In the emergence of the species, the data showed that the use of different treatments (seed density, types of fertilizers, types of crops, time) exerted a significant influence on the emergence of seeds, and some factors may explain these results.
In the field, the emergence of C. pachystachya may have been affected by the depth of planting, because this species has very small seeds, since this species is photoblastic positive requiring light for its germination, data that corroborate the observations of Jesus et al. (2017).
The absence of emergence of C. antisyphilitica may be related to predation of seeds and seedlings before the first evaluation that occurred at 90 days, because in studies by several researchers, the field emergence rates are higher than 50% (Salomao et al. 2003; Scremin-Dias et al. 2006).
The low emergence rate observed may be due to the various ecological filters, both biotic and abiotic, which interfere with the success of using this technique. Among these filters, seed size (Camargo et al. 2002; Tunjai and Elliott 2012; Meli et al. 2018), seed predation (Guarino and Scariot 2014), competition with grasses (Doust et al. 2006; Pereira et al. 2013; Cava et al. 2016), and climatic factors (Vieira and Scariot 2006; Silva et al. 2015), are highlighted. The low percentage of emergence and establishment has been a constant in most direct seeding studies (Woods and Elliott 2004; Doust et al. 2006, Sampaio et al. 2007; Palma and Laurance 2015; Cava et al. 2016; Ceccon et al. 2016, Meli et al. 2018).
The density used has significantly affected the emergence of the species, because as the density increased, the greater the number of individuals. Regarding the density of 10 seeds that obtained 833 individuals in 669.6 m2, it is suggested to thin at least 30% of the individuals to reduce competition, because styolate plants can be sensitive to fungal attacks and herbivory of leaf-cutting ants, because due to the low incidence of light the leaves of these plants tend to be more palatable to ants, that is, the leaf ends up getting softer and more attractive, which can decrease the success in forest restoration due to the increase in plant mortality (Brancalion et al., 2015).
Considering seed emergence at both densities, in one hectare a density of 6.303 and 12.440 seeds/ha is estimated. And this result is relevant with regard to direct sowing in forest restoration, both for the purpose of implementing arrangements in agroforestry systems and for the recovery of degraded areas, since in traditional models used in planting seedlings, the density in general varies from 1.666 (Davide et al. 2000).
When considering a biodiverse SAF that on average present around 400 to 1100 tree individuals per hectare (Padovan et al. 2017), the use of direct sowing to compose these arrangements is promising. The variation of species composition has been also observed by some researchers, who indicate an optimal seed density for restoration planting between 6.000 and 13.000 seeds per hectare (Meli et al. 2018).
Direct sowing can favor diversified and functional spatial arrangements in agroforestry systems and provide superior results to those found in planned arrangements with seedling planting. According to Notaro et al. (2021), the structural and functional diversity of agroforestry systems linked to species diversity and the spatial arrangement of different crops has resulted in significant differences in production between the associated which was proven in this study.
Some species maintained a dissimilarity of the groups formed by the treatments, namely: Astronium urundeuva, Bixa orellana, Didymopanax morototoni, Libidibia ferrea and Lithraea molleoides.
Seeds dormancy may have been a determining factor in the germination of the species used in this study, since they present physical and physiological dormancy. It is suggested that the significant difference in the time variable can be explained by the tegumentary /physical dormancy of some species, such as the case of Hymenaea courbaril (Fabaceae), which obtained its highest peak of emergence at 270 days. Libidibia ferrea (Fabaceae) is also a species that presents tegumentary dormancy, and not overcoming dormancy may have hindered its germination in the field. Water seed coat impermeability is the most common dormancy mechanism in the Fabaceae family (Baskin and Baskin 2014).
The species Myrsine umbellata and Calophyllum brasiliense present physiological dormancy, and even if they showed viability in the tetrazolium test for germination, possibly the presence of inhibitory substances or absence of substances that promote germination prevented germination in the field (Baskin and Baskin 2014).
Another relevant factor to consider is the physiological behavior of the forest seeds used, because according to the classification of Roberts (1973), the seeds being recalcitrant, can not be dehydrated below a certain degree of moisture, without any physiological damage occurring, and being orthodox can be dehydrated at low moisture levels (5 to 7% moisture) and stored in low temperature environments, so in the field, orthodox seeds can have an initial advantage in germination under adverse conditions.
Among the species with the highest dissimilarity in the NMDS, it is known that Bixa orellana is orthodox (Amaral et al. 1995) due to physical dormancy; Didymopanax morototoni has physical dormancy (Carvalho 2002); Lithraea molleoides presents physical dormancy, being classified as an orthodox species (Carvalho et al. 2006), Astronium urundeuva, presents an orthodox physiological behavior (Medeiros et al. 2000); thus, it is believed that the physiological behavior of these species and the type of dormancy identified may have delayed the germination of these seeds during the time in which the experiment was evaluated in the field. It should be noted that the species L. molleoides and A. urundeuva had the worst emergence rates, as both had only one individual during the time of analysis of the work.
Other factors may be related to low emergencies of these species, such as competition with exotic grasses, predation, seed dissection among others. Some authors emphasize the importance of understanding the reproductive strategies of plant species, especially in arid environments, from species with rapid germination that can have advantages with sporadic rainfall, as well as knowing the species that present late germination; such knowledge can avoid risks in restoration strategies (Duncan et al. 2019).
The overcoming of dormancy must be performed manually with the aid of utensils such as knife and/or scissors, or with sulfuric acid, or just subjecting the seeds to thermal shock, action commonly performed in nurseries with the seeds before sowing (Ky-Dembele et al. 2022). Thus, it is recommended to overcome the dormancy of these species before planting to homogenize the emergence.
