, F.; Movedi, E.; Paleari, L.; Gilardelli, C.; Foi, M.; DellÓro, M.; Confalonieri, R. Paulo. Estimating leaf area index in tree species using the PocketLAI smart app. App. Veg. Sci. 2015, 18, 716–723. [Google Scholar] [CrossRef]
  65. Tichy, L. Field test of canopy cover estimation by hemispherical photographs taken with a smartphone. J. Veg. Sci. 2016, 27, 427–435. [Google Scholar] [CrossRef]
  66. Latawiec, A.E.; Strassburg, B.B.N.; Brancalion, P.H.S.; Rodrigues, R.R.; Gardner, T. Creating space for large-scale restoration in tropical agricultural landscapes. Front. Ecol. Environ. 2015, 13, 211–218. [Google Scholar] [CrossRef]
Forests 14 02140 g001
Figure 1. Photosynthetically active radiation (% PARUND) and percentage of canopy opening at different chemical thinning intensities: 0%, 30%, 60%, and 100% of the total basal area, respectively, over time. Measurements were compared over time: before thinning (February 2018); three months after thinning (3 mo; July 2018); one year after thinning (1 y; February 2019). Different letters indicate significant differences after the generalized mixed models (all p < 0.05).
Figure 1. Photosynthetically active radiation (% PARUND) and percentage of canopy opening at different chemical thinning intensities: 0%, 30%, 60%, and 100% of the total basal area, respectively, over time. Measurements were compared over time: before thinning (February 2018); three months after thinning (3 mo; July 2018); one year after thinning (1 y; February 2019). Different letters indicate significant differences after the generalized mixed models (all p < 0.05).
Forests 14 02140 g001
Forests 14 02140 g002
Figure 2. Correlation (Pearson’s r correlation) between photosynthetically active radiation (%PARUND) and canopy opening (%) across all plots (r = 0.76) and split per chemical thinning intensities: 0% (purple dots and deviation, r = 0.48), 30% (blue, r = 0.34), 60% (green, r = 0.4), and 100% (yellow, r = 0.66) of the total basal area (all p < 0.001).
Figure 2. Correlation (Pearson’s r correlation) between photosynthetically active radiation (%PARUND) and canopy opening (%) across all plots (r = 0.76) and split per chemical thinning intensities: 0% (purple dots and deviation, r = 0.48), 30% (blue, r = 0.34), 60% (green, r = 0.4), and 100% (yellow, r = 0.66) of the total basal area (all p < 0.001).
Forests 14 02140 g002
Table 1. Fast-growing and timber species planted in the tropical forest restoration site, in which the chemical thinning experiment was performed, in Araras (SP), Southeastern Brazil. Fast-growing species are pioneers, while timber species are non-pioneers often used for tropical forest restoration [9].
Table 1. Fast-growing and timber species planted in the tropical forest restoration site, in which the chemical thinning experiment was performed, in Araras (SP), Southeastern Brazil. Fast-growing species are pioneers, while timber species are non-pioneers often used for tropical forest restoration [9].
SpeciesFamily
Fast-growing trees—planted in January 2014
Acnistus arborescens (L.) Schltdl.Solanaceae
Apeiba tibourbou Aubl. Malvaceae
Croton floribundus Spreng.Euphorbiaceae
Guazuma ulmifolia Lam.Malvaceae
Heliocarpus popayanensis Kunth.Malvaceae
Inga vera Willd.Fabaceae
Senna alata (L.) Roxb.Fabaceae
Senna multijuga (Rich.) H.S.Irwin & BarnebyFabaceae
Solanum granuloso-leprosum DunalSolanaceae
Trema micranthum (L.) BlumCannabaceae
Timber species—planted in Oct/Nov 2015 in the understory of fast-growing trees
Anadenanthera colubrina (Vell.) BrenanFabaceae
Astronium graveolens Jacq.Anacardiaceae
Balfourodendron ridelianum (Engler) EnglerRutaceae
Cariniana estrellensis (Raddi) KuntzeLecythidaceae
Cariniana legalis (Mart.) KuntzeLecythidaceae
Centrolobium tomentosum Guillen. ex Benth Fabaceae
Cordia trichotoma (Vell.) Arrabida ex Steudel Boraginaceae
Handroanthus heptaphyllus MattosBignoniaceae
Parapiptadenia rigida (Benth.) BrenanFabaceae
Peltophorum dubium (Spreng.) Taub. Fabaceae
Zeyheria tuberculosa (Vell.) Bureau ex Verl.Bignoniaceae
Table 2. Resprouting of fast-growing trees four months after chemical thinning with glyphosate, in a tropical forest restoration planting in Araras (SP), Southeastern Brazil. Different letters among species indicate differences for resprouting frequency (Dunn test, p < 0.05).
Table 2. Resprouting of fast-growing trees four months after chemical thinning with glyphosate, in a tropical forest restoration planting in Araras (SP), Southeastern Brazil. Different letters among species indicate differences for resprouting frequency (Dunn test, p < 0.05).
SpeciesTrees Submitted to ThinningFrequency
of Resprouting (%)
Acnistus arborescens (L.) Schltdl.5750.88 b
Croton floribundus Spreng.8864.77 a
Croton urucurana Baill.319.68 c
Guazuma ulmifolia Lam.9782.47 a
Heliocarpus popayanensis Kunth.5527.27 bc
Inga vera Willd.2638.46 b
Senna multijuga (Rich.) H.S.Irwin & Barneby6033.33 b
Solanum granuloso-leprosum Dunal16524.85 bc
Trema micrantha (L.) Blum944.44 b
Alltogether58844.05
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Barros, A.J.; Loiola, P.d.P.; Viani, R.A.G. Chemical Thinning and Fisheye Clip for Managing Light Intensity in the Understory of Forest Restoration. Forests 2023, 14, 2140. https://doi.org/10.3390/f14112140

AMA Style

Barros AJ, Loiola PdP, Viani RAG. Chemical Thinning and Fisheye Clip for Managing Light Intensity in the Understory of Forest Restoration. Forests. 2023; 14(11):2140. https://doi.org/10.3390/f14112140

Chicago/Turabian Style

Barros, André Junqueira, Priscilla de Paula Loiola, and Ricardo Augusto Gorne Viani. 2023. "Chemical Thinning and Fisheye Clip for Managing Light Intensity in the Understory of Forest Restoration" Forests 14, no. 11: 2140. https://doi.org/10.3390/f14112140

APA Style

Barros, A. J., Loiola, P. d. P., & Viani, R. A. G. (2023). Chemical Thinning and Fisheye Clip for Managing Light Intensity in the Understory of Forest Restoration. Forests, 14(11), 2140. https://doi.org/10.3390/f14112140

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