Introduction

In the state of Pará in the Brazilian Amazon, forest and agroforestry plantations with native species are on the rise. The availability of disturbed areas and global pressure to preserve the Amazon rainforest have allowed the introduction of monocultures, consortia, windbreaks and agroforestry systems; the tree species Schizolobium parahyba var. amazonicum is the most used in these crops. ^{Cordeiro et al. (2009)} found that these systems generate environmental benefits and increase the supply of wood for reforestation and income for the people who manage the cultivated areas; so they are an alternative to restore areas with different degrees of degradation and abandoned by shifting cultivation. But to promote stability of these crops you need to plan forest products, control the process of operation, increase profits and maintain the balance between supply, demand and environment. For this purpose, you must apply a set of techniques to manage forest management units. These techniques are essential to estimate productivity of local species, since they contribute to the determination of the annual crop in the rotation period of the appropriate species (^{Vargas-Larreta et al., 2010}). Therefore, a major challenge in the Amazon jungle is to reforest degraded areas with native species that meet industry needs to improve productivity.

Of the different farming systems used in the state of Pará, S. parahyba var. amazonicum (Huber ex Ducke) barneby (gavilán) plantations tend to be the main source of raw material for the manufacture of veneer and plywood. The choice of the species is due to its excellent forestry response since its growth is superior to most species (^{Cordeiro et al. 2009}), also its physical and mechanical properties for lamination are optimum (^{Lanza de Sá, 2004}) as well as its use in laminated wood beams (^{Terezo and Szucs, 2010}). The species grows naturally in the Amazon, especially in Brazil, in areas of primary and secondary forests, upland soils (^{Ducke, 1939}; ^{Pereira et al., 1982}). In Pará, during the period 2007-2009, the areas reforested with S.parahyba var. amazonicum increased from 41 100 to 79 159 ha, and went from 11 to 18.6 % of the total plantations with other species, as Switenia macropylla, Bertolhetia excelsa, Eucalyptus sp., Tectona grandis (SBS, 2013).

Studies of growth in the tropics are limited, often because the growth rings of trees are not visible. Dendrochronological researches are related to introduced and fast-growing species, mainly Pinus and Eucalyptus. Therefore, the growth of trees and the various climatic conditions data are obtained through periodic measurements of variables such as diameter, height, volume, weight, and biomass. Studies by ^{Pereira et al. (1982)}, ^{Rondon (2002)}, ^{Tonini et al. (2006)} and ^{Nascimento et al. (2012)} in gavilán plantations found that climatic factors, soil, topography, biological inter- and intra-specific competition and other byproducts of human activities (thinning of the ground and fires), often affect physiological processes and are reflected on the height and diameter.

^{Cordeiro et al. (2009)} found that the cropping systems influence the growth of the species; also in gavilán plantations the appropriate mix of species with economic value makes a better use of space and generates social and environmental benefits. In this respect, the cultivation of A. comosus var. erectifolius (curauá), bromeliad producer of fiber, associated with S. parahyba var. amazonicum, is justified by the use of the site in the early years of the establishment of forest species, along with the possibility to earn income from the production of leaves, seeds and fibers with various crops. Thus, profits and income are generated in a short period, and the growth of S. amazonicum increases (^{Cordeiro et al., 2010}). In addition to these responses and characteristics of the species, there is a need for information on changes in the growing conditions of native species.

The differences in growth in Schizolobium plantations in relation to the presence of the agricultural component can explain the development of gavilán. As a way to verify this influence the objective of the study was to examine the growth in height and diameter of S. parahyba var. amazonicum in the presence and absence of the agricultural component Ananas comosus var. erectifolius in Aurora do Pará, Brazil.

Materials and Methods

Results and Discussion

The growth of H and DBH showed significant differences (p≤0.05) between planting systems with presence and absence of curauá at 3 and 5 years of age, and a highly significant difference at 4 years of age (p≤0.01). Moreover, there were significant differences of the variation source over time (p≤0.05). The interaction time for sowing per crop in gavilán plants of 3 and 5 years of age was significant (p≤0.05), but not for the 4 year-old plant (p>0.05) (Table 2).

Gavilán plants of 3 and 4 years old in the presence of curauá differred significantly from those grown in the absence of agricultural species (Table 3). Growing systems plants, five years old, did not follow the same trend of younger plants. According to ^{Cordeiro et al. (2006)}, the initial increase in growth driven by fertilizers and bromeliad leaves residues deposited on the soil after each harvest, justifies the adoption of the technique.

Plants cultivated in the presence of curauá showed higher growth in DAP, as compared to farming systems of the same age in the absence of agricultural crop (Table 3). ^{Ohashi et al. (2010)}, ^{Silva et al. (2011)} and ^{Ruivo et al. (2012)} obtained similar results, whereby the gavilán crop planted with the agricultural species, regardless of the plantation age, showed an average increase of 9.5, 15.1, 18.07 and 11.5 m high, and 20.36, 11.6, 14.42 and 25.74 cm in diameter, with respect to plants in monoculture.

