Population and community dynamics of a semideciduous forest from south Minas Gerais, Brazil

The Parque Ecológico Quedas do Rio Bonito (PEQRB; “Falls of Nice River Ecological Park”) belongs to the Abraham Kasinski Foundation (FAK) and is located in the municipality of Lavras, in the Southern region of Minas Gerais State (21°19'S and 44°59'W), Brazil (Fig. 1), with elevations ranging from 950 and 1200 meters. (Oliveira Filho and Fluminhan-Filho 1999).

Within the park, the forest is distributed among valleys, on slopes and adjacent to watercourses, forming a heterogeneous environmental gradient with the occurence of typical mountain forest species such as Protium widgrenii Engl. (Burseraceae), Clethra scabra Pers. (Clethraceae), Podocarpus sellowii Klotzsch ex Endl. (Podocarpaceae), Euplassa incana (Klotzsch) I.M.Johnst. (Proteaceae) and Drimys brasiliensis Miers (Winteraceae) (Oliveira Filho and Fluminhan-Filho 1999). In addition, there are natural gaps and dense bamboo cover distributed throughout the forest analyzed in this study. The area of forest examined in this study is classified as Seasonal Semi-deciduous Upper-montane Forest (Oliveira Filho and Fluminhan-Filho 1999).

In 1999, 90% of the current area of the PEQRB was designated as protected in a decree from Lavras’ city hall, which includes the assignment to FAK. Before it was designated as a protected area, the PEQRB was subject to various disturbances. Disturbances such as free movement of cattle, logging for charcoal production and construction of housing and recreational areas (Dalanesi et al. 2004, Oliveira Filho and Fluminhan-Filho 1999).

Investigation of floristic and structural composition of the tree community in PEQRB, its distribution over soil habitats and evaluation of the interaction of plants with environmental factors, were studied by Dalanesi et al. (2004). In the present study, the authors resurveyed two stands (called B and C), located 480 m apart, using plots of 300 m^2. Stand B was surveyed with 26 plots in 2000 comprising 0.78 hectares, which were kept and resurveyed in 2005 and 2011constituing its long-term monitoring. Stand C was surveyed in 2001 with 38 plots (1.14 hectares), then again in 2006 and 2011. The total cover of sampling area was 1.92 hectares.

The stands were arranged as transects (Fig. 2) perpendicular to the watercourse which bisects the park, and extends into two adjacent slopes, following principles outlined by Causton (1988). The samplings plots were contiguously allocated on each stand (Fig. 2). This sampling design of the was previously planned aiming to catch more environmental heterogeneity in the transects of both stands in order to analyze the relations among trees distribution with soil and topograghy (Dalanesi et al. 2004). All trees with diameter at breast height (DBH) greater than or equal to 4.99 cm were measured and permanently tagged. In the subsequent samplings, the surviving trees in both stands were remeasured, as well as all individuals which reached the criterion of inclusion. Additionally, the DBH of multi-stemmed trees was calculated as the square root of the sum of all squared stem DBH’s. Only multi-stemmed trees with DBH ≥ 4.99 cm were included in the survey as recruits.

Individuals were identified either in the field or through collection of samples of whole branches, leaves, and where possible, fruits. These samples were then compared with the existing collection present in herbarium “Herbário ESAL” of the Federal University of Lavras. In addition, samples were verified using appropriate literature and where necessary, specialists were consulted. The classification system followed that of the APG IV (Angiosperm Phylogeny Group) (2016) and we verified spellings and synonymous to the species through TNRS page (Taxonomic Name Resolution Service) Boyle et al. (2013).

Data analyses

Species diversity and richness

Species richness was compared between stands B and C stands using a Wilcoxon Rank Sum Test. The species diversity and evenness per stand were calculated by Shannon-Weaver (H) and Pielou (J) respectively, using the package “vegan” (Oksanen et al. 2017). To compare the total number of individuals and basal area per plot within each stand, a Nested ANOVA was carried out followed by a post-hoc test using the functions lmer and difflsmeans from the package lmerTest (Kuznetsova et al. 2016). The pairwise comparisons of number of individuals and basal area between B and C were conducted with a Two-Sample T-test of independent samples. All analyses mentioned above were carried out in R software version 3.3.0 (R Development Core Team 2016). Shannon-diversity between B and C was compared in Past software (Hammer et al. 2001) with a Hutcheson T-test (Hutcheson 1970).

