Forests of the Iguaçu National Park : Structure , Composition , and Richness

Considering the importance of the Iguaçu National Park for the conservation of the Atlantic Forest and the absence of scientific or technical studies characterizing the ecology of forest species after seven and a half decades of its existence, a phytosociological survey of the arboreal vegetation was conducted to identify the various existing species and their successional stages. A total of 54 families, 135 genera, and 218 species were found in this survey. Euterpe edulis Mart. was the most frequently occurring species, which together with Aspidosperma polyneuron Müll. Arg., characterize the seasonal forests in the central and south regions of the park. In the north region, located 700 m asl, Araucaria angustifolia (Bertol.) Kuntze and Ilex paraguariensis A. St.-Hil. were observed along with some seasonal species, characterizing a transitional environment between seasonal and ombrophillous forests. In general, forests in the park were classified in advanced stages of ecological succession.


INTRODUCTION
Aiming to avoid the complete deterioration of the Atlantic Forest Biome, laws have been enacted to ensure that degraded areas are recovered and the use of the remaining areas on farms is managed rationally.In addition, several protected units (UC) such as the Iguaçu National Park (INP) have been created.
Despite the effectiveness of surveillance and protection within the boundaries of the INP, numerous farms, residences, and sawmills had already been established there before the Park was created, mainly in its southwest region, where the vegetation was completely cleared for agriculture and livestock uses.In other areas, there was selective logging, leading to virtual disappearance of some of the prevailing species and reduction of the potential for natural regeneration in some places due to loss of the seed bank (Ferreira, 1999).
In this context, the Park's first management plan of this UC called for detailed studies of the floristic structure and phytosociological and ecological successional stages of the vegetation in different regions.According to Ziller (1998), these studies would establish the structural patterns of vegetation and species occurrences, which would direct the management and recovery in areas where natural succession had been compromised.
In characterizing the structure of a forest, the number of trees and species distribution are directly associated with the growth habits of the species and environmental conditions of the site (Lin et al., 2013).The assessment of parameters of horizontal and vertical structure must also be observed in characterizing the structure, as well as the percentages of importance and coverage (Mueller-Dambois & Ellenberg, 1974).
After characterization of a particular forest area is performed, Meira & Martins (2002) advised that the comparative floristic aspect should be emphasized, wherein different remnants could have their floral compositions confronted or related by similarity index (Ríos et al., 2010) or analysis grouping (Avila et al., 2011).Meira & Martins (2002) also mentioned that such methods enable observation of the floristic proximity between different forest formations, which is useful to the understanding of the Brazilian forest phytogeography.
The importance of the INP for the conservation of forest species in the Atlantic Forest and the absence of technical information after seven and a half decades of its existence substantiate this study, which was conducted in order to identify the forest species and succession stages of the different existing vegetation formations.

