Effects of Natural Atlantic Forest Regeneration on Soil Fauna , Brazil

The stage of natural forest regeneration may influence soil fauna. This study aimed to test the hypothesis that there are differences in the structure and composition of the soil fauna communities between areas undergoing less advanced (LAS) and more advanced (MAS) stages of natural regeneration of Seasonal Semideciduous Forest at Pinheiral, RJ. Soil fauna was sampled using pitfall traps, during dry and rainy seasons. Total abundance, abundance of the saprophagous/predator group, mainly Formicidae, and the relative participation of Orthoptera were higher in MAS, while the relative participation of Acari, Araneae, Coleoptera, Diptera and the herbivorous group were higher in LAS, during both climatic seasons. Some taxonomic groups were restricted to one of the areas. Richness, evenness and diversity tended to present higher values in LAS (dry season). The higher complexity of the soil fauna community was correlated to the higher leaf litter standing stock in LAS.


INTRODUCTION
Logging aims to meet different human needs.However, it leads to habitat fragmentation, loss of biodiversity and soil erosion (Siminski et al., 2004).As a result, there are many environmentally vulnerable forest fragments, usually small and with different formats in varying stages of natural regeneration (Caldas & Francelino, 2009).Depending on the disturbance, history of land use and availability and proximity to forest remnants as sources of propagules, some of the deforested areas can regenerate spontaneously, after been abandoned (Guariguata & Ostertag, 2001).If this process does not occur spontaneously however, it is necessary to implement measures to accelerate forest regeneration in degraded areas.Edaphic organisms may act as bioindicators to evaluate this process, because the activity of these organisms changes biological, chemical and physical processes occurring in the soil (Snyder & Hendrix, 2008).
According to some authors, abundance, richness and diversity of soil fauna increases, as secondary succession in tropical forest ecosystems advances (Barberena-Arias & Aide, 2003;Negrete-Yankelevich et al., 2007;Morais et al., 2010;Menezes et al., 2009;Camara et al., 2012;Szinwelski et al., 2012;Rousseau et al., 2014;Machado et al., 2015).Additionally, the predators and saprophagous are both functional groups that are somehow favored in areas undergoing more advanced stages of forest regeneration (Menezes et al., 2009;Camara et al., 2012;Rousseau et al., 2014;Machado et al., 2015).However, there are divergent results in terms of Formicidae.It has been observed in Brazilian Amazon (Morais et al., 2010) and Atlantic Forests (Menezes et al., 2009;Camara et al., 2012) that the abundance or relative participation of this saprophagous-predator group was higher in areas undergoing a less advanced stage of tropical forest regeneration than a more advanced stage.
By contrast, ants may also be favored in areas at more advanced stages of Atlantic Forest regeneration (Machado et al., 2015).These results demonstrated that areas at different stages of tropical forest regeneration present differences in the structure and composition of their soil organism communities.Therefore, monitoring the soil fauna assembly, which contributes to the carbon and nutrient cycling, helps to evaluate the soil ecological functions of the tropical forest remnants.The present study aimed to test the hypothesis that there are differences in the structure and composition of the soil arthropod communities between two areas of Seasonal Semideciduous Forest at different stages of natural forest regeneration (LAS: less advanced stage; MAS: more advanced stage) at Pinheiral, Rio de Janeiro, Brazil.

MATERIAL AND METHODS
The study was carried out in the municipality of Pinheiral, located between latitudes 22° 29 ' 03" and 22° 35' 27" South and longitudes between 43° 54' 49" and 44° 04' 05" West, State of Rio de Janeiro, Brazil.The climate is classified as Cwa -humid subtropical climate with dry winter and hot summer (Köppen, 1948).The predominant soils are Ultisols Red-Yellow and Inceptsol on the hillside, Oxisols and Red-Yellow both on top and upper third of the slope (Menezes, 2008).The intense transformations of the landscape and soil degradation began more than 180 yr ago, with the establishment of coffee crops in the region.The secondary forest began through natural regeneration at sites undergoing minor human pressure, when this activity ended about 120 yr ago (Menezes, 2008).The original vegetation is Seasonal Semideciduous Forest that belongs to the Atlantic Forest Biome, but nowadays the predominant vegetation cover consists of implanted grasslands and spontaneous unmanaged abandoned grasslands, which generate areas with different stages of natural forest regeneration (Menezes et al., 2009).