Tree Dynamics

The changes in the tree community over the time were determined for each stand by calculating the annual mean rates of mortality (M) and recruitment (R) of individuals (based on species abundance) and basal area loss (L) and gain (G) according to Sheil et al. (1995), Sheil and May 1996 and Sheil et al. (2000). The time series were 11 years to stand B (surveyed in 2000, 2005 and 2011) and 10 years to stand C (surveyed in 2001, 2006 and 2011) constituting two periods to the calculation of the rates (B: 2000 and 2005, 2005 and 2011; C: 2001 and 2006, 2006 and 2011). In addition, the net rates of change in number of individuals and basal area were also calculated, based on the relationship between the abundance and basal area recorded in the first and most recent inventories. The net rate of change between inventories was calculated considering both abundance of trees (Ch_N) and their basal area (Ch_AB) Korning and Balslev 1994. To describe the rate of change in tree community, the turnover rates regarding both abundance (T_N) and basal area (T_AB), were calculated Phillips et al. 2004, Phillips 1996 for each stand.The turnover rates to number of individuals and basal area are respectively calculates as the averages of mortality, recruitment, and the loss and gain of basal area rates. . The difference between the number of dead and recruited trees was calculated using Poisson Counting (Zar 2010). This analysis was performed by calculating Exact Poisson Tests using R version 3.3.0 (R Development Core Team 2016) with the package “exactci” (Fay 2010).

Tree Dynamics per diameter classes

Diameter classes with increasing amplitudes were created (5-10 cm, >10-20 cm, >20-40 cm and >40-80 cm). This approach compensates for the sizeable decrease in abundance of the largest diameter individuals, which is a pattern commonly observed in tree diameter measurements and is characterized by the negative exponential distribution (Appolinário et al. 2005). To describe the temporal variations in each class, all individuals that underwent the following events: death, total ingrowth (inter-class imports through recruitment and growth) and total outgrowth (inter-class exports through growth and death) (Lieberman et al. 1985), were counted. The same procedure was used to calculate the absolute number of dead, absolute ingrowth (the absolute number of previously unrecorded individuals) and absolute outgrowth (the absolute number of individuals no longer present) per diameter class. To verify whether the frequency of the total number of dead trees within each stand (B: 2005 and 2011; C: 2006 and 2011) were dependent on diameter classes based on the frequencies expected from the second and last inventory diameter distribution, we used a G-Test of Goodness-of-Fit carried out with the package “DescTools” (Signorell 2016). The comparison between the total ingrowth and total outgrowth per class was carried out by calculating Exact Poisson Tests with the package “exactci” (Fay 2010). Both analyzes were carried out in R version 3.3.0.

To verify whether the frequency of dead trees within each stand (B: 2005 and 2011; C: 2006 and 2011) were dependent on diameter classes based on the frequencies expected from the second and last inventory diameter distribution

Dynamics of the most abundant species

The 10 most abundant species in each stand were selected and their mortality and recruitment rates were calculated. These species were also classified into regeneration guilds following the descriptions of Swaine and Whitmore (1988) and the field knowledge on the species of the authors of this study. This classification was used to aid in the deduction of the successional stage of the two forest stands. The difference between the absolute number of dead and recruits within the species was evaluated by Exact Poisson Tests in software R version 3.3.0 with the package “exactci” (Fay 2010).

The Parque Ecológico Quedas do Rio Bonito (PEQRB; “Falls of Nice River Ecological Park”) is a particular protected with 235 hectares, located in the municipality of Lavras, in the Southern region of Minas Gerais State, with altitudes varying between 950 and 1200 metes.

21°19' and ; 44°59' and .

