INFLUENCE OF THE REPLANTING AGE ON YIELD AND GROWTH OF EUCALYPT CLONAL STANDS

The growth of an eucalypt plantation should be monitored to identify factors that infl uence its development, helping in the decision-making process, aiming to reduce productivity losses. Thus, the objective of the present study was to evaluate the infl uence of the age of replanting on the yield and growth of eucalypt stands. The experiment was conducted in an area of CENIBRA S.A. Company, and established in a commercial plantation in August 2011. The application of herbicide and the ant control were performed in total area before planting. Seedlings of Eucalyptus urophylla × Eucalyptus grandis clones in 3.0 × 2.5 m spacing were used. Limestone (1,500 kg ha) was applied in total area before planting and 100 g plant-1 of NPK fertilizer (06-3006) was applied immediately after planting. Four months after the installation of the experiment, 300 kg ha of NPK (06-10-29) was applied. Treatments consisted of four dates of seedling replanting (0, 20, 40 and 80 days after planting) without complementary fertilization, and two treatments (replanting 40 and 80 days after planting) with supplementary fertilization (100g plant NPK 06-30-06). The individual volume of replanting trees was 46.6% lower than of non-replanted ones. Treatments with complementary planting fertilization did not diff er (p > 0.05) by the T-test. It is concluded that the longer the time between planting and replanting, the smaller the individual volume of the replanting trees and that the complementary fertilization in seedlings replanted does not favor their growth.


INTRODUCTION
Brazilian eucalyptus stands are among the most productive in the world Binkley et al., 2017). The average productivity at seven years old, in the 1970s was close to 15 m³.ha -1 .year -1 (Queiroz and Barrichelo, 2007), and close to 35.7 m³ha -1 year -1 in 2016 (IBÁ, 2017). To this end, it was necessary to ensure the adequacy of the technical recommendations and quality of forestry operations (Trinidad et al., 2017), which bring improvements in the distribution of inputs and ensures the development of a more uniform and productive forest. There is a positive relationship between uniformity and productivity of eucalyptus stands (Stape et al., 2010;Luu et al., 2013;, which are aff ected by the quality of silvicultural operations (Radtke et al., 2003).
The presence of individuals of diff erent ages in the stand also aff ects the quality of the forest and occurs due to the replanting (Correia et al., 2011). Replanting is a costly activity, and it is related to the poor quality of forest deployment activities (Chichorro et al., 2017) and when performed out of time, can lose its initial goal of ensuring the highest productivity of the stand. Late replanting causes greater competition for resources between plants, as older trees grow faster than younger trees because they use resources more effi ciently (Binkley, 2004).
Dominated trees are undesirable in planted forests due to its undergrowth, susceptibility to pests and diseases (Alfenas et al., 2004) and increased vulnerability to environmental stress conditions. The increase in dominated plants within the stand causes a loss in production potential (Schneider et al., 2015). In this sense, the uniformity of a stand will only be considered critical once the heterogeneous growth of the trees generates loss of forest productivity and, consequently, economic damage.
The growth of a eucalyptus plantation should be monitored to identify factors that infl uence its development, helping to make decisions to correct or prevent possible productivity losses. The objective of this study was to evaluate the infl uence of the replanting season on the yield and growth of eucalyptus stands.

MATERIAL AND METHODS
The experiment was conducted in an area belonging to the company Celulose Nipo-Brasileira S.A. (CENIBRA S.A.), located in the municipality of Belo Oriente, Minas Gerais, that has a Latosolic Cambisol (CXbd5). The climate is characterized as Aw (Köppen), mesothermal, tropical rainy, with annual average precipitation of 1,208 mm, annual average temperature of 25,2ºC and average relative humidity of 65,2%. The region is located at 19º 10'S, 42º 20' W, with altitude ranging from 220 to 425 m.
The planting of the experiment was carried out in a commercial plot deployed in August 2011, following the technical recommendations and operations of the company. Herbicide application and ant control were performed in total area before planting. Clonal seedlings of Eucalyptus urophylla trees S.T. Blake x Eucalyptus grandis Hill ex Maiden (Myrtaceae) were planted at 3.0 × 2.5 m spacing. Fertilization was carried out with 1,500 kg.ha -1 of limestone applied in total area before planting and 100 g.plant -1 of NPK fertilizer (06-30-06), applied immediately after planting, in two lateral holes. Four months after the installation of the experiment a cover fertilization with 300 kg.ha -1 NPK (06-10-29) was made.
Treatments consisted in four dates of seedling replanting (0, 20, 40 and 80 days after planting) without complementary fertilization in the planting, plus two treatments (replanting 40 and 80 days after planting) with supplementary fertilization in the planting (+ 100 g/plant -1 NPK 06-30-06) ( Table 1). The experiment was made in a randomized block design with four replications.
The experimental plot had nine rows with nine plants. The replanting of the nine seedlings, in which the treatments were applied, was done so that each replanted seedling had a double border of nonreplanted seedlings. The entire plot was planted, and after 12 days the seedlings of the hole to be replanted were plucked and the replanting was made according to the treatments. The eff ect of the season of replanting in the volume of individual trees and average volume increase (AMI) in the volume of replanted trees, at 43 months, was evaluated by regression with 5% of signifi cance level in the F-test. The eff ect of supplementary fertilization in the planting was evaluated from the individual volume between treatment with and without supplementary fertilization in the last year of measurement, by T-test with 5% of signifi cance. For processing the data it was used the statistical software Statistica version 12 (STATSOFT, INC., 2014).
The diametric distribution of the trees in the stand was based on the grouping of the trees in the plots in class centers with amplitude of 3.0 cm (class center of 1.5 cm).