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Effects of Natural Atlantic... Floresta e Ambiente 2018; 25(1): e20160017 According to Santos (2014), the more favorable edaphic conditions (higher values of pH, available P, exchangeable K and Mg, and soil moisture content) in MAS occurred because of the relief, even though it influenced the differences between the areas in terms of the stage of natural forest regeneration (Table 1).We installed one plot (20 x 30 m) in each different hill slope position (shoulder, backslope and footslope) in both LAS and MAS areas (totaling three plots in each area).Soil mesofauna and macrofauna were sampled by means of eight pitfall traps randomly installed in each plot, at least 10 m apart from each other (totaling 24 pitfall traps in each area).Each trap was considered an experimental unit.Traps consisted of plastic containers (17 cm deep, 9.7 cm diameter) filled with 100 mL of a 1% formaldehyde solution with three drops of detergent, that were buried in the forest floor with the opening near to the interface with litter.The traps remained in the field for 10 consecutive days in both LAS and MAS areas, at the end of the dry season (October/2012) and the rainy season (April/2013).
The arthropods caught in each trap were filtered through a funnel and transferred to a Petri dish, with the aid of a squeeze with distilled water.Then, the arthropods were stored in marked, small plastic containers (10 mL) with a solution of ethyl alcohol 70% for subsequent evaluation.The soil organisms were quantified and categorized into taxonomic groups (order or family) and functional groups (trophic guilds) (CSIRO, 1991).Total abundance, abundance of both taxonomic groups and functional groups (number of individuals trap -1 day -1 ), richness (R, total number of groups), evenness (U, Pielou index), and diversity (H' , Shannon index) were estimated.Menezes et al. (2009) and Machado et al. (2015) have previously evaluated the effect of the stage of forest regeneration on soil arthropod community in Pinheiral, by means of hand sorting from soil monoliths (Anderson & Ingram, 1993) and pitfall traps, respectively.However, both of them occurred in different areas from the present work.
In order to correlate the soil fauna community with the accumulated leaf litter lying on the forest floor, 10 samples of this material were randomly collected within a 0.25 m × 0.25 m (0.0625 m 2 ) wooden quadrat at each plot, both in the dry and rainy seasons.In the laboratory, samples were packaged in plastic bags and placed in a 2.0 mm mesh sieve to remove soil particles and organic matter at advanced stages of decomposition.Then, they were dried in a forced air oven (65 °C, 72 h) to obtain the dry weight and to estimate the dry mass of the total leaf litter standing stock (LSS; Mg ha -1 ).Thereafter, the material was ground in a Wiley mill (mesh < 2 mm) and digested for determining N, P, K, Ca, and Mg concentrations (Tedesco et al., 1995).
The values of total abundance, abundance of the taxonomic groups and functional groups, leaf litter standing stock, and nutrient concentrations were subjected to analysis of variance and the averages for the areas with different stages of natural forest regeneration were compared using the Mann-Whitney non-parametric test at 5% significance, with BioEstat statistical 5.3 software version (Mamirauá Institute, Belém, Brazil).The principal component analysis (PCA) was also performed to identify the taxonomic groups that could be used to differentiate or indicate similarities between the forest fragments at different stages of natural regeneration, within the climatic seasons, considering the leaf litter attributes.Thus, we only considered the average abundance of the taxonomic groups and the leaf litter standing stock attributes that presented correlation coefficients up to 0.70% with the axis 1 or the axis 2. We processed this multivariate analysis by using the PAST software (Hammer et al., 2001).