Results

Structure, diversity and species richness

In stand B, the survey which took place in the year 2000 identified 1364 trees from 118 species (83 genera, 50 families); in 2005, 1313 trees in from 115 species were identified (80 genera, 48 families) and in 2011, 1251 trees from 106 species (75 genera, 46 families) were identified (Table 1). In stand C, in 2001, 1941 trees from 157 species (107 genera, 55 families) were identified; in 2006 1970 trees from 160 species were identified (107 genera, 55 families) and in 2011 1810 trees from 157 species were identified (105 genera, 53 families) (Table 1). The species richness was significantly different between stands B and C in each of the censuses (Table 2). In stand B the species richness decreased between 2000 and 2011 and in the stand C it was higher in 2006 (Table 2). The diversity in the stand B in all censuses was lower compared to stand C, according to Hutcheson T. comparisons (p<0.05; Table 2). Pielou’s evenness remained the same in stand B in 2000 and 2005, but decreased in 2001 (Table 2). On the other hand, stand C presented different evenness among all censuses with the highest degree of evenness detected in the 2011 census (Table 2).

In the stand B there was no significant difference in total basal area (F = 0.53, p = 0.593) or in total number of individuals (F = 0.23, p = 0.791) across all censuses. The same was evident in total basal area (F = 1.28, p = 0.279) and total number of individuals (F = 1.61, p = 0.201) in stand C (Table 2). The total number of individuals did not differ between stands across all of the censuses. There were significant differences in total basal area between stands across all of the censuses (Table 2).

The monitoring period of 11 years in stand B presented a decrease in the number of individuals per hectare, and an increase in basal area per hectare, from 2000 to 2011 (Table 2). The increase of basal area per hectare was also observed in stand B from 2001 to 2011, but the number of individuals per hectare decreased from 2006 to 2011 (Table 2).

Tree Dynamics

There was a decrease in abundance and increases in basal area during both intervals in stand B (2000-2005 and 2005-2011; Table 3). This clear loss of individuals was confirmed by the negative net change in both intervals, which was higher in the second interval (-0.96 % year^-1), associated with an increase in mortality rate 3.02 % year^-1) and a reduction in recruitment rate (1.63 % year^-1). This was also reflected in a higher turnover (2.45 % year^-1) in number of individuals. In fact, the number of dead trees was significantly higher compared to recruits in both intervals (2000 to 2005: Z = 2.94; p = 0.003; 2005 to 2011: Z = 3.65; p = 0.0003). There was a net increase in basal area in both intervals (2000-2005 = 1.04 % year^-1 and 2005-2011 = 1.17 % year^-1), which means that there is also an increase in biomass storage for the tree community during the 11 years of monitoring. This clear storage of biomass increased the turnover in basal area (3.14 % year^-1) in the second interval, which was driven by the increase of gain in basal area rate (3.84% year^-1).

In stand C, the number of individuals increased in the first interval (2001 to 2006) and decreased in the second (2006 to 2011). Basal area increased in both intervals (Table 3). In the period between 2006 and 2011, the net change rate was negative (-1.67 % year^-1) resulting in a progressive loss of individuals. Consequently, the turnover rate increased (2.71 % year^-1) and the number of dead individuals was significantly higher than recruits (Z = 7.11; p = < 0.0001). The biomass accumulation observed between 2001 and 2006 was elevated due to its positive net change (1.02 % year^-1). However, the turnover in basal area during the second period (2006 to 2011) demonstrated a higher increase in biomass (3.08 % year^-1).

Tree Dynamics per diameter classes

Stand B showed higher total outgrowth (2005 to 2011: p = < 0.0001, Table 2) in the 5-10 cm diameter class in both intervals, which was the result of a higher absolute number of outgrowth in relation to absolute ingrowth. In the >10 to 20 cm class in 2011, the total outgrowth was significantly higher than total ingrowth (p = < 0.0001). This was due to an increase in the number of mortalities and a reduction in the raw ingrowth (Table 4). Conversely, between 2000 and 2011, the >20 to 40 cm class exhibited an increase in abundance, where 2005 showed a higher total ingrowth than total outgrowth (p = 0.0057). The observed frequency of dead trees per diameter class in both 2005 and 2011 differed significantly from that expected under the null hypothesis, according to the G Test (p = < 0.0001), demonstrating that the frequency of mortality differs per diameter class and is dependent on which class it is in.