RESULTS
The individual volume of replanted trees was 46.6% lower than non-replanted trees and their lowest value (ŷ = 0.0635 m³) was observed when replanting was performed 80 days after replanting. The treatments with complementary planting fertilization, performed at 40 and 80 days of replanting, did not diff er (p > 0.05) by the T-test (Figure 1).
By the F-test, the AMI was not signifi cantly aff ected, considering the trees in these plots, the diff erent treatments, despite the reduction in volume of individual trees according to the replanting season (Table 1 and Figure 2).
The trees with larger DBH measured after 32 months were those with the largest increase in DBH at 43 months of age. The largest increase in DBH was observed in the individuals that the replanting was performed 20 days after planting, while the lowest value was in replanting that occurred 40 days after planting (Figure 3).
The diametric classes of lower value showed the smallest migration of trees to the class above. The 15.5 cm class center had an increased percentage from 9.10 to 31.00%, and after 43 months, 18.5% individuals entered the class center (Table 2).

DISCUSSIONS
The initial phase of forest implantation goes from planting until the end of the replanting, which can be done between 45 and 80 days after the beginning of the activities, and any replanting after this, leads to dominated seedlings (Stape et al., 2001). Seedling replanting should be performed if mortality exceeds 10%. Values below 10% do not represent loss in forest productivity, as long as the failures do not be together, forming a focus (Silva & Angeli, 2006). Decision-making on replanting takes into account, in addition to technical factors, also economic factors,  so that the operation is not economically unviable (Mafi a et al., 2005). The coppicing began to gain more attention from researchers and foresters for its economic viability and for satisfactorily meeting the producer's need for wood production (Gonçalves et al., 2014).
The individual volume of the trees from the planting was higher than that presented by the trees from the replanting, regardless of when it was done. The largest production of wood emphasizes the importance of carrying out the activities of planting following quality standards to ensure maximum survival and reduce unnecessary spendings since replanting is a costly activity (Summers et al., 2015). When evaluating the eff ect of replanting in the growth of seedlings of eucalyptus, diff erently from the present study, it was observed that when the replanting was made 20 days after planting the growth of the stand was not compromised . The diff erence in outcome is explained by the diff erence in the evaluation season since the authors monitored one year after replanting. By evaluating the eff ect of plant heterogeneity on the productivity of a eucalyptus forest, it was found that in the absence of genetic and species diversity, heterogeneity of planting has a negative eff ect on wood volume .
The complementary fertilization in the replant of the seedlings did not represent a signifi cant increase in their volumetric growth. Plants have nutrient absorption capacity limited to the volume of their root system and their physiological growth (Bordron et al., 2019). The fertilization of eucalyptus plants in higher than adequate doses impairs their development and consequently the quality of the plants ( Rocha et al., 2013). Therefore, the availability of additional fertilizer for a replanted seedling is not able to compensate for the loss of productivity due to the diff erence in days between planting and replanting.
The uniformity of trees in a stand of eucalyptus is a priority in its implementation (Hakamada et al., 2015), however, the growth of larger trees can compensate for the smaller ones, and the fi nal volume will not be compromised (Canh et al., 2013). The main factors that aff ect the growth of a eucalyptus stand are the productive capacity of the site, the genetic material and the uniformity of the planting. The interaction of these factors can have negative eff ects on forest productivity (Resende et al., 2018). This fact was evident in the present study since the AMI did not vary in the tested situations, despite the diff erence in the individual volume of the trees in replanting.
The greatest variation in the size of the trees in the stand results in higher variability in their growth (Otto et al., 2014). Nevertheless, the effi ciency in the use of nutrients in forest species is related to age, where older plants have higher nutritional effi ciency compared with those younger (Barros Filho et al., 2017). The lower effi ciency in nutrient absorption by the plant hinders its proper development (Nascimento Lima et al., 2005).
The growth rate is higher in trees in higher class center so that the largest trees at an early age will reach higher classes in future ages (Souza et al., 1993). The largest trees can also grow faster than smaller trees in the same stand, effi ciently using more resources in timber production (Binkley, 2004). Assessing the eff ect of diff erent height classes on the growth of a eucalyptus hybrid, it was found by the authors that dominant trees grow larger than suppressed trees due to several factors such as: competition for light, water, and nutrients (Cezana et al., 2012 ).
That is a tendency that replanted seedlings become, over time, trees increasingly dominated inside the stand. This increase in heterogeneity in monoclonal eucalyptus stands can reduce stand-level production by 18-20% (Stape et al., 2010;. In addition to the impacts caused by replanting on stand productivity, it also increases implementation costs.

CONCLUSIONS
A longer period for the replanting aff ects negatively the individual volume of the trees and the complementary fertilization of these replanted seedlings does not ensure their best development. Replanting should not be performed, up to 11% mortality, because it does not positively impact the productivity of the plantation. The fi nal volume of wood is not aff ected by the replanted seedlings because they become, over time, dominated trees.