There were no differences between the different stages of natural forest regeneration neither for the abundance of microphagous/saprophagous nor for the herbivorous abundance, in both climatic seasons.The same pattern was observed in relation to predators and saprophagous, during the rainy season.However, the effect of the forest regeneration stage was observed when considering the relative participation of these functional groups.The relative participation of herbivorous decreased as the natural forest regeneration advanced, both in the dry season (from 21% in LAS to 17% in MAS) and in rainy season (from 15% in LAS to 9% in MAS).This reduction in the relative participation throughout the forest regeneration also occurred during the rainy season for microphagous/saprophagous (from 68% in LAS to 40% in MAS) and predators (from 4% in LAS to 2% in MAS).
The soil organisms were distributed in 25 taxonomic groups.Most of them (16 groups) occurred in both stages of natural forest regeneration, at least in one of the climatic seasons: Acari, Araneae, Auchenorryncha, Collembola, Coleoptera, Dermaptera, Diplura, Diptera, Formicidae, Heteroptera, Hymenoptera, Isopoda, Opilionida, Orthoptera, Pseudoscorpionida, and Psocoptera.Six taxonomic groups presented restricted occurrence.Isoptera and larvae of Lepidoptera, both in the dry season, and Thysanoptera, in the rainy season, were sampled only in LAS.On the other hand, Blattodea, Diplopoda, Coleoptera larvae, and Symphyla occurred only in MAS, in the rainy season.The taxonomic groups that presented very low relative participation (less than 2%) were reunited and classified as "Others" (Table 3).Auchenorryncha, Dermaptera, Heteroptera, and Hymenoptera belonged to Others in the two stages of forest regeneration, during both climatic seasons.
Only seven of these taxonomic groups were responsible for more than 95% of all sampled individuals: Acari, Araneae, Collembola, Coleoptera, Diptera, Formicidae, and Orthoptera (Figure 1).Among them, Collembola and Formicidae were predominant in LAS and MAS, respectively, regardless of the climatic season.The relative participation of Acari, Araneae, Coleoptera, Diptera, others (both climatic seasons), and Collembola (rainy season) decreased as the level of natural forest regeneration progressed (Figure 1).The opposite pattern occurred for Formicidae, as previously mentioned, and for Orthoptera, where relative participation increased throughout the process of the natural forest regeneration (both climatic seasons).
In general, the values of richness, diversity (both in the dry season), and evenness (in both climatic seasons) were higher in LAS in comparison with MAS (Table 4).In terms of the attributes of the leaf litter standing stock, no consistent pattern was observed between the two stages of forest regeneration by means of N, P, K and Mg concentrations.However, the LSS dry mass was higher in LAS during both climatic seasons, whereas Ca concentrations were higher in MAS in both climatic seasons (Table 5).
In the principal component analysis graphic, the variables (taxonomic group abundance and the attributes of the leaf litter standing stock) were divided into two axes (60.61% for axis 1 and 26.74% for axis 2) that explained 87.35% of the total variability between the different stages of natural forest regeneration, during the climatic seasons (Figure 2).Along the axis  1 (main axis), it can be easily noticed that the natural stages of forest regeneration were separated from each other.The abundance of the most soil fauna organisms, dry mass and K concentration of the leaf litter standing stock were correlated to LAS though restricted to the right portion of the graphic.Whereas Formicidae and concentrations of P, Ca, and Mg in the leaf litter standing stock were correlated to MAS and restricted within the left portion of the graphic, along the two climatic seasons.
Most of the taxonomic groups (Acari, Auchenorryncha, Coleoptera, Diptera, and Hymenoptera) were correlated to the stage of forest regeneration and climatic season (LAS Dry) because of the increased leaf litter standing stock (Figure 2).Araneae was correlated to the K concentration in the leaf litter standing stock in LAS, in the rainy season.On the other hand, in MAS only Formicidae was correlated to the leaf litter attributes (P and Ca concentration in the leaf litter standing stock), in the rainy season.None of the taxonomic groups correlated to MAS, in the dry season.