MATERIAL AND METHODS
Study area -The Iguaçu National Park (INP) is located in the western region of the state of Paraná and encompasses a total area of 185,262.50 hectares (ha).The geographic region occupied by the INP is characterized by Cfa climate (Alvares et al., 2013).The terrain is determined by the Iguaçu River watershed and lies between 100 and 750 m asl as from the river bank.Bhering (2007) published the latest soil classification conducted in Parana state; for the region of the INP, the following classes have been identified: Ortic Rendzic Chernosol, Haplic Gleysol, Eutrophic Litholic Neosol, Red Disferric Latosol, Eutrophic Red Latosol, and Red Eutroferric Nitosol, with predominance of Nitosol and Latosol.
Forests in the INP are composed of different vegetation formations.Alluvial, Submontane and Montane formations of Semi-deciduous Forest (FES) predominate in the south and central regions and, in the north region, an ecotone between FES and Ombrophillous Mixed Forest (FOM), as well as Alluvial FOM are observed (Souza et al., 2017).
Data and analysis -Seven groups of three plots were installed along the existing altitudinal gradient in the region from the Iguaçu River bank to the northernmost region of the Park.The plots were installed at intervals of 100 m asl in the West-East direction (Figure 1).In total, 21 permanent plots were installed, each sampling plot comprising an area of 2,000 m 2 (20 x 100 m) totaling 4.20 ha.
Plot groups consisted of three plots: group one consisted of plots 1, 2, and 3; group two was composed of plots 4, 5, and 6; and so on.Finally, group seven included plots 19, 20, and 21.At each elevation, plots were positioned at variable distances from each other and parallel to the river course.They were distributed along the drainage slopes from their base up to the plateau regions near the watershed boundaries.
All living trees with circumference ≥15.70 cm (DBH ≥5.00 cm) were included in the survey and their respective dendrologic materials were sent to the Botanical Museum of Curitiba for identification.The names were determined through a database search of the Missouri Botanical Garden (tropicos.org).Family classification followed the APG III (2009).Species were classified into Pioneer (PI), Light-Demanding Climax (CL), and Shade-Tolerant Climax (CS) according to adaptation from Oliveira-Filho et al. (1994) to the system proposed by Swaine & Whitmore (1988), and considering the bibliographies of Ziller (1998), Jarenkow & Waechter (2001), Silva et al. (2008), Gasper et al. (2013a), andGasper et al. (2013b), as well as to field observations.The species were also classified by vegetation formation based on the analysis of the distribution records of species available at SpeciesLink (splink.org.br).
Vegetation sampling was conducted to ensure the observation of environmental changes in the INP, stratified into two levels so that all plots were installed in different environments.Even with the adoption of this sampling criterion, in order to verify the efficiency of the survey in relation to its floristic scope, a species-area curve was constructed to enable observation of the relationship between the number of species and the cumulative sampling effort (Felfili et al., 2011).
Characterization of the horizontal structure was performed by plot, in which 10 diameter classes with amplitude of 10 cm from the minimum diameter considered were arbitrarily defined to avoid an excessive number of classes to be grouped as trees with diameter ≥95 cm.To characterize the vertical structure, heights from the ground to the morphological inversion point of trees were measured using a retractable graduated rod, and were then distributed into 11 height classes with amplitude of 2 m from the ground surface.
Plots were classified into three succession stages: initial, intermediate, and advanced, according to the following attributes: species richness (S); dominance (DOA) (m 2 .ha - ), density (DE) (trees.ha - ), and cover value (CV) for the ecological groups; horizontal and vertical structure of vegetation.Decisions were also subsidized by contributions reported by Whitmore (1989), Schorn & Galvão (2009), Holz et al. (2009), andGasper et al. (2013b).The CONAMA resolution no. 2 of 18 March 1994 (Brasil, 1994) was observed for the ecological succession analysis despite not having been applied as a criterion for decisions.
Cover value for each ecological group was calculated by the following equation: CV = DR + DOA, where: DR refers to the ratio between the density obtained for the ecological group and the total density observed in the plot; DOA refers to the ratio between the dominance of each ecological group and the total dominance observed in the plot.
Aiming at a good floristic characterization of the forest, the tree species observed by Ziller (1998) during a Rapid Ecological Assessment of the INP were added to the list.In this floristic survey, Ziller (1998) visited observation points distributed throughout the Park.Likewise, as before, all botanical material was sent to the Botanical Museum of Curitiba for identification.