The growth trend of plants was similar during the experimental period, and between 12 and 24 months there was a significant increase in growth followed by a slight decrease in growth. Thus, for both variables the juvenile stage and rectilinear period were characterized in height and partly diameter, but it was impossible to verify the seasonal growth period (Figures 1 and 2).

Figure 1 Variation in height growth of Schizolobium parahyba var. amazonicum between 6 and 36 months of study in the presence and absence of Ananas comosus var. erectifolius. Tramontina Belem Experimental Station SA, Aurora do Pará (PA). G: Gavilán, L: Laurel; C: Mahogany (Caoba); c: curauá. 

Figure 2 Variation in the growth of Schizolobium parahyba var. amazonicum in diameter at breast height (DBH) within 6-36 months of study in the presence and absence of Ananas comosus var. erectifolius. Tramontina Belem Experimental Station SA, Aurora do Pará (PA). G: Gavilán, L: Laurel; C: Mahogany (Caoba); c: curauá. 

In trees, the variable height generally presented more pronounced changes in growth, especially in young age; the rapid change in height was evident in short periods of time.Therefore, gavilán plants (Figure 1) in the systems studied are influenced in their growth not only in the initial stage, but also at later stages, as they depend on environmental conditions. ^{Imaña-Encinas et al. (2005)} observed that these variations in height and diameter of trees depend on several factors that limit growth, and are not always controlled or supervised. ^{Husch et al. (1982)} stated that for each species and tree a time period would be necessary to complete their life cycle. According to ^{Schwartz et al. (2013)}, through silvicultural techniques, such as the adoption of different initial spacings and fertilizer application the behavior of growth can change and its curve can be anticipated.

The gavilán is a fast growing species and its juvenile phase is very short (one to three years); the second phase extends for a longer period. The beginning of the stationary phase is difficult to determine accurately since it depends on factors such as climate and soil conditions.

Height growth is the result of the cell division activity in the bud or terminal. Then, due to the apical dominance of gavilán, the growth process in height seems to be related to the intense production of auxin and gibberellin in the first and second years, though it declines after the third year. This assumption is consistent with the findings by ^{Morey (1980)}, who states that tropical woody plants of rapid growth have an accelerated pace in the first two years, and then the diffusible growth regulators are no longer produced, but directed to change (cambial) activity.

Diameter growth increased in the initial stage; it was followed by a slow and steady growth between 12 and 18 months, and rose again between 18 and 24 months. Then we observed a less marked growth trend up to 36 months (Figure 2). The gradual growth in diameter is given in terms of the activities of vascular change (^{Husch et al., 1982}). In trees, diameter growth is influenced mainly by age, plant spacing and site conditions, as well as plant hormones, and interrelated environmental and genetic factors. Thus, ^{Cordeiro et al. (2009)} verified in 12-month-old gavilán plants a positive influence on the growth of diameter when they were associated with agricultural species.

The diameter curve appeared when the tree was 1.30 m tall, and the juvenile stage had already begun. This type of growth occurs abruptly, whereas the rectilinear phase usually takes a while and the annual rate substantially decreases. Even when gavilán exhibited this behavior, it was not possible to predict that of the species in the stages after the juvenile, since the study covered a period of only 36 months. In this regard, ^{Scolforo (1994)} reported that the value of the variables was produced by the physiological activity of the plant (primary and secondary or exchange meristem), but decreased as the time period of observation of variables became less precise over the changes in biological growth, noting that the growth of a tree shows different variations in height, diameter, basal area, volume and weight, and depends on several factors that are not always controlled or monitored, such as genetic and interactions with the environment. In a study carried out in central Mexico with Taxodium mucronatum, ^{Correa-Díaz et al. (2014)} observed that climatic variables are indicators of the growth pace of trees. These authors suggested that temperature influences the plant meristematic activity and photosynthesis activity, which can lead to a higher growth during the growing season.

From the results, it is clear that the establishment of agroforestry meets the need of rapidly having trees with an appropriate and desirable diameter for the industrial use of wood, and contribute to reinforcing the adoption of sustainable and ecological practices.

In the selection of species for commercial plantations, the most used variable is volume, and the good performance of S. parahyba var. amazonicum plants indicates that it is possible to practice agroforestry rationally.

The difference between these productions biologically justify sowing A. comosus var. erectifolius in conditions similar to those of the species studied. However, one aspect of this production that could pose problems would be the quality of wood obtained by the rapid initial development.

Wood formation is influenced by environmental variations, cultural practices of the species and time of planting. When young, physiology does not ensure that plants fix carbon, synthesize new tissues and earn the specific mass expected (^{Trugilho et al., 2015}). Thus, any change in the quality of wood influences the processing and industrialization of rough lumber.

Conclusion

Schizolobium parahyba var. Amazonicum plants, regardless of the cultivation system used, in the presence or absence of the agricultural component Ananas comosus var. erectifolius, follow the normal growth trend, both in height and diameter (at breast height); the latter is more pronounced in the first two years of planting, and from that period onwards the intensity of growth decreases. The growth of gavilán is favored by the presence of the agricultural component curauá.