DISCUSSION
The higher total abundance of the soil arthropod community in the MAS was a consequence of the higher abundance of the saprophagous/predator group in the MAS, in both climatic seasons.This in turn reflected the higher relative participation of Formicidae in MAS, in comparison with LAS.In fact, Formicidae was the only group that presented higher abundance in MAS (rainy season), when compared to LAS.Formicidae also presented increased abundance/density along the development of forest regeneration in a Mexican Cloud Forest (Negrete-Yankelevich et al., 2007) and of Atlantic Rain Forest in the understorey of abandoned eucalyptus plantations (Camara et al., 2012).By contrast, the abundance of both predator and saprophagous groups were higher in LAS in comparison to MAS, in the dry season.The presence of different groups of predators and saprophagous indicates that the ecosystem presents high structural complexity, functional redundancy and redistribution of energy along the food chain (Begon et al., 2005;Menezes et al., 2009).------------------(g kg -1 )- ----------------

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Effects of Natural Atlantic... Floresta e Ambiente 2018; 25(1): e20160017 Collembola, which was the first and second group with higher relative participation in LAS and MAS, respectively, was also predominant at different stages of the Atlantic forest regeneration, under eucalyptus plantations (Camara et al., 2012) and in secondary forest fragments in Pinheiral (Machado et al., 2015).Most of the individuals that represent Formicidae are usually restricted to the nest and thus any method of soil fauna sampling tends to underestimate the population density values for this group (Correia & Oliveira, 2000).Despite this, Formicidae is often one of the most abundant soil taxonomic groups in different forest ecosystems (Moço et al., 2005;Copatti & Daudt, 2009;Menezes et al., 2009;Morais et al., 2010;Rousseau et al., 2014), regardless the soil fauna sampling method (Sabu & Shiju, 2009).
In contrast to the present study, Negrete-Yankelevich et al. (2007), Menezes et al. (2009), Camara et al. (2012), Rousseau et al. (2014), and Machado et al. (2015) reported the increased abundance of Araneae, Coleoptera, and Dermaptera as the stage of tropical forest regeneration progressed.In relation to Formicidae, the abundance of this group was favored in both less (Menezes et al., 2009;Camara et al., 2012) and more advanced stages of tropical forest regeneration (Machado et al., 2015).
The set of results obtained in the present study indicated that eight taxonomic groups (Acari, Araneae, Coleoptera, Dermaptera, Diptera, Isoptera, larvae of Lepidoptera, and Thysanoptera), which were distributed in a wider range of functional groups (predator, saprophagous, herbivorous, and microphagous/saprophagous), were somehow favored in LAS.In general, this fact influenced higher values of both richness and evenness, which in turn led to greater diversity in LAS.On the other hand, only two taxonomic groups, Formicidae (saprophagous/predator) and Orthoptera (herbivorous), were favored in MAS, which influenced lower values of evenness in this ecosystem.Thus, we observed the effect of the stage of natural forest regeneration on the structure and composition of the soil arthropod communities, in areas of Seasonal Semideciduous Forest at Pinheiral.The values for total abundance/density and richness generally increased over the course of the natural regeneration of subtropical and tropical forests in different sites (Table 6).Our results corroborated this fact only in relation to the total abundance.The higher complexity of the soil fauna community is a consequence of the higher structure of the plant community in advanced stages of natural forest regeneration, in comparison with initial stages of tropical forest regeneration (Negrete-Yankelevich et al., 2007;Menezes et al., 2009;Camara et al., 2012;Szinwelski et al., 2012;Rousseau et al., 2014;Machado et al., 2015).However, in terms of the effect of the natural forest regeneration stage on evenness and diversity of soil fauna community, the literature presented divergent data.
The variability in the estimates of soil fauna structure is probable due to the employment of different extraction methods to recover these animals (Stork & Eggleton, 1992).Camara et al. (2012), Szinwelski et al. (2012), Machado et al. (2015), and the present work captured the soil arthropods by means of pitfall traps.On the other hand, Negrete-Yankelevich et al. (2007), Menezes et al. (2009), and Rousseau et al. (2014) extracted the animals from soil monoliths according to the Anderson & Ingram (1993) method.Other probable reason for this variation may be changes within one single climatic season a year, in comparison to the previous or next year.Thus, studies focusing on at least two consecutive years could help to refine the results.
The higher leaf litter standing stock contributed to a soil fauna community with greater complexity in LAS, especially during the dry season.According to Santos (2014), lower gravimetric moisture in the surface soil (0-10 cm) of LAS slowed litter decomposition and thus favored a higher accumulation of leaf litter standing stock on the forest floor in this ecosystem, when compared with MAS.Higher leaf litter standing stock promotes a more suitable microclimate with lower light intensity and, consequently, lower temperatures, which favors the reproduction and survival of the soil fauna organisms in tropical ecosystems (Davis et al., 2003;Negrete-Yankelevich et al., 2007;Szinwelski et al., 2012).This importance of the leaf litter standing stock was more evident during the dry season, when the higher leaf litter standing stock can minimize the drastic fluctuations in soil temperature and the decreasing in soil moisture (Facelli et al., 1999;Wolkovich, 2010).Furthermore, Santos (2014) considered that the tree community in LAS presented higher values of richness and diversity.This fact may have also influenced the higher complexity of the soil fauna in this ecosystem, because higher plant diversity may support a soil fauna community with richer, more diverse taxonomic groups (Moço et al., 2005;Menezes et al., 2009;Machado et al., 2015).Tropical forests with higher tree diversity present more heterogeneous leaf litter, which implies a more varied food resource for soil fauna (Negrete-Yankelevich et al., 2007;Correia & Andrade, 2008).Thus, similarity of the soil fauna community between areas with secondary forest and areas with mature native forest increases as the process of natural forest regeneration develops (Davis et al., 2003;Camara et al., 2012).