RESULTS
Floristic cover -In 10 plots, it was possible to sample 151 species, or 90% of the total.The remaining 11 plots contributed little to the increase in the number of species sampled, with addition of only 16 species, indicating that a large number of species occurred in common between the plots.In 20 plots, 100% of the species had already been sampled.
Floristic composition -Sampling of the plots showed occurrence of 4,299 trees that, when added to the species found by Ziller (1998), represented 54 botanical families, 135 genera, and 218 species (Table 1).Two trees measured in the plots could only be identified at the family level, which were grouped and assigned to the family Myrtaceae.Another nine trees could not be identified due to absence of leaves caused by seasonality, and were assigned to the "Unknown"      group.For the same reason, six species could only be identified by Ziller (1998) at the genus level.
Among the 218 species listed, 13 were not classified into ecological groups and vegetation formation because they were not identified at the species level or were exotic.Among the 205 remaining species, 78 (38.05%) were classified as presenting FES characteristics, 17 (8.29%)as FOM, and 110 (53.66%) are of occurrence in both formations.Regarding successional stage, 70 species (34.15%) were classified as Shade-Tolerant Climax, 92 (44.88%) as Light-Demanding Climax, and 43 (20.98%) as Pioneer.
Successional stage -In general, high values of richness and dominance were recorded in the plots and, in some cases, an expressive range of diameters and predominance of climax species were observed (Table 2).These results indicate that the forest remains well preserved.
In plot 6, low values of dominance and density were recorded (22.02 m 2 .ha - and 675 trees.ha - ), attributed to the high occurrence of Chusquea Kunth.(Criciúma) and Cyathea sp.(Xaxim-bravo), as well as to the presence of canopy gaps opened by the falling of large trees.The smaller diameter range observed in some plots suggested intermediate stages of succession.Hydromorphism was observed in the soil of plot 4, which limited the occurrence of large trees and justified its advanced successional classification.In plot 2, despite the limited range of diameter class (70 cm), the dominance value of 30 m 2 .ha - indicated vegetation in good conservation condition.In plots 8 and 9, located on the bottom of a drainage slope, presence of Guadua chacoensis (Taquaruçu) contributed to the low density values and their classification in intermediate stages.
Preserved forests present points of morphological inversion distributed in different strata, reaching expressive heights.This characteristic could be observed in all plots and, despite the positive asymmetry and negative kurtosis, the distribution curves extended to heights >13 m, as shown in Table 3.The highest relative frequencies were found below nine meters, justified by the high density in the initial diameter classes and recurrence of Shade-Tolerant Climax species.
Presence of Araucaria angustifolia above 19 m was observed in plots 19, 20, and 21.This species is associated with P. rigida, Casearia decandra, and Nectandra lanceolata between 11 and 17 m, and the high density of C. canjerana, C. xanthocarpa, and Ilex paraguariensis in the understory, between 3 and 7 m, characterized the vertical structure of this transitional vegetation between FOM and FES.Specimens of emergent species in FES were identified within these plots in the classes of 7, 9, and 11 m, including A. polyneuron, C. trichotoma, and M. frondosus.Jarenkow & Waechter (2001), Giehl & Jarenkow (2008), Scipioni et al. (2011), Ríos et al. (2010), and Bianchini et al. (2003) identified 55, 82, 72, 64 and 116 species, respectively.In this research, the botanical families Fabaceae and Myrtaceae were the most representative in number of species, corroborating the studies by Oliveira-Filho & Fontes (2000) in an FES in southeastern Brazil and  Giehl & Jarenkow (2008) reported richness only for Meliaceae, associated with early succession in the former study and with alluvial forest in the latter.Meira & Martins (2002) performed a comparative analysis of similarity between fragments of montane FES in Minas Gerais state (between 650 and 800 m asl) and semideciduous forests in Sao Paulo and northern Parana states.Based on the results, the authors hypothesized that the floristic similarity between montane and submontane FES increases proportionally to latitude.
Comparison between the species that occurred in plots located in the submontane FES of the INP (between 100 and 600 m asl) identified 27 species in common with the study by Meira & Martins (2002), apparently confirming their hypothesis.Some species even presented high density and dominance values, namely, C. gonocarpum, M. stipitatum, and S. bonplandii.
Also in support of the hypothesis of the aforementioned authors, high amplitude of dispersion along the altitudinal gradient was found for 52 seasonal species in the INP.These species are altitude indicators in the state of Sao Paulo, as described by Meira et al. (1989).Results of this analysis revealed 13 species occurring in the INP, 11 of which found in submontane FES: Alchornea triplinervia, Luehea divaricata, C. canjerana, Cedrela fissilis, C. decandra, Casearia obliqua, Allophylus edulis, C. speciosa, Handroanthus albus, Myrsine umbellata, and Pisonia ambigua.Cupania vernalis occurred only in montane regions 600 m asl, whereas Roupala brasiliensis was restricted to an ecotone between FES and FOM, 700 m asl.Also corroborating this result, floristic similarity was observed between the montane FES (600-700 m asl) and the submontane Decidual Forests at higher latitudes below 550 m asl, as described by Jarenkow & Waechter (2001) and Scipioni et al. (2011).Those studies found a total of 55 and 79 species, respectively, of which 30 (54.54%) and 42 (53.16%)were common to those of the present study.Budowski (1965) reported that in dense undisturbed forests or in forests in more advanced successional stages, the recruitment of Pioneer species is subject to emergence of canopy gaps, which may explain the low cover value for this ecological group in the INP.Holz et al. (2009) reported that the native forests of northeastern Argentina were mostly composed of Light-Demanding Climax and Shade-Tolerant Climax species, whereas Pioneer species accounted for 25%.

Successional stage -
Shade-Tolerant Climax species are also widely recurrent and represented in greater abundance by E. edulis, S. bonplandii, Sebastiania brasiliensis, N. megapotamica, O. diospyrifolia, B. riedelianum, and C. gonocarpum, also in agreement with the results found by Holz et al. (2009).In the INP, this ecological group amounted to 100.53% of the total cover value for vegetation and, together with the Light-Demanding Climax species, to 183.68%.Ziller (1998) described the central region of the Park as showing fewer traces of anthropogenic activities, illustrated by the lush vegetation and high floristic diversity.Furthermore, in addition to A. polyneuron, other species characteristic of vegetation in advanced-stage seasonal forests were recurrent in this region, including A. leiocarpa, M. frondosus, B. riedelianum, Jacaratia spinosa, Lonchocarpus muehlbergianus, and Holocalyx balansae.Also noteworthy is the wide range of diameters observed in the plots established in that region (plots 7 to 18).However, some of the plots located on the slopes of the river valley of the central region showed a narrower range of diameters and recurrence of Pioneer species at intermediate stages of ecological succession.This finding may be associated with the rugged terrain and increased water availability (Muchailh et al., 2010).Another related factor may be the increased light incidence in the understory of the plots located on the drainage slopes oriented to the East, resulting in an edge effect (Schorn & Galvão 2009).
The narrower range of diameters and the high concentration of trees with morphological inversion point <7 m indicate intermediate successional stages for two plots in the southern and southwestern parts of the INP (plots 1 and 6).Ziller (1998) pointed out that, unlike the logging that occurred in other regions, the anthropogenic activities in this region included clearing of vegetation for agricultural use, which slowed the restoration process to its original state.
Further North in the Park, in the transition zone between Semideciduous and Ombrophillous Forests, ecological succession proceeds at an intermediate stage, indicated by reduction in dominance, lower range of diameters, and lower morphological inversion point.This result can be explained by the high level of anthropogenic disturbance because of the forest proximity to the municipality of Santa Tereza do Oeste (Ziller, 1998).Despite the intensified logging activities occurred in this area, the vegetation was not completely removed, and thus maintained its potential for recovery.Evidence of this potential is observed in the presence of species of high commercial value typical of Ombrophillous Forests.Evidence of the effect of altitude and latitude on the distribution of species of seasonal forests was observed to compare the results of this survey with those of studies conducted in the Southeast and extreme South regions of Brazil.