The groups formed by the different fertilizers used are composed of species that had lower mortality rates, a positive observation for the use of fertilizers in direct sowing. Organic fertilization can increase the quality of the plants, favor a good nutrient reserve for the plant and consequently increase its resilience against adversities in the field (Gonçalves 1995). However, it is necessary to pay special attention to the dosage of the fertilizer that is intended to be used, because an inadequate fertilization can harm the establishment of the plant in the field.
This reflection also occurred for the consortium with different agricultural crops, where the species with the largest emerging individuals were those that were grouped within the treatments with agricultural crops in the NMDS. It is believed that the agricultural crops tested did not affect the emergence of the species studied. This can be explained by the fact that they are planted between the rows, so there is no initial competition. In the restoration of riparian forests, the intercropping of tree species with agricultural crops has shown a positive economic impact of intercropping, and it is possible to verify that the growth of tree species has not been affected by intercropping with agricultural crops (Daronco et al. 2012).
Of the species studied only E. uniflora, E. myrcianthes and J. decurrens emerged in all treatments, and showed the highest emergence rates, with 312, 356 and 115 individuals respectively.
The high emergence rates obtained for these species demonstrate their potential to compose agroforestry arrangements, since in addition to serving the forest component, they can generate income with the commercialization of their fruits. In addition, E. uniflora and E. myrcianthes are zoochoric species, attractive to seed dispersing fauna that, when feeding, bring along seeds of other species, which can increase the diversity of the site, thus promoting the restoration of ecological processes in the permanent preservation area.
Silva (2017) also pointed out the germinative potential of E. uniflora, E. myrcianthes and correlates this performance to seed size. According to Doust (2006), the larger seeds have a greater potential for emergence and establishment in the field, when compared to the smaller ones, and especially when they are subjected to stressful conditions, such as drought, shading or flooding.
Among the 23 species used in direct sowing, mortality was noticeable in some species: Anadenanthera peregrina, Bixa orellana, Calophyllum brasiliense, Eugenia myrcianthes, Eugenia involucrata, Eugenia uniflora, Hymenaea courbaril, Jacaranda decurrens, Lithraea molleoides and Lonchocarpus cultratus. It is believed that the survival found in this study can be considered high, based on studies by Corrêa and Cardoso (1998), who tested several species for restoration, and defined that species with rates less than or equal to 60 between 61 and 80% are considered of medium survival, and if it is greater than or equal to 81% the survival rate is considered high.
In the NMDS ordination, the species Bixa orellana, Eugenia myrcianthes, Hymenaea courbaril and Lithraea molleoides, were the most dissimilar with the types of fertilizer and culture, however there was no significant difference to explain the influence of these treatments used.
The species that had the highest mortality rates were E. myrcianthes and E. uniflora, the high mortality rate of these species is justified by the large number of individuals that emerge over the 270 days of observation of the experiment. Other factors also contributed to the mortality of some species, such as competition with grasses and foraging of leaf-cutting ants, because some species of ants can perform several cuts on the same plant, in several periods, removing all leaves of the plant, causing its senescence and consequently the establishment of the same in the forest restoration process (Roglin et al. 2013).
The relationship between diameter and height was significant, being explained with more than 75% of the coefficient of determination for most species. Over time there was an increase of the species in diameter and height, which can be considered a positive point for the use of these species in the field.
Some zoochoric species showed a rapid growth gradually during the evaluation time as, Solanum mauritianum, Bixa orellana, Guazuma ulmifolia, Schinus terebinthifolia. These species are considered pioneers, which develop in clearings, on the edges of the forest or in open places, being clearly dependent on conditions of greater luminosity, not occurring, in general, in the understory (Gandolfi et al. 1995); these zoochoric pioneer species are potential for use in agroforestry systems for being the first to stand out in the growing recovery process and for providing food for the dispersing fauna, which will consequently disperse their seeds and propagules in adjacent areas and also increase the diversity of species by releasing their droppings on the perching trees.
The species Astronium urundeuva, Didymopanax morototoni, Libidibia ferrea, Psidium guajava, Eugenia myrcianthes, Eugenia uniflora, Calophyllum brasiliense and Myrsine umbellata, are late secondary, species that grow exclusively in permanently shaded understory and, in this case, small trees or large tree species that grow slowly in shaded environments and may reach the canopy or be emerging (Gandolfi et al. 1995); therefore the growth of these species in the field throughout the monitoring was a reflection of this characteristic, however, despite the somewhat late development, they will be responsible for the agroforestry system to evolve from an early successional stage to an advanced successional stage, a determining factor to prove the environmental resilience of the agroforestry system.
When making an inventory of the costs of this direct sowing technique for species composition in agroforestry systems, it was observed that the highest cost of direct sowing is the seeds R$ 8.383,81 (US$ 1.631,1) followed by the maintenance of the area. Contudo, considerando os dados obtidos neste trabalho, podemos indicar uma redução no número de sementes pela metade o que reduziria em muito o custo da implantação (R$ 9.334,10 - U$$ 1.815,9). For planting in total area with seedlings the costs vary between R$ 15.000 to R$ 20.000 (US$ 2.918,3 to US$ 5.836,6) (Medeiros et al. 2019), thus, direct sowing represents a very viable alternative in reducing costs. In addition, the producer can further reduce the cost of native seeds by collecting from adjacent native areas through seed collectors. Cabe ainda mencionar que a longo prazo o SAF ainda pode continuar gerando renda ao agricultor, desde que este faça o manejo das espécies florestais e insira espécies de ciclo longo como café e pupunha. Thus, the SAF, in addition to restoring ecological processes, promotes food security and income for the farmer.