CONCLUSIONS
The abundance of the soil arthropod community was greater in the area at a more advanced stage of natural Atlantic Forest regeneration, due to the higher abundance of Formicidae.On the other hand, richness, uniformity, and diversity were higher in the area at a less advanced stage of forest regeneration, mainly influenced by the higher dry mass of the leaf litter standing stock.
The soil arthropod community acted as a good bioindicator.Acari, Araneae, Coleoptera, Collembola, Dermaptera, Diptera, Isoptera, larvae of Lepidoptera, and Thysanoptera were favored in the area at a less advanced stage of natural Atlantic Forest regeneration.By contrast, Blattodea, Diplopoda, Formicidae, larvae of Coleoptera, Orthoptera, and Symphyla were favored in the more advanced stage of forest regeneration.

Figure 1 .
Figure 1.Relative participation (%) of the soil arthropod taxonomic groups in the less advanced stage (LAS) and more advanced stage (MAS) of Atlantic Rain Forest regeneration, during the dry and rainy seasons.
30 replicates in each area.Average values (standard deviation) in the column, in the same climatic season, followed by the same letter are not significantly different at P = 0.05, according to the Mann-Whitney test.LSS: dry mass of the total leaf litter standing stock; N, P, K, Ca and Mg: concentration of these nutrients in the leaf litter standing stock.

Figure 2 .
Figure 2. Principal component analysis of the abundance of the soil arthropod taxonomic groups and leaf litter standing stock attributes in the less advanced stage (LAS) and more advanced stage (MAS) of Atlantic Rain Forest regeneration, during the dry and rainy seasons.LSS: dry mass of the leaf litter standing stock; P, K, Ca and Mg: concentration of these nutrients in the leaf litter standing stock.

Table 1 .
Mean values of tree community and soil attributes in the less advanced stage (LAS) and more advanced stage (MAS) of Atlantic Rain Forest regeneration(Santos, 2014).
aValues in the column, in the same soil depth, followed by the same letter are not significantly different at P = 0.05, according to the Tukey test.Ni: number of individuals; R: richness; U: index of evenness; H': Sahnnon index of diversity; BA: basal area; RPC: relative participation of climax species; SM: soil moisture by gravimetric method.4/10Camara R, Santos GL, Pereira MG, Silva CF, Silva VFV, Silva RM Floresta e Ambiente 2018; 25(1): e20160017

Table 2 .
Average abundance (individual trap -1 day -1 ) of the soil arthropod functional groups in the less advanced stage (LAS) and more advanced stage (MAS) of Atlantic Rain Forest regeneration, during the dry and rainy seasons*.
*Average of 24 replications in each area.Values of average abundance (standard error) in the line, in the same climatic season, followed by the same letter are not significantly different at P = 0.05, according to the Mann-Whitney test.S/P: Saprophagous/ Predator; M/S: Microphagous/Saprophagous; H: Herbivorous; P: Predator; S: Saprophagous.

Table 3 .
Distribution of the soil arthropod taxonomic groups classified as "Others" in the less advanced stage (LAS) and more advanced stage (MAS) of Atlantic Rain Forest regeneration, during the dry and rainy seasons.

Table 4 .
Structural attributes of the soil arthropod community in the less advanced stage (LAS) and more advanced stage (MAS) of Atlantic Rain Forest regeneration, during the dry and rainy seasons*.

Table 5 .
Leaf litter standing stock attributes in the less advanced stage (LAS) and more advanced stage (MAS) of Atlantic Rain Forest regeneration, during the dry and rainy seasons*. -

Table 6 .
Structural attributes of the soil arthropods in different stages of natural regeneration of Tropical Forests.