Figure 1 .
Figure 1.Localization of seven groups of plots installed in the Iguaçu National Park.

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Souza RF, Machado SA, Galvão F, Figueiredo  Filho A, Picoli AC Floresta e Ambiente 2019; 26(1): e201502675.CONCLUSIONSIn general, forests in advanced successional stage were observed throughout the Iguaçu National Park (INP).The central region presents few characteristics indicative of anthropogenic activities and portrays, more accurately, the original seasonal forests that occurred in the Parana River basin.The forests of the South and far North areas of the INP still present signs of anthropogenic activities, where some species show low recurrence and depend on a long period of in disturbance and isolation to return to its original state.

Table 1 .
Floristic checklist of the tree species in the Iguaçu National Park with their classification in ecological groups (GE), vegetation formation, occurrence in plot groups, and registry by similarity to voucher specimens deposited in the Botanic Museum of Curitiba (MBM).

/Species GE Vegetation Formation Occurrence in Plot Groups Voucher in the MBM
*Exotic plants; PI -Pioneer; CL -Light-Demanding Climax; CS -Shade-Tolerant Climax; NC -Not classified; FES -Semi-deciduous Forest; FOM -Ombrophillous Mixed Forest.The species exclusively observed by Ziller (1998) do not provide information on occurrence in the plot groups and on the MBM registry.*Exotic plants; PI -Pioneer; CL -Light-Demanding Climax; CS -Shade-Tolerant Climax; NC -Not classified; FES -Semi-deciduous Forest; FOM -Ombrophillous Mixed Forest.The species exclusively observed by Ziller (1998) do not provide information on occurrence in the plot groups and on the MBM registry.
Ziller (1998)s; PI -Pioneer; CL -Light-Demanding Climax; CS -Shade-Tolerant Climax; NC -Not classified; FES -Semi-deciduous Forest; FOM -Ombrophillous Mixed Forest.The species exclusively observed byZiller (1998)do not provide information on occurrence in the plot groups and on the MBM registry.
Ziller (1998)s; PI -Pioneer; CL -Light-Demanding Climax; CS -Shade-Tolerant Climax; NC -Not classified; FES -Semi-deciduous Forest; FOM -Ombrophillous Mixed Forest.The species exclusively observed byZiller (1998)do not provide information on occurrence in the plot groups and on the MBM registry.
Ziller (1998)s; PI -Pioneer; CL -Light-Demanding Climax; CS -Shade-Tolerant Climax; NC -Not classified; FES -Semi-deciduous Forest; FOM -Ombrophillous Mixed Forest.The species exclusively observed byZiller (1998)do not provide information on occurrence in the plot groups and on the MBM registry.
The highest dominance and density values were observed in plot 12, associated with the presence of Aspidosperma polyneuron -the largest diameter class, Light-Demanding Climax species (Apuleia leiocarpa, Cabralea canjerana, Diatenopteryx sorbifolia, and Ficus luschnathiana) -70, 80 and 90 diameter classes, and the high density of E. edulis and S. bonplandii -the first diameter class.Such a physiognomy is typical of seasonal forests with low levels of human disturbance.
Ziller (1998)s; PI -Pioneer; CL -Light-Demanding Climax; CS -Shade-Tolerant Climax; NC -Not classified; FES -Semi-deciduous Forest; FOM -Ombrophillous Mixed Forest.The species exclusively observed byZiller (1998)do not provide information on occurrence in the plot groups and on the MBM registry.

Table 2 .
Relative frequency (%) by diameter class, cover value for the ecological groups, and successional stage (SS) of plots installed in the Iguaçu National Park.

Table 3 .
Relative frequency (%) by height class to the morphological inversion point for the 21 plots installed in the Iguaçu National Park.