A progressive decrease of abundance in stand C was observed between 2001 and 2011 in the 5-10 cm class (Table 5). This was due to total outgrowth being significantly higher than total ingrowth in 2011 (p = < 0.0001) which was in turn caused by the increased mortality rate compared to 2006 (Table 3). In the >10 to 20 cm class the total outgrowth was higher than total ingrowth in both intervals (2006: p = <0.0001; 2011: p = 0.0395) as a result of the increased rates of mortality and raw outgrowth from 2006 to 2011. Conversely, in 2006 in the >20 to 40 cm class, total ingrowth was greater than total outgrowth (p = 0.0258). The frequency of dead trees in both periods was independent from the class in which it occurs, according to the G Test (2006 e 2011: p = < 0.0001).

Dynamics of the most abundant species

Among the 10 most abundant species in stand B (Table 6), four shade tolerant trees showed a significant pattern: Amaioua intermedia. Copaifera langsdorfii. Faramea latifolia and Myrsine umbellata. There was no observed net change in the number of individuals of C. langsdorfii and F. latifolia between 2000 and 2005, though both species did increase their numbers of individuals between 2005 and 2011 (0.67 % year^-1 and 1.16 % year^-1. respectively), while the net change rate in basal area decreased (0.99 % year^-1 and 0.31 % year^-1. respectively). On the other hand, A. intermedia (Table 6) exhibited a higher recruitment than mortality (2005: Z = 2.08. P = 0.03; 2011: Z = 3.46. P = 0.0005), which resulted in a higher number of individuals in both intervals. Myrsine umbellata was only amongst the most abundant species in 2000, and showed higher mortality rate than recruitment rate in 2011 (Z = 2.89. P = 0.03).

Of particular interest were the light-demanding species in stand B, specifically Croton echinocarpus, Psychotria vellosiana, Pera glabrata and Tapirira obtusa. Psychotria. vellosiana showed higher rates of mortality than recruitment in both intervals (2005: Z = 2.0040. P = 0.04; 2011: Z = 3.06. P = 0.0021). Its turnover rate in number of individuals was higher between 2000 and 2005 equating to 16.20 % year^-1. Conversely, P. glabrata exhibited a progressive accumulation of biomass (basal area) from to 2000 to 2011, presenting higher turnover in basal area in 2011 (2.31 % year^-1). Tapirira obtusa showed an increased mortality as recruitment decreased (Z = 2.89. P = 0.03; Z = 2.94. P = 0.03) in both periods. Having presented neither significant mortality nor recruitment rates, the pioneer species C. echinocarpus did not change significantly in abundance after the survey in 2000. The light-demanding species in stand C, Miconia sellowiana, Myrcia splendens and Vochysia magnifica, presented significant differences in the number of mortalities or recruitments. The first two were notable for high rates of mortality in 2011 (Z = 6.58. P = <0.0001 e Z = 7.92. P = <0.0001 respectively), whereas V. magnifica did not present recruitment and showed significant mortality in both intervals (2006: Z = 3.46. P = 0.0005 and 2011: Z = 3.68. P = 0.0002).

Eremanthus erythropappus also did not present recruitment in the second interval (between 2006 and 2011), in conjunction with higher rates of mortality (Z = 5.19. P = <0.0001) and only remained among the most abundant species in 2001. The shade tolerant E. acutata e R. jasminoides increased in basal area and abundance in both intervals (Table 6), but did not differ in mortality or recruitment.

PEQRB Population and Community Dynamics (2001-2011)

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http://www.gbif.org/dataset/a8f27b2e-67a9-43cb-ad18-df43e0152c33; http://www.gbif.org/dataset/89f30480-54fd-4de2-ba51-c2249